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Engineering Plastic-POM
POM (Polyoxymethylene resin) is defined as a linear polymer without side chains, characterized by high density and high crystallinity. Depending on the chemical structure of its molecular chain, POM can be categorized into homopolymer POM and copolymer POM. The key differences between these two types are: homopolymer POM has higher density, crystallinity, and melting point but exhibits poorer thermal stability and a narrower processing temperature range (approximately 10°C), with slightly lower acid and alkali resistance; whereas copolymer POM has lower density, crystallinity, melting point, and strength, but offers better thermal stability, less susceptibility to decomposition, a wider processing temperature range (approximately 50°C), and improved acid and alkali resistance. POM is an engineering plastic with excellent comprehensive properties, featuring good physical, mechanical, and chemical performance, especially outstanding wear resistance. It is commonly referred to as "acetal" or "delrin," and ranks as the third most widely used general-purpose plastic. Suitable for making wear-reducing and wear-resistant parts, transmission components, as well as parts for chemical and instrumentation applications.
General Properties:
POM is a smooth, glossy, hard, and dense material, typically light yellow or white, with thin sections appearing semi-transparent. It burns easily, continuing to burn after removal from the flame, with a flame that is yellow at the top and blue at the bottom, accompanied by molten droplets and a strong formaldehyde odor and fishy smell. POM powder is generally opaque, easy to color, with a specific gravity of 1.41-1.43 g/cm³, a molding shrinkage rate of 1.2-3.0%, and a molding temperature of 170-200°C. Drying conditions require 80-90°C for 2 hours. While POM does not have high long-term heat resistance, it can withstand short-term temperatures up to 160°C, with homopolymer POM having a short-term heat resistance about 10°C higher than copolymer POM, but long-term heat resistance being approximately 10°C higher for copolymer POM compared to homopolymer POM. POM can be used over a long-term temperature range of -40°C to 100°C. POM decomposes easily at 240°C, releasing irritating and corrosive gases during decomposition. Therefore, corrosion-resistant materials are recommended for mold steel.
Mechanical Properties:
POM has high strength and stiffness, good elasticity, and excellent wear-reducing and wear-resistant properties. Its mechanical performance is superior, with a specific strength reaching up to 50.5 MPa and a specific stiffness up to 2650 MPa, closely resembling metals. The mechanical properties of POM change little with temperature, with copolymer POM showing slightly more variation than homopolymer POM. POM has high impact strength, though it is not as good as ABS and PC under conventional impact conditions. Notably, POM is sensitive to notches, which can reduce impact strength by up to 90%. POM's fatigue strength is particularly outstanding, reaching 35 MPa after 10 cycles of alternating loads, significantly higher than PA and PC at 28 MPa. POM's creep behavior is similar to PA, with a creep rate of only 2.3% at 20°C, 21 MPa, and 3000 hours, with minimal influence from temperature. POM has a low friction coefficient and excellent wear resistance (POM > PA66 > PA6 > ABS > HPVC > PS > PC), with a high limit PV value and good self-lubricating properties. However, POM products can produce a screeching noise under high load conditions when rubbed against each other.
