| 摘要 |
Asbestos-cement mixes are rendered readily extrudable or mouldable into shaped products by incorporating in the mix a small amount of a hydromodifier, e.g. 0,05 to 10%, preferably 0,1 to 5% by weight. Suitable hydromodifiers include methylcellulose, hydroxy propoxy methyl cellulose, carboxy methyl hydroxy ethyl cellulose, ethylene oxide polymer, hydroxy ethyl cellulose ether, partially hydrolysed sodium polyacrylamide, acrylamide/acrylic acid copolymer, casein, hide glue, acrylamide polymer, carboxy methyl starch ether, polyvinylalcohol, singly or in admixture, the suitability of a particular hydromodifier for any mix being determined by carrying out a preliminary test as described in the Specification. The mixes may include 10 to 85%, (preferably 20 to 70%) of a hydraulic cement, e.g. Portland, calcium aluminate, supersulphated slag, natural, pozzolana, or lime cement and up to 55% (preferably up to 40%) of an auxiliary cementing agent (which reacts with the cement) e.g. silica flour, fly ash, calcined clay, fine sand, blast furnace slag, from 1 to 60% (preferably 5 to 40%) of any grade or type of asbestos, e.g. amphobile, amosite, crocidolite, tremolite, authophyllite, 14 to 50% (preferably 18 to 35%) of water, and up to 25% (preferably up to 10%) of fillers, e.g., stoneflour, ground shale, perlite, kaolin, pigments. Dyes, setting accelerators e.g. lime, retarders, e.g. sugar solution, and wetting, fixing and plasticizing agents, and other fibres e.g. glass, nylon, may be incorporated in the mixes. In compounding the mixes all the constituents may be mixed at once or the solid constitutents may be dry mixed and water added; alternatively an aqueous solution of the hydromodifier (0,25 to 20% strength), may be added to a dry mix of the other constituents; the wet mix is then plastic-formed into the desired shape and the shaped article cured, e.g., by autoclaving for 12 to 20 hours under a steam pressure of 100 p.s.i.g. or by storing under highly humid conditions for 7 to 30 days. |
