US2936055A - Overload protected mechanical press - Google Patents

Description

May 10, 1960 N. J. KASSNEL 2,936,055

OVERLOAD PROTECTED MECHANICAL PRESS Filed Oct. 3, 1956 4 Sheets-Sheet 1 ,CLUTC H co/vmoz i CIRCUIT 0 k 62 65 g a 6 56 r y I 1 75 94 92 I. 6 V0 6 76 INVENTOR. 64 W JW BY L g y 1960 N. J. KASSNEL 2,936,055

OVERLOAD PROTECTED MECHANICAL PRESS Filed Oct. 3, 1956 4 Sheets-Sheet 2 May 10, 1960 N. J. KASSNEL 2,936,055

OVERLOAD PROTECTED MECHANICAL PREIS Filed Oct. 3, 1956 4 Sheets-Sheet 3 IN VEN TOR.

May 10, 1960 N. J. KASSNEL 2,935,055

OVERLOAD PROTECTED MECHANICAL PRESS Filed Oct. 5, 1956 4 Sheets-Sheet 4 'OVERLOAD rnorncrnn MECHANICAL PRESS Nicholas J. Kassnel, Chicago, Ill., assignor to Verson Allsteel Press Company, Chicago, 111., a corporation of Delaware 7 a Application October 3, 1956, Serial No. 613,693 Claims. or. 192-429) An additional object is to provide a novel hydraulic mechanism for incorporation in a mechanical press for protecting the press against overloads.

Still another object is to provide a novel mechanical press in which one of the diesupports will yieldina situation which would otherwise overolad the press and in which the relative positions of the dies is automatically restored when the overload producing condition is removed.

Yet another object of the present invention is to provide a novel hydraulic system in a mechanical press for protecting the press against overload and in which there is no leakage of hydraulic fluid even after extended operation of the press. I) d Other objects and advantages will become apparent from the following description of a preferred embodiment of my invention which is illustrated in the accompanying drawings.

In the drawings, in which similar characters of reference refer to similar parts throughout the several views- Fig. 1 is a vertical medial sectional view through a press slide, showing features of the invention; This view may be considered as taken in the direction of the arrows substantially along the line 1-1 of Fig. 4;

Fig. 2'is a detail from Fig. l, drawn to larger scale to illustrate important features of the invention;

' 2,936,055 Patented May 10, 19 60 ment of the dies produces an overload which may, under some conditions, seriously damage l the press or dies.

Such overload conditions usually are produced by the inadvertent use of a blank which is thicker than the dies are set to operate upon, or commonly, ."particularly in presses which are automatically fed, by the sticking together of two blanks, such that the thickness of the metal between the dies is twice that intended.

Briefly, in one form of the invention, the present system provides a novel hydraulic connection within the press slide of such a nature that this connection is rigid and substantially unyielding so long as no overload condition prevails, but which will yield under conditions of overload and permit a displacement of the slide of the order of one-half inch or so without movement of the upper die member, during which period the clutch can 7 be disengaged. l

Fig. 3 is a side elevation of the press slide shown in Fig. 1; I

Fig. 4 is a front elevation thereof;

Fig. 5 is a vertical sectional view similar to'Fig. 1,

Fig. 6 is a diagrammatic representation of the by draulic circuit which forms a portion of the slide of "Figs. 1 to 5; and Y 7 Fig. 7 is a vertical sectional view of a modified form of the invention, shown embodied in a press bed.

Metal shaping pressesare of two general types. In hydraulic presses the dies are moved toward each other by hydraulic cylinders so as to draw the sheet metal blank and in such pressesoverload conditions are generally no problem since the dies automatically refuse to move whenever the resistance is equivalent to the pressure produced by the hydraulic system.

Mechanical presses, on the other hand, have a crank or an eccentric mechanism of some sortwhich rotates and communicates reciprocating movement to the slide through one or more connecting rods. This type of press has advantages in many applications, particularly where speed of operation is a factor, but since the -arnount;of movement .of thewdies :is fixed by athethrow of the crank shaft or eccentrics, anything which limits closing move- When the overload condition is removed (as when the slide moves upwardly) the upper die is automatically restored. to its proper position without attention on the part of the press operator; 7 All this is accomplished in a mechanism which is so arranged that there is no possibility of oillcakage from the cushioning arrangement onto the press working surface or dies which under most conditions is highly objectionable. 1 In the first embodiment of the invention to be described (illustrated in Figs l to 6) the press frame, bed,

drive mechanism including the crank or eccentric and pitman, may be considered as entirely conventional and no description is necessary, the invention being incorporated in the slide, which is driven in a reciprocatory fashion by the pitman and which moves vertically between guides secured to the. press frame as is customary. Similarly also, the stationary die member is carried upon the upperlface of the press bed while the upperor movable die member isattached to the lower surface oftheslide.

The lower portion of the pitman or connecting rod is indicated at 10, this pitman having a cylindrical lower end which engages a bearing surface forming member 12, which in turn is carried atthe upper end of a cylindrical member 14. The lower end of the member '14 is machined to provide a screw 16 threaded to a nut 18. The lower end of the pitman 10 is retained in placegrelative to the bearing member 12, bya cross pin 2%. The screw ldand nut 18, therefore, reciprocate upwardly and downwardly along with the pitman- 10 as the press crank shaft or eccentric rotates. V p A sleeve 22 surrounds the cylindrical member 14 and forms a sliding fit therewith to prevent side to side dis- Ihe placement of thescrew during press operation. lower end of the sleeve 22 is secured to a generally circujla-r plate 24 which underlies the lower surface of the nut 18, a layer of bearing metal, such as bronze, for instance, separating these elements as is indicated at 2.6..

The nut 18 is rotated by a' ring gear 28 driven by a pinion 30'which is rotated through a speed reducing drive train, indicated at 32, by a reversible electric motor :34. By running this motor in one direction or-the other, the nut 18 can :be rotated and therefore the nut will move upwardly or downwardly along the screw 16 so as to vary the distance between the plate 24 and the center of rotation of the crank shaft so as to adjustvthe closed position of the dies at the bottom of the press stroke to whatever is desirable.

A heavy plate 36 bolted to sleeve .22 through the plate 24 has a central cavity 38 formed in the upper surface thereof to provide clearance for the end of the screw 16. The lower face of the plate -36, as indicated .at 40, bears against the upper plate 42 .of a collapsible .,hydraulic cushion mechanism indicated. generally: by}! v numeral .44. This hydraulic mechanism will he. 1

may be considered simply as being an arrangement in which the upper plate 42 is separated from the lower portion 46 of the ram or slide, the lower surface 48 of which carries the upper die member, by a distance of approximately one-half inch or so, this spacing being maintained by hydraulic fluid confined between the elements.

The lower portion 46 of the ram extends upwardly at the sides as indicated at 50, to a position near the top other.

The space between the top surface 'of the wings 52 and the top edge 58 of the opening through the member 50 provides room at each side for a blockor'shim 60. The shims 60, as shown, have a thickness from top to bottom such that when the ram 46 is lifted by the counterbalancing cylinders (customarily used in presses for counterbalancing the weight of the slide mechanism) the upper surface of the wings 52 will bear against the lower surface of the shims 60, which in turn rest against the upper surfaces 58 of the openings through the side members 50 so as to provide a space between members 42 and 46 of about one-half inch whenever the hydraulic pressure between members 46 to 42 is sufiicient to overcome the lifting effect of the slide counterbalancing cylinders. if desired, however, shims of difierent thickness can be used to obtain a diiferent degree of separation between members 42 and 46 or shims may be used which are one-half inch thicker from top to bottom than those shown, in which case the space for the hydraulic fluid between the members 42 and 46 will be entirely closed so as to result in the slide from top to botto'mbeing completely rigid. This is a useful feature, since some operations, as restriking, for instance, impose only a light load, but should be extremely precise.

Referring now more particularly to Fig. 2, the top surface of the lower ram member 46 is machined to provide a shallow cavity, the upper portion of which is cylindrical as at 62, while below this cylindrical portion the side wall of the cavity is rounded inwardly over a large radius as at 64, so that the cavity is essentially the lower outer quarter of a torus with a tangential cylindrical upward extension at the larger diameter. The upper cylindrical member 42 is of such size as to form a slip fit at its edge within the cylindrical portion 62, and each of the members 42 and 46 have large diameter central portions which have flat parallel adjacent faces 68 and 70 spaced apart approximately one-half inch when the parts are in the position shown in Figs. 1 and 2.

This structure provides a cavity 73 which in section at its periphery is well rounded about the lower and central portions, but which has a square corner at its upper edge. This corner is filled in by an annular ring 72 of generally triangular section which has an upper surface in contact with the lower face of the plate 42 at its periphery and a cylindrical vertical surface which fits the cylindrical portion 62 of the cavity. This ring 72, for a purpose to be pointed out presently is made of brass or some other metal having relatively low modulus of elasticity. With the ring 72 in place, the entire contour at the periphery of the cavity thus produced is comparatively smoothly curved and a rubber diaphragm 74 is provided which fits this surface. It has annular beads 76 and 78 at its upper and lower edges, respectively. These beads are clamped by rings, 80 and 82, respectively, which are retained in place by circular rows of cap screws indicated at 84 and 86, respectively. The

' ring 80 at its inner vertical edge 86 forms a close fit with a similar vertical edge 88 machined from the metal of the upper plate 42, and sealing against leakage through this space is accomplished by a rubber O-ring 90 retained in an annular groove cut into the face at the surface 88. A similar arrangement is used for sealing against leakage about the 'lower diaphragm retaining ring 82, the O-ring in this instance being indicated by the numeral 92. This system, as is best seen in Fig. 2, completely seals the periphery of the hydraulic cavity and results in an arrangement such that the external surface of the diaphragm 74 is smoothly contoured without sharp corners which might otherwise injure the diaphragm.

The reason why the annular ring 72 is formed of a metal having low modulus of elasticity is that under the pressure which is developed within the cavity 73, the metal of the member 46 which forms this cavity will stretch so as to enlarge the cavity side wall diameter by a matter of ten-thousandths of an inch or more. This normally would produce a clearance space into which the rubber of the diaphragm 74 would be extruded at each stroke of the press, thereby causing the material to be rather rapidly eroded away until the diaphragm finally became perforated. The ring 72, however, has a sufiiciently low elastic limit that any pressure within the space confined by the diaphragm 74 which tends to enlarge the cavity will have the result of stretching the ring 72 so that it follows the cavity wall 62 outwardly, thereby always providing for full support for the diaphragm 74 at the upper outer corner as well as elsewhere thereby insuring that no crack occurs into which the material of the diaphragm 74 could be forced, with the ultimate result that the life of the diaphragm 74 is greatly extended. When the pressure in the chamber 73 is relieved, the wall 62 contacts and compresses the ring 72 to its original size.

In assembling this portion of the mechanism the diaphragm 74 is placed in the cavity against the surface provided in the member 46, the O-ring 92 is put in place, the retaining ring 82 is slid into position and retained by the cap screws 86. Thereafter, the upper retaining ring 80 is properly located with a downwardly extending supporting ring 94 resting against the upper surface of the ring 82 so as to support the ring 80 in approximately its proper location. Thereafter the ring 72 is positioned and the plate 42, with the O-ring 90 located in its groove, is lowered into place, so that the plate 42 pushes the ring 72 downwardly, thereby urging the upper edge of the diaphragm 74 inwardly so as to cause its bead to be located in the retaining slot of the ring 80. The cap screws are then inserted from the top side of the plate 42 and tightened so as to complete the assembly.

The lower member 46 is drilled to provide an oil passageway 96 from the cavity 73 to a booster pump 116. A second passage 98 also communicates with this space 73 and at its inner end, which is at substantially the center of the chamber, this passage is provided with a vertical tubular fitting 100 which extends into a clearance space 102 drilled into the lower surface of the plate 44. This passage 98 is for the purpose of bleeding air from the hydraulic system when the cavity 73 and passages are filled. This air passage 98 is connected at its outer end to a valve 103 which is opened to bleed air and foam from the system, after which it is closed and remains closed unless more air collects.

The hydraulic circuit for the apparatus is shown diagrammatically in Fig. 6, where, in so far as possible, the same numbers have been used. The hydraulic system is so arranged that it is carried entirely within the slide as shown, excepting for a low pressure air line connection indicated at 100. Within the slide this line branches with one branch passing through a check valve 102 to the upper portion of a sealed hydraulic fluid reservoir 104,

sesame the lower portion of which is filled with oil as indicated at 106. The other air line branch shown at 108 passes through a shut-off valve 110, a strainer 112, a pressure regulator 114 and finally to a pneumatically operated booster pump 116. The oil inlet connection for this pump is connected by a line 118 to the reservoir 104 below the level of the hydraulic fluid therein, While the outlet fitting from the booster connects with the filling passage 96 previously mentioned.

A "second hydraulic fluid outlet line 122 passes from the reservoir through a check valve 124 to a manifolding passage 126 which is connected to the filling passage 96, a pressure gauge 128, and the inlet of a relief valve 130, the outlet of which, indicated at 132, is connected back to the reservoir 104.

The booster pump at 116 is conventional and simply is operated by air pressure to pump hydraulic fluid. The hydraulic pressure developed is of the order of sixty times the air pressure and therefore the hydraulic pressure can i conveniently be set by adjusting the pressure regulator 114. The amount of fluid necessary to be displaced by the booster is comparatively small and the pump operates only intermittently and thus its air consumption is comparatively inconsequential.

The hydraulic system operates as follows: Air from the supply line enters the reservoir 104 and places the hydraulic fluid therein under a pressure of the order of 80 pounds per square inch, compressed air. at this pressure being generally available in locations where presses are installed. This causes hydraulic fluid to flow upwardly through the check valve at 124and to fill the space confined by the rubber diaphragm 74 to low pressure. The space confined by the diaphragm 74 is indicated by the numeral 73 in Figs. 1, 2, and 5. Air pressure also operates the booster pump 116 which takes oil from the reservoir through the line 118 and raises the pressure within the space 73 to anything desired up to a maximum of say 3500 pounds per square inch, depending upon the operating condition. This increase in pressure closes the check valve 124 thereby preventing return of the hydraulic fluid through the line 126 to the reservoir 106.

If at any time the pressure within. the space 73 exceeds the setting of the relief valve 130, hydraulic fluid will be drained from the space 73 by way of the manifolding line 126 and relief valve 130 until the maximum pressure set by the relief valve has been restored. Whenever fluid is expelled through the relief valve- 130, and. the pressure within the chamber 73 subsequently drops below the selected working pressure for the pump 116, the pump will go into operation until the working pressure is restored. If the pressure should drop below 80 p.s.i.g., the cavity 73 will be filled to that pressureby way of the checkvalve 124, after which the pressure will be quickly built up to the selected Working pressure by operation of the pump 116. i

In conditioning the press for operation, thepressure needed within the cavity 73 to prevent collapse of the coupling under the normal loading conditions of use is determined. The pressure regulator 114 is then set to give a proper air pressure to the pump 116 to give about this hydraulic pressure and the relief valve 130 is set to a somewhat higher pressure. Now with the press in operation, so long as the work being handled is within the capacity of these settings, the pressure within the cavity 73 will rise slightly when the dies are working the metal blank, but ordinarily no flow will take place through the relief valve. 80' long as the press is operating normally, therefore, the ram is substantially rigid;

If a condition producing an overload should arise, however, the pressure within the cavity 73 will exceed the setting of the relief valve. Hydraulic fluid then flows from the cavity 73, through the relief valve 130 and back -to the reservoir 104. This permits the upper main portion of the slide to continue downwardly while the lower portion and upper die remain stationary. If this movemechanism. This stops the downward movement of the entire slide.

As soon as'the dies' are freed and the slide retracted,

the cavity 73 is refilled and pressurized automatically as described above to condition the press for further operation.

Note that the entire mechanism with the exceptio of the low pressure air line'is embodied within the press slide and that all high pressure hydraulic conduits can be formed by drilling the heavy member 46 as at 96 and 98,

and thus, no high pressure hydraulic piping is required.

Furthermore, no leakage of hydraulic fluid is possible since there are no running or sliding elements having packing glands. I

The embodiment of the invention illustrated in Fig. 7 differs from the one previously described in that the mechanism for protecting the press against overloads is incorporated in the bed of the press rather than in the slide. As shown, the press bed structure is illustrated at 150. This structure has a flat upper surface which supports the lower cushioning member 152 which may be considered as the counterpart of the portion of the structure 46 which forms the lower portion of the cavity 73. As in the previous example, there is a circular member 154 which telescopes thereinto from the top, this member being substantially identical to the plate 42 previously discussed. These two members produce a hydraulic '150by side members 164.

Ordinarily the hydraulic pressure within the space 156, which is maintained in a manner identical to that used for the embodiment previously discussed, pushes the upper plate 154 and the die carrying base upwardly against theside rails162 with a force which is slightly above the tonnage rating of the job being handled. At any time the loading of the press exceeds this amount, the plate 160 will be urged downwardly, thereby expelling'hydraulic fluid in the manner previously discussed.

The arrangement of Fig. 7 has an advantage in that it is less expensive and easier to install in an existing press. It also has more area, and therefore lower operating pressures can be used. It has the disadvantage, however, that it precludes the use of a cushion in the press bed.

If it is desired to use the bed without overload protection, the hydraulic pressure within the space 156 is simply reduced until it no longer supports the members 154 and 160. If stripping loads tend to lift these members, this is prevented by inserting shims between the top of the bed 160 and lower surfaces of the lugs 1 62 so as to collapse the assembly and keep it rigid.

From the above description of a preferred embodiment of my invention, it will be appreciated that modifications and variations in the structures shown can bemade without departing from the spirit or scope of the invention,

a stroke of fixed length, a second slide member secured to said first member and adapted to move slightly parallel to the direction of the stroke relative to saidfirst 7 slide member, means for preventing any other movement of said slide members relative to each other, said second slide member being adapted to carry an upper die element, means forming a hydraulic expansible cavity between said members for urging said members apart when said cavity is filled and pressurized with hydraulic fluid, the last said means comprising means forming a large diameter short length piston and cylinder combination, a free floating metal ring within saidcylinder formed of a material of low yield strength overlying the circular juncture line between the piston face and the cylinder wall, a rubber diaphragm ring within said cylinder statically sealed to said cylinder at one edge and statically sealed to said piston at the other edge and overlying said ring, the surface of said ring in contact with said diaphragm being concave about an arc which is substantially tangent at its ends to the face of said piston and the wall of said cylinder, a hydraulic circuit connected for filling and pressurizing said cavity including a pneumatically pressurized reservoir connected for filling said cavity, a check valve in the last said connection for preventing return of fluid to said reservoir, a pneumatically actuated booster pump connected for pressurizing said cavity from said reservoir and having a capability of appreciably expanding the diameter of said cylinder, a pressure relief valve connected between said cavity and said reservoir, said hydraulic circuit being secured to and moving with said second slide member, means for supplying air under pressure to said reservoir, means connected for supplying air under pressure to said booster pump, and the last said connection including an adjustable automatic pressure regulator.

2. In a metal working press, a first slide member, mechanical means for reciprocating said member through a stroke of fixed length, a second slide member secured to said first member and adapted to move slightly parallel to the direction of the stroke relative to said first slide member, means for preventing any other movement of said slide members relative to each other, said second slide member being adapted to carry an upper die element, means forming a hydraulic expansible cavity between said members for urging said members apart when said cavity is filled and pressurized with hydraulic fluid, the last said means comprising means forming a large diameter short length piston and cylinder combination, a metal ring within said cylinder formed of a material of low yield strength overlying the circular juncture line between the piston face and the cylinder Wall, a rubber diaphragm ring within said cylinder statically sealed to said cylinder at one edge and statically sealed to said piston at the other edge and overlying said ring, the surface of said ring in contact with said diaphragm being concave about an are which is substantially tangent at its ends to the face of said piston and the wall of said cylinder, a hydraulic circuit connected for filling and pressurizing said cavity and having a capability of appreciably expanding the diameter of said cylinder, and a pressure relief valve connected for bleeding fluid from said cavity when the pressure setting of said valve is exceeded.

3. In a metal working press, a yieldable mounting for one of the dies of a die set mounted in said press, said yieldable mounting including means forming a hydraulic expansible cavity for urging said dies toward eachother slightly when said cavity is filled and pressurized with hydraulic fluid, the last said means comprising means forming a large diameter short length piston and cylinder combination, a metal ring within said cylinder formed of a material of low yield strength overlying the circular juncture line between the piston face and the cylinder wall, a rubber diaphragm ring within said cylinder statically sealed to said cylinder at. one edgeand statically sealed to said piston at the other edge and overlying said ring, the surface of said ring in contact with said diaphragm being concave about an art which is substantially tangent at its ends to the face of said piston and the wall of said cylinder, a hydraulic circuit connected for filling and pressuring said cavity including a pneumatically pressurized reservoir connected for filling said cavity, a check valve in the last said connection for preventing return of fluid to said reservoir, a pneumatically actuated booster pump connected for pressurizing said cavity from said reservoir and having a capability of appreciably expanding the diameter of said cylinder, a pressure relief valve connected between said cavity and said reservoir, means for supplying air under pressure to said reservoir, means connected for supplying air under pressure to said booster pump, and the last said connection including an adjustable automatic pressure regulator.

4. In a metal working press, a yieldable mounting for one of the dies of a die set mounted in said press, said yieldable mounting including means forming a hydraulic expansible cavity for urging said dies toward each other slightly parallel to the direction of the stroke when said cavity is filled and pressurized with hydraulic fluid, the last said means comprising means forming a large diameter short length piston and cylinder combination, a metal ring within said cylinder formed of a material of low yield strength overlying the circular juncture line between the piston face and the cylinder wall, a rubber diaphragm ring within said cylinder statically sealed to said cylinder at one edge and statically sealed to said piston at the other edge and overlying said ring, the surface of said ring in contact with said diaphragm being smooth and being substantiallyrtangent at its ends to the face of said piston and the wall or" said cylinder, a hydraulic circuit connected for filling and pressurizing said cavity and having a capability of appreciably expanding the diameter of said cylinder, and a'pressure relief valve connected for bleeding fluid from said cavity when the pressure setting of said valve is exceeded. I r Y 5. A hydraulic device comprising means forming a large diameter short length piston and cylinder combination, a metal ring within said cylinder formed of a material of low .yield strength overlying the circular juncture line between the piston face and the cylinder wall, a rubber diaphragm ring within said cylinder statically sealed to said cylinder at one edge and statically sealed to said piston at the other edge and overlying said ring, the surface of said ring in contact with said diaphragm being concave about an are which is substantially tangent at its ends to the end face of said piston and the wall of said cylinder, and a hydraulic circuit connected for filling and pressurizing said cavity and having a capability of appreciably expanding the diameter of said cylinder.

References Cited in the file of this patent I v UNITED STATES PATENTS 1,870,527

2,652,241 Williams Sept. 15, 1953

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