    Plastic injection moulding, granular plastic
is fed by gravity from a hopper into a heated barrel. As the granules are
slowly moved forward by a screw-type plunger, the plastic is forced into a
heated chamber, where it is melted. As the plunger advances, the melted plastic
is forced through a nozzle that rests against the mould, allowing it to enter
the mould cavity through a gate and runner system. The mould remains cold so
the plastic solidifies almost as soon as the mould is filled.
Rubber Transfer Moulding is an extension of compression molding optimized for higher volume production runs. Unlike compression molding, transfer molding uses a closed mold. This allows tighter tolerances and more intricate parts to be produced in a higher quality manner. Plastic Injection Moulding Rubber Transfer Moulding A thermosetting plastic, also known as a thermoset, is polymer material that irreversibly cures. The cure may be done through heat (generally above 200 °C (392 °F)), through a chemical reaction (two-part epoxy, for example), or irradiation such as electron beam processing. Thermoset materials are usually liquid or malleable prior to curing and designed to be moulded into their final form, or used as adhesives. Others are solids like that of the molding compound used in semiconductors and integrated circuits (IC's). According to the IUPAC (International Union of Pure and Applied Chemistry) recommendation: A thermosetting polymer is a pre-polymer in a soft solid or viscous state that changes irreversibly into an infusible, insoluble polymer network by curing. Curing can be induced by the action of heat or suitable radiation, or both. A cured thermosetting polymer is called a thermoset.
Thermoplastic
A thermoplastic, also known as thermosoftening plastic, is a polymer that turns to a liquid when heated and freezes to a very glassy state when cooled sufficiently. Thermoplastic polymers differ from thermosetting polymers in that they can be re-melted and remoulded. Many thermoplastic materials are addition polymers; e.g., vinyl chain-growth polymers such as polyethylene and polypropylene.
Injection Moulding
Injection moulding is a manufacturing process for producing parts from both thermoplastic and thermosetting plastic materials. Material is fed into a heated barrel, mixed, and forced into a mould cavity where it cools and hardens to the configuration of the mould cavity. Injection moulding is widely used for manufacturing a variety of parts, from the smallest component to entire body panels of cars.
Process Characteristics
Applications Injection moulding is used to create many things such as wire spools, packaging, bottle caps, automotive dashboards, pocket combs, and most other plastic products available today. Injection moulding is the most common method of part manufacturing. It is ideal for producing high volumes of the same object. Some advantages of injection moulding are high production rates, repeatable high tolerances, the ability to use a wide range of materials, low labour cost & minimal scrap loss. There is little need to finish parts after moulding. Some disadvantages of this process are expensive equipment investment, potentially high running costs, and the need to design mouldable parts.
Transfer molding is an extension of compression molding optimized for higher volume production runs. Unlike compression molding, transfer molding uses a closed mold. This allows tighter tolerances and more intricate parts to be produced in a higher quality manner. Transfer molding combines the dimensional stability and excellent surface finish possible with compression molding with shorter cycle times but you also get the low cost and high-automation capabilities of injection molding. This combination makes transfer molding a natural choice for high quality high volume rubber products. A rubber transfer molding press is ideal for product consistency allowing you to repeat the same specialized molded form every time. Transfer molding presses combine the best values of a compression molding process with the advantages of injection molding. The transfer molding process is where a measured amount of
uncured rubber compound is inserted into a portion of the mold called a “pot”
and then preheated. A “plunger” that is
tightly fit into the pot is then used to transfer the material through channels
known as a “sprue” into the mold cavity.
The mold remains closed as the material is transferred into the part
cavity. Once the part cavity is filled
the material remains for a set amount of time while the heated mold causes the
curing reaction in the material. When
the cure cycle is complete the mold is then opened allowing the removal of the
product(s).
Advantages of Transfer Molding
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