US2283124A - Piston operated press and the like - Google Patents

Description

May 12, 1942.

v. w. PETERSON ETAL 2,283,124

PISTON OPERATED PRESS AND THE LIKE Jrzveruns 08 07 ZflPeZersort one 0550 J Mafia.

Patented May 12, 1942 1 PISTON GPERATED PRESS AND THE LIKE Victor -W. Peterson-and Otto .L'Maha, Chicago, Ill., assignorsto Hannifin Manufacturing '00., Chicago, 111., a corporation of'lllinois .Al plicationAugust .19, 1937, Serial No. 159,874.

3 Claims. (Cl. 121-38) This invention relates to piston operated presses and the like, and among otherobjects aims to provide means for-improving the operation of the piston. 1

The nature of the invention may be readily un derstood by reference to one illustrative embodiment thereof shownin the accompanying draw- In said drawing: Fig. 1 is an elevation, somewhat diagrammatic andweight may be securedby employing intensifying means l5 by which pressures substantially higher than the maximum pump pressure, may be developed during the short interval in which the plunger is performing its work. The relatively lower pump pressures will serve to advancethe in form, of a yoke riveter connected to a pressure supply mechanism; and Fig. 2 is anenlarged section of theoperating piston and a portion of the cylinder.

In piston operated presses and the like the plunger is generally given a stroke substantially greater than that in which its work is performed, in order, among other objects, to allow the plunger to clear the work and tofacilitate placing and removing of the articles operated on. It is desirable, however, to curtail the time consumed in the idle portions of the forward and-return stroke by shortening the return stroke when a longer stroke is, for any reason, unnecessary.

For example, if -thepiece of work operated upon plunger into contact with the work and to with draw the plunger from the work. Pressure intensifying mechanism" such as that disclosed in our co-pending application, Serial No. 91,630, now Patent No. 2,241,645, maybe employed, It should be understood,h owever, that the invention is not limited to any particular pressure intensifying mechanism, nor indeed, to presses employing intensified pressure since many opera- .tions may be performed withrelatively low pump pressures. During the forward stroke of the plunger line l4 isopen todischarge and on the return stroke line I3 is opento discharge.

In riveting operations for cold heading, for example, a %-in. rivet, the ,pump should'be capable ofsupplying ,oil pressuresup .to approximately 1,000 lbs. persquare in. with a capacity is small and easily moved into-and out of operating position, the returnstroke may be much shorter than for a large piece of work or one which is not so readily placed inandremoved from the press. Again, riveting-where the rivets are close together, a rapid sequence of operations is possible and the return stroke may advantageously be shortened-to an amount just sufiicient to allow shifting from one'rivet to-the next. Under the foregoing and other circumstances, a-new cycle of operations is advantageously started immediately and-without the delay which would ensue while the plunger returned the remainder of its stroke a-nd thenad- I vanced by the same amount. v

The invention is here shown embodied in a hydraulic yoke riveter 10, but it will be understood that its use is not limited to riveting presses. The hydraulic pressure (preferably oil pressure) is supplied to the riveter cylinder. H j

from any appropriate pressure supply means ofabout .1.cu..f,t. per minute. Such pressure and capacity are employed, toadvance the riveter plunger quickly to engagement with the work and to removeall slack from the, system priorto the application of intensified pressure which functions only to complete the heading of the rivet. Indeed,.the directpumppressure is generally sufficient. partially toheadthe rivet. The

intensified pressures. may reach 5,000 ,lbs.,per square in.

When the rivet is headed, the stroke of" the plungerv piston Hi islreversed (either automatically or manually) by application ,of pressure to the opposite face of. the piston through thereturn line I4. 7 Unless interrupted, the piston will i be returned to engagement with the cylinder head, at which time the return pressures will be built-up sufficiently .to neutralize the pressure employed. It comprises a simple electric push button switch like the switch I! to operate a solenoid, controllingthe starting and stopping of a cycle of operations. The cycle continues so long as the solenoid isenergized but whenthe push button is released and the solenoid desized, the ycle is interrupted and pressure is supplied to return line I4 to start piston IS on its return stroke. Another cycle can be started at any point on the return stroke simply by depressing the push button.

As a practical matter, however, if the return speed of the plunger be too great, it is difiicult to interrupt its return in mid-stroke, in which event the next operation is delayed until the plunger has traversed the idle or unnecessary portion of its return stroke. Among other advantages, the illustrative apparatus effects such retardation of the return plunger stroke and acceleration of the forward stroke as to minimize idle time and secure eflicient operation. In riveting operations, for example, the time consumed in idle travel (backward and forward) of the plunger should not greatly exceed the time consumed in shifting the riveter from one rivet to the next. In the present instance, the accelerated forward and retarded return speeds of the plunger are secured by by-passing a portion of the pressure liquid around or through the piston.

- As here shown, piston I6 is provided with a by-pass passage 20, leading from one face to the other. The passage is controlled by a valve 2| which serves to close the passage when the oil pressure on the head or operating face of the piston exceeds that on the opposite face. The valve is here shown in the form of a disc adapted to seat against the face 22 of recess 23 to close the passage 20. The passage 20 in this case communicates with the return side of the piston through a passage 24 in plunger 25. The recess 23 in which the valve disc 2|, is seated is closed by a plug 26, having a passage 21 connecting the valve chamber 23 with the cylinder space.

The forward speed of the plunger and its piston l6 depends to someextent upon the rate at which the liquid below the piston can be displaced and also .on the rate at which the larger volume of liquid can be forced into the head end of the cylinder therefore accelerated by by-passing ordisplacing a portion of the liquid simply from the lower portion of the cylinder to the head end, thereby minimizing the volume of liquid required to travel to discharge through the supply and return lines l3 and I4 and their associated valves and passages. The latter displacement occurs (notwithstanding the total pressure differential which causes the piston to advance) because the unit pressure onthe head end of the piston is actually less than that on. its opposite face, thereby raising valve 2| and short-circuiting a portion of the liquid. In passing into the head end of'the cylinder, the by-passed liquid, because of its greater pressure, actually performs work on the piston, hastening its advance. Despite the lowerrunit pressure'on the head end of the piston, the total pressure thereon is greater than on its opposite face because of the-formers substantially greater area, the plunger 25 reducing the effective area of the opposite face of the piston. In the present instance, the area of the head end is about '7 sq. in., whereas the effective area of the opposite face is only about 5 sq. in.

It should be understood that the aforesaid unit pressure on the under'face of the piston develops as a result of the resistance of the liquid to discharge from the cylinder through line H. When, however, the plunger engages work, the highly increased resistance to further advance automatically results in the building up of the Such forward speed is unit pressure on the head end of the piston to a point where it substantially exceeds that on the opposite face, thereby closing valve 2| and holding it tightly on its seat to prevent further short-circuiting of the liquid.

To return the plunger after completion of its operation, oil pressure is shifted to return line I4, line l3, of course, being opened to discharge. The unit pressures on the underside of the piston then very substantially exceed those in the head end of the cylinder (since it is now open to discharge), again opening valve 2|. However, as contrasted with former conditions, the liquid now passes into the end of the cylinder (i. e. the head end) from which liquid must be displaced to permit return of the piston, and greatly increases the volume to be displaced. The substantial increase in the volume of liquid to be discharged of course causes an increase in the back pressure or resistance to such discharge and thereby substantially retards ,the return stroke of the pistonand allows sufficient time interval within which to operate the button IT to interrupt return and start a new cycle.

The speed of return of the piston may be varied by employing plugs, 26 with a larger or smaller passage 21. If passage 21 be more re stricted, the speed of return will be increased; if larger, it will be retarded. Indeed, if it be too large, the piston will not-be returned sincethere would be insufiicient resistance to the travel of the fluid, through the passage to develop a pressure differential below the piston. Hence passage 21 must always be restricted sufliciently to develop the necessary pressure differential.

The upper face of valve 2| is slotted or otherwise is provided with a passage 2| so as not to close access to passage 21.

If the piston be permitted to complete its return stroke, engagement with the cylinder head 28 serves to close passage 21, thereby making it possible (as in the apparatus of said copending application) to utilize the building up of the return line pressures to a predetermined value to actuate control devices which operate to cut off pressure supply and condition the apparatus for starting another cycle. For this purpose, the end of plug 26 is ground so that it seats tightly against the cylinder head surface in order effectively to closepa'ssage 21 and thereby shut off further by-passing of liquid to the head end of the cylinder. The maximum stroke of the piston may be reduced if desired in any case by inserting in the cylinder head a plug which projects inwardly an amount equivalent to the desired shortening of the stroke. The end of the plug is ground andfunctions in place of the cylinder head for causing neutralization of the pressure supply apparatus and for closing passage 2'|.

When it is possible, as in the present design,

to interrupt the return stroke at any point and immediately start the piston on the forward stroke of a new cyle, the time consumed by the piston in unnecessary return and forward movements and operations incident thereto is. of course, eliminated.

The by-pa'ssing of the oil around the piston when the valve 2| is open also advantageously provides oil circulation between both faces of the piston, thereby dissipating heat which would otherwise accumulate in the cylinder through non-circulation and also dissipating the air which may be trapped above and below the piston.

It should be understood, of course, that the valve controlled by-pass need not be placed in the piston, but may be incorporated in lines connected with the cylinder and extending from one side of the piston to the other.

If mobility of the press be desirable, as in riveters, the unit may be connected to the pressure supply means by flexible hose lines l3 and M. Flexible hose, capable of transmitting the aforesaid high pressures without excessive expansion or distortion, may be secured upon the open market. One satisfactory type embodies a reinforcing of woven wire wherein the strands run diagonally or spirally around the hose and are covered truth a rubberized protective fabric. The inside of the hose is lined with a flexible leakproof composition. The wire reinforcing, although quite flexible, is of such strength as to prevent undue expansion of the hose under pressure, thereby minimizing the volume of fluid (and waste energy) consumed in expansion or stretching of portions of the apparatus under the high pressures developed.

Additional mobility in a yoke riveting press, for example, may be secured by making the yoke or frame of a heat-treated alloy steel having a strength of about 200,000 lbs. per sq. in. and capable of withstanding Working stresses up to about 125,000 lbs. For cold heading a in. rivet, where the maximum heading pressure exerted by the riveter plunger is about 35,000 lbs., the use of steel of this character makes it possible to make a yoke riveter which, with the piston riveting tool and cylinder, weighs only about 50 lbs. and which, therefore, may be maneuvered more easily and quickly than heretofore from one rivet to the next. Moreover, the small size of the riveter makes it possible to reach rivets which have, heretofore, been inaccessible for cold heading.

Obviously the invention is not limited to the details of the illustrative construction since these may be variously modified. Moreover it is not indispensable that all features of the invention be used conjointly, since various features may be used to advantage indifferent combinations and sub-combinations.

Having described our invention, we claim:

1. In apparatus of the character described, the combination comprising a work cylinder having a double-acting piston and plunger, control mechanism for opening the head end of said cylinder to discharge and for delivering pressure fluid to the plunger end to move the piston on its return stroke, a by-pass for passing fluid from the plunger end of said cylinder to the head end thereof on the return stroke to increase the volume of fluid to be discharged from said head end and thereby retard the return movement of said piston, said by-pass being restricted to develop pressure on the plunger face of said piston suflicient to move said piston, and a check valve in said by-pass to prevent travel of fluid from said head end to said plunger end,

2. In apparatus of the character described, the combination comprising a work cylinder having a double-acting piston and a work plunger, said plunger reducing the effective area of the plunger side of said piston so that said piston may be caused to advance with unit pressure in the head end less than the unit back pressure in the plunger end of said cylinder, control mechanism for opening the head end of said cylinder to discharge and for delivering pressure fluid to the plunger end and vice versa, a by-pass for passing fluid from the plunger end to the head end of said cylinder on the forward stroke of the piston, a check valve in said by-pass operative to close said by-pass when the unit pressure in the head end of said cylinder exceeds that in the plunger end thereof, said by-pass also passing fluid from the plunger end of said cylinder to the head end thereof on the return stroke to increase the volume of fluid to be discharged from said head end and thereby retard the return movement of said piston, said by-pass being restricted to develop pressure on the plunger face of said piston sufficient to move said piston, and means for closing said by-pass when said piston reaches the end of its return stroke.

3. In apparatus of the character described, the combination comprising a work cylinder having a double-acting piston and a work plunger, said plunger reducing the effective area of the plunger side of said piston relative to that of its opposite face so that said piston may be caused to advance with a total pressure exceeding the total back pressure but with unit pressure in the head end less than the unit back pressure in the plunger end of said cylinder, control mechanism for delivering pressure fluid to the head end of said cylinder and for opening the plunger end to discharge and for maintaining said plunger end open to discharge throughout the advance stroke of said piston, said control mechanism also operating to deliver pressure fluid to said plunger end and to open said head end to discharge for the return stroke of said piston, means forincreasing the speed of advance of said piston including a by-pass for by-passing fluid from the plunger end to said head end on the advance stroke of said piston in addition to the fluid simultaneously passing to. discharge, said by-pass being restricted to permit the development of pressure on the piston adequate to return the piston against back pressure thereon, and a check valve in said by-pass to prevent flow from said head end to said plunger end, said check valve also being adapted to interrupt flow through said by-pass when through increase in resistance to advance of said plunger unit pressure in said head end exceeds'the unit back pressure in said plunger end.

VICTOR W. PETERSON. OTTO J. MAHA.

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