Hardness polyacetals

A comparison of the abrasive wear by Bohm (1990) found that the hard and more brittle plastics, such as polyacetals, polyamide-imide, and polycarbonates, are less abrasion resistant than softer and tougher materials such as the polyethylenes and polyurethanes. Table 7.2 details some comparative... 

Rigid sub-assembly components, e.g. filter canister bodies, and mountings for valves, eyepieces and speech modules, were originally made of metal but tend more now to be made of polymers. In the SI0, polyacetal is used as it is not only chemically hard but also has mechanical properties that allow snap-fitting, which reduces production costs and allows easy replacement of parts. 

Polyacetals are engineering plastics because of their high hardness, rigidity and tensile strength, good abrasion and wear resistance, and favorable low frictional properties, all of which are advantages over other materials. Since polyacetals absorb virtually no water, they have excellent weight retention characteristics. Polyacetals only dissolve in hexafluoroacetone hydrate at... 

In a certain sense, the abrasion tests can also be counted among the hardness tests. Abrasion is affected partly by the hardness and partly by the frictional properties of the sample. Among thermoplastics, the best abrasion resistance is shown by polyureas, followed by the polyamides and polyacetals. 

It is seen in Table 2.9, that flexural moduli improve considerably upon incorporation of 25 to 50% of glass fibre in the formulation. Epoxy resins are an exception, carbon fibre also improves the flexural modulus of PC from 2.8 to 13 GPa and with polyacetal the addition of carbon fibre improved the flexural modulus from 2.6 to 17.2 MPa. For PP the addition of 20% calcium carbonate produced hardly any change in flexural modulus. 

The incorporation of carbon fibre produces hardly any change in Izod impact strength of polyacetal (0.04 kj/m), compared to that of the base polymer (0.06 kj/m). Various other additives hardly affect Izod impact strength as shown in Table 2.13. 

Linear, hard, tough synthetic resins produced by the polymerisation of formaldehyde (for acetal homopolymers) or of formaldehyde with trioxane (for acetal copolymers). Acetal resins are also called as polyacetals and are used as substitutes for metals. 

Polyacetal, a strong, hard plastic with relatively good temperature resistance, is being increasingly used for various hot- or cold-water plumbing components such as fittings, valves, and faucets. 

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