Patent ID: 8043538

Claim:
A mold temperature control circuit of an injection molding device comprising: a fixed mold and/or a movable mold; a supply-side manifold connecting the molds with supply pipings of a heating-use medium, a cooling-use medium and scavenging compressed air; a discharge-side manifold connecting the molds with discharge pipings of the heating-use medium, the cooling-use medium and the scavenging compressed air; a plurality of heating/cooling common-use fine pipings which are housed inside the molds and joined to these manifolds; and a mold temperature sensor installed on the molds; wherein in an injection step of closing the molds to effect clamping and thereafter injecting a resin, such a molding cycle is repeated that, prior to injection of the resin, the heating-use medium is returned to the molds and heated to a temperature suitable for resin injection, after injection of the resin, the heating-use medium is switched to the cooling-use medium, thereby the cooling-use medium is returned to the molds to conduct cooling so as to give a temperature equal to or lower than a temperature at which the resin is solidified, the mold temperature control circuit of the injection molding device which is provided with an on-off valve of the supply piping of the heating-use medium, an on-off valve of the supply piping of the cooling-use medium, an on-off valve of the supply piping of the scavenging compressed air for discharging the heating-use medium and the cooling-use medium from inside the pipings and the molds, and a junction piping of combining the respective supply pipings of the heating-use medium, the cooling-use medium and the scavenging compressed air into one, thereby the junction piping is able to use commonly the respective supply pipings of the heating-use medium, the cooling-use medium and the scavenging compressed air to the molds and the respective discharge pipings thereof, and comprising: mold bypass piping for coupling the supply-side junction piping of a heating medium with the discharge-side junction piping thereof; a mold bypass on-off valve installed on the mold bypass piping; a passed heating medium sensor for detecting passage of the heating-use medium, the cooling-use medium and the scavenging compressed air on the heating medium supply piping and/or the discharge piping or a timer of adjusting opening/closing timing of the mold bypass on-off valve; and a mold-temperature adjusting control device which stores a mold temperature determination program for comparatively determining a target mold temperature preset as a control program and a mold temperature detected by the mold temperature sensor as well as a passed heating medium determination program for determining a type of passed heating medium by using completion of the time preset by a timer for adjusting opening/closing timing of the mold bypass on-off valve and/or a signal detected by the passed heating medium sensor, thereby adjusting the opening/closing timing of the mold bypass on-off valve.