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Rubber transfer molding requires creating a raw mix or rubber compound that is cut and weighed, or made into “pre-forms”. Where transfer molding differs from compression molding is that the rubber is not put into the cavity of the mold and then compressed, rather, it is compressed and injected into the mold.

The Transfer Molding Process

Our transfer molding process involves these key steps:

Preparing the Mold and Material

Before the transfer molding process begins, it’s important to prepare the mold and rubber material. Transfer molds vary in shape and size and typically contain a high number of cavities, depending on the needs of the application. Once the mold is prepared, raw rubber materials are cut and weighed or made into pre-forms.

Loading the Rubber Material

Transfer molds contain a transfer pot and a ram. Once the raw materials are prepared, they are placed in the transfer pot located above the cavity area.

Applying Heat and Pressure

As the transfer mold closes, the ram compresses or pushes the compounded rubber materials through a sprue system into the cavity below. Utilizing heat and pressure, the rubber compound vulcanizes or cures, taking on the shape of the mold.

Hardening and Cooling

Once the rubber part cures, it is allowed to harden and cool inside the mold.

Ejecting the Finished Product

After the part has completely cooled, it is ejected from the mold. Any excess cured rubber, or flash, is trimmed and removed from the finished product.

Benefits of Transfer Molding in Rubber Manufacturing

Rubber transfer molding is an accurate and effective alternative to other molding techniques. Some of its benefits include:

Precision and Complexity

The process allows for much tighter tolerances, enabling it to produce more intricate or complex parts that may be difficult to achieve with compression molding. This level of precision ensures that all specific design requirements can be met while ensuring optimal quality.

Enhanced Product Quality and Consistency

The rubber transfer molding process is more consistent than compression molding. Because the mold is closed before the rubber is injected, parts are more dimensionally consistent across a production run. This level of consistency minimizes part variations and defects, resulting in enhanced performance and reliability.

Versatility and Flexibility

Rubber transfer molding offers versatility when it comes to material selection and product design. For example, the process allows for sharper edges and is also suitable for thin-walled parts as well as overmolding plastic or metal inserts. Because of its flexibility, rubber transfer molding can accommodate a diverse range of application requirements.

Time and Cost Savings

Transfer molding offers faster cycle times compared to compression molding, as you only have to cut one pre-form of rubber rather than cutting one pre-form of rubber per mold. Additionally, it can produce parts with minimal or no flash, reducing the need for time-consuming deflashing processes. This helps to streamline the manufacturing process, leading to reduced costs and greater production efficiency.

Rubber Transfer Molding by Stern Rubber

Rubber transfer molding offers numerous advantages that make it a popular choice for producing a wide range of products. At Stern Rubber, we’re a custom manufacturer of rubber molded products with over five decades of experience. Our rubber transfer molding expertise ensures we complete your project on time and on budget without compromising on quality.

For more information about our rubber transfer molding capabilities, or to get started on your next rubber molding project, contact us today.

Last week, we wrote about the 3 main types of molding that we do at Stern Rubber Company: compression, transfer and injection.  Last week we discussed compression, and this week, we will cover transfer molding.
Transfer molding is similar to compression molding, as they are run the same presses.  These presses are run at high hydraulic pressure, and have electrically heated platens that are run in the 300 to 400 degrees Fahrenheit range.  The difference is all in the tooling, and not in the press.  Similar to compression, it is good for low to medium volume parts, and can be used for high volume parts, if the part is small.  Transfer and compression molding are both good for rubber to metal bonding.
Here are a few links to learn more about the presses that we use for compression and transfer molding, from some of the suppliers where we purchase presses.
https://www.wabashmpi.com/products/transfer-presses

Presses & Parts


Like compression, these types of molds are made from steel or aluminum.  The shape of the part is cut into the mold.  The main difference between compression tooling and transfer tooling, is that in transfer, the rubber is fed, or “transferred” through small feed holes from a “pot” into each cavity.
In transfer molding, you can place one large piece of rubber material into the pot, instead of having to load rubber in each of many cavities.  A simple part that is molded compression can be made on a 2 plate mold.  Half of the part cavity is cut into each half of the mold.  With transfer, you still have the 2 cavity plates, but in the top plate, you have to add the feel holes, and on top of the top plate, we add the pot, and aluminum plunger, or lid that forces the rubber through the feed holes and into the cavities.
The tool is held closed for 5 to 15 minutes depending on the thickness of the part.  When the cure time is complete, the tool is opened, the flash pad is removed, and the part is removed.
The advantages are very similar to compression molding as they both include lower cost tooling, and are both good for small production runs, as the set up time is normally very low, as the tool normally just has to be slid into the press and heated, and it is ready to run.  There is also no wasted material for set up, as you load the rubber into the tool, and do not have to use rubber to clean out the injection unit, like we do with an injection tool.  As in compression molding, transfer molding is also a good way to produce large parts that take a significant amount of material, or a long cure time to manufacture.  The one advantage that transfer does have over compression, is that it is much faster to load the material, as discussed above.  This also reduces the material prep time.  Transfer also usually allows for less flash than compression, and therefore we can usually allow tighter tolerances than compression.
Some of the disadvantages include slower process times compared to injection, and greater waste of material, even when compared to compression.  With transfer, we have the waste of the material that stays in the pot and feeds.  The tolerances that can be held are still not as tight as injection molded parts.
If you have want to learn more about this process, or think you have a project that will be a good fit for compression molding, please contact us at sales@sternrubber.com.