July 14, 2022

What kind of injected plastic can support high temperature?

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It’s a small plastic injected piece that will be submitted to short period of time (2 seconds) of high temperature (95-105ºC approx.) in every cycle; this high temperature is produced by a filament where electric current passes through (like a house light bulb but hotter) for no more than 2 seconds in the process cycle. A complete process cycle last for about 45 seconds where the piece has time to cool off again. This plastic piece has to work for about 45-50 complete process cycles.

PP or Nylon will work well (PE is very hard to flame retard and has a much lower softening point). I would however suggest that you look at a flame retarded nylon 6 or 66 that is specifically designed for this type of exposure. You want to look at the Glow Wire Flammability Index (IEC 60695-2-12) of the grade. You want to make sure that the materials rating (maximum temperature) is higher (maybe 50-100°C higher than your conditions, temperature, exposure time, part thickness, I say this because it is very difficult to estimate the radiated heat and resultant temperature). These grades are made by Sabic-IP (under the Starflam tradename), Lati, RTP, BASF and others.

But the shrinkage difference between Nylon and other standard or engineering materials is usually significant. Nylon is normally in the 0.016 to 0.020 in/in range versus a range of around 0.005 to 0.014 in/in for PP. So, if your mold was designed for conventional PP thermoset materials the use of nylon in the mold could be problematic. In that the shrinkage rate for typical nylon resins is probably going to create a tooling problem for you. There are a few specialized nylons available, with lower than normal shrinkage, but they’re very expensive, which may be an issue. There are also some acetals available that would be more easily matched to your mold design, if it was designed around LDPE (frankly, LDPE would be the last resin I would expect anyone to consider for an application), but like nylon, acetal brings wear issues to bear, both for your screw/barrel and your tool.

I have used ULTEM (SABIC innovative plastics) PEI (polyetherimide) in high thermal service components such as hard drive parking ramps, insert molded side looking LED optics, motion sensor windows, and missile fuse optics in the past with good success. It also has high lubricity and it is easily used in molds designed for both commercial and engineering grade materials with shrinkage of 0.005 to 0.007in/in.. It comes in a variety of application grades with a 94VO rating.

By selecting such a material (instead of one that is not flame retarded), you will have a significant margin of safety in the event the exposure is longer (due to malfunction or something) resulting in ignition. If I were doing it, I would just for the risk minimization (it would be worth the same premium in material cost).

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