Introduction:
What is Silicone Rubber and where is it used?
Over the years, Silicone Rubber has gained attention industrially. The reason is its remarkable properties (both Electrical and Mechanical) at differing temperatures. From Medical to Aerospace devices, it is considered to be a more obvious and natural choice for many applications. Silicon rubbers can be manufactured with different carbon and organic groups, as well as additives and fillers that are integrated into their molecular framework.
Silicon Rubber has a chemical structure based on alternating units of silicon and oxygen. The reason that silicone rubbers are available in such a wide range of forms is because of the combination of organic groups and the compounding methods used. This is the reason why silicone rubbers are such an all-rounder and adaptable by most to make an almost countless number of products. Hence, it is important and will be very interesting to understand how the processing and fabricating of this material works.
In today’s article, we will learn in-depth about various methods of processing Silicone Rubber, their advantages for using each method and get some insights on the uses required for a different type of products manufactured.
What are the processes for silicone rubber transformation?
It is important to consider what method of moulding a silicone rubber manufacturer uses as there are a few different processes of moulding Silicone Rubber, each with its own benefits. Several factors have to be kept in mind before choosing the processing techniques. Factors like Size of the component, number of units to be produced, its complexity, budget available to produce, endurance, need for special characteristics and many more have to be taken into consideration.
Considering the major factors following are some of the most widely used processes:
- Compression Molding
- Injection Molding (High Consistency Rubber & Liquid Silicone Rubber)
- Transfer Molding
- Extrusion
- Calendering
Let us try to understand these processes in detail.
- What is Compression Molding?
Silicone Compression Moulding is a more commonly used and basic process alongside Liquid Silicone Injection Moulding. The basic definition goes as – unvulcanized silicone is placed into a mould, which is then assembled, pressed and heated, and cycled, thereby vulcanising the silicone rubber.
Once heated and sealed, the mould is ready for the process. Rubber is placed in the mould cavity and closed. Using temperature and pressure parameters, heat and pressure are applied accordingly. After the process is complete and the rubber is removed, the post moulding process starts which includes deflashing, inspection, postcuring, etc.
This is widely used for the production of medical and dental devices, kitchenware, electrical parts and many more. The process is very simple yet effective, good for a larger volume of production.
- What is Liquid Silicone Rubber (LSR) Injection Molding Process?
Liquid silicone rubber is high-purity platinum cured silicone with a low compression set. Injection moulding of LSR is a process to produce flexible and durable parts in high volume. The raw material or unheated liquid is directly poured using an injection nozzle into the cavity of the mold using pressure that results in instantly filling the cavity and is later closed. LSR has good stability and is able to resist extreme temperatures of heat and cold, which are ideally suitable for the production of parts where high quality is the first priority.
This process is used for baby products, and kitchen tools like baking pans and spatulas, etc. They have short and definite molding cycles, almost negligible waste and have cost-friendly processing.
- What is the High Consistency Rubber (HCR) Injection molding Process?
High Consistency Rubber is made from reactive silicon with very heavy macromolecules. It can be found in various applications, because of its versatility and durability. It’s also known as Heat Cured Rubber or High-Temperature Vulcanising (HTV) silicone rubber. High-quality HCR Injection molding helps produce a large number of products and their types and so many types of Industries depend on it.
The major difference between HCR and LSR is Viscosity (thickness). In the process, the raw material is heated at high temperatures and injected directly into the mold cavity. It easily flows and fills the mold cavity completely because the injection screw has already heated the silicone. This reduces the viscosity. The end result will be of the highest quality with minimum irregularities.
This is mainly used for food packaging materials, paramedical applications, aerospace, healthcare, etc. Because preheating of mold curing time becomes less, pre-forms are not required which results in less development time. The rubber can be layered over other materials like plastic and metal.
- How does the Silicone Rubber Transfer Molding process work?
In this process, the required amount of raw material or uncured rubber is placed onto the top of the closed mold having a small hole or space to let the silicone fill into it. Then with the help of hydraulic pressure, silicone is pushed into that hole which helps it to completely fill the mold cavity. It then takes the shape of the mold. The important thing to be kept in mind is that the mold should be completely and tightly secured so that the rubber can take the required shape. After opening the mold, parts can be removed and any extra parts can be trimmed away.
One of the important positive takes of the Transfer Molding process is that it can be used to overmold other materials, this helps in creating high precision parts, also enabling accurate results in more complex geometries.
Spark plug wires, rubber face seals used in the natural gas industry, wires to mold connector seals around the wire, sharp lip seals and lip or U-cup designs in the hydraulic industry are some of the places where we can see the use of the Transfer molding process. Shorter production Cycles, precise results with complex molds, overmolding over other materials are some of the advantages of using this process.
- How does the Silicone Rubber Extrusion work?
In this process, a preformed strip consisting of HCR compound with catalysts is used. This raw material is then passed through an extruder. The preform is then heated, pressurized and passed through hard steel die with a cut-out mold. It passes through a heated chamber. And then it is cured by pulling it continuously in the oven.
Before processing, fine silica particles are present in the silicon rubber. It then turns into a translucent paste that has various uses.
This process can be used to make chords, rods, wire insulations, and automotive applications. Also, the product is fire resistant and has its workability in extreme temperatures, has excellent mechanical properties, very adaptive in various fields.
- How does Silicone Rubber Calendering work?
In this mechanical process, the raw material, usually HCR, is preheated to soften it or extruded. Then it’s forced through heated cylindrical rolls, which continuously move to smoothen and compress the raw material by moving it through them. These aligned, double or multiple cylindrical rolls are known as ‘Calendars’. They are pre-adjusted according to the requirement of the product – such as invariable thickness, and predetermined texture for silicone rubber, which can either have shine or matte, smooth, embossed, etc.
Calendering is used in the production of cloth materials like – viscose, and polyesters. Also for medical applications, glass, plastic, belts, food products, etc. The advantages of this process are – one can produce a huge quantity of quality products continuously, smooth and/or textured surfaces.
Conclusion:
So here we learnt in-depth about the different processes used to process and mold Silicone rubber. We also gained good knowledge about their advantages and for which industries are they mostly used. We would be glad to have feedback from our readers. It helps us to give better output every time when we get connected to our viewers. Keep viewing and stay connected with us.