GB2029315A - Hydraulic screw press drive - Google Patents

Abstract

A drive of a hydraulic screw press comprises a power cylinder (6) incorporating a movable member (15) connected with the press slide (2), and a chamber (A) communicating with a low-pressure hydraulic line (11) through a discharge valve (12). This valve is actuated by a device comprising a pneudraulic cylinder (19) whose above-piston hydraulic chamber (24) communicates alternately with the chamber (A) of the power cylinder (6) and with the low- pressure line (11) while its rod (22) is connected with the control element (13) of the discharge valve (12) by a limit switch (20). When the slide (2) actuates a limit switch (29), a valve (26) opens to place the chamber A in communication with the chamber (24) via an adjustable flow restrictor (25). The piston (21) then moves against the gas pressure in the chamber (23) until the rod (22) actuates the switch (20) and causes the discharge valve (12) to open. This arrangement ensures stepless adjustment of the time of tool action on the blank with a preset force thus reducing considerably the tool wear and improving the quality of the pressed parts. <IMAGE>

Description

SPECIFICATION Hydraulic screw press drive The present invention relates to hydraulic screw presses and more particularly, to their drives.

In accordance with the invention, disclosure is made of a drive of a hydraulic screw press comprising: a power cylinder connected by its movable member with the press slide and communicating through an inlet valve with a pneudraulic accumulator which is in communication with a pneumatic line and a source of pressure and,via a discharge valve provided with a control element and its actuating device, with a low-pressure hydraulic line, said discharge valve actuating device comprises a pneudraulic cylinder whose under-piston pneumatic chamber is in constant communication with the pneumatic line while the above-piston hydraulic chamber can communicate alternately with the chamber of the power cylinder and the lowpressure hydraulic line, and a limit switch connected with the control element of the discharge valve and installed in the extreme position of the free end of the rod of the pneudraulic cylinder in which its above-piston hydraulic chamber is in communication with the power cylinder.

Such a technical solution provides forstepless adjustment within wide limits of the time of tool action on the blank with a preset force. Thus the time of tool action on the blank can be greatly reduced at the moment when the kinetic energy accumulated by the slide is fully transferred onto the blank ot, if necessary, it becomes possible to hold the tool with its force applied to the blank within a required period which reduces considerably the wear of the tool, rules out warping of the workpiece after pressing and improves its quality. Moreover, such a distribution of forces in the process of part shaping steps up considerably the efficiency of the press.

It is practicable that alternate communication of the hydraulic chamber of the pneudraulic cylinder with the power cylinder and the low pressure hydraulic line should be effected by the use of an adjustable flow-restrictor and shutoff valves each valve being provided with a control element and one of said valves being installed between the above-piston hydraulic chamber of the pneudraulic cylinder and the low-pressure hydraulic line so that the control element of said valve is connected with the limit switch of the pneudraulic cylinder whereas the other shutoff valve and flow restrictor are installed consecutively between the above piston hydraulic chamber of the pneudraulic cylinder and the power cylinder in the direction towards the pneudraulic cylinder so that the control element of said second shutoff valve is connected with the press slide by a press-mounted limit switch.

Given below is a detailed description of an embodiment of the present invention with reference to the accompanying drawing which is a schematic longitudinal section of the hydraulic screw press and a hydrokinematic diagram of its drive according to the invention.

The hydraulic screw press comprises a frame 1 accommodating a reciprocating slide 2 which carries the top die 3. Installed under the slide in the frame 1 is a table 4 with the bottom die 5.

Reciprocating motion of the slide 2 is effected in the hydraulic screw press by a drive which comprises a power cylinder 6, a pneudrauliu accumulator 7, an inlet valve 8, a pneumatic line 9, a source of pressure 10, a low-pressure hydraulic line 11, a discharge valve 12 with a control element 1 3 and its actuating device 1 4.

The movable member of the power cylinder 6, i.e. its barrel 15, is connected with the slide 2 and has a chamber "A" accommodating a hollow plunger 1 6 which is secured in the press frame 1 and serves as the fixed member of the power cylinder 6. The external cylindrical surface of the barrel 1 5 of the power cylinder 6 is provided with a not self-locking screw thread (with the helix angle largerthan the angle of friction) which is screwed into a nut 1 7 secured in the frame 1. The barrel 15 is moved in the nut 17 (during the working stroke of the slide 2) by the pressure of fluid in the chamber "A", said fluid being delivered through the hollow plunger 1 6 from the pneudraulic accumulator 7.

The pneudraulic accumulator 7 has a pneumatic chamber 7a pre-charged by a any known method, and a hydraulic chamber 7b communicating with the chamber "A" of the power cylinder through the inlet valve 8 and with the source of pressure 10 which is constituted by a motor-driven H.P. pump. The pump may be of any known design suitable for the purpose.

The chamber "A' 'of the power cylinder 6 communicates with the low-prëssure hydraulic line 11 via the discharge valve 12.

To return the barrel 1 5 of the power cylinder 6 to the initial position, the drive incorporates a plunger-type cylinder 1 8 whose plunger is connected-with the slide 2, the cylinder 18 being in constant communication with the hydraulic chamber 7b of the pneudraulic accumulator 7.

It ihas already been stated above that the discharge valve 1 2 is provided with a control element 1 3 and its actuating device 14, the latter, according to the invention, comprising a pneudraulic cylinder 19 and a limit switch 20 connected by any known method with the control element 1 3 of the discharge valve 12.

The pneudraulic cylinder 19 has a piston 21 with a rod 22, an under-piston pneumatic chamber 23 and an above-piston hydraulic chamber 24. The under-piston chamber 23 is in constant communication with the pneumatic line 9.

The above-piston hydraulic chamber 24 of the pneudraulic cylinder 19 Can be put in communication alternately with the chamber "A"of the power cylinder 6 and the low-pressure hydraulic line 11 through an adjustable flow restrictor 25 and two shutoffvalves 26 and 27 of any known type suitable for the given purpose.

The limit switch 20 is installed on the path of the rod 22 of the piston 21 of the pneudraulic cylinder 19 for interaction with the free end of the rod 22 in its extreme position in which the abovepiston hydraulic chamber 24 of the pneudraulic cylinder 1 9 is in communication with the chamber "A" of the power cylinder 6.

The shutoff valve 26 is provided with a control element 28 which is connected by a pressmounted limit switch 29 with the press slide 2 for opening the shutoff valve 26 and by a limit switch 20 with the rod of the pneudraulic cylinder 19 for closing said shutoff valve 26. The connection of the control element 28 with the limit switches 29 and 20 may be of any type, e.g. electrical, and is not dealt with here since it is well known to those skilled in the art. The limit switch 29 is installed on the path of the slide 2 in such a position of the latter when the gap "S" between the top and bottom dies 3 and 5 is equal to the maximum height of the blank.

The shutoff valve 26 and the adjustable flow restrictor 25 are installed between the abovepiston hydraulic chamber 24 of the pneudraulic cylinder 19 and the chamber "A" of the power cylinder 6 consecutively in the direction toward the pneudraulic cylinder 19 (as shown in the drawing).

The shutoff valve 27 is provided with a control element 30 and installed between the above-piston hydraulic chamber 24 of the pneudraulic cylinder and the low-pressure hydraulic line 11, the control element 3C of the shutoff valve 27 being connected with the limit switch 20 and the control element 13 of the discharge valve 12 by any known method which makes it possible to actuate the shutoff valve 27 and put the hydraulic chamber of the pneudraulic cylinder 19 in communication with the low-pressure hydraulic line 11.

The control elements 30 and 13 can be disconnected by a limit switch 31 installed on the path traversed by the slide 2 in its motion to the topmost position and connected by any known means with the control elements 30 and 13.

The control elements 28, 30 and 13 as well as the inlet and discharge valves 8 and 12 can be constituted by any mechanisms known to those skilled in the art, provided they are cut into the drive of the hydraulic screw press in compliance with the claimed layout.

The drive of a hydraulic screw press functions as follows.

The pneumatic chamber 7a of the pneudraulic accumulator 7 is charged with gas by any known method. Then the motor of the pressure source is turned on and the hydraulic chamber 7b of the pneudraulic accumulator 7 is charged with fluid by a known method.

The slide 2 occupies the topmost position while the piston 21 with the rod 22 of the pneudraulic cylinder 19 is in the extreme right position (in the plane of the drawing).

The inlet valve 8 is turned on and the fluid starts flowing under pressure from the pneudraulic accumulator 7 through the inlet valve 8 into the chamber "A" of the power cylinder 6. Acted upon by the fluid pressure in the chamber "A" and owing to the notself-locking thread, the barrel 1 5 of the power cylinder performs a helical motion, moving down onto a blank B located in the gap "S" on the bottom die 5 of the press.

Coming short of the downmostposition by the distance equal to the height of the blank "B", the slide 2 interacts with the limit switch 29.

The limit switch 29 sends a signal to the control element 28 and the latter opens the shutoff valve 26. The fluid flows from the chamber "A" of the power cylinder 6 through the shutoff valve 26 and adjustable flow-restrictor 25 into the above-piston hydraulic chamber 24 of the pneudraulic cylinder 1 9. The piston 21 and the rod 22 move to the left (in the plane of the drawing) within a preset time period which can be adjusted by the flow restrictor 25. Gas is forced out of the under-piston pneumatic chamber 23 of the pneudraulic cylinder 1 9 into the pneumatic line 9.

This motion takes place before the free end of the rod 22 comes in contact with the limit switch 20.

With in this time period the slide 2 moves down and shapes the workpiece. On completion of this process and on attaining the required height of the workpiece the slide 2 stops.

As the free end of the rod 22 of the pneudraulic cylinder 19 comes in contact with the limit switch 20, the latter sends a signal to the control element 13 of the discharge valve 12 and to the control element 28 of the shutoff valve 26. The discharge valve 12 opens and puts the chamber "A" of the power cylinder 6 in communication with the lowpressure hydraulic line 11. Pressure in the chamber "A" is relieved.

Simultaneously, the limit switch 20 sends a signal to the control element 30 of the shutoff valve 27 which puts the above-piston chamber 24 of the pneudraulic cylinder 19 in communication with the low-pressure hydraulic line 11.

Acted upon by the pressure of gas entering the under-piston chamber 23 from the pneumatic line 9, the piston 21 with the rod 22 move to the right (in the plane of the drawing), to the initial position.

The slide 2 is returned by the cylinder 18 to the initial topmost position and interacts with the limit switch 31 which turns off the control elements 30 and 13.

During pressing of the next blank the operating cycle of the press is repeated over again as described above.

Claims (3)

1. A drive of a hydraulic screw press comprising: a power cylinder connected by its movable member with the press slide and communicating through an inlet valve with a pneudraulic accumulator which communicates with a pneumatic line and a source of pressure and, via a discharge valve provided with a control element and its actuating device, with a lowpressure hydraulic line; said discharge valve actuating device comprises a pneudraulic cylinder whose under-piston pneumatic chamber is in constant communication with the pneumatic line while the above piston hydraulic chamber is capable of communicating alternately with the chamber of the power cylinder and the lowpressure hydraulic line, and a limit switch, connected with the control element of the discharge valve, installed in the extreme position of the free end of the rod of the pneudraulic cylinder in which its above-piston hydraulic chamber is in communication with the power cylinder.

2. A drive according to Claim 1 wherein the above-piston hydraulic chamber of the pneudraulic cylinder is put in alternate communication with the chamber of the power cylinder and the low-pressure hydraulic line by means of an adjustable flow restrictor and shutoff valves provided, each with a control element and wherein one of said shutoff valves is installed between the above-piston hydraulic chamber of the pneudraulic cylinder and the low-pressure hydraulic line and its control element is connected with a limit switch while the other shutoff valve and the adjustable flow restrictor are installed consecutively between the above-piston hydraulic chamber of the pneudraulic cylinder and the chamber of the power cylinder in the direction towards the pneudraulic cylinder, the control element of this shutoff valve being connected with the press slide by a press-mounted limit switch.

3. A drive of a hydraulic screw press realized substantially as disclosed in the description with reference to the accompanying drawing.