Custom rubber molds in aerospace applications
A mold can simply be described as two or more pieces of material (usually steel) which, when fitted together, form a cavity that resembles the shape of the product. This will be a very basic pattern. Casting is by far the most important curing process, in which uncured rubber is placed in a heated mold, shaped into the shape of the final product, and then vulcanized.
Mold
It can range in size from a clenched fist to the size of a car and can have a single compartment to make one product at a time, or enough compartments to make hundreds of products or more. up. Most custom rubber molds are based on the introduction of a solid compound into the mold, although urethane and silicon can be introduced as solids or liquids. A rather high mechanical pressure is required to close the mold and thus form the shape of the product; This pressure is guaranteed by a press. So the mold must be strong enough to not be flattened. Tool steels tempered to a Rockwell C hardness of about 60 may be required.
Mold design
A basic compression die design should have both die register halves (matching up exactly). Usually the mounting pins on the top part fit snugly into the holes drilled in the bottom half. Any collision between the pin and the hole can cause the top half of the product to deviate from the bottom half. If the joint is too tight, trying to open the mold manually can be difficult. Click here Minhui LSR Liquid Silicone Rubber Injection Machine for more details.
Since some composite materials expand with heat (raw rubber elastomers are the main concern) by at least one order of magnitude more than steel, they will also contract accordingly when cooled when removed from steel mold. As a result, mold sizes are usually designed to be about 1.5% larger (based on linear dimensions) than required in rubber products, to compensate for the difference in expansion between rubber and steel. . This percentage of vulcanization shrinkage may be higher for FKM and silicone compounds and lower for compounds containing large amounts of fillers. The overflow (flash or spew) is machined around the cavity. In theory, this is to accommodate rubber that exceeds the volume of the cavity. In practice for compression molds, it is not uncommon that when closing the mold, the material fills the cavity, then overflows the overflow groove, even on an area outside the groove called flat, and then out of the mold. This excess material is called flash.
Put the compound in the mold
There are different ways to introduce the compound into the mold, some of which involve changes to the basic design. Each offers certain advantages not found in the others. a) In the most basic design, pieces of rubber compound are placed in the lower cavity and compressed by the upper half of the mold. b) The first modification is mold transfer, which can be visualized as holes drilled through the outer face of the top half of the compression die into the cavity. Therefore, the mold can remain closed while the rubber compound is fed through these holes into the cavity using the force applied by the presser shaft. c) If a separate device, not attached to the presser shaft, is used, which will inject the compound through the holes; this would be rubber injection molding. visit here https://minhuiglobal.com/product/lsr-liquid-silicone-rubber-injection-machine/ to know more information.
