Three Ways Rubber Parts Can Be Molded


Have you ever picked up a rubber grommet and wondered how it was made? Wonder no more, because rubber molding commonly follows one of three processes: compression molding, transfer molding, and injection molding. Here are the basics of these three types of rubber molding and why each one works well for custom rubber parts.

1. Compression molding

Compression molding is well known for leaving lots of "flashing" on the parts it creates. (Flashing is excess material that has to be trimmed off later.) This is because compression molding is a process that makes it hard to use the exact right amount of material each time. It starts out with solid, unmelted plastic, unlike transfer molding and injection molding. Once the material is in the mold, the next step is to compress it by stamping down hard with a tool or with the other side of the mold. Heat and pressure are applied simultaneously until the plastic softens and conforms to the shape of the mold, with the excess material running out around the edges as flashing. Despite the flashing waste, compression molding is known as one of the less wasteful types of molding.

2. Injection molding

Injection molding uses liquid rubber material, which is piped through holes in the mold until the mold cavity is filled. This is a versatile process and great for mass production, although it's less suited for making smaller runs of a product because the steel or aluminum molds can be relatively expensive to make and require expensive machinery to operate. For making small runs of products that don't need to be mass-produced, compression molding is a better bet.

3. Transfer molding

Transfer molding can be thought of as a cross between injection molding and compression molding. It can use melted material, but like compression molding, it forces the rubber into place with a plunger or similar implement. This removes air bubbles and makes sure the rubber material is distributed evenly throughout the mold. Despite the lack of flashing, this is actually a less material-efficient way to produce parts, because the holes used to let air bubbles out also allow some material overflow.

These are three of the most common processes used on rubber molding for parts such as rubber grommets. A grommet, since it's a small part that likely requires a large production run, may be well suited to injection molding, but theoretically it could be made through any of the three methods. 

For more information, contact Accurate  Products Inc. or a similar company.


22 July 2016

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