GB2080421A - Fluid operated piston and cylinder assembly and metal drawing apparatus embodying same - Google Patents

Abstract

A piston and cylinder assembly has a hollow piston rod (3) secured to the piston (2) and extending out of the cylinder (1), a fluid inlet/outlet (11) at the cylinder end having the rod, and a fluid outlet (10) at the opposite cylinder end. The piston side opposite the rod is open to the interior of the rod, and the rod has fluid ports (4) adjacent the piston, allowing communication between the cylinder chambers on each side of the piston. A spool (5) is axially slidable in the rod (3) and can be positioned to either close or open the ports (4). With inlet/outlet (11) pressurised and outlet (10) open, the piston moves leftwards. To reverse the stroke outlet (10) is closed to build up pressure ahead of and a the piston thereby to cause displacement of the spool (5) and opening of the ports (4). Once ports (4) are open pressure acts on the full area side of the piston to return the latter. <IMAGE>

Description

SPECIFICATION Fluid operated piston and cylinder assembly and metal drawing apparatus embodying same This invention relates primarily to piston and cylinder assemblies wherein the control of the assembly to effect a return stroke after an operative stroke is simple and reliable and which is particularly applied to metal drawing apparatus for pulling metal stock through a drawing die in which case the metal stock is engaged by means of'a gripper assembly associated with the piston.

Piston and cylinder assemblies of a double acting type, and which are suitable for use in drawing metal stock through sizing dies generally require fairly complex, and thus costly, control circuits which, as with any complex control circuits, can tend to break down more frequently than a simple arrangement.

It is the object of this invention to provide a piston and cylinder assembly which will require only simple control circuits in order to operate same effectively and which is thus well suited to application in the drawing of metal stock through sizing dies.

It is a second object of this invention to provide metal drawing apparatus embodying a piston and cylinder assembly according to this invention and wherein the control circuits are thus simplified relative to what would be required if prior art.

piston and cylinder assemblies were employed.

In accordance with this invention there is provided a piston and cylinder assembly comprising a cylinder and co-operating piston axially slidable in reciprocating manner therein, a hollow piston rod attached to the piston and extending out of one end of the cylinder and a spool valve located within said hollow piston rod or the piston itself, the spool valve having two terminal positions one in which a flow path for fluid is provided between the two sides of the piston and one in which such flow path is closed and means for moving the spool valve from an open position to a closed position when required.

Further features of the invention provide for the cylinder to be provided with a single valve controlled inlet/outlet at the end thereof opposite the hollow piston rod side of the piston; for the opposite end of the cylinder to be provided with a single valve controlled inlet for fluid under pressure; for the spool valve to be adapted to operate in unison with an axially movable rod located within the hollow piston rod; and for said axially movable rod to be adapted to operate as an ejector for a gripper assembly associated with the free end of the piston rod.

The invention also provides metal drawing apparatus including a piston and cylinder assembly as above defined, a control system for the valves associated with the two ends of the cylinder, gripper means attached to the end of the hollow piston rod, a push pointer assembly located in co-linear relationship relative to the piston and cylinder assembly but spaced apart therefrom and a die supporting assembly located between the push pointer and the piston and cylinder assembly, the push pointer also being operable by means of fluid under pressure and being connected to said control circuit to be operated thereby.

The above and other features will become more apparent from the following description of one embodiment of the invention in which the piston and cylinder assembly particularly applied to metal drawing apparatus and is described in relation thereto. In this description reference will be made to the accompanying sketches in which: Fig. 1 is a longitudinal sectional elevation of a piston and cylinder assembly according to the invention and, Fig. 2 is a simplified diagrammatic illustration of metal drawing apparatus according to the invention and embodying the piston and cylinder assembly illustrated in Fig. 1.

As illustrated in Fig. 1 a piston and cylinder assembly has a cylinder 1 within which is axially slidable in reciprocating manner a piston 2. The piston is carried at one end of a tubular piston rod 3 which has ports 4 passing through its wall adjacent the piston 2.

The ports are in co-operating relationship to an axially slidable spool 5 and, the tubular piston rod and spool 5 together form a spool valve. The spool valve has two terminal positions, one in which the spool is moved to the end most remote from the free end of the piston rod and in which position it is ciosed, and the other being where the spool is moved towards the free end of the piston rod and the ports are thus open and provide a passageway defined through the ports via the tubular piston rod to the opposite side 6 of the piston.The piston is shaped as indicated to provide for proper flow of fluid so as to act on substantially the entire area of the piston opposite that from which the tubular piston rod extends and, this area being greater than the area presented to.fluid under pressure on the side of the piston from which the tubular rod extends, will mean that the piston will move to extend the piston rod when the valve is open.

The spool 5 itself is actually located within a sleeve 7 which extends between an end stop 8 and a series of co-operating spring washers 9 which serve to cushion any impact from the valve spool 5 at the end of its stroke.

An outlet 10 is provided for fluid from the end of the cylinder opposite the piston rod and an inlet 11 is provided for the end of the cylinder through which the piston rod extends.

For operation the abovedescribed piston and cylinder assembly is provided with a single control valve for the outlet 10 and also a single control valve for the inlet 11 or is provided with an angle control valve which serves both apertures. The piston and cylinder assembly is, for this embodiment of the invention, adapted to be operated hydraulically.

Commencing with the piston rod in an extended condition and thus the piston itself near the inlet 11. hydraulic fluid is introduced through the inlet by opening the valve associated therewith. At the same time, the valve associated with the outlet 10 will be open, while the spool valve is closed. A stroke thus commences and the piston is withdrawn into the cylinder and hydraulic fluid is exhausted through the outlet 10. At a desired point during this stroke and when return of the piston to its starting position is required, all that is effected is that the valve associated with the outlet is closed and this causes pressure to build up in the cylinder to oppose further movement of the piston. Alternatively, fluid is admitted through aperture 10.This build up in pressure causes the spool 5 to move axially to a position in which the ports 4 are open and hydraulic fluid can then flow through the ports into the opposite side of the cylinder. Since, as mentioned above, this side of the piston has a greater surface area, the piston will thus move in a return stroke movement. The spool valve can be mechanically closed, for example by means of an axially movable rod, in which cause another operative stroke will commence once the valve associated with the outlet 10 is opened.

The abovedescribed piston and cylinder assembly, when particularly adapted for use in metal drawing apparatus according to the invention, has its spool adapted to co-operate with an ejector rod 12 for ejecting metal stock from a gripper 13 (Fig. 2) carried by the free end of the tubular piston rod.

Referring to Fig. 2, located co-axially with the piston and cylinder assembly, but spaced apart therefrom, is a push pointer 14 adapted to push metal stock through a die assembly 1 5 positioned between the piston and cylinder assembly and the push pointer. Clearly the gripper on the free end of the piston rod will be directed towards the die and the remainder of the piston and cylinder assembly will extend away therefrom.

The drawing apparatus described above has a control circuit which is of very much simplified design having regard to the prior art. All that is required is an hydraulic circuit which can be designed by any skilled hydraulics engineer and which is adapted to initially push metal stock through the die until such time as sufficient length of stock protrudes from the die to enable the gripper to operate to grip its free end and the pushing action of the stock on the ejection rod causes closure of the spool valve. Closure of the spool valve combined with other control functions will then enable a drawing stroke of the piston and cylinder assembly to be effected and suitable limit switches associated with the gripper end of the hollow piston rod are adapted to cause the main control function.Thus a limit switch 1 6 is adapted to activate hydraulic or mechanically release means for the gripper and also, through suitable latching relay, to cause closure of the outlet valve which, in turn, will cause the ejection rod to operate. Alternatively any device capable of sensing that the drawn stock has completely left the drawing die may provide the signal for the commencement of the sequence: jawspening; stock ejection from gripper, and.commencement of return stroke.

A second limit switch 1 7 associated with the opposite end of the stroke of the piston rod causes activation of the push pointer and closure of the inlet valve for hydraulic fluid to the piston and cylinder assembly. Only once the push pointer has operated to move the gripper and ejection rod axially will the limit switch operate to cause opening of the inlet valve to the piston and cylinder assembly whence a complete new cycle commences.

It will be understood that many variations may be made to the above described embodiment and application of the invention without departing from the scope hereof. In particular the spool valve arrangement can be varied widely and the means of closing the spool valve once It has opened could be changed as required or, alternatively, as the application of the piston and cylinder assembly dictates.

The control system briefly described could also be varied as required without departing from the scope of the invention.

It is considered that the invention provides a piston and cylinder assembly and metal drawing apparatus embodying same which results in a very much simplified control circuit being required and thus enhances trouble free operation of the apparatus.

Claims (10)

1. A piston and cylinder assembly comprising a cylinder and cosperating piston axially slidable in reciprocating manner therein, a hollow piston rod attached to the piston and extending out of one end of the cylinder and a spool valve located within said hollow piston rod or the piston itself, the spool valve having two terminal positions one in which a flow path for the fluid Is provided between the two sides of the piston and one in which such flow path is closed and means for moving the spool valve from an open position to a closed position when required.

2. A piston and cylinder assembly as claimed in claim 1 in which the piston side opposite the rod is in communication with the rod interior, and at least one fluid part is located in the rod wall near the piston, the spool being moveable between a position in which the parts are sealed from the rod interior, and a position away from the piston wherein the parts communicate with the rod interior and said piston side opposite the rod.

3. A piston and cylinder assembly as claimed in claim 2 in which the spool valve is adapted to operate in unison with an axially moveable rod located within the hollow pistdn rod.

4. A piston and cylinder assembly as claimed In claim 3 in which the spool is located within a sleeve in the hollow piston, the sleeve having wall openings co-inciding with the rod parts, and the axially moveable rod within the piston rod has a mechanical stop acting in use against spring washers located at the sleeve end remote from the piston, the opposite sleeve end having an annular end stop for the spool.

5. A piston and cylinder assembly as claimed in any one of the preceding claims in which the cylinder is provided with a single valve controlled inlet/outlet at the end thereof opposite the hollow piston rod side of the piston, the opposite cylinder end being provided with a single valve controlled inlet for fluid under pressure.

6. A piston and cylinder assembly as claimed in any one of the preceding claims in which the axially moveable rod is adapted to operate as an ejector for a gripper assembly associated with the free end of the rod.

7. A piston and cylinder assembly as claimed in any one of claims 1, 2, 5 or 6 in which the spool valve is adapted to operate in unison with an axially moveable rod located within the hollow piston rod.

8. Metal drawing apparatus including a piston and cylinder assembly as claimed in any one of the preceding claims, a control system for the valves associated with the two ends of the cylinder, gripper means attached to the end of the hollow piston rod, a push pointer assembly located in colinear relationship relative to the piston and cylinder assembly but spaced apart therefrom and a die supporting assembly located between the push pointer and the piston and cylinder assembly, the push pointer also being operable by means of fluid under pressure and being connected to said control circuit to be operated thereby.

9. A piston and cylinder assembly substantially as herein described with reference to, and as illustrated in, any of the accompanying drawings.

10. A metal drawing apparatus substantially as herein described with reference to, and as illustrated in, any of the accompanying drawings.