US2431165A - Testing machine grip - Google Patents

Description

7- F. s. BUCKINGHAM TESTING MACHINE GRIP Filed Aug. 24, 1944 INVENTOR Francs S Buckin h A TORNEY Patented Nov. 18, 1947 TESTING MACHINE GRIP Francis S. Buckingham,

Baldwin Locomotive Works, a corporation of Pennsylvania to The Glenolden,

Pa., assignor Application August 24, 1944, Serial No. 550,998

9 Claims. (Cl. 24-2635) This invention relates generally to materials testing machine grips and more particularly to grips having removable gripping face inserts.

A great many attempts have heretofore been made to provide removable gripping face inserts in order to avoid recutting the gripping face on a solid block type of grip which sometimes must be completely discarded because of the difficulty or impossibility of reforming the face. The problem of providing economical and durable grips capable of repeated use has long existed without adequate solution. In some instances removable inserts have been formed from strips of hardened file stock on which gripping teeth are out. The strips were inserted longitudinally in a main grip block and anchored at the bottom of the block to resist the tension pull of the specimen. These inserts repeatedly failed by cracking very quickly after being placed in use.

It is an object of my invention to provide an improved gripping face insert that reduces cracking to a minimum while still providing a gripping face that is sharp, durable and economical in construction, operation and maintenance.

A further object is to provide an improved file type grip insert that may be easily and quickly removed from or replaced in a grip holder.

Other objects and advantages will be more apparent to those skilled in the art from the following description of the accompanying drawing in which:

Fig. 1 is a fragmentary side elevation of the upper end of a testing machine adapted to employ my improved grips;

Fig. 2 is a perspective of one half of a grip holder in which my improved inserts are disposed;

Fig. 3 is afragmentary perspective view of the lower end of the grip holder showing a stop plate for aligning the lower ends of the grip inserts;

Fig. 4 is a partial sectional view taken on the line 4-4 of Fig. 2;

Fig, 5 is a perspective of one insert;

Fig. 6 is a fragmentary perspective showing the back surface of an insert;

Fig. 7 is a fragmentary section of a flat face grip; and

Fig. 8 is a longitudinal section showing the inclined relation of the grip face.

As is well-known, testing machine grips as diagrammatically indicated at l and 2 are supported in opposed crossheads 3 and4 of a materials testing machine to grip a tension specimen 5 when the crossheads are moved away from each other through application of a loading force by any suitable mechanism well-known in the art. The upper and lower sets of grips are identical except that one set extends upwardly and the other downwardly, and hence the description of one will sufiice for both. Also, each set of grips is formed in right and left hand halves, otherwise identical, each consisting of a tapered block or holder 1 provided with any suitable means such as gear teeth 8 for raising and lowering it within a usual tapered socket in the crossheads to separate or close the halves during insertion or removal of a specimen. The holder as shown is provided with a V-shaped recess 9 extending lengthwise of the holder, although this recess may have any other form to provide usual and well-known types of grip faces. Identical gripping face inserts ID are positioned in the two preferably smooth backs 9a. of groove 9 and each insert is provided with tapered edges H to interlock with a complemental undercut edge l2 of the grooves. The angle of the tapered edges II' is such that the inserts at the bottom 91) of the grip V have interlocking engagement with each other over the complete surface area of their adjacent edges as at l3. The insert with its tapered edges ll may, of course, be used in a fiat faced grip such as diagrammatically indicated at M, Fig. 7. The inserts are preferably made of hardened file stock with any suitable file cuts l5 on the gripping face l5 specifically shown herein as being straight across. An aligning plate It of relatively light construction is secured to the lower end l6 of the grip holder by screws H or other suitable means while the grip inserts are held at their upper ends by screw held removable washers l8.

To overcome the problem of excessive breakage of relatively thin elongated grip inserts ID, particularly when made of file stock which is generally of uniform thickness throughout its entire length from top to bottom, as in the present disclosure, I have found that instead of trying to anchor the grip insert I0 entirely at its lowermost end surface It as heretofore proposed with resultant crushing of such lower end, it is possible to obtain a highly eifective grip insert by utilizing the entire back surface area 9a of the groove 9 and the lateral compression gripping force on the grip insert 10 in combination with a gripping type surface I 9 on the back of the insert whereby during gripping of the specimen the inserts ID are supported against lengthwise movement over an extended portion of the insert and the unit stresses in the insert are correspondingly smaller by reason of being distributed over a wide area. To allow the lateral compression force to cause a pressure activated supporting action on surface [9, I form very :finely out teeth l9, Fig. 6, on the back surface IQ of each insert. In actual practice I have made these cuts as fine as one hundred per inch as compared to the gripping face cuts [5 which have been as coarse as ten teeth per inch. The cuts iii are preferably of criss-cross form, although other quivalent arrangements may, of course, be employed. As a result of having teeth out in the back surface of the inserts the compression action of the specimen on the grip face will force the teeth [9 into biting contact with the entire back surface of groove 9 throughout at least that portion of its length in contact with the specimen shank thereby providing an extraordinary holding area over a substantial length of the gripping face instead of it being supported solely at its lower end 16 as heretofore. As a result of my improved cooperative action of the compression gripping forces and utilization of the entire area of surface 9, the gripping faces will actually remain in position even without the use of the aligning plate 16 whose principal function in my present invention is merely to align the ends of the inserts. Hence, instead of having the entire supporting force for the grip faces localized at the lower end which has undoubtedly heretofore caused concentrated stresses in the face with resultant breakage thereof I have distributed the holding uniformly over a large area.

It will also be noted as shown in Fig. 8 that the insert slopes inwardly toward its upper end 20a. Preferably this slope amounts to approximately the depth of one tooth as measured at the lower end of the insert and as shown by the spacing from the vertical line 20'. As a result of this arrangement, the end of the usual specimen shank will be first engaged by a few gripping teeth and as the tension load increases with consequent wedging movement of the holders the gripping teeth will progressively bite into the shank until finally its full length is gripped. This action is particularly helpful with hard specimen material and it has the additional advantage of more uniformly wearing the teeth along an extended area instead of just at the end of the grip as is the case with a true vertical face. In addition, the progressive biting in of the teeth cause pressure to be initially impressed at the upper area of the supporting surface l9 and to be gradually expended until the full length of such gripping surface is in supporting engagement with the holder. It is thus seen that this inclined relation of the grip insert If! is adapted to have a cooperative relation to the supporting or resisting teeth on the backside 19 of the insert. Any attempt to use an inclined insert with a smooth back would merely result in the insert being crowded and compressed at its lowermost end, although it is of course apparent that my improved back supporting surface of the insert may be used with an insert which is perfectly vertical.

My improved type of grip insert has overcome in a simple, economical and effective manner the problem of providing a reasonably durable and satisfactory removable gripping face insert which may be renewed at relatively small cost whenever the specimen gripping teeth I5 become excessively worn.

It will of course be understood that various changes in details of construction and arrangement of parts may be made by those skilled in the art without departing from the spirit of the invention as set forth in the appended claims.

I claim:

1. A materials grip comprising, in combination, a holder having a supporting surface extending generally in the lengthwise, direction of pull on material being gripped, and a removable material gripping member having a back surface adapted to bear against said supporting surface and a front side with teeth to grip the material, one of said surfaces having teeth adapted to be rendered operative by being laterally pressed into biting contact with said other surface under the action of a compression gripping force exerted on the material during pulling thereof, whereby longitudinal movement of the gripping member is resisted.

2. The combination set forth in claim 1 further characterized in that the pressure activated resisting teeth are positioned on the back surface of the removable gripping member and are of relatively fine formation.

3. The combination set forth in claim 1 further characterized in that the pressure activated resisting teeth are positioned on the back surface of the removable gripping member and extend continuously through the length thereof.

4. The combination set forth in claim 1 further characterized in that the pressure activated resisting teeth are disposed on and extend continuously throughout the length and width of the removable member.

5. The combination set forth in claim 1 further characterized in that the removable gripping member has lengthwise edges which are transversely tapered and the holder has a complementary recess to receive such tapered edges.

6. The combination set forth in claim 1 further characterized in that the removable gripping member has lengthwise edges which are transversely tapered and the holder has a complementary recess to receive such tapered edges, and the angle of said tapered edges being such that two gripping members may be arranged in a V-formation with the adjacent tapered edges in contact with each other over their full area.

7. The combination set forth in claim 1 further characterized in that said supporting surface of the holder is relatively smooth and the gripping member is held onto said smooth surface by the pressure activated teeth which become embedded in such surface under the lateral compression gripping force.

8. The combination set forth in claim 1 further characterized by the provision of an aligning member at the lower end of the removable member, and removable means supported by the holder for engaging the upper end of the gripping member whereby the latter may be removed upwardly from the holder.

9. The combination set forth in claim 1 further characterized in that the gripping face of the insert is inclined inwardly toward the end of a specimen whereby the successive gripping teeth progressively bite into the specimen as a test load increases thereon.

FRANCIS S. BUCKINGHAM.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,849,216 Adair Mar. 15, 1932 2,288,851 Sharp July '7, 1942 2,347,922 Nelson May 2, 1944 1,496,803 Amsler June 10, 1924 1,556,094 Fletcher Oct. 6, 1925 1,559,932 Bogen Nov. 3, 1925

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