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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 team@kemstertek.com


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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

(phr)

Solution Compound

(phr)

Cushion Gum Compound

(phr)

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.

BHARAJ MAKE 200MM PIN BARREL EXTRUDER WITH TREAD DIE HEAD

BHARAJ MAKE 200MM PIN BARREL EXTRUDER WITH TREAD DIE HEAD

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.

Solution

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 kpspltd@gmail.com


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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.

Introduction

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.

Tire_Buffing_Machine

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

100ºC-125ºC

Tread Composition-

Process-Patterns

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 kpspltd@gmail.com


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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 engage@rubbermachineryworld.com for your customized offering.


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Practical Modern Solutions For Tyre And Rubber Industry

Change is inevitable. Changes in the business environment happen all the time. The economy fluctuates up or down on a daily basis, frequently causing businesses to alter the way they operate. New competitors enter the marketplace while others leave. Advancements in technologies, products and innovation lead to change in a business environment.

Sustaining and innovating amidst changes is the hallmark of exemplary leadership. Pelmar Group has been displaying dynamic leadership for the last 50 years! Hence, in this special edition of Know Your Supplier’s cover story, we showcase for you Pelmar Engineering Ltd., the Practical Modern Solution Providers For Tyre And Rubber Industry.

We understand from our conversation with Jacob Peled, Founder and Executive Chairman, that Pelmar had three consecutive record years. And is now planning expansion of both its commercial and technical activities in Israel and worldwide.

It’s not easy to achieve three record years consecutively handling a range of activities that include pre-owned machinery, new equipment, complete engineering services, raw materials, military technical rubber production, technology transfer, M&A activity and more. Because, this requires efficiency and focus.

Don’t miss our main interview to know how Pelmar has been consistently outperforming customer expectations year-on-year.

Know-Your-Supplier-Pelmar-May-2016

Click on the image to read

(You may read this digital edition either on Youblisher and/or Yumpu platform.)

An anecdote shared by Peled in his own words that I choose to mention here.

“I was asked a question yesterday evening by one of the persons I admire most in the industry, Michael Labbe the Managing Director of Rema TipTop, how could I and Pelmar cope with handling so many various subjects efficiently at the same time. He referred mainly to Pelmar handling pre-owned machinery, new equipment, complete engineering services, raw materials, military technical rubber production, technology transfer, M&A activity and more. I did not have a proper answer.

This morning I had breakfast with the technical director of one of the major Tier 1 tyre companies, who asked me how could I with the size of our Group, with the international spread, with the diversity of functions handle only one industry, the tire and rubber industry. I tried to explain that tire and the technical rubber industry are separate, but found myself mumbling.

The worst thing about the above is that both questions are absolutely correct and in place. The only answer that I can think of is that because we are handling “just one industry” we can and should be involved in as many aspects of this industry as possible.”

Pelmar Engineering Ltd.

Identifying and capitalizing on the opportunities swiftly along with thirst for growth has helped Pelmar diversify their expertise, spread reach globally and offer single-stop shop total solutions for rubber and tyre industry.

Additionally, on this digital edition, we have two knowledge-enriching topics from our portal aptly titled ‘Insight’ and ‘Tips’ sections.

Download PDF of this special edition here

I hope you find the contents informative to learn more about this leader in rubber and tyre industry.


If you found this supplier details informative, please do share with your colleagues, customers and friends who could benefit. And if you would like to be informed of our articles regularly, please register with us for free updates today.


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 engage@rubbermachineryworld.com for your customized offering.


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Will Post Cure Inflator Machinery Ever Die?

Few weeks back, I shared Jacob Peled’s presentation ‘The Future of Tire Plants’ and more recently, ‘Visions of the Future’ on our LinkedIn Page. On reading, an industry friend asked me this question – ‘Will Post Cure Inflator Machinery Ever Die?

While Jacob’s presentation envisions the shortening of curing time by use of higher temperatures and pressure, automation, development of bladder, materials etc, there have been no specific mention of Post Cure Inflators.

So where did this question rise from, I was curious.

Historically, the process of Post Curing Inflation has seen its popularity rise and fall at different time intervals. Tyre technology has been evolving to embrace increased efficiency at all stages of manufacturing. And Post Curing Inflation is not really an energy efficient process, reasoned my friend clarifying the basis for his question.

So, what is Post Cure Inflator Machinery?

Post Cure Inflator (PCI) machinery cools the tyre under pressure immediately after it has been cured.

post-cure-inflator-tire-machinery

Image: L&T Make Post Cure Inflator

For the tyre, this stage involves mounting them on the flanges, inflating it and cooling it according to a selected procedure. You may do this for one or two cycles (Note: one cycle is equal to the time taken for one curing cycle) depending on the specification arrived at for the time your cured tyre takes to cool down to room temperature.

Types of Post Cure Inflator Machinery

There are two types of Post Cure Inflator machinery, viz. Automatic and Semi-Automatic, in the market for use with tyres of passenger cars, light trucks, trucks and off-the-road equipment.

  1. Automatic Post Cure Inflator units are installed at the rear of tyre curing presses, to receive the cured tyres from the curing presses. The tyres are cooled to ambient temperature under controlled air pressure to avoid distortion of plies. After cooling, tyres are discharged onto the takeaway conveyor rollers. Post Cure Inflators are available in 2-position and 4-position designs, which allow for inflation time equivalent to curing time and double the curing time respectively.
  2. Semi Automatic Post Cure Inflator units are located in the curing area and cured tyres are loaded into these units. Tyres are cooled to the ambient temperature under controlled air pressure and are manually discharged from these units.

Machinery suppliers offer design features like adjustable inflation, auto/manual rotation, and adjustable bead width. These features enable Post Cure Inflator machinery to also function as a testing stand for secondary, manual inspection of sidewall or runout rejects.

To examine the importance of this tyre machinery further, let’s understand the process deeper.

Post Curing Inflation Process & its Significance

Post Curing Inflation is recommended especially for tyres of nylon carcass construction. This is because nylon has a unique property of shrinking while it is heated.  When you have nylon in your tyre carcass (i.e. the skeleton of the tyre), there is a tendency for it to shrink as you heat the tyre to vulcanize.

Since vulcanizing of the tyre happens inside a curing press, it is not possible for these nylon cords to shrink. This is because there is high pressure inside the tyre which keeps these nylon cords in the stretched condition. But when the curing is completed and you release the pressure inside the bladder, the nylon cords tend to shrink since your tyre is still hot.

To avoid this hot or thermal shrinkage, the tyre is to be cooled under pressure. If you skip this process, the tyres may lose shape or get distorted or have changes in dimensions.

Post Cure Inflator machinery stabilizes the shape of your tyre in production. When you delay Post Curing Inflation, the damage caused would be irreversible and highly undesirable – both for your company’s reputation and customers safety.

If your customer is given a tyre which was affected by Post Curing Inflation delay, its dimensions will be different from normal tyres. This leads to uneven wear, problems to the axle and bearings of their vehicle. The distortion in shape further leads to tyre uniformity problems that adversely impacts the level of comfort and performance of tyres in the highly advanced vehicles. Last but not the least, a distorted tyre is not safe and lead to accidents.  Needless to say, all of the above creates a negative impact on the company’s image and lead to economic and legal implications for your company.

When the design of your tyre construction changes, Post Curing Inflation process allow your tyres to maintain their designed profile and performance characteristics as they reach road temperatures.

Summarizing, while the popularity of Post Curing Inflation process (and hence Post Cure Inflator Machinery) may shift back and forth, this tyre machinery will not die soon.

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Know The Structure of A Mechanical Bladder Curing Press

Curing is the process of applying pressure to the green tyre in a mould. This gives it its final shape. There is heat energy applied to stimulate a chemical reaction between the rubber compounds and other materials.

In curing process, you will observe (a video) that the green tyre is transferred onto the lower mold bead seat, a rubber bladder is inserted into the green tire, and the mold closes while the bladder inflates. As the mold closes and is locked the bladder pressure increases so as to make the green tire flow into the mold, taking on the tread pattern and sidewall lettering engraved into the mold.

The bladder is filled with a circulating heat transfer medium (such as steam, hot water, or inert gas). At the end of cure the pressure is bled down, the mold opened, and the tire stripped out of the mold.

Various suppliers manufacture curing bladders to fit to the different curing press types viz. Bag-o-Matic (BOM), Autoform and Hydraulic (Bagwell).

A bladder curing press cure bladders. Sizes vary because there are radial and bias type curing bladders for the passenger car, light truck, OTR (Off-The-Road), agricultural, bicycle, and motorcycle tyres. You will also find curing bladders for tire retreading and air spring production.

Here’s a structure of a compact mechanical bladder curing press.

Know A Bladder Curing Press

Additionally, you would also find this L&T newsletter informative on technical aspects.

A good curing bladder has following key features

  • It is made of a sustainable and flexible compound
  • The bladder contour is optimized to tire contour
  • A good surface structure to prevent trapped air
  • Durable and simple to use during service

If the bladder contour and venting system are not optimized, the tyre plants experience higher level of trapped air and blisters. This is predominant in motorcycle tyres when compared to other tyre segments.

A good bladder has minimum inner-liner consumption. It also facilitates a smooth and simple final inspection of the tyre due to its constant surface structure. Imperfections, if any, can be easily detected  which in turn gives you extra ordinary final finish.

So choose your bladder curing press wisely and operate it smartly to produce the best curing bladder for your customers.

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