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What is Silicone Molding?
Silicone molding (moulding) is a manufacturing technique used to transform uncured (unvulcanized) silicone rubber into a pre-defined shape. Several molding techniques may be used, including compression, injection, and extrusion. The choice depends on the size and complexity of the component, required volumes, and budget available for tooling.
The most popular manufacturing method: molding, is ideal for making silicon rubber components consistently and efficiently. The pressure of the press ensures that the material is forced into all areas of the cavity and the heat of the mold cures the silicon rubber making it retain its shape.
- Compression Molding
The simplest method is compression molding which is ideal for lower volume requirements. The process begins with material selection, a suitable grade must be carefully selected or custom formulated that provides the physical properties processing characteristics, and industry approvals required for that application.
Once mixed, the silicon rubber compound is cut into pieces of the appropriate size and weight, this process is called blanking. The blanks are then placed directly into each cavity of the tool and the molding process begins. The finished components are removed by hand, and any excess material or flash is removed.
For very high volumes, compression molding may be inefficient and injection molding is often the preferred solution. With this technique, the computer-controlled press automatically injects the correct amount of material into the mold ensuring a quicker process.
- Injection Molding
The injection molding process involves rapidly injecting an exact amount of silicone material from a tube or cylinder into a closed heated mold. The injection press closes the heated mold and applies pressure to keep the mold closed during the injection and curing cycles, the screw then injects the rubber through the nozzle into the mold. The silicon rubber travels through the mold via a system of runners and sprues and finally enters the mold cavities through a gate. It then fills and packs the cavities to form the desired part rubber.
Injection molding offers economical advantages including a short molding cycle, lower per-unit cost, high dimensional tolerances in absence of flash, and little scrap or waste.
Both molding techniques allow for a combination of other materials metals or plastics.
- Silicone Extrusion
Silicone rubber can be forced through a shaped die (a stainless steel disc with a pattern cut out) to produce cords, complex profiles, and cross-sections. This is called ‘extrusion’. Silicone extrusions typically show a huge improvement over other materials – they last longer, come in a multitude of colors and stand up to a wider variety of environmental conditions. Extrusion products are mainly applicated in Medical equipment, electronic accessories, etc.
Extrusion is the process whereby the silicone material is forced through a shaped die to produce tubes and cross-sectioned profiles. The process begins with material selection, a suitable grade must be carefully selected or custom formulated that provides the physical properties processing characteristics, and industry approvals required for that application.
Once mixed, the material is fed into the extruder where it is forced through the die. It then passes through a heated compartment on a conveyor this hot box cures the material, enabling retention of the shape whilst continuous laser-controlled measurement allows precise tolerances to be maintained.
Even though the extrusion is now cured, there may remain some residual chemicals. These are removed during a post-curing process where the product is exposed to a lower temperature for several hours following post-cure.
The extrusion is reeled up for delivery or prepared for further processing which includes: cutting to precise lengths and joining these to create custom-sized silicon rubber gaskets. Many types of extrusion are possible, including very small or large profiles and tubes complex cross-sections can be multi-layered to produce a product with multiple performance properties.
