US3189377A - Steel plate lifting clamps - Google Patents

Description

June 15, 1965 E. M. GARDNER 3,189,377

STEEL PLATE LIFTING' CLAMPS Filed May 21, 1962 2 Sheets-Sheet 1 lllmm 'H 56 64 I I H umll I l 6 5" 68 I n 26 I :36 1 1 [I 5 I, I I {1| n i I 70 I I In 5 I F 30 I g 78 1 90 7s 72 I8 I I I" "H 74 24 32 28 3e 82 I6 24 INVENTOR.

Edward Merrill Gardner ATTORNIEYS June 15, 1965 EwMJGARDNER I 3,189,377 STEEL PLATE LIFTING CLAMPS Filed May 21, 1962 2 Sheets-Sheet 2 FIG. 3

INVENTOR Edward Merrill Gardner ATTORNEYS United States Patent York Filed May 21,1962, Ser. No. 196,194 2 Claims. (Cl. 24-1ll1) My invention described and claimed in this application relates to improvements in gripping and lifting clamps of the type used for gripping and lifting heavy steel plates or other heavy structures.

This application is a continuation-in-part of my pending application Serial No. 148,623, filed October 30, 1961, which has become abandoned, for Steel Plate Lifting Clamp.

Known lifting clamps include a body having spaced opposed depending jaws between which a plate to be lifted is received and gripped between a serrated gripping cam and a fixed serrated pad respectively mounted in the jaws facing each other. The gripping surface of the cam is cut on an arc and usually coupled by a linkage with the liftshackle of the clamp for the purpose of applying gripping pressure to the cam. Lifting clamps of this or other type sometimes include springs connected with the linkage or gripping cam for biasing the grioping cam toward the plate to be lifted. Clamps including a lifting linkage con nected to the gripping cam are usually quite suitable for lifting ordinary plates when the thickness range is small and the plates are not regarded as heavy.

However, such clamps are not entirely satisfactory because it is difficult to get a full grip on plates when lifting from the horizontal and when there is a wide range of grip on a single clamp, and it is difficult to manipulate the clamp where the gripping pressure applied to the gripping cam depends on a linkage connected to a lifting shackle or on a li ht spring biasing the gripping cam. Also on heavy plates the problem is exaggerated because the linkage exerts ununiform leverage causing danger of slippage on one thickness and excessive jamming on another which requires overweight clamp bodies and causes releasing difficulties on the latter size plates. A constant angle with no linkage such as in the clamp of my invention can be controlled to give the exact conditions for any requirements on varying thicknesses of plates in a single clamp, with or without teeth, on soft or hard, smooth or rough, red hot or cold plates.

Having in mind the structures and deficiencies of the known types of lifting clamps, the primary object of my invention is to provide a clamp adapted to grip and safely lift steel plates or steel structures varying widely in thickness or texture and weighing up to or 75 tons.

Another very important object of my invention is the provision of a lifting clamp which has a simple relatively light weight structure and which is easy to operate, and inexpensive to produce.

Another very important object is to satisfy safety engineers by making the clamp inoperable unless the cam has had its actuating spring swung into its operating and locked position. When teeth are new and sharp and cam angle is high in prior clamps, operators get away without the inconvenience of pulling over a heavy spring, but later when dull, the plate will drop. My clamp cannot be used without throwing over the lever to apply the spring and operate the cam.

A further object of my invention is to provide a lifting clamp having a structure so that one clamp can be applied to horizontal plates of a wide variation in thickness without rocking and slipping, so that such plates may be gripped fully up in the throat and be safely lifted and handled.

According to my invention the improved lifting clamp for gripping and lifting steel plates and other structures varying in thickness from approximately 2 inches or more and weighing as much as 10 or tons as a single unit comprises a clamp body structure having spaced opposed portions or jaws providing a plate-receiving space, open at the projecting ends of the jaws, a lifting shackle located in the upper part of the body of the clamp above said space, a serrated or smooth gripping pad mounted in the face of one of the depending portions or jaws of the clamp facing the other depending portion or jaw across said space and freely slidable along the face of the jaw in which it is mounted, a gripping cam pivotally mounted in the other depending portion or jaw of the clamp operable independently of the lifting shackle, said gripping cam having an arcuate serrated or relatively smooth plategripping surface facing toward the gripping pad, and a single spring mechanism pivoted in the body of the clamp and connected to the gripping cam which must either force the gripping cam against a plate or must hold it away from a plate engaging position, since there is no neutral position where it can repose.

In a preferred construction the arcuate surface of the cam is provided with an angle of contact with the plate to be lifted which is so acute that an extremely high gripping pressure is exerted by the cam on the plates when the plates are lifted, this pressure which is uniformly related to the weight lifted and not affected by the plate thickness is so high as to imbed the serrations of the cam and gripping pad respectively in the opposite surfaces of the plate without the aid of a supplementary mechanical advantage. Usually the gripping came. of conventional lifting clamps are cut on the arc of one or two circles, while the serrated arcuate surface of the cam according to my invention is provided with an arcuate gripping surface having a nearly constant low angle of contact with the plate to be lifted regardless of the thickness of the plate. Clamps made according to the present invention for lifting plates varying in thickness up to 2 inches or more and weighing up to 10 or more tons have been found to hold their grip on the plate even with all of the cam and pad teeth worn olf or ground off relatively smooth.

In the preferred construction referred to, it will be un derstood that the heavy gripping pressure applied, be cause of the low angle of cam contact, is such as to jam the plate between the teeth of the cam and those of the gripping pad. Therefore, the preferred construction includes the freely slidable gripping pad located in an elongated recess in the face of the jaw in which it is mounted. When the clamp is applied to a plate, the pad may be placed inwardly from its outer position so that when lifting starts, the pad slides outwardly allowing the cam to hold most of the weight which rotates it and causes the grip. The weight is held by the cam and partially by friction on the back of the pad against the recess. When the pad reaches the end of the recess and since the pad teeth have imbedded into the plate, the pad then holds more Weight and resists further cam rotation and excessive binding. When a lifted plate is brought to rest on the ground, or on some supporting structure, the pad slides inwardly relative to the body of the clamp as the latter is moved down, primarily by the stress in the clamp acting downwardly though the cam, thereby rotating the gripping cam toward the open position and breaking the jammed position on the plate to give a relaxed contact.

When the gripping cam is rotated and its grip broken in this Way, it is only necessary to further rotate the cam to its retracted position. Accordingly, the improved clamp is provided with a hand-actuated operating mechanism including a strong tension spring which pivots the cam to its retracted position. The structure of this mechanism Patented June 15, 1965 is such that one end of the spring is connected to the heel of the cam, while the other end is connected to one end of a lever arm. The other end of the lever arm is pivoted to the clamp body in a position to provide an overcenter arrangement so that the end of the spring connected to the lever arm may be rotated over a dead center position which will snap the arm in between the plates of the frame to both positions of either on or off. When off, it will lift the cam to its retracted position. When the end of the spring attached to the lever arm is swung to the opposite position, it biases the cam to the plate engaging position. It cannot come to rest on dead center position.

.Since the cam is operable independent of the lifting shackle and its operation is not interfered with, the spring arrangement has the advantage of holding the cam in contact with the plate at all times during the handling of the plate and prevents disengagement of the cam even when the plate is lowered to the ground during a handling operation. Another advantage is that the spring, which has a strong tension, gives an initial bite on the plate to be lifted before the plate is actually lifted by the crane from the lifting shackle. If through some malfunction the cam is jammed on a plate and the clamp is to be removed. the spring in opened position gives an opening torque to the cam so that the instant the cam teeth are jarred loose from the plate, the cam will open fully. This will allow it to be lifted off and placed on another plate. Furthermore, the operator is always able to tell when the grip of the cam on the plate has been released because the spring actually pops the cam to open position,

' In its preferred construction the improved lifting clamp is provided with a slope at the inner end of the space between'the jaws directed gradually outwardly and toward the jaw in which the gripping cam is mounted. It was found that in using the clamp to lift plates from the horizontal position, the clamp after being applied to the plate had a tendency to tip or roll on the pad because of the weight of the body of the clamp and shackle at the side of the plate. This tipping or rolling action resulted in the clamp being pulled partly oil the plate causing an unsafe condition. However, because of the sloping inner end space between the jaws, it was found possible to push the clamp onto a horizontal plate, so that its upper inner edge engaged the slope and prevented tipping. This feature is particularly advantageous in connection with the lifting of plates which are substantially thinner than the thickest plates acceptable by the clamp.

The features of the invention are described more in detail in connection with an embodiment of the invention as shown in the accompanying drawings forming a part of this application.

In the drawings:

FIG. 1 is an elevational view partly in section of a lifting clamp for lifting heavy steel plates shown in engaged gripping position with respect to a horizontal steel plate to be lifted. The clamp is a welded steel structure including steel side plates, but in this view one of the side plates of the clamp is removed in order to reveal the interior mechanism;

FIG. 2 is an elevational view of the top edge of the clamp shown in FIG. 1;

FIG. 3 is an elevational view of the clamp shown in FIG. 1, showing the clamp in upright position with the gripping cam and its operating mechanism in open or released position; and

FIG. 4 is a broken sectional view taken on the line 4-4 of FIG. 1. l

' Referring to FIGS. 1 and 2 of the drawings, the lifting clamp, as illustrated therein, comprises a clamp body provided with fixed jaws 12 and 14 spaced apart and facing each other to provide an opening or space 15 therebetween for receiving heavy steel plates, for example the plate 16 shown in the fully-gripped position with a lifting force applied.

The body lb of the clamp includes a pair of spaced steel side plates 18 and 2d of similar contour held in spaced relation with respect to each other by a thick inverted L-shaped steel spacer block 22 which extends entirely through the jaw 12 and across the clamp beyond the closed end of the plate-receiving opening 15. The plates 18 and Zil are secured to the block 22 and held together by rivets 24 and also by peripheral welding, as indicated. In some cases they are drop forged in two integral parts with the division through the center of 22, when no welding is needed. At the projecting end of the jaw 14, the plates are held in the same spaced relation by a spacer sleeve 26, while the plates at that point are held together by a rivet 28 extending through the sleeve.

At the lifting side of the clamp the plates 18 and extend beyond the spacer block 22 and provide means for securing a heavy lifting shackle 30 which is pivoted between the platcs on a shackle pin 32 extending through the plates and provided with a nut secured by a cotter pin. The portions of the plates 1-8 and 2t) forming the jaw 14 house a gripping cam 34 having an arcuate serrated camshaped gripping edge surface 36, as illustrated. The cam 34 includes an enlarged hub portion 37 having a pivot bearing opening through which a pivot pin 38 extends for pivoting the cam between the side plates 18 and 20. The pin 38 is located considerably back from the plate-receiving opening i5 and about midway along the jaws 14. The pin 38 extends through side plates 18 and 29 on the respective sides of the cam hub 37 and is secured in place by a nut fastened by a cotter pin.

A gripping pad 42 having a serrated face, facing toward the cam 34 is mounted in an elongated oval-shaped recess 44 cut in the inner face of the block 22. The pad 42 includes a large back surface area and a smaller axiallyextending shank 46 extending through an oval-shaped opening 48, the projecting end of the shank being provided with threads and secured by a nut 54 held from turning by a cotter pin. The nut 50 and the threaded end of the shank 46 are located between the plates 13 and 20 in a recess 52 in the back of the block 22. The serrations on the pad 42 are preferably concentric sharp projections parallel to the faces of the jaws, as illustrated, and adapted to bite into the steel plate being lifted, as shown in FIG. 1. The pad 42 is mounted in the jaw 12 so that it is freely slidable longitudinally in the oval-shaped recess 44, the function and operation of which is explained hereinafter in describing the operation of the clamp as a whole.

The body of the clamp at the inner end of the opening 15 between the jaws is provided with a sloping surface 53 extending from a selected position of the inner end of the opening 15 outwardly and toward the jaw 14 housing the cam 34. The angle of the slope as illustrated in FIG. 1 is approximately 60 with respect to the face of the jaw 12', or the plate, and it may extend entirely across the opening 15. In any case it must extend from a position such that the corner edge nearest the cam of a plate of minimum thickness for the clamp, i.e. the corner along the edge toward the jaw 14 engages the slope 53 and is the only part of the plate engaging the end of the opening 15.

If it is assumed that the plate 16 in FIG. 1 has a minimum thickness for which the clamp with the particular cam 34 is adapted, it will be noted that the edge along the plate 16 in the dotted line position in FIG. 1 is the only part of the plate engaging the inner end of the opening 15. The sloping structure is particularly important and useful in applying the clamp for lifting plates from the horizontal or nearly horizontal position, as explained hereinafter in connection with the illustration in FIG. 1.

The cam 34 is biased and operated by a mechanism, shown at the top in FIG. 1 and in FIG. 2, comprising an overcenter mechanism including a strong spring 54 acting on the cam. In the mechanism, as illustrated, the ends of the spring 54 are respectively wound around and secured to cone-shaped attachment members 56 and 58, the latter of which is pivoted between a pair of spaced projecting lugs 69 on a pivot pin e2 (FIG. 2). The pivot pin 62 is inserted from the outside before the cam is mounted in the body of the clamp and extends only through the inside lug. The lugs 6% are integral with the hub of the cam and located to the side adjacent the plate 20 and on the opposite side of the pin 38 from the engagement edge 36 of the cam. The member 56 is pivotally mounted on a pin 64, having a threaded projecting end, and a nut 66, retained by a cotter pin. The nut on the projecting end of the pin 64 retains the member 56 in place adjacent to a spacer sleeve 68 which is welded to the outer movable end of an arm 7%. The pin in extends through the sleeve 68, the end of the arm 70, a curled friction spring washer 72 and one end of an operating handle 74. The projecting upper end of the pin 64- is threaded and carries a nut 76 held in place by a cotter pin.

The arm 7 ti comprises a relatively long rigid steel bar, one end of which carries the sleeve 68 and pin or, While the other end is pivoted to the side plate 18 in slightly spaced relation to the cam hub 37 by means of a stud pin '78 extending through a hole in the end of the arm 76 and a spacer Washer 89 and which is threaded into the side plate 18. The stud 78 is prevented from rotation by a Dutchman type key 82. The cam operating and biasing mechanism described above is protected against damage by being arranged Within the confines of the side plates 13 and 2t), and for this purpose, the inner corners of these plates are cut away by arcuate bevel type cut-outs $4 and 36.

The handle 74 in the position shown in FIG. 2 lies along the arm 7t) partly in the cut-out recess 84 of the plate 18. The handle, however, when in use is swung outwardly on th pivot pin 64 as shown in FIG. 3. In its folded position the handle 74 is shown in FIG. 2 as retained by a springpushed detent or pin ht which snaps into a recess in the handle 74 when the handle is moved to the folded position, but this detent may be omitted and the curled spring washer '72 relied on for that purpose. The handl 74 as shown in FIG. 3 may be folded-up in like manner. The handle is provided with holes 92 to be engaged by a hook and chain for remote operation.

The clamp as described above is particularly useful for lifting and handling heavy steel plates weighing from to 75 tons and having a thickness range in a single clamp of approximately 2 or more inches. The parts of the clamp are, therefore, constructed and arranged in accordance with these conditions. For example, the gripping face of the cam as is provided with a contour such as to give a substantially constant angle of contact with the plate to be lifted, regardless of th thickness of the plate within the given range. The pivot axis of the cam 34 is below the position of the axis of the pad 42, and in FIG. 1 the angle of contact is illustrated as being the angle between two dot-and- dash lines 94 and 96 extending from the pivot axis of the cam, the line 94 extending through the contact position of the cam with the plate 1.6, while the line 96 extends normal to the face of the plate 16 or to a plane along the face of the gripping pad 42. The lines 94 and )6, of course, may represent planes extending through the axis of the pin 38. Several of the teeth of the cam 34 engage and imbed into the plate 1'6 at a position opposite that of the pad 42 and the contact position is taken at the initial point of contact before penetration of the teeth into the plate which is approximately midpoint of the series of teeth engaging the plate. The angle between the lines or planes 94 and 96 is designated as t1 and preferably has a value approximating This value may vary within a few degrees but is advantageously within the range of from approximately 10 to approximately The smaller angles give a jamming pressure for certain purposes and in the use of non-marring clamps having large area smooth cams and pads, while the larger angles are used where ease of release is most important and teeth are used.

The full line position of the cam 34 in FIG. 3 is theretracted position in which the cam is located between the side plates 15 and 2d and held there by-the overcenter mechanism, including the spring 54 which is always under tension. The cam is independent of shackle 30 and,

the spring with the leverage provided on the cam is adapted to lift the cam to the retracted position when the overcenter mechanism is swung to the position shown in FIG. 3. FIG. 3 also shows the cam in dotted line position gripping a four inch plate 16', also shown in dotted line position. In this instance the angle of contact a is approximately the same as that in FIG. 1, approximately 13 to 14. When the angle of contact is made so acute that a very high gripping pressure results when the plate is lifted, the plate is actually jammed or wedged between the surfaces of the cam and those of the pad The teeth of the cam and pad being imbedded are interlocked so that to reverse the cam motion, the teeth on a non-sliding pad would have to displace some metal on the plate.

In the lifting of steel plates from the horizontal or nearly horizontal position, especially where these plates were somewhat thinner than the width of the opening between the jaws of the clamp, it was discovered that the clamp, without the sloping surface 53, when applied to the plate would roll on the pad and tip because of the Weight of the shackle and end portion of the clamp extending over the edge of the plate, so that when a lifting force was applied to the shackle, the gripping cam would roll on the surface of the plate, causing an engagement which was not far enough from the edge, thereby impair ing the safety of the lifting operation.

These disadvantages are overcome in the clamp accord ing to the present invention by the provision of the sloping surface 53 which in use prevents the tipping or rolling of the clamp on the pad. This is explained in connection with the operation of the clamp for lifting the plate 16 in accordance with the showing in FIG. 1 of the drawings. In this figure the plate 16 and the parts of the clamp are illustrated in their final full-line position after the horizontal plate is gripped by the clamp. When applying the.

clamp to the horizontal plate 16, the cam i in the retracted position illustrated in FIG. 3, and the operator slides the clamp onto the plate 16 and then applies the overcenter mechanism to rotate the cam into engagement with the upper surface of the plate. This has the effect of lifting the body of the clamp relative to the plate to move it to about the relative position shown in FIG. 1.v

After the clamp i in this position, and before any lifting force is applied to the clamp, the operator slides the clamp farther onto the plate, while keeping the pad up against the underside of the plate, until the corner edge is at the dotted line position in engagement with the sloping surface 53. This is the only point at which the plate engages the end of the opening 15 in the clamp and the slope is such that the plate is caught on the sloping surface 53, thereby preventing the clamp from rolling on the pad 42 or tipping with respect to the plate 16 so that the inner surfaces of the jaws of the clamp are held practically parallel with the plate.

With the clamp held in the position described, the teeth of the cam 34 will partially imbed in the surface of the plate because of the pressure of the spring 54, and the same will be true of the serrations in the pad 42, and the:

without any slippage, and as the plate is lifted, the clamp.

will move slightly relative to the plate until the plate is at about the full-line position in FIG. 1 and the pad 42 has slid outwardly in the clamp to the outer end of the recess 44.

It will be understood that any plate having a thickness greater than the plate, 16 and less than the full width of the space 15, when lifted from the horizontal position,

will have its upper edge engaging the sloping surface 53, so that no tipping or rolling of the clamp occurs while it is being applied to the plate.

The slope of the surface 53 should be such that the edge corner of the plate will not readily slide thereon when the cam and pad engage the plate. The slope illustrated in the drawings is approximately 60 with respect to the surface of the plate or to the inner surface of the jaw 12. This slope may be within the range of from 45 to 75.

If a cam were provided in the clamp illustrated in the drawings which would be long enough to be useful for lifting plates as thin as /8 inch, it will be understood that the slope 53 would necessarily extend entirely across the inner end of the opening 15. As illustrated in FIG. 1, the plate 16 has about the minimum thickness to be lifted by the clamp as shown and, therefore, the sloping surface 53 is extended only a short distance below the upper surface of the plate. The sloping surface prevents the rolling and tipping of the clamp and riding of the plate when it is'applied to the plate and, therefore, promotes the safe operation of the clamp in the lifting of heavy plates of the type referred to.

If the plate 16 is placed in a vertical position at the point of location after being lifted by the clamp, the clamp is lowered relative to the plate and pad until the edge 55 engages the slope 53, whereupon the clamp is released in the manner described hereinafter in connection with FIG. 3. If the plate is located in a horizontal position after lifting, the release of liftingpressure on the clamp will permit the tremendous stress and strain in the clamp to effect slight counterclockwise rotation of the cam 34 and the sliding of the pad 42 in the recess 44. Then the operator can swing the overcenter mechanism to the position shown in FIG. 3, whereupon the cam 34 will be retracted into the body of the clamp so that the clamp is completely released.

Only if extenuating circumstances exist will the cam stick when the overcenter mechanism is moved to the position in FIG. 3, because the internal stress along line 94 is so great that its component force downward is sufficient to slide the clamp body downward on the back of the pad 42. Cam 34 can roll in its tracks without metal displacement until it is free. Then the pad teeth can move outwardly from its deep teeth impressions. The cam contact angle is critical here, as too high an angle will not grip, but too low an angle will not release, so the proper constant angle is critical.

In the operation and use of the clamp for lifting plates in an upright position as shown in FIG. 3, with the lifting shackle 39 attached to a crane or other lifting mechanism, the clamp, with the cam in the retracted position as shown in FIG. 3, is let down over a plate, such as the 4 inch plate 16', until its left-hand corner engages the sloping surface 53. When the clamp has been lowered to this position, the operator, by the use of the handle 74, swings the overcenter mechanism to the position shown in FIGS.

1 and 2, thereby rotating the cam on its pivot pin 38 into engagement with the plate. The tension of the spring 54- is such as to apply a strong gripping pressure sufficient to slightly imbed the teeth of the cam and the pad into the plate. When the clamp and plate are lifted, the teeth are further imbedded into the plate, a spreading strain is on the jaws and the cam is rotated slightly. This results in the plate slipping on the pad, if it is all the way down, until equilibrium is established between the stresses and strains in the clamp, and the plate is jammed between the cam and pad because of the small acute angle of contact. position shown inFIGS. 1 and 3, that is, at the bottom of the oval recess 44. The pad is freely slidably mounted in the jaw 12 so that when the clamp is in upright position and not gripping a plate, it is always in the lower position.

7 After the plate 16 is lifted to the desired location or In these operations the gripping pad 42 is in they e2 set to rest upright on the ground, the clamp is lowered by the crane and the weight of the clamp and downward reactive force of the cam on the clamp body carries it downwardly with respect to the plate and pad, because the pad 42 slides upwardly in the recess 44 while it is still in engagement with the plate. The clamp moves down and is held by the spring actuated cam which has rolled back almost to its point of beginning where the cam is held only by the spring in the grooves it made when the load was started to be applied, thereby loosening the pressure of its teeth in the surface of the plate caused by lifting. At this point the operator either by hand or by a hook pulls out the handle 74 and swings the arm 76 and pring 54- around to the position shown in FIG. 3, so that the spring tension is applied in a direction to move the cam 34 to the retracted position shown in FIG. 3. If the plate 16 is let down to a horizontal position after being lifted, the clamp is released in the manner described above with respect to FIG. 1.

While the cam 34 has some weight and may be lightly caught in the indentations by the spring pressure, the spring 54 has such a force and is connected at such a distance from the pivot axis of the cam that when rcversed, it applies a torque to the cam sufficient to actually flip the cam to the retracted position and hold it there. The overcenter mechanism comprising the bar or arm 7%) and spring 54 are located completely within the borders of the plates 18 and it} in either position, so that they cannot be damaged it the clamp is banged around. The handle 74 is also foldable in on the side of the bar 70.

In the operation of a clamp provided with a low cam angle the plates are wedge and jammed in the clamp when lifted because of the small contact angle of the cam. The vertically slidable gripping pad 42, therefore, cooperates with the cam to effectively loosen the jamming grip when the plate is set down and the clamp permitted to move relative to and farther onto the plate. The pad 42 is provided with a large surface surrounding the shank 46, as apparent from the showing in FIG. 4, for example, so that the back surface of the pad slides readily on the back surface of the oval cut-out or recess 44.

if during the handling of a plate, such as the plate 16, it is set down momentarily and the clamp allowed to move downwardly with respect to the plate 16 moving the gripping pad upwardly and rotating the cam, the clamp will not be released from the plate because of the continuing stress applied by the spring 54. There is, therefore, no danger of the clamp losing its grip on the plate because, with the spring 54 and bar 7d in the position shown in FIG. 1, the plate may be relifted, and when it is, the pad 42 merely slides down to its lower position and the cam rotates back to its jamming position, with the teeth of both occupying their original positions in the plate.

The safety and ease of operation of the clamp is greatly enhanced by the sloping surface 53 particularly in lifting plates from the horizontal position. The clamp is also safe because the gripping cam is not linked to the shackle and no plate can be lifted unless the operator applies the clamp, i.e., unless the overcenter mechanism is operated to put the cam in engaging position on a plate. Where in known types of clamps the cam may contact the plate Without the spring pressure being applied, the operators using such clamps sometimes lift the plates without applyinr the spring tension against the cam. This is impossible in my arrangement and because of this, some safety engineers have declared it a great safety feature.

Since only one illustrative example of a lifting clamp according to the invention has been described, it is to be understood that certain modifications and changes may be made without departing from the spirit and scope of the invention as defined by the appended claims. For'example, while the clamp may be made of steel, it is understood that it may be made of other suitable alloys and that the cam and pad will be made of hardened steel or other suitable hardened alloys, also that the parts may be made of forgings or castings where some of the parts may be combined into less parts With reinforcing ribs and parting lines altered.

I claim:

1. In a clamp of the type used for lifting steel plates including a body having spaced opposed projecting jaws defining a U-shaped structure and providing a p1ate-re ceiving space between the jaws open at the projecting ends of the jaws, said space being adapted for receiving a steel plate to be lifted by the clamp, a lifting shackle for the clamp opposite said space, a gripping pad carried by one of said jaws and having a gripping surface facing the other jaw across said space, and a gripping cam having an arcuate plate gripping surface and being pivotally mounted in the other jaw with its arcuate gripping surface facing toward the gripping surface of the pad, the improvement in which said pad is slidably mounted for lengthwise movement relative to the inner face of said one jaw, the inner face of said one jaw including a recess extending lengthwise of said one jaw, said gripping pad including a head slidably located in said recess and having a serrated portion projecting from the inner face of said one jaw, said one jaw being provided with an opening extending lengthwise of the recess, and a shank on the back of the head of the pad extending into said one jaw and movable lengthwise in said opening.

2. A clamp as claimed in claim 11, in which the cam is arranged independent of the lifting shackle, and an overcenter mechanism comprising a tension spring one end of which is attached under tension to the heel of the cam and which in one position forces the arcuate surface of the cam into gripping engagement with a steel plate located in said space and which in another position holds the cam in the jaw in which it is mounted.

References Cited by the Examiner UNITED STATES PATENTS 747,()65 12/03 Harnann 294-101 2,370,411 2/45 Monaco 294104 2,446,610 8/ 48 Renfroe 294-104 2,986,422 5/61 Renfroe 294101 SAMUEL F. COLEMAN, Primary Examiner. ANDRES H. NIELSEN, LOUIS J. DEMBO, Examiners.

Claims (1)

1. IN A CLAMP OF THE TYPE USED FOR LIFTING STEEL PLATES INCLUDING A BODY HAVING SPACED OPPOSED PROJECTING JAWS DEFINING A U-SHAPED STRUCTURE AND PROVIDING A PLATE-RECEIVING SPACE BETWEEN THE JAWS OPEN AT THE PROJECTING ENDS OF THE JAWS, SAID SPACE BEING ADAPTED FOR RECEIVING A STEEL PLATE TO BE LIFTED BY THE CLAMP, A LIFTING SHACKLE FOR THE CLAMP OPPOSITE SAID SPACE, A GRIPPING PAD CARRIED BY ONE OF SAID JAWS AND HAVING A GRIPPING SURFACE BEING THE OTHER JAW ACROSS SAID SPACE, AND A GRIPPING CAM HAVING AN ARCUATE PLATE GRIPPING SURFACE AND BEING PIVOTALLY MOUNTED IN THE OTHER JAW WITH ITS ARCUATE GRIPPING SURFACE FACING TOWARD THE GRIPPING SURFACE OF THE PAD, THE IMPROVEMENT IN WHICH SAID PAD IS SLIDABLY MOUNTED FOR LENGTHWISE MOVEMENT RELATIVE TO THE INNER FACE OF SAID ONE JAW, THE INNER FACE OF SAID ONE JAW INCLUDING A RECESS EXTENDING LENGTHWISE OF SAID ONE JAW, SAID GRIPPING PAD INCLUDING A HEAD SLIDABLY LOCATED IN SAID RECESS AND HAVING A SERRATED PORTION PROJECTING FROM THE INNER FACE OF SAID ONE JAW, SAID ONE JAW BEING PROVIDED WITH AN OPENING EXTENDING LENGTHWISE OF THE RECESS, AND A SHANK ON THE BACK OF THE HEAD OF THE PAD EXTENDING INTO SAID ONE JAW AND MOVABLE LENGTHWISE IN SAID OPENING.

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