Polyacetals molded parts

Traditionally, material design requirements that suit such demanding end-use applications have been limited within the domain of engineering plastics based on polyamide 6 or 66, polyester alloys, and polyacetal type resins. However, as described in Chapter 1, glass fiber-reinforced polypropylene (GFRP) composites continue to gain a market share in automotive molded parts. 

The rate of depolymerizing polyacetal to formaldehyde is the subject of much research, because the rate of depolymerizing is a critical factor in MIM costs, and there is not that much proven information on it. Removal of binder is determined by various factors, namely, binder removal temperature, about 120°C (248°F) catalyst linear or random degradation of polyacetal resin fineness of powder mold part shape and size and catalytic debinding furnace. The catalytic furnace developed for debinding... 

Fig. 5.71 Semicrystalline thermoplastics, such as a polyacetal, shown in polarized light (A) do not appear spherulitic after the addition of calcium carbonate (B). llie surface of such a filled, molded part can exWbit a matte finish due to poor wetting of the particles with the pol)nner. SEM observation of the molded surface (C) shows pock marks which are particles in cavities not filled with pol)nner. EDS mapping (D) shows the particles contain calcium.

Articles made from polyacetals vary from door handles to gears and bushings, carburetor parts to aerosol containers. The major use of polyacetals is for molded grades. 

Polyacetals and other engineering plastics cost about half that of cast metals, and are therefore used as replacements for cast metal-intense applications. They have been approved by the Food and Drug Administration for contact with foods. Some of the uses of molded polyacetals are as valves, faucets, bearings, appliance parts, springs, automotive window brackets, hose clamps, hinges, video cassettes, tea kettles, chains, flush toilet float arms, gears, shower heads, pipe fittings, pasta machines, desktop staplers, and air gun parts. 

In rotational molding, release agent is necessary to aid part removal. Release agents are either polymeric or oligomeric. Polysiloxanes are used widely as mold release agents for polyolefins, polystyrene, polyacetal, nylon, and ABS.copolymers. 

Although the principal application of blow molding has been for bottle fabrication, it is being used increasingly for other parts such as automotive fuel tanks, seat backs, flexible bellows, and toys. High density polyethylene, polypropylene, poly(vinyl chloride) (PVC), and poly(ethylene terephthalate) (PET) are the principal resins molded in this way. For more special applications, however, other thermoplastics such as nylon, polyacetal, ABS, polycarbonate and ultra-high-molecular-weight polyethylene also are used. ... 

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