Custom Plastic Molding

Injection Molding is the most advanced typical method of molding rubber products. Injection molding produces the most consistent results by automating all aspects of how the custom rubber gets into the mold. In injection molding, the rubber is worked and warmed and then squirted into the mold at controlled speeds, pressures and temperatures. Advantages of Injection Molding are: Provides the maximum product consistency, Allows the most control of flash, Because the rubber is warmed before going into the mold, fastest cycle times, Disadvantages of Injection Molding.

Composites with polypropylene (PP) and jute fiber were prepared by injection molding technique. One of the important investigations of the research was the effect of fiber attrition, which occurred during the injection molding, on the mechanical performance of jute/PP composites. Contribution of a fiber to strengthening the composite performance is considerably high, when the fiber is sufficiently longer than the critical length. On the other hand, the higher the adhesion between fiber and matrix polymer, the shorter is the critical fiber length. The ideal situation occurs when the fibers in the composite are longer than the critical fiber length and when the adhesion between the fibers and the matrix polymer is high. Generally, hydrophilic jute fibers do not adhere well to PP, which is hydrophobic.

Injection molding caused a high fiber attrition resulting in an average fiber length of 390 and 350 µ m for formulations with and without coupling agent, respectively. The effect of jute fibers on the tensile and bending strengths was poor when there was no coupling agent. The addition of MAPP as coupling agent improved the composite performance by enhancing the adhesion between jute fibers and PP. The improved adhesion did partially offset the fiber attrition and the associated strength loss that resulted from injection molding. Fiber orientation occurred mainly in the melt-flow direction.

Approximately 30% of all plastic products are produced using an injection molding process. Of this 30%, a large amount of these products are produced by using custom injection molding technology. Six steps are involved in the injection molding process, after the prototype has been made and approved. The first step to the injection molding process is the clamping of the mold. This clamping unit is one of three standard parts of the injection machine. They are the mold, the clamping unit and the injection unit. The clamp is what actually holds the mold while the melted plastic is being injected, the mold is held under pressure while the injected plastic is cooling. Next is the actual injection of the melted plastic. The plastic usually begins this process as pellets that are put into a large hopper. The pellets are then fed to a cylinder; here they are heated until they become molten plastic that is easily forced into the mold. The plastic stays in the mold, where it is being clamped under pressure until it cools. The next couple of steps consist of the dwelling phase, which is basically making sure that all of the cavities of the mold are filled with the melted plastic. After the dwelling phase, the cooling process begins and continues until the plastic becomes solid inside the form. Finally, the mold is opened and the newly formed plastic part is ejected from its mold. The part is cleaned of any extra plastic from the mold.

Reaction Injection Molding (RIM) produces parts with intricate detail that are dimensionally stable, chemically resistant, physically tough, and wear resistant. This process is an excellent choice for larger plastic parts produced in short run or low volume production quantities. Considerable design freedom is possible, including thick and thin wall sections that are not good for injection molding, due to the uniform shrink characteristics. Foamed polyurethanes are natural thermal and acoustic insulators. Excellent flowability allows for the encapsulation of a variety of inserts.