US3697118A

US3697118A - Automatic lifting tongs

Info

Publication number: US3697118A
Application number: US93698A
Authority: US
Inventors: Crichton Lockhart Johnstone; John Woodhouse Paton
Original assignee: Individual
Current assignee: Individual
Priority date: 1969-12-02
Filing date: 1970-11-30
Publication date: 1972-10-10
Anticipated expiration: 1989-10-10
Also published as: JPS4935375B1; GB1326743A; DE2058858A1; BE759705A; CA941860A; NL7017584A; FR2073445B1; FR2073445A1

Abstract

Lifting tongs have a pair of primary arms forming a pair of jaws for engagement with a workpiece. A latch mechanism interlocks the two arms so that the tongs can be opened and closed automatically by successive movements opening the jaws. Following a first movement opening the jaws, the latch mechanism is engaged to hold the jaws open; the latch mechanism is disengaged by a subsequent movement opening the jaws whereupon it releases the arms to allow the jaws to close. The latch mechanism includes a pivoted latch member mounted on one arm, which latch member is movable between two equilibrium positions to define the engaged and disengaged positions of the latch mechanism.

Description

United States Paten J ohnstone et al.

[ AUTOMATIC LIFTING TONGS [72] Inventors: Crichton Lockhart Johnstone, 135 Avon Street, Motherwell; John Woodhouse Paton, 3 Clark Street, Newmains, both of Scotland [22] Filed: Nov. 30, 1970 [21] Appl. No.: 93,698

[30] Foreign Application Priority Data Dec. 2, 1969 Great Britain ..58,899/69 [52] US. CLI ..294/ll0 R, 294/119 [51] Int. Cl. ..B66c 1/44 [58] Field of Search ..294/109, 110, 119, H8, 106, 294/1 16; 292/338, DIG. 4

[56] References Cited UNITED STATES PATENTS 2,337,177 12/1943 Breslav ..294 /l 10 [451 Oct. 10,1972

Primary Examiner-Even C. Blunk Assistant Examiner.lohnny D. Cherry Attorney-Holcombe, Wetherill & Brisebois [57] ABSTRACT Lifting tongs have a pair of primary arms forming a pair of jaws for engagement with a workpiece. A latch mechanism interlocks the two arms so that the tongs can be opened and closed automatically by successive movements opening the jaws. Following a first movement opening the jaws, the latch mechanism is engaged to hold the jaws open; the latch mechanism is disengaged by a subsequent movement opening the jaws whereupon it releases the arms to allow the jaws to close. The latch mechanism includes a pivoted latch member mounted on one arm, which latch member is movable between two equilibrium positions to define the engaged and disengaged positions of the latch mechanism.

' 10 Claims, 5 Drawing Figures PATENTEnw'wwn 3.697.118

SHEET 1 [IF 3 PATENTED 3.697.118

' sum-2 0F 3 AUTOMATIC LIFIING TONGS This invention relates to lifting tongs. The invention is particularly applicable to lifting tongs which are intended to lift relatively heavy workpieces, for example, ingots such as are handled in Steel Works, and which must for safety reasons be remotely controlled.

Lifting tongs of this kind must be capable of retaining in an open position the jaws which engage with the workpiece and provide quick and easy closure of the jaws onto the workpiece after they have been placed in the correct position with respect to the workpiece. The tongs must in addition provide for quick and easy opening of the jaws to release the workpiece when this has been hoisted into position and subsequently again to retain the jaws open for a further sequence of operatrons.

One method of meeting these requirements has been to operate the jaws by means of a mechanism known as dogging gear which is actuated by a cable independently of the cable by which the tongs are hoisted. This system, while satisfactory and reliable under arduous conditions such as are encountered in an ingot soaking pit, requires the hoisting crane to be provided not only with an additional and independent operating mechanism for the gear, but also with an additional set of manual controls which require operation in an already complex console.

Attempts have been made to overcome the cost and operational difficulty of dogging, by providing tongs with means which automatically lock and unlock the jaws in response to the upward thrust against the arms of the tongs themselves.

A number of such tongs in which the means generally comprise a latching mechanism have been proposed; however, these have been found susceptible to impact, for example, by surging against the sides of the soaking pit and have been found unsatisfactory either in this respect or in respect of cost.

According to one aspect of the present invention, there is provided lifting tongs comprising a pair of primary arms pivotally connected to one another to form a pair of jaws for engagement with a workpiece, and a latch mechanism connected to the primary arms, the latch mechanism including a pivotally mounted latch member which adopts a first position where it prevents closure of the jaws, and a second position where it allows closure of the jaws, in response to successive opening movements of the jaws.

Preferably, the latch member is pivotally mounted upon one arm of the tongs and is adapted to engage with a cooperating projection provided on the other arm.

In one embodiment the latch member is pivotally mounted on one arm and has an opening to receive a cooperating projection on the other arm, the opening being so shaped that the projection is moved around at least part of the periphery of the opening by the said successive opening movements.

Preferably, the opening has a region adapted to restrain the projection against movement corresponding to closure of the jaws, the periphery may include a re-entrant portion for engaging the projection to restrain its movement with respect to the latch member in the direction corresponding to closure of the jaws. Alternatively, however, such selective restraint against movement may be provided by an auxiliary latch member which is displaced by the projection on one part of its movement corresponding to opening of the jaws and which subsequently acts to restrain the projection against movement corresponding to closure of the aws.

Preferably, the said first and second positions of the pivoted latch member are two equilibrium positions. In one such embodiment the latch member reaches each equilibrium position during relative movement between itself and the projection on the said other arm of the tongs corresponding to closure of the jaws, and is displaceable from the equilibrium position only by relative movement corresponding to opening of the jaws. In this case the projection in one equilibrium position is urged against that region of the opening which contains the re-entrant portion or auxiliary latch, to permit engagement to occur. In response to an opening of the jaws the latch member subsequently is moved into the second equilibrium position in which the projection is urged against the opposed region of the opening preventing re-engagement with the re-entrant portion as the cycle is continued.

Preferably the latch member is moved between the equilibrium positions by cam reactions between the projection and the profile of the opening. The equilibrium positions may be maintained solely by gravity or may be assisted by an over-center spring arrangement suitably incorporated into the latch mechanism.

The projection may incorporate a roller effective to reduce the frictional drag produced by movement relative to the periphery.

Preferably, the arms of the tongs are in the form of spaced plates secured together by bridges; in this case the latch mechanism is disposed between the plates to provide protection particularly against mechanical impact. The latch mechanism may be secured between any region of any pair of arms of the tongs which cooperate to produce opening and closure of the jaws.

One embodiment of the invention will now be particularly described by way of example, with reference to the accompanying drawings in which:

FIG. 1 is a perspective side view of the tongs according to the invention,

FIG. 2 is a sectional side view which shows the tongs fully extended with the jaws closed in engagement with a workpiece,

FIG. 3 is a sectional side view of the tongs shown in FIG. 1 and in one operational position, and

FIG. 4 is a fragmentary view of the latch mechanism shown in FIG. 2 but in a second operational position.

FIG. 5 is a view of an alternative latch mechanism shown in the same position as the latch mechanism of FIG. 4.

Referring to the drawings and in particular to FIG. 1, the lifting tongs comprise two primary arms 2 and 4 each in the form of two identical spaced plates secured together by bridges S in a manner well known in the art. The arms are pivoted to one another at a point substantially between their normally upper ends and their lower ends which constitute the jaws for engagement with the workpiece. To assist the jaws to grip, in this case the sides of an ingot being lowered into and raised from a soaking pit, the jaws are provided with tapered tips 8 effective to bite into the ingot sides and lessen the risk of accidental release during hoisting.

Two

secondary arms

9 and 10 have their lower ends secured by way of

pivots

12 and 14 to arms 2 and 4 and have both their upper ends pivoted to a yoke 16 by which the tongs can be secured to the hook or sling of a suitable lifting crane. In use, hoisting produces lifting of the tongs as a whole while causing the jaws 8 to close upon and grip a workpiece located between them. I

A latch mechanism is provided to automatically maintain the jaws in the open position to receive a workpiece and subsequently automatically to release the jaws for closure.

The latch mechanism comprises a member 20 secured to arm 4 by way of a pivot 21 and having a profiled opening 22 terminating at its upper end in a substantially linear guide portion 24, which although shown open-ended may be closed off. A projection 26, which may be in the form of a fixed spigot or a roller mounted upon primary arm 2 is arranged to be received within the opening 22 and to slidably move cyclically around its periphery.

With the jaws in the closed position as shown in FIG. 2, either engaging a workpiece or otherwise, the projection 26 will lie at the upper end of the guide portion 24. The length of the guide portion 24 is selected to be sutficient to accommodate the excursion of the spigot 26 for any particular degree of closure which is limited by an abutment 36 provided on arm 4 and arranged for engagement with arm 2.

As the tongs are lowered onto a supporting surface, upward thrust, applied directly or indirectly to the arms 2 and 4 by way of a workpiece, produces opening movement of the jaws and causes the projection 26 to move down the guide portion 24 until it reaches the lower guide limit defined by elbow 30.

The center of gravity of the member 20 is selected such that at this stage it is in a first equilibrium position whereby further downward movement of the projection relatively to the opening 22 automatically allows the member to tilt for engagement of the projection with a re-entrant portion 32 of the opening periphery (see FIG. 3). The shape of the re-entrant portion is effective to prevent disengagement while the weight of the tongs is supported solely by the yoke 16 and prevents closure of the jaws 8.

A successive and independent upward thrust against the arms 2 and 4 by re-lowering of the tongs against the supporting surface reopens the jaws to release the workpiece, if originally held. Reopening continues the cyclic movement of the spigot around the periphery of the opening 22 to the lowermost point 34 (see FIG. 4); further closure when this point is reached being prevented by an additional abutment 28.

At this stage the member 20 is moved into its second equilibrium position by reaction between the projection 26 and the profile of the opening 22 so that with further closure of the jaws produced by lifting of the tongs, the portion 40 of the channel profile is urged against the projection 26. This enables the projection to continue and complete its cycle to the top of the guide portion 24 without re-engagement with portion 32.

The tongs are now ready for a further cycle of operation in response to successive forces applied to arms 2 and 4.

In use, the crane which hoists the automatic lifting tongs of the invention is controlled from a cabin often at considerable height above the ground level. To enable the operator to obtain a clear indication of the extent to which the jaws have opened, particularly to see if they have opened sufficiently to positively operate the latch mechanism, a suitable indicator may be provided on the tongs. This may be of any type well known in the art, for example a pointer arm, which conveniently is constituted by an extension of the linear guide portion 24 of the latch member 20.

It will be appreciated that while a re-entrant portion 32 has been described as automatically preventing closure, this could otherwise be achieved, for example, by a further pivoted latch.

It will also be appreciated that while the tongs have been described as provided with jaws in the form of tapered tips, any form of jaw adapted to engage with different types of workpieces, for example, barrels, planks, sacks, not necessarily connected with the steel industry, may be used.

For the sake of safety the crane hook is fitted with an attachment or is adapted, as is well known, to prevent release of the tongs if these are excessively lowered.

FIG. 5 shows an alternative latch mechanism in the same position as the latch mechanism of FIG. 4. The alternative latch operates on substantially the same principle except that an auxiliary latch 50 is provided in place of the re-entrant portion 32. The latch 50 is pivoted at 51 and biased in a counter clockwise direction by a spring 52 against a stop 53. The pivoted latch member 20 is moved by cam reaction with the projection 26 in exactly the same way as the preceding embodiment but a spring 54 is provided in an overcenter arrangement to assist in biasing the latch member 20 to its equilibrium positions. The spring 54 is compressed between a stop 55 mounted on the arm 4 and a stop 56 formed on the far end of an opening 57 in the latch member 20, within which the spring 54 is located. The position of the over-center spring in the other equilibrium position is shown at 58 in broken outline.

We claim:

1. Lifting tongs comprising:

a pair of primary arms pivotally connected to one another and defining a pair of jaws for engagement with a workpiece; and

a latch mechanism mounted on said primary arms, said latch mechanism including a latch member having an internally profiled opening pivotally mounted on one of said arms and a projection rigidly mounted on the other of said arms, said projection being retained in and co-operating with said opening;

the internal profile of said opening so shaped and the mounting points on said primary arms of said projection and latch member being so positioned that, in response to successive opening movements of said jaws, said projection moves within said opening around the periphery of said opening and pivots said latch member between a first position preventing closure of said jaws and a second position allowing closure of said jaws.

2. The lifting tongs of claim 1, wherein said periphery of said opening has a region integral with said latch member adapted to restrain said projection against movement corresponding to closure of said jaws.

3. The lifting tongs of claim 2, wherein said region includes a re-entrant portion for engaging said projection to restrain its movement with respect to said latch member in the direction corresponding to closure of said jaws.

4. The lifting tongs of claim 3, wherein said region includes an auxiliary latch member displaceable by said projection on the part of its movement corresponding to opening of said jaws and which subsequently acts to restrain said projection against movement corresponding to closure of said jaws.

5. The lifting tongs of claim 1, wherein said first and second positions of said pivoted latch member are equilibrium positions.

6. The lifting tongs of claim 5 wherein said latch member reaches each equilibrium position during movement of said primary arms corresponding to closure of said jaws, said latch member being placeable from said equilibrium position only by movement of said primary arms corresponding to opening of said aws.

7. The lifting tongs of claim 5 wherein said latch member is moved between said equilibrium positions by cam reactions between said projection and said internal profile of said opening.

8. The lifting tongs of claim 5 wherein said equilibrium positions of said latch member are maintained by a spring in an over-center arrangement.

9.The lifting tongs of claim 5 wherein said equilibrium positions of said latch member are maintained by gravity, said latch member being mounted with its pivot below its center of gravity.

10. The lifting tongs of claim 1, wherein said arms of said tongs are in the form of space plates having bridges securing said spaced plates together, said latch mechanism being disposed between said spaced plates.

UNITED STATES PATENT OFFICE CERTIFICATE F CQ'RECTION Patent 3,697,118 Dated October 10 1972 CRICHTON LOCKHART JOHNSTO NE and I JOHN WOODHOUSE PATON It is certified that error appears in the above-identified patent Y and that said Letters Patent are hereby corrected as shown below:

[73] Assignee: The British Steel Corporation, London, England Signed and sealed this 22nd day of May 1973.

(SEAL) Attest:

Y EDWARD M.FLET CHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents F ORM PO-l 050 (10-69) USCOMM-DC 6Q376-P69 k U.S. GOVERNMENT PRINTING OFFICE: 1969 Q3$6-3S4

Claims

1. Lifting tongs comprising: a pair of primary arms pivotally connected to one another and defining a pair of jaws for engagement with a workpiece; and a latch mechanism mounted on said primary arms, said latch mechanism including a latch member having an internally profiled opening pivotally mounted on one of said arms and a projection rigidly mounted on the other of said arms, said projection being retained in and co-operating with said opening; the internal profile of said opening so shaped and the mounting points on said primary arms of said projection and latch member being so positioned that, in response to successive opening movements of said jaws, said projection moves within said opening around the periphery of said opening and pivots said latch member between a first position preventing closure of said jaws and a second position allowing closure of said jaws.

6. The lifting tongs of claim 5 wherein said latch member reaches each equilibrium position during movement of said primary arms corresponding to closure of said jaws, said latch member being placeable from said equilibrium position only by movement of said primary arms corresponding to opening of said jaws.

9. The lifting tongs of claim 5 wherein said equilibrium positions of said latch member are maintained by gravity, said latch member being mounted with its pivot below its center of gravity.