US2891497A - Fluid compensator and overload safety devices for mechanical presses - Google Patents

Description

R. B. TREER FLUID COMPENSATOR AND OVERLOAD SAFETY June 23, 1959 DEVICES FOR MECHANICAL PRESSES Filed Aug.

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57 f B BY W 5 2% United States Patent G FLUID COMPENSATOR AND OVERL'OADSAFETY DEVICES FOR MECHANICAL PRESSES Ross B. Treer, Lakewood, Ohio Application August 3, 1954, Serial No. 447,551

1 Claim. (Cl. 113-38) This invention relates to mechanical presses in general and relates more particularly to a fluid compensator for automatically adjusting the press action to varying thicknesses of material and to means for preventing jamming or breaking when the resistance encountered by the toolcarrying parts exceeds the rated worked force of the press.

With mechanical presses, the movement of the toolcanrying parts toward and away from one another in the ordinary work cycle is adjustable to produce the required force upon the work pieces. Once the dies have been adjusted properly and the approach of the dies set by the driving mechanism, theoretically the work should progress until the job is finished. As a practical matter however, changes in temperature, wearing of dies, and variation in stock thicknesses will require adjustment of the press from time to time during the work period. This invention provides a fluid compensator whereby the press is adjusted mechanically to produce a maximum approach of the dies and which limits the force of the dies in the event that the press is cold or the stock is oversize.

Further, jamming and breaking of presses arises from .a number of causes. For example, tools and pieces of metal accidentally left between the press tools are such causes. In the drawing, the press used for illustration of the invention is adapted primarily for progressive, deep drawing operations. To properly draw, a reasonable tonnage capacity is required but if there should be a very slight over-adjustment of the dies, coining takes place and the stress increases to such a high degree that damage is often done, especially if repeated frequently.

The present invention provides a press combination which avoids jamming or breaking of the press and which, when the tools of the press encounter a resistance that in ordinary presses would cause jamming or breaking, allows the press to complete its cycle of operation without stopping. However, if the press isv stopped, the press parts may be backed off.

It is the object of this invention to provide a mechanical hydraulic drive combination for a press to protect against overstressing of the press.

Another object of this invention is to provide a linkage in the drive system for such a press which linkage is locked by fluid under pressure with an overload release means which releases only at pressure and never allows the fluid pressure to drop below a predetermined minimum.

' A further object of this invention is to cause a .fluid injection into the linkage system during each stroke of the press regardless of the need for additional fluid and the continual bleeding-off of any excess pressure through an overload relief means.

Other objects and a fuller understanding of the invention may be had by referring to the following description and claims, taken in conjunction with the accompanying drawing, in which:

Figure 1 of the drawing is a side view partly in section,

reciprocated as well as the slide.

lee

2 partly broken away, showing the hydraulic linkage system in the drive mechanism of a Well-known inverted type press;

Figure 2 of the drawing is an end view also partly in section and partly broken away to further reveal the preferred construction; and

Figure 3 is a graphic illustration of the principal work portion of the press cycle.

In presses, one of the tool-carrying parts is usually a stationary bed located at the lower part of the press and the other tool-carrying part is a slide which reciprocates toward and from the bed; but the position of the bed and slide are sometimes reversed, the press is sometimes horizontal and sometimes inclined, and sometimes the bed is Furthermore, some presses have the driving pitman above the bed and force the moveable die holder toward the bed whereas other types of presses have the driving pitman below the bed and draw the die holder platen downwardly by means of draw rods. The press illustrated is of the latter type having a stationary bed 11 and a reciprocating platen 1 0.

The illustrated press is substantially standard for that type of press except for the particular features of a hydraulic safety device to prevent over-stressing 0f the press. This press employs a crank shaft 12 with a flywheel 13 adapted to receive driving power from some prime mover. A cross head 14 is vertically reciprocably guided by ways 15 and driven in the vertical reciprocal path by means of a pitman 16 operated by the crank shaft 12. The platen 10 is vertically reciprocated from the cross head 14 by means of draw bars 17.

As indicated, the press is substantially standard in all respects other than the improvement of this invention and, accordingly, the foregoing brief description is believed sufficient to set forth the environment in which the present invention resides and will be readily understood by those skilled in the art of press construction and operation.

A piston 20 in the illustrated embodiment of the invention, is driven by the pitman 16 and fits into a cylinder 21 provided in the cross head 14. The piston and cylinder define a chamber 22 which may be filled with fluid preferably a non-compressible hydraulic fluid.

There is less force required to lift the platen 10 than employed on the work stroke and, consequently, a mere mechanical connection between the piston 20 and the cross head 14 is all that is required to provide the upward movement. An adjustment ring 23 threadably engaged into the interior wall of the cylinder 21 near the top edge thereof provides an abutting shoulder to hold the piston 20 to a maximum degree of withdrawal out of the cylinder 21. The fluid in the chamber 22 resists movement of the piston 20 into the cylinder 21, and also holds the piston 20 in tight engagement with the adjustment ring 23. Adjustment ring 23 is provided with a ring gear portion 24 adapted to be driven for rotating the adjustment ring. A drive spur 25 having a stud 26 thereon to receive a conventional wrench or power drive is employed to rotatively drive the ring 23 through the ring gear 24. R0- tation of ring 23 in one direction or the other will adjust the closed height of the platen 10.

The hydraulic system of the present invention also includes a reservoir 32 and a relief valve 33 in the crosshead 14. Relief valve 33 is readily accessible from the exterior of the press and may be readily exchanged in a few moments in the event that wear destroys its proper functioning. Such check valves are extremely inexpensive as compared with the cost of replacing or repairing major portions of a press. A manual valve 34 by-passes the valve 33 for the purpose of allowing liquid to be drained from the chamber 22. if it should be desired to run the piston 20 into the cylinder 21 to reduce the clearance sure and to hold the pressure at which it is set.

a graphic illustration of the desired pressure holding is set forth. Numeral A indicates the full stroke of platen .10. Numeral B indicates an arbitrary distance representative of what may be a work stroke. Numeral C indicates the pitman travel during the work stroke. Those acquainted with press design will realize that the pressure increases tremendously as the pitman covers the distance C to a bottom center position X. At the position X the press should not be exerting a force greater than its maximum safety force. Because of the possibility of exerting extreme pressures with a pitman drive, as the pitman nears position X, it is possible to exceed the maximum safe stress for the draw rods 17 or other component parts of the press. For example, if the maximum safe pressure were reached at position Y, it would be seen that after the pitman had traveled the distance D, a tremendous overload would have been encountered if the dies had closed upon a solid workpiece and had begun a coining operation beyond the intended amount of forming or coining. Nevertheless, it is not desirable to reduce the pressure after the maximum force is exerted at the position Y. It is desirable to hold that pressure through the balance of the work stroke.

With the fluid system of the present invention, when using the relief valve 33, the fluid will be released at maximum pressure and only in amounts necessary to pre vent excess pressure build-up. Thus, the stroke will continue at the full desired pressure capacity in spite of the escape of fluid from the chamber 22 but with no overloading of the press.

The provision of the hydraulic cushion which maintains the desired pressure at all times serves a very important function other than mere safety. The adjustment of the dies in a mechanical press to close to the exact desired degree is very exacting and is subject to change due to temperature and other factors. Consequently, readjustment of such presses is necessary from time to time. Hydraulic presses have the advantage in this respect that a given hydraulic pressure can be established once and will be maintained at that pressure always. This invention provides the advantages of both the mechanical and hydraulic press. The dies are adjusted with respect to one another by rotation of the adjustment ring 23 as previously described. However, by adjusting the dies to the fullest extent of approach with respect to one another and then establishing the correct working forces by means of the hydraulic cushion, any over-adjustment will be compensated for by the hydraulic cushion. Thus, the operator can safely close the dies to the fullest extent with the assurance that the piston 20 will move down into the cylinder 21 a slight amount if the adjustment should be too close. This provides for a close adjustment by mechanical means with a hydraulic feature providing for exact tolerances.

With the present invention, fluid is pumped to the chamber 22 on each upward stroke of the press without regard to the pressure therein. Thus, if there is a need for fluid to bring the pressure in chamber 22 up to standard, that fluid will be supplied, if the fluid is in excess, it will merely open the valve 33 and escape.

In the illustrated embodiment of the invention, the reg ular injection of fluid into chamber 22 is brought about by a positive displacementpump action produced by a piston 37 operating in a pump cylinder 29. A spring 38 is provided to urge the piston 37 to the starting position and to draw fluid from the sump 32 into the chamber of the pump. A check valve 30 illustrated simply as a ball check in the drawing is employed to prevent the discharge of fluids in the reverse direction during the charging stroke of the pumping apparatus. Driving force for the piston 37 is provided by a contact actuator 27 which is simply a rod having a threaded portion 35 threadably engaged into a stationary hanger 28 carried by the press. The actuator 27 is thereby vertically adjustable with respect to the head of the piston 37 and is locked into a desired position by means of a lock nut 36. Because adjustment of the ring 23 will cause a repositioning of the entire crosshead 14 and consequently reposition the piston 37, the actuator 27 is normally adjusted an amount substantially equal to the adjustment of the crosshead.

Although the invention has been described in its pre ferred form with a certain degree of particularity, it is understood that the present disclosure of the preferred form has been made only by way of example and that numerous changes in the details of construction and the combination and arrangement of parts may be resorted to without departing from the spirit and the scope of the invention as hereinafter claimed.

What is claimed is: v

In a power press comprising a frame member and a reciprocatory platen member with a plurality of draw rods extending therefrom to a vertically reciprocatory cross head positioned beneath said frame member and a rotatably driven crank shaft having a pitman thereon with means connecting said pitman to said cross head, said means including a piston reciprocable in a cylinder in said cross head with said cylinder being closed at one end and defining with the piston a chamber, and an adjusting ring in said cylinder for limiting movement of said piston in said cylinder in a direction away from the closed end of said cylinder, the improvement comprising a liquid reservoir provided in said cross head, a positive displace ment liquid pump comprising a cylinder carried by said reciprocatory member and a pump plunger, first conduit means connecting said pump cylinder with said liquid reservoir, second conduit means connecting said pump cylinder with said chamber, adjustable pump plunger connecting means carried by frame member for actuating said pump plunger upon movement of said reciprocatory member to cause said pump plungerto pump liquid from said reservoir to said second conduit means, and res sure relief valve means connected to said chamber.

References Cited in the file of this patent UNITED STATES PATENTS

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