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435 Technical Terms You Need To Know in Rubber Industry (Part 2)

Concluding from earlier post, here are alphabets (M-Z). (You may also like to download the PDF at the end of this article and add to your digital library.)


216. mm Hg : Millimeters of Mercury. In vacuum work, a measure of absolute pressure, being the height of a column of Mercury that the air or other gas will support. Standard atmospheric pressure will support a Mercury column 760 millimeters high. Any value less than that represents some degree of vacuum.

217. Mandrel : A bar, serving as a core, around which rubber is extruded, forming a center hole.

218. Masterbatch :  A homogeneous mixture of rubber and one or more materials in known proportions for use as a raw material in the preparation of the final compounds. Masterbatches are used to facilitate processing or enhance the properties of the final product, or both.

219. Mastication : The breakdown or softening of raw rubber by the combined action of mechanical work (shear), and atmospheric oxygen, sometimes accelerated by the use of a peptizer, and frequently at elevated temperatures.

220. Mechanical Bond : A method of physically bonding rubber to inserts through the use of holes, depressions or projections in the insert.

221. Memory : The tendency of a material to return to original shape after deformation.

222. Microhardness : An electronic measurement of rubber hardness for specimens below .25 inch in thickness. Microhardness, like Shore A durometer, is also a measure of indentation.

223. Mill : A machine used for rubber mastication, mixing, or sheeting, having two counter-rotating rolls with adjustable longitudinal axis separation that usually rotate at different speeds.

224. Mirror Finish : A bright, polished surface.

225. Mismatch : A mold defect which produces an asymmetrical part, caused by dissimilar cavities in mating mold plates.

226. Mixer : A machine that incorporates and disperses compounding ingredients into rubber to form a mix or a compound through the action of mechanical work (shear).

227. Mixer, Internal : A machine with a closed chamber in which specially shaped rotors masticate the rubber or incorporate and disperse compounding materials, or both, into the rubber.

228. Modulus : The ratio of stress to strain; that property of a material, which, together with the geometry of a specimen, determines the stiffness of the specimen. In the physical testing of rubber, the force necessary to produce a stated percentage of elongation.

229. Modulus of Elasticity : One of several measurements of stiffness or resistance to deformation, but often incorrectly used to indicate specifically static tension modulus.

230. Mold Cavity : Hollow space, or cavity, in the mold, which is used to impart the desired form to the product being molded.

231. Mold Finish : The uninterrupted surface produced by intimate contact of rubber with mold surface at vulcanization.

232. Molding, Compression : The process of forming a material to a desired shape by flow induced by a force applied after material is placed in the mold cavity.

233. Molding, Injection: The process of forming a finished product by forcing material from an external heated chamber through a sprue (runner, gate) into the cavity of a closed mold. This is accomplished by means of a pressure gradient that is independent of the mold clamping force

234. Mold Lubricant : A material usually sprayed onto the mold cavity surface prior to the introduction of the uncured rubber, to facilitate the easy removal of the molded part.

235. Mold Marks : Indentations or ridges embossed into the skin of the molded product by irregularities in the mold cavity.

236. Mold Register : Accuracy of alignment/fit of mold sections.

237. Molding Solutions : In the field of custom molded rubber or plastic, the solution to your problems.

238. Mooney Scorch : The measurement of the rate at which a rubber compound will cure or set up by means of the Mooney Viscometer test instrument.

239. Molding Shrinkage : The difference in dimensions between a molded product and the mold cavity in which it was molded, both the mold and product being at normal room temperature when measured.

240. Molding, Transfer : The process of forming a material by forcing it from an auxiliary heated chamber through a sprue hole (runner, gate) into the cavity of a closed mold by means of a pressure gradient that is dependent on the mold clamping force.

241. Monomer : A low molecular weight substance consisting of molecules capable of reacting with like or unlike molecules to form a polymer.

242. Mold Marks : A surface imperfection transferred to a molded product from corresponding marks on a mold.

243. Mooney Viscosity : Measurement of the plasticity or viscosity of an uncompounded, or compounded vulcanized, elastomer seal material by means of the Mooney Shearing Disk Viscometer.


244. Naphthenic Oil : A hydrocarbon process oil containing more than 30 %, by mass, of naphthenic hydrocarbons.

245. Necking : The localized reduction in cross section that may occur in a material under tensile stress.

246. Nerve : The elastic resistance of unvulcanized rubber or rubber mixes to permanent deformation.

247. Nip : The radial clearance between rolls of a mill or calendar on a line of centers.

248. Neoprene (GR-M) : A DuPont Dow Elastomers polymer of chloroprene which is prepared from coal, salt and limestone.

249. Nitrile : (see also Buna-N) The most commonly used elastomer for O-Rings because of its resistance to petroleum fluids, its good physical properties, and its useful temperature range.

250. Nominal Dimension : Nearest fractional equivalent to actual decimal dimension.

251. Non-aromatic : Straight chain organic structures, such as petroleum type solvents.

252. Non-blooming : The absence of “bloom”.

253. Non-fill : A defect resulting from the failure of the rubber material to fill out all of a mold cavity.

254. Non-Sulfur Vulcanizing System : A vulcanizing system not requiring free or donated sulfur.


255. Occlusion : (A) The mechanical process by which vapors, gases, liquids or solids are entrapped within folds of a given substance during working or solidification; (B) the materials so trapped.

256. Off-register : Misalignment of mold halves causing asymmetrical parts, i.e. top and bottom mold plates don’t line up properly..

257. Oil Resistant : Ability to vulcanize rubber to resist the swelling and deteriorating effects of various types of oils.

258. Oil Swell : The change in volume of a rubber article due to absorption of oil or other fluid.

259. O-Ring : A product of precise dimensions, molded in one piece, to the configuration of a torus (doughnut) with a circular cross section, suitable for use in a machined groove for static or dynamic sealing.

260. O-Ring Seal : The combination of a gland and O-Ring providing a fluid tight closure. (Some designs permit minimum leakage.)

261. O-Ring Seal / Moving (Dynamic) : O-Ring seal in which there is relative motion between some gland parts and the O-Ring; oscillating, reciprocating or rotary motion.

262. O-Ring Seal / Non-moving (Static) : O-Ring seal in which there is no relative motion between any part of the gland and the O-Ring. (Distortion from fluid pressure or swell from fluid immersion is excluded.)

263. Optimum Cure : State of vulcanization at which the most desirable combination of properties is attained.

264. Outgassing : A vacuum phenomenon wherein a substance spontaneously releases volatile constituents in the form of vapors or gases. In rubber compounds, these constituents may include water vapor, plasticizers, air, inhibitors, etc.

265. Over-Cure : A degree of cure greater than the optimum, causing some desirable properties to be degraded. Usually results in a loss of elongation and an increase in hardness.

266. Overflow Groove : A groove around the mold cavity used to accept excess material from the cavity and to create a better “pack” for the part.

267. Oxidation : The reaction of oxygen on a compound, usually detected by a change in the appearance or feel of the surface, or by a change in the physical properties, or both.

268. Oxygen Bomb : A chamber capable of holding oxygen at an elevated pressure which can be heated to an elevated temperature. Used for an accelerated aging test.

269. Ozone Resistance : Ability to withstand the deteriorating effect of ozone (which generally causes cracking.)


270. Packing : A flexible device used to retain fluid under pressure, or seal out foreign matter. Normally refers to a dynamic seal.

271. Paraffinic Oil : A hydrocarbon process oil, most or all of which is composed of alkanes

272. Parting Line : The line on the surface of a molded part where the mold plates meet.

273. Peptizer : A compounding material used in small proportions to accelerate, by chemical action, the softening of rubber under the influence of mechanical action, or heat, or both.

274. Permanent Set : The deformation remaining after a specimen has been stressed in tension for a definite period, and released for a definite period.

275. Permeability : The rate at which liquid or gas, under pressure, passes through a solid material by diffusion and solution. In rubber terminology : the rate of gas flow, expressed in atmospheric cubic centimeters per second, through an elastomeric material, one centimeter square and one centimeter thick.

276. Permeation : The diffusion of a media (generally a gas) through a rubber or plastic component.

277. PH : Determines the concentration of either an acid or a base.

278. PHR : Abbreviation for parts per hundred of rubber, used for indicating the proportions of ingredients in a rubber compound.

279. Pigment : An insoluble compounding material used to impart color to rubber.

280. Pit (or Pock) Mark : A circular depression, usually small.

281. Plasticity : When subject to sufficient shearing stress, any given body will be deformed. After stress is removed, if there is no recovery, the body is completely plastic. If recovery is complete and instantaneous, the body is completely elastic. A balance between the two is required.

282. Plasticizer : A substance, usually a heavy liquid, added to an elastomer to decrease stiffness, improve low temperature properties, and improve processing.

283. Plastometer : An instrument for measuring the plasticity of a raw or unvulcanized compounded rubber.

284. Polymer : A material formed by joining together many (poly) individual units (mer) of one or more monomers; synonymous with elastomer.

285. Polymerization : Chemical reaction whereby simple materials, either one or more, are converted to complex material which possesses properties entirely different from the original materials used to start the reaction.

286. Polyurethane : An organic material noted for its high abrasion, ozone, corona and radiation characteristics.

287. Porosity : Quality or state of being porous – the presence of numerous small cavities.

288. Post Cure : The second step in the vulcanization process for some specialized elastomers. Provides stabilization of parts and drives off decomposition products resulting from the vulcanization process.

289. Pot : The chamber, in the transfer or injection mold, where raw material is placed before it is transferred into the cavity.

290. Pot Life : The period of time during which a reacting thermosetting composition remains suitable for its intended use, after mixing with a reaction-initiating agent.

291. Prevulcanization Inhibitor (PVI) : A compounding material that increases the time to incipient vulcanization of a rubber mix. Unlike a retarder, a PVI does not significantly affect the vulcanization rate.

292. Primary Accelerator : The principal highest concentration accelerator used in a vulcanizing system.

293. Processability : The relative ease with which raw or compounded rubber can be handled in rubber machinery.

294. Processing Aid : A compounding material that improves processability of a polymeric compound by reducing nerve, providing better dispersion of dry material, increasing the extension rate, reducing power consumption during mixing, producing smoother surfaces on calendered and extruded products, improving knitting, etc.

295. Process Oil: A hydrocarbon oil derived from petroleum or other sources, used as an extender or process aid.

296. Pure Gum State : A non pigmented, translucent basic polymer.


297. Radiation : An emission, of varying content, from a disturbed atom undergoing internal change. There are two broad classifications : (A) Corpuscular, comprising streams of particles, either neutral or charged, e.g. protons, neutrons, electrons; and (B) Electromagnetic, comprising wave-like emissions as gamma, ultraviolet, etc.

298. Radiation Damage : A measure of the loss in certain physical properties of organic substance, such as elastomers, due principally to ionization of the long chain of molecules; believed to result in redundant cross-linking and possible scission of the molecules. The effect is cumulative.

299. Radiation Dosage : The total amount of radiation energy absorbed by a substance. This value is usually expressed in “ergs per gram”, and is denoted by the following units : (a) Roentgen – a quantity of gamma or X-Ray radiation equal to approximately 83 ergs of absorbed energy per gram of air; (b) REP (Roentgen Equivalent – Physical) – a quantity of ionization that causes an energy absorption of approximately 83 to 93 ergs per gram of tissue; (c) REM (Roentgen Equivalent – Man) – similar to REP, except used to denote biological effects; and; (d) RAD – the unit of dosage related to elastomers, independent of type of radiation specimen, and denoting energy absorption level of 100 ergs per gram of elastomer : approximately equal to 1.2 Roentgens.

300. Rebound : A measure of the resilience, usually as a percentage of vertical return of a body which has fallen and bounced.

301. Rebound Test : The method of determining the resilient properties of vulcanized rubber by measuring the rebound of a steel ball or pendulum from a defined height onto a rubber sample.

302. Recipe :
A formula, mixing procedure, and any other instructions needed for the preparation of a rubber compound.

303. Reclaimed Rubber : Vulcanized rubber that has been thermally, mechanically, and/or chemically plasticized for use as a rubber diluent, extender, or processing aid.

304. Reciprocating Seal : Seal used in linear motion application.

305. Register : The accurate matching of the plates in a mold.

306. Reinforcement: The act of increasing the mechanical performance capability of a rubber by the incorporation of materials that do not participate significantly in the vulcanization process.

307. Reinforcement Agent : Material dispersed in an elastomer to improve compression, shear or other stress properties.

308. Relative Humidity : The ratio of the quantity of water vapor actually present in the atmosphere, to the greatest amount possible at a given temperature.

309. Release Agent (Mold) : A substance applied to the inside surface of a mold or added to a material to be molded, to facilitate removal of the product from the mold.

310. Resilience : Ability of an elastomer to return to original size and shape after deforming forces are removed; generally expressed in per cent of the ratio of energy removed, to the energy used in compressing. (Resilient : having that capability.)

311. Resin : An organic material of indefinite and relatively high molecular mass that may be used as a softener, processing aid, vulcanizing agent, or reinforcing agent.

312. Retarder : A material used to reduce the tendency of a rubber compound to vulcanize prematurely.

313. Reversion : Deterioration of vulcanizate properties that may occur when vulcanization time is extended beyond the optimum.

314. RMS : Root mean square. A measure of surface roughness, calculated as the square root of the sum of the squares of micro-inch deviation from true flat.

315. Rotary Seal : A seal, such as an O-Ring or a Quad-Ring seal, exposed on either the ID or OD sealing surface to a rotating component, e.g. shaft seals.

316. Rough Trim : Removal of superfluous material by pulling or picking; usually the removal of a small portion of the flash or sprue which remains attached to the product.

317. Rubber : A material that is capable of recovering from large deformations quickly and forcibly, and can be, or already is, modified to a state in which it is essentially insoluble. Also see Elastomer.

318. Rubber, Bound : The portion of the rubber in a mix that is so closely associated with the filler as to be unextractable by the usual rubber solvents.

319. Rubber, Cellular, Closed cell : A cellular material in which practically all the individual cells are non-connecting.

320. Rubber, Expanded : Cellular rubber having closed cells made from a solid rubber compound.

321. Rubber, Gel : The portion of rubber insoluble in a chosen solvent.

322. Rubber Hardness Degree, International : A measure of hardness, the magnitude of which is derived from the depth of penetration of a specified indenter into a specimen. Commonly referred to as IRHD.

323. Rubber, Natural : cis-1,4-polyisoprene that is obtained from a botanical source, usually Hevea Brasiliensis.

324. Rubber, Oil-extended : A grade of raw rubber containing a relatively high proportion of processing oil.

325. Rubber, Raw : Natural or synthetic elastomer, usually in bales or packages, that is the starting material for the manufacture of rubber articles.

326. Rubber, Sponge : Cellular rubber consisting predominantly of open cells and made from a dry rubber compound.

327. Rubber, Synthetic : Rubber produced by polymerizing one or more monomers with or without post-polymerization chemical modification.

328. Rubber, Vulcanized Compound : A crosslinked elastic material compounded from an elastomer, susceptible to large deformations by a small force and capable of rapid, forceful recovery to approximately its original dimensions and shape upon removal of the deforming force.

329. Runner (Injection or Transfer mold) : The secondary feed channel for transferring material under pressure from the inner end of the sprue to the cavity gate.

330. Runner : The system for leading rubber and plastic materials into the gate of an injection mold.

331. Runout (Shaft) : Expressed in inches and/or TIR (Total Indicator Reading); refers to twice the radial distance between shaft axis and axis of rotation.


332. Salt Bath : A heat transfer apparatus, utilizing molten salts as the heating medium, generally used for vulcanization. Commonly used in extrusion systems.

333. SBR : Copolymer of Butadiene and Styrene; an all purpose type synthetic, similar to natural rubber. (Butadiene is a gaseous material of petroleum; Styrene, a reaction product of ethylene and benzene.)

334. Scorch : Premature curing or setting up of a raw compound during processing.

335. Seal : Any device used to prevent the passage of a fluid, gas or liquid.

336. Seal-Off : A minimum .032 inch (.813 mm) step on an insert that minimizes flash on the OD, and prevents flash from forming across the insert.

337. Secondary Accelerator : An accelerator used in smaller concentrations compared to the primary accelerator, to achieve a faster rate of vulcanization.

338. Service : Operating conditions to be met.

339. Set : The strain remaining after complete release of the force producing the deformation.

340. Shaft : Reciprocating or rotating member, usually within a cylinder; not in contact with the walls.

341. Shelf Aging : The change in a material’s properties which occur in storage with time.

342. Sheeting : The process of converting a rubber, rubber mix, rubber dough, or latex into a sheet.

343. Shelf Life : The period of time after production during which a material or product, that is stored under specified conditions, retains its intended performance capabilities.

344. Shock Load : The sudden application of an external force.

345. Shore A : See Durometer.

346. Shore M : A Durometer hardness instrument, using a micro-indentor designed for the purpose of measuring O-Ring hardness.

347. Shrinkage :
1) The ratio between a mold cavity size and the size of a product molded in that cavity, 2) Decreased volume of a seal, usually caused by extraction of soluble constituents by fluids followed by air drying.

348. Silicone Rubber : Elastomer that retains good properties through extra wide temperature ranges.

349. Size, Actual : Actual dimension of the product, including tolerance units.

350. Size, Number : Number assigned to indicate inside and cross section diameters of an O-Ring; established in the SAE standard AS 568, adopted by the military and industry.

351. Skin : A relatively dense layer at the surface of a cellular polymeric material.

352. Sliding Core : A pin on a mold that automatically retracts when the mold opens.

353. Softener : A compounding material used to produce a mix of reduced viscosity, which facilitates incorporation of rubber additives.

354. Sorption : A term used to denote the combination of adsorption and absorption processes in the same substance.

355. Specific Gravity : Ratio of the weight of a given substance, to the weight of an equal volume of water, at any specific temperature.

356. Specimen, Test : A piece of material appropriately shaped and prepared so that it is ready to use for a test.

357. Spew : Surplus material forced from a mold on closure under pressure. Synonym for flash.

358. Spiral Failure : Seal failure in reciprocating applications that result from a twisting

359. Spiral Twist : A type of seal failure in reciprocating application that results from the twisting action that strains or ruptures the rubber.

360. Splice : The uniting of two parts of a vulcanized rubber product to form a continuous length.

361. Sprue : The primary feed channel that runs from the outer face of an injection or transfer mold, to the mold gate in a single cavity mold, or to the runners in a multiple cavity mold.

362. Sprue Hole : The passageway through which a rubber is forced into a mold.

363. Sprue Marks : Marks left on the surface of a rubber part, generally elevated, after removal of the sprue or cured compound in the gate, through which the compound is injected or transfer molded.

364. Squeeze : Cross section diametrical compression of O-Ring between surface of the groove bottom and surface of the other mating metal part in the gland assembly.

365. Stabilizer : A substance present in or added to raw rubber to maintain properties at or near their initial values during its production, processing, and storage.

366. Static Seal : Part designed to seal between parts having relative motion. (See Gasket)

367. Statistical Process Control (SPC) : The use of statistical techniques on processes and their output, to establish process stability and increase capabilities.

368. Stiffener : A compounding material used to increase the viscosity of an unvulcanized rubber mix.

369. Stiffness : That property of a specimen that determines the force with which it resists deflection.

370. Stiffness, Bending : The force required to produce a bent configuration under specified conditions.

371. Strain : Deflection due to force.

372. Strainer : A machine designed to force a rubber or rubber mix through a sieve to remove extraneous material.

373. Stress : Force per unit of original cross section area.

374. Stress Relaxation : Decreasing stress with constant strain over a given time interval. (Viscoelastic response.)

375. Stock : Unvulcanized, mixed rubber compound of a definite composition.

376. Sublimation : The direct conversion of a substance from solid state to vapor state, passing through a transitory liquid state. The vapor, upon recondensing, reforms into the solid state with no intervening liquid phase.

377. Surface Finish : A numerically averaged value of surface roughness, generally in units of microinches or micrometers.

378. Sulfur Donor Vulcanizing System : A vulcanizing system in which there is no elemental sulfur present, and all of the sulfur available for the crosslinking is provided by the partial decomposition of sulfur-containing materials.

379. Sulfur, Free : The uncombined sulfur in a rubber mix or vulcanizate.

380. Sulfur, Total : All the sulfur present in a material irrespective of its chemical form or origin.

381. Sun Checking : Surface cracks, checks or grazing caused by exposure to direct or indirect sunlight.

382. Swell : Increased volume of a specimen, caused by immersion in a fluid (usually liquid).


383. Tack : The property that causes contacting surfaces of unvulcanized rubber to adhere to each other.

384. Tackifier : A compounding material that enhances the ability of vulcanized rubber to adhere to itself or another material.

385. Tear : Mechanical rupture initiated and propagated at a site of high stress concentration caused by a cut, defect, or localized deformation.

386. Tear Strength : The force required to rupture a sample of stated geometry. The maximum force required to tear a specified test specimen, the force acting substantially parallel to the major axis of the specimen.

387. Tear Resistance : Resistance to growth of a cut or nick when tension is applied to the cut specimen. Commonly expressed as pounds per square inch thickness.

388. Temperature Range : Maximum and minimum temperature limits in which a seal compound will function in a given application.

389. Tensile Strength : Force, in pounds per square inch, required to cause the rupture of a specimen of rubber material.

390. Tensile Stress : A stress applied to stretch a test specimen.

391. Tension Fatigue : A fracture, through crack growth, of a component or test specimen subjected to a repeated tensile deformation.

392. Tension Set : The extension remaining after a rubber specimen has been stretched and allowed to retract.

393. Tension Modulus : Resistance to being stressed; defined as the force, in pounds, necessary to stretch a piece of rubber, one square inch in cross section, a specified amount. Normally expressed as a percentage of original length, and the stress as pounds per square inch at the fixed elongation.

394. Terpolymer : A polymer consisting of three different monomers, chemically combined.

395. Thermal Carbon Black : A soft carbon black formed by the thermal decomposition of natural gas.

396. Thermal Degradation : Irreversible and undesirable change in the properties of a material due to exposure to heat.

397. Thermal Expansion : Expansion caused by increase in temperature; may be linear or volumetric.

398. Thermoplastic : A plastic capable of being repeatedly softened by increase of temperature, and hardened by decrease of temperature.

399. Thermoplastic Elastomer (TPE) : A diverse family of rubber-like materials that, unlike conventional vulcanized rubbers, can be processed and recycled like thermoplastic materials. Often referred to as TPR (thermoplastic rubber).

400. Thermoplastic Vulcanizate (TPV) : A thermoplastic elastomer with a chemically cross-linked rubbery phase, produced by dynamic vulcanization.

401. Thermoset Rubber : An elastomer or plastic cured under application of heat or chemical means, to make a product substantially infusible or insoluble.

402. Thiokol : An organic polysufide.

403. Threshold : The maximum tolerance of an elastomer to radiation dosage, expressed as a total number of ergs per gram (or rads) beyond which physical properties are significantly degraded. This is generally an arbitrary value, depending on function and environment.

404. Torque : The turning force of a shaft.

405. Torr : The unit of pressure used in vacuum measurement; equal to 1/760 of a standard atmosphere, and for practical purposes, is equivalent to one millimeter of Mercury (mmHg).

406. Torsion Strength : Ability of rubber to withstand twisting.

407. Total Indication Reading (TIR) : System that measures the roundness of a part in relationship to a center line.

408. TR-10 : A measure of the low temperature capability of an elastomer. It is the temperature at which a stretched and frozen specimen has retracted 10% of the stretched amount. TR stands for “temperature retraction”.

409. Transfer Molding : A method of molding in which material is placed in a pot, located between the top plate and plunger, and squeezed from the pot through gates (or sprues) into the mold cavity.

410. Trapped Air : Air which is trapped in a product or a mold during cure. Usually causing a loose ply or cover, or a surface mark, depression or void.

411. Trim : The process involving removal of mold flash.

412. Trim Out : Damage to mold skin or finish by close trimming.


413. Under Cure : Degree of cure less the optimum; may be evidenced by tackiness, loginess or inferior physical properties.

414. Ultimate Elongation : A measure of how far a material will stretch before breaking; expressed as a percentage of its original length.

415. Undercut : A groove on either the outside or the inside of a molded part.

416. UV Absorber : A compounding material that, through its ability to absorb ultraviolet radiation and render it harmless, retards the deterioration caused by sunlight and other UV light sources.


417. Vacuum : The term denoting a given space that is occupied by a gas at less then atmospheric pressure. For degrees of vacuum, see Vacuum Level.

418. Vacuum Level : The term used to denote the degree of vacuum evidenced by its pressure in torr (or mmHg) :
(a) Rough vacuum = 760 torr to 1 torr, (b) Medium vacuum = 1 torr to 10-3 torr, (c) High vacuum = 10-3 torr to 10-6 torr, (d) Very High vacuum = 10-6 torr to 10-9 torr, (e) Ultra High vacuum = below 10-9 torr.

419. Vapor : The gaseous state of a fluid that normally exists as a liquid under atmospheric conditions, i.e. a gas whose temperature is below its critical temperature.

420. Vapor Pressure : The maximum pressure exerted by a liquid or a solid, heated to a given temperature in a closed container.

421. Vibration Dampening : The ability of an elastomer to absorb vibrational or shock energy.

422. Viscoelasticity : A combination of viscous and elastic properties in a material, with the relative contribution of each being dependent on time, temperature, stress, and strain rate.

423. Viscosity : The property of fluids and plastic solids by which they resist an instantaneous change of shape, i.e. resistance to flow.

424. Void : The absence of material, or an area devoid of materials where not intended.

425. Volatilization : The transition of either a liquid or a solid directly into vapor state. In the case of a liquid, this transition is called evaporation, whereas in the case of a solid, it is termed sublimation.

426. Volume Change : A change in the volume of a seal as result of immersion in a fluid; expressed as a percentage of the original volume.

427. Volume Swell : An increase in the physical size caused by the swelling action of a liquid.

428. Vulcanization : An irreversible process during which a rubber compound, through a change in its chemical structure (for example, crosslinking), becomes less plastic and more resistant to swelling by organic liquids, while elastic properties are conferred, improved, or extended over a greater range of temperature.

429. Vulcanizing Agent : A material which produces vulcanization of an elastomer.

430. Vulcanizing System : The combination of vulcanizing agent and, as required, accelerators, activators, and retarders used to produce the desired vulcanizate characteristics.


431. Water Absorption : The amount of water absorbed by a material under specified test conditions.

432. Weather Resistance : The ability to withstand weathering factors, such as : oxygen, ozone, atmospheric pollutants, erosion, temperature cycling and ultraviolet radiation.

433. Weathering : The detrimental effect upon an elastomer or plastic after outdoor exposure.

434. Width : Seal cross-section or thickness.

435. Wiper Ring : A ring employed to remove excess fluid, mud, etc., from a reciprocating member before it reaches the packings.

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435 Technical Terms You Need To Know in Rubber Industry (Part 1)

Here is a compilation of 435 Technical Terms in Rubber Industry.

Being a long list, I have split this into two posts. Here are alphabets (A-L)



  1. Abrasion : The wearing away of a surface in service by mechanical action, such as rubbing, scraping or erosion.
  1. Abrasion Resistance : The ability of a rubber compound to resist mechanical wear.
  1. Abrasion Resistance Index : A measure of the abrasion resistance of a rubber relative to that of a standard rubber under the same specified conditions, expressed as a percentage.
  1. Absorption : The physical mechanism by which one substance takes up another substance (liquid, gas or vapor) into its interior.
  1. Accelerated Life Test : Any set of test conditions designed to reproduce, in a short time, the deteriorating effect obtained under normal service conditions.
  1. Accelerated Service Test : A service or bench test in which some service condition, such as speed, temperature or continuity of operation, is exaggerated in order to obtain a result in shorter time.
  1. Accelerator : A compounding material used in small amounts, with a vulcanizing agent, to increase the speed of vulcanization.
  1. Acid Resistance : The ability to resist the action of identified acids within specified limits of concentration and temperature.
  1. Acrylic : A polymer for which resistance to air and hot oil at temperatures above 30 degrees Fahrenheit are required.
  1. Adhere : To cling or stick together.
  1. Adhesion : Tendency of rubber to bond or cling to a contact surface.
  1. After Cure : Continuation of vulcanization after the desired cure is effected and the heat source removed (also referred to as Post-Cure).
  1. Ageing : To undergo changes in physical properties with age or lapse of time.
  1. Ageing, Accelerated : Tests run on various rubbers to find out, in as short a period as possible, the destructive influence of light, oxygen, heat and ozone.
  1. Ageing, Oxygen Bomb : A means of accelerating the change in the physical properties of rubber compounds by exposing them to action of oxygen at an elevated temperature and pressure.
  1. Ageing , Air Bomb : Similar to an oxygen bomb, but used with air.
  1. Ageing, Shelf : Ageing during storage.
  1. Agglomerate, Compounding material : A cluster of particles of one or more compounding materials loosely held together. Most commonly used to describe carbon black.
  1. Air Checks : Surface markings or depressions due to trapping air between the material being cured and the mold surface.
  1. Air Curing : Vulcanization of a rubber product in air, as distinguished from in a press or steam vulcanizer.
  1. Alpha Particles : Positively charged particles composed of two protons and neutrons (often referred to simply as helium atom molecule); characterized by limited penetration.
  1. Ambient Temperature : The surrounding temperature relative to the given point of application.
  1. Aniline Point : The lowest temperature at which equal volume of pure, fresh aniline and oil will completely dissolve in one another is the aniline point of the oil.
  1. Antidioxidant : An organic substance which inhibits or retards oxidation.
  1. Antiozonant : A substance that retards or prevents the appearance of cracks from action of ozone when the elastomer is exposed under tension, either statically or dynamically, to air containing ozone.
  1. Antirad : A material which inhibits radiation change.
  1. Aromatic Oil: A hydrocarbon process oil containing at least 35%, by mass, of aromatic hydrocarbons.
  1. Atmospheric Aging Resistance : Loss of physical properties due to the normal action of its surroundings (weather).
  1. Atmospheric Cracking : Cracks produced in the surface of rubber articles by exposure to atmospheric conditions.
  1. Autoclave : A vessel used for vulcanizing rubber products by means of steam under pressure.
  1. Axial Seal : A term usually applied to an O-Ring where the squeeze is applied on the top and bottom surfaces. Another term for face seal.



  1. Backrind : A molding defect in which the rubber adjacent to the parting line shrinks below the surface of the molded product, with the parting line often being ragged and torn.
  1. Back-Up-Ring : (Anti extrusion device) A ring of relatively hard and tough material, placed in the gland between the O-Ring and groove side walls, to prevent extrusion of the O-Ring.
  1. Bake Out : A process whereby a vacuum system is heated for a given time at some predetermined temperature to degas all the components, i.e. gauges, fittings, valves, seals.
  1. Banbury Mixer : A specific type of internal mixer used to blend fillers and other ingredients with an elastomer.
  1. Bank: The reservoir of material at the opening between rolls of a mill or calendar.
  1. Batch : The product of one mixing operation.
  1. Bench Marks : Two marks of known separation, applied to a specimen to measure the strain of the specimen during extension.
  1. Bench Test : A modified service test in which the service conditions are approximated, but the equipment is conventional laboratory equipment and not necessarily identical with that in which the product will be employed.
  1. Blank : A portion of a rubber compound of suitable volume to fill the cavity of a mold.
  1. Beta Particles : Negatively charged particles or electrons, characterized by limited penetration.
  1. Bleeding : Migration to the surface of plasticizers, waxes or similar materials, to form a film or bead.
  1. Blemish : A mark, deformity or injury which impairs appearance.
  1. Blister : A raised spot in the surface, or a separation between layers, usually forming void or air-filled space in the vulcanized article.
  1. Bloom : A dusty or milky looking deposit that sometimes appears on the surface of an molded product after molding and storage, caused by migration of a liquid or solid to the surface. Not to be confused with dust from external sources.
  1. Blow : The volume expansion that occurs during the production of cellular or sponge rubber.
  1. Blowing Agent : A compounding material used to produce gas by chemical or physical action, or both, in the manufacture of hollow or cellular articles.
  1. Bond : The term commonly used to denote the attachment of a given elastomer to some other member. Bonds may be classified by types, as follows:
  1. Mechanical – purely physical attachment accomplished by such means as “through” holes, interlocking fingers, envelope design, riveting, etc.;
  2. Cold – adhesion of previously vulcanized elastomer to another member through use of suitable contact cements;
  3. Vulcanized – adhesion of an elastomer to a previously primed surface using heat and pressure, thus vulcanizing the elastomer at the same time.
  1. Break : A separation or discontinuity in any part of an article.
  1. Break-Out : Force to inaugurate sliding. Expressed in same terms as friction. An excessive break-out value is taken as an indication of the development of adhesion.
  1. Brittleness : Tendency to crack when deformed.
  1. Brittle Point: The highest temperature at which a rubber specimen will fracture under sudden impact.
  1. Buna -N : See Nitrile.
  1. Buna-S : A general term for the copolymers of butadiene and styrene. Also known as SBR and GRS.
  1. Butaprene : See Nitrile.
  1. Buffing : The grinding of a vulcanizate, producing a roughened or velvety texture.
  1. Bumping, Moulding Process : The application, release, and reapplication of pressure prior to the start of vulcanization to vent entrapped gases, thereby facilitating complete filling of the mould cavities.
  1. Butt Joint : Joining two ends of a seal whereby the junction is perpendicular to the mold parting line.
  1. Butyl : A copolymer of iso-butylene and isoprene.



  1. Calender : A machine with two or more parallel, counter-rotating rolls, with controllable roll-to-roll spacing, rotating at selected surface speeds and controlled temperatures.
  1. Carbon Black : A material consisting essentially of elemental carbon in the form of near-spherical colloidal particles and particle aggregates. It is produced by partial combustion or thermal decomposition of hydrocarbons. Primarily used as a reinforcing agent, but also affects many other dynamic properties of a rubber compound.
  1. Catalyst : A chemical that, in small quantities, accelerates a chemical reaction without itself necessarily becoming part of the final product.
  1. Cell : A single small cavity surrounded partially or completely by walls.
  1. Cell, Closed : A cell totally enclosed by its walls, hence not interconnected with other cells.
  1. Cell, Open : A cell not totally enclosed by its walls and hence interconnected with other cells.
  1. Cellular Rubber : A generic term for materials containing many cells (either open, closed, or both) dispersed throughout the mass of rubber.
  1. Cellular Material, Collapse : An undesirable densification of a cellular material resulting from the breakdown of its cellular structure.
  1. Cement, Rubber : An adhesive that is either a liquid dispersion or solution of raw or compounded rubber, or both.
  1. Chalking : The formation of a powdery residue on the surface of a rubber, commonly resulting from surface degradation.
  1. Checking : The short, shallow cracks on the surface of a rubber product, usually resulting from damaging action by environmental elements.
  1. Chemical Bonding : A method of bonding rubber to inserts by applying special adhesives to the insert prior to molding.
  1. Chemigum : See Nitrile.
  1. Closure Dimension : Dimensions of a molded rubber product that are affected by flash thickness (mold closure) variation.
  1. Coagent: A compounding ingredient used in small amounts to increase the crosslinking efficiency of certain non-sulfur vulcanizing systems (especially organic peroxides), or to modify the properties given by such systems.
  1. Coating : A uniform layer of chemical primers or adhesives to produce a chemical bond between the rubber and substrate. May also refer to special surface treatments that can be applied to rubber to achieve special properties.
  1. Coated Fabric : A flexible product composed of a textile fabric and an adherent polymeric material applied to one or both surfaces.
  1. Coefficient of Thermal Expansion : Average expansion per degree over a stated temperature range, expressed as a fraction of initial dimension. May be linear or volumetric.
  1. Cold Checks : A defect on calendered sheeting consisting of surface roughness.
  1. Cold Flexibility : Flexibility following exposure to a predetermined low temperature for a predetermined time.
  1. Cold Flow : Slow deformation, under gravitational force, at or below room temperature. Sometimes referred to as “creep”.
  1. Cold Resistance : Able to withstand the effects of cold or low temperatures without loss of serviceability.
  1. Commercially Smooth : Degree of smoothness of a surface of an article which is acceptable for use.
  1. Compound : A term applied to a mixture of polymers and other ingredients to produce a usable rubber material.
  1. Compound, Standard: A control or reference compound prepared according to a prescribed formula and mixing procedure.
  1. Compression Molding : Molding process in which the material is placed directly in the mold cavity and compressed to shape by closure of the mold, under heat and pressure.
  1. Compression Modulus : The ratio of the compression stress to the resulting compression strain (the latter expressed in the direction of force). Compression Modulus may be either static or dynamic.
  1. Compression Set : The permanent deformation experienced by a rubber material when compressed for a period of time. The term is commonly used in reference to a test conducted under specific conditions wherein the permanent deformation, expressed as a percentage, is measured after a prescribed period of time. A low compression set is desirable in molded rubber parts such as seals and gaskets, which must retain their dimensions to maintain an effective seal.
  1. Conditioning (Environmental) : The storage of a rubber, under specified conditions (time, temperature, humidity) prior to testing.
  1. Conditioning (Mechanical): The prescribed program of deformation of a specimen prior to testing.
  1. Conductive Rubber : A rubber capable of conducting electricity. Most generally applied to rubber products used to conduct static electricity.
  1. Copolymer : A polymer consisting of two different monomers chemically combined.
  1. Corona Resistance : The ability of a rubber acting as insulator to withstand the effects of high voltage discharge. Indications of failure appear as surface cracks.
  1. Corrosion (Packing) : Corrosion of rigid member (usually metal) where it contacts packing. The actual corroding agent is fluid medium trapped in the interface.
  1. Corrosive (Packing) : A property of packing whereby it is assumed (often incorrectly) to promote corrosion of a rigid member of a trapped fluid.
  1. Cracker : A heavy-duty mill having two deeply corrugated or pyramid-cut rolls for breaking down a rubber or a mix, or for cutting rubber or a mix into pieces.
  1. Crack : A fissure originating in the surface of a rubber vulcanizate or product as a result of natural weathering.
  1. Crack, Flex : A fissure originating in the surface of a rubber vulcanizate, resulting from cyclic deformation (usually bending).
  1. Crack, Ozone : Fissures originating in the surface of a rubber vulcanizate, caused by exposure to an ozone-containing environment; these fissures are perpendicular to the direction of strain, and usually occur in rubbers having main chain unsaturation.
  1. Cracking : The sharp break or fissure in the surface. Generally due to excessive strain.
  1. Crazing : Formation of a random pattern of shallow cracks on a rubber surface usually due to ageing by light. Unlike ozone cracking, crazing does not depend on the presence of a tensile strain in the rubber.
  1. Creep : The progressive relaxation of a given rubber material while it is under stress. This relaxation eventually results in permanent deformation, or “set”.
  1. Crosslink : The chemical bond bridging one polymer chain to another.
  1. Crosslinking : Formation of chemical bonds between polymer chains to give a network structure.
  1. Cross-Linking Agents : A chemical, or chemicals, that bonds the polymer chains together to form a thermoset rubber product.
  1. Cross-Section : A seal as viewed if cut at right angles to the molding line, showing internal structure.
  1. Crystallinity : Orientation of the disordered long chain molecules of a polymer into repeating patterns. The degree of crystallinity effects stiffness, hardness, low temperature flexibility, and heat resistance.
  1. Cure : The thermo process that causes a chemical change in the raw stock, turning it into the finished rubber part . Also see Vulcanization.
  1. Cure Date : The date a rubber product was molded. Normally expressed, for example, as 1Q04, meaning the first quarter of the year 2004.
  1. Cure Meter : A testing device that measures the progress of vulcanization.
  1. Curing Temperature : The temperature at which the rubber product is vulcanized.
  1. Cure Time : The preset time needed to complete the curing process
  1. Cylinder : Chamber in which piston, plunger, ram, rod or shaft is driven by, or against, the system fluid.



  1. Damping : The quality of an elastomer to absorb forced vibrational energy. That property of a material or system that causes it to convert mechanical energy to heat when subjected to deflection; in rubber the property is caused by hysteresis.
  1. Deflashing : Any of various processes used to remove the waste edge from a molded rubber part.
  1. Degassing : The intentional, but controlled, outgassing of a rubber substance or other material.
  1. Density : The mass per unit volume of a material. Also referred to as specific gravity.
  1. Desiccant : A compounding material used to irreversibly absorb moisture, particularly for the purpose of minimizing risk of porosity during vulcanization.
  1. Die Swell : The difference between the dimensions of the cross section of an extrudate, and the corresponding dimensions of the die orifice from which the extrudate was formed. It is usually expressed as the percent increase in the cross-sectional area.
  1. Diene Polymer : A polymer formed from one or more monomer species, at least one of which is a diolefin.
  1. Dielectric Properties : The ability of a material to resist puncture due to electric stress. The property is expressed in terms of “volts per MIL thickness”.
  1. Dielectric Strength: The measure of a vulcanizate’s ability to resist passage of a disruptive discharge produced by an electric stress.
  1. Diffusion : The mixing of two or more substances (solids, liquids, gasses, or combinations thereof) due to the intermingling motion of their individual molecules. Gasses diffuse more readily than solids.
  1. Dispersion : The application of shearing forces to distribute one or more compounding materials uniformly throughout the mass of a rubber compound.
  1. Dumbbell Specimen : A flat specimen of rubber having a narrow straight central portion of essentially uniform cross section with enlarged ends. Used for testing purposes.
  1. Durometer : An instrument for measuring the hardness of a rubber; measures the resistance to the penetration of an indentor point into the surface of the rubber.
  1. Dusting : The application of a powder to a rubber surface, generally to prevent adhesion to another surface.
  1. Dynamic : An application in which the seal is subject to movement, or moving parts contact the seal.
  1. Dynamic Packing : A package employed in a joint whose members are in relative motion.
  1. Dynamic Properties : Mechanical properties exhibited under repeated cyclic deformation.
  1. Dynamic Seal : A seal required to prevent leakage past parts which are in relative motion. Also means a seal which is subjected to reciprocating, rotational, or oscillating motion.



  1. Ejector Pins : Pins or blades that, when activated internally to the mold, eject the part from the mold cavity. Sometimes referred to as “knock outs”.
  1. Elasticity : The property of an article which tends to return to its original shape after deformation. A rubber’s ability to return to its original size and shape after removal of the stress causing deformation such as stretching, compression, or torsion. It is the opposite of plasticity. The term elasticity is often loosely employed to signify the “stretchiness” of rubber.
  1. Elastomer : Any natural or synthetic material with resilience or memory sufficient to return to its original shape after major or minor distortion.
  1. Electron Volt : Unit of energy in atom calculations equal to 1.602 X 1012 ergs.
  1. Elongation : Extension produced by a tensile stress.
  1. Elongation, Percent : The extension of a uniform section of a specimen expressed as percent of the original length.
  1. Elongation, Ultimate : The elongation at the time of rupture.
  1. EPDM : Terpolymer of Ethylene-Propylene-Diene (noted for excellent ozone resistance).
  1. Erg : Unit of energy (C.G.S.) equal to one dyne centimeter, or approximately equal to the work done by force of One (1) milligram, causing a movement of one (1) centimeter.
  1. Evaporation : The direct conversion from liquid to vapor state of a given fluid.
  1. Explosive Decompression : The rupture of a rubber article caused by the rapid reversal of pressure, causing dissolved gases in the rubber to escape quickly to the surface of the vulcanizate.
  1. Extender : A material (usually organic) used to augment the polymer in a compound.
  1. Extensometer : A device for determining elongation of a specimen as it is strained.
  1. Extrudate: The material that issues from an extruder.
  1. Extruder : A machine designed to force rubber through an orifice, which is shaped to the geometry of the desired end product.
  1. Extrusion : The continuous shaping of a material during passage through a die.
  1. Extrusion (seal) : Distortion, under pressure, of a portion of a seal into the clearance between mating metal parts.



  1. Face Seal : A seal between two flat surfaces. In an O-Ring, this means it seals on the top and bottom, not the ID and OD. Also referred to as an axial seal.
  1. Fatigue Breakdown : The deterioration of an elastomeric product during repeated deformation.
  1. Fatigue Life : The number of deformations required to produce a specified state of fatigue breakdown in a test specimen or product that is deformed under a prescribed set of conditions.
  1. Feather Edge : The sharp, thin edge on parts, such as wiper seals and cups. (Also called “Knife Edge”).
  1. Filler : A solid compounding material, usually in finely divided form, which may be added in relatively large proportions to a polymer for technical or economic reasons. The most commonly used filler is carbon black. Most fillers also function as reinforcing agents.
  1. Filler, Inert : A filler having no reinforcing effect.
  1. Fixed Dimension : Dimensions on a rubber product that are not affected by flash thickness or mold closure variation.
  1. Flame Resistance : The resistance to burning of material that will not withstand combustion under ordinary conditions.
  1. Flash : Excess rubber left around a rubber part after molding, due to space between mating mold surfaces; removed by trimming.
  1. Flex Cracking : A surface cracking induced by repeated bending or flexing.
  1. Flex Life : The number of cycles required to produce a specified state of failure in a specimen that is flexed in a prescribed method.
  1. Flexometer : A machine that subjects a test specimen to repeated deformation by compression, tension, shear, bending, torsion or any combination thereof.
  1. Flex Resistance : The relative ability of a rubber article to withstand dynamic bending stress.
  1. Flexural Strength : The ability of a material to flex without permanent distortion or breaking.
  1. Flock : Fibrous filler sometimes used in rubber compounding.
  1. Flow : Ability of heated plastic, or uncured rubber, to travel in the mold and runner system during the molding process.
  1. Flow Cracks : Surface imperfections due to improper flow and failure of stock to knit or blend with itself during the molding operation.
  1. Flow Marks : Marks or line on a molded product, caused by imperfect flow of the raw compound during forming.
  1. Fluid : A liquid or a gas.
  1. Fluorocarbon : A polymer designed to meet the most rigid requirements in oils, solvents, synthetic lubricants and corrosive chemicals, at elevated temperatures.
  1. Friction : Resistance to motion due to contact of surfaces.
  1. Friction (Break Out) : Friction developed during initial or starting motion.
  1. Friction (Running) : Constant friction developed during operation of a dynamic O-Ring.
  1. Frosting : The formation of a matte, whitish appearance on a rubber surface exposed to air, resulting from the action of ozone. Often confused with bloom.
  1. Fuel (Aromatic) : Fuel which contains benzene or aromatic hydrocarbons; causes little swell of rubber.
  1. Fuel (Non-Aromatic) : Fuel which is composed of straight chain hydrocarbons; causes little swell of rubber.
  1. Furnace Carbon Black : A type of carbon black produced by the decomposition reaction of hydrocarbons, when injected into a high velocity stream of combustion gases under controlled conditions.



  1. Gamma Radiation : Electromagnetic disturbance (photons) emanating from an atomic nucleus. This type of radiation travels in wave form, much like X-Rays or light, but has a shorter wave length (approx. 1 Ado or 107 mm). It is very penetrating.
  1. Gasket : A deformable material clamped between essentially stationary faces to prevent the passage of matter through an opening or joint. A static mechanical seal.
  1. Gas Permeability : The degree to which a substance resists permeation of gas under pressure.
  1. Gates : The openings in an injection or transfer mold that ensure the even flow of material into the cavity.
  1. Gate Mark : A raised spot or small depression on the surface of an injection or transfer molded part, where the gates interface the cavity. (Also called “Sprue Mark”)
  1. Gland : The cavity into which an O-Ring is installed. Includes the groove and mating surface of the second part, which together confine the O-Ring.
  1. Glass Transition Temperature : The approximate mid-point of the temperature range over which a reversible change in a polymer occurs from (or to) a viscous or rubbery condition to (or from) a hard and relatively brittle one.
  1. Grain : The unidirectional orientation of rubber or filler particles in a rubber strength: the resistance to deformation of rubber stock in the uncured state.
  1. Groove : The machined recess into which a seal is fitted.ground vulcanized rubber: vulcanized rubber in particulate form; used as an extender or filler.
  1. Guayule Rubber: A form of natural rubber, cis polyisoprene, obtained from the shrub, Parthenium Argentatum.
  1. Gum Compound : A rubber compound containing only those ingredients necessary for vulcanization and small amounts of other ingredients for processing, coloring, and for improving the resistance to ageing.



  1. Hardness : Resistance to a disturbing force. Measured by the relative resistance of a material to an intender point of any one of a number of standard hardness testing instruments. (Also see Durometer).
  1. Heat Aging : A test for degradation of physical properties as a result of exposure to high temperature conditions.
  1. Heat Build-up : The accumulation of thermal energy generated within a material as a result of hysteresis, evidenced by an increase in temperature.
  1. Heat Deflection Temperature : The temperature at which a standard plastic test bar deflects 0.010 in. under a stated load of either 66 psi or 264 psi.
  1. Heat History : The accumulated amount of heat a rubber stock has been subjected to during processing operations. Incipient cure or scorch can take place if heat history is excessive.
  1. Hermetic Seal : An airtight seal having no evidence of detectable leakage.
  1. Homogeneous : A material of uniform composition throughout.
  1. Homopolymer : A polymer formed from a single monomer species.
  1. Hydrocarbon Solvents – Aromatic : Solvents having basic benzene structure, usually coat tar types such as benzene, toluene orxylene.
  1. Hysteresis Loss : The loss of mechanical energy due to hysteresis.
  1. Hysteresis : The conversion of mechanical energy to heat in rubber undergoing strain.


  1. Identification : Colored dots or stripes on seals for identification purposes; seldom used.
  1. Immediate Set : The deformation found by measurement immediately after removal of the load causing the deformation.
  1. Immersion : Placing an article into fluid, generally so it is completely covered.
  1. Impact : The single, instantaneous stroke or contact of a moving body with another, either moving or at rest, such as a large lump of material dropping on a conveyor belt.
  1. Impact Resistance: Resistance to fracture under shock force.
  1. Impact Strength : A measure of the toughness of the material, as the energy required break a specimen with a single blow.
  1. Inhibitor : A material used to suppress a chemical reaction.insert: typically, a metal or plastic component to which rubber is chemically and/or physically bonded during the molding process.
  1. IRHD (International Rubber Hardness Degrees) : International Rubber Hardness Degrees. An alternate method of measuring rubber hardness. IRHD units are approximately equivalent to Shore A durometer units, although a different apparatus is used.
  1. Injection Molding : Molding in which the rubber or plastic stock is heated and, while in the flowable state, is forced or injected into the mold cavity.
  1. Insert : Typically, a metal or plastic component to which rubber or plastic is chemically and/or physically bonded during the molding process.
  1. Isoprene-acrylonitrite Rubber : A low-plasticity copolymer with around 34 per cent ACN.



  1. Knit Line : An internal or external defect in a vulcanizate, where raw stock did not unite into a homogeneous mass during vulcanization.
  1. Knuckles : Small tough rubber pieces scattered throughout a bale of raw rubber that do not disperse easily or accept carbon black and other compounding materials during mixing.



  1. Leakage Rate : The rate at which a fluid (either gas or liquid) passes a barrier. Total Leakage Rate includes the amounts that diffuse or permeate the material of the barrier as well as the amount that escapes around it.
  1. Life Test : A laboratory procedure used to determine the amount and duration of resistance of an article to specific sets of destructive forces or conditions.
  1. Linear Expansion : Expansion in any one linear dimension, or the average of all linear dimensions.
  1. Liquid Curing Medium (LCM) : A molten phase, generally a mixture of sodium nitrate, that is used as a heating medium for the continuous vulcanization of a rubber mix, usually following extrusion.
  1. Logy : Sluggish, low snap or recovery of a material.
  1. Low Temperature Flexibility : The ability of a rubber product to be flexed, bent or bowed at low temperature without cracking.


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Editor’s Pick: Four Steps to Effective Rubber-Metal Bonding

My friends at Kemstertek, a consulting organization dedicated to Elastomers and its related areas, shared the contents from their e-book ‘Core Rubber Concepts‘.

Rubber in its different forms demonstrates the ability to bond to all kinds of metals. And bonded rubber is stronger. Rubber to metal bonding is a means by which rubber is mechanically bonded to a metal insert during the moulding process. Typical applications for rubber to metal bonding include, any part requiring the combination of the flexibility of rubber and the stability of a metal.

You may have observed that manufacturers across many industries rely on rubber to metal bonding for their components. This is because rubber not only produces a very strong bond on metal, but it also can be used to combine several components into a single assembly. Automotive and industrial manufacturers increasingly are turning to rubber to metal technology to reduce their raw number of components, eliminate vibration and improve the performance of individual components and sub-assemblies used in harsh environment applications.

Examples of Rubber-Metal bonded include small mounts for motors to large locomotive suspension parts, parts used for the isolation of noise and vibration in automotive and engineering applications, larger components designed to decouple translational movement for bridges and buildings.

Rubber-Metal Bonding Process

Briefly, the Rubber-Metal bonding process begins with the inserts that are first prepared for production using a grease removing system to rid your parts of any contaminants before the adhesive is applied. Subsequently, the heated adhesive is applied on to the inserts using a technique similar to your spray painting. Once the metals are prepared, the inserts are then physically placed, one at a time, into each cavity of your mold. Next, the rubber moulding process is started using the appropriate rubber moulding machinery. After the mold is closed, and the moulding begins, the adhesive on the metals is activated, allowing the inserts to bond to the rubber.

Flow chart for manufacturing of moulded rubber-metal parts

Source: Camberley Rubber

Four Steps to Effective Rubber-Metal Bonding

This is a topic from Kemstertek’s book ‘Core Rubber Concepts‘. Read on.

The scope of the following discussion limits only to bonds formed with metal parts while the rubber undergoes vulcanization. This does not cover bonding of vulcanizates with metals at the raw stage or after curing is completed.

  1. Part Design and Manufacturability: The geometry of the metal insert should be such that proper rubber filling should happen while molding and the areas adjoining the insert should get enough molding pressure. The mould should be designed for a positive shut-off on the metal insert to cut the amount of flash. Provision should be made to vent off entrapped air or otherwise it will lead to blisters or weak spots at the interface of rubber and metal that will lead to a lack of bonding and premature failure.
  2. Metal Preparation: Generally a freshly sanded or grit blasted surface should be sufficient to give a strong bond. If more strength is required, chemical adhesive treatments are to be done. Commercial adhesives are available in two pack systems, a primer, and an adhesive. Proper application as prescribed by the manufacturer in terms of grammage, curing, and ageing are to be strictly followed. Adhesive application or molding should be done immediately as the surface of sand blasted metal is prone to oxidation which will affect the bond quality. For high-performance bonds, the brass coating can be made on the metal surface by electro deposition of copper and zinc followed by diffusion and maturation process to form a durable brass coating. Conventional metal coatings processes like phosphating, galvanizing, and polyisocyanate treatments were also reported to be useful.
  3. Adhesion Promoters: Adhesion promoters can play a vital role in the adhesion and sustenance of a bond due to ageing in hot and humid conditions. Cobalt salts like cobalt naphthenate are proven adhesion promoters in tyre skim compounds that come in contact with steel cords. Other additives like silica, organic resin formers, organic sulphides, zinc oxide, and organofunctional silanes are also found effective.
  4. Base Polymer and Fillers: Generally polar rubbers are found to be easier to bond than non-polar rubbers like butyl rubber. Sulphur cured rubbers are easier to bond as sulphur is believed to interact with some of the added bond promoters in the recipe. Fillers are to be carefully selected so as to reduce the differential stress at the interface. Excessive loading of fillers reduce the rubber hydrocarbon percentage at the interface and is not advisable. Epoxy modified natural rubber as an adhesion promoter is found to improve the adhesion properties.

Reach out Kemstertek on

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The Art of Owning and Operating Rubber Calenders

Calendering is one of the oldest rubber processing technologies. This is a mechanical process by which rubber is pressed into textiles (cloth, fabric, tire cord) forming composite sheets.

Rubber Calendering is classified into two based on what you are calendering. Your guiding principle for calender line
operation should be consistency and continuity.

The machinery that helps you do rubber calendering is known as a Rubber Calender and it performs various functions. This is a heavy-duty machinery consisting of two or more rolls that revolve in opposite directions.

Today, you have a wide range of new and used calender purchase options. Choosing the right Calender is important; learning to operate it smartly is equally key for your success with this rubber machinery. This edition covers all these aspects in a descriptive manner.

Calenders_July 2016 Cover

Click on cover to read.

(This digital edition is available on – Youblisher and Yumpu)

Download PDF Here

In addition, we have the ‘Insight’ section that is an infographic on ‘7 Proven Strategies To Methodically Grow Your Business’. I hope you enjoy this issue.

I hope you find this special supplement informative. Let me know.

(Disclaimer: All the pictures and statements in this special supplement are sourced from web or shared by respective companies. All copyrights belong to actual owner. Rubber & Tyre Machinery World does not independently verify them nor will vouch for their genuineness, hence will not be liable for any misrepresented data. The images are used here for representation purpose only.)

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Editor’s Pick: Manufacture of Cold Retreading Material (Part 2)

This is a continuation to Part 1 of this informative article on Manufacture of Cold Retreading Material shared by Dr.S.N.Chakravarty.

Cold Retreading Material - Part 2

Advantages of ‘Pre Cured’ Process:

  1. Precured rubber generally gives more mileage than the conventional rubber due to richer compound, denser tread and flatter profile;
  2. For radial tires, pre-cure retreading is the most ideal process. Radial tire, in its construction, has an inextensible belt. In the conventional retreading process the matrix (rigid mould) should have exact dimensions matching the dimensions of a built radial tire.  Even a small difference in the matrix dimension affects the ultimate performance of the retreaded tire.  But in the case of pre-cure retreading, radial tires are cured in a chamber and not confined to a rigid matrix or mould, hence there is no distortion.
  3. Longer casing life because tire is retreaded in inflated normal road running condition. Thus the casing is not put under tension and over stressed as it happens inside a rigid mould.  (Due to distortion of casing, the number of times a tire can be retreaded with conventional retreading is always lesser than with pre-cure retreading).
  4. Better balancing, due to uniform thickness of tread and better buffing and building techniques.
  5. Better traction due to flatter profile of buffing.

Advantages of Conventional retreading process

  1. More economical (compared to cold cure retreading).
  2. Comparative advantage ( pre cure retreading due to difficulties in setting up franchisees everywhere in case of latter – high investment).
  3. Better aesthetics (compared to pre cure retreading since better finish given to the tire sidewall also).

Tire Retreading Processes 1

Tire Retreading: Salient Features

  1. Since labour is one of the main components of tire retreading in the organized sector, it is more profitable to undertake high value addition business in the organized sector (i.e. retreading of truck and bus, light truck, jeep etc.). Hence, pre cure retreading of other categories of tyres (especially farm, two wheelers etc.) is not as popular.
  2. Retreading, as per international experience, finds greater and ready acceptance in the commercial segment since the main objective is ‘savings’ whereas in the passenger segment the focus is ‘safety’ followed by ‘aesthetics’. Moreover, savings are also very low in passenger segment.
  3. In India, trucks carrying loads above 16 ton and plying on long distance routes do not find operational economy in using retreaded tires. However, trucks and buses plying short distance routes (and loading pattern upto 12 ton) find retreading a more economical option.
  4. The current trend is going in favour of pre-cured primarily due to the following reasons:
  • Better road conditions (with resultant less damage to tire casing)
  • Better driving habits (getting more mileage even from retreaded tires)
  • Overloading is comparatively less
  • Presence of large number of ‘job shops’ for retreading with each specializing in a special part of the process – repairing, buffing, curing etc. being handled by different persons/processors who, over the years, have gained sufficient experience and expertise in conventional retreading.


Pre-cured Tread Manufacturing Process

Compound Mixing

Typical Compound Formulation of Pre-cured Tread, Solution and Cushion Gum

 Ingredients Pre-Cured Tread Compound


Solution Compound


Cushion Gum Compound


Natural Rubber ( RMA 4 ) 70 100 100
Polybutadine Rubber (High cis type) 30 0 0
Rubber crumb ( 40 mesh ) 5 0 0
 WT Reclaim Rubber 5 0 10
Peptizer 0.15 0.2 0.3
Zinc Oxide (White Seal) 4 4 5
Stearic Acid 3 1.5 1.5
Antioxidant TDQ 1 1 1.5
Antioxidant 4020 1 0 0
MC Wax 0.8 0 0
Carbon Black N 339 / 220 65 0 0
Carbon Black N 550 0 35 30
Rubber Process Oil 710 12 12 0
Pine Tar 0 0 12
Wood Rosin 0 6 5
PF Resin 0 2 4
MF Resin 0 2.8 0
Insoluble Sulfur 0 0 3
Sulfur 2.3 3 0
Accelerator  NOBS 0.8 0 1
Accelerator TMTD 0 0 0.25
Retarder PVI 0.1 0 0.15
200.15 167.50 173.70

Rubber compound is prepared by mixing rubber with different ingredients like fillers, process oil, activators, accelerators, curing agents, antioxidants etc. In order to achieve desired level of properties of the product. It is necessary to reinforce rubber with different fillers and vulcanize with sulfur with the help of accelerator etc.

Mixing and mastication are carried out in an Internal Mixer or Kneader or Two Roll mixing mill.

Rubber compounding is one of the most difficult and complex subjects to master in the field of Rubber Technology. There is no simple mathematical formulation to help the compounder. That is why compounding is so difficult a task. (More on this subject)

Kobelco Make Mixers

L&T Marketed Kobelco Make Internal Mixers

Principles of Mixing 

Vulcanizable polymers cannot be used without compounding. Various additives like curative system, protective system, reinforcing agents, cheapeners and other process aids have to be mixed to the polymer or polymer blend ‘to make a coherent homogeneous mass of all these ingredients, which will process satisfactory and on Vulcanization will give the product capable of giving the desired performance, all with the minimum expenditure of machine time and energy.’ (More on this topic)

Extruder and Extrusion Process

Extruders are machines, which shape rubber to a profiled strip by forcing it through a die. (More on this topic)

The rubber compound is passed through a hot feed or cold feed extruder to produce rubber blanks of suitable size (width and thickness) for use in the next manufacturing step i.e. curing in a hydraulic press.



The extruded and cut rubber blanks are placed in tread dies and cured in a steam-heated hydraulic press at suitable curing temperature and pressure. After the curing cycle is completed cured treads with desired tread pattern are taken out and cooled.

Cushion Gum

A three roll calendering machine is used to prepare “cushion gum” i.e. uncured rubber sheet that acts as an adhesive layer between the pre-cured tread and tyre casing during the pre-cured retreading process.

Cushion Gum Roll

Cushion Gum Roll

The term “to calendar” is defined as “to press between rollers or plates in order to make smooth & glossy sheet”.

Calender can be of two bowl or three bowl or multiple bowl machines which is used for Calender rolls are not perfectly cylindrical but have different shape.


A solution churner vessel is used for the preparation of cement solution (contact adhesive) applied to the casing and helps provide increased adhesion between the casing and the cushion.


Here is a flow chart for you summarizing the production process.

Pre-cured Tread - Production Flow Chart

Dr. Chakravarty can be reached on

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Editor’s Pick: Manufacture of Cold Retreading Material (Part 1)

Dr.S.N.Chakravarty shared this informative article on Manufacture of Cold Retreading Material.

Here is Part 1 of this two-part series.


Commercial tire retreading provides an economical means of extending the asset utilization of worn-out tires. The worn-out tire, referred to as the casing, is a valuable resource that is often not utilized to the fullest potential. By replacing the worn tread with a new one, the retreaded tire provides performance similar to that of the new tire at a fraction of the cost.

Retreading often offers a less expensive alternative to the purchase of a new tire. For the truck tire customer, however, retreading is an integral part of a tire maintenance and purchasing programme.  A truck tire casing must be able to be retreaded two to three times.

Cold Retreading Material - Part 1

Considering that only about one-fifth of a tire is worn out in service, it makes economic sense to retread the tires for multiple use. Although both cross ply and radial tires can be retreaded. 4 to 8 ply bias tires can be the most easily retreaded. However, the structural performance may fall short of the new tires and service conditions may have to be more closely controlled.

Tire Retreading

Tire Retreading can be done by the two processes (a) conventional ‘hot’ capping and (b) pre-cured tread rubber process.

The two primary methods currently used to retread tires, include – mould cure and pre-cure processes. The preparation of the casing is essentially the same in both cases.

In the mould cure process, the tread rubber is applied in the uncured state to the tire casing, and the product is cured in much the same manner as new tires.

Tire Retreading Processes

Pre-curing Method (Right) and Moulding Method (Left). Image from Web

In the pre-cured technology, the tread is supplied to the retreading factory cured, with the tread pattern already in place. The treads are supplied in rolls of various lengths (typically 3.5 to 10 meters in length), or as rings that can be stretched onto the casing. In the application of both pre-cured methods, a bonding material, the cushion, is applied to the tread or the casing prior to the application of the tread.

The majority of the tires retread today consists of truck tires, produced using the pre-cured technologies. A description of this method is given below.

  1. Conventional Process (also known as ‘mould cure’ or ‘hot cure’ process) – In this process an un-vulcanized rubber strip is applied on the buffed casing of the tire. This strip takes the pattern of the mould during the process of vulcanization.
  2. Precure Process (also known as ‘cold cure’) – In this process a tread strip, where the pattern is already pressed and precured is applied to the casing. It is bonded to the casing by means of a thin layer of specially compounded uncured rubber (known as cushion or bonding gum) which is vulcanized by the application of heat, pressure and time.

In the pre-cured rubber (cold process) retreading, better mileage is obtained than with the hot capping process.

The tire is inspected for cuts, ply separations, etc. and after inspection, it is repaired with repair compound or patches, and then buffed under inflated conditions to facilitate bonding. Thereafter, the tire is again inflated on an expandable hub and coated with vulcanizing cement on its buffed surface. A layer of bonding / cushion gum is applied around the surface of the tire. The trapped air between the layers is removed and the vulcanized tread strip is applied, its ends spliced and stitched.

After this operation, the expandable hubs are collapsed and the tire is deflated and removed for vulcanization. The tire is fitted on suitable rims and inflated with the use of a tube. The inflated tire is then slipped into an envelop and vulcanized in a curing chamber or autoclave at lower temperatures than is normally used for new tire vulcanization.

Tire Preparation

The buffing process provides a contaminant-free surface of uniform texture to allow adhesive of the new tread. During the buffing process, the casing is also brought to a uniform circumference, with the correct thyroidal radius and width, to accept the proper tread size for the casing.


After buffing and skiving the casing, a thin layer of contact adhesive is applied to the casing. This material usually referred to as cement, aids in the retread tire fabrication process and helps provide increased adhesion between the casing and the cushion. The cementing of the casings is optional, but widely used in retreading. Cements are solvent-or water based materials.

It is at this point that the majority of the repair to the casing is performed. The main purpose of repairing the casing is to restore the ability of the casing to maintain air pressure and to return mechanical properties of the casing to a level high enough to endure at least the next use life.

After the completion of the repairing of the casing, the tread can be applied. The application of the tread is referred to, as building the tire, and there are a number of variations to the building process.

The main components used in the tire building are the tread and cushion. The tread is supplied to the retread factory fully cured with the desired design and tread width. The back side of the tread is prepared at the manufacturer end by buffing with a wire brush drum and the application of a contact adhesive. A polyethylene film is placed on the cemented side of the tread to prevent contamination.

The cushion is supplied to the factory in either calendared sheets or as strip stock to be used in an extruder. The calendared cushion is supplied in different widths and thickness. As the first step of the building processes, the casing is placed on a builder machine equipped with an expandable hub, like that on the buffer. The hub is expanded and the leading edge of the tread is cut to provide a uniform uncontaminated surface.

Precured Tread Application

Application of Pre-cured tread on the prepared casing

Enveloping & Curing

The next step in the process is the placing on the “built” tire in a rubber containment device called an envelope.

The enveloped tires are placed in a curing chamber that is essentially a large autoclave, steam or electrically heated. The enveloped tires are suspended from a rail system inside the chamber and are connected to exhaust lines inside the chamber (via the valves in the envelope). The tire is then moved down the rail to the rearmost portion of the chamber. Once the desired number of tires is in the camber, the chamber door is closed and the heating and pressurization is started. During the pressurization, the air is allowed to evacuate from inside the envelope.

The operating pressure of the chamber is typically at least 0.3 MPa, with curing temperature between 100°C and 141°C. The cure time is dependent on the thickness of the treads and the composition of the cushion.

Autoclave 1

Earlier it was stated that cold retreading of tire using pre–cured tread gives better performance – higher mileage. Why ?

Because abrasion (wear) loss of the tread is much lower giving rise to higher mileage. This is because cold tread material is more compact due to much higher pressure (hydraulic) applied during curing of the tread in a hydraulic press compared to a new tire curing in tire mould where pressure is limited because of the steam / pressure relationship.

Cold Cure Process: Pre-requisites

It has been well established that heat is the most damaging cause of tire deterioration / ageing, and therefore, its eventual failure.

The critical temperature of rubber is 115ºC, beyond which ageing and deterioration of the tire casing is accelerated, resulting in premature reduction in body strength and leading to failure.  So, technically any retreading system with curing temperature lower than the critical temperature can only be genuinely called a ‘cold process’.

However, another view is that it is the pre-cured tread which is the difference, not lower temperature per se.

In the cold cure process,  factory-cured treads are dense, tough and are of uniform consistency and resilience, as they receive heat and pressure uniformly while moulding, unlike in the conventional retreading process.  The toughened, cured tread is bonded to the tires at considerably lower temperatures, compared to cure mould retreading.

Comparative Features: Conventional versus Pre-cured Retreading

Feature Conventional Pre-cured /cold
Mileage Lower Higher
Investment Comparatively lower.  However, for comparable levels (as that of cold cure process), higher investment is required Higher
Shelf Life Limited shelf life for uncured tread strips Long shelf life
Range Besides truck and bus, larger tires like OTR tires can also be retreaded Generally only truck and bus, LCV and  Passenger Car tires
Curing Temperature Higher temperature

140ºC – 160ºC

Comparatively lower


Tread Composition-


Natural rubber (NR) extruded unvulcanized strips used

usage of different tread pattern is restricted

– Generally synthetic rubber (SR) or a blend or NR/SR with high quality carbon black

-extruded and vulcanized (moulded with various designs) strips are used

– flexibility in having different tread patterns

Range Not suitable for radial tires Ideal for retreading radial tires
Distortion Tire undergoes distortion while curing in the mould due to variations in tire dimensions No distortion in tires as no moulds are used
Cost Lower cost Marginally higher cost

All the operations such as buffing the tire, building the tread and curing while retreading are carried out in the inflated ‘road running condition’, without causing any distortion to the original casing unlike the case of mould retreading.

However, this is not in the case of smaller pre-cured retreaders not having proper equipment.

In Part 2 of this article, you will read on Pre-cured Tread Manufacturing Process.

Dr. Chakravarty can be reached on

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Handling Green Tyre? 3 Interesting Videos You Must See

You need to exercise utmost care while handling Green tyres to prevent their deformation right from Tyre Building Machine through spray painting and sorting to storage buffer. Hence, most green tyre handling solutions are focused on the vulnerability of the tyre and the utilization of the Tyre Building Machine.

Ergonomics, capacity, and speed are critical success factors of the Green Tyre Handling solutions. Here are 3 interesting animation videos on Green Tyre Handling for you that throws more light on this subject.

The first video is from Positech. The 2:36 min video is on an end effector to aid in the handling of green tyres. You can see how an industrial lift assist will pick a green tyre, rotate it horizontal and place it into a rack. This video will help you appreciate the subject of green tire handling and acknowledge the automation challenges shown in the next two videos better.

Green Tire Handling with Positech Industrial Manipulator

This second video is from Beumer Crisplant.  The 4.09 min long video exhaustively showcases Crisplant’s Tire Tray System that the company claims to delivers fast, safe, reliable transport and sortation of green and cured tyres. This video will help you visualize the nuances and complexities of green tyre handling and storage really well.

Green Tire Handling Storage from Beumer

The third video  is from Uteco Contec on automatic ware house concept. You will find this 2:46 min long video giving additional dimensions on green tyre conveying and storage challenges.

Green Tyre Automatic Warehouse_Uteco Contec

Were these informative? Would you like to share more with us?

Let me know your thoughts.

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