Rubber Injection Molding: Process, Type, Material, and Application

Rubber injection molding is a manufacturing process widely used in producing rubber parts and products with intricate designs and tight tolerances. This method is highly efficient and can produce large volumes of parts quickly and consistently. This article delves into the detailed process, different types of rubber injection molding, and the various applications of this versatile technology.

Introduction to Rubber Injection Molding

Rubber molding is a manufacturing process used to process rubber materials into parts or products with a specific shape and size. The process involves placing an unvulcanized rubber mixture into a mold, applying heat and pressure to make it flow and fill the mold cavity, and finally undergoing a vulcanization reaction to form a strong and durable finished product. Rubber molding technology is widely used in various industrial fields, including automotive, medical, consumer goods and industrial equipment. The following is a detailed introduction to the rubber forming process.

Steps for Creating Rubber Parts

Creating rubber components involves a series of precise steps to ensure the final product meets design specifications and performance requirements.

Rubber Mold Design

Mold design is crucial in rubber injection molding. Key considerations include:

• Component Design: Clearly define the shape, size, and tolerance requirements of the part. Design considerations include rubber flow characteristics and shrinkage rates.
• Material Selection: Choose appropriate rubber materials based on the part’s intended use and performance requirements, such as natural rubber, silicone, or synthetic rubber.
• Mold Material: Mold materials must have high strength and heat resistance, typically using steel or aluminum. Different materials affect mold lifespan and molding quality.

Production of Rubber Molds

The manufacturing process of high-quality rubber molds typically includes the following steps:

Mold Processing:

• Casting Molds: Use heat-resistant materials (e.g., cast iron or aluminum) to create molds through casting processes suitable for large sizes and simple shapes.
• CNC Machining: Utilize CNC machine tools to precisely process mold cavities and core parts, suitable for high precision and complex geometries.
• EDM Machining: Employ electrical discharge machining (EDM) to process complex shapes and fine structures, particularly effective for hard mold materials like hardened steel and titanium alloys.

Assembly and Testing:

After mold processing is complete, assemble and conduct initial testing to ensure proper alignment of mold parts. Subsequently, perform trial production runs to verify the mold’s ability to produce parts that meet design requirements.

Vulcanization

Vulcanization enhances the elasticity and strength of rubber by heating the rubber with a vulcanizing agent (e.g., sulfur). The process involves:

• Preheating Rubber: Heat the rubber compound before injection to improve flowability, ensuring complete filling of mold cavities during injection.
• Injection Molding: Inject preheated rubber into the heated mold cavity under high pressure, fully filling the mold and forming the desired shape.
• Vulcanization: After injection, maintain the mold under high pressure and temperature to allow the rubber to undergo vulcanization, enhancing its physical properties.
• Cooling and Demolding: Once vulcanization is complete, cool the mold, remove the finished parts from the mold, and trim excess flash.

Why do Rubber Injection Molding?

• Enables rapid production of large quantities of parts, enhancing production efficiency for mass production requirements.
• Capable of manufacturing parts with intricate geometries and details, meeting diverse design requirements.
• Ensures high precision and consistency of molds, maintaining quality and dimensional accuracy of each part.
• Allows the use of various types of rubber materials, choosing the optimal material based on specific application requirements.
• Despite higher initial mold costs, unit costs for large-scale production are lower, making it suitable for bulk manufacturing.

Types of Rubber Injection Molding

Rubber injection molding can be categorized into several types based on the specific techniques and materials used:

1.Injection Molding

Rubber injection molding is divided into the following types:

Organic rubber injection

Organic rubber injection is an advanced rubber molding technology, which uses an injection machine to heat and plasticize the pre-mixed rubber material, and then inject the molten rubber material into the mold cavity through high pressure. In the mold, the rubber material goes through a vulcanization reaction for a period of time, and finally solidifies into the desired rubber product.

Advantages:

• Simplified process: Compared with traditional rubber molding process, organic rubber injection greatly simplifies the production steps. The injection machine has a high degree of automation, which reduces the tedious links of manual operation and improves the production efficiency.
• Reduce energy consumption: Organic rubber injection machines are usually equipped with precise heating and cooling systems that can precisely control the temperature, making the heating and cooling process faster and more efficient. This helps to improve energy efficiency and reduce production costs.
• Increased production efficiency: Since the injection machine can quickly heat and cool the rubber material, the entire production cycle is greatly shortened. In addition, the injection machine can also achieve continuous production, further improving production efficiency.
• Good uniformity and high stability: by controlling the temperature and pressure of the injection machine, the rubber material can be evenly distributed in the mold cavity, so as to obtain rubber products with good uniformity and high stability. This is of great significance for improving product quality and reducing scrap rate.

Cons:

• High production costs: Organic rubber injection requires special injection molding machines and molds, and the manufacturing cost of these equipment is higher. In addition, due to the high requirements for raw materials, equipment, molds, etc., in the production process, production costs are also increased.
• High processing technical requirements: organic rubber injection requires high skills of the operator. The operator needs to master the operation skills of the injection machine and understand the characteristics and vulcanization process of rubber to ensure the smooth progress of the production process. In addition, it is also necessary to carry out regular maintenance and maintenance of the mold to ensure its service life and product quality.

Applications:

Organic rubber injection technology is widely used in the production of high-end rubber products, such as automobiles, electronics, power equipment, communication equipment, medical instruments and other fields. Specifically, it can be used to produce a variety of seals, shock absorbers, protective parts and other rubber products, such as automotive seals, electronic components gaskets, electrical equipment insulation parts and so on. These products need to have excellent sealing, oil resistance, high temperature resistance and other properties to meet the needs of different fields of use.

Liquid Injection Molding (LIM)

Liquid silicone rubber (LSR) injection molding is a method of injection molding using the excellent fluidity and vulcanization characteristics of LSR. LSR is a low-viscosity liquid material that flows easily into complex areas of the mold before injection and then solidifies into the final product through a vulcanization reaction within the mold.

Advantages:

• Low compression and permanent deformation of products: LSR has excellent elastic recovery ability, and the finished products can still maintain good shape and performance after long-term use.
• Strong resistance to extreme temperatures: LSR can maintain stable performance over a wide temperature range (-50°C to +200°C or more) and is suitable for a variety of extreme environments.
• Excellent chemical resistance: It is resistant to a variety of chemical substances, such as acids, alkalis, fats, etc., so that it can maintain stable performance in a variety of application scenarios.

Cons:

• Limited grades of silicone available: Although LSR comes in a variety of types, there are still limited grades of silicone available compared to other rubber materials, which may limit its use in some specific applications.
• High production time and cost: Due to the special properties of LSR, such as the need for specific processing temperatures and vulcanization times, this can lead to a long production cycle. At the same time, the raw material price and processing equipment cost of LSR are also relatively high, which increases the production cost.

Applications:

LSR injection molding technology is widely used in many areas requiring high precision, high quality rubber products, including but not limited to:

• Consumer electronics: such as mobile phone casings, keys, seals, etc., LSR’s excellent performance and appearance make it an ideal choice for consumer electronics products.
• Automotive field: automotive seals, shock absorbers, pipe joints, etc. LSR’s high temperature resistance, chemical corrosion resistance and other characteristics make it a key material in the automotive industry.
• Medical field: Medical devices, surgical tools, baby pacifiers, etc., LSR’s physiological innocuity and good biocompatibility make it the preferred material for the medical industry.

Thermoplastic rubber injection

Thermoplastic rubber injection is a method of injection molding using the thermoplastic properties of thermoplastic rubber (TPE). TPE is a rubber elastic plastic material whose unique thermoplasticity allows it to be rapidly formed through heating and cooling processes.

Advantages:

• Fast forming speed: thermoplastic rubber can be quickly heated to a molten state and quickly injected into the mold cavity by an injection molding machine. After cooling, the product can be demoulded, greatly shortening the production cycle.
• Waste can be recycled: compared with traditional rubber materials, thermoplastic rubber has excellent recyclability. Waste and scraps in the production process can be reused through reprocessing, reducing production costs and meeting environmental requirements.
• Good elasticity and wear resistance: thermoplastic rubber products have good elasticity and wear resistance, and can meet various use needs. These characteristics make thermoplastic rubber products widely used in the field of cable sheath, seal and so on.

Cons:

• Some thermoplastic rubber has limited high temperature resistance: Although the heat resistance of thermoplastic rubber is relatively good, the high temperature resistance of some varieties is still limited. This limits its application in high temperature environments, such as around automotive engines.

Applications:

Thermoplastic rubber injection is often used in the production of rubber products such as cable sheaths and seals that need rapid prototyping and recycling. Thermoplastic rubber injection technology has been widely used in these fields because of its advantages such as fast molding speed, recyclable waste and good elasticity and wear resistance.

Custom rubber injection molding

Customized rubber injection molding is a method of customizing molds and injection molding processes to produce rubber products with specific shapes and properties according to the specific needs of customers.

Advantages:

• Can meet the individual needs of customers: Custom rubber injection molding allows customers to design and produce rubber products according to their specific needs. This means that the shape, size, color, hardness, elasticity and other properties of the product can be customized according to the needs of customers, so as to meet the individual needs of customers.
• Flexible production: Since custom rubber injection molding is carried out according to the specific needs of customers, it allows producers to quickly adjust production plans and product specifications according to market demands. This flexibility allows producers to respond more quickly to market changes and meet the diverse needs of their customers.

Cons:

• High cost of mold development: The first step in custom rubber injection molding is to design and manufacture molds that meet customer needs. Since the design and manufacture of molds requires a high degree of specialized knowledge and skills, the process requires a large investment of time and money. The higher the complexity and precision requirements of the mold, the higher the design and manufacturing costs.
• The production cycle may be long: from mold design and manufacturing to the production of rubber products, the entire process of customized rubber injection molding needs to go through multiple links. These steps need to be taken in turn, and each step needs a certain amount of time to complete. Therefore, compared with the production of standard rubber products, the production cycle of customized rubber injection molding may be longer.

Applications:

Custom rubber injection molding is widely used in the production of rubber products requiring special shapes, properties or functions. For example, in the automotive industry, custom rubber injection molding can be used to produce special seals, suspension system parts, etc. In the field of healthcare, it can be used to produce medical devices, gloves, bottle caps, etc. In the field of electronic devices, it can manufacture anti-shock, anti-slip, sealing and other components of electronic materials.

2. Transfer Molding

In transfer molding, the rubber compound is placed in a chamber and then transferred into the mold cavity using a plunger. This process is ideal for molding parts with inserts or overmolding applications. Transfer molding offers good control over material flow and minimizes the risk of air entrapment.

Advantages:

• Uniform curing: rubber transfer molding can achieve a uniform curing process, so that the density and hardness of the product to maintain consistency, improve product quality.
• Short production cycle: Compared with traditional die molding, rubber transfer molding has a shorter production cycle and improves production efficiency.
• High dimensional accuracy: Due to the design of the mold gate and runner, the dimensional accuracy of the product is guaranteed, and the flash modification is relatively easy, and the inserts and cores are not easy to deform.
• Suitable for the production of inlays: Rubber transfer molding is particularly suitable for the production of products with inlays, such as rubber products with metal inlays or plastic inlays.

Cons:

• High mold costs: Because rubber transfer molding requires the use of special molds, the manufacturing costs of molds are high, increasing the initial investment cost.
• Slightly higher single consumption of raw materials: In the process of rubber transfer molding, some materials will remain in the mold cavity, gate and runner, which usually cannot be recycled, resulting in a slightly higher single consumption of raw materials.

Applications:

Rubber transfer molding is widely used in the following fields:

• Automotive seals: automotive manufacturing requires a large number of seals, such as door seals, window seals, etc., these seals usually require good sealing performance and weather resistance, and rubber transfer molding can meet these requirements.
• Electronic component sealing: Electronic components need to be protected from dust, moisture and other external environment erosion during the working process, and rubber transfer molding can manufacture electronic component seals with excellent sealing performance.
• Rubber pipe: rubber transfer molding is also widely used in the production of rubber pipes, such as water pipes, oil pipelines, etc. These rubber pipes need to have good pressure resistance and corrosion resistance.

3. Compression Molding

Compression molding involves placing a pre-measured amount of rubber compound directly into the mold cavity. The mold is then closed, and pressure is applied to shape the material. This method is suitable for large and simple parts but can be less efficient for high-volume production compared to injection molding.

Advantages:

• Simple equipment: The equipment required for compression molding is relatively simple, the operation is also more convenient, suitable for small-scale production environment.
• Low cost: Due to the simple equipment and easy operation, the production cost of compression molding is relatively low, which is suitable for the production of rubber products with simple shape and low precision requirements.
• Suitable for small-scale production: Due to the small investment in compression molding equipment and simple operation, it is suitable for small-scale production, especially for start-ups or small factories, which is a more economical choice.

Cons:

• Low production efficiency: Compared with the more automated molding methods, the production efficiency of compression molding is relatively low, because the entire molding process requires manual operation and the vulcanization time is longer.
• The dimensional accuracy and surface quality of products are greatly affected by human factors: due to the need for manual operation in the compression molding process, such as feeding, closing, opening, etc., the dimensional accuracy and surface quality of products will be affected by human factors, resulting in unstable product quality.

Applications:

Rubber compression molding is often used to produce some simple shape, precision requirements are not high rubber products, such as rubber MATS, rubber plates, soles and so on. These products have a wide range of applications in daily life, such as as non-slip pads, cushion pads, sound insulation pads and so on. At the same time, in industrial production, rubber compression molding is also used to produce some simple seals, gaskets and so on.

Materials Used in Rubber Injection Molding

In the rubber injection molding process, the choice of materials is crucial to ensure the performance and quality of the final product. According to different application requirements, manufacturers can choose a variety of rubber materials. The following are several commonly used rubber materials and their characteristics and applications.

Materials Used in Rubber Injection Molding

Rubber injection molding involves the use of a variety of materials, each selected for its unique properties to meet specific application requirements. The choice of material impacts the final product’s performance, durability, and suitability for different environmental conditions.

Natural Rubber (NR)

Natural rubber is known for its high elasticity and strength, making it ideal for applications requiring significant flexibility and durability. Its excellent abrasion and tear resistance make it suitable for high-wear environments, such as automotive and bicycle tires, as well as various seals and gaskets. The material’s resilience ensures that it can withstand significant mechanical stress without losing its structural integrity.

Styrene-Butadiene Rubber (SBR)

Styrene-butadiene rubber is valued for its good abrasion resistance and cost-effectiveness. It is commonly used as a more affordable alternative to natural rubber, particularly in the production of automotive tires and footwear. SBR performs well in high-wear conditions, making it a popular choice for products that require durability but are also cost-sensitive.

Nitrile Rubber (NBR)

Nitrile rubber is highly resistant to oils and fuels, making it suitable for applications involving exposure to such substances. It also possesses good mechanical properties, including abrasion and tear resistance. NBR is widely used in the automotive and industrial sectors for manufacturing oil seals, O-rings, and fuel hoses. Its ability to maintain performance in oily environments makes it indispensable for these applications.

Fluoroelastomers (FKM)

Fluoroelastomers are used in environments that demand high temperature and chemical resistance. These materials can withstand extreme conditions, making them suitable for aerospace and automotive applications, particularly in seals and gaskets exposed to harsh chemicals and high temperatures. FKM’s durability under such conditions ensures long-lasting performance and reliability.

Hydrogenated Nitrile Butadiene Rubber (HNBR)

Hydrogenated nitrile butadiene rubber offers enhanced temperature and ozone resistance compared to standard NBR. It also provides high tensile strength and elongation, making it suitable for demanding applications such as automotive belts and seals, as well as oilfield components. HNBR’s robustness in harsh conditions makes it ideal for high-performance applications.

Chlorinated Polyethylene (CM)

Chlorinated polyethylene is chosen for its excellent weather and ozone resistance, as well as good chemical resistance. These properties make it suitable for use in industrial and automotive hoses and cable jackets. CM can withstand various environmental conditions without degrading, ensuring the longevity of the products made from it.

Chloroprene Rubber (CR)

Chloroprene rubber is known for its good weather and ozone resistance, making it ideal for outdoor applications. It also exhibits flame resistance, which is beneficial for applications that require fire retardancy. CR is widely used in seals, gaskets, and wetsuits for diving and surfing, where exposure to harsh weather conditions and the need for fire safety are paramount.

Butyl Rubber (IIR)

Butyl rubber is prized for its low gas permeability, making it excellent for air and gas containment. Its good chemical resistance and flexibility further enhance its suitability for a variety of sealing applications. IIR is commonly used in tire inner tubes and pharmaceutical closures due to its effective containment properties and durability.

Thermoplastic Vulcanizates (TPV)

Thermoplastic vulcanizates combine the properties of thermoplastics and elastomers, offering durability and flexibility. These materials are also recyclable, making them environmentally friendly and cost-effective. TPVs are used in automotive parts such as weather seals and interior components, providing both strength and flexibility.

Thermoplastic Elastomers (TPE)

Thermoplastic elastomers are versatile materials that combine the properties of rubber and plastic. They are easy to process and suitable for injection molding and extrusion. TPEs are used in a wide range of products, from soft-touch grips for tools and appliances to flexible components in medical devices.

Polyurethane (PU)

Polyurethane is known for its exceptional abrasion resistance and high tear strength, making it ideal for high-wear applications. It is widely used in industrial wheels, rollers, and various sealing applications where durability is crucial. PU’s ability to withstand mechanical stress ensures the longevity and reliability of products made from it.

Ethylene Propylene Diene Monomer (EPDM)

Ethylene propylene diene monomer is chosen for its excellent weather and ozone resistance, as well as good electrical insulation properties. These characteristics make EPDM suitable for automotive seals, roofing membranes, and other outdoor applications. Its resilience in various weather conditions ensures the durability of the products.

Silicone Rubber (SI)

Silicone rubber is valued for its high-temperature stability and biocompatibility. It can maintain its properties over a wide temperature range, making it suitable for medical devices and food industry applications where materials must be safe for contact with the body or food and withstand extreme temperatures.

Fluorosilicone Rubber (FVMQ)

Fluorosilicone rubber combines the properties of silicone and fluoroelastomers, offering excellent temperature and chemical resistance while maintaining flexibility. It is used in aerospace and automotive seals exposed to fuels and oils, as well as in industrial applications requiring high chemical resistance. FVMQ’s versatility makes it ideal for demanding environments.

Isobutylene Isoprene Rubber (IIR)

Isobutylene isoprene rubber, with its low gas permeability and good flexibility, is used in tire inner tubes, sports equipment bladders, and pharmaceutical stoppers. Its ability to maintain airtight seals makes it essential for applications requiring effective gas and air containment.

Considerations for Material Selection

When selecting materials for rubber injection molding, several factors must be considered. The specific performance requirements of the application, such as flexibility, strength, and temperature resistance, are crucial. Additionally, environmental conditions, including exposure to chemicals, oils, and weather, must be assessed to ensure the material can withstand these factors. The material’s suitability for the intended molding process and equipment is also essential, along with its cost-effectiveness and availability for large-scale production. The following is a comparison table, you can choose the right material according to the specific application needs.

Material	Characteristics	Non-Applicable Scenarios	Applicable Scenarios
Natural Rubber	High strength, good ductility, wear resistance, tear resistance	Poor oil and heat resistance	Tires, conveyor belts, seals
Nitrile Rubber (NBR)	Oil resistance, wear resistance, solvent resistance	Poor cold resistance	Automotive oil seals, fuel lines, seals
Fluorocarbon Rubber (FKM)	High temperature resistance, oil resistance, chemical resistance	High cost	High-temperature seals, chemical industry products
Hydrogenated Nitrile Rubber (HNBR)	Better oil, heat, and chemical resistance than NBR	High cost	High-performance automotive and industrial products
Chlorinated Polyethylene (CM)	Weather resistance, ozone resistance, flame retardancy	Relatively low mechanical strength	Electrical cable jackets, building materials
Neoprene (CR)	Oil resistance, weather resistance, flame retardancy	Average heat resistance	Automotive seals, electrical cable jackets
Butyl Rubber (IIR)	Excellent airtightness, water resistance	Slightly poor oil resistance	Tire inner tubes, medical bottle stoppers
Thermoplastic Vulcanizates (TPV)	Combines rubber elasticity and plastic processability, recyclable	Not suitable for specific high-temperature environments	Automotive seals, electrical cable jackets
Thermoplastic Elastomers (TPE)	Fast molding, recyclable waste, good elasticity and wear resistance	Not suitable for specific chemical environments	Electrical cable jackets, sealing strips
Polyurethane (PU)	Wear resistance, oil resistance, chemical resistance, good elasticity	Not suitable for high-temperature environments	Tires, seals, shoe soles
Ethylene Propylene Diene Monomer (EPDM)	Weather resistance, heat resistance, ozone resistance	Not suitable for specific chemical environments	Roofing materials, electrical cable jackets
Silicone (Silicone Rubber)	High temperature resistance, chemical resistance, good biocompatibility	Relatively poor wear resistance	Medical devices, baby products
Fluorosilicone	Excellent high-temperature and chemical resistance	High cost	Seals and pipes requiring extreme performance
Isobutylene-Isoprene (IIR/IP)	Good airtightness, water resistance, ozone resistance	Slightly poor oil resistance	Tire inner tubes, medical bottle stoppers

Rubber Products Manufactured By Rubber Injection Molding

Rubber injection molding is a versatile manufacturing process that produces a wide range of rubber components essential across various industries. These components are prized for their flexibility, durability, and resistance to different environmental conditions.

Rubber O-Rings

Rubber O-rings are small, circular seals used to prevent the leakage of fluids or gases between two or more parts. They are essential in applications such as automotive engines, hydraulic systems, and industrial machinery. The high elasticity of rubber allows O-rings to maintain a tight seal under various pressure conditions, ensuring the reliability and efficiency of the equipment.

Rubber Seals

Rubber seals are designed to prevent leaks and protect components from contaminants like dust and moisture. These seals are used in automotive engines, hydraulic systems, and pneumatic devices, where they ensure that fluids stay within designated areas. Rubber seals must withstand a wide range of temperatures and pressures, making their material composition critical for performance and longevity.

Rubber Gaskets

Rubber gaskets are used to fill the space between two or more mating surfaces, preventing fluid and gas leaks while under compression. These gaskets are commonly found in automotive engines, aerospace components, and industrial machinery. The compressibility of rubber allows gaskets to conform to irregular surfaces, creating a reliable seal that maintains system integrity.

Rubber Tubes

Rubber tubes are used for conveying fluids and gases in applications such as automotive cooling systems, medical devices, and industrial machinery. The flexibility and durability of rubber tubes allow them to bend and stretch without breaking, making them suitable for environments requiring high flexibility and movement. Additionally, rubber tubes resist chemicals and extreme temperatures, ensuring long-term performance.

Rubber Bearings

Rubber bearings, or elastomeric bearings, are cylindrical components designed to support structures and absorb vibrations. They play a crucial role in reducing the impact of movements and loads on structures such as bridges and buildings. Rubber bearings provide flexibility, allowing structures to move slightly without transferring excessive stress to other parts, which enhances structural integrity and longevity.

Rubber Bushings

Rubber bushings are cylindrical components designed to reduce vibration and noise in mechanical systems. They are widely used in automotive suspension systems, industrial machinery, and electrical equipment. By absorbing shock and minimizing movement between parts, rubber bushings help extend the lifespan of mechanical components and improve overall system performance.

Rubber Stoppers

Rubber stoppers are used in laboratory and medical applications to seal test tubes, bottles, and other containers. They provide a secure and airtight seal, preventing contamination and preserving the integrity of the contents. Industrial applications also use rubber stoppers to ensure airtight seals, which are critical for maintaining product quality and safety.

Rubber Diaphragms

Rubber diaphragms are flexible membranes that respond to pressure changes, controlling and regulating fluid and gas flow in pumps, valves, and sensors. Their elasticity allows them to flex under pressure, maintaining a seal while accommodating movement. This makes them ideal for precise control applications where responsiveness and accuracy are crucial.

Rubber Washers

Rubber washers are used to distribute the load of a threaded fastener and to prevent leaks in plumbing, automotive, and electrical applications. Their compressibility allows them to create a tight seal, reducing the likelihood of leaks and providing additional support to fastened joints. Rubber washers are crucial for ensuring reliable and leak-free connections in various systems.

Rubber Isolators

Rubber isolators are used to absorb and dampen vibrations in mechanical systems, reducing noise and protecting sensitive equipment. They are essential in automotive engines, industrial machinery, and electronic devices, where they help prevent damage caused by vibrations. By isolating vibrations, rubber isolators enhance the longevity and performance of the equipment.

Rubber Bumpers

Rubber bumpers absorb impact and protect surfaces from damage in automotive, industrial, and consumer applications. They are commonly used as bumper guards in vehicles, furniture protectors, and in industrial machinery. The ability of rubber bumpers to absorb shock helps prevent damage to both the bumper and the object it comes into contact with, making them essential for impact protection.

Rubber Suction Cups

Rubber suction cups create a vacuum seal on smooth surfaces, allowing for temporary attachment. They are used in industrial automation, material handling, and consumer products. The flexibility of rubber allows suction cups to conform to surfaces, creating a strong hold that can be easily released and reused. This makes them ideal for applications requiring temporary and adjustable attachment solutions.

Advantages and Disadvantages of Rubber Injection Molding

Rubber injection molding is a widely used manufacturing process that offers numerous benefits but also comes with certain drawbacks. Understanding these advantages and disadvantages can help manufacturers make informed decisions about when and how to use this process.

Advantages of Rubber Injection Molding

• High Production Efficiency: Rubber injection molding is ideal for high-volume production. The process can produce large quantities of parts in a relatively short amount of time, which is beneficial for meeting high demand and reducing per-unit injection molding costs.
• Precision and Consistency: The process allows for the production of highly precise and consistent parts. This is particularly important in industries where exact specifications and tight tolerances are crucial, such as automotive, aerospace, and medical device manufacturing.
• Complex Geometries: Rubber injection molding can create parts with complex shapes and intricate details that would be difficult or impossible to achieve with other molding methods. This capability expands the design possibilities for engineers and designers.
• Material Versatility: A wide range of rubber materials can be used in injection molding, including natural rubber, synthetic rubbers, and specialized elastomers. This versatility allows manufacturers to select the best material for their specific application, ensuring optimal performance and durability.
• Reduced Waste: Injection molding generates less waste compared to other molding processes, as the precise amount of material required is injected into the mold. This not only reduces material costs but also minimizes the environmental impact of production.
• Automation and Integration: The injection molding process can be highly automated, which reduces labor costs and improves efficiency. Automated systems can handle the entire process, from material feeding to part ejection, with minimal human intervention.

Disadvantages of Rubber Injection Molding

• High Initial Costs: The initial setup costs for rubber injection molding can be high due to the need for specialized machinery and custom molds. Designing and manufacturing the molds requires significant investment, which can be a barrier for small-scale production or startups.
• Long Lead Times for Molds: Creating custom molds can be time-consuming, leading to longer lead times before production can begin. This can be a disadvantage when rapid prototyping or fast market entry is required.
• Material Limitations: While many types of rubber can be used, not all rubber materials are suitable for injection molding. Some materials may not flow well or may degrade under the high temperatures and pressures used in the process, limiting material choices.
• Design Constraints: Despite its ability to produce complex parts, there are still some design constraints in rubber injection molding. For instance, achieving uniform wall thickness and avoiding undercuts can be challenging, requiring careful design considerations.
• Cycle Time: Although injection molding can be efficient, the cycle time for each part can be relatively long compared to other mass production methods, such as stamping or extrusion. This can impact overall production speed for extremely high-volume requirements.
• Post-Processing: Some rubber injection molded parts may require additional post-processing, such as trimming or secondary operations, to remove flash or achieve the desired surface finish. This adds to the overall production time and cost.

Process of Rubber Injection Molding

The rubber injection process involves a variety of molding methods.

Injection Molding Process

Injection molding is a high-precision manufacturing process commonly used for producing rubber parts. The process involves several key steps:

1. Feeding: In the initial stage of injection molding, the preheated rubber is added to the cylinder of the injection machine according to a certain amount (or a constant volume). The feeding should be quantified to maintain the continuity of operation and the consistency of product quality.
2. Softening and preheating of the compound: In the cylinder, the compound will be heated at high temperature, gradually softening and reaching a molten state suitable for injection. At the same time, the temperature is controlled to ensure the quality of the compound, which usually needs to be higher than the melting point of the plastic to ensure the full plasticization of the compound.
3. Injection pressure (injection) : When the adhesive reaches the set melting state, the injection machine starts to work. Under high pressure, the screw pushes the molten glue through the nozzle and quickly enters the mold cavity. Ensure that the compound can quickly and evenly fill the mold cavity, while avoiding the formation of injection molding defects such as bubbles.
4. Vulcanization and setting: heat and pressure in the mold to vulcanize and set the rubber in a certain time (such as 30-60 minutes). Vulcanization can make the rubber from the molten state to the solid state, and give the product the required physical and chemical properties.
5. Cooling curing: After curing, the product needs to be further cooled and cured in the mold. In this process, the cooling system in the mold will be passed into the cooling medium such as cooling water, oil or air to cool the mold, so that the products will gradually cool and solidify.
6. Take out the product: When the product is completely cooled and cured, the mold will be opened to take out the molded product. At the same time, the mold also needs to be cleaned and maintained to prepare for the next injection molding.

Transfer Molding Process

Transfer molding combines elements of both injection and compression molding and is suitable for producing complex parts with inserts. The process involves:

1. Preparation stage: The mixed, simple shape and limited number of semi-finished rubber strips or rubber blocks are ready. These semi-finished compounds need to have a greater fluidity before reaching the curing temperature, and a faster curing rate after reaching the curing temperature. Materials that can meet this requirement include phenolic aldehyde, melamine formaldehyde and epoxy resin.
2. Feeding stage: Put the prepared rubber strip or rubber block semi-finished product into the material cavity of the die casting mold. The capacity and shape of the chamber need to match the amount and shape of the compound to ensure that the compound can enter the mold cavity smoothly.
3. Extrusion and filling stage: Through the pressure of the die casting plug (plunger), the rubber material in the chamber is squeezed and pushed through the pouring system (including gate and runner) into the mold cavity. This process needs to ensure that the compound fills the entire mold cavity evenly and quickly to avoid bubbles or unfilled areas.
4. Vulcanization setting stage: In the mold, by heating and maintaining a certain pressure, the vulcanization reaction occurs under the action of heat and pressure, so that it changes from a viscous flow state to a solid state. Vulcanization time and temperature need to be determined according to the type of rubber and product requirements. During the vulcanization process, the heat preservation and pressure holding system of the mold needs to ensure that the rubber material can be uniformly and fully vulcanized.
5. Take out the product stage: after the rubber material is fully vulcanized in the mold and cooled to a certain temperature, open the mold and take out the product. Careful operation is required when taking out the product to avoid damage or deformation of the product.

Compression Molding Process

Compression molding is a simpler process used for producing large or relatively simple rubber parts. The steps involved are:

1. Preparation of rubber material: the mixed rubber material is weighed according to the product requirements and processed into a shape suitable for the mold cavity. And select the mold that matches the product, and install and debug to ensure that the mold can work normally.
2. Feeding stage: Put the processed rubber material into the prepared mold cavity. Pay attention to the placement and quantity of the adhesive to ensure that it is evenly distributed in the mold.
3. Compression stage: The mold is closed and ready for compression molding. The mold is fed into a plate vulcanizing machine, through which the mold is pressurized and heated. Depending on the type of rubber and the requirements of the product, the parameters of pressure and heating, for example, some rubber may require a higher temperature and pressure to achieve complete vulcanization, while some products may require a longer vulcanization time to ensure its stable performance.
4. Vulcanization and setting stage: maintain a certain time in the vulcanization machine, so that the rubber is fully vulcanized and set under the action of heat and pressure. The length of vulcanization time depends on the type of rubber, the thickness and complexity of the product and other factors.
5. Take out the product: After the rubber material is fully vulcanized in the mold and cooled to a certain temperature, open the mold and take out the product.
6. Post-treatment: the necessary post-treatment of the removed product, such as deburring, checking the quality, etc. These post-processing steps can further improve the quality and performance of the product.

Deburring

Deburring is a post-molding process that removes excess material, known as flash, from molded rubber parts. Flash occurs when rubber leaks between the mold halves during molding. Deburring techniques include:

1. Manual Trimming: Workers use knives or scissors to trim excess rubber from the part. This method is labor-intensive but precise.
2. Cryogenic Deflashing: Parts are cooled to very low temperatures using liquid nitrogen, making the flash brittle. The parts are then tumbled or blasted with media to break off the flash.
3. Mechanical Deburring: Tumbling parts in barrels or vibrating containers with abrasive media to remove flash. This method is efficient for large batches of small parts.
4. Laser Deflashing: Using a laser to precisely remove flash. This technique is highly accurate and suitable for complex geometries.

Common Defects in Rubber Injection Molding

Rubber injection molding is a sophisticated process that can encounter various defects. Understanding these defects and their causes can help in devising effective solutions to ensure high-quality production.

Flash

Flash, also known as burrs or excess material, typically occurs at the parting line of the mold, such as the split line between the moving and stationary halves, around inserts, or near ejector pins.

Causes:

• Insufficient clamping force of the machine.
• Uneven mold cavity distribution or lack of parallelism.
• Imbalanced force on mold components or sliding cores.
• Poor mold venting.
• Excessive flowability of the rubber material or overuse of lubricants.
• Incorrect processing parameters such as temperature, pressure, and speed.

Solutions:

• Use a machine with adequate clamping force.
• Adjust the mold structure to ensure balanced forces.
• Improve the mold venting system.
• Reduce the flowability of the rubber material and decrease the use of lubricants.
• Optimize processing parameters, such as temperature, pressure, and speed.

Short Shot (Underfill)

A short shot occurs when the mold cavity is not completely filled, resulting in incomplete parts.

Causes:

• Insufficient shot volume.
• Low barrel temperature.
• Low injection pressure or speed.
• Inadequate injection time.
• Low mold temperature.
• Poor fit between the nozzle and mold gate.

Solutions:

• Adjust the shot volume appropriately.
• Increase the barrel temperature.
• Increase injection pressure and speed.
• Extend the injection time.
• Increase the mold temperature or redesign the mold’s cooling channels.
• Ensure a proper fit between the nozzle and mold gate.

Contamination

Contamination refers to the presence of unwanted substances in or on the product.

Causes:

• Contaminants in the raw material.
• External pollutants or screw carbonization.
• Grease stains from molds and equipment.

Solutions:

• Source high-quality raw materials.
• Maintain a clean production environment.
• Regularly inspect and maintain molds and equipment.

Warping

Warping is the deformation or twisting of a part after it has cooled and solidified.

Causes:

• Differential shrinkage in different directions.
• Residual internal stress.

Solutions:

• Optimize mold design, including gate position and number, and enhance the cooling system.
• Adjust process parameters, such as lowering injection pressure and speed, and increasing mold temperature.
• Select suitable rubber materials with low shrinkage and internal stress.

Voids

Voids are internal bubbles or hollow spaces within a part.

Causes:

• Excessive moisture or volatile content in the raw material.
• Low injection pressure or high injection speed.
• Incorrect mold gate location or poor mold venting.

Solutions:

• Pre-dry the raw material and remove fines.
• Adjust injection pressure and speed.
• Modify mold design parameters, such as gate location and venting system.

Applications of Rubber Injection Molding

Rubber injection molding is used in a wide range of industries due to its versatility and ability to produce complex and high-quality parts. Some of the key applications include:

1. Automotive Industry

Rubber injection molding is extensively used in the automotive industry to produce parts such as seals, gaskets, O-rings, bushings, and vibration dampening components. These parts require high precision and durability to withstand harsh conditions and ensure vehicle performance and safety.

2. Medical and Healthcare

In the medical field, rubber injection molding is used to manufacture medical devices, seals, syringes, and tubing. The process ensures that the parts meet stringent hygiene and quality standards required for medical applications.

3. Consumer Goods

Many consumer products, such as kitchen utensils, toys, and electronic device components, are made using rubber injection molding. This process allows for the production of parts with complex shapes, vibrant colors, and various textures, enhancing the functionality and aesthetic appeal of consumer goods.

4. Industrial Applications

In industrial settings, rubber injection molding is used to produce parts for machinery, equipment, and tools. These parts often include gaskets, seals, and vibration isolation components that require high strength and resistance to wear and tear.

5. Aerospace and Defense

The aerospace and defense industries utilize rubber injection molding to create parts that can withstand extreme conditions and rigorous performance requirements. Components such as seals, grommets, and vibration dampening parts are essential for the reliability and safety of aerospace and defense equipment.

BOYI – Custom Rubber Injection Molding Services

At BOYI, we specialize in providing top-tier custom rubber injection molding services tailored to meet your specific needs. Our state-of-the-art facilities, coupled with a team of experienced professionals, ensure that we deliver high-quality rubber products with precision and efficiency.

Partner with BOYI for your custom rubber injection molding needs and experience the difference in quality, precision, and service. Contact us today to discuss your project requirements and discover how we can help bring your ideas to life.

FAQ

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Catalog: Injection Molding Guide