General Molding Silicone

Crestmat is a leading rubber material and rubber product supplier in China. The factory has been devoted in special rubber compounding for more than 30 years. The products mainly include rubber materials like fluorosilicone (FVMQ), arylate rubber (ACM), Hydrogenated Nitrile (HNBR), fluoroelastomer (FKM) and rubber calendering products such as HNBR sheet, FKM sheet, fluorosilicone sheet and rubber extruded products such as fkm o ring cord, HNBR rubber cord, fkm profile and high quality ffkm oring. The products are widely used in aviation, automobile, petroleum, marine, semi-condutor and many other fields. The rubber compounding factory is well equiped with Japan-made banburies, two-roller mixers, reaction kettle, strainer; the rubber product factory is equiped with Rotocure machine, press machine, extruder. The lab is equiped with Rheometer, Hardness Testor, Elongation Testor, Rotary Viscosimeter, Biochemitry Incubator.

It is important to consider what method of molding a silicone rubber manufacturer uses when deciding to choose one. There are a few different methods of molding silicone components, each with their own benefits and disadvantages.

Compression molding consists of a process that uses labor intensive silicone rubber. The silicone rubber used is pre-catalyzed by adding powder to the silicone. This enables the silicone to cure once introduced to heat. To add pigment to the silicone, the silicone must be mixed using a two-mill roll. This is a labor-intensive process that has the possibility for contamination of the silicone. Once the material is pre-catalyzed and pigment is added it is weighed and often shaped to the approximate size and configuration of the desired part. It is then placed directly into the mold cavity. The rubber is then compressed between the top and bottom plates. These plates are heated to melt the silicone and vulcanize (cure) the silicone.

Compression molding is the simplest form of silicone rubber molding, but it is also an open-air labor intensive process. This allows for the possibility of contamination to get into the silicone. Compression molding also has the use of fillers that are added to the silicone to lower the cost of material for manufacturing.
Liquid silicone injection molding or LIM, is a custom injection molding method of liquid silicone rubber (LSR). While normal injection molding typically uses a High Consistency Rubber (HCR) which is also known as gum stock, LIM uses a high viscosity liquid silicone rubber. LSR consists of two parts, an A and a B. Both parts are a liquid, but only one part contains the catalyst which is platinum. LSR is naturally translucent and typically comes in pail kits or drum kits which are 80lbs and 800lbs. LIM is a closed-loop system which means that the raw silicone is sealed, as well as any pigment that may be added. The Part A, and Part B are connected to a dispensing machine that seals the material and uses pressure to pump the material from the original containers into the machine. The pigment which colors the silicone is a silicone based pigment that is connected to the dispensing machine as well. The material and pigment are injected into a water-cooled barrel that keep the material from catalyzing. The material is then injected into a hot mold but the runner gate and sprue are typically smaller due to having a lower viscosity than gum stock. Due to the platinum cure system, Liquid Silicone Rubber cures at a much faster rate than typical gum stock. This allows for frequently lower piece prices than traditional compression molding. The rapid curing also makes LIM the desired choice for high volumes. This can cause an issue for low volume production that requires consistent material purging which can add to the final cost of the product.

Using a closed-loop system helps keep contamination to a minimum. Lowering the amount of handling greatly decreases the chance of contaminating the silicone components. LIM is the desired choice for the Medical Industry because the pails or drum kits of uncured LSR are loaded and sealed into the dispensing machine which can be injected or cured without human contact.

One widely used method is liquid injection molding (LIM). LIM involves injecting liquid silicone rubber (LSR) into a mold, where it quickly hardens and takes the desired form. This method is known for its precision and efficiency, making it suitable for producing intricate parts in large volumes.

Another common technique is injection molding. Similar to liquid injection molding, this process involves melting silicone and injecting it into a mold. The mold's temperature and pressure are carefully controlled, ensuring the silicone solidifies uniformly and maintains the desired shape. Once the part is cooled, it is removed using an ejector pin.

Compression molding is an older, yet still relevant, method for molding silicones. It involves placing a pre-measured amount of silicone into the mold, which is then compressed under high temperature and pressure. Although this process is slower than injection molding, it is cost-effective for lower-volume production runs.

Transfer molding is another technique used to manufacture silicone parts. In this process, the material is preheated in a separate chamber before being transferred into the mold cavity, where it hardens and takes shape. Transfer molding is a suitable option for moderately complex designs and smaller production volumes.

Reaction injection molding (RIM) is a method that combines elements of injection molding and chemical reactions. In this process, two or more reactive components are mixed, injected into the mold, and allowed to cure. RIM is particularly well-suited for large, lightweight parts with complex geometries.

Finally, overmolding refers to the process of molding one material over another. In the case of silicones, this process allows you to create multi-material parts with different properties (e.g., soft and hard areas), enhancing the overall functionality and aesthetics of the final product.