Prepn. of sinter mouldings from a mixt. of a sinterable powder and an oxymethylene binding agent - involving removal of binding agent by treatment with a gaseous acid which is solid at room temp.

摘要

Prepn. of sinter mouldings comprises: (a) forming a mixt. of (i) a sinterable ceramic or metallic powder and (ii) polyoxymethylene or a copolymer with predominantly oxymethylene units, as binding agent, to a green body; (b) removal of binding agent by novel treatment with a gaseous acid (which is solid at room temp., and which sublimes, or melts and vaporises, at higher temps.); and (c) sintering the mixt. ADVANTAGE - Use of an acid which is solid at room temp. reduces problems relating to corrosion and disposal. In an example, Iron powder (grain size 3.5 microns; 2000g) was kneaded with a polyoxymethylene copolymer of 198g of trioxan and 4g of butanediolformal (with an av. mol. wt. of 150,000) and 44g of polyethylene (with an av. mol. wt. of 800). The mixt. was worked into rods (5x7x65 mm3). The rods were treated, at 135degC and normal pressure, with anhydrous oxalic acid (150g) and nitrogen (500 l/hr), as carrier gas, for 6hrs. in a 50l oven. The resulting rods showed no surface oxidn. After sintering at 1280degC. the prods. showed a sintering density Ds of 7.64g/cm3.