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Rubber Compression Molding

What Is Compression Molding?

Compression molding is a rubber manufacturing process that starts with mixed raw material or a special rubber compound. The compound material is either cut or weighed, or a pre-form is created. The pre-forms take the basic shape of the final product. Since the material is compressed between parts of a cavity, more material is required than will be in the end product. This ensures the entire cavity of the rubber mold is filled with compound when the custom rubber product is created.

Benefits of Rubber Compression Molding

Rubber compression molding is a popular process across numerous industries due to its ability to produce high-quality components at a relatively low cost. Other key benefits of rubber compression molding include:

Cost-Efficiency

Because compression molding doesn’t involve a transfer or injection cycle, it offers lower tooling and equipment costs. This makes it a more cost-effective alternative to transfer and injection molding when it comes to producing custom parts. Additionally, creating a mold for compression molding is a one-time cost, meaning all subsequent runs will cost less than the initial run. Its cost-efficiency also makes rubber compression molding a good choice for prototyping as well as small production runs.

Versatility

Rubber compression molding offers a high degree of production flexibility and works well for components of various sizes, shapes, thicknesses, and production volumes. Since raw materials are loaded directly into the mold cavity, the process enables manufacturers to more easily create larger objects and thicker parts with special features. Compression molding can produce a wide range of durable, long-lasting parts that meet specific environmental and chemical requirements.

Repeatability

Compression molds can be used again and again to create identical parts. Once the mold is created, the process is easily repeatable and offers relatively fast cycle times, making it a great option for mass production.

Durability

Because compression-molded parts are made from rubber, they are naturally durable. Rubber components can withstand exposure to oil and moisture without degrading, making compression molding an ideal choice for producing O-rings and other seals.

Typical Rubber Compression Molding Applications

Rubber compression molding is a versatile manufacturing process that produces durable parts, making it useful for many applications. Common uses include:

  • Fuel, Electrical, and HVAC Systems. Compression molding creates highly precise seals and other rubber parts designed to protect critical fuel, electrical, and HVAC systems.
  • Seals and O-rings. The versatile process of compression molding is suitable for creating reliable gaskets, O-rings, seals, and large bulky components.
  • Powersports. The powersports industry relies on rubber compression molding to produce parts such as O-rings and seals meant to protect closed systems.
  • Food and Beverage Applications. Compression-molded seals and other components are commonly found on sterile rubber hoses for food and beverage applications.
  • Kitchen Equipment. Many kitchen tools, appliances, and utensils have parts that are created using compression molding.

Rubber Compression Molding by Stern Rubber

Rubber compression molding offers numerous advantages that make it a popular choice for producing custom parts across diverse industries. At Stern Rubber Company, we’ve been providing custom-molded rubber products for our customers since 1969. With over five decades of experience, we have the necessary skills and expertise to deliver quality compression-molded products in low, medium, and high production volumes.

For more information about our rubber compression molding capabilities, or to get started on your custom solution, contact Stern Rubber Company today.

 

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Here at Stern Rubber, we do 3 main types of molding: compression, transfer and injection.  Over the next 3 blogs, I will describe each of them in detail, and will start with compression molding.
Compression molding is the most simple of the three, as you load rubber into the cavity, close the tool, squeeze out the extra, and let it cure.  It is good for low to medium volume parts.
These types of molds are made from steel or aluminum.  The shape of the part is cut into the mold.  The tool is run into a hydraulic press that has heated platens.  The rubber has to be held at high pressure and high temperature.  The platens can be heated by electric heating elements or hot oil or steam.  Stern Rubber uses all electrically heated platens.  Parts are normally cured at a 300 to 350 degrees Fahrenheit.
The tool is heated through simple contact with the platens of the press.  The rubber is loaded in the cavity of the mold, and the tool is closed.  Any extra rubber is squeezed out of the cavity.  The presses run at high pressure, with clamp pressures from 10 to 1000 tons.
The tool is held closed for 5 to 15 minutes depending on the thickness of the part.  When the cure time is complete, the tool is opened and the part is removed.
The advantages include lower cost tooling, and it is good for small production runs.  It also does not use gates, sprues, or runners, which consume extra material, and can detract from the cosmetic requirements.  It is also a good way to produce large parts that take a significant amount of material to manufacture.
Some of the disadvantages include slower process times, and greater waste of material, as this type of molding requires the cavity to be over-filled to ensure there is enough material to wash out any possible trapped air.  It also difficult to control the amount and thickness of flash, or the extra rubber that overflows out of the cavity.  This also means that the parts have more variation in thickness, so the parts normally need to allow for more dimensional tolerance.
If you have want to learn more about this process, or think you have a project that will be a good fit for compression molding, please contact us at sales@sternrubber.com.