Ever wondered which silicone rubber processing method suits your application best? The method you choose dictates the properties of your silicone rubber end products. It also determines which manufacturer to work with. There’s seldom a manufacturer who can accommodate different processing techniques.
In this article, you’re going to learn the most widely used processing methods for silicone. Hopefully, this can help you choose the right products. And, of course, the manufacturer that handles them.
1. The Factors that Affect Which Processing Method to Choose.
Let’s look at the typical factors that can influence your decision when choosing a method:
- The number of your units — Do you need a large batch or a small one?
- How complex are your end products? — Would they require an intricate production technique?
- Your unique specifications — Silicone rubber can have varying properties and appearances.
- Lastly, your available budget — Some methods are more expensive than others.
2. The Different Processes for Silicone Rubber Molding.
Here are four of the most widely used techniques for molding silicone rubber:
Each of these processes is composed of different sets of procedures. And as mentioned, each produces different resulting products. These products vary in mechanical and physical properties. Examples include varying hardness, tensile strength, and temperature resistance, to name a few.
Let’s look at the different processing methods in more detail.
2.1 Injection Molding
Injection molding is a popular silicone rubber manufacturing process. It’s performed by injecting hot, liquid silicone into a mold. The mold takes the shape of the end product. Injection molding is often the first choice for molding intricate but small products.
There are two main ways to do injection molding—one for Liquid Silicone Rubbers and one for High-Consistency Rubbers.
Liquid Silicone Rubber(LSR) is a two-part, high-performance polymer linked by a chemical bond. Unlike high-consistency rubber, its curing method is exclusive to platinum curing.
LSRs are thermoset polymers, which means they have irreversible hardening. Because of this characteristic, LSRs must undergo additional treatment. For example, manufacturers perform distributive mixing before the silicone is molded.
The Advantages of LSR Injection Molding：
- It has a more efficient production output, producing more units in one go.
- The manufacturing procedures used are more cost-effective.
- LSRs are highly-adaptable. You can create tons of products with LSRs for different functions.
- It has a faster curing time and better mold release, resulting in a shorter production cycle.
Much like other silicone rubber variants, LSRs see a lot of industry applications. They’re used extensively in the automotive, consumer product, and food sectors.
LSRs also possess many advantageous characteristics. These include superior aging resistance, chemical resistance, heat stability, and shelf life
High-consistency rubbers(HCR) are polymers with high molecular weight and long polymer chains. For HCRs, you can use either peroxide or platinum as the curing agent.
A manufacturer should be able to modify HCRs to exhibit your desired characteristics. There are many ways to do this. One is by using suitable raw materials to improve the properties end product.
You also have the option to have it mixed with multiple additives. Now, all of these translate into a wide range of customization options that can meet countless requirements.
The Advantages of HCR Injection Molding：
- You can easily maintain product consistency throughout the production process.
- Its cost per unit can be cheaper.
- It doesn’t leave out as many waste materials.
- It allows for superior accuracy and precision, ideal if you’re molding complex shapes.
- You can mix mold HCRs with other materials, like metals and some polymers.
HCR exceeds standard organic elastomers in many ways. It performs better in extreme temperatures (ranging from -50°C to +300°C). Like LSR, it also possesses good aging and chemical resistance, not to mention heat stability.
These characteristics (along with customizability) mean HCRs see extensive use in diverse industries. Some examples include healthcare, aviation, electronics, construction, and more.
Extrusion is when performed HCR strips are fed into an extruder via a roller feed wheel. Manufacturers choose this technique when creating tubes, hoses, and cross-sectional components.
The process begins by preforming a catalyzed HCR material into strips. The HCR strips then go through an extruder. Extrusion happens inside a pre-shaped die and mandrel assembly. Once profiled, the HCR will pass through a heated section via a conveyor. This process is what cures the silicone rubber.
The Advantages of Silicone Rubber Extrusion：
- Extruded silicone has excellent transparency and clarity. This quality makes it ideal for making clear tubings and hoses.
- Extruded silicone tends to be a good electrical insulator. It will resist regular current when exposed.
- This process is ideal for creating tubes, rods, gaskets, and seals. As you know, these products have countless applications, notably in healthcare.
- You can use lower-priced raw materials while producing large quantities of sound products.
2.3 Compression Molding
Compression molding is one of the oldest methods used to shape elastomers. In this process, manufacturers place unvulcanized silicone into a heated mold cavity. It’s then sealed inside the cavity and squeezed using immense pressure.
The compression force ensures that the uncured silicone fills the entire mold cavity. Once that’s done, the curing process begins. For the silicone to cure inside the mold, you only need to maintain the right temperature and compression.
This process is similar to injection molding in that you use force to fill a mold cavity. The main difference is that, in this process, you must supply the mold before sealing. In injection molding, the silicone is force-injected into an already sealed cavity.
Compression molding is favored when making basic shapes and designs. It’s also efficient in producing sizable components you can’t make from extrusion. Many applications for a diverse range of industries use this process. Some examples include automotive, healthcare, and electronics.
The Advantages of Silicone Rubber Compression Molding：
- Like injection molding, it does not produce too many waste materials.
- Compression molding has a longer cycle time compared to injection molding. But it’s a cost-effective choice for low to medium production quantities.
- Extrusion molding can’t produce materials with sizable dimensions. Manufacturers turn to compression molding to create these large components.
- It’s ideal for molding visually and artistically creative parts, such as those with complex curves.
In calendering, raw silicone material is compressed and smoothed by continuously passing through multiple heated rollers. These high-temperature rollers are known as calendars.
You can adjust the pressure of these calenders to produce the silicone rubber finish you want. You can alter pressure to get different thicknesses and textures.
The process starts by heat-softening and extruding the uncured silicone material. Manufacturers then place it into the calendar rolls. It will continually run until it compresses into a long silicone sheet.
The silicone can be intentionally exposed to various substrate materials during this time. The additives used depends on the client’s desired end characteristics.
The Advantages of Using the Calendering Method：
- This process lets you coat silicone rubber with other materials, like fabric.
- Its continuous processing flow means you can create high quantities of consistent products.
- Calendering allows production at a rate of up to three surface meters/minute.
- Compared to molding processes, calendering has a lower tooling cost.
2.5 Transfer Molding
This process uses a plunger to transfer uncured HCR from a charge to a pre-shaped mold cavity below it. It is similar to compression molding in that you use pressure to fill a cavity.
The difference is that, in transfer molding, you place the HCR silicone into a charge above the mold. A plunger then pushes it via a sprue into the mold chamber itself. In compression molding, you simply put the silicone directly into the mold cavity at the top plate.
The mold will seal once the HCR enters the cavity. It is then heated until the silicone completely cures and solidifies, taking the shape of the mold.
Transfer molding allows for high-precision molding. You can also use it to cross-mold with other materials. Therefore, It’s ideal for creating parts with complex geometries and angles.
This versatility makes for exceptional finishes in terms of design. Still, transfer molding is not without its drawbacks. This method can leave out excess waste in the pot once the silicone cures. You must remove these wastes through manual processes, like trimming and grinding.
The Advantages of Silicone Rubber Transfer Molding：
- The method can efficiently process molds pre-positioned with various reinforcement fibers. These materials include carbon, glass, natural plant fibers, and aramid.
- Transfer molding has a short production cycle. You can produce more units in short timeframes.
- Its two-part process allows for consistency in manufactured products.
- It accepts small tolerances more than compression molding.
Final Thoughts: Which one suits your application?
If you made it through all the way here, you know that choosing the suitable method depends on many factors. No two methods are the same. And each produces differing results.
For instance, you may require end products with complex geometrical shapes. In that case, the versatile transfer or injection molding methods might suit your needs. On the other hand, if you’re going for products with sizeable dimensions, it may be best to go with compression molding.
At GX Silicone, we always take time to guide clients regarding the proper manufacturing process for their specific requirements. Cost-effectiveness and efficiency are two of the most significant factors we consider.
Contact us to learn more about how these processing methods work. Our 10 years of combined knowledge and experience are at your disposal. We’d be happy to provide the proper guidance so you can make the right decision.