Hydraulic RAM assembly

Abstract

 A hydraulic ram assembly capable of providing a force varying over a wide range has a first ram with a fixed cylinder and a movable piston which is capable of supplying a force at the lower end of the range and a second ram with a fixed cylinder and a piston which is movable into engagement with the piston of the first ram to assist the first piston to thereby provide an increased load.

Description

[0001] This invention relates to an assembly of two hydraulic rams.

[0002] In certain industrial applications, it is desirable for a hydraulic ram assembly to provide a force varying over a very wide range. It is very difficult to design a single hydraulic ram which is capable of acting accurately and efficiently over a wide range of forces.

[0003] Accordingly, the present invention relates to an assembly of a first ram comprising a housing defining an open-ended cylinder, a piston displaceable in the cylinder and means for introducing fluid under pressure into the cylinder to displace the piston in the direction towards the open end of the cylinder; and a second ram comprising a housing defining a cylinder and a piston displaceable in the cylinder, characterised in that the cylinder of the second ram is in communication with the cylinder of the first ram through an opening in the housing of the first ram which is opposite the open end of the cylinder, means for introducing fluid under pressure into the cylinder of the second ram to displace the piston in the direction towards the opening and the piston of the second ram having an extension which projects through the opening in the housing and is engageable with the piston of the first ram.

[0004] Preferably, the engaging surfaces of the extension and the piston of the first ram are such as to permit limited relative inclination between the axis of the extension and the axis of the cylinder of the first ram.

[0005] Depending on the force which is to be developed, either the first ram only is employed or the two rams can be operated together.

[0006] Since the extension of the piston in the second ram is engageable with the piston of the first ram, but is not permanently connected thereto, when hydraulic fluid is introduced into the cylinder of the first ram, it acts against the full surface of the piston therein and it also acts against the extension to displace the piston in the second ram in the direction to separate the extension from the piston in the first ram. When only the first ram is being used, only one seal, i.e. that between the piston of that ram and the cylinder wall, is employed. This permits slight tilting between the piston and the cylinder wall.

[0007] With both cylinders in operation, there are three seals in use, the seals being positioned between the pistons and the walls of their respective cylinders and between the extension and the housing of the first ram.

[0008] In order that the invention may be more readily understood, it will now be described, by way of example only with reference to the accompanying drawing which is a diagrammatic section of a ram assembly according to the present invention.

[0009] In the arrangement shown in the figure, the ram assembly is used to displace a chock 1 of a rolling mill stand relative to a fixed housing 2 of the mill stand. An assembly according to the present invention is located in a recess 3 formed in the housing. The assembly consists of a housing 4 having a side wall 5 and an end wall 6 and together they define a cylinder 7 which is open-ended. A piston 8 having a wall seal 9 is displaceable in the cylinder 7 to constitute a ram.

[0010] Separate from, but mounted on this housing 4, there is a further housing 10 which has a slide wall 11 and an end wall 12 and together with the end wall 6 of the first ram they define a cylinder 13. A piston 15 is displaceable in the cylinder 13 to constitute a ram and there is a seal 16 between the piston 15 and the wall of the cylinder. The piston has an extension 17 which projects through an opening 18 in the end wall 6 of the housing 4 and there is a seal 19 between the extension and the wall of the opening.

[0011] The lower end of the extension projects into the cylinder 7 and is engageable with the adjacent surface of the piston 8. It is preferable for the end face of the extension 17 and the adjacent face of the piston 8 to be of convex and concave form, respectively, so that limited inclination can take place between the piston 8 and the extension and there can be relative inclination between the longitudinal axis of the extension and that of the cylinder 7.

[0012] The part of the cylinder 13 which is between the piston 15 and the wall 6 of the housing 4 is kept open by way of a permanent connection 20 to drain. The part of the cylinder 13 above the piston 15 is connected by a fluid line to a port on a solenoid valve 21 and the cylinder 7 is also connected to a port on the solenoid valve 21 by a fluid line. In the arrangement shown, the solenoid valve has a connection from a controllable hydraulic source 22 directly to the cylinder 7 and the part of the cylinder 13 above the piston 15 is connected through the solenoid valve to drain. In this way, the hydraulic fluid supplied to the cylinder 7 causes a force to be applied to the piston 8, and the piston 15 is forced upwardly to the top of its cylinder so that it is not in contact with the piston 8 by the force of the fluid acting on the extension 17. Thus, the force of the fluid in the cylinder 7 acts over the entire surface of the piston 8. When the solenoid valve 21 is connected in its opposite operating position, fluid under pressure is supplied to the cylinder 7 and to the cylinder 13 above the piston 15 and, hence, the extension 17 is forced downwardly into engagement with the piston 8 to provide a combined force acting on the chock 1. It will be seen, therefore, that either the ram consisting of the piston 8 in the cylinder 7 can be brought into operation on its own, or it can be in operation along with the piston 15 in the cylinder 13, thus providing a much greater force on the chock 1.

[0013] Even when both rams are in operation, the extension 17 can be inclined slightly with respect to the axis of the piston 8. When both rams are in . operation, there are three seals in use, but the seal friction is not so critical when large operating forces are being produced.

[0014] Various forms of transducers (not shown) can be employed to give an indication of the relative positions of the pistons with respect to the fixed mill housings 2.

Claims

1. An assembly of a first ram comprising a housing (4) defining an open-ended cylinder (7), a piston (8) displaceable in the cylinder and means for introducing fluid under pressure into the cylinder to displace the piston in the direction towards the open end of the cylinder;
and a second ram comprising a housing (10) defining a cylinder (13) and a piston (15) displaceable in the cylinder, characterised in that the cylinder of the second ram is in communication with the cylinder of the first ram through an opening (18) in the housing (4) of the first ram which is opposite the open end of the cylinder, means for introducing fluid under pressure into the cylinder of the second ram to displace the piston in the direction towards the opening and the piston of the second ram having an extension (17) which projects through the opening in the housing and is engageable with the piston (8) of the first ram.

2. An assembly as claimed in claim 1, characterised in that the piston (8) of the first ram is provided with one peripheral seal (9) which permits limited tilting of the piston relative to the cylinder (7).

3. An assembly as claimed in claim 1 or 2, characterised in that the surface of the extension (17) which is engageable with the piston (8) of the first ram is of convex form and the corresponding surface of the piston (8) is of concave form thereby permitting limited inclination between the axis of the extension and that of the piston.

4. An assembly as claimed in claim 1, 2 or 3, characterised in that it includes control valve means (21, 22) which permits fluid to be supplied to the cylinder of the first ram and optionally to the cylinder of the second ram.

5. An assembly as claimed in claim 2, characterised in that there is one peripheral seal (19) between the extension and the wall of the housing which defines the opening and one peripheral seal (16) on the piston of the second ram.