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Compression molding is a simple, high-pressure situation where vulcanized rubber is transformed into a strong, useful rubber part. These parts play a vital role in reducing noise and friction and support high-functioning machines and tools for global businesses. Compression molding produces millions of pieces like this and is a highly effective way to create precision rubber molded components. Read on to learn more about the compression molding process for rubber and how to find custom rubber parts that exactly meet your specs.
Want to read The Engineer’s 7-Minute Guide to Rubber Molded Parts? Go here to get insight into everything from cost, types, challenges and solutions for molded rubber products.
Compression molding results in rubber products that are very strong, free of residual stress and are highly ablative. These homogenous parts and products are useful in a number of applications. The process of compression molding is fairly straightforward and time-tested. It requires different equipment and steps compared to transfer molding or an injection mold. Due to its simplicity - it is one of the mold cost effective rubber molding methods.
To illustrate the compression molding process, we’ll consider the use of silicone rubber. The most common elastomers used are Nitrile (NBR), SBR, EPDM, Viton or Silicone. Let's dive into the compression method for silicone molding.
The kind of equipment used for compression molding of rubber is similar to the kind used to mold thermoplastics. Put simply, there must be mold plates, mold cavity, alignment bushings and pins and a place to inject uncured rubber preform. While similar, compression molding is more cost effective. Thermoplastics or TPE's typically require injection molding which is more expensive. Compression molding is more cost effective to use with elastomers such as NBR, SBR, EPDM etc.
Compression molding should meet the following manufacturing and quality standards:
To prepare, raw rubber is subject to heat, which bonds the sulfur to carbon-hydrogen chains. These randomly connected chains begin to form a 3D web. This arrangement locks together. The chemical work in play means that rubber compression bypasses the typical “heating, then cooling” operation to create compounds. The resulting parts are able to withstand extremely high temperatures. Vulcanized rubber is then the material used for rubber compression molding.
Handling the vulcanized rubber is the key to achieving a useful rubber part or rubber product. Engineers calculate vital characteristics and requirements, including:
Depending on the type of product being created from this process, it will have to exactly align with these specifications. The geometry and materials are adjusted by engineers before the compression molding process even begins.
It’s also important to note that a calculation frequently utilized is the cost, which is directly related to the weight of a compression molded rubber part. When possible, this is reduced (by trimming material) while retaining the integrity of the part to perform. There are CAD software programs that can aid in these calculations.Modern 3D modeling allows us to calculate the volume of rubber required much more quickly. Resulting in quicker turn around times during the quoting process.
The final stage of preparation is prototyping. Compression mold tooling involves creating molds that are capable of the molding process required. Compression molds have to be specifically designed and created. Most often, two plate compression molds are preferred. The goal, in addition to achieving the exact measurements, is to create the most efficient cycle possible. Sometimes this requires additional plates or cores and assembly structures. For higher production capacity, it may be advisable to turn to injection rubber molding. You can learn more about that here.
Once all of the above elements are in place, vulcanized rubber is subject to compression on prepared molds.
Here are the steps of the rubber compression molding process:
There are numerous benefits to this simple and effective process.
Beyond the usefulness of the parts themselves, rubber molding has the following benefits:
There are a few drawbacks to rubber compression molding, including that it produces intermediate tolerances, lengthy cycle processes and may require transfer or injection molds.
Many manufacturers utilize rubber injection molding and custom rubber molding as a solution.
The low cost of molds is a valuable aspect of compression molding. However, when very specific parts are required, it may mean multiple stages or transfers. This can quickly deteriorate the cost savings. If this happens, many businesses turn to custom rubber molding options.
Customization is done by highly qualified companies like RPM. We have a very specific process that offers our clients end-to-end service for custom rubber molding. Our three steps are:
This is a simple way to sidestep the challenges of multi-stage rubber compression molding. Contact us to learn more.
Molded rubber products are more than a final piece of the puzzle. Because they effectively reduce equipment stress, they can prolong the life of vital and valuable machines. Here are examples of the molded rubber products you can buy:
As you already know, these items are essential to the form and function of equipment in many industries. Medical facilities, manufacturers, precision mechanics, automobiles and endless other spheres benefit from compression molded rubber parts every day.
At RPM, we work with your timeline and budgets. Our cost-effective prototypes can be populated in small production runs that align with your schedule. We understand and meticulously implement the best tactics for achieving high-quality custom rubber products for your company. Get in touch to learn more and order your custom rubber part.