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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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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

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Global Approach To Rubber Machinery Technology

Make in India is an initiative launched by the Government of India in 2014 to encourage multi-national and national companies to manufacture their products in India. While this initiative has garnered significant international attention and keenly watched, few Indian machinery companies have been steadily building up their repute with global approach and right technology.

In this special edition of Know Your Supplier’s cover story, we feature one such company Bharaj Machineries Pvt. Ltd., through an interactive conversation with Amardeep Singh, Director – Sales & Projects.

Established in 1982 with a vision, to always produce most advanced and quality machinery for the rubber industry, Bharaj has transformed into a giant machinery supplier. Read the full interview here of how Bharaj’s aspiration to be leaders in their various business segments’ is filled with passion and backed with technology.

KYS Cover-June-2016

Click image to read

(This digital edition is available on Youblisher and Yumpu)

Based in Mumbai, India, Bharaj manufactures and supply high-quality and advanced machinery for the rubber industry. They specialise in rubber mould manufacturing, rubber moulding, extrusion and mixing technology.

They are a preferred choice for many rubber related industries starting from Tyre, Automotive, Sports, Footwear, Pharmaceutical, Aerospace and Specialized Silicon Rubber Industry with exports to USA, UK, France, Canada and many Asian Countries.

Here is a teaser from the interview.

Q) What products and services can a prospective equipment buyer expect when they approach you?

ASB: Yes, we offer complete solutions in rubber mould manufacturing, rubber moulding, extrusion and rubber mixing areas. Bharaj designs and manufactures latest technology rubber machinery that saves power, compact in size, has low maintenance, requires minimum labour through smart automation and are user-friendly. Our prospects can choose from a range of Cold Feed Extruders (Plain/Vent Types), Heavy duty Rubber Mixing Mills, Rubber Dispersion Kneaders, Hot Feed Extruders, Refiner Mills, Cracker Mills, Grinding Mills, Calenders with complete lines, Batch-Off Units, Vulcanizers, Bale Cutters, Conveyors, Stock Blenders, Vacuum Compression Type Rubber Moulding Machines, etc.

Bharaj Machineries

Q) How do you compete technologically on your product offerings? 

ASB: Starting as a small manufacturing unit, today Bharaj Machineries has evolved into a well-respected machinery supplier for the rubber industry in India as well as in the Global Market in the areas of rubber mould manufacturing, rubber moulding, extrusion and mixing technology. We focus on providing high quality machinery at a competitive price. The wide range of quality machinery made by Bharaj is well-accepted worldwide. Our competitively priced equipment performs consistently and we extend prompt back-up. We export to developed countries like USA, UK, France, Canada and many Asian countries. Hence, it is also apt to mention here that Bharaj manufactured machinery are considered as a first choice for many rubber related industries starting from Tyre, Automotive, Sports, Pharmaceutical, Footwear, Aerospace and Specialized Silicon Rubber Industry. Depending on the equipment, we offer quick delivery to our customers. Some of our equipment is delivered in as low as 25 days.

Download PDF of this special edition here

As they pursue global growth, Bharaj management respects and value every equipment buyers’ desire for optimum technology in their production floor. Emphasizes, Amardeep Singh Bharaj,

“We recommend the right machinery with right features that gives our customers the best return on his investment. This means we consult him on equipment selection to match his production process, share layout drawings and take great care to clarify his genuine queries in the most practical manner feasible. Depending on availability, we arrange equipment visits for our prospects either at our 30,500 Sft ultramodern and state-of-the-art manufacturing plant near Mumbai or at any of customer sites.”

I hope you find the contents on this leading rubber and tyre industry equipment supplier, and their global approach to rubber machinery technology, informative .

Below is the rubber machinery supplier info image-card of Bharaj Machineries and their contacts, if you would like to reach them quickly.

Bharaj Info Card

In addition, we have two other knowledge-enriching topics from our portal in the ‘Insight’ and ‘Tips’ sections of this special edition.

Let me know your thoughts.

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Know Your Supplier is an advertorial initiative of Rubber & Tyre Machinery World. 

If you would like your organization to be promoted on Rubber Machinery World, please see the opportunities on Partner Me or Contact Me at for your customized offering.

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How to Solve Issues With Calender Gauge Control? (Part 3)

This concluding part on ‘How to Solve Issues With Calender Gauge Control?’ is a continuation from Part 2 on force induced variations in calendered gauge (or thickness) and focuses on the three tips.

  • Limit the temperature rate of change at all times to a maximum of 3 degrees per minute.
  • Minimize speed changes.
  • Mill management

Rubber Calender Line

3. Limit the temperature rate of change at all times to a maximum of 3 degrees per minute.

Because faster rates can damage or warp the rolls.

The control system on the TCU should be designed and operated to limit the rate of temperature change for each calender roll water circuit to 3 degrees per minute. Faster rates of change do not allow for equalization of mechanical expansion throughout the rolls, bearings, and calender frames. Differential expansion can stress various components of your calender. In extreme cases, they can actually crack or warp the rolls, or even damage the bearings.

Heating usually is limited by the available heating capacity but the cooling system frequently has the capacity to rapidly cool the rolls and therefore also has the potential to cause damage if not limited to 3 degrees per minute.

Again, it is important to keep the calender running during warm-up and during cool down. Stopping
the calender and turning off the TCU circulation pumps before the calender reaches ambient is not considered good practice.

If the temperature control system has rate of change limits properly set, cooling down is easy, since all the operator must do is to lower the temperature set points to ambient and then 60 to 90 minutes later return back to the operator console to turn off the TCU.

4. Minimize speed changes.

Because changes in your calender speed result in gum wall gauge thickness variations that are undesirable. 

When the calender is running there are forces generated that try to separate the rolls, as explained earlier. And these
separating forces are proportional to calender speed (although the relationship is not linear).

The hardness of your rubber stock and bank temperature determines the magnitude of separating forces. The
thickness of the gum wall being calendered also affects the separating force – thinner gum walls generate higher separating forces. Separating forces of 160,000 to 300,000 lbs at each actuator literally stretches the calender frame. When the forces vary, the amount of stretch varies. This further results in the roll-gap varying that in turn causes the gum wall gauge to vary.

Hence,  speed changes should be avoided to the extent practical. A speed reduction from 45 mpm (meters per minute) to 9 mpm can result in a gauge decrease of approx. 0.002 inches. Similarly, the vice-versa holds for a gauge increase with roll speed increase.

Calenders are of different types. And different calendars have different degrees of frame stiffness so the quantum of the gauge change for a given speed change will vary accordingly.

5. Mill management

Maintain consistency

You can substantially reduce gauge variations by feeding the calender consistently.

A consistent, uniform, dwell times on the cracker and feed mills, as well as consistent bank size, will give consistent rubber stock temperatures and work history. The stock temperatures, bank sizes, and work history directly influence calender roll-separating forces.

When you minimize variations in these 3 important process parameters, you will minimize variations in roll separating forces, and this in turn will minimize gauge variations of your calendered sheet.

Further, good mill and bank control practices also give improved uniformity for other final calendered gum and/or fabric properties.

When you feed to the calender, you must also ensure that the rubber bank does not have areas that could stagnate. Because, if rubber remains in the bank on the calender for an excessive amount of time it will partially cure and become much harder. Edge trim process that returns to the bank and stagnates is a common source of this problem.

Such cured and hardened compound will introduce gauge variations as well as negatively influence other properties of your calendered material. In extreme cases, burnt lumps will appear in the calendered gum.

Presence of hard stock makes it difficult to properly penetrate the cord and may cause cord disturbance and improper cord distribution.

In such cases the cushion force causes lateral movement in the nip and this further results in cord displacement that is visible. Paired cords are often the first indicator. You will observe that the calendered thickness will be heavy and there will be cord displacement or irregularities. However, the weight of test samples will not be significantly affected.

Localized cord disturbance in cord distribution does not usually affect fabric weight, whereas redistribution of the cord does. Overall cord distribution problems can affect fabric weight in the case of fabric calenders.

Rubber Calender Collage 1

For example, incorrect cord distribution may reduce the average EPI (Ends Per Inch) in the center of the fabric and increase the EPI (Ends Per Inch) on the outer edges. This will affect fabric weight and thickness – the weight of the center would be light, while the outer edges would be heavy.

In steel cord calendering, visible cord displacement and cord pairing after the cushion nip is to be expected in the areas where the cord EPI count is excessive.

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