Silicone Compression Molding

Silicone Compression Molding

Silicone compression molding is an economical and versatile production process for silicone products. It has become an ideal choice for manufacturing components in various industries. This article will provide you with a detailed explanation of advantages, equipment, production process and applications of silicone compression molding. If you want to customize silicone products, this article can help you to clearly understand this craftsmanship.

What is silicone compression molding?

Silicone compression molding is a process for manufacturing silicone products. First, a predetermined amount of silicone raw material needs to be placed in the open mold cavity. The process of closing a heated mold and applying pressure with a compression molding machine to fill the cavity of the compound and vulcanize and set it.Finally, a solid finished product is formed.

Silicone compression molding is a mature silicone production process. Components produced by silicone compression molding can be applied in numerous fields such as electrical and electronic, aerospace, and consumer products.

Advantages of Silicone Compression Molding

Cost-effective

Silicone compression molding uses a more cost-effective manufacturing process. Compared with the liquid silicone rubber injection molding process, the mold structure for silicone compression molding is generally simpler and does not have a complex hot runner system.

Therefore, its processing and manufacturing cycle is shorter and the initial investment cost will also be lower.What’s more, the mold will not deform even after long-term use and does not need to be replaced. It can also achieve the one-time production of various silicone components. Moreover, the material utilization rate of silicone compression molding is relatively high, and the energy consumption in production is also lower.

Produce Strong Parts

Silicone compression molding has a slow flow process of the material and uniform vulcanization pressure. Therefore, the final products produced are less prone to warping and deformation, and can keep dimensional stability during long-term use. And it can also combine multiple materials to produce composite products. Usually,the produced products are durable and corrosion-resistant.

Superior Material Properties

Unlike silicone die cutting, the compound formed by silicone compression molding has a short flow distance in the mold cavity and is subjected to less shear force. Therefore, the product can better keep the original properties of the material, such as high elasticity and high tensile strength.

Material Usage Flexibility

Silicone compression molding can use materials of different viscosities. It can process not only high-viscosity solid silicone but also special silicone materials, such as conductive fillers and thermal conductive fillers. And these materials are usually not allowed by liquid silicone rubber injection molding.

Limitations of Silicone Compression Molding

High Labor Costs

Traditional silicone compression molding relies on manual operation during the transfer and unloading of goods. And the skills and experience of the operators are required to be high. What’s more, the flash during compression molding also needs to be removed manually. Therefore, all these blackouts have increased the difficulty of labor costs and product consistency management.

Low Production Efficiency

Compared with injection molding, the degree of automation in silicone compression molding is relatively low. The production processes of compression molding, such as loading, closing the mold, venting, opening the mold, and removing parts, are relatively slow, and the production cycle takes a long time. Therefore, the efficiency is relatively low in large-scale production.

Limited Product Precision and Complexity

Silicone compression molding is typically used to produce silicone components with complex structures, relatively thick walls and large sizes. It cannot produce silicone products with fine details and thin walls like liquid silicone rubber injection molding. Silicone compression molding cannot fully rely on pressure to fill every detail of the cavity. Therefore, its molding accuracy and replication ability are usually lower than injection molding.

Yield Rate Challenges

Many steps in compression molding rely on manual operation. Therefore, even minor differences caused by human operation may lead to slight variations in weight and size between batches of products.

Secondary Processing Requirements

The open mold cavity and exhaust slots used in silicone compression molding are bound to cause flash in the product. Therefore, almost every product needs to undergo post-processing, which undoubtedly increases the production cost and procedures.

Production Equipment

The main equipment for silicone compression molding is the compression molding machine and molds. The silicone compression molding machine mainly provides the temperature and pressure required for the molding of the compound. The quality of the mold directly determines the size, appearance and production efficiency of the product.

Types of Silicone Compression Molding Machine

Hydraulic Compression Molding Machine

This type of compression molding machine is the most common and fundamental one. It mainly drives the equipment through a hydraulic system to mold, pressure and open the mold. The pressure, temperature and time of the equipment operation are manually set by the workers on the control panel of the equipment.

This type of equipment has a low cost and is mainly suitable for small-batch products, multi-variety production, sample making or low requirements of automation production.

Vacuum Compression Molding Machine

If the products you customize have very high quality requirements or you want to customize high-end products, then this kind of machine becomes the first choice for production. This equipment adds a vacuum system on the basis of a compressor. It can completely eliminate defects such as bubbles and pores caused by air inside the compound. For products with thick walls, complex structures and high quality requirements, it can improve the pass rate and quality of the products.

Vacuum compression molding machines are more expensive and are more suitable for manufacturing products with strict requirements such as medical devices, optical components, and highly transparent products.

Fully Automatic Compression Molding Machine

This type of machine integrates an automated unit on the basis of a vacuum compression forming machine. It has higher production efficiency and a more stable production cycle. Secondly, no personnel operation not only reduces the cost of labor but also guarantees the consistency of product quality. Therefore, it is more often applied in modern factories to achieve medium and large-scale production.

Mold

According to the design of your customized product, the corresponding mold needs to be customized.Custom mold usually needs to consider two aspects, that is, mold material selection and fuzzy structure design.

Material Choice

For general production, the most commonly used and cost-effective pre-hardened mold steel is the first choice for custom molds. This material is suitable for the production of most silicone products.

If the product you customize has higher production requirements, the mold can be made of quenched and tempered mold steel. These materials are usually wear-resistant, corrosion-resistant and have excellent polishing performance, such as NAK80, S136, etc.

The specific materials still need to be comprehensively considered based on your production batch, budget, appearance requirements, production formula, etc.

Mold Structure Design

The design of molds needs to take into account many aspects of elements. If you are customizing large-sized and high-precision products, single-cavity molds are usually designed. If small-sized products are to be customized and mass-produced, multi-cavity molds need to be designed.

Moreover, the surface of the mold also needs to be treated according to the surface requirements of your product. The position and size of the mold exhaust groove, the type of heating system adopted, and the demolding method all need to be fully considered when designing the mold.

Silicone Compression Molding Process

Preparation of Silicone Compression Molding Process

Raw Material

The raw materials used for compression molding are usually high-temperature vulcanized (HTV) silicone rubber and high consistency rubber (HCR). This kind of silicone is a high-viscosity gel-like substance. The manufacturer needs to process the raw materials according to the characteristics of the products you customize.

Generally speaking, reinforcing fillers and structured control agents need to be added inside the raw materials first. The manufacturer also needs to select the vulcanization system of the silicone according to your requirements. This directly determines the performance and application fields of the product.

Vulcanization Systems

Vulcanization systems are generally classified into two types: peroxide vulcanization systems and platinum vulcanization systems.

The former has a lower cost, but it may retain an odor after vulcanization and has limited transparency. It is more suitable for industrial seals, gaskets and other fields where the requirements for odor and bio-compatibility are not high.

The latter has no odor after application, high transparency and excellent bio-compatibility. Its ability to resist compression deformation is superior to the former. Therefore, it is more suitable for application in medical devices, food, baby products, and highly transparent products.

Mixing

At this stage, all components need to be evenly mixed in the base polymer to form a uniform semi-finished compound. When mixing compounds, it is necessary to guarantee that the components are evenly and consistently dispersed, without coking or pollution. Good mixing can lay a solid foundation for high-quality products.

Primary Silicone Compression Molding Process

Weighting and Metering

The uniformly mixed raw materials need to be cut into specific shapes and sizes according to the volume of your customized product and the size of the mold cavity. This allows the compound to be better loaded into the mold cavity, facilitating it better filling and flow within the mold cavity. It is worth noting that the weight of the compound needs to be precisely controlled. Too much or too little compound will affect the quality of the product.

Besides preparing raw materials, it is also necessary to install the mold on the compression molding machine, guaranteeing the balance and tightness of the mold installation. Then, the manufacturer will start the heating system to heat the mold to the required vulcanization temperature. It is essential to verify uniform mold temperature, which is a prerequisite for the synchronous vulcanization of the product.

Insert Raw Materials

Put the weighed compound into the cavity of the preheated mold. The compound should be placed at the center of the bottom of the mold to prevent air from being trapped.

Vulcanization and Molding

When the upper mold is closed, the compression molding machine will apply pressure and heat to the material. Under the influence of pressure and heat, the solid compound flows in the mold cavity like a liquid until the mold cavity is filled.

Meanwhile, the vulcanizing agent in the compound will decompose, and the compound will change from a plastic state to an non-plastic elastomer to achieve the final physical properties.

Vulcanization and setting require strict control of temperature and time. And these parameters depend on the thickness of the product you customize, the vulcanization system and the temperature.

Demolding

After the set vulcanization time is over, the machine will automatically relieve pressure and open the mold. After the product is formed, it needs to be cooled to achieve the best physical properties. Usually, the ejection system inside the automated equipment will remove the formed product from the mold.

Post-processing

Flash Cutting

Most silicone compression molding products have flash, so they need to be trimmed and cut. Flash trimming is usually done by hand trimming, cold trimming and machine punching. The specific method to be used also needs to be selected based on your product requirements and production volume.

Secondary Vulcanization

If the product you customize uses platinum vulcanization, then the product usually does not need secondary vulcanization. Secondary vulcanization is mainly aimed at silicone products with peroxide vulcanization systems. Secondary vulcanization can remove the by-products generated during the vulcanization process, and improve product’s resistance to permanent compression set and thermal stability.

Inspection and Packaging

The final step of silicone compression molding is to implement quality control on the final product. This requires a comprehensive inspection or sampling inspection of the product. The inspection mainly includes whether there are any defects on the appearance of the product, whether the dimensions meet the production standards, and whether the product performance meets your usage requirements.

Products that pass the inspection will be cleaned. If you have any assembly requirements, we will select appropriate packaging materials for packaging after assembly and deliver it to you.

Application of Silicone Compression Molding Products

Silicone compression molded products can be widely applied in various industries, fundamentally due to the superior performance of HCR itself.

Automotive Industry

Silicone molded products are applied in the automotive industry due to their high-temperature resistance, excellent sealing performance, low compression set and electrical insulation. Typical products include O-rings, gaskets, spark plug caps, sealing rings, etc.

Healthcare Industry

Medical-grade silicone vulcanized with platinum has excellent bio-compatibility and is non-toxic. It can guarantee the safety of silicone in contact with human tissues and will not inhibit or interfere with drugs. Moreover, the sterilizing property, transparency and chemical inertness of silicone are also the reasons why it can be applied in the medical field. Common breathing masks, handles and gaskets of surgical instruments are all molded products.

Consumer Goods

Silicone molded products can be applied in the consumer goods and food industries, given their food safety, easy cleaning and good touch. HCR has passed certifications such as FDA and LFGB. And it can withstand high and low temperatures and can be steamed or boiled without cracking or deforming.

Products such as ice cube trays, kitchenware sealing rings, baking molds, and baby pacifiers are all common molded products.

Industrial Sector

Gaskets, shock-absorbing pads, O-rings and sealing strips are common molded products in the industrial field. Some special seals can also be applied in the fields of aerospace, energy and chemical energy. This is due to its aging resistance, temperature resistance and the ability to closely adhere to the equipment, guaranteeing the safe operation of the equipment.