Patent ID: 7066236

Claim:
An injection device for a light metal injection molding machine comprising: a melting device for melting light metal material into molten metal, said light metal material supplied in the form of cylindrical rod-shaped billets equivalent to a shot volume of a plurality of shots, said melting device including: a melting cylinder, the melting cylinder having a length capable of holding a plurality of billets, the melting cylinder wrapped around by a plurality of heaters, forward heaters for being set to a melting temperature and at least a base end heater for being set to a low temperature, the melting cylinder for heating and melting the plurality of billets supplied from a rear end of the melting cylinder to generate molten metal equivalent to a volume of a plurality of shots at a front side, the plurality of billets for being subjected to preliminary heating at a base end of the melting cylinder in a state where softening is prevented, and said plurality of billets for being strongly heated while passing from a middle part of the melting cylinder to a forward end of the melting cylinder to rapidly melt at the forward end; a billet supply device positioned at a rear end of the melting cylinder for supplying the plurality of billets one at a time, at the time of material supply, in such a manner that the plurality of billets are inserted from the rear end of the melting cylinder, and a billet inserting device positioned behind the billet supply device, said billet inserting device containing a pusher, the pusher for forcing molten metal for one shot volume into an injection cylinder using a billet when metering, or said pusher for inserting a billet into the melting cylinder using a billet at the time of material supply; a plunger injection device for carrying out injection of molten metal using a plunger after molten metal is metered into the injection cylinder from the melting device; a connecting member including a connecting passage for connecting the melting device and the plunger injection device; a backflow prevention device for preventing backflow of molten metal by opening and closing the connecting passage; most of a cylinder bore, except for a base end of the melting cylinder, provided with a dimensional relationship for causing a gap with a side surface of a tip of a softened billet; a cooling member at a base end of the melting cylinder, the cooling member for cooling a base end of a billet to such an extent that there is no deformation due to pressing force at the time of metering; and a cooling sleeve, being of a small volume member, being peripherally exposed to a space between a rear end of the melting cylinder and the cooling member, and being positioned between the melting cylinder and the cooling member, the cooling sleeve for cooling molten metal, the cooling sleeve having an annular groove for forming a seal member of a solid material around a billet, the seal member solidified from molten metal to such an extent as to prevent backward flow of molten metal.