Silicone Extrusion

What is silicone extrusion?

Silicone extrusion is a process method for making silicone. Silicone extrusion is a continuous process. After the silicone is drawn into the feeding system, the rotating screw inside the mold pushes the material to the die with a specific cross-sectional shape, extruding continuous profiles.These profiles have to go through a series of processes to produce the final product for sale.

Steps of Silicone Extrusion

Silicone extrusion is not a simple production process of feeding and extrusion. It is a dynamic production process, a systematic production engineering that requires precise control of variables. The following is the specific production process of silicone extrusion.

Preparation

In the preparation stage, uniform, pure, high-quality compound is the basis for successful production. When preparing the material, the production equipment must also be in a state that can be used for normal production.

Mixed Compound

First, the raw material and catalyst, curing agent and pigment should be mixed evenly.The production of different silicone products need to add different catalysts and curing agents to achieve different properties of products.The stored compound must be remilled in the two-roll mill.After refining the compound can restore its uniformity and plasticity.

Compound Filtration

The mixed compound needs to be filtered. The compound passes through a screen changer with muti-layer wire mesh packs. This process can remove impurities from the raw materials. For high-specification silicone products, such as medical and food-grade silicone products, the filtration step is mandatory. Any impurities may cause problems with the products produced.

Strips Preparation

After filtration, the compound needs to be pressed into continuous strips of uniform thickness. The width of the strip should match the feed throat. Avoid changes in the size of the extruded profiles caused by feeding fluctuations. The width and thickness of the strip must be kept in a reasonable range to keep the stability and continuity of production.

Equipment Preheating and Inspection

Before feeding, the extruder barrel, die head and die need to be heated to the preset process temperature. Preheating can prevent equipment damage and poor plasticization of the mixture. After preheating, it is necessary to check whether the equipment’s operating status is normal.

Extrusion Steps

Feeding

The feeding device needs to continuously and evenly feed the strips into the feed throat.Uneven feeding will lead to varying profile sizes. This is also the most common reason. Feeding too much will lead to equipment pressure increasing, which may cause equipment overload or cause the defects of profiles. Feeding too little will lead to material shortage in the product, making it thinner and finer.

Plasticizing and Delivery

The screw rotates inside the barrel, mixing, shearing and compressing the compound. The screw can further plasticize the compound to present a viscous flow state while continuously conveying it forward.

Exhaust

After compression, the pressure of the compound decreases, and the air and moisture need to be removed by the vacuum pump.If the exhaust is not implemented completely, bubbles will appear inside the product. Exhaust can improve the compactness of the product.

Shaping

Under the thrust of the screw, plasticizing uniform compound  through the die, forming a shape of a cross section profile. At this stage, it is worth noting that the most common phenomenon is die swell. In other words, the compound will expand and become larger after leaving the die. Therefore, experienced engineers usually predict this when designing dies. And it will compensate for the expansion rate according to different formulas.

Curing/Vulcanization

After extrusion, the compound will enter the oven for curing. At this stage, silicone will change from a malleable compound to an unmalleable elastomer. Generally speaking, silicone curing uses heat or UV light to improve its durability. You can choose different curing methods according to the products you customize.

There are two other vulcanization methods, hot air vulcanization and microwave vulcanization. Hot air vulcanization refers to feeding the compound into a dozens of meters long pipe, which is filled with hot air at 200℃ to 300℃ inside. The heat of the hot air penetrates from the surface to the interior of the product. This method requires precise control of temperature and speed.

Microwave vulcanization involves passing the profile through a microwave section first and then into a hot air insulation section. Microwaves can generate heat both inside and outside the rubber compound simultaneously, achieving rapid and uniform vulcanization. However, the material must be able to absorb microwave energy before this method can be used.

In the curing process, the temperature, pressure, speed and time of curing need to be adjusted according to the material. Generally speaking, temperature and time are key points. You must find the temperature and time that can help the product to achieve the best performance. The best temperature and time can help you to avoid the situation where the performance of the product declines or fails to meet the standards after vulcanization.

Cooling

After vulcanization，the temperature of the product is very high. Therefore, the product must be cooled through a water bath or a cooling air duct. Note that the cooling process must be slow and uniform. If the product is cooled suddenly or unevenly, it will contract unevenly and deform. This will largely affect the stability and service life of the product. If you use water baths for cooling, it is essential to guarantee high water quality to avoid leaving stains on the product surface.After cooling, the performance and stability of the product have a great improvement, which can achieve that the long-term service life of silicone products is not compromised.

Post-processing

After the main process of silicone extrusion is finished, it is necessary to carry on the follow-up finishing treatment to the product. The factory needs to cut and pack the products according to your customized requirements. If you have assembly requirements, factory can also pack the products after assembly and then prepare to send them to you.

Different Types of Silicone Extrusion

Liquid Silicone Rubber Extrusion

Liquid silicone extrusion is mainly for liquid silicone rubber that does not need to be plasticized.In this way, a metering pump is used instead of a screw. It can achieve precise quantity delivery.The two different LSR stocks were uniformly mixed and cross-linked by a static mixer.Finally sent direct export die forming.

LSR extrusion is highly suitable for manufacturing pipes with extremely high softness and transparency.It can also be used in the production of high precision micro pipe.The energy consumption of LSR extrusion production mainly comes from metering pump and temperature controller, so the energy consumption is very low. Moreover, it can achieve high-speed automated production with extremely high production accuracy.

Twin-Screw Extrusion

Twin-screw extruders are used rarely. It is mainly used for the continuous mixing and direct extrusion of conductive silicone, a type of composite material. It mainly uses the rotation of two screws in the barrel to achieve the effect of strong shearing and kneading. The two screws can scrape against each other to achieve the effect of cleaning the surface. The production and transportation are stable, and the exhaust performance is excellent.

Hot Feed Extrusion

This extrusion method mainly uses hot feed extruders and two-roll mills. The screw of a machine is usually relatively short. The compound needs to be preheated in the two-roll mill and does not need to be plasticized for a long time in the extruder.

This is more suitable for the production of high surface finish products.For difficult plasticizing rubber, hot feed extrusion can achieve more uniform plasticizing. Besides, this kind of equipment has a simple structure and a lower cost.

However, this mode of production needs more skilled workers, with high labor costs and low automation. In addition, during the production process, the two-roll mill needs to be continuously heated, resulting in high production energy consumption.

Cold Feed Extrusion

This process mainly uses cold feed extruders. The screw of this kind of machine is usually long and large.It allows the stock to be fully mixed and plasticized in the barrel. The machine can integrate processes such as plasticizing and compressing.These processes can be accomplished by shear and external heating of the screw.

This process is suitable for most products. For instance, the majority of silicone tubes and silicone sealing strips. For some products with high quality requirements, silicone extrusion can also achieve excellent results, such as the sealing parts inside automobiles and the sealing strips of electrical appliances. For colored products, this extrusion method can better keep the purity of the pigments because it reduces the step of machine preheating and can effectively avoid contamination.

A series of plasticizing processes can be finished inside the machine, and the preheating of the machine is also reduced, providing great convenience for the entire extrusion process. This extrusion method is controllable, eliminating the influence of human factors, and the product consistency can reach a relatively high level. In addition, it simplifies the production process, reduces labor costs, and allows automated continuous production.

Quality Inspection and Control

Strict quality inspection can ensure the accuracy and durability of products. Only products that have been tested can meet production standards.And products can also satisfy the high requirements of user customization.Testing not only needs to test the appearance of products, but also needs to test the performance of different dimensions of products.

Online Detection

The online detection system mainly uses laser diameter gauges and other equipment to check the product’s outer diameter, width, thickness and other key dimensions. The factory will also check the surface of the product by using a monitor. Through this way to check whether the product surface has defects such as bubbles, impurities, and scratches. In addition, the degree of vulcanization is rapidly tested through instruments to ensure the stability and service life of the product.

Offline Detection

Besides online inspection, it is also necessary to test the performance of the products in the laboratory.The physical properties of the product such as hardness and tensile strength are tested by specific equipment. In addition, the heat resistance, anti-aging performance and deformation rate of the product should also be tested, especially for some sealing products. These properties are of vital importance. For products used in the medical field, they need to be tested in accordance with relevant standards to ensure their safety.

Advantages of Silicone Extrusion

High Efficiency 

Silicone extrusion is mostly suitable for large-scale continuous production.Compared with silicone injection, silicone extrusion is a continuous production process. Once the silicone extrusion equipment starts, it can continuously operate. Silicone extrusion is a large-scale and automated production process. The entire process has greatly reduced the reliance on skilled workers. Production equipment can operate automatically for a long time, greatly improving production efficiency and significantly reducing the possibility of human factors affecting production.

High Quality

Extrusion is a stable, continuous and integrated process. The products manufactured by silicone extrusion are higher quality. Because the screw inside the equipment achieves uniform mixing of the compound.These are the important reasons why the product has no flaws in appearance and stable physical properties. Besides, an excellent vulcanization environment is also an important reason for achieving product consistency.Accurate curing temperature and speed to get the ideal product elasticity, strength and durability.

Minimal Waste

Compared with the silicone injection and molding, silicone extrusion is a continuous production process, and the feeding and output of silicone extrusion are almost balanced. Less production waste scraps are generated during the production process, which guarantees the minimization of material waste. In addition, the silicone extrusion production is stable. Although some waste is generated, it is very easy to recycle. This greatly reduces raw material waste during the production process and lowers raw material costs.

Design Versatility

The shape of the silicone extruded product is determined by the die. Therefore, silicone extrusion can not only produce simple products but also those with complex cross-sections. More importantly, silicone extrusion can combine silicone of different colors and functions to produce multi-functional products.Silicone extrusion can also make products of different sizes and different application fields. It can manufacture products of different shapes, sizes and functions according to your customized requirements.

Low Cost

The cost advantage of silicone extrusion is mainly reflected in its production continuity and automation. It can greatly achieve a high utilization rate of materials, reduce labor costs and improve production efficiency. However, low cost is only effective for large-scale production of specific types of products.For more complex products, silicone extrusion may not be able to maximize production efficiency.

Application

Silicone Seals

You can see that silicone extrusion can produce some products with sealing performance. These sealing products are widely used in construction, industry and other fields. Silicone sealing products have excellent water resistance, temperature resistance and chemical resistance. For instance, sealing strips for some industrial equipment, window seals, etc. Besides, silicone gaskets produced by silicone extrusion are also applied in the industrial and electronic fields.

Electrical Insulation

Silicone has good insulating properties. Silicone extrusion can extrude a layer of silicone coating on the surface of the base material. Therefore, silicone extrusion is highly suitable for the production of insulated wires and cables. It can effectively isolate the influence of static and environmental factors, guaranteeing safe use.

Silicone Hoses and Silicone Tubes

Silicone extrusion production is highly flexible. Whether applied in the medical field or the industrial field, silicone extrusion is highly suitable for the production of pipes. For instance, silicone base can be used to produce various specifications of medical catheters, drainage tubes, water pipes, etc.

Conclusion

Silicone extrusion is the best choice to produce different sizes and shapes of pipes,cables,seals,and more. This production method has many advantages,like high efficiency,low cost,high quality and so on. Moreover,Silicone extrusion can flexibly customize the products you need. If you want to purchase our products or customize products you need, please contact us freely.