When a building needs to hold up enormous loads, it is reinforced with steel. Known as rebar, this material is extremely strong and durable.
When injection molding PEEK, there are several unique considerations that must be made. This plastic requires high processing temperatures and cooling requirements that are not always easy to meet.
Temperature Control
The injection molding process for PEEK is unique and requires proper temperature control. This is especially important when the process involves using a filled grade, as the fillers can significantly change the mechanical properties of the final part.
PEEK has a high processing temperature and must stay above 200oC in the mold to avoid defects such as discoloration. The cooling rate is also important for the quality of the finished product. A fast cooling rate can cause areas of amorphous PEEK to form, resulting in poor product quality.
The ideal cooling rate for PEEK is slow enough to prevent damage to the resin and maintain crystallinity. This is why it’s critical to use a good temperature controller and ensure that the injection mold is well-insulated.
Injection Pressure
Peek is a high-performance thermoplastic that offers exceptional strength and ductility for a wide variety of applications. It also has good fatigue resistance and can withstand large impacts. For these reasons, companies across a range of industries turn to Peek for plastic parts.
When injection molding with peek, certain extra precautions must be taken. These include: good temperature control, big gates, and clean dry raw materials. The process requires special equipment as well, so it is a good idea to find a company that specializes in this type of molding.
The raw material feeds through a heated barrel with a reciprocating screw. This helps to reduce the heating time, and the screw’s heavy flutes help mix the polymer before delivering it into the mould. However, it is important to avoid letting the screw heat up too much, as this could cause the product to lose its crystalline properties and become amorphous. This discoloration can be seen as a brown section in the molded part, where some sections are crystalline and others are amorphous.
Shrinkage
PEEK is an engineering thermoplastic that has outstanding mechanical properties and is resistant to a wide range of chemicals. It is also capable of handling a high degree of thermal degradation.
The ability to control the shrinkage rate of injection-molded parts is key to achieving quality parts, especially when working with complex, high-performance plastics like PEEK. Shrinkage is influenced by the material’s composition and processing conditions, the part geometry and design (including wall thickness, gate location and mold constraints) and the packing characteristics of the molding process.
In addition, the molecular and fiber orientations within a molded part affect linear shrinkage rates. This is known as anisotropic shrinkage and it results in regions of the part that shrink differently from each other, causing warpage. Predicting shrinkage can help stave off costly and time-consuming tool adjustments that would otherwise be required to correct for out-of-tolerance parts. Using simulation tools can help engineers test the effects of different processing and part design changes on shrinkage to determine which one will produce the most consistent part.
Fillers
Polymers have largely put metal out of business since the first Tupperware container hit the market, but to maximize their functionality engineers often add various minerals, carbon and fiber fillers to the original base material. Glass fibers, for example, increase tensile strength without adding weight. Carbon and graphite fibers reduce thermal expansion and friction. PTFE reduces chemical resistance and silicon dioxide increases strength.
Many types of filler are available for use with PEEK, including the workhorse calcium carbonate. Mined from marble and limestone, it makes plastic parts opaque but doesn’t interfere with the colorants in the resin. Engineers can also add talc, which helps the resin form thicker wall sections without increasing sink or warpage.
Conductive carbon black is another common choice. Some fillers slough off invisible dust during the injection process, however, which can destroy electronic circuitry. Engineers look for nonsloughing fillers when creating parts with electronic functions. They can also opt for surface-treated kaolins, which offer improved dispersibility and mechanical properties.peek molding
