Peek injection is a technique used in the injection molding of plastics, specifically poly ether ketone (PEEK). It can be difficult to process as it requires high temperature and large gates, but it offers superior strength, good ductility and chemical resistance. It is often used in applications such as medical devices and aerospace components.
The tensile strength of injection-molded PEEK is higher than that of polymethyl methacrylates (PMMA), and it is comparable to that of some metals. This high mechanical strength is due to its unique chemical structure, which consists of a repeating unit that binds three benzene rings together and connects them with ketone and ether groups.
However, the superior physical properties of PEEK do not necessarily translate to good performance in all conditions. It is important to know how to optimize the injection process for this material. Injection temperatures, injection pressures and injection speeds all affect the final product. This is especially important for cored parts, which must be injected into a cavity with the correct pressure. The right injection pressure will also help to ensure proper surface finish.
If the injection temperature is too low, the molten PEEK will cool and solidify before it can be molded. This can cause abrasion of the surface and lead to premature failure of the injection molded part. In addition, the lower injection temperature can make it difficult to release the molded part from the mold and cause warpage.
Other factors that can cause problems with injection molded PEEK include the presence of moisture and gas in the melt, uneven cooling, and the use of abrasive fillers. Moisture in the melt causes surface abrasion, which degrades the mechanical properties of the material. This can be corrected by adding a lubricant such as PTFE to the melt before injection into the mold.
When working with PEEK, it is also important to be sure that the injection equipment is completely clean before running the material. This includes the screw and barrel as well as the nozzle and runners. This is because other materials that are processed in the same machine may degrade during the injection of PEEK. This can leave residues that will show up as dark specks in the molded plastic. This can also be prevented by dedicating the injection machine to PEEK only.
PEEK can be formulated with fillers such as glass, carbon and graphite fibers to improve its abrasion resistance, heat resistance and surface hardness. These additives can also reduce weight and friction. It is important to understand the effects of these additives on the physical properties of PEEK, so that it can be designed with them in mind.
Peek can be molded in conventional injection machines with some extra precautions. These extras include keeping the injection temperature low, ensuring that the gate is large enough and making sure that the machine has clean dry raw materials. It is best to dedicate the injection machine to PEEK only, so that other materials will not be degraded in the process.