Rubber Manufacturing Process

We are all aware of the revolution happening around vehicles. EVs are taking over the IC engines, but one thing has not changed. That is the tyres of the vehicle. They are still made from rubber.

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For centuries, rubber has been the most versatile material. It is used most extensively in tyres and as insulators, but has many other applications.

What is rubber?

Rubber is an elastic, non-abrasive material. The primary property of rubber is that it can stretch and shrink. Other properties include rubber is resistant of heat and electricity making it an ideal insulating material.

Is rubber a natural material?

Yes and no. Rubber can be sourced from both, natural and synthetic processes. Interestingly, both of these are in high demand by manufactures and hold a very important place.

Natural - Natural rubber is an elastomer, meaning it is an elastic substance and can recover back to its original shape when stretched. Natural rubber is typically sourced from Hevea brasiliensis or the Pará rubber tree.

Synthetic - Synthetic rubber can be produced artificially via the polymerisation of monomers into polymers. This can be done in two ways, either by solution polymerisation or emulsion polymerisation.

Rubber is elastic and will restore to it's original shape and form.

Then the question comes, if the rubber always restores to it's original shape then how do we manufacture different products from this? Almost all rubber products needs to undergo vulcanization.

What is Vulcanization?

It is the enhancement of the properties via chemical process. Vulcanization is performed on most of the elastomers including natural and synthetic rubber products. It is considered as the most revolutionized invention in the polymer industry.

Types of rubber product manufacturing processes

Lets take a look at what are the different methods to manufacture rubber products.

The different rubber manufacturing processes are

• Injection Molding

• Compression Molding

• Transfer Molding

• Rubber Extrusion

• Rubber to Metal Bonding

Injection Molding

A modified version of the plastics technique is used to manufacture rubber injection moulded items. Rubber is heated during this procedure, which also puts it under much more pressure in the moulding. In contrast, materials used in plastic injection moulding are chilled and put under a lot less pressure.

Over time, there have been numerous advances made to the injection moulding procedure. Injection moulding is presently one of the most effective methods for producing rubber parts for a wide range of products, uses, and industries.

The Injection Molding Rubber Parts Manufacturing Process

1. The preparation of the materials is the first step in the rubber injection moulding process.

2. placement of uncured rubber using a screw feeder mechanism in the machinery. No performing is necessary for this process.

3. The screw feeder is used by machinery to feed as much material into the mould as is required. By doing so, all ambiguities are removed, as well as the creation of material waste.

4. Rubber is moved to the barrel, heated to make it more flexible, and then pushed into the runner system.

5. Material begins filling the mould cavities and begins the curing process.

6. The components can be taken out after the curing process is finished to make way for the incoming materials.

Compression Molding

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Preforms made from a rubber compound or a combination of raw materials are loosely moulded to resemble the target result during the compression moulding process. To achieve a complete fill of the cavity, these preforms need a lot of material.

This method is perfect for medium-hard compounds, low-volume operations, or applications requiring pricey raw materials. Compression moulding also aids in minimising excess produced during the moulding process.

The Compression Molding Rubber Parts Manufacturing Process

1. The quantity of material required to fill each cavity is determined by the operators.

2. The uncured rubber is then preformed to these measurements by operators.

3. the rubber is inserted into the mould chamber.

4. covering the rubber components with the mold's lid.

5. Depending on the materials and components, applying heat and pressure to the material for a predetermined period of time.

6. Taking the fully-cured component out of the mould after opening it.

7. Trimming excess material or flash can be done manually or with a deflasher.

Transfer Molding

Similar to compression moulding, transfer moulding calls for the fabrication of preforms using secondary source materials. The key distinction is how ingredients are added to a pot between the top plate and plunger.

The Making of Rubber Parts via Transfer Molding

1. The quantity of material required for a component is determined by operators.

2. With these measurements, operators do the rubber.

3. Preform is inserted into a mold's cavity.

4. Mold should be closed and pressed.

5. pushing rubber through a sprue, a small aperture.

6. Mold cavities are filled with substance.

7. While the rubber dries, additional heating and pressure should be applied to the mould.

8. Mold eradication and component release.

9. Flash or overflow material is eliminated.

Rubber Extrusion

Depending on the components used, rubber extrusion can take many different forms. The procedure entails pushing the components through the cross-sectional die while it is being compressed by an extruder. Soft, unvulcanized rubber compounds are also a part of it. As a result, the extrusion produces rubber that is supple and malleable. To transform these materials into usable components, such as vulcanization or hardening, post-processing is necessary.

Process of extrusion

1. Whether hot or cold extrusion is necessary is decided by designers and operators.

2. Fill the hopper with the rubber before it is vulcanised. The conveyor contains a container called a hopper.

3. The rubber is then guided onto the conveyor by gravity after passing through the hopper's bottom.

4. Rubber is sent to the die while being heated and compressed by a screw.

5. The rubber is softened before it enters the die at the end of the conveyor.

6. The rubber starts to shape itself inside the die.

7. The rubber is then forced through the die in the finished form of the component.

8. The optimal post-processing techniques for the component are chosen by operators. These procedures include drilling, coiling, dusting, and vulcanization. In the post-processing stage of rubber extrusion, vulcanization is essential.

Summary

• Rubber is softened before going through any manufacturing process.

• Rubber is recyclable material and can be repurposed after some curing process.

• Rubber to metal bonded parts range in size from smaller inserts to larger components. Overmolded components are also applicable in a wide variety of applications and industries.

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The methods of manufacturing rubber are similar for all producers World-Wide. Variances, however, may occur regarding specific compounds, each manufacturer’s production methods and levels of sophistication.

Formulation and Mixing of Rubber Compounds:

VIP-Polymers process a variety of rubber materials, both natural and synthetic, into compounds suitable to face the most challenging performance and environmental criteria.

Natural rubbers are supplied from traditional countries in the Far East such as Malaysia and Indonesia. Synthetic rubber is primarily manufactured at chemical plants in Industrial Europe and the U.S.A.

On its own, basic rubber is of little use and must be formulated to make it suitable for manufacture and to ensure desired properties in finished products.

Following laboratory development, precise formulations are used in production mixing operations to blend compounds into strip or slab form suitable for later processing. This is accomplished as follows:

• Blend using a roll milling process.
• Under computer control, each ‘Batch’ is processed through a series of heavy-duty mixing systems to add more ingredients and finally discharge batches at a designated time and/or temperature.
• Weigh designated formulation ingredients into specified batches using computer control to ensure accuracy.
• Finally, the material is formed into strips or slabs and then automatically cooled.

The processed material compound is now suitable for moulding or extrusion. Test coupons are also sent from each ‘Batch’ to Quality Control and subjected to a testing programme before releasing to production.

How rubber products are manufactured:

Industrial Rubber components are usually manufactured by one of the following methods:

• Injection Moulding – Using strip compound produced as previously described.
• Compression Moulding – Requires secondary operations to process material into suitable forms of the correct weight and/or shape to suit particular products.
• Extrusion – Using strip compound produced as previously described.

Injection and Compression moulding require highly accurate single or multi-cavity moulds, typically made in high-grade steel and designed and made using CAD/CAM programmes.

Injection Moulding:

Injection moulding has a number of elements operating automatically on timed sequences with moulding temperatures usually between 165°C and 200°C.

Moulding cycle:

• Mould closes.
• A plasticising screw rotates to force the injection of an accurate volume of pre-plasticised rubber compound into the mould.
• Material is directed into the mould via a system of runners to each individual cavity, each having small injection ports.
• Material is cured for a pre-determined time during which the plasticising screw retracts and plasticises sufficient rubber for the next injection.
• The mould opens and parts are removed manually or automatically by robotic or other systems.
• The cycle is repeated.

During each machine cycle an operator may perform a variety of operations including: Trimming excess rubber (flash), inspection, packaging or assembly. Alternatively, the part may be forwarded for trimming by other methods.

Compression Moulding:

This simpler process is slower in operation than injection moulding in that special uncured preformed and weighed blanks are used. The process employs hydraulic presses with pre-heated platens at (150-170°C) that in turn heat up the mould.

Moulding cycle:

• Open mould and remove the product from the previous cycle.
• Load required blanks into each cavity.
• Close mould and move into a hydraulic press.
• Activate hydraulic press. The closing action causes displacement of rubber to fill each mould cavity. To overcome certain conditions, pressure is sometimes released and the mould “bumped” to allow air escape.
• Cure – Time is determined as a function of material and cross-section of the part being moulded.
• Remove part(s) manually or automatically after pulling mould from the press.
• Repeat cycle.

Again the operator may have tasks to perform as described for injection moulding. Compression moulding is generally more suited to low volume production or where tooling costs are to be kept to a minimum. Compression moulding is also not suitable for moulding complex shapes.

Extrusion:

Extrusion is used for either of two functions:

• Manufacture of long lengths of cured sections for fabrication of items too large for injection or compression moulding.
• The production of blanks for compression moulding.

Continuous Vulcanisation:

VIP-Polymers utilise a manufacturing process known as Continuous Vulcanisation for production of cured extrusion for conversion into certain finished products as follows.

Two items of machinery are required for this process:

• An extruder with a barrel and screw, and a die of the correct cross-section at the outlet end.
• A heating source to cure the rubber which may be one of the following:
  • A hot air oven.
  • A microwave unit/hot air oven combination.
  • A specialised bath containing molten salt.

The “Continuous Vulcanisation” process is as follows:

• Strip rubber is fed into the extruder. It is then plasticised by the screw and extruded through the die orifice. The extruder operates under controlled conditions of temperature and screw speed.
• The continuous extrudate is passed down the heating medium which causes it to cure. Again, speed and temperature are accurately controlled.
• The emerging cured profile is cooled and cut to length automatically or rolled onto drums for subsequent secondary operations.
  
  

This process invariably involves a line length of as much as l00 feet, and optional operations may utilise a U-format to economise on space.

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