Transfer Molding Made in the USA

Jefferson Rubber is a USA manufacturer of transfer molding.

Transfer molding is a simplified method of injection molding providing many of the benefits of both
injection and compression molding. It facilitates the creation of small, detailed parts as well as
providing high levels of control. Cycle times are typically longer than for injection molding, but the
costing can still be very competitive as it has a shorter cure time due to the material being heated
before reaching the mold.

Transfer molding is best suited to low to medium volume production of small to medium sized parts.
It is a flexible solution offering the ability to produce intricate-shaped products and allows for the
addition of colored and translucent compounds. It was developed to allow for the creation of
molded products that require narrow holes or metal inserts. Because the mold is closed prior to the
material entering, the amount of shift is limited.

The Process

Closed rubber molding offers ease of use, similar to compression molding as well as some of the
technical advantages of injection molding. Like compression molding, the material is weighed out
into a pre-form in advance, but in this case, the pre-form is placed into a transfer pot instead of
directly into the cavity of the mold.

The material is then heated, and when the ram is closed the heated material is “transferred” into the
cavities of the mold through a runner and gate system similar to that of an injection process. The
part is then held under pressure and temperature until it is fully cured, after which the part is
removed from the mold and separated from the pad.

Using Transfer Molding

Advantages

Since the pot can feed many cavities simultaneously, transfer molding is more labor efficient than
compression molding, which reduces both cycle time and costs. Additionally, transfer systems are
typically not as complicated as injection systems, which also keeps tooling costs comparatively low.

Since transfer molding is a closed system it allows for more complex part geometries, is well suited
to applications that require bonding to metal, and allows for better material and quality control
when compared to compression molding ensuring that all parts are uniform.

It is quick to set up the molds, and there is less flash than compression molding because the cavity
plates are closed. In the case of multi-cavity tools, the cost of labor is lower than compression
molding as only one pre-form is needed.

Disadvantages

Transfer molding has a higher degree of material waste than injection molding because the excess
material that forms the pad is cured and needs to be discarded at the end of the cycle and there is
some material degradation that is generated.

Limitations in terms of materials include the inability to process high durometer materials, the
requirement of a pre-form (pre-measured amounts of material), and the transfer molding is not
well-suited for the use of filled materials.

Labor costs are higher than with injection molding, and the press, tooling and additional equipment
mean that the initial investment cost is higher than for compression molding.

Wear and tear means that tool maintenance costs are generally high than for compression molding,
and while cavity wear is less than that of injection molding, gates and runners are subject to erosion.

Applications

Rubber transfer molding can be used to produce a variety of products that are molded with ceramic
or metallic inserts which are placed in the cavity of the mold and when the rubber is heated it bonds
with the insert surface. The process is also used widely to encapsulate other items such as plugs,
connectors, pins, coils, studs, and integrated circuits.

In the natural gas industry transfer molding is used to create metal-to-rubber face seals for gas
valves. Electrical applications include products such as spark plug wires where wires are inserted
into the mold cavity, and connector seals are molded around the wire.
In the hydraulic industry, transfer molding is routinely used for lip or U-cup designs as the process
allows for sharper cut-offs. A better-defined lip edge ensures sharp lip seals and nearly flash-free
parts.

If you are looking for a transfer molding manufacturer in the United States, call us today.

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