FORCE APPLICATOR

Abstract: A force applicator comprises a ram operable by fluid under pressure. A pressure pad (7) is located between one movable part of the ram (3) and the load (9) and means are provided which enable relative movement to take place between the pressure pad and the ram in a direction at right angles to the direction of operation of the ram. The means may take the form of a fluid chamber (15) between the pressure pad and the ram or a disc of PTFE between them.

Description: FORCE APPLICATOR Rams operable by fluid pressure are employed in many industrial applications in order to apply a force, usually between a rigid foundation and a load plate. The ram consists basically of a piston displaceable in a cylinder with a part projecting from one end of the cylinder and, in use, either the cylinder bears against a rigid foundation and the piston is displaced to apply force to the load plate, or the piston bears against the rigid foundation and the cylinder is displaceable to apply a force against the load plate. In some applications it is desirable to slide the load plate relative to the part of the ram against which it abuts. This is usually impossible to attain once pressure has been applied to the ram. According to the present invention, a force applicator comprises a ram having a cylinder, a piston displaceable in the cylinder with a part projecting from one end of the cylinder, and means for introducing fluid under pressure into the cylinder to displace the piston; and a pressure pad abutting against either the end wall of the cylinder opposite the end from which the part projects or the end wall of the part projecting from the cylinder, said pressure pad being slideable with respect to the surface against which it abuts in a direction normal to the direction of movement of the piston. The force required to bring about relative movement between the ram and the pressure pad is conveniently less that 10% of the applied load. 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 drawings, in which:- Figure 1 shows diagrammatically the force applicator applied to a part of a rolling mill; Figure 2 shows an alternative embodiment of the invention applied to a rolling mill; and Figure 3 shows an alternative form of pressure pad. Referring to Figure 1, a hydraulically operable ram comprises a piston 1 displaceable in a cylinder 3 and having a part which projects out of the cylinder. To displace the piston, fluid is introduced into the cylinder chamber 5 by means (not shown) . An outer wall surface 6 of the cylinder 3 extends transverse to the direction of relative movement between the piston and the cylinder and a pressure pad 7 bears against this surface. The opposite surface of the pressure pad bears against a load plate 9 which forms a chock for rotatably supporting one end of the roll of a rolling mill. The pressure pad 7 is centred relative to the cylinder 3 by actuating means such as springs 11 or hydraulic means within an annular bracket 13 on the underside of the cylinder 3. The surface of the pad 7 which is adjacent the surface 6 of the cylinder is recessed over its central portion and the space 15 defined by the walls of the recess and the surface 6 of the cylinder is in communication with the chamber 5 by way of a bore 17 extending through the wall of the cylinder. Alternatively, the surface of the pad may be flat and the surface 6 of the cylinder having a recess therein. In use, the force applicator is positioned between the load plate 9 and a rigid foundation 19 and fluid is introduced into the chamber 5 of the ram in order to apply a load between the foundation and the load plate 9. The area of the space 15 between the pressure pad and the cylinder is approximately 80% of the area of the chamber 5 and, if the same fluid pressure exists in the chamber 5 and the space 15, the force between the pressure pad and the cylinder is considerably reduced and, by suitable selection and lubrication of the sliding surfaces, a coefficient of friction of about 0.2 between them can be achieved. This means that the side force required on the pressure pad 7 to displace it transverse to the line of action of the load exerted by the ram is approximately 4% of this load. A limited transverse movement of the pressure pad 7 is caused by movement of the load plate 9 transverse to the line of action of the force applied by the ram. In the arrangement shown in Figure 2, the cylinder 21 of the ram defines a chamber 22 in which the piston 23 is displaceable. The ram is mounted on a rigid foundation 25 and a pressure pad 27 is located between the outer surface 28 of the piston and a load plate 29 which may constitute a chock for rotatably mounting one end of the roll of a rolling mill. The upper surface 28 of the piston is of concave spherical form and the adjacent surface of the pressure pad 27 is of corresponding convex form. A recess 30 is formed in the upper surface of the piston and this recess is in communication with the chamber 22 of the cylinder by a bore 31 extending through the piston. Again, the area of the recess 30 is conveniently 80% of the area of the chamber 22.and the sideways force required to bring about tilting of the pressure pad 27 with respect to the piston 23 is approximately 4% of the load applied by the ram between the rigid foundation 25 and the load plate 29. In an alternative arrangement the space 15 or recess 30 is not in communication with the interior of the cylinder but is connected to a separate external source of fluid under pressure. Referring to Figure 3, the underside of a cylinder 41 has a pressure pad 43 secured to it. The pad comprises a substantially circular plate 45 having a pair of notches 47 formed in a pair of opposite edges. At the notches, the edges of the plate 45 are stepped. The plate is secured to the underside of the cylinder by a pair of brackets 49 which fit into the notches and are bolted to the underside of the cylinder. The inner edges 51 of the brackets are also stepped and the steps on the brackets fit underneath the steps on the plate 45. Spring loaded plungers, indicated generally by reference numeral 53, are located in the brackets 49 and bear against the plate 45 to centralise the plate with respect to the brackets. The upper surface of the plate 45 has a central recess containing a disc of PTFE 55 and an outer channel adjacent the edge of the plate containing an '0' ring 57. The coefficient of friction between the PTFE disc and the adjacent surface of the cylinder is of the order of .007 at a pressure of 280 bar. This means that, when the load applied to the plate 45 due to the action of the piston-cylinder device is of the order of 100 tons, a force of only 7 tons will cause transverse movement of the plate 45 with respect to the cylinder. The disc 55 may be of composite form with a re-inforced PTFE outer edge surrounding a disc of virgin PTFE. As an alternative to PTFE, other low coefficient friction material may be used. In the arrangements described above, the direction of movement of the piston or cylinder has been generally vertical but the free applicator can be used so that the direction of movement of the piston/cylinder is generally horizontal. An application for such an arrangement is the use of the applicator to control the vertical edger rolls of a rolling mill.

Claims: Claims: 1. A force applicator comprising a ram having a cylinder, a piston displaceable in the cylinder with a part projecting from one end of the cylinder, and means for introducing fluid under pressure into the cylinder to displace the piston; and a pressure pad abutting against either the end wall of the cylinder opposite the end from which the part projects or the end wall of the part projecting from the cylinder, said pressure pad being slideable with respect to the surface against which it abuts in- a direction normal to the direction of movement of the piston. 2. A force applicator as claimed in claim 1, in which the pressure pad comprises a plate retained against said wall by support means which permit limited movement of the plate in said direction. 3. A force applicator as claimed in claim 2, in which the plate is retained against said wall by means including actuating means which cause the plate to take up a predetermined position relative to the end wall when no load is applied to the plate by the action of the ram. 4. A force applicator as claimed in claim 2 or 3, in which the face of the plate which abuts against the end wall or the end wall is recessed to form a space which is in communication with a source of fluid under pressure. 5. A force applicator as claimed in claim 4, in which the space is in communication with the interior of the cylinder. 6. A force applicator as claimed in claim 1, 2 or 3, in which the surface of the pressure pad which abuts against said end wall is constituted at least in part by low friction material such as PTFE. 7. A force applicator as claimed in claim 6, in which the PTFE material is in the form of a disc retained on the pad. 8. A force applicator as claimed in claim 7, in which the disc comprises an annular ring of re-inforced PTFE surrounding virgin PTFE. 9. A force applicator as claimed in any preceding claim, in which the abutting surfaces of the plate and said wall are of arcuate form.

Inventors: BATHORY BELA ISTVAN, BATHORY, BELA, ISTVAN
Applicants: DAVY MCKEE SHEFFIELD, DAVY MCKEE (SHEFFIELD) LIMITED
Application year: 1990
Main classification: E02D27
IPC codes: B21B31, E02D27