Rubber Molding: Custom Rubber Molded Parts Manufacturing

custom rubber parts, rubber injection molding

These days, rubber molding products are found in almost every industry. They are essential for tasks like insulation, abrasiveness, sealing, and more. They are therefore essential to maintaining the high standards of the industry and to development in the fast-paced world of today. Rubber molding is one of various technologies used in the production of rubber goods.

Three primary types of rubber molding, typical rubber materials, and industrial uses will all be covered in this article.

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Rubber Molding Overview

Rubber molding stands out as a prominent process in rubber manufacturing, transforming raw rubber materials into final plastic products through the use of a metal mold. This method involves filling the mold cavity with rubber, applying heat and pressure to achieve the desired shape, all under the supervision of skilled labor and engineers.

The efficiency and cost-effectiveness make it a preferred choice in industrial settings. Rubber molding yields high-quality parts with precise accuracy and desirable mechanical properties, contributing to its widespread adoption by various industries.

The realm of rubber molding encompasses diverse methods, each characterized by its unique production procedures, advantages, and drawbacks. In this overview, we will delve into the details of three prominent variants: injection molding, compression molding, and transfer molding.

Rubber Injection Molding

Rubber injection molding is a process similar to plastic injection molding, but specifically designed for working with uncured rubber. The process begins with uncured rubber strips that are fed into the machine through a hopper. Inside the machine, the rubber is heated and compressed in the screw chamber, using external heaters and the movement of the screw.

As the rubber nears the end of the screw, it reaches a highly fluid state. It is then injected into the mold at high pressure, filling the cavity created within the rubber mold. The flow properties of the rubber ensure that every intricate detail of the mold is filled.

After injection, the mold gradually cools down, allowing the rubber to solidify. Once solidified, the mold opens and the finished product is ejected, preparing the machine for the next cycle.

rubber injection molding

Advantages of Rubber Injection Molding

  • High Accuracy:
    The combination of pressurized injection and the flow properties of rubber ensures precise filling of the mold, resulting in highly accurate final products.
  • Complex Geometry:
    This method enables the production of designs with intricate features such as holes, curves, and sharp contours. The mold cavity design offers flexibility and can incorporate elements like cores, allowing for complex features in the rubber molding parts.
  • High Mechanical Strength:
    The application of pressure and sufficient curing time during the molding process results in rubber molding parts with excellent mechanical strength and durability.
  • Minimal Finishing Required:
    Rubber molding products have fewer defects or excess material that needs post-processing. Apart from a small parting line and gate vestige, the output is almost the final desired shape.
  • Efficient Process:
    Modern control technologies ensure precise control of heat and pressure in injection molding machines. Optimization of these processes can lead to shorter curing cycles, providing a significant time advantage.
  • Economies of Scale:
    Apart from the initial tooling costs, the per-item molding cost is relatively low. This makes rubber injection molding highly profitable for mass production.

Disadvantages of Rubber Injection Molding

  • Material Limitations:
    One drawback of rubber injection molding is the requirement for rubbers with good flow properties. Not all rubber materials possess these properties, limiting the range of raw material options. However, most rubber materials can still be processed through injection molding.
  • High Initial Costs:
    The tooling cost and the machinery required for rubber injection molding can be expensive. Consequently, it may not be financially viable for low-volume production runs.
    Rubber compression molding is a process that, like injection molding, utilizes heat and pressure. However, the application of heat and pressure in compression molding differs significantly, as explained below.

Rubber Compression Molding

The mold used in compression molding consists of two halves, each containing a portion of the desired cavity. Initially, the uncured raw material, known as the charge, is pre-heated and placed in the lower half of the mold. Both halves of the mold are also heated beforehand.

Once the material is appropriately positioned, the movable half of the mold, called the plug, descends into the fixed mold. The pressure exerted by the plug causes the charge to take the shape of the mold cavity. Heat is then applied to the mold, curing the rubber into its final shape. Finally, the molded rubber product is released as the end result.

Advantages of Rubber Compression Molding

  • Low Cost:
    The tooling required for compression molding is relatively inexpensive due to its simple design. Additionally, production costs decrease as the volume of production increases.
  • Low Maintenance:
    The straightforward design and absence of complex sprue networks make cleaning, repairs, and polishing of the mold easy and cost-effective. Maintenance time is also reduced compared to more intricate mold designs.
  • Material Variety:
    Compression molding can accommodate a wide range of rubber materials since it does not rely on material flow like injection molding.
  • No Gate Vestige:
    The absence of a gate in the mold means that the final product does not have any remnants of the gate. This improves the product’s aesthetics and reduces the need for finishing operations.

Disadvantages of Rubber Compression Molding

  • Dimensional Tolerance:
    While compression molding offers good manufacturing accuracy, it may not achieve the same level of precision as injection molding. Slight deviations from the mold cavity can occur, particularly in areas with high curvatures or pockets.
  • Finishing:
    Although there is no gate vestige, finishing operations are still necessary to remove flashes and parting lines. Grinding or cutting processes require additional time and incur costs.

Rubber Transfer Molding

Rubber transfer molding is a unique method that involves a specific mold design. The mold consists of two halves, similar to other molds, but the upper half has an open-ended cavity called the pot. A sprue network connects the pot to the main cavity. The preform is placed in the pot and then “transferred” into the cavity through the application of high pressure and heat using a plunger.

Once in the cavity, the raw material cures and solidifies. The final product is ejected from the mold after it has cooled down and undergone vulcanization.

Advantages of Rubber Transfer Molding

  • Tight Tolerance:
    Transfer molding can achieve excellent dimensional tolerance, making it suitable for manufacturing precise part geometries.
  • Metal Bonding:
    Transfer molding is particularly effective for rubber-to-metal bonding. It is a convenient method for producing parts such as combined metal-rubber mounts.
  • Large Parts:
    The mold design used in transfer molding can accommodate large cavities with ease, allowing for the production of larger rubber molding parts.
  • High Cavity Count:
    The preform used in transfer molding is a simple shape that requires minimal preparation. As a result, the same preform can be reused for many cycles without much hassle, saving time and effort.

Disadvantages of Rubber Transfer Molding

  • High Tooling Cost:
    The mold used in transfer molding has additional features like the pot and sprue, which increase its complexity in terms of design and manufacturing. This added complexity adds to the initial setup cost.
  • Finishing:
    Deflashing, the removal of excess material, is always necessary when using transfer molding due to the presence of the sprue network.
  • High Cycle Time:
    Compared to other molding processes, transfer molding requires a longer curing time. This can be a significant consideration in certain applications where cycle time is crucial.

Material Options for Rubber Molding

Rubber molding offers a wide range of material options, each with specific qualities that make them suitable for different applications. Here are some popular types of rubbers used in the industry:


  • Natural Rubber (NR):
    Derived from rubber trees through a process called lapping, natural rubber offers a balanced set of properties. It has high strength, resilience, and stretchability. It is commonly used in its raw form, known as latex, either alone or blended with other compounds.
  • Styrene-Butadiene Rubber (SBR):
    SBR is a synthetic rubber known for its excellent abrasion resistance. It is durable, resistant to compression set, and can withstand water swell, making it suitable for demanding applications.
  • Neoprene Rubber:
    Another synthetic rubber, neoprene, maintains its mechanical properties across a wide temperature range. It is often used in applications such as tubing for engine fluids and friction belts. Neoprene rubber exhibits high chemical stability and corrosion resistance.
  • Nitrile Rubber (NBR):
    NBR is a high-performance rubber with exceptional compression set and mechanical integrity. It resists chemical degradation from common machinery fluids like oil and gas, making it ideal for sealing components.
  • Butyl (IIR):
    Butyl rubber is known for its flexibility and impermeability to gases. This combination of properties makes it highly sought after by sealant companies.
  • Fluoroelastomer Rubber:
    Fluoroelastomer rubber offers high resistance to fluid permeation, making it suitable for applications where resistance to water, oxygen, ozone, and other fluids is required.
  • Silicone Rubber:
    Silicone rubber possesses several advantageous properties, including biocompatibility, fire resistance, ozone impermeability, and availability in various colors.

How to Select a Suitable Rubber Material

When selecting a suitable material for rubber molding, several considerations come into play. Here are some key factors to keep in mind:

  • Material Properties:
    The desired properties of the rubber, such as strength, durability, abrasion resistance, and impermeability to specific fluids, should align with the requirements of the end product. Consider factors like temperature resistance, chemical compatibility, and mechanical load-bearing capabilities.
  • Industrial Applications:
    The intended applications of the final product play a crucial role in material selection. Different rubber materials are designed to excel in specific environments, such as high temperatures, high humidity (including exposure to various fluids), chemical exposures, and specific loading conditions. Understanding the application requirements will help determine the most suitable material.
  • Budget:
    Budgetary constraints are an important consideration. Some rubber materials may come at a higher cost but offer added advantages or specialized properties. On the other hand, there are more economical options that may slightly compromise on certain qualities. For example, comparing EPDM and Silicone, both have similar properties and applications. However, EPDM is generally less expensive than Silicone but may require more frequent replacements in similar environments. It’s essential to strike a balance between cost and quality based on your specific requirements.

By carefully considering these factors, you can make an informed decision when selecting the appropriate rubber material for your rubber molding project.

Rubber Molded Parts Showcase

The rubber industry encompasses a vast array of markets, and here we highlight just a small fraction of its diverse applications:

  • Rubber O-Rings:
    O-rings are widely recognized as one of the most prevalent rubber molding products. These circular seals play a crucial role in fluid sealing applications, such as in piston-cylinder assemblies. Different rubber materials are utilized based on specific requirements, including strength, durability, and shore hardness.
  • Rubber Seals:
    Rubber seals find application in various scenarios where the conventional ring-like shape of O-rings may not be suitable. They come in a range of shapes and sizes, serving purposes such as leak-proofing flange couplings, bellows, vent ducts, and more.
  • Rubber Gaskets:
    Gaskets are essential components for optimal performance in automotive applications. They are utilized in high-pressure sealing situations and can be customized to suit specific needs, such as sealing engine blocks and other critical areas.
  • Rubber Tubing:
    Rubber tubing serves as conduits for fluid transfer. It is used both for the piping itself and as a coating for other materials. In addition to preventing leaks, rubber tubing provides valuable thermal insulation. For instance, rubber-coated tubing is commonly employed in domestic piping systems in colder regions.
  • Rubber Mounts:
    Rubber’s exceptional damping properties make it ideal for vibration suppression. Heavy machinery prone to vibration-induced damage often utilizes rubber mounts to extend its lifespan and enhance performance. CNC machines, for example, rely on rubber mounts to achieve tight tolerances.

At our facility, we specialize in manufacturing high-quality rubber molding products. With state-of-the-art injection molding equipment and experienced professionals, we offer impeccable research and development, as well as manufacturing services to our esteemed clientele.

Custom Rubber Molding at Sungplastic

The capacity to customize the processes used to make rubber molding parts is a major benefit. With the technologies that have been discussed, engineers may now build unique rubber molding parts that are perfectly matched to their goods. This improves user experience, encourages innovation, and increases revenue. You have the chance to establish your brand identity with items that cater to your users with bespoke rubber molded parts.

Our precision rubber molding equipment can achieve superior manufacturing tolerances and unmatched rubber curing when it comes to bespoke rubber molding.

Our team of creative and technical professionals is highly skilled and has years of experience in developing intricate custom molded parts for our esteemed clients. Our specialty is offering solutions tailored to meet your demands. From a list of excellent possibilities, we choose the best rubber material based on your application through targeted research.

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