GB2086302A - Prefill Valve System - Google Patents

Abstract

In a prefill valve system wherein a ram (not shown) slides in a main cylinder 1 to close a mould, fluid is initially supplied to a cavity in the ram through a booster tube (2) supported at its fixed end (3) in a back plate (4). The supply to the cavity produces a rapid advance of the ram during mould closure. A prefill valve sleeve (7) surrounding the booster tube, allows low pressure fluid to enter the cylinder through a port 6 during such rapid advance. A plurality of hollows pistons (13) for closing the valve sleeve (7) are fixed in the back plate (4) or prefill valve (7) respectively and extend substantially parallel with the booster tube into cylindrical chambers (14) in the prefill valve or back plate respectively. The back plate (4) has a passage (12) for passing fluid, to be fed to the booster tube, additionally to the hollow pistons, and the hollow pistons have ports (16) to allow fluid to pass into the main chamber (1) when the ports are uncovered after sufficient movement of the prefill valve, to enable high pressure fluid fed to the booster tube to be applied via a fluid passage 18 and the cylinder 1 to the ram to hold the mould closed. <IMAGE>

Description

SPECIFICATION Prefill Valve System.

The present invention relates to so-called "prefill" valve systems" of the kind which are used particularly on mould closing hydraulic cylinders.

Moulds for use in moulding plastics materials under pressure are normally held closed by a hydraulic cylinder and ram system. As the volume of the cylinder is large because the mould halves have to move apart a considerable distance to enable the moulded product to be removed and because a high clamping force is required to maintain the mould halves in the closed position during moulding, conventional hydraulic cylinder assemblies for such moulds include a so-called booster cylinder acting over a smaller area than the main cylinder to enable the pump supplying hydraulic pressure to close the mould quickly by supplying pressurized fluid to the smaller volume booster cylinder.In order to enable the main cylinder to be filled as quickly as the booster cylinder closes the mould halves together, and thus to save down time in mould operation, the main cylinder is gravity fed through a large port or ports which can be closed by a valve when the mould has substantially completed its closing motion and a large force is required to be provided by the main cylinder to maintain the mould closed during moulding. This closable valve is known as a prefill valve.

It is known to provide a tube forming the booster cylinder located usually concentrically within the main cylinder, the ram which slides in the main cylinder and which closes the mould having a cylindrical chamber in which the free end of the booster tube is a sliding fit. In order to close the mould quickly, by moving the ram, hydraulic fluid is pumped into the booster tube. At the same time the same hydraulic fluid is fed under gravity from the source into the main cylinder through a port which can be closed by a sleeve-type prefill valve slidable within the main cylinder. Once the mould is closed or nearly closed a valve or valves are actuated to cause the prefill valve to slide to the closed position and to allow the pressurized fluid to flow into the end of the main cylinder to pressurize it and maintain the mould in the closed position.Such a prefill valve system will hereinafter be referred to as "of the kind described".

In one known system a plurality of hollow plungers, sliding in bores, are acted upon at one end by pressurized fluid to engage, at their other, free, ends, the end of the prefill valve to close it.

When at or near the finish of their movement ports in the plungers align with ports in ducts leading from the fixed end of the booster tube so that the fluid supplied to the booster tube is passed additionally through the plungers and out of ports adjacent their free ends into the main cylinder to pressurize it. In an alternative construction the plungers are solid, but each have a central reduced diameter position around which fluid can flow to the main cylinder once the plunger has moved sufficiently far forward for the reduced portion to reach the end of the bore in which it slides.While this system is satisfactory in operation, the need to provide for movement of the plungers and high pressure for actuation to the one ends of the plungers requires the back plate, in which the plungers and the bores in which they are slidable are located, to be of an extremely robust construction to accommodate the high pressures required for actuation and to house the plungers.

In accordance with the present invention a prefill valve system of the kind described has a booster tube supported at its fixed end in a back plate; a prefill valve sleeve surrounding the booster tube, but spaced therefrom to provide a fluid passage therebetween; and a plurality of hollow pistons fixed in the back plate or prefill valve respectively and extending substantially parallel with the booster tube into cylindrical chambers in the prefill valve or back plate respectively, the back plate having a passage or passages for passing fluid, to be fed to the booster tube, additionally to the hollow pistons, and the hollow pistons having ports to allow fluid to pass into the main chamber when the ports are uncovered after sufficient movement of the prefill valve.

By means of such a system it is possible to dispense with a separate supply of pressurized fluid which is normally supplied to the back of the plungers of the prior art in arder to cause them to move and in turn move the sleeve valve. Instead, the pressurized fluid which is supplied in any case to the booster tube is passed through the hollow pistons and acts, within the hollow pistons between the prefill valve sleeve and the back plate to bias the prefill valve sleeve towards its closed position. To balance the closing force the prefill valve sleeve may have an enlarged diameter portion at its end adjacent the back plate, the enlarged diameter portion sliding in a correspondingly enlarged diameter portion of the main cylinder and pressurized fluid being supplied to the enlarged diameter portion of the cylinder to counter the closing force on the prefill valve.

When pressure within the enlarged portion of the main cylinder is relieved then the prefill valve is urged to the closed position by the pressurized fluid within the hollow pistons.

One example of a prefill valve constructed in accordance with the present invention will now be described with reference to the accompanying drawing which is a section through the system, the upper half showing the prefill valve in the closed position and the lower half showing the prefill valve in the open position.

The system comprises a main cylinder 1 at the far right hand end of which (not shown) slides a ram which is attached to a mould closing linkage.

Concentrically disposed within the main cylinder is a booster tube 2 which is held in a fixed position at its rear end 3 in a back plate 4 which is attached to the main body 5 in which the prefill valve system is located.

The booster tube opens at its other end into a cylindrical chamber formed in the end of the ram (not shown) so that when fluid is supplied at A to a fixed end of the booster tube, under pressure, the ram is caused to close the mould. Whilst the ram is moving forward the same hydraulic fluid from a tank or other suitable source, is fed into the main cylinder 1 under gravity through a port 6 across which is slidable a prefill valve 7.

The prefill valve is slidable to close the port 6 to prevent communication of fluid between the main cylinder and the source when required. At its rearward end (the left hand end of the figure) the prefill valve 7 has an enlarged diameter portion 8 sliding within a correspondingly enlarged cylindrical bore 9 formed at the rear end of the main cylinder. A chamber 10 is thus formed in the enlarged bore 9 to which pressurized fluid can be supplied through a duct 11.

When the mould is being closed by means of fluid flowing through the booster tube part of the fluid entering at A is passed via transverse ducts 12 to the interior of hollow pistons 13 which are fixed in position in the back plate 4 and which extend forwards into cylindrical bores 14 in the rear end of the prefill valve 7. Suitable seals 1 5 seal the hollow pistons 13 into the bores 14 to prevent leakage of fluid therefrom. Thus, fluid pressure within the hollow pistons 13 tends to bias the prefill valve 7 to the closed position. In order to counter this, fluid is maintained under pressure within the chamber 10 until such time as the mould is closed or nearly closed, when the pressure is relieved and the prefill valve is thus allowed to move forward under the action of the pressure within the hollow pistons 13.As the prefill valve 7 moves forward ports 16 in the hollow pistons 13 are uncovered and fluid from the pump supplying the pressure to the booster tube is thus allowed to flow into the gap 17 which opens between the back plate and the rear end of the prefill valve 7 and between the prefill valve 7 and the booster tube through a long annular channel 18 formed by suitable spacing apart of the prefill valve from the booster tube, into the main cylinder 1 to pressurize the mould halves and maintain them in the closed position.

After moulding, pressure at A is relieved and the ram moves backwards under the action of an additional chamber (not shown) which is formed externally of the ram to provide a double acting feature for the mould closure system. The prefill valve 7 is returned to the position shown in the bottom half of the drawing by pressure acting within the chamber 10. To enable the prefill valve to open completely fluid from within the gap 17 is vented through ports 19.

Claims (3)

Claims

1. A prefill valve system of the kind described which has a booster tube supported at its fixed end in a back plate; a prefill valve sleeve surrounding the booster tube, but spaced therefrom to provide a fluid passage therebetween; and a plurality of hollow pistons fixed in the back plate or prefill valve respectively and extending substantially parallel with the booster tube into cylindrical chambers in the prefill valve or back plate respectively, the back plate having a passage or passages for passing fluid, to be fed to the booster tube, additionally to the hollow pistons, and the hollow pistons having ports to allow fluid to pass into the main chamber when the ports are uncovered after sufficient movement of the prefill valve.

2. A system according to claim 1, in which the prefill valve sleeve has an enlarged diameter portion at its end adjacent the back plate, the enlarged diameter portion sliding in a correspondingly enlarged diameter portion of the main cylinder, whereby pressurized fluid can be supplied to the enlarged diameter portion of the cylinder to counter the closing force on the prefill valve provided through the hollow pistons.

3. A system according to claim 1, substantially as described with reference to the accompanying drawings.