One of the most widely used manufacturing methods for engineering rubber components is transfer moulding. Combining the precision of injection moulding with the material versatility of compression moulding, transfer moulding is commonly used to manufacture anti-vibration mounts, rubber-to-metal bonded components, seals, bushes and other complex rubber products.
When selecting rubber components for industrial equipment, design engineers and procurement professionals must balance performance, consistency, cost and manufacturability. While the finished component often receives the most attention, the manufacturing process itself plays a significant role in determining product quality and long-term reliability.
In this guide, we explain what transfer moulding is, how the process works, its advantages and limitations and why it remains a preferred manufacturing method for many industrial rubber components.
What Is Transfer Moulding?
Transfer moulding is a rubber manufacturing process in which pre-measured rubber material is placed into a transfer pot before being forced under pressure into a closed mould cavity.
Unlike compression moulding, where rubber is placed directly into the mould cavity, transfer moulding uses a transfer pot, sprue, runner system and gates to move the material into the tool. This allows more precise control over material flow and is particularly beneficial for components with intricate geometries or bonded inserts.
The process is commonly used for manufacturing:
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Anti-vibration mounts
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Rubber bushes
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Rubber-to-metal bonded components
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Gaskets and seals
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Electrical insulation components
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Precision engineering rubber parts
For many OEM applications, transfer moulding provides an excellent balance between cost, accuracy and production efficiency.
How Does Transfer Moulding Work?
Although transfer moulding is highly engineered, the process itself follows a relatively straightforward sequence. Typical process parameters include transfer pressures of 5-30 MPa, curing temperatures of 140-200°C and cycle times ranging from approximately 5-30 minutes, though these vary with compound selection and component geometry.
1. Tool Preparation
The mould tool is heated to the required curing temperature and prepared for production. Mould venting is checked to ensure trapped air can escape during filling, inadequate venting is a common cause of short shots, porosity and poor surface finish in transfer moulded components.
If the component contains metal inserts, these are positioned within the mould cavity before moulding begins.
For rubber-to-metal bonded products, surface preparation is critical. Inserts are often degreased, grit blasted or pretreated, and then coated with a two-coat bonding system, a primer coat followed by a cover coat to ensure a durable bond between the rubber and metal substrate.
2. Loading the Transfer Pot
A pre-measured quantity of uncured rubber compound, often referred to as the ‘charge’, is pre-formed into a specific shape, typically a disc or pellet, and is pre-heated. Pre-heating the charge reduces compound viscosity, lowers the transfer pressure required to fill the cavities and can significantly reduce cycle time.
The prepared charge is then placed into the transfer pot. The amount of material is carefully controlled to ensure consistent filling of each cavity and to minimise waste.
3. Material Transfer
Once the mould is closed, a plunger applies pressure to the rubber charge. The material is forced through the sprue, along runners and through gates into the mould cavities. The sprue is the primary channel connecting the transfer pot to the runner system and is a key design element affecting material flow balance.
As the mould is now closed, transfer moulding offers excellent dimensional consistency and allows rubber to flow into complex shapes that may be difficult to achieve using compression moulding. Properly designed venting of each cavity ensures complete filling and eliminates trapped air, which would otherwise compromise the integrity and structure of the component.
4. Vulcanisation
Once the mould cavities are filled, heat and pressure initiate the vulcanisation process.
Vulcanisation creates cross-links within the rubber's molecular structure, transforming the material from a pliable compound into a durable engineering component with mechanical properties. The cross-linking mechanism depends on the cure system used. Sulphur-based systems are common for general-purpose compounds such as natural rubberand nitrile, while peroxide cure systems are typically specified for materials requiring higher temperature resistance or improved compression set performance, such as silicone and EPDM.
Optimum cure time is determined through rheometry, most commonly using a Moving Die Rheometer (MDR). The resulting cure curve defines key parameters, including scorch time and the time to reach 90% of full cure, which directly inform production cycle times.
Depending on the material and component geometry, curing times may range from a few minutes to significantly longer for larger components.
5. Post-Cure Processing
Certain compounds may require a secondary post-cure processing cycle after demoulding. This is particularly common with peroxide-cured materials, silicone and fluoroelastomers. Post-cure cycles typically range from 1 to 24 hours at higher temperatures and should be factored into production planning and lead time estimates.
6. Demoulding and Finishing
After curing, the mould is opened and the finished components are removed. Any flash that forms during the cycle is removed through deflashing.
Common deflashing methods include cryogenic tumbling, mechanical tumbling and hand trimming, with the method selected according to component geometry and production volume.
The level of flash present is a useful indicator of tool condition and process control, excessive flash may signal worn tooling or incorrect clamping pressure.
For critical applications, additional testing may include:
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Hardness testing
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Dimensional inspection (accounting for mould shrinkage, see below)
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Bond strength verification
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Compression set testing
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Material verification
Dimensional Accuracy and Mould Shrinkage
A key consideration in transfer moulding is material shrinkage. Rubber compounds typically shrink as they cool from curing temperature to ambient conditions. Therefore tooling must be designed with appropriate shrinkage allowances to achieve the required finished dimensions.
Shrinkage rates vary by compound type, filler loading and cure system, and must be established for each specific formulation. For components with tight tolerances, accurate shrinkage data is essential during the tooling design stage.
Why Is Transfer Moulding Used for Engineering Rubber Components?
Transfer moulding offers several advantages that make it suitable for industrial applications.
Improved Dimensional Accuracy
Because the mould remains closed during filling, transfer moulding typically produces tighter dimensional tolerances than traditional compression moulding.
This is especially important for components that must integrate precisely with surrounding assemblies.
Excellent Rubber-to-Metal Bonding
Many anti-vibration mounts and engineering components rely on strong rubber-to-metal bonding.
Transfer moulding allows inserts to remain securely located during mould filling, helping achieve consistent bond quality across production batches. The controlled, lower-velocity flow of material through the gate system reduces the risk of insert displacement compared with injection moulding processes.
Suitable for Components With Complex Geometries
Components featuring intricate profiles, thin sections or multiple inserts can often be produced more effectively using transfer moulding than conventional compression moulding.
The controlled material flow improves cavity filling and reduces the risk of trapped air or incomplete moulding.
Transfer Moulding vs Compression Moulding
Although both processes are widely used within the rubber manufacturing industry, they each offer distinct advantages.
| Characteristic | Transfer Moulding | Compression Moulding |
| Typical Tolerance | Excellent | Good |
| Tooling Cost | Moderate | Lower |
| Geometry Complexity | High (thin walls, multiple inserts) | Moderate (simpler profiles) |
| Material Waste | Higher (sprue/runner waste) | Lower (flash only) |
| Insert Bonding | Excellent (inserts fixed before fill) | Good (risk of displacement) |
| Best Suited Volume | Medium | Low to medium |
The choice ultimately depends on the application, performance requirements and production volumes involved.
Transfer Moulding vs Injection Moulding
For many specialist engineering components, transfer moulding remains a highly effective manufacturing solution, particularly where production volumes do not justify the higher tooling investment associated with full injection moulding.
Applications of Transfer Moulded Components
Transfer moulding is used throughout a wide range of industries where precision and durability are essential.
Rail & Mass Transit
Transfer moulded rubber components are commonly used in suspension systems, vibration isolation assemblies and equipment mountings throughout rail infrastructure and rolling stock.
Power Generation
Generators and auxiliary equipment frequently utilise transfer moulded anti-vibration mounts to reduce vibration transmission and improve reliability.
Construction & Off-Highway Equipment
Heavy-duty machinery relies on durable rubber components capable of withstanding shock loading, harsh environments and prolonged operational cycles.
Industrial Manufacturing
Transfer moulded components are widely used in machinery, processing equipment and automation systems where vibration control and equipment protection are required.
How AV Industrial Products Can Help
At AV Industrial Products Ltd, we manufacture a wide range of rubber and rubber-to-metal bonded components for industrial applications. Our engineering expertise extends beyond product supply, supporting customers through material selection, product design and manufacturing consultation.
Whether developing a new anti-vibration mounting system or sourcing replacement rubber components, our team works closely with OEM design engineers and procurement professionals to ensure the most appropriate manufacturing process and material specification are selected.
Through a combination of engineering knowledge, manufacturing capability and quality assurance, we help deliver reliable rubber components that perform consistently in demanding industrial environments.
For more information on our rubber manufacturing capabilities or anti-vibration product range, get in touch with our team today.
