POM (Polyacetal or Polyoxymethylene)
Applications
Acetals have a low coefficient of friction and good dimensional stability. This makes it ideal for use in gears and bearings. Due to its high temperature resistance, it is used in plumbing (valve and pump housings), and lawn equipment.
Injection Molding processing conditions
Drying |
Not usually required but the material should be stored in a dry atmosphere. |
Melt Temperature |
180 - 230 C (356 - 446 F) for homopolymer; 190 - 210 C (374 - 410 F) for copolymer |
Mold Temperature |
50 - 105 C (122 - 221 F); Higher mold temperatures are preferred for precision molding which reduce post-molding shrinkage |
Material Injection Pressure |
70 - 120 MPa |
Injection Speed |
Medium - High |
Runners and Gates
Any type of gate may be used. When using tunnel gates, the short type is preferred. Insulated, hot tip runners are preferred for homopolymers; both internally and externally heated hot runners may be used in the case of copolymers.
Chemical and Physical Properties
Acetals are tough, resilient materials and exhibit good creep resistance, dimensional stability, and impact resistance even at low temperatures. Acetal grades are either homopolymers or copolymers. Homopolymers have better tensile strength, fatigue resistance and hardness but are difficult to process. Copolymers have better thermal stability, chemical resistance and processibility. Both homopolymers and copolymers are crystalline and have low moisture absorption.
Copolymers may be used continuously at air temperatures up to 100 C (212 F); homopolymers have slightly higher temperature resistance. Many grades of acetal materials are available, tailored to different applications.
High crystallinity levels of acetals lead to relatively high shrinkage levels of 0.02 - 0.035 mm/mm. Differential shrinkage is observed with reinforced grades.
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