Compression Molding Rubber

Coi Rubber utilizes the rubber compression molding process to produce a range of precision rubber molded components. The benefits of rubber compression molding are realized in a number of areas from low to medium volume applications and for some specialty high volume components. Products produced from Coi’s proprietary compression molding rubber process can be designed to be high precision, low waste, and near flash-less out of the mold.

Compression Molding Rubbermolding rubber, compression, transfer, injection, compression molding rubber

  • Perfect for large “bulky” parts and expensive, exotic compounds
  • We feature a 72″ x 72″ Press, 10′ x 42″ Press, 10′ x 30″ Press, 54″ x 60″ Press, and several smaller presses
The rubber compression molding process begins with a piece of uncured rubber which has been performed to a controlled weight and shape. This preform is placed directly into the rubber mold cavity prior to mold closure. As the mold is closed, the material is compressed between the plates causing the compound to flow to fills the cavity. The material is held in the mold under high pressure and elevated temperature to activate the cure system in the rubber compound (rubber is vulcanized). The cycle time is established to reach an optimal level of cure. At the end of the cycle, the parts are removed or ejected from the cavities and the next cycle begins.

Advantages of Compression Molding Rubber

  • Tooling can be less complex and lower cost to construct
  • Lower percentage material runner scrape vs. traditional injection or transfer molding
  • Process is suitable from most elastomers and cure systems

Disadvantages of Compression Molding vs. other rubber molding methods

  • Labor for preforming material can add cost (however offshore manufacturing curtails this problem)
  • Cycle times may be longer (additional shifts counter this problem)

Compression Molding: A Low Cost Option

Compression molding rubber is a manufacturing process that involves rubber being inserted directly into the cavity of a heated mold. The rubber is forced to conform to the shape of the mold through the application of heat and pressure which are maintained until the rubber has cured or vulcanized.

Compression molding rubber is often used to form large or intricate parts and produces very little wasted material. It is one of the lowest-cost molding methods especially when you work with Coi Rubber because we produce your parts in-house from start to finish. If you need large or intricate rubber parts, we often recommend a compression molding solution. This is a highly efficient option, and we can handle every step of the manufacturing process, from start to finish. You send us the print, and we’ll take care of the rest. We will create your mold (or use your supplied mold), determine the proper rubber formulation to meet your specifications, mix the rubber, preform it and manufacture your parts.

Custom Molded Rubber 

As a manufacturer of high precision components and assemblies, FDA Class 1, 2 and 3 products, Coi Rubber Products specializes in finding solutions to tough applications which require the molding and assembly of close tolerance components. We offer a wide range of technical services and production capabilities for producing close tolerance injection molded plastic components, assemblies and sub-assemblies. Our specialty processes and services include:

  • High performance plastics such as PEEK, Torlon®, Aurum® PI and more.
  • Custom Seals and Shapes
  • Insert Molding in Thermoplastics, Rubber and Silicone
  • Two shot molding
  • LSR Molding
  • Rotary Seal Rings and Thrust Washers
  • Rubber to TPE Conversions
  • Metal to Plastic Conversions
  • Bonding for plastic to metal, plastic to rubber and plastic to plastic
  • Over molding
  • Hotplate, rotational and ultrasonic welding
  • Adhesive bonding, hot stamping and machining
  • Product testing, assembly and packaging
  • Unified project management

Rubber Transfer Molding Process

Transfer molding begins with pre-formed uncured rubber that is placed into the transfer pot of a closed molding system. The ram/plunger then distributes the rubber into the cavities to be shaped into the part, which is then cured by the application of pressure and heat for a specified time period. Transfer molding can be used for highly complex part geometries and precision applications, as well as over-molding. The process is suitable for molding parts with traditional organic black rubber as well as pigmented materials.

Compression Molding Rubber & Injection Molding Process

Injection molding of liquid silicone rubber (LSR) is a process to produce pliable, durable parts in high volume. Liquid silicone rubber is a high purity platinum cured silicone with low compression set, great stability and ability to resist extreme temperatures of heat and cold ideally suitable for production of parts, where high quality is a must.

Our in-house rubber formulation and molding facilities can meet our customers’ most precise requirements for customized precision rubber components used in the Automotive, Consumer Electronics and Mobile industries. We have a completely automated mixing facility from the third floor down with full automation and quality compression molding rubber through automated mixingcontrol.  We also have the expertise required to produce rubber to metal bonded bushing and very high demanding applications.  Coi Rubber offers Rubber Compression and Injection Molding services and is equipped with a wide range of molding machines with clamping forces ranging from 30 to <650 tons.  Our highly skilled engineers and technicians work on our computerized injection molding machines to ensure that each molded part meets the product specifications of our customers. These are complemented with various secondary processes including ultrasonic welding, laser marking and robotic spray painting. This integrated solution reduces total manufacturing time and manages overall cost effectively.

Our capabilities include:

  • Design and fabrication of molding tools (up to 850 tons)
  • Injection molding machines (30 to 650 tons)
  • Molding of precision engineering parts, including high-speed, electric, vertical, and double shot molding
  • Secondary processes such as ultrasonic welding, heat staking, laser marking, robotic spray painting, and assembly

To gain a better understanding of the compression molding processes, materials and technical considerations involved in the design and manufacture of custom-molded rubber and plastic parts contact us today!

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