Delrin 570 Plate, 20% Glass Filled

Acetal homopolymer with 20 percent glass fiber - the stiff, dimensionally stable plate in the acetal family. The glass roughly halves thermal expansion and raises stiffness sharply, so this is the grade for a part that has to hold a tolerance across a temperature swing rather than one that has to slide.

Published figures: tensile strength 7,700 to 8,700 psi, tensile modulus 675,000 psi, Rockwell M81, melting point 347F, long-term service to 185F with intermittent use to 300F, water absorption 0.15 percent at 24 hours - lower than the unfilled grade. Specific gravity is 1.56, about 10 percent heavier than unfilled at 1.42, which is a real difference on a freight quote. The natural color is a white-cream rather than the unfilled natural.

Read this before you specify it for a bearing: DO NOT. Glass fiber is abrasive and will wear the mating surface, which is the opposite of what a bearing plate is for. The PTFE-filled grades are the wear materials here. Glass is also harder on your tooling - expect to change inserts more often than on unfilled acetal.

Where it goes: structural brackets and housings, parts that locate something precisely over a temperature range, pump and valve bodies, and anywhere the unfilled grade flexes more than you can allow.

No food-contact claim is made on this grade, and that is not caution for its own sake. The FDA acetal sections clear the resin and a short list of adjuvants; the filler in this grade is not among them. Published compliance charts list the filled acetal grades as not FDA compliant. If you need a food-contact acetal, ask us about the unfilled or a purpose-built food grade and we will tell you what the certificate actually covers.

The warning worth more than any number on this page: CHLORINE ATTACKS ACETAL AT 3 TO 5 PPM. That is ordinary municipal tap water and ordinary sanitizing concentration. Acetal in a chlorinated circuit, a pool system or a sanitized wash-down line will craze and fail, and almost nobody prints this. Strong acids and strong bases attack it too, and the homopolymer's window is the narrower one. If chlorine is anywhere in the application, ask us before you machine it.

Machining notes. It is among the easiest engineering plastics to machine well and takes a genuinely fine finish - sharp tools, positive rake, generous chip clearance, coolant optional on light cuts. Thermal expansion is high for a plastic, so a part machined warm measures differently cold; let heavy sections normalize before the finishing cut. Homopolymer is the harder and more brittle of the two acetals, so inside corners want a radius.

Safety, and this is specific rather than boilerplate. Acetal evolves FORMALDEHYDE above 446F and also on contact with strong acids or strong bases. OSHA's permissible exposure limit is 0.75 ppm over eight hours with a 2 ppm short-term cap, and it is a sensitizer, so repeat exposure matters. Keep tools from overheating the cut, use local exhaust, and never let acetal swarf mix with PVC, because halogenated polymers can trigger sudden formaldehyde release from it. Ask us for the manufacturer's Safety Data Sheet and work to it rather than to this paragraph.

How this is sold: by the square foot, cut to the size you need. The mills supply plate in full sheets and we cut from them, so give us the dimensions and we will quote the cut piece rather than making you buy a whole sheet.