US3561252A

US3561252A - Presses

Info

Publication number: US3561252A
Application number: US796815A
Authority: US
Inventors: Hubert Veare Norton; Leslie Buckingham Norton; Douglas Edwin Norton
Original assignee: Norton Tool Co Ltd
Current assignee: Norton Tool Co Ltd
Priority date: 1968-02-08
Filing date: 1969-02-05
Publication date: 1971-02-09
Anticipated expiration: 1988-02-09
Also published as: DE1906223A1; FR2001521A1; JPS5014392B1; CH486988A; GB1181941A

Abstract

A C-FRAME PRESS IN WHICH GAPING OF THE GAP DUE TO THE PRESSING FORCE IS MINIMISED BY PROVIDING A TIE-BAR ACROSS THE GAP ASSOCIATED WITH TENSIONING MEANS WHICH APPLY TO THE TIE-BAR A TENSION SUBSEQUENTLY PROPORTIONAL TO THE PRESSING FORCE.
D R A W I N G

Description

' I- H. v. NORTON ETAL 3,561,252

PRESSES 2 Sheets-Sheet l Filed Feb .1969

United States Patent Oihce US. Cl. 72455 9 Claims ABSTRACT OF THE DISCLOSURE A C-frame press in which gaping of the gap due to the pressing force is minimised by providing a tie-bar across the gap associated with tensioning means which apply to the tie-bar a tension substantially proportional to the pressing force.

This invention relates to presses of what may be termed the open-frame or C-frame type. The invention will be described for convenience in relation to upright presses in which a forwardly projecting lower portion of the frame supports a fixed press tool, while an overhanging upper portion of the frame carries a vertically movable press tool actuated by a crank mechanism or a hydraulic ram. It is to be understood, however, that the invention is applicable to presses of the C-frame type generally, irrespective of whether the motion of the movable press tool is vertical, horizontal or inclined.

In a press of the C-frame type the reaction to the pressing force applies a bending moment to the frame which tends to cause the gap of the C to widen or gape. This may produce misalignment of the press tools or other disadvantages.

Also, when the pressing force is released the elasticity of the frame causes the gap to narrow again but the inertia of the frame causes the gap to narrow too much so that a reversed bending moment is applied. The elasticity of the frame then widens the gap again, and so on, the frame vibrating at its natural resonant frequency until the energy stored in the frame by the initial bending has been dissipated. This vibration not only wastes energy but also causes noise, wear and inaccuracy.

According to the present invention, a press of the C- frame type is provided with at least one tie-rod across the gap of the frame and tensioning means adapted to apply to the tie-rod a tensile force substantially proportional to the pressing force.

Thus gaping of the frame is wholly or substantially eliminated and the above-mentioned disadvantageous effects of misalignment and vibration are minimised.

In one form of the invention one end of the tie-rod is attached directly to the frame above or below the gap and the other end of the tie-rod is attached to the frame below or above the gap indirectly through the tensioning means. In the case of a hydraulic press the tensioning means may be connected to a high pressure part of the hydraulic system of the press. Thus, as the pressure in the hydraulic system rises, the pressure in the hydraulic tensioning means rises also and applies an increasing tension to the tie-rod. In the case of a mechanical crank press the hydraulic tensioning means could be actuated by means of a source of hydraulic pressure such as a high pressure pump which supplies fluid to the tensioning means at a pressure determined by load-sensing means associated with the crank mechanism.

If the tie-rod were omitted, the pressing force would cause the frame to gape by elastically bending the frame Patented Feb. 9, 1971 about an imaginary centre somewhere to the rear of the gap, the position of this centre depending upon the geometry of the frame. Preferably, in the case of a hydraulic press, the ratio between the effective pressurised area of the hydraulic tensioning means and the effective area of the hydraulic ram is substantially equal to the inverse ratio between the respective distances of their axes of operation from the said centre. In this way the bending moment produced on the frame by the hydraulic pressing force is substantially counterbalanced by the bending moment produced in the opposite direction by the hydraulically tensioned tie-rod.

In one form of the invention, the tensioning means comprises an annular hydraulic piston and cylinder arrangement, one end portion of the tie-rod passing through this annular arrangement and the annular piston bearing against a collar or shoulder at this end of the tie-rod. The other end of the tie-rod may be attached to the frame directly in a quickly detachable manner. This permits 20 the latter end of the tie-rod to be quickly detached and the tie-rod moved out of the way by withdrawing the tie-rod through the tensioning means, to facilitate access to the gap of the press, for example, when setting up the press tools.

Alternatively, one end of the tie-rod may be directly attached to the frame in a quickly detachable manner and the tensioning means may be pivotally attached to the frame to enable the tie-rod to be swung clear of the gap, when not under tension, without removing it from the 30 tensioning means.

In another form of the invention the tensioning means act upon the rear end of a lever the front end of which is pivoted to the front portion of the frame below or above the gap, one end of the tie-rod being connected to 35 an intermediate point of the lever and its other end being connected to the frame above or below the gap. This arrangement enables a smaller tensioning means to be used, advantage being taken of the leverage to increase the tensioning force. It also has the advantage that the 4.0 end of the tie-rod connected to the lever is disposed further to the rear than would otherwise be possible, to afford access to the gap without having to remove or displace the tie bar.

In the case of a hydraulic press, a pressure line may connect the high pressure side of the ram with the hydraulic tensioning means so that the force applied to the tie-rod by the tensioning means is directly proportional to the pressing force.

The invention may be performed in various ways and some specific embodiments will now be described by way of example wth reference to the accompanying diagrammatic drawings, in which:

FIG. 1 is a side view of a C-frame press of the hydraulic ram type, shown partly in section;

FIG. 2 is a fragmentary section showing one arrangement for the connection of the tie-rod to the tensioning means and to the frame;

FIG. 3 is a fragmentary cross-section taken on the line III-1II in FIG. 2;

FIG. 4 is a diagrammatic view of an arrangement having a pivoted tensioning means;

FIG. 5 shows another embodiment, employing a lever;

FIG. 6 is a side view of a further embodiment in which the press operates by a crank mechanism; and

FIG. 7 is a view similar to FIG. 3, showing another form of attachment of the tie-rod to the frame.

Referring to FIG. 1, there is shown a C-frame press 10 of the hydraulic ram type. The frame 11 of the press is generally in the form of a letter C, having a gap 12 in which the pressing operation takes place. The lower portion 13 of the frame below the gap carries a fixed press tool 14 on which is placed a workpiece 15 to be subjected to the pressing operation. The upper portion 16 of the frame above the gap accommodates the hydraulic ram mechanism. This comprises a cylinder 17 in which can slide a piston 18 connected to a piston rod 19 which passes out through the lower end of the cylinder 17 through a seal 20. At the lower end of the piston rod 19 is fitted a movable press tool 21. The piston 18, piston rod 19 and movable press tool 21 are forced downwards to perform the pressing operation by means of high pressure hydraulic fiuid admitted through a line 23 to the cylinder 17 below the piston 18. The hydraulic system for raising and lowering the piston is conventional and is not further illustrated or described.

If the press as so far described were operated to perform a pressing operation, the reaction to the downward force exerted on the press tool .21 by means of the

hydraulic ram parts

17, 18 and 19 would produce a bending moment on the frame 11 about an imaginary centre 24 somewhere to the rear of the gap 12, tending to enlarge the gap. This would have two adverse effects. In the first place the bending of the frame could cause some misalignment of the working parts with consequent wear, and of the press tools with consequent inaccuracy. Secondly, the elasticity of the frame would tend to cause it to virbrate at its natural resonant frequency, as already described.

The additional parts provided in accordance with the invention and now to be described minimise these adverse effects.

Secured to the front of the lower portion 13 of the frame is a bracket 25. Pivotally attached to the bracket 25 by means of a pin 26 is a tie-rod 27 which extends across the gap 12. The upper end of the tie-rod 27 is connected to the upper portion 16 of the frame through tensioning means 28. The tensioning means illustrated in FIG. 1 comprises a hydraulic cylinder 29 containing a piston 30 fixed to the upper end of the tie-rod 27. The tie-rod 27 passes through the lower end wall of the cylinder 29 and is sealed by means of a seal 31. A conduit 32 connects the cylinder space below the piston 30 of the tensioning means to the cylinder space above the piston 18 of the hydraulic ram. Thus, when the hydraulic ram is on its working stroke and the space above the piston 18 is under pressure, this pressure is transmitted through the conduit 32 to the under-side of the piston 30 so that the tie-rod 27 is placed under tension, this tension opposing the hydraulic ram force which would otherwise tend to widen the gap 12 as already described.

The axis 33 of the hydraulic ram and the axis 34 of the tie-rod are respectively at distances A and B from the parallel axis 35 through the centre of bending 24. The leverage by which the tension in the tie-rod 27 opposes the leverage of the hydraulic ram tending to produce the bending is in the ratio B/A. By making the areas of the

pistons

30 and 18 in the inverse ratio A/B, the bending effect produced by the hydraulic ram is substantially neutralized by the tension in the tie-rod. Thus, bending of the frame does not occur and the adverse effects which would otherwise arise are minimised.

As the tie-rod 27 is in front of the gap 12 its presence may reduce accessability to the workpiece and press tools. To facilitate access to the gap, the tie-rod may be made removable as shown in FIGS. 2 and 3. For this purpose the tensioning means is in the form of an annular cylinder 41, the cylinder containing an annular piston 42. The upper end of the tie-rod 37 passes through the hollow interior space 43 of the cylinder 41 and is provided at its :upper end with a collar or shoulder 44. The piston 42 bears against the underside of the collar or shoulder 42, being provided for this purpose with a tubular extension or sleeve 45. The cylinder space below the piston 42 is connected to the conduit 32.

At the lower end of the tie-rod 37 there is an annular groove 46 which fits into a slot 47 in a bracket 48. The width of the slot 47 is narrower than the diameter of the tie-rid 37, so that the tie-rod is restrained against vertical movement relative to the bracket 48. When it is desired to remove the tie-rod, while it is not under tension, it is swung forward slightly until the annular groove 46 is clear of the slot 47 in the bracket. The clearance in the interior space 43 of the tensioning means is suflicient to permit this. The tie-rod can then be withdrawn upwardly through the interior space 43. After the press tools have been set up, the tie-rod is replaced by reversing the procedure.

A modified form of attachment for the lower end of the tie-rod is shown in FIG. 7. Instead of being provided with an annular groove 46 as shown in FIGS. 2 and 3, the lower end of the tie-rod 54 has a pair of lugs 49 which ordinarily lie beneath side portions 50 of the bracket 51. When it is desired to remove the tie-rod 54, while not under tension, it is rotated through 90 so that one of the lugs is in register with a gap 52 in the bracket behind the tie-rod while the other lug is in register with a gap 53 in front of the tie-rod. The tie-rod 54 can then be removed by raising it through the hollow interior space 43 of the tensioning means. Since the tie-rod does not have to be tilted, the clearance in the space 43 can be very small. If it is desired to remove the tie-rod 54 completely, the lugs 49 can be detachable, but generally sufficient accessability is obtained merely by raising the tie-rod.

Another arrangement for affording accessibility is shown in FIG. 4. This does not necessitate removing or raising the tie-rod. The lower end of the tie-rod 57 is attached to the lower portion of the frame in a readily detachable manner, such as already described with reference to FIGS. 2 and 3. In this case the tensioning means 28 is as shown in FIG. 1, but is attached to the upper portion of the frame by a pivot 55 so that when the lower end of the tierod 57 has been released the tensioning means and the tierod can be tilted sideways as shown in dotted lines in FIG.

4. The fluid conduit is a length of flexible piping 56 connected to some point in the high pressure part of the hydrauli ram system.

Another way of facilitating access to the gap 12 and to the parts therein is shown in FIG. 5. In this case the tensioning means 60 is secured to the rear of the frame 10, the cylinder space above the piston 61 of the tensioning means being connected to a high pressure part of the hydraulic ram system by a line 62. A piston rod 63 attached to the piston 61 of the tensioning means is connected to a pivot 64 at the rear end of a lever 65 the front end of which is pivoted at 66 to the side of the lower portion 13 of the frame. The arrangement is such that when the hydraulic ram is performing its working stroke under pressure, the tensioning means is tending to force the lever downwards about the pivot 66. Pivoted at 67 to the side of the upper portion 16 of the frame is an inclined tie-rod 68. The lower end of this tie-rod is pivoted at 69 to an intermediate point of the lever 65. Thus, the downward force on the lever imparted by the tensioning means 60 applies a tensile force to the tie-rod 68. The dimensions of the various parts described are such that the force tending to narrow the gap 12, applied by the upward reaction at the front end 66 of the lever 65 and the downward force applied at the pivot 67 by the tension of the tie-rod 68, substantially counterbalances the hydraulic ram force tending to widen the gap, so there is virtually no tendency for the frame to bend about the point 24.

FIG. 6 shows the application of the invention to a press 70 of the mechanical crank type. In this case the movements of the press tool 21 are provided by means of a rotary crank 71 the crank pin 72 of which is connected to the upper end of a connecting rod 73. The movable press tool 21 is mounted on the lower end of a slide member 74 which reciprocates in guides 75. The upper end of the slide member is connected to the lower end 76 of the connecting rod 73 through a load-sensing device 77. This device consists of a cylinder 78 connected to the lower end 76 of the connecting rod and containing a piston 79 connected to the upper end of the slide member 74. The cylinder space above the piston 79 contains hydraulic fluid which is put under pressure on the working stroke of the press.

Mounted on the lower portion 13 at the front of the press is a bracket 25 to which is connected a tie-rod 27 as shown in FIG. 1. Similarly, on the front of the upper portion 16 of the press there is provided tensioning means 28 as shown in FIG. 1. A flexible pipe 82 connects the upper cylinder space of the load-sensing device 77 to the lower cylinder space of the tensioning means 28. The pipe 82 thus transmits to the tensioning means a hydraulic pressure equal to that in the load-sensing device and therefore proportional to the pressing force. The dimensions are so selected that the tension in the tie-rod 27 substantially counterbalances the reaction of the mechanical pressing force.

Various modifications can be made to the constructions described. For example, the arrangement shown in FIG. 6 can utilise an electrical load-sensing device such as a strain gauge, connected through suitable electronic circuitry to any appropriate form of tensioning means, e.g. it could influence a pressure control valve of a hydraulic tensioning system. The tensioning means could be other than hydraulic, e.g. mechanical or pneumatic. There could be two or more tie bars and two or more tensioning means.

What we claim as our invention and desire to secure by Letters Patent is:

1. A press comprising a C-frame having a rear portion, a front upper portion and a front lower portion spaced by a gap from said front upper portion, means in one of said front portions to apply a pressing force to a workpiece inserted in said gap, at least one tie-rod extending across said gap, tensioning means, and an operative connection between said tensioning means and said tie-rod to apply to said tie-rod a tensile force substantially proportional to said pressing force.

2. A press according to claim 1 including first attachment means attaching one end of said tie-rod directly to one of said front portions of said frame, second attachment means attaching the other end of said tie-rod to said tensioning means, and means attaching said tensioning means to the other of said front portions of said frame.

3. A press according to claim 1 including a lever having a front pivot, a rear pivot and an intermediate pivot, means connecting said tensioning means to said rear pivot, said front pivot being connected to one of said front portions of said frame, said intermediate pivot being connected to one end of said tie-rod, and the other end of said tierod being connected to said other front portion of said frame.

4. A press according to claim 2 in which said tie-rod has a shoulder at one end, said tensioning means comprises an annular piston and an annular hydraulic cylinder. said end of said tie-rod passing through said annular piston and cylinder with said annular piston bearing against said shoulder, and said first attachment means is quickly detachable.

5. A press according to claim 2 in which said first attachment means is quickly detachable and said tensioning means is pivotally attached to said frame enabling said tie-rod to be swung clear of said gap.

6. A press according to claim 1 which is a hydraulic ram press and said tensioning means is hydraulic, and which includes a connection connecting said tensioning means to a high pressure part of said hydraulic ram press.

7. A press according to claim 6 in which the ratio between the eifective pressurized area of said hydraulic tensioning means and the effective area of said hydraulic ram is substantially equal to the ratio between the distances of said hydraulic ram and of said hydraulic tensioning means from the centre of bending of said frame due to said pressing force.

8. A press according to claim 1 which is a mechanical crank press and which includes load-sensing means associated with the crank mechanism, control means to influence the tension applied to said tie-rod by said tensioning means, and means responsive to said load-sensing means to actuate said control means.

9. A press according to claim 8 in which said tensioning means is hydraulic and said load-sensing means influences the hydraulic pressure applied to said tensioning means.

CHARLES W. LANHAM, Primary Examiner G. P. CROSBY, Assistant Examiner US. Cl. X.R.