Stern Rubber Company - Rubber Molding. Compression Molding and More.

With over 50 years of experience, Stern Rubber Company has developed into an industry leader in rubber molding and manufacturing. Our team provides customers worldwide with innovative, custom rubber molding solutions to meet the demands of their specific applications. We utilize production methods like rubber injection molding, compression molding, and transfer molding to ensure the best fit for your product, delivering every project on time and within budget. Learn more about the rubber molding process, our services, and the benefits this manufacturing technique lends to applications in diverse industries.

What Is Rubber Molding?

Rubber’s combination of elasticity and durability makes it an ideal material for molded components. Manufacturers can utilize either natural elastomers and rubber materials or synthetic, chemically generated varieties. Rubber molding utilizes a shaped mold, heat, and pressure to form uncured rubber material into a finished part or product.

While different molding processes have different stages, rubber molding typically involves transferring pre-heated rubber into a metal mold cavity, heating the mold and using compressive force to cause chemical reactions like vulcanization and curing for cross-linking polymer chains, and then cooling the product at ambient temperatures to finally result in a part in the shape of the mold.

Rubber Molding Processes

Rubber molding is actually an umbrella term for a number of individual, differentiated molding processes. Each method follows its own unique steps to achieve a complete molded part and has its own benefits. Understanding the common rubber molding processes we use at Stern Rubber Company will help you select the right option for your application.

Injection Molding

A similar process to plastic injection molding, rubber injection molding begins by passing uncured strips of rubber into a machine’s hopper. From there, the rubber proceeds into a screw chamber for heat application through external heaters. A moving screw in the chamber provides friction, compressing the molten rubber and then injecting it into the mold cavity. The rubber experiences vulcanization when its chemical bonds cross-link and, after a set period of time, the rubber will have taken the shape of the cavity. Operators then open the mold and remove the parts so that they can finish cooling at ambient temperatures.

The distinct advantages of rubber injection molding include the following:

  • Creating strong, durable parts
  • Achieving components with complex geometries
  • Enabling high-volume production
  • Requiring minimal secondary treatments or finishing
  • Cost-efficiency
  • Reducing material waste

Compression Molding

This process is a bit like rubber injection molding in that it also uses high temperatures and compressive force to create parts. However, in compression molding, the pre-heated mold is split into two halves, with either molten rubber or rubber pre-forms going into the cavity of the stationary lower portion of the mold. The mobile half of the mold, or the plug, lowers until it applies compressive force on the rubber, called the charge. As a result of the plug’s pressure and the mold’s heat, the rubber cures, taking the shape of the mold cavity.

The benefits of rubber compression molding include:

  • Simplicity of the process
  • Capability to manufacture large parts
  • Compatibility with a myriad of rubber materials
  • Minimized tooling costs
  • Cost-effectiveness for prototyping and smallscale production
  • Little material waste creation

Transfer Molding

While the die mold for transfer molding also consists of two halves, it’s unlike other molds in its design. The upper portion contains a pot, or an extra open-ended cavity, where the heated rubber charge will be. The pot has transfer holes that connect to a network of sprues. When a ram compresses the compounded rubber in the pot, the heated material transfers through the sprues to enter the heated mold cavities in the lower half of the mold. The rubber cures, forming parts in the shape of the cavities.

Rubber transfer molding is beneficial for its ability to:

  • Create components with delicate features
  • Produce large parts
  • Achieve components with close tolerances
  • Enable rubber and metal to bond, allowing for rubber parts with metal inserts
  • Save time and labor with a single pre-form

Rubber Molding Benefits

Whichever process you choose, rubber molding will offer your project the following overarching benefits:

  • Flexibility. Rubber molding is highly versatile, allowing manufacturers to achieve parts with complex shapes or unique features. Depending on the molding process you use, it’s also well-suited to low-, medium-, and high-volume production.
  • Repeatability. As manufacturers will use the same mold to generate the necessary volume of products, rubber molding produces highly accurate, repeatable parts with good uniformity.
  • Cost. Once the mold is created, manufacturers can produce large volumes of parts for better price-per-unit costs. Also, compression molding, for example, is cost-efficient for its low tooling costs and capability to create prototypes for evaluation prior to full-scale production.

Rubber Molding Industries & Applications

Stern Rubber Company can mold and shape rubber into widely varied and complex forms. Given rubber’s flexibility and durability, widespread industries make use of rubber-molded components. Rubber parts assist in decreasing vibration and noise, isolating components, supporting wear resistance, and preventing metal surfaces from coming into contact. Common industries and applications that rubber molding serves include:

  • Agriculture. Rubber molding can create bushings, bumpers, extrusions, suspension components, and engine mounts, as well as seals for agricultural equipment doors and windows.
  • Automotive and transportation. Along with door and window seals, rubber molding can generate transport components such as grommets, bumpers, extrusions like tubing, and engine mounts.
  • Construction. Machinery for the construction sector often uses rubber-molded buttons, knobs, bushings, belts, and engine mounts.
    General industry. Industrial companies can use rubber-molded parts in everything from power generators to gas meters.
  • Healthcare. The medical and dental sectors benefit from rubber-molded gaskets, cords, tubing, extrusions, catheters, syringes, hearing aid parts, dental grips, diaphragms, and wheels for patient beds.
  • Military and defense. Belts, tracks, and mounts are examples of rubber-molded parts for military and defense. Rubber molding can also provide products for equipment and rifle isolation.
  • Mining. Mining operations utilize rubber components to assist with wear resistance in equipment for sifting, sorting, and material handling.
  • Waterworks. Rubber molding is useful for creating gaskets, ductile iron castings, and water valve components.

Quality Rubber Molding Services at Stern Rubber Company

At Stern Rubber Company, we understand that every project is different, which is why we’ve provided comprehensive rubber molding services to meet our clients’ varied needs since 1969. We’re a full-service, ISO 9001:2015-certified custom rubber manufacturer offering high-quality molded products and exceptional customer support.

From our three facilities in Minnesota, we operate round the clock, working on production runs ranging from a single part to millions. In addition to our molding services, we also offer rubber-to-substrate bonding, off-shore sourcing, design support, material selection, custom milling and compounding, testing, and quality assurance to best serve you. We bond and over-mold rubber to plastic, metal, other rubbers, and related substrates.

Contact us to discuss the rubber molding process that best fits the specific requirements of your project, or request a quote today to get started.


This document contains a list of all the rubber manufacturing and quality assurance equipment we use. Stern Rubber Company has provided this list in order to showcase our equipment and quality assurance devices. Let us know if you have a question.