US2323770A - Hold-down means for shears and the like - Google Patents

Description

July 6, 1943- M. w. HAZELTON HOLD-DOWN MEANS FOR SHEARS AND THE LIKE Filed Nov. 3, 1942 2 Sheets-Sheet l INVENTOR. 64125. ra/v.

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HOLD-DOWN MEANS FOR SHEARS AND THE LIKE Filed Nov. 3, 1942 2 Sheets-Sheet 2 r I IIIIIIIII/ I4 VIII ll .FJQJ.

INVENTOR. B Ma qlu W #4227. TOM

ATTORNEYS.

Patented July 6, 1943 Merrill W. Hazelton,

Cincinnati, Ohio, assignor to The Cincinnati Shaper Company, Cincinnati,

Ohio, a corporation of Ohio Application November 3, 1942, Serial No. 464,349

12 Claims.

Hydraulic hold-downs for jshears and .the like have been provided in accordance with Patent No. 1,881,185 to R. T. Hazelton. The purpose of these hold-downs is to clamp the work and hold it against movement while it is being sheared or otherwise operated upon. Broadly, these holddown means comprise a series of smallhydraulic cylinders with downwardly directed plunger means, mounted above the work table of the machine. The cylinders are connected together and to an hydraulic pressure device mounted on the frame of the machine. In this device there is a body of oil forming a reservoir, and a pressure cylinder which is connected to the first mentioned hydraulic cylinders. The piston of the pressure cylinder is arranged to be actuated in some suitable fashion, as by a cam on the main shaft of the machine. Thus when the shear head descends, the hydraulic cylinders are subjected to pressure, and their plungers clamp the work against the work table. On the upstroke of the shear head, or when the shear is not operating, the hydraulic cylinders are relieved of pressure; their plungers may be returned by springs; and the work is free to be moved about on the work table as the operator desires. The hydraulic pressure device also contains a relief valve to eliminate excessive pressures.

My present invention provides improvements on the means just described. It is an object of my invention to provide hold-down means which are silent, though positive in operation, and to provide means which are safe because the operator cannot get his fingers under the hold-downs.

It is my object to provide a hold-down means which is leak proof, and which will not deposit oil on the work or on the work table.

It is my object to provide a hold-down which operates without impact. When this is accomplished, the hold-down devices do not mar the work, nor do they produce a vibration likely to displace the work. Thus more accurate cutting can be accomplished, and the shear can handle polished sheets of, say, aluminum or stainless steel, without scratching or marking the sheet surfaces.

It is my object to provide hold-down devices of simpler mechanical construction in that they do not contain-parts subject to significant wear. Thus my means are not subject to disorder requiring repair and replacements.

It is an object of my invention to provide a hold-down means having a greater possible stroke but requiring a very small volume of oil to make them clamp the work.

These and other objects of my invention which will be set forth hereinafter or will be apparent to one skilled in the art upon reading these specifications, I accomplish by that certain construction and arrangement of parts of which I shall now describe an exemplary embodiment. Reference is made to the drawings forming a part hereof, and in which:

Figure 1 is a front elevational view of a shear equipped with my hold-down means.

Figure 2 is a vertical section taken through one of my hydraulic cylinders.

Figure 3 is a. vertical sectional view of the lower portion thereof taken along the line 3-3 of Figure 2.

Figure 4 is a similar view, but showing the device in work engaging position.

Figure 5 includes a vertical sectional view of the pressure device taken along the line 5-5 of Figure 1. and one of the hydraulic cylinders, .to show the connections. draulic system in unloaded condition.

Figure 6 is a partial sectional view showing the pressure means in loaded condition.

Figure 7 is a partial sectional view of the pressure device showing the operation of the relief valve.

In Figure 1, I generally indicates a shear as an exemplary apparatus to which my hold-downs may be applied. A series of hydraulic cylinders 2 are mounted above the work table 4. These cylinders are interconnected by a feed line 6 and a return or leakage line 'I. These lines are connected to a by-pass valve 8, and through it to a pressure device 9. These elements will hereinafter be described in detail. The particular con-- struction of the shear mechanism does not constitute a limitation on the invention and will not be set forth. My hold-down means may also be used with machines other than shears.

Each of my hydraulic cylinders has a casing or body I0, preferably provided at the top with means II by which it may be attached to the overhead framework of the shear I. I prefer to form integral with the casing portions of the feed line 6 as at II, I I. These portions-of successive cylinders may be connected together or to a conduit as by means of a coupling as shown at I3 in Figure 5. I

The casing is otherwise in the form of a cylinder in which a piston I6 moves in a short path. Below the path of travel of the piston the cylinder has the overflow or leakage conduits attached to it a at I4. These may-be coupled together to form the conduit I of Figure 1. A piston rod I1 is attached to the piston I6. I provide a flexible but leak proof connection between the piston and the cylinder. This is in th form of a bellows or flexible corrugated tube I8. One end of the tube is caught between a shoulder on the piston rod and the piston I6. The piston rod has a smaller extension I la. which passes through. a perforation in the piston, and is threaded to accept a nut I9. The nut clamps the piston, piston rod, and the upper end of the bellows together in The figure shows the hy-.

a leak proof connection. At the lower end of the bellows it is attached to a collar 20 in a leak proof manner. This collar has a press fit in the restricted lower end |(|a of the casing. The piston rod operates through the collar 28. By this construction, I obviate both a packing gland where the piston rod emerges from the casing, and the necessity of a gasket, ring or the like on the piston. The piston it may indeed have a relatively loose fit in the cylinder of the casin allowing very free up and down movement. Any oil which leaks past the piston cannot get out of the cylinder, and is returned through the conduit I.

The top of the casing may be closed by a plug l2 of such size as to permit the introduction of the operating parts in assembling the cylinders.

The piston rod I1 is preferably slotted as at 2 and a set screw 22, riding in the slot, prevents rotary motion of the piston rod.

Beyond the casing Hi, I fit my piston rods with hold-down feet 23. These preferably have a relatively broad flat portion conforming to the work table 4, and upturned edge portions. The pressure of the work against these upturned edge portions will serve to raise the feet when the hydraulic cylinders are not under pressure. I preferably omit the curved configuration of the feet 23 at the rear where they approach the lower shear knife i5. Figure 4 shows a piece of work 24 clamped for shearing by the knives I5 and 25.

In Figure 5, the pressure conduit 6 and the leakage conduit I are shown connected to the hollow interior 26 of the by-pass valve 8. The leakage conduit is connected to the by-pass valve above the pressure conduit. The by-pass valve is connected as at 21 to the pressure mechanism. A plunger 28, actuated by a spring 29 operates in the hollow interior26 of the by-pass valve. When fluid under pressure is introduced through the connection 21, the plunger 28 rises against the compression of the spring connecting the 'conduits 21 and 6 together. A shoulder on the upper part 8a of the by-pass valve prevents the plunger from rising beyond the position shown in Figure 6. As soon however, as the pressure is relieved through connection 21, the plunger 28 is driven by the spring 29 to the position shown in Figure 5. This results in the immediate connection of the pressure line 6 to the leakage line 1 and 53 through the by-pass valve, and the instantaneous de-energization of the hydraulic cylinders.

The pressure device 9 has a base 38 in which there is formed a pressure cylinder 3| and a passageway 32 in communication with the connection 21 to the by-pass valve. A second passage- .way 33 connects the pressure cylinder with a relief valve cylinder 34. A third passageway 35 branches into the passageway 33. At this point I locate a valve seat for a ball check valve 36, which may be retained by a plug 31. The other end of the passageway 35 opens above the base 30.

To the base 30 I attach housing means 38, 39. These not only serve to house the pressure and relief mechanisms, but the lower of them at least has a liquid tight connection with the base 30. so that it forms a reservoir in which a supply of oil may be retained as at 40.

The pressure cylinder 3| has a piston 4| which may be actuated in any desired manner. In the exemplary embodiment I have indicated at 42 an extension of the main shaft of the shear or a shaft driven in synchronism with the shaft which operates the shear ram. Within the housing 38 this shaft extension has a cam 43 keyed to it. The cam operates the piston 4| through a cam follower roller 44 mounted on the piston. In the cylinder 3| I may provide a compression spring 45 tending to raise the piston and keep the cam follower in contact with the cam. The pressure cylinder 3| may, if desired, be provided with ports 46 located above the upper end of the useful stroke of piston 4|, to lubricate the piston rod and the walls of the cylinder. This, however, is not necessary, especially where, as can readily be accomplished, the level of the oil 48 in the reservoir is normally maintained above the top of the pressure cylinder 3|.

It will be evident that as the piston 4| is driven downwardly under power, pressure will be built up beneath it and transmitted to the hydraulic cylinders through the by-pass valve and the pressure line 6.

The relief valve cylinder 34 is provided with a plunger 41 to which I attach a flanged cup shaped member 48. The walls of this member lie outside the walls of the cylinder 34, and the flange forms an abutment for a heavy compression spring 49. A head 58 held to the base 3|! by bolts 5| (one of which is shown) forms the other abutment for the spring. The relief valve cylinder 34 is provided with ports 52 to allow the excess volume of oil to escape. The relief valve is shown in the actuated position in Figure 7. The spring 49 is heavy enough to resist the desired effective pressure in the system. The relief valve plunger operates at every stroke of the shear, first moving up to the position shown in Figure 7, allowing the excess oil to escape, then settling down to the position shown in Figure 6 for the rest of each pressure cycle. The relief valve plunger settles slightly below ports 52 to make up for leakage past pistons 4| and ii; and plunger 41. Since the hold-down feet 23 are always in contact with either the table or the work piece, only a very small volume of oil is needed to make them clamp the work piece. The displacement of the piston 4| is constant for each cycle and almost all of the oil displaced is forced out through the relief valve ports 52. Oil is taken in through the ball check valve 38 on the up stroke of piston 4| to make up for the oil forced out through relief valve.

I prefer also to connect the leakage line I with the pressure device 9 by a small conduit 53, which enters the pressure device casing and is so dis posed that its end lies below the level of the oil 40. This permits the oil in the leakage line 1 to return quickly to the reservoir and also permits the necessary flow of oil when the hold-down plungers are raised by the work piece.

Finally, at the far end of the pressure line I prefer to provide a valve 54 which is connected by a small conduit 55 to the pressure device 9. This enables me rapidly to get rid of any air which may enter the system, by opening this valve and operating the hold-down mechanism through a few cycles.

It will be seen that my system is silent in operation. The shape of the feet on my hold-downs is such that the work can raise the hold-down plungers to the required height. The by-pass valve immediately de-energizes and relieves the pressure on the hydraulic hold-down cylinders as soon as the piston 4| begins to rise. Yet I do not have to provide springs for the return of my holddown plungers. Thus, although the work is freed immediately upon the relief of pressure, the holddown feet may remain at all times in contact with any work which may be under them. In clamping the work, the hold-down plungers do not have to move through a substantial distance before contacting the work. Hence the operation of clamping does not involve impact. The work may thus be more accurately measured, positioned and cut. The act of clamping does not tend to displace the work. Moreover, since there is no impact. the hold-downs do not tend to mark the work.

The operation of the system is automatic in its adjustment to various thicknesses of work. It is also leak proof.

Modifications may be made in my exemplary structure without departing from the spirit of my invention. Having thus described my invention in an exemplary embodiment, what I claim as new and desire to secure by Letters Patent is:

1. In a hold-down device, a cylinder, a piston in said cylinder, a piston rod attached to said piston and passing through one end of said cylinder, and a flexible, leak proof means connecting said piston and the end of said cylinder through which said piston rod passes, said cylinder having a connection for fluid under pressure at one side of the path of movement of said piston, and a connection for leakage fluid at the other side, and a presser foot having up-curved edge portions, attached to said piston rod.

2. The structure claimed in claim 1 including means for preventing the rotation of said piston rod in said cylinder, said presser foot having an irregular shape.

3. In a hold-down device, a cylinder, a piston in said cylinder, a piston rod attached to said piston and extending through one end of said cylinder, a source of fluid under pressure, a line connecting said source with said cylinder above said piston, a leakage line for fluid connected to said cylinder below said piston, and an automatically acting valve for connecting said pressure line with said leakage line upon relief of pressure in said pressure line.

4. In a hold-down device, a cylinder, a piston in said cylinder, a piston rod attached to said piston and extending through one end of said cylinder, a source of fluid under pressure, a line connecting said source with said cylinder above said piston, a leakage line for fluid connected to said cylinder below said piston, and an automatically acting valve for connecting said pressure line with said leakage line upon relief of pressure in said pressure line. a reservoir for fluid, a connection between said reservoir and said source, and a connection between said leakage line and said reservoir.

5. The structure claimed in claim 4 wherein said cylinder includes a flexible, bellows tube connection between said piston and the end of said cylinder through which said piston rod passes.

6. In a hold-down mechanism, a pressure device having a base configured to provide a pressure cylinder and a relief valve cylinder, a passagewa connecting said cylinders and a pressure line. and a check valved feed passageway, a spring actuated relief valve plunger in said relief valve cylinder, a power actuated plunger in said pressure cylinder, means above said base for holding fluid to provide a reservoir, an hydraulic cylinder, a pressure connection between said cylinder and the first mentioned passageway in said base, and a leakage connection between said cylinder and said reservoir. l

7. In a hold-down mechanism, a pressure device having a base configured to provide a pressure cylinder and a relief valve cylinder, a passageway connecting said cylinders and a pressure line, and a check valved feed passageway, a spring actuated relief valve plunger in said relief valve cylinder, a power actuated plunger in said pressure cylinder, means above said base for holding fluid to provide a reservoir, an hydraulic cylinder, a pressure connection between said .cylinder and the first mentioned passageway in said base, and a leakage connection between said cylinder and said reservoir, and a by-pass valve connecting said pressure line and said leakage line and having a plunger automaticall acting to disconnect. said pressure line and said leakage line upon the application of pressure, and to open the one line into the other immediately upon the cessation of pressure.

8. The structure claimed in claim '7 in which said hydraulic cylinder has a piston with a piston rod passing through one end of said cylinder, and in'which there is a flexible bellows tube connecting said piston and the end of said cylinder throughwhich said piston rod passes.

9. In a hold-down device, a casing shaped to provide a cylinder, a pair of tubular connections into said cylinder near one end thereof, a pair of tubular connections into said cylinder at a point removed from the first mentioned connections, a piston having a path of travel lying between said pairs of connections, a piston rod connected to said piston and passing through one end of said cylinder, a flexible bellows tube engaged at one end between said piston and piston rod, and a collar having a fluid tight connection with said bellows tube, and having a press fit in the open end of said cylinder, said piston rod passing through said collar.

10. In a shear or like mechanism having a work table and an upper framework, hold-down means comprising a series of hydraulic cylinders attached to said upper framework, said cylinders having pistons, piston rods attached to said pistons and passing through the lower ends of said cylinders, presser feet having up-curved edges. on said piston rods, a pressure line connected to said cylinders above said pistons, a leakage line connected to said cylinders below said pistons. a source of fluid under pressure, a connection between said source and said pressure line including a by-pass valve to which said leakage line is also connected, and automatically acting means in said by-pass valve for interconnecting said lines for the passage of fluid upon relief of pressure from said source.

11. The structure claimed in claim 10 in which the presser feet normally rest on the work table, and in which the source of fluid under pressure is actuated by operation of the shear or like mechanism, there being a relief valve in the system whereby the stroke of said pistons can accommodate itself to work pieces. of varying thickness.

12. The structure claimed in claim 10 in which the presser feet normally rest on the work table, and in which the source of fluid under pressure is actuated by operation of the shear or like mechanism, there being a relief valve in the system whereby the stroke of said pistons can accommodate itself to work pieces of varyin thickness, said cylinders each having a flexible fluid tight connection between their pistons and the ends of the cylinders through which said piston rods pass.

MERRILL W. HAZEL-TON.

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