GB2044671A

GB2044671A - Fluid Powered Presses

Info

Publication number: GB2044671A
Application number: GB8005820A
Authority: GB
Original assignee: Advance Automation Assembly Ltd
Current assignee: Advance Automation Assembly Ltd
Priority date: 1979-03-06
Filing date: 1980-02-21
Publication date: 1980-10-22

Abstract

A press has an output piston 18 responsive to an intensified hydraulic pressure in a chamber 17, resulting from downward movement of a pneumatically operated piston 10. The output piston 18 is also movable by a pneumatically operated piston 34, to provide a relatively rapid, low force, approach stroke. The effective area of the piston 34 is sufficient to overcome the force applied by return springs 28 for the output piston 18. <IMAGE>

Description

SPECIFICATION Fluid Powered Presses This invention relates to fluid powered presses, and in particular to such presses having a ram which causes a force to be applied steadily and relatively slowly to a work piece.

It is known to obtain the required force on the work piece by applying a relatively low fluid pressure to a first piston of relatively large diameter, the first piston acting on a smaller second piston which in turn displaces fluid within a chamber, the fluid pressure in the chamber acting on a diameter of the press ram, this ram diameter being larger than that of the second piston. Such an arrangement is known as in intensifier. It is usual to provide the press ram with return springs, so that the ram will be urged away from the zone of a work piece even in the event of fluid pressure failure.

In order to speed up operation of such presses it is desirable that during an initial part of its stroke the ram should approach the work piece rapidly, before slowing to apply the required force to the work piece.

The force required to urge the ram over the approach portion of its stroke is considerably less than that required to be applied to the work piece.

It has been proposed to effect a fast approach stroke by applying the lower fluid pressure directly to the aforesaid ram diameter. However, the resultant force on the ram must be sufficient to overcome the bias of the return springs, and it has been found that the relative diameters of the pistons and ram to provide a satisfactory intensifier are such that the spring bias cannot readily be overcome.

It is an object of the invention to provide a press in which a relatively low fluid pressure may be used to overcome bias applied by return springs, in such a manner as to effect a relatively rapid approach stroke.

According to the invention a fluid pressure operated press comprises a first piston, means for applying a first fluid pressure to said first piston, a second piston having an effective area less than that of said first piston and being coupled to said first piston for movement therewith, a chamber containing a second fluid, said second piston being slidable in said chamber to displace said second fluid a third piston slidable in said chamber and having an effective area greater than that of said second piston, said third piston providing an output element for said press, a fourth piston operably connected to said third piston and having a larger effective area than said third piston, and means for applying a third fluid pressure to said fourth piston, to urge said third piston in an operating direction in which it is urged as a result of movement of said first piston under the influence of said first fluid pressure.

In a preferred embodiment said fourth piston slidably surrounds said chamber.

In a particular embodiment said first, second, third and fourth pistons are axially aligned.

An embodiment of the invention will now be described by way of example only and with reference to the accompanying drawing, which shows, somewhat diagrammatically, a pneumatic/hydraulic press.

The press shown has a first piston 10 movable within a cylinder 11 against a spring 12 by means of an air pressure which is applied from a source 13 by way of a valve 14 which is operated in a manner to be described. The piston 10 has a stem whose free end provides a second piston 1 5 which passes sealingly through a transverse wall 16 into a cylindrical chamber 1 7. A third piston 18 is slidable within the chamber 1 7 and provides an output ram for the press as a whole. The chamber 1 7 and piston 1 8 are axially aligned with the pistons 10, 1 5, and the piston 18 has an axial blind bore 18a, adapted to receive the piston 1 5.

The transverse wall 16 has a first bore 19 which is sealingly engaged by the piston 1 5 at all times, and a second bore 20 which is sealingly engaged by the piston 1 5 only when the latter is moved downwardly against the spring 12 by the piston 10. An oil reservoir 21 can communicate with chamber 17 by way of an annular clearance zone 22 between the bores 1 9, 20. Oil within the reservoir is pressurized by air from the source 1 3.

Thus, if the piston 1 5 is moved downwardly from the position shown, the reservoir 21 is shut off from the chamber 1 7 by reason of the sealing angagement of the piston 1 5 with the bore 20.

Further downward movement of the piston 1 5 displaces fluid within the chamber, including that within the axial bore of the piston 1 8, urging the piston 1 8 downwardly. The piston 1 8 has an effective area approximately 5 times that of the piston 15, and the piston 10 has an effective area approximately 36 times that of the piston 1 5.

Thus the axial output force obtainable from the piston 1 8 is 5 times the axial force on the piston 1 5, and the pressure in chamber 17, after the bore 20 has been closed by the piston 15, is 36 times that of the pressure obtainable from the source 13.

Secured to a crosshead 23 of the piston 1 8, by means of pillars 24 is a plate 25. Two further pillars 26 extend slidably through a fixed frame 27 of the press, and springs 28 are compressible between the frame 27 and heads of the pillars 26.

The springs 28 thereby bias the piston 1 8 upwardly to the position shown.

The spring 12 and the stem of the piston 10 pass with clearance through a transverse wall 30 in the cylinder 11. A sleeve 31 surrounds the spring 12 and extends sealingly between the wall 30 and the wall 1 6. An outer cylinder wall 32 combines with the sleeve 31 to define an annular cylinder 33 in which a fourth piston 34 is slidable.

Rods 35 are secured to the plate 25 and pass sealingly through the frame 27 and wall 1 6 to engage the piston 34. The piston 34 may be urged downwardly by air pressure from the source 13, under control of a suitable valve device 40. The effective area of the piston 34 is approximately 5.4 times that of the piston 18, so that the pressure in the source 1 3 is sufficient to urge the piston 34, and hence the piston 18, downwardly against the springs 28, even though the pressure at the source 1 3 applied directly to the piston 18 through the oil in the reservoir 21, would be insufficient to effect this downward movement.

The rate of downward movement during the approach stroke is effectively dependent on the rate of admission of air above the piston 34. Since the piston 34 has a smaller effective area than the piston 10, for a given rate of air admission the piston 34 will move downwardly faster than the piston 10. Moreover, movement of the piston 34 is transmitted directly to the crosshead 23, instead of experiencing the speed reduction inevitable between the pistons 10 and 1 8. The piston 34 thus provides a rapid approach stroke.

Nuts 36 engage a threaded portion of the frame 27 and are engageable by the plate 25 to provide a limit on the downward movement of the piston 1 8. Carried on the crosshead 23 is a guide rod 37 upon which an actuator 38 is slidable, the actuator being biassed towards engagement with the crosshead 23 by a spring 39. Downward movement of the crosshead 23 causes the actuator 38 to engage the upper of the nuts 36, and thereby to be moved upwardly relative to the rod 37. This upward movement of the actuator 38 causes the latter to co-operate with the valve 14 which is mounted on the plate 25. The position of the crosshead 23 at which the valve 14 is operated is dependent on the axial position of the nuts 36.The aforesaid actuation of the valve 14 causes the pressure from the source 1 3 to be applied to the piston 10, which moves the piston 1 5 downwards to shut off the bore 20.

Subsequent movement of the piston 1 8 is thus dependent on displacement of fluid within the chamber 1 7 by the piston 1 5. The position of the upper of the nuts 36 may thus be adjusted to change the point on the stroke of the piston 18 at which the fast approach ceases and the high force, slower working stroke starts.

Return of the piston 1 8 after the end of its downward working stroke may be assisted or hastened by admission of air under pressure to the cylinder 33 below the piston 34, the air pressure above the piston being vented during the return stroke. Supply and venting of air in the cylinder 33 is effected by the valve 40.

Claims

1. A fluid pressure operated press comprising a first piston, means for applying a first fluid pressure to said first piston, a second piston having an effective area less than that of said first piston and being coupled to said first piston for movement therewith, a chamber containing a second fluid, said second piston being slidable in said chamber to displace said second fluid, a third piston slidable in said chamber and having an effective area greater than that of said second piston, said third piston providing an output element for said press, a fourth piston operably connected to said third piston and having a larger effective area than said third piston, and means for applying a third fluid pressure to said fourth piston, to urge said third piston in an operating direction in which it is urged as a result of movement of said first piston under the influence of said first fluid pressure.

2. A press as claimed in claim 1 in which said first, second, third, and fourth pistons are axially aligned.

3. A press as claimed in claim 1 or claim 2 in which said fourth piston slidably surrounds said chamber.

4. A press as claimed in any preceding claim in which a part of said chamber is provided by a bore in said third piston.

5. A press as claimed in any preceding claim which includes a port for admitting said second fluid to said chamber during movement of said third piston by said fourth piston in said operating direction, said second piston being operable by said first piston to shut said port.

6. A press as claimed in any preceding claim in which said first and third fluid pressures are obtained from a common source, and which includes valve means, operable in a predetermined position of said third piston, for applying said first fluid pressure to said first piston.

7. A press as claimed in claim 6 which includes means for adjusting the predetermined position of said third piston to which said valve means responds.

8. A press as claimed in any preceding claim in which said fourth piston is double acting, and there is provided a further valve means for selectively applying said third fluid pressure to respective sides of said fourth piston.

9. A fluid pressure operated press, substantially as hereinbefore described with reference to and as shown in the accompanying drawings.