GB2046659A

GB2046659A - Hydraulic Closing Device

Info

Publication number: GB2046659A
Application number: GB8009468A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1979-03-20
Filing date: 1980-03-20
Publication date: 1980-11-19
Also published as: FR2451788A1; IT1150954B; ES489673A0; IT8020762A0; ES8104026A1; JPS55126362A

Abstract

The invention relates to a hydraulic closing device for injection moulding machines or other moulding machines, the device comprising a closing piston 5, which is hydraulically slidable in a cylinder 1 and is connected by guide members 6 to a clamping plate 7 on which a mould half 8' is mounted. Cylinder chambers 23', 23'' on both sides of the closing piston 5 communicate through each of ducts 22', 22'' provided with a respective non-return restrictor valve 24', 24'' with a changeover valve 20 which is also connected to a pressure pump P and a tank T. Both cylinder chambers 23', 23'' can be pressure-biased or pressure- relieved alternately by means of the directional valve 20 in order to move the piston 5 (and thus the plate 7 and mould half 8') towards or away from the other mould half 8. Apertures 9 in piston 5 are closed by respective valve seats 12 towards the end of the mould-closing movement of piston 5 to permit the pressure from pump P to exact a large force on piston 5 through chamber 23' thereby thrusting the mould halves 8, 8' against each other with a large force. <IMAGE>

Description

SPECIFICATION Hydraulic Closing Device The invention relates to a hydraulic closing device of the kind for closing and opening of a divided mould, the component parts of which are secured on a mounting platen and on a closing plate, more particularly but not exclusively on injection moulding machines.

Known closing devices of this kind are of complicated construction. In particular, there is a large number of electrical, mechanical and hydraulic components which effect changeover from the rapid to the slow motion as well as reversal of direction and prevent the mould being damaged or even destroyed by foreign bodies which are clamped between the mould halves.

Furthermore, separate return pistons are provided in known devices for opening the mould. All these result in a high degree of susceptibility to trouble and dead time in the working cycle.

According to the invention, a hydraulic closing device more particularly for injection moulding machines, for the most rapid possible movement of the closing plate with low force and subsequent pressing of said plate against the mounting platen with a high force, with a closing piston, connected to the closing plate by means of piston rods which extend through a cylinder cover and having at least one aperture which is closable by a valve towards the end of the closing motion, comprises a changeover valve, which alternately pressurizes cylinder chambers on both sides of a closing piston which is associated with a plunger piston, biased with hydraulic fluid during the closing motion.

Preferably, the invention provides a device which is of simple construction and calls for only a small number of auxiliary components.

In this way, a single changeover valve is sufficient in place of the plurality of valves required in known closing devices.

In a further embodiment of the invention, it is proposed in incorporate hydraulic components, which act automatically in a specific manner, namely parallel connected non-return valves and restrictors, into the feed ducts extending to the cylinder chambers so that the number of controlled components is still further reduced, susceptibility to trouble reduced and the working speed is increased.

Preferably, mould safety, hitherto achieved by means of limit switches and the like, can be achieved by adjustable stop abutments for the shanks of the valves which close the apertures in the closing piston.

The invention will now be described by way of example with reference to the accompanying drawing, which shows a longitudinal section of a hydraulic closing device according to the invention.

The drawing shows a cylinder 1, which is closed by cylinder covers 2' and 2", and which is connected by means of studs 3 to a stationary mounting platen 4. A closing piston 5 in the cylinder 1 is connected to a slidable closing plate 7 by means of push rods 6 which extend in a sealingly sliding manner through the cylinder cover 2'. Mould halves 8' and 8" are secured to the mounting platen 4 and to the closing plate 7.

The piston 5 is provided with at least one aperture 9 through which a valve 10 extends. The two valves 10 in the example are shown in the drawing. Each valve 10 has a shank 11 which extends through the rear cylinder cover 2'. The diameter of D, of the shank is larger than the effective diameter D2 of a valve seat 12.

A tubular plunger piston 13, which also sealingly extends through the rear cylinder cover 2', is mounted on the closing piston 5, namely on the side of the closing piston which is distal from the push rods 6. A supply tube 16, which is inserted into a fixed cylindrical extension 15 of the cover 23, merges axially into an internal chamber 14 of the plunger piston.

On its external diameter, the extension 15 is provided with screwthreads 17, having mounted thereon a manually adjustable stop abutment 19 which is associated with the shank 11 of the valve 10, and is secured by a lock nut 18.

A single change over valve 20 is provided for controlling the motions of the closing piston 5. A first outlet (A) of the valve communicates via a duct 21 with the supply tube 16 of the plunger piston 13. A connecting duct 22' extending to a rear cylinder chamber 23' branches from the duct 21. A second outlet (B) of the changeover valve 20 communicates via a duct 22" with a front cylinder chamber 23".

An adjustable restrictor 24', 24" is installed into each of the two ducts 22', 22" respectively; a non-return valve 25' 25", which is adapted to open in a direction towards an appropriate cylinder, is connected in parallel with the aforementioned ducts.

The method of operation of the apparatus is as follows.

To close the mould, the valve 20 is connected so that the outlet A communicates with a pump P, and the outlet B is vented to an oil tank or a tank T. Hydraulic fluid is therefore delivered on the one hand via the duct 21 into the internal chamber 14 of the plunger piston 13, and on the other hand via the duct 22' into the cylinder chamber 23'.

The non-return valve 25' permits unobstructed flow. However discharge flow from the cylinder chamber 23" is restricted by the restrictor 24", so that a pressure, although slight, is built up in all the chambers, whch are biased with hydraulic fluid. A closing motion commences since the diameters of the piston 5, the push rods 6 and plunger piston 13 are selected so that the closing hydraulic forces are greater than the opening hydraulic forces. Oil consumption is slight since, on the one hand, the restrictor 24" allows only insignificant quantities of oil to discharge and, on the other hand, the cylinder chamber 23' is charged predominantly via bypass flow (C) through the port 9 from the cylinder chamber 23".

During the closing operation, the valves 10 continue to bear on the stop abutment 19 by virtue of the hydraulic pressure. This pressure is adjusted so that the valves 10 block the ports 9 when the mould halves 8', 8" are closed or immediately prior thereto. Since bypass flow of hydraulic oil delivered from the cylinder chamber 23' is then no longer possible and, on the other hand, the pressure in the cylinder chamber 23" is relatively rapidly relieved via the restrictor 24", it follows that the pump develops its full head. The head act one-sidedly on the piston 5, so that the closing plate 7 thrusts the mould halves 8', 8" against each other with a large force.By virtue of the previously described embodiment of the valve 10 it ensures the closure of the ports 9 in the piston 5 without the need for its own control elements such as those required in known devices. it can be advantageous to reduce the closing rate in steps over the last part. According to the invention this can be achieved either by constructing the valves with different lengths or by providing separate adjusting means on the stop abutment 19 for each valve. In both cases the valve will close earlier so that restriction of the overflow through a port of the piston reduces the speed thereof. This is particularly advantageous in the case of resiliently supported mounting platens of the kind employed for moulds with movable inserts.

A separate mould safety device is not required.

If a foreign member is-trapped between the mould parts, the relatively low force during closing will not be able to continue moving the piston 5.

Instead the latter will stop, the valves 10 will not close and the cylinder chamber 23" cannot be pressure relieved.

Mould stripping merely requires changeover of the changeover valve 20. By bypassing the restrictor 24", the pump can completely pressurize the cylinder chamber 23" via the nonreturn valve 25" and at the same time the cylinder chamber 23' is relieved via the restrictor 24'; at the same time the internal chamber 14 of the plunger piston 13 is depressurized. Mould stripping takes place under a large force until the valves 10 open. Pressure equalization between the cylinder chambers 23' and 23" therefore takes place and as the piston 5 continues to retract, hydraulic fluid will flow in the direction of the arrow D through the ports 9.Since simultaneously the pressure drops substantially, only a small quantity of hydraulic fluid will discharge through the restrictor 24' and the return motion of the piston 5 is performed at a high speed. By contrast to known devices no separate control function is required even at the end of the return stroke in order to prevent a severe pressure rise, since the hydraulic fluid delivered by the pump is able to discharge via the restrictor 24' accompanied by an only moderate rise of pressure.

If the moulds 8', 8" are exchanged, the stop abutment 19 is set to a new mould height where necessary. By arranging the stop abutment on the rear cylinder cover 2' and because of the free contact of the valve shank 11, the function of the valves 10 will not be affected by expansion of tbe guide members 3 or deformations of other highly stressed parts. Forming at high force over a substantial distance conveniently calls for supporting of the shank via a spring on the stop abutment and not directly, and the spring is dimensioned, so that it withstands a low force during closing. The spring is however compressed by the high pressure in the cylinder chamber 23" through the valves 10, so that initially the ports 9 remain closed. It is only when the opening resistance and therefore the pressure chamber 23" fall, that the spring is relaxed and the valves 10 are displaced towards the closing plate, the bypass ports 9 are released and the rapid opening motion commences. The same action can be achieved by a stop abutment which is resiliently supported on the extension 15. The restoring force can be applied by a spring as well as by a cylinder-piston unit which is biased by hydraulic pressure. Instead, it is also possible to hydraulically adjust a non-resilient stop abutment by means of screwthreads.

Claims

1. Hydraulic closing device, more particularly for injection moulding machines, for the most rapid possible movement of the closing plate with low force and subsequent pressing of said plate against the mounting platen with a high force, with a closing piston, connected to the closing plate by means of piston rods which extend through a cylinder cover and having at least one aperture which is closable by a valve towards the end of the closing motion, comprises a changeover valve, which alternately pressurizes cylinder chambers on both sides of a closing piston which is associated with a plunger piston, biased with hydraulic fluid during the closing motion.

2. Hydraulic closing device according to claim 1, wherein a device which offers no resistance to flow into the cylinder chamber but offers a resistance, more particularly adjustable, to the flow from the cylinder chamber, is incorporated into the supply duct of the cylinder chamber, which is distal from the closing plate.

3. Hydraulic closing device according to claim 1, wherein a device which offers no resistance to flow into the cylinder chamber but offers a resistance, more particularly adjustable, to flow from the cylinder chamber is incorporated into the supply duct of the cylinder chamber, which is nearest to the closing plate.

4. Hydraulic closing device according to claim 2 or 3, wherein the device comprises a non-return valve and a restrictor, connected in parallel.

5. Hydraulic closing device according to claim 1, wherein the valve, which closes the port in the closing piston, extends through the cylinder cover which is distal from the closing plate and the valve shank at that place has a diameter which is larger than the diameter of the valve seat.

6. Hydraulic closing device according to claim 4, wherein the valve shank bears freely on a mechanically or hydraulically axially adjustable stop abutment.

7. Hydraulic closing device according to claim 6, having the provision of at least two valves whose effective length is different or can be adjusted independently of each other.

8. Hydraulic closing device according to claim 6, wherein the valve shank is supported on the stop abutment via a spring, more particularly an adjustable spring.

9. Hydraulic closing device according to claim 6, wherein the stop abutment is resiliently supported in the direction towards the closing plate.

10. Hydraulic closing device according to claim 9, wherein the resilient action is obtained by a cylinder-piston unit, which can be biased with pressure, more particularly variable pressure.

11. Hydraulic closing device substantially as herein described with reference to the accompanying drawing.