Rubber Molding: Custom Rubber Products Guidelines

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Rubber is a high-quality material for common products, such as seals, gaskets, O-rings, and other rubber components with complex shapes. Rubber molding plays a vital role in custom rubber products manufacturing.
Did you know that custom rubber molds doesn’t have to cost more than standard, off-the-shelf molds? Discuss with Sungplastic, as a professional rubber parts manufacturer, we’ll work with you to ensure you get the best solution for your project.
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History of Rubber Molding

The history of rubber molding dates back to the early 19th century when rubber was first discovered and its unique properties were recognized. The process of rubber molding evolved alongside the development of rubber itself, with advancements in technology and manufacturing techniques.

The discovery of rubber as a material with versatile properties is credited to Charles Goodyear, an American inventor. In 1839, Goodyear accidentally dropped a mixture of rubber and sulfur on a hot stove, resulting in the vulcanization process. Vulcanization involved heating rubber with sulfur, which created cross-links between the polymer chains, making the rubber more durable, stable, and resistant to heat and chemicals.

With the development of vulcanized rubber, the possibilities for manufacturing custom rubber products expanded. Rubber molding became a popular method for shaping rubber into various forms, allowing for mass production of rubber components with consistent quality.

In the early days, rubber molding was primarily done through compression molding. This technique involved placing the rubber material into a mold cavity and applying pressure to shape it. The mold was then heated to cure the rubber, resulting in the desired shape and properties.

As technology advanced, injection molding emerged as another prominent rubber molding method. Injection molding involves melting the rubber material and injecting it into a mold under high pressure. The mold is then cooled, and the rubber solidifies to form the desired shape.

Over time, other rubber molding techniques, such as transfer molding and blow molding, were developed to cater to specific manufacturing requirements and product designs. Transfer molding involved transferring the rubber material from a pot through channels into the mold cavity, while blow molding utilized compressed air to shape the rubber material into hollow objects.

Rubber molding found widespread applications in various industries. It revolutionized the automotive sector by enabling the production of rubber components like seals, gaskets, and tires. The consumer goods industry benefited from rubber molding for manufacturing products such as rubber grips, seals, and buttons. Additionally, rubber molding played a crucial role in the medical field, where it was used to create medical devices, surgical gloves, and other healthcare products.

Advancements in rubber molding technology continue to enhance efficiency, precision, and the range of possible applications. With the development of advanced materials and innovative techniques, rubber molding has become an integral part of modern manufacturing processes, contributing to the production of high-quality custom rubber products across industries.

What is Rubber Molding?

Rubber molding is a manufacturing process used to shape raw rubber materials into various forms and products. It involves the application of heat and pressure to mold rubber compounds into specific shapes and sizes. Rubber molding is widely used in industries such as automotive, consumer goods, electronics, medical, and engineering.
The process of rubber molding typically begins with selecting the appropriate rubber compound based on the desired properties of the final product. Rubber materials can vary in terms of hardness, elasticity, chemical resistance, and other characteristics, allowing manufacturers to tailor the rubber to meet specific requirements.

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Applications of Rubber Molding

Rubber molding has a wide range of applications across various industries due to its versatility and ability to create customized rubber parts. Here are some common applications of rubber molding:

  • Automotive Industry
    Gaskets and seals for engines, transmissions, and other components.
    Rubber hoses for coolant, fuel, and hydraulic systems.
    Anti-vibration mounts and bushings for dampening vibrations and reducing noise.
    Weatherstripping and seals for doors, windows, and trunks.These rubber components contribute to sealing, noise reduction, vibration isolation, and overall safety in automotive systems. Rubber molding ensures precision in creating rubber parts that meet strict industry standards.
  • Electronics and Consumer Goods
    Soft-touch grips and handles for tools and appliances.
    Rubber keypads and buttons for electronic devices.
    Seals and gaskets for water-resistant and dust-resistant enclosures.
    Cable grommets and strain reliefs for managing wires and cables.Rubber molding provides protective coatings, gaskets, and keypads for electronic devices. It enhances user comfort, durability, and electrical insulation.
  • Medical and Healthcare Sector
    Medical tubing, including catheters and IV lines.
    Seals and gaskets for medical equipment to maintain sterility.
    Diaphragms and valves for medical devices and instruments.
    Components for prosthetics and orthopedic devices.Medical rubber molding must adhere to stringent regulations, ensuring biocompatibility, sterility, and chemical resistance. Materials used must be safe for patient contact.
  • Industrial Applications
    Conveyor belts for material handling and transportation.
    Seals for pumps, valves, and industrial machinery.
    Rubber linings for tanks, pipes, and other containers to resist corrosion.
    Shock absorbers and vibration dampeners for industrial equipment.Rubber molding’s ability to withstand harsh conditions, dampen vibrations, and provide flexibility makes it valuable in engineering applications. It helps protect machinery and enhances operational efficiency.
  • Aerospace and Defense
    Seals and gaskets for aircraft engines and components.
    O-rings for sealing hydraulic and fuel systems.
    Rubber parts for military equipment, vehicles, and aircraft.
  • Sporting Goods and Recreation
    Grips for sports equipment like racquets and handles.
    Rubber parts for fitness equipment and machinery.
    Seals and gaskets for water sports and outdoor equipment.
  • Construction and Architecture
    Rubber seals for windows, doors, and building joints.
    Expansion joints for bridges and structures.
    Anti-vibration pads for construction machinery.
  • Marine and Maritime Industry
    Seals for marine engines and equipment.
    Rubber fenders and bumpers for docking and protection.
    Gaskets and seals for water-tight compartments.

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Materials Used in Rubber Molding

Various materials are used in rubber molding processes, each with its own unique properties and suitability for specific applications. The choice of material depends on factors such as the desired characteristics of the final product, its intended use, and the molding process being employed. Here are some common materials used in rubber molding:

  • Natural Rubber (NR)
    Derived from latex obtained from rubber trees, natural rubber offers good resilience, flexibility, and tear resistance. It is often used in applications requiring high elasticity, such as vehicle tires and conveyor belts.
  • Synthetic Rubber (SBR, NBR, EPDM, etc.)
    Synthetic rubbers are produced by polymerizing various chemicals to achieve specific properties. Different types include:
    Styrene Butadiene Rubber (SBR): Offers good abrasion resistance and is often used in tires, footwear, and industrial goods.
    Nitrile Butadiene Rubber (NBR): Known for oil and fuel resistance, used in seals, gaskets, and hoses.
    Ethylene Propylene Diene Monomer (EPDM): Resistant to weathering, heat, and ozone, commonly used in automotive weatherstripping and roofing materials.
  • Silicone Rubber (VMQ)
    Silicone rubber has excellent temperature resistance and is often used in high-temperature applications, medical devices, and food-grade products.
  • Fluoroelastomers (FKM)
    Also known as Viton®, fluoroelastomers offer exceptional chemical and high-temperature resistance. They are commonly used in seals and gaskets for harsh environments.
  • Polyurethane (PU)
    Polyurethane rubber offers a wide range of hardness and is used in applications such as wheels, rollers, and industrial components.
  • Liquid Silicone Rubber (LSR)
    LSR is a two-part liquid silicone material that cures into a flexible and durable rubber. It is often used in medical devices, baby products, and electronics due to its biocompatibility and heat resistance.
  • Chloroprene Rubber (CR)
    Also known as Neoprene, this rubber provides good resistance to weathering, ozone, and chemicals. It’s used in applications like wetsuits, hoses, and industrial belting.
  • Acrylonitrile Butadiene Styrene (ABS)
    ABS is often used in overmolding applications where a rubber layer is molded over a plastic substrate.
  • Thermoplastic Elastomers (TPE) 
    TPEs combine the properties of rubber and thermoplastics. They can be molded using conventional plastic processing equipment and are used in various applications, including consumer goods and automotive components.
  • Ethylene Propylene Rubber (EPM/EPDM)
    Similar to EPDM, EPM is used in automotive seals, gaskets, and hoses due to its resistance to heat, weathering, and chemicals.

Properties and Characteristics of Rubber Compounds

Rubber compounds are formulated by mixing various types of rubber polymers with additives, fillers, and curing agents to achieve specific properties and characteristics. The composition of a rubber compound can be tailored to meet the requirements of different applications. Here are some key properties and characteristics of rubber compounds:

  • Elasticity and Flexibility
    Rubber compounds are known for their exceptional elasticity and flexibility, allowing them to return to their original shape after being stretched or compressed. This property is crucial for applications such as seals, gaskets, and tires.
  • Tensile Strength
    Tensile strength refers to a material’s ability to resist stretching forces without breaking. Rubber compounds can be engineered to have varying levels of tensile strength, making them suitable for different load-bearing applications.
  • Compression Set Resistance
    Rubber compounds should resist permanent deformation (compression set) when subjected to compressive forces over time. This property is essential for gaskets and seals that need to maintain their shape under pressure.
  • Abrasion Resistance
    Rubber compounds can be formulated to withstand wear and abrasion, making them suitable for applications like conveyor belts, tires, and industrial components.
  • Tear Resistance
    Tear resistance is the ability of a rubber compound to resist propagation of a tear. This property is important for products like hoses, belts, and protective gear.
  • Chemical Resistance
    Different rubber compounds exhibit varying degrees of resistance to chemicals, oils, fuels, and solvents. Compounds can be formulated to withstand specific chemicals and environments.
  • Temperature Resistance
    Rubber compounds can be designed to perform well across a wide temperature range, from extremely cold to high heat. Some compounds, like silicone rubber and fluoroelastomers, offer exceptional temperature resistance.
  • Weathering and UV Resistance
    Compounds used in outdoor applications should resist degradation due to exposure to sunlight, ozone, and weather conditions.
  • Electrical Insulation
    Certain rubber compounds, such as silicone rubber, have excellent electrical insulation properties and are used in electrical and electronic applications.
  • Hardness
    Rubber compounds can have varying degrees of hardness, measured using the Shore hardness scale. Softer compounds provide better sealing and conformability, while harder compounds offer better durability and wear resistance.
  • Aging and Degradation
    Rubber compounds may age and degrade over time due to factors like heat, light, oxygen, and environmental conditions. Compounds can be formulated to resist premature aging.
  • Curing and Processing Characteristics
    The curing process, which involves applying heat or chemicals to solidify the rubber, affects the final properties of the compound. Different curing methods can result in variations in hardness, flexibility, and other characteristics.
  • Color and Appearance
    Rubber compounds can be pigmented to achieve specific colors, making them suitable for products where aesthetics are important.
  • Cost and Availability
    The choice of rubber compound also considers factors such as cost, availability of raw materials, and manufacturing feasibility.

Rubber compounds are highly customizable to meet the diverse requirements of different industries and applications. Carefully adjusting the formulation of rubber compounds to achieve the desired balance of properties for each specific use case.

Considerations for Material Selection in Rubber Molding

Selecting the right material for rubber molding is a crucial decision that directly impacts the performance, durability, and cost-effectiveness of the final product. Here are some key considerations to keep in mind when choosing a material for rubber molding:

  • Application Requirements
    Understand the specific requirements of your application. Consider factors such as temperature range, chemical exposure, mechanical stresses, weathering conditions, and any regulatory or industry standards that need to be met.
  • Physical Properties
    Evaluate properties like tensile strength, elongation, compression set resistance, tear resistance, and hardness. Choose a material with properties that align with the functional needs of your product.
  • Chemical Compatibility
    Consider the types of chemicals or fluids the rubber will come into contact with. Some rubber compounds are more resistant to oils, solvents, acids, and other chemicals than others.
  • Temperature Resistance
    Determine the temperature range the product will operate in. Select a material that can withstand the anticipated temperature extremes without significant degradation.
  • UV and Weather Resistance
    For outdoor or exposed applications, choose a material with good resistance to UV radiation, ozone, and weathering to prevent premature degradation. 
  • Electrical Properties
    If electrical insulation or conductivity is important, consider materials with suitable dielectric properties.
  • Wear and Abrasion Resistance
    Depending on the application, choose a material with the appropriate wear resistance to ensure a longer service life.
  • Cost Considerations
    Balance the desired material properties with the project budget. Some specialized rubber compounds can be more expensive, so it’s important to find a cost-effective solution that meets your requirements.
  • Processing and Molding Requirements
    Different rubber compounds have varying processing characteristics. Consider the molding method (compression, injection, etc.) and the ease of processing the chosen material.
  • Durability and Longevity
    Assess the expected service life of the product. Choosing a material with good aging and durability characteristics can help extend the product’s useful lifespan.
  • Availability and Supply Chain
    Ensure that the selected material is readily available from reliable suppliers to avoid potential production delays.
  • Testing and Prototyping
    Conduct testing and prototyping to validate the material’s suitability for your application before proceeding with large-scale production.
  • Special Requirements
    Some applications may have unique requirements, such as flame resistance, low smoke generation, low toxicity, or specific color requirements. Consider these factors if applicable.

Rubber Molding Process

Rubber molding is a manufacturing process used to create a wide range of custom rubber products with specific shapes and properties. It involves the shaping of raw rubber material into the desired form using various molding techniques. There are several types of rubber molding processes, each suited for different applications and product requirements. Here are some common rubber molding processes.

Rubber Injection Molding

Rubber injection molding involves injecting molten rubber into a closed mold under high pressure. The mold is cooled, and the rubber solidifies to take on the mold’s shape. Rubber injection molding is highly efficient and is often used for producing intricate and precise rubber parts.

Precise control over material distribution and curing.
High production rates and efficiency.
Suitable for complex geometries.
Minimal post-processing required.

Initial tooling costs can be high.
Limited to relatively small to medium-sized parts.
Material waste during setup and shutdown.


Overmolding involves molding rubber over a substrate, usually a plastic or metal component. This process is often used to create soft-touch grips or handles on tools and consumer products.

Enhanced Grip: Overmolding provides a comfortable and ergonomic grip, improving user experience.
Vibration Dampening: The rubber layer can absorb vibrations, reducing discomfort and fatigue.
Aesthetic Appeal: Overmolding offers design flexibility, enabling unique color combinations and textures.
Protection: The rubber layer shields the substrate from impact, moisture, and wear.
Sound Dampening: Overmolding can reduce noise generated by metal or plastic components.
Seamless Integration: The rubber bonds tightly with the substrate, creating a unified product.
Customization: Overmolding allows for branding, logos, and decorative patterns.

Complex Process: Overmolding requires precise control of material, temperature, and mold design.
Tooling Costs: Developing molds for overmolding can be expensive upfront.
Material Compatibility: The substrate and overmolding material must be compatible to ensure proper adhesion.
Limited Substrates: Not all substrates can withstand the molding process or adhere well to rubber.
Cycle Time: Overmolding can extend production time due to the multi-step process.
Quality Control: Ensuring consistent adhesion and appearance can be challenging.
Design Constraints: Designing for overmolding requires considering material flow and adhesion.
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Blow Molding

This process is used to create hollow rubber products, such as bottles, hoses, and inflatable items. Rubber is first molded into a preform, which is then placed in a mold cavity. Air pressure is used to expand the preform and shape it to the mold.

Suitable for hollow or tubular rubber products.
Can achieve uniform wall thickness.
Good for producing items like hoses and bellows.

Limited to certain geometries.
Tooling costs can be high.
Material waste during setup and shutdown.

Transfer Molding

Similar to rubber injection molding, transfer molding uses a plunger to force the rubber through channels into the mold cavities. It allows for better control over material flow and is suitable for molding products with inserts, like metal parts or fabric.

Better control over material flow compared to compression molding.
Suitable for intricate designs and complex shapes.
Can use a variety of rubber materials.

Longer cycle times than injection molding.
Tooling costs are higher than compression molding.
Post-processing and trimming may be necessary.

Compression Molding

In this process, a pre-measured amount of rubber is placed into a heated mold cavity. The mold is then closed, and pressure is applied to force the rubber to take the shape of the mold. The heat and pressure cure the rubber, resulting in the final product. Compression molding is suitable for producing a variety of simple to complex shapes.

Lower tooling costs compared to injection molding.
Suitable for both small and large parts.
Can use a wide range of rubber compounds.

Slower cycle times compared to injection molding.
Material distribution may be less uniform.
More manual labor may be required.

Extrusion Molding

While technically not a rubber molding process, extrusion is used to create continuous lengths of rubber with a specific cross-sectional shape. A rubber compound is forced through a die, resulting in a continuous profile that can be cut into specific lengths.

Continuous process for creating consistent profiles.
Suitable for producing rubber sheets, strips, and tubing.
Lower tooling costs compared to some other methods.

Limited to certain cross-sectional shapes.
Not ideal for complex three-dimensional parts.
Surface finish may require additional processing.

Liquid Injection Molding (LIM)

LIM is a variation of rubber injection molding that uses liquid silicone rubber (LSR) instead of traditional solid rubber. LSR is injected into a closed mold, and heat is applied to cure the rubber. LIM is commonly used for producing medical and electronic components due to its biocompatibility and heat resistance.

Precision: LIM provides accurate part dimensions, great for small and intricate items.
Biocompatibility: LSR is safe for medical use due to its body-friendly properties.
Temperature Resistance: LSR can handle both high and low temperatures.
Chemical Resistance: It withstands various chemicals, enhancing part durability.
Less Flash: LIM usually has less excess material, reducing post-processing needs.
Color Options: LSR can be colored or made transparent for versatile designs.
Reduced Waste: LIM generates less waste during setup and shutdown.

Costly Material: LSR is more expensive than traditional rubber.
Tooling Expense: Initial mold creation can be costly.
Limited Material Choice: LSR’s properties may not suit all needs.
Slower Process: Curing LSR takes time, leading to longer production cycles.
Size Limitations: LIM is better for smaller to medium-sized parts.
Complex Molds: Complicated molds can increase costs.
Surface Finish Challenges: Certain textures might need extra work.

Rotational Molding (Rotocasting)

In this process, a hollow mold is filled with liquid rubber, which is then rotated to evenly coat the inside of the mold. The rubber is then cured, and the part is removed from the mold.

Suitable for large, hollow parts.
Can produce parts with consistent wall thickness.
Minimal material waste.

Limited to hollow or semi-hollow shapes.
Surface finish may require additional work.
Slower cycle times compared to other methods.

Factors Influencing Rubber Molding

The rubber molding process is influenced by a variety of factors across different categories. Here are the factors that influence rubber molding.

Design Considerations

  • Mold Design and Construction:
    The design of the mold affects material flow, cooling, and part ejection. A well-designed mold ensures consistent quality and reduces defects.
  • Parting Line Considerations:
    Proper placement of the parting line prevents flash and ensures uniformity in the final product.
  • Gate and Runner Design:
    The location and design of gates and runners impact material flow and distribution within the mold cavity.

Process Parameters

  • Mold Temperature and Pressure:
    Controlling mold temperature and pressure affects curing, material flow, and part properties. Different rubber compounds require specific conditions. 
  • Curing Time and Temperature:
    Proper curing ensures the rubber reaches the desired properties. Factors like compound type, part thickness, and mold temperature influence curing. 
  • Injection or Compression Force:
    In injection molding, the injection force determines material flow. In compression molding, the force affects the part’s density and curing.

Quality Control and Testing

  • Inspection Methods for Rubber Molded Parts:
    Visual inspection, dimensional checks, and non-destructive testing ensure parts meet specifications and have no defects. 
  • Testing for Mechanical Properties and Durability:
    Tensile strength, hardness, elongation, and other mechanical tests validate the part’s performance under stress. 
  • Quality Assurance and Control Measures:
    Implementing protocols, such as process monitoring, statistical process control, and corrective actions, ensures consistent quality over time.

Which Type of Rubber Molding is Right for Your Projects Application

To choose the right type of rubber molding for your project, consider the following factors:

  • Part Complexity: Does your project involve simple or complex part geometries?
  • Production Volume: Are you producing a few prototypes, small batches, or high volumes?
  • Material Properties: Do you require specific material properties such as heat resistance, chemical resistance, or flexibility?
  • Cost Considerations: What is your budget for tooling, production, and post-processing?
  • Part Size: Consider whether the process can accommodate the size of your parts.
  • Lead Time: Some processes may have longer lead times than others.

Selecting the appropriate rubber molding method for your project’s application hinges on several critical considerations.

For intricate parts demanding precise material distribution and high production rates, Injection Molding might be the answer, though initial tooling costs could be substantial. You should consider if you need precise control over material distribution, and you’re willing to invest in higher initial tooling costs for long production runs.

Compression Molding is cost-effective and suitable for straightforward designs, particularly in moderate production volumes. You should consider if you need to manufacture custom larger parts with simpler geometries in moderate production volumes, your part design is relatively straightforward, and you’re looking for a cost-effective option without high initial tooling costs.

Transfer Molding offers better material flow control and suits complex shapes. You should consider if you need to create parts with intricate details, complex shapes, and varying material properties, and you need better control over material flow compared to compression molding and are open to managing slightly longer cycle times.

Liquid Injection Molding (LIM) is a must for projects requiring biocompatibility and heat resistance, such as medical devices and electronics. You should consider if your project demands high precision, biocompatibility, and excellent heat resistance.

Blow Molding excels in crafting hollow items with minimal material waste. Extrusion Molding is ideal for uniform profiles like strips and tubing. You should consider if you need hollow or tubular rubber products, such as hoses, bellows, and certain containers, and your design involves hollow shapes and requires a method that minimizes material waste.

Rotational Molding is fitting for larger, hollow parts. You should consider if you need large, hollow parts that require uniform wall thickness, and your project involves creating larger, hollow items and you can accommodate slightly longer cycle times.

Overmolding plays a pivotal role in projects requiring enhanced grip, vibration dampening, and aesthetic appeal, often seen in consumer goods and electronics. You should consider if your projects need to add a rubber layer onto a substrate (plastic, metal, etc.).

The choice should factor in design complexity, desired material properties, production scale, and budget. Consulting with Sungplastic in rubber molding can provide tailored guidance aligned with project specifics.

Sungplastic: Best-Served Custom Rubber Parts Manufacturer

At Sungplastic, we provide rubber injection molding service, compression molding service, overmolding service, transfer molding service, blow molding service, extrusion molding service, etc. and a wide range of rubber materials to choose.

We provide rubber molding services not only for mass production, but also for low-volume production.

We offer a prototyping service and pilot molds so to check functionality on rubber parts before building the definitive mold.

We also provide custom and design services so to make you able to deliver rubber products with peculiar shapes and extremely high aesthetic qualities.

Last, but not least, if you need us to start the production of rubber parts for your industry projects, please note that we also offer a service of rubber molding service from start to finish, from the pre-production of batches to the delivery of your finished products.

Are you searching for custom rubber products molding services? We have what you need!

About Sungplastic

About Sungplastic

Sungplastic is a plastic product manufacturer with rich experience in injection molding. According to the different product development requirements, we flexibly adjust the manufacturing process to achieve high quality, high efficiency and more economical.

We offer a variety of manufacturing services: Rapid Prototyping, Tool Making, Injection Molding, Product Design and Development, CNC Machining and Metal Stamping. You can choose from a variety of plastics, silicone rubber, or metal for your product. Regardless of mass production or small batch customization, Sungplastic has always been committed to providing assured, efficient and more economical one-stop processing services for your projects.

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