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The Injection Molding Process

Injection Molding

Mainly associated with the use of thermoplastics, injection molding has become one of the most cost-effective ways to create custom molded rubber products and, as such, has become a commonly used manufacturing process. It is particularly ideal for creating smaller parts.

Injection molding offers several advantages over other processes such as compression molding.

These include:

  • High production rates and shorter production cycles (results in lower per unit cost);
  • Allows for close tolerances in small intricate parts;
  • Requires little post-production work because parts have a finished look upon ejection;
  • Full automation is possible, which leads to reduced production costs.

Essentially, injection molding is a process wherein heated rubber is forced into a mold cavity under intense pressure.

Here is a step-by-step outline of the process:

1. After a product is designed, molds are made from metal – usually steel or aluminum – and machined to form the features of the desired part. Molds can consist of a single cavity or multiple cavities, depending on product requirements.

2. Following mold construction, a predetermined amount of uncured rubber elastomer is fed into a temperature-controlled injection barrel in the form of a constant, unbroken strip approximately 1.25″ X .375″ in size. The material is worked and further heated by a screw-type plunger located in the barrel.

3. Rubber builds up in the anterior of the screw forcing it backward. The screw plunges forward under extreme pressure, pushing the rubber through a system of feed runners, sprues and gates, which further heat the compound until it reaches the mold cavity.

4. The rubber cures in the heated mold and the screw prepares to refill the injection barrel for the next shot.

5. An injection press closes the heated mold and applies pressure keeping the mold shut during the injection and curing cycles.

6. The rubber conforms to the contour of the mold as it cools and hardens.

Mark Tool specializes in custom molded rubber products for use in farm equipment, the oil and gas industry, valves, electrical distribution, railroad, heavy truck, and a variety of other applications. Contact us to learn more or to receive a quote.

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