Some caps are threaded and screw on to the outside of a pipe or tube to cover the end. Other caps are more like a plug that fits snugly into the end of the tube to protect the inside. Plastic end caps are typically manufactured using one of the following processes: plastic dip molding, plastic injection molding, or plastic extrusion.
The plastic dip molding process uses a heated mandrel which is dipped into a pool of liquefied plastic. As the heated mandrel enters the liquid plastic, some of the plastic adheres to the surface of the mandrel. The mandrel is then removed and heated again to allow the plastic to fuse.
The plastic is allowed to cool, and it is removed from the mandrel, leaving the final product. Different material properties can be achieved by altering the mandrel temperature, dip time, and dip speed. With plastic injection molding, a plastic material is heated until it has become a liquid and then injected into a mold. Once the material cools, it can be removed from the mold, and any excess plastic is usually trimmed off before the process is finished.
In the plastic extrusion process, the material is heated and stretched over an object that holds it in place and presses it into the correct shape. Less heat is required when this method is used, and it can be much faster than plastic injection molding if the process is properly optimized.
Other features of plastic end caps can be modified, including their color. During the manufacturing process, different dyes can be added to the plastic to alter its color and to match the products they will be used in. Plumbers often use large plastic end caps to seal off pipe lines or to create an access point for future maintenance. Some caps are created with a beveled edge to create a smoother end on the tube or pipe and make protruding parts less dangerous.