The processing of high-viscosity silicone rubber and high-viscosity silicone rubber elastomer includes five steps: grinding and softening and catalysis, preparing preforms, extrusion or molding, vulcanization, and finishing.
Softening and catalysis, the initial step in the processing of high consistency silicone rubber elastomers for use in any extrusion or molding application is grinding softening and catalysis. This procedure undoes any “crepe hardening” that has been stored in the inventory of the supplier or manufacturer during the elastomer. Grinding also uses the manufacturer to add a peroxide catalyst to the free radical curing elastomer, if necessary, or to mix the two parts of the addition curing elastomer before manufacturing. Silicone tube production process can be divided into the following five steps:
1. Preparation of preform
Once the high consistency elastomer is fully compounded, the next step in the manufacturing process is the preparation of preforms. This does not require special equipment, but is very labor intensive, especially in large batch applications that are almost continuous in nature. Used for extrusion and injection molding applications, the preform is cut into strips by cutting an elastomer sheet, which is used to feed the extruder for simple preparation. In transfer molding operations, the preform is typically cut with a die-cutting machine and will fit the plug of the transfer reservoir in a multi-station press. For compression molding applications, the process is slightly more complicated because the preform must be cut in the basic geometry of the final part.
2. Extrusion
For high-consistency elastomers, extrusion is done using a single-screw extruder. The preformed belt is fed to the extruder from the roller feed wheel to the extruder barrel, and the elastomer is extruded through a die and mandrel assembly to form the desired contour.
3. Molding
The application of high-viscosity silicon depends on the type of molding equipment used. The transfer and injection molding process requires an operator to load the elastomer into the device and demold the finished part. For compression molding, the operator must place all single cavity preforms in each mold.
4. Vulcanization
The vulcanization of extruded products is usually realized with hot air vulcanization furnace, or HAVS. These HAVS are in horizontal and vertical configuration. In the horizontal mode, the extruded profile passes through the oven, hot air is forced on the extrudate to initiate the vulcanization mechanism and is laid on a continuous belt
5. Finishing
The degree of finishing depends on the specific application. For the extrusion method, finishing involves visual inspection and cutting the tube to a specific length. If the tube has been cured with peroxide, the automatic finishing process also requires an oven-cured by-product to remove peroxide.
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