Hydraulic control for plastic injection molding machine

Claim 2

A system as defined in claim 1 wherein an hydraulically operable variable pressure relief valve is provided with its inlet connected to said main line downstream of said first and second pumps and with its outlet connected to said reservoir, a second servo valve is connected between said main line and said relief valve and has a drain connection to said reservoir to control hydraulic pressure acting on said relief valve, and means is provided for modulating the operation of said second servo valve to select and vary the pressure in said main line.

Claim 3

A system as set forth in claim 3 wherein the means for modulating said first and second servo valves is electrical.

Claim 4

The system as defined in claim 1 wherein said spool has at leasT one axial metering slot to assure some flow from said second pump to said reservoir in substantially all positions of said spool and to increase such flow as said spool is moved toward its other end.

Claim 5

The system of claim 5 wherein the first servo valve is constructed and arranged to admit fluid at minimal pressure to said other end of the spool in the event of operative failure of said means for modulating the said first servo valve, thus assuring maximum by-pass flow from said second pump to said reservoir in the event of such failure.

Claim 6

An hydraulic control system for a plastic injection molding machine having mold halves which are opened and closed hydraulically by a reversible fluid motor actuated by a die control valve and having a plastic melt injecting means which is advanced by a reversible fluid motor actuated by an injection control valve, said system including a low pressure reservoir and means defining a main line for pressure flow from the reservoir to both said control valves and a drain from both said control valves to said reservoir, a first driven pump in said main line capable of high pressure but relatively low rate delivery to provide the final closing force on the mold halves, a second driven pump capable of high rate but relatively low pressure delivery to provide the force for most of the relative movement of the mold halves and having its inlet connected with said reservoir and having an outlet connection with said main line which permits flow only toward said main line, a bypass valve connected between the outlet of said second pump and said reservoir and including a member hydraulically movable to vary the flow between said outlet and reservoir and thereby to vary the flow from the said second pump to the main line, a first servo valve connected between said main line and by-pass valve and having a drain connection to said reservoir and being adapted to control the hydraulic pressure on said movable member, and electrical means programmed for operation of said mold halves and said injecting means modulating the operation of said servo valve to effect movement of said movable member.

Claim 7

The system of claim 7 wherein an hydraulically operable variable pressure relief valve is provided with its inlet connected to said main line, a second servo valve is connected between said main line and relief valve and has a drain connection to said reservoir to control the operating hydraulic pressure on said relief valve, and means is provided for modulating the operation of said second servo valve to select and vary the pressure in said main line.

Claim 8

A system as provided in claim 8 wherein the means for modulating said second servo valve is electrical and programmed for operation of said mold halves and injecting means.

Claim 9

An hydraulic control system for a reciprocating screw-type plastic injection molding machine having mold halves which are opened and closed hydraulically by a reversible fluid motor actuated by a die control valve and having a reciprocating screw which is rotated to plasticize plastic material by an hydraulic motor controlled by an isolation valve and which is thrust forwardly to inject plasticized melt by a reversible fluid motor actuated by an injection control valve, said system including a low pressure reservoir and means defining a main line for pressure flow from the reservoir to both said control valves and said isolation valve and a drain to said reservoir from said control valves and isolation valve, a first driven pump in said main line capable of high pressure but relatively low rate delivery to provide the final closing force on the mold halves and the final injecting movement of the screw, a second driven pump capable of high rate but relatively low pressure delivery to provide the force for the remainder of movement of the mold halves and injecting movement of the screw and having its inlet connected with said reservoir and having an outlet connection with said main line which permits flow only toward sAid main line, a by-pass valve connected between the outlet of said second pump and reservoir and including a member hydraulically movable to vary the flow from said outlet to said reservoir and thereby to vary the flow from said second pump to said main line, a first servo valve connected between said main line and by-pass valve and having a drain connection to said reservoir and being adapted to control the hydraulic pressure on said movable member, and electrical means programmed for operation of said mold halves and for rotation and injection of said screw modulating the operation of said servo valve to effect movement of said movable member.

Claim 10

The system of claim 10 wherein an hydraulically operable variable pressure relief valve is provided with its inlet connected to said main line, a second servo valve is connected between said main line and relief valve and has a drain connection to said reservoir to control the operating hydraulic pressure on said relief valve, and means is provided for modulating the operation of said second servo valve to select and vary the pressure in said main line.

Claim 11

A system as defined in claim 11 wherein the means for modulating said second servo valve is electrical and programmed for operation of said mold halves and for rotation and injection movement of said screw.