US3754474A

US3754474A - Gripper pad

Info

Publication number: US3754474A
Application number: US00176952A
Authority: US
Inventors: A Palynchuk
Original assignee: Corod Manufacturing Ltd
Current assignee: Corod Manufacturing Ltd
Priority date: 1971-09-01
Filing date: 1971-09-01
Publication date: 1973-08-28
Anticipated expiration: 1990-08-28

Abstract

A gripper pad, for use in a track-type continuous rod service rig, is provided. The pad comprises a deformable elastomer block having a series of aluminum studs embedded in its upper face. The provision of the studs results in higher pressure being applied to the rod, against which the pad is squeezing, than is applied to the block itself by the rig track.

Description

0 q ilmte States Patent 11 1 1111 3,754,474 Palynchuk 1 Aug. 28, 1973 GRIPPER PAD 3,305,048 2/1967 Brilando 188/251 3,585,102 6/1971 Bur ess 188/251 [751 Invent: Alexander Palynchuk, Edmnmn, 2,775,869 1/1957 P0151 74/162 Alberta Canada 2,841,961 7/1958 Lucas 74/162 [73] Assignee: Corod Manufacturing Ltd.,

Edmonton, Alberta, Canada Primary Examiner-Charles .l. Myhre Assistant ExaminerWesley S. Ratliff, Jr. [22] Flled' sept' 1971 Attorney-Ernest Peter Johnson 21] App1.No.: 176,952

[57] ABSTRACT [52] US. Cl. 74/162, 188/251 A [51] Int. Cl. F16d 41/20 A grfpper f for use m a track'type cfmtmuous rod [58] Field of Search. 188/24 7 4/162, serv1ce rig, 1s provided. The pad compnses a deform- 26o/75 77 5 able elastomer block having a series of aluminum studs embedded in its upper face. The provision of the studs [56] References Cited results in higher pressure being applied to the rod, against which the pad is squeezing, than is applied to UNITED STATES PATENTS the block itself by the rig track. 1,891,723 12/1932 Novak 188/251 3,003,609 10/1961 Lang 4 Claims, 7 Drawing Figures PAIENIEDmzams 3,754,474

SHEET 2 OF 2 END LOAD I? S.

l I l l l l 0 I000 2000 3000 4000 5000 $00 GRIPPER PAD BACKGROUND OF THE INVENTION This invention relates to a gripper pad. More particularly, it is concerned with a gripper pad which is adapted for use in one of the endless tracks of a continuous string service rig.

In US. Pat. No. 3,559,905, I describe a service rig which is suitable for tripping a continuous rod or tubing string (generically termed in the claims as an oilfield string"). The rig is equipped with a pair of opposed, spaced, endless tracks. Each track includes a sprocketdriven chain which carries a row of gripper pads. In operation, the rod string is gripped between the opposed rows of gripper pads and the tracks are driven to feed the string into or out of the well.

SUMMARY OF THE INVENTION It is an object of the invention to provide a novel gripper pad which is sufficiently flexible to accomodate normal changes in rod or tubing diameter and the passage of paraffin scrapers and yet which can be squeezed against the oily, wax-covered string to generate the frican upper face which is termed its working face. This face is preferably concave in contour. The block itself is formed of an elastomer, preferably having a hardness greater than 80 on the Shore A scale. In the best mode known to me, the block is formed of polyurethane having a hardness within the range 45 to 55 on the Shore D scale.

The studs are embedded in the block. The upper end surface of each stud is disposed substantially flush with the blocks working face. The stud is preferably made of a metal such as aluminum or aluminum alloy since these materials have desirable work-hardening characteristics and a high coefficient of friction when in contact with steel. They are also softer than steel and thus will not score the string.

The block is encased in a rigid container to provide a gripper unit". The container tightly encloses the ends, bottom and sides of the block and, when in use, is affixed to the rig track.

It will be appreciated that a very large side force must be applied by the track and gripper pad on the rod or tubing string to generate frictional forces in an amount sufficient to suspend the string in a well. For example, in order to suspend a 6,000 foot long string of 5t; inch diameter oil-coated rod, it may be necessary to apply a side force on the rod of 4000 p .s.i. or more. A side force of this magnitude tends to deform the pad at it's working face to such an extent that shearing or failure of the elastomer can easily occur. By incorporating the rigid, free-floating studs into the elastomer block, I find that higher side forces are generated at the rod face then would be the case if the studs were not present.

This increment in force appears to arise from the movement of the elastomer past the stud body. The increase in side force, of course, means that there is a corresponding increase in friction force. Additionally, the high co-efficient of friction which derives from the contact of metal with metal is an aid in increasing the friction forces.

The novel pad has two particularly advantageous features: it can deform to accomodate changes in size of the rod string moving past it; in addition, it is adapted to provide adequate friction forces at the rod face without undue deformation of the elastomer.

DESCRIPTION OF THE DRAWINGS In the drawings:

FIG. 1 is a perspective view of the gripper unit;

FIG. 2 is a bottom view of the gripper pad;

FIG. 3 is an end view of the gripper pad;

FIG. 4 is a section view along the line AA in FIG.

FIG. 5 is a side view of a stud; FIG. 6 is a side view of another stud; FIG. 7 is a plot of the side load applied to a pair of opposed gripper pads versus the end load required to cause a rod gripped between the pads to slip. Curve 1 relates to gripper pads equipped with studs. Curve 2 relates to gripper pads without studs.

DESCRIPTION OF THE PREFERRED EMBODIMENT Turning now to FIG. 1, a gripper unit is designated by the numeral 1. The gripper unit 1 consists of a container 2 and a gripperpad 3. The pad 3 includes a block 4 having studs 5 embedded therein. Collapse holes 6 are formed in the back of the block 4.

The block 4 is generally rectangular in shape. It has a concave upper working face 7 and one or more spaced, stud-receiving cavities 8 formed in its upper segment. These cavities 8 are aligned in spaced relation along the longitudinal axis of the block 4. A plurality of downward opening, inward directed, tapered holes 6 are formed in the lower segment of the block 4.

The block 4 is formed of a defonnable elastomer material. It has a hardness greater than 80 on the Shore A scale; if it is softer, the material may deform to such an extent that failure can occur. I prefer to use polyurethane having a hardness within the range 45 55 on the Shore D scale. This material is capable of transmitting the loads which are involved without much deformation; yet it is sufficiently flexible to accomodate normal variations in string diameter. The best elastomer for this use of which I am aware has a hardness within the preferred range and has the following physical characteristics:

compression set (ASTM B) 33% tear strength (psi) I tensile strength (psi) 7500 elongation 400 The collapse holes 6 are provided in the bottom segment of the block 4. These holes 6 are not essential; however, when the block 4 is subjected to load, the elastomer deforms around and closes the holes rather than bulging out at the working face 7, where the danger of failure of the material is greater. The size and shape of the holes 6 has some efi'ect on the performance of the elastomer. Tests show that if the holes have a diameter greater than about 15/64 inches, the

proportional relationship between side load and deformation is lost; this is not desirable as the pad begins to act as a rigid block. I prefer to provide holes which are inches deep and taper inwardly from a diameter of 13/64 inches to a diameter of 9/64 inches. The centers of the holes are spaced about it; inches apart.

The rigid studs 5 are pressed into the cavities 8. The top surface or end of each stud S is preferably flush with the block working face 7, although the surface may be located a small distance above or below the working face 7 without affecting the operation of the gripping pad 3. The inner end of each stud 5 is spaced inwardly from the face of the block 4 which is opposite to the working face 7. The studs 5 are formed of a metal which is softer than steel, preferably aluminum or an aluminum alloy. They may be provided with locking means, such as the groove 9, shown in FIG. 5, or the flange 10, shown in FIG. 6. Studs which are of very small diameter, in the order of less than one-eighth inch, have a tendency to shift into a misaligned position when loaded; therefore, studs having a diameter of about one-half inch or larger are preferable. When using a 4 X 1.25 X 1 inch gripper block, Iprefer to pro:

vide 0.50 inch diameter x 057mm long cylindriail studs in combination with 0.90 inch square x 0.69 inch long square studs, as illustrated in FIG. 1.

In FIG. 8, curves 1 and 2 illustrate the surprising advantage which is gained by the use of the studs. The curves shown are developed by gripping an oily rod between two gripper pads using rams to squeeze the pads against the rod. Another ram is applied axially to the rod. The pressure at which the rod slips is recorded for different side loads. At a side load of 4000 p.s.i., it will be noted that there is a 100% improvement obtained as a result of including the studs in the gripper pad.

The gripper pad 3 fits into a groove 11 formed in container 2. The side walls of the container 2 extend up to the working face 7. Pins 12 are inserted through openings 13 to abut the ends of the pad. In this manner. the pad 3 is restrained in all directions but one. The container 3 is attached in any conventional manner to the tracks of the rod rig.

In operation, the tracks of the rig press two opposed gripper units 1 against a rod string which extends between them. The elastomer block 4 grips the rod firmly without biting into it and is capable of transmitting side forces in the order of 4000 p.s.i. without failure. The rigid container and rod minimize deformation of the elastomer. The studs 5 bite through the oil film on the rod and transmit a side force to it which is greater than the force originally applied to the elastomer block.

What is claimed is:

1. A gripper unit comprising:

a gripper pad comprising a deformable elastomer block having a working face,

and

at least one rigid stud embedded in the block, the

outer end of the stud being disposed substantially flush with the working face and its inner end being spaced inwardly from that face of the block which is opposite to the working face; and

rigid container means tightly encasing the sides of the block, up to the working face, as well as the end and bottom surfaces of the block.

2. The gripper unit as set forth in claim 1 wherein:

the elastomer has a hardness greater than about shore A.

3. The gripper unit as set forth in claim 1 wherein:

the elastomer is polyurethane having a hardness within the range 45 55 shore D, and the stud is formed of aluminum.

4. The gripper unit as set forth in claim 2 wherein:

the block has a plurality of small, inwardly extending holes formed therein whereby the elastomer may initially be deformed to close the holes.

* It 1r

Claims

1. A gripper unit comprising: a gripper pad comprising a deformable elastomer block having a working face, and at least one rigid stud embedded in the block, the outer end of the stud being disposed substantially flush with the working face and its inner end being spaced inwardly from that face of the block which is opposite to the working face; and rigid container means tightly encasing the sides of the block, up to the working face, as well as the end and bottom surfaces of the block.

2. The gripper unit as set forth in claim 1 wherein: the elastomer has a hardness greater than about 80 shore A.

3. The gripper unit as set forth in claim 1 wherein: the elastomer is polyurethane having a hardness within the range 45 - 55 shore D, and the stud is formed of aluminum.

4. The gripper unit as set forth in claim 2 wherein: the block has a plurality of small, inwardly extending holes formed therein whereby the elastomer may initially be deformed to close the holes.