| 摘要 |
PURPOSE:To improve wear resistance, molten metal resistance and heat insulating characteristic by forming the innermost cylinder of our injection molding sleeve of dense type silicon nitride ceramics which are specified in a fracture toughness value and theoretical density ratio and forming the intermediate layer of porous silicon nitride ceramics specified in thermoelectrical conductivity. CONSTITUTION:The innermost cylinder 2 of the injection molding sleeve 1 for a molten metal is formed of the dense type silicon nitride ceramics which contains 1 to 5pts.wt. Ti or Ti compsn. in terms of Ti per 100pts. silicon nitride and has >=25kg/mm<3/2> fracture toughness value and >=95% theoretical density ratio. The intermediate cylinder 7 is formed of the porous silicon nitride ceramics which contains 3 to 40pts.vol. alphaSi3N4 fibers and beta-SiC fibers having 0.2 to 5mum wire diameter and 5 to 50mum length per 100 true pts.vol. and has <=5 Kcal/mh deg.C thermoelectrical conductivity. The outermost cylinder 7 is shrinkage- fitted to the intermediate cylinder 5 to produce the composite ceramics cylinder. The innermost cylinder 2 and the intermediate cylinder 5 are hardly shifted from each other and are hardly cracked in this way, by which the composite ceramics cylinder having the high structural strength is obtd. |
