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Hydraulic system in an injection molding machine

  • US 5,129,806 A
  • Filed: 06/07/1991
  • Issued: 07/14/1992
  • Est. Priority Date: 06/08/1990
  • Status: Expired due to Fees
First Claim
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1. In a combination of a clamping unit for use in an injection molding machine and a hydraulic system for actuating said clamping unit, whereinsaid clamping unit comprisesa movable mold carrier for carrying a movable part of an injection mold,a hydraulic locking cylinder, which contains a locking piston, which defines in said locking cylinder a high-pressure chamber and a low-pressure chamber on opposite sides of said locking piston, wherein said locking piston is formed with transfer passage means, through which said high-pressure and low-pressure chambers are adapted to communicate with each other,at least one hydraulic advance-retract cylinder containing a stationary piston and connected to said movable mold carrier and adapted to impart to said movable mold carrier a mold-closing movement and a mold-opening movement to and from a mold-clamping position, respectively, wherein said locking piston is connected by a first piston rod to said movable mold carrier and is adapted to lock said movable mold carrier in said mold-clamping position under a fluid pressure in said high-pressure chamber, and said stationary piston defines in said advance-retract cylinder on opposite sides of said stationary piston a first cylinder chamber, which is nearer to said movable mold carrier, and a second cylinder chamber, which is remote from said movable mold carrier, andat least one compensating cylinder containing a compensating piston, which defines in said compensating cylinder a compensating cylinder chamber communicating with said low-pressure chamber and is connected by a second piston rod to said movable mold carrier, andsaid hydraulic system comprisesa hydraulic pump,a pressure line connected to said pump,a reservoir,a return line connected to said reservoir,transfer valve means controlling the communication between said high-pressure and low-pressure chambers through said transfer passage means,a first communicating passage connected to said first cylinder chamber,a second communicating passage connected to said second cylinder chamber,a first branch passage connecting said first communicating passage to said high-pressure chamber,a second branch passage connecting said second cylinder chamber to said low-pressure chamber,first and second shut-off valves controlling said first and second branch passages, andcontrol means including means for controlling the flow of pressure fluid to and from said first and second cylinder chambers in dependence on a fluid flow volume program and means for a superimposed control of the fluid pressure in said first and second cylinder chambers, which control means include a pressure sensor in each of said communicating passages, a displacement-voltage converter, which is responsive to the movement of said advance-retract cylinder relative to said stationary piston, and a directional control valve for controlling the communication between said first and second cylinder chambers and said pressure line and said reservoir line, in dependence on said pressure sensors and said displacement-voltage converter,the improvement residing in thatsaid hydraulic system comprises a third branch passage, which by-passes said directional control valve and connects said second cylinder chamber to said pressure line and includes a non-return valve permitting a flow from said second cylinder chamber to said pressure line,and said directional control valve consists of a 4/4-way valve for controlling the velocity of said mold-closing movement and the pressure in said first and second cylinder chambers and is adapted to assume during a major part of said mold-closing movement a differential control position, in which the 4/4-way valve connects said second cylinder chamber to said third branch passage, and to assume before and after said differential control position a transitional control position, in which said 4/4-way valve connects said second cylinder chamber to said return line, and to connect said pressure line to said first cylinder chamber in said differential and transitional control positions.

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