How to engineer with Performance Plastics and what to watch out for:
If you start engineering with Performance Plastics, you might compare it to another product you used before. While Performance Plastics offer you a wider range of properties and improve your parts in many ways, there are also some characteristics which will affect your design if not considered from the beginning.
There are many different materials available which could suit your design. Make sure you understand what chemicals the materials will be touched by, in order tohave a long lasting part and not be surprised by failures.
Most plastics absorb moisture to some extent. This once again is important for your tolerance and application. The more moisture the material absorbs the more it expands. The way the water absorption rate is documented and reported differs from supplier to supplier.
The important values you are looking for are in general the saturation data, which tells you how much water the material absorbs at a maximum, and/or the 24 hour absorption rate.
Plastic materials develop internal stress during the production process. This stress level can be reduced through annealing at an appropriate temperature and for an appropriate time. Time and temperature differ from one material to another.
Annealing is important when you plan to machine parts. Machining causes more stress as well as “movement” in the material. “In-Between-Cycle” Annealing is recommended if parts are heavily machined or very complex.
Besides the internal stress there is external stress (chemicals, electricity, mechanical, and thermal) which has an affect on the material. Mechanical stress can deform materials permanently. The so called “Yield Point” is the point, at which material won’t return to its original shape and size. The time needed to reach this point is called “creep” or “cold flow” which becomes shorter as temperature increases.
Materials change properties and maybe compliances once they are filled with othercomponents. Make sure that you refer to the exact requirements for your finished part. For example glass filler increase the stiffness, heat transfer and wear properties. Some fillers like glass, carbon or even color may effect a requested food compliance.
Many factors are reported at maximum levels to make materials look better. To arrive at a safe working value you should generally divide data by 4.