Silicone has earned its name in many fields. Many people are using silicone products daily. The modern world relies mainly on silicone products for their different needs. This is because these silicone products are non-toxic comparing to plastic products. Moreover, these products are tasteless and can resist high-temperature changes. (Click here to know more our Silicone moulded prodcuts production service.)

 

What is silicone moulding?

 

 

The silicone moulding process is a manufacturing technique used to transform raw silicone material into the desired shapes.

 

Silicone moulding process

There are various methods available to mould silicone. We will discuss the most common ones here.

 

1) Compression moulding

Compression moulding is the most straightforward moulding technique in use. The silicone and mould are incorporated with each other to determine the shape of the silicone product.

The silicone is cut into desired size and weight by the process called blanking. These blanks are placed into the pre-heated moulds along with the vulcanizing agent. The hot plunger closes and applies pressure of 15,000 to 20,000 psi. Under high temperature and pressure, the silicone melts and flows through the cavities of mould. Applied force and temperature will remain constant until the curing of the material is complete. After this, the labour will eject the material from the mould after opening it.

This technique is ideal for low volume requirements. For high product requirements, manufacturers usually use the injection moulding process. Injection moulding uses a computer-controlled press to manufacture massive products automatically.

 

Related Silicone products: Gasket, cushioning pads, seals, O-rings, silicone washer, automotive parts like hoods and fenders.

 

Benefits of compression moulding

1. Economical for start-up companies

2. Low to medium productivity

3. Suitable for mass production

4. Short set-up time

5. Less material wastage

6. Can manufacture small parts to more complex shapes

 

Production challenges for the compression moulding process

1. Flash can be a problem

2. Curing the product

3. Mould surface finish can affect material flow.

4. Keeping the cavities clean

5. and identification of both halves of the mould cavity.

2) Injection moulding

 

Injection moulding uses a combination of plastic and silicone to make a product. Products made using this process are of high quality. They also show good thermal stability, cold resistance, excellent electrical insulation performance, and are non-toxic when burning.

 

The injection moulding process involves the forcing of material into two halves of the mould. A ram or screw-type plunger will push the material through the heated cavity. The silicone flows through different runners and sprues of the mould and finally enters into the mould cavity. It fills the mould cavities to form desired products.

 

Injection moulding has short cure cycle times and low viscosity. It makes it suitable for various products. This method can produce products that can vary significantly in size, complexity, and application.

 

Related products: Small parts, swimming supplies, automobile parts, kitchen tools.

 

Benefits of injection moulding

1. Can give high output production

2. Manufacturers can use multiple materials at the same time

3. Can be automated

4. The price for single-piece production is low

5. The moulding cycle is short

6. No preform preparation required

7. Trimming of the mould design is not required

8. It is ideal for products demanding precise dimensional tolerance or uniformity.

 

Production challenges for the injection moulding process

1. Flash, bubbles, sinks, and wrapping can be a problem

2. Insufficient shot volume can lead to unfilled mould sections

3. In multi-cavity moulds, balancing the moulds to optimize material flow

4. Venting is required to eliminate trapped air via quick fill and short scorch times

5. Refreshing the material before moulding to improve part yield

6. Cleaning and identification of the cavities

7. Curing of the product

8. Best suited for thin-walled products

 

3) Liquid injection moulding

 

The liquid injection moulding process is invented to create product materials in the cavities. This process is accomplished by injecting liquid material through an injection nozzle into the heated mould cavity. This process relies on the mechanical mixing of the raw material. The liquid raw material will flow into the heated cavity, taking the crater’s shape. A little flash occurs during this process which represents fast turn-around time.

The mixing of raw material before inserting is necessary. Mixing is done via a series of plungers. One plunger has base material, which additives or fibers may reinforce. The other plunger has a catalyst compound to initiate and speed up the mixing reaction. This mixed compound is injected into the mould cavity. After curing, the manufacturer will eject the final product from the mould.

 

Related Products: Gasket, seals, keypads, O-rings, cable tools, shielding, electronic contacts.

 

Benefits of liquid injection moulding

 

1. Shorter cure time as compared to compression and transfer moulding

2. Ideal for intricate designs, good precision, and close tolerance parts.

3. Suitable for mass production

4. It can be automated, which will increase cost-effectiveness and decrease the run time.

5. Technicians can use thermal imaging technology to detect errors such as moulding flaws and design problems.

 

Production challenges for the Liquid injection moulding process

1. Flash can be problematic because of the low viscosity, which creates secondary operations.

2. Keeping the cavities clean for identification

3. The moulding machine relies on a metered pumping system

4. Possible increment in maintenance due to cavity wear

5. Curing of the product

6. Prevention of leakage within a mould cavity

 

4) Extrusion moulding

 

Extrusion moulding uses a shaped die (a stainless-steel disc with a pattern cut out) to produce complex profiles, cords, and cross-sections. Silicone extrusion shows a massive benefit over other materials. They last longer, come in various colours and withstand a wider variety of environmental conditions. Silicone extrusion products are mainly used in medical equipment and electronic accessories. It can also act as a buffer in packaging materials.

 

Extrusion moulding uses a raw silicone material and manufactures a product from it using a die. The extrusion process takes raw material through an extruder, with temperature changes and the rotating action of the screw. Once the material is in the extruder, it will pass through the die. It then passes through a hot compartment for the curing of the material. During curing, retaining the shape of the material is necessary. Moreover, the use of continuous laser-controlled measurement maintains precise tolerances.

 

After curing, there may remain some residual chemicals. The producer will remove these chemicals during a post-cure period by exposing the product to a lower temperature for several hours. After post-curing, the product is washed and cooled. Finally, the material is cut into desired product specification.

 

Related products：Seals, gaskets, tubing.

 

Benefits of extrusion moulding

1. This process can consume low-price materials.

2. Tooling costs are less.

3. Large production capacity

4. Short lead times

5. Ideal for seals, large gaskets, tubing rods, and wire insulation.

 

Production challenges for the extrusion moulding process

1. The price per part varies depending on the complexity of the die.

2. Post-forming activities to basic shapes can resolve a complex die cost.

3. It is a slow, detailed mechanical process

4. Short piece extrusion

5. Difficult to maintain tolerance criteria

 

5）Transfer moulding

 

The transfer moulding process is specially designed and used for creating silicone rubber from cavities. This procedure involves forcing material into the mould cavity. It is left there until it cools and attains the shape of the crater. A plunger uses a funnel or sprue to force the material into the cavity. The mould is heated to melt the material. The material will remain in the cavity until its curing is complete.

 

Transfer moulding requires the production of secondary raw materials with specific shapes, just like compression moulding. The only difference is that in transfer moulding, the preforms are present between the top plate and plunger in the area known as ‘pot.’

 

The major disadvantage of transfer moulding is the increased waste or excess material left into the pot during the moulding procedure. The removal of this waste is necessary. Manual trimming, cryogenic processing, precision grinding or tumbling are various methods to remove excess material.

 

Related products: Smaller and more detailed products.

 

Benefits of transfer moulding

1. A short cycle of production

2. Smaller tolerances are possible as compared to the compression moulding

3. Manufacturers can create more complex shapes.

4. If part configuration traps air, transfer moulding is a better option

5. Reasonable control over dimensional tolerance

 

Production challenges for the transfer moulding process

1. Pressure-sensitive to produce a quality product

2. Flash can become problematic with poorly designed moulds

3. Temperature consistency is necessary

4. Cavity control and identification

5. While using a warm or hot transfer pot, minimize material contact with heat before it fills out the mould.

 

6) Calendering

 

Calendering is the process of creating products into sheets before processing them into the final product. This process uses multiple rollers to compress the material into a uniformly thick sheet. The speed of the rollers varies depending upon the specific product criteria.

 

Related products: Die-cut seals and thin sheets of materials.

Benefits of Calendering process

1. It can produce products up to a rate of three surface meters per minute

2. Many compounds will benefit from moll freshening before processing on a calendar

3. Products can be used as a fabric coating

4. Calendering of silicone rubber usually occurs at room temperature

5. The process may be supported or unsupported

 

Production challenges for the Calendering moulding process

1. It is mandatory to heat the rolls to prevent sticking

2. Manufacturers must avoid overheating. As overheating can cause scorching of the product

3. Carefully select the speed of rolls to help remove air from the product

4. Transfer to fabric may produce bad or intermittent results due to insufficient tack

5. While using a release liner, strip the sheet when it is still warm to prevent possible tears or sticks

6. Creeping of the product is a concern

 

Conclusion

In summary, the selection of the correct method to produce silicone products is dependent on many variables. The final product’s design, cost, production quantity, and delivery time all play a part in the decision. Each moulding process has its advantages, disadvantages, and production difficulties. You have to grasp all the sensitive details of each method before converting your raw material into the product.