US3163904A - Strand chucks - Google Patents

Description

965 R. P. ZlOLKOWSKl 3,163,904

STRAND CHUCKS Filed June 24, 1965 80 FIG, 6

r y 7/4; 10 M F I G 5 Ronald Bzlz fiififi United States Patent Office messes Patented Jan. 5, 1965 3,163,904 STRAND CHUCKS Ronald I. Ziollsowsiri, Chicago, Illh, assignor to Supreme Products Corporation, Chicago, Ill. Filed June 24, 1963, Ser. No. 289,924 5 Claims. (Ci. 24-426) This invention relates to improvements in strand chucks used for line connectors and as anchor grips, which are designed for repeated attachment to, and release from wire cable, as employed for example, in prestressed concrete structural members. Certain forms of chucks of this character are shown and described in U.S. Patent No. 3,049,775, granted August 21, 1962 to Elmer I. Ondeck, and assigned to the same assignee as this application.

Essentially, such chucks comprise a body having a frusto-conical bore receiving a plurality of generally wedge-shaped jaws tapered complementarily to the bore, each jaw having an interior face provided with teeth engaging the cable to implement the friction of the jaws on the cable. Circumferentially-disposed constricting means are provided to maintain the jaws in axial alignment for operation as a set. Thus, when the cable is' seized by the jaws and the cable and chuck are subjected to a separating force the jaws are drawn into the bore and, by reason of the slidable engagement thereof with the bore in the body, they are forced to close on the cable. The gripping action increases with increase in tension.

In the case of jaws which have a smooth taper on their exterior, as in the patent aforementioned, the breaking strength of the cable fails to reach an optimum value during laboratory test. in this connection it will be understood that the jaw teeth will indent or notch the wires comprising the cable and that, when the cable is tensioned to the breaking point during test, it will part at the region of deepest indentation, assuming uniformity in the composition of the cable and teeth of equal form and dimensions. Moreover, the planes of rupture of the individual wires appear as so-called shear breaks rather than the desirable so-called tension breaks. A shear break is evidence that the pressure of the teeth is greater in the region of the break than at another point along the longitudinal extent of the cable coextensive with the jaws. Tests have demonstrated that a cable which fails in a shear break separates adjacent the smaller end of the jaws, thereby indicating application of greater pressure in that region than in the remaining length of the jaws. Inasmuch as a tension break is not the result of shear induced at an excessively indented region along the wires, or at least it is fair to state that in such case the indentations do not contribute materially to a tension break, it is desirable to avoid the deleterious effects of excessive indenting in a localized zone.

Accordingly, the principal object of this invention is to provide an improved strand chuck so characterized that the adverse effects of localized excessive indentation, as aforesaid, are materially reduced and the breaking strength of the cable greatly enhanced.

Another object is to provide the result just mentioned with minimal alteration in the parts presently recognized as constituting a commercially acceptable device, and at minimum additional cost.

Other objects and advantages will become apparent from the ensuing description which, taken with the accompanying drawing, discloses a preferred mode of carrying the principles of the invention into practice.

In this drawing:

FIG. 1 shows a longitudinal crosssection of a chuck of a well-known type, as for example, in accordance with FIG. 3 of the patent mentioned above, but including the improved jaws of the present invention, and prior to application of its gripping force on the cable;

FIG. 2 shows the chuck of FIG. 1 with the force applied to the cable;

FIG. 3 is a side elevation of the jaw assembly incorporating one embodiment of the improvement of the present invention;

FIG. 4 is a longitudinal cross-section of an alternative form of the invention;

FIG. 4a is a longitudinal cross section, similar to that of FIG. 1, but with the cable omitted, showing a modilied form of the invention;

FIG. 5 illustratesthe shear break in a cable; and

FIG. 6 illustrates the tension break in a cable.

Regarded in its broad aspect, the invention comprises a sleeve having a frusto-conical axial bore therein, together with a plurality of generally wedge-shaped jaws carried within the bore, preferably together with circumferentially-disposed constricting means to maintain the jaws in axial alignment for operation as a set. Considered as a group, the jaws have a common exterior configuration which is substantially complementary to the interior of the bore when the cable is inserted therebetween but prior to application to the cable of the force for which a particular size of chuck has been designed. At this juncture, it will be recognized that these chucks will vary in dimensions depending upon the nominal diameter of the cable and the tension to be maintained therein by the chuck which is restrained against a fixed abutment. However, commercial chucks are frequently arranged to take more than one size, e.g., cable of and /2" diameter, the tapered surfaces being so dimensioned as to permit some reasonable range of accommodated diameters of cable. Moreover, it will be understood that the curved exterior face of the jaws will not necessarily be contiguous to the conical surface of the bore throughout the entire range of longitudinal relative positions of the jaws and sleeve. However, the design is such that, when the chuck is locked up with the cable in final position, the respective arcuate surfaces of the jaws and bore are essentially in abutment so as to obtain maximum bearing. One type of chuck in common use comprises the sleeve, the set of jaws and means embracing the jaws circumferentially to preserve their longitudinal alignment as a set while permitting the jaws to diverge radially; while another type includes a compression spring and a retaining cap therefor whereby the jaws are urged into the bore as a group. It has been found that when the jaws have a uniform taper on the exterior, bore-engaging surface, the chuck has been engaged with the cable and axial force has been applied, that the jaw teeth penetrate the wires of the cable to a greater degree in the region of the smaller end of the jaws than at the larger end and that, when breaking tension has been applied, rupture will occur in that region as a shear break. As previously mentioned, a shear break indicates that rupture has been induced largely by localized excessive indentation by thejaw teeth as contrasted with rupture occurring solely by stretching of the wires, as would be the case where a member is subjected to stretching in a testing machine.

I have found that, by relieving the indenting in the region of the smaller end of the jaws a substantial increase in breaking strength results. Accordingly, the present invention comprises jaws which are relieved on their outer faces by providing a taper which is steeper than the taper of the bore in the body (both tapers being measured as an acute angle to the common longitudinal axis). The steeper taper is desirably adjacent the smaller end of the jaws for a distance approximately /3 to /z of the length of the jaws but may extend farther, even over the whole length of the jaws. Thus, assuming a uniform diameter of the strand-engaging teeth and teeth of equal form, and application of appropriate separating force, i.e. tension, between the cable and the jaws, these latter will be drawn into the bore of the body to exert the counte'rbalancing gripping force, that is to say, the thinner wall portion of the jaws, coextensive with the steeper taper, will yield sufliciently in a radial sense to relieve the pressure in that region and, therefore, the depth to which indentation is present. It will be understood that yielding of the jaws will be greatest at the smaller end and will gradually diminish as the opposite end of the taper is approached. In an alternative aspect the objects of the invention may be obtained by relieving the interior wall of the jaws by tapering the gripping face presented by the teeth while keeping the tooth form uniform throughout so that, adjacent the smaller end of the jaws, the crest of the teeth lie on a frusto-conical reference surface having its larger base at the smaller end of, the jaws. Such surface extends longitudinally preferably to /2 of the length of the jaws but may extend the whole'length. In the case where the interior wall of the jaws is relieved for only a portion of their length the inner end of the frusto-conical reference surface will merge into a cylindrical surface of uniform diameter, upon which the crest of the remaining teeth willlie.

It will therefore be apparent that, by increasing the angle of taper of the exterior of the jaws or, alternatively, locating the teeth on a conical surface, there will be provided a graduated gripping action on'the cable so that whatever indentation occurs will be substantially uni formly distributed over the whole axial extent of the jaws.

Turning now to the drawing, there is shown (FIG. 1) a strand chuck in accordance with the invention comprising a sleeve having a frusto-conical axial bore 11 flanked on the left end by a short cylindrical bore 12 to avoid bottoming of the jaws, and on the right end by a threaded bore 13. This latter receives a cap 16 having a threaded boss 17. engageable with the bore 13 and a knurled rim 18, for digital rotation of the cap into assembled position as seen in FIG, 2. A compression spring 21 is received in a recess 22 in the cap 16 and is adapted to urge the jaw assembly toward the smaller end of the bore 11. The immediately preceding features are well-known and optional, and are disclosed in said Patent No. 3,049,775.

The jaw assembly (FIG. 3) comprises a plurality of individual generally wedge-shaped jaws 31, in this case three in. number, curved on their exterior to be complementary to the bore 11 when the cable is tensioned to the ratedmaximum and the jaws occupy the position shown in FIG. 2. In order that the jaws 'will'be retained as a group of jointly movable members and retainedin axially aligned relation pending locking-up of the chuck resilient means are provided which embrace the joint circumference. For example, an O-ring 33- of some elastomer encircles the jaws and is retained in a groove 34 of semicircular cross-section cut into each jaw. In the interest of clarity, the jaws are illustrated as spaced apart in the position they will assume when a cable of appropriate diameter is received therebetween, it being understood that, in the absence of the cable, the jaws will be in adjacency by reason of the resilient member 33. The interior face of each jaw is provided with a plurality of teeth 36, usually of V-form with rounded crest cut as a modified buttress thread into an appropriate blank, whereafter the jaws are formed by slitting the blank longitudinally. Alternatively, the teeth may be annuli. However, the teeth are formed most economically as a helix of uniform diameter in an unslitted blank by means of a tap. The configuration of the teeth as to tooth form and whether helically cut or as individual annuli is well known and, specifically, may be as disclosed in the mentioned patent.

In accordance with the invention, the arcuate exterior surface of each jaw or, for that matter, of the jaws regarded as a group is, in the illustrative embodiment, provided with a double taper. At the larger end the taper x, measured as an angle with the longitudinal axis, is the same as the taper of the wall surface of the bore 11, and such taper obtains for some portion B of the axiallymeasured length A of the whole taper. In one commercially successful form the distance A is 1.594" and the distance B is 0.875" or approximately /2 the whole distance A, and the distance C is 0.719". However, the proportions may vary depending upon the characteristics of the material of the chuck and cable but a preferred range for the ratio of B to A may be on the order of from 1:2 to 2:3. The remaining length C has some steeper taper y. In the commercial form just referred to the angle of taper of the bore 11 is 6 and the angles x and y are 6 and 7, respectively, measured with respect to the common longitudinal axis.

FIG. 1 shows the several parts of the exemplificative chuck exploded for clarity of illustration and the cable Ztl positioned within the jaws and subjected only to the slight constrictive force of the resilient member 33. In

. FIG. 2 the chuck parts have been assembled and the cable has been tensioned to the desired limit. It will be obvious that separating force applied between the chuck and cable has caused the jaws 31 to be forced into the bore 11 and the teeth 36 caused to grip the cable. More over, it will be understood that, in accordance with known practice, the chuck is held in a fixed position against a suitable abutment (not shown). The spring 21 acts continuously to urge the jaws toward the smaller end of the bore 11 and, as tension is built up, in the cable, the friction between the same and the teeth fixes the ultimate position of the chuck with respect to, the stretched cable, all as is well-known in this art. I i

As tension in the cable is increased, the jaws 31 are drawn toward the smaller end of the bore 11. and compressed into gripping relation with, the cable. Meanwhile, the portion C of each jaw is bent untilthe taper over the distances B and C lie on a common conical surface which is the same as the taper of the bore 11. The angle x is so selected as to urge the teeth 36 coextensive with the distance C into gripping engagement with the cable to some degree of indentation which is graduated from a minimum at the smaller end of the jaws to a maximum at the dividing plane between the distances B and C. Indentation of the teeth over the region Bis, substantially uniform. Tests have demonstrated that, by minimizing indentation in the region C substantially improved breaking strength of the cable is achieved. For example, a set of jaws as shown and described in connection with FIG; 3 was assembled as shown in FIG. 1 and the cable and chuck subjected to a breaking test. The same series of tests was conducted with. conventional jaws having a uniform taper. The cable employed was Type 270K of /2" diameter, manufactured by John A. Roeblings Sons Division of TheColorado Fuel and Iron Corporation, Trenton, NewJersey (Bulletin RC. 955). In the case of the conventional jaws the average breaking, point of twentyone test was 18.1 tons and, in the case of the jaws according to FIG. 3 the average breaking point was,20.3 tons, or an increase of 15% approximately. Furthermore, the break in the cable when using conventional jaws was of the shear type (FIG. 5) and, when using the jaws of the invention, the break was of the tension type (FIG. 6). The advantages inherent in the latter result have been fully explained above.

Although not confirmed, it appears that the tension in the cable combined with the bending of the jaws over the distance C modifies the tooth angle and allows the cable, during stretching, to slide on the teeth to produce indentations which are not notches thereby to minimize parting of the cable.

It is Within the scope of the invention to extend the portion C throughout the whole tapered length of the jaws, at an angle, y say of 7, and to maintain the taper x of the bore 11 at, say 6 (FIG. 4a). Thus, a graduated gripping effect, i.e., may be obtained over the whole length of the teeth 36 with results similar to those heretofore described.

The distance C and the difference in the angles x and y may, as pointed out, vary from one size or range of sizes of chuck to another and in accordance with the number and size of strands in the cable, the number and size of the wires composing the strands and their composition and heat treatment, as well as the presence or absence of a core and lubricant. It has been found that the length and angle of the taper C is best established empirically by testing with chucks employing various combinations thereof. Accordingly, where herein I refer to the steeper taper viz. x, as extending over some portion, viz. C, of the jaws beginning at the smaller end thereof, I intend to imply that such taper may terminate at any point along the jaws, including the right-hand end thereof. Stated otherwise, the length C and the angle x will be so selected as to be sufficiently good for the purposes of the invention.

In FIG. 4 there is shown an alternative form of the invention wherein the jaws 31b have a uniform exterior taper corresponding to the taper of the bore 11 but in which the teeth 36b are uniform and have their crests lying on a conical surface D at an angle 2. The surface D is subject to the same considerations as those set forth in connection with the surface C (FIG. 3). That is to say, the surface D begins at the smaller end of the jaws and extends some, or all of the length of the jaws. It is to be understood that the teeth of the modified embodiment, regarded individually, are of conventional form, say V-form buttress, with the crests positioned on a conical surface which is of gradually diminishing diameter over the distance D, and that the teeth are not truncated. However the crest may be rounded off slightly, if desired. Thus, as the jaws are actuated into gripping relation with the cable, the teeth will engage the same with a graduated degree of indentation which is less at the smaller end of the jaws than at the larger end, with a resulting function as described in connection with the jaws of FIG. 3.

While I have shown particular embodiments of my invention, it will be understood, of course, that I do not wish to be limited thereto since many modifications may be made and I, therefore, contemplate by the appended claims to cover any such modifications as fall within the true spirit and scope of my invention.

I claim:

l. A strand chuck comprising in combination a body having a frusto-conical bore of some predetermined uniform taper referred as an angle to the longitudinal axis, a plurality of jaws received in and engageable as a set with said bore to grip the strand as the chuck and strand are subjected to a separating force, each jaw being generally wedge-shaped having an interior surface to grip the strand and an arcuate outer surface having a taper complementary to the bore for sliding engagement therewith, the interior surface of the jaws throughout the active length thereof being provided with transverse teeth of uniform V-form, the crest of the teeth for a portion of the length of the jaw adjacent the smaller end thereof being disposed on a frusto-conical surface having its larger diameter at said smaller end, and the crest of the remaining teeth being disposed on a cylindrical surface forming a continuation of said frusto-conical surface whereby, when the jaws are converged into gripping relation with the strand, the teeth adjacent said larger diameter of the frusto-conical surface impart a lesser gripping action which gradually increases toward the smaller diameter of said surface.

2. A strand chuck comprising in combination a body having a frusto-conical bore of some predetermined uniform taper referred as an angle to the longitudinal axis, a plurality of jaws received in and engageable as a set with said bore to grip the strand as the chuck and strand are subjected to a separating force, each jaw being generally wedge-shaped having an interior surface to grip the strand and an arcuate outer surface having a taper complementary to the bore for sliding engagement therewith, the interior surface of the jaws throughout the active length thereof being provided with transverse teeth of uniform V-form, the crest of the teeth being disposed on a frusto-conical surface having its larger diameter at the smaller end of the jaws and its smaller diameter at the larger end of the jaws whereby, when the jaws are converged into gripping relation with the strand, the teeth adjacent said larger diameter of the frusto-conical surface impart a lesser gripping action which gradually increases toward the smaller diameter of said surface.

3. A strand chuck for the purpose described comprising a body having a frusto-conical bore of some predetermined angle of taper and a plurality of generally wedgeshaped jaws operating as a set jointly movable axially in said bore into converging relation, said jaws each having an arcuate exterior surface for abutting engagement with the wall of the bore and an interior surface gripping the strand upon convergence of the jaws, said interior surfaces, when in gripping relation with the strand, lying on a common, substantially cylindrical surface, the exterior slant surface of a longitudinal portion of each jaw extending inwardly from the smaller end of the jaw a distance of substantially one-third to one-half of the axially-measured length of the jaw having a taper, meas ured when the jaws are not converged into said gripping relation, which is of some angle greater than the taper of the bore, the remainder of said exterior jaw surface measured in the same manner, having the same taper as the bore, all tapers being referred as acute angles to the common longitudinal axis of the bore and jaws whereby, when the jaws are fully converged, the said exterior jaw portions are deformed radially outwardly into abutting relation with the wall of the bore.

4. A strand chuck for the purpose described comprising a body having a frusto-conical bore of some predetermined angle of taper and a plurality of generally wedge-shaped jaws operating as a set jointly movable axially in said bore into converging relation, said jaws each having an arcuate exterior surface for abutting engagement with the wall of the bore and an interior surface gripping the strand upon convergence of the jaws, said interior surfaces, when in gripping relation with the strand, lying on a common, substantially cylindrical surface, the exterior slant surface of a longitudinal portion of each jaw extending inwardly from the smaller end of the jaw a distance of at least one-half of the axiallymeasured length of the jaw having a taper, measured when the jaws are not converged into said gripping relation, which is of some angle greater than the taper of the bore, the remainder of said exterior jaw surface measured in the same manner, having the same taper as the bore, all tapers being referred as acute angles to the common longitudinal axis of the bore and jaws. whereby, when the jaws are fully converged, the said exterior jaw portions are deformed radially outwardly into abutting relation with the wall of the bore.

5. A strand chuck for the purpose described comprising a body having a frusto-conical bore of some predetermined angle of taper and a plurality of generally wedge-shaped jaws operating as a set jointly movable axially in said bore into converging relation, saidjaws each having an arcuateexterior surface for abutting engagement with the wall of the bore and an interior surface gripping the strand upon convergence of the jaws, said; interior surfaces, when in gripping relation withthe strand, lying on a common, substantially cylindrical surface, the entire slant, exterior surface of each jaw having a taper which is of some angle greater than the taper, measured when the jaws are not converged into said gripping relation of the bore, both tapers being referred as acute angles to the common longitudinal axis of the bore and jaws whereby, when the jaws are fully said slant. surfaces in abutting relation. with the wall of the bore. 7

References Cited by the Examiner UNITED STATES PATENTS M. HENSON WOOD, In, Primary Examiner.

converged, the same are urged radially outwardly with 5 DONLEY STOCKING, Examinell UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 3,1o3 ,904 January 5, i965 Ronald P. Ziolkowski It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 7, line 10, after "taper" insert measured when the jaws are not converged into said gripping relation, same column 7, lines 11 and 12, strike out measured when the jaws are not converged into said gripping relation Signed and sealed this 18th day of May 1965* (SEAL) Attest:

ERNEST w. SWIDER EDWARD J. BRENNER Attesting Officer Commissioner of Patents UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent V0 3,163 ,o-O l 7 January 5, 1965 Ronald P. Ziolkowski It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 7, line 10, after "taper" insert H measured when the jaws are not converged into said gripping relation, same column 7, lines 11 and 12, strike out measured when the jaws are not converged into said gripping relation Signed and sealed this 18th day of May 1965.

(SEAL) Attest:

ERNEST W. SWIDER EDWARD J. BRENNER Aitesting Officer Commissioner of Patents

Claims (1)

1. 3. A STRAND CHUCK FOR THE PURPOSE DESCRIBED COMPRISING A BODY HAVING A FRUSTO-CONICAL BORE OF SOME PREDETERMINED ANGLE OF TAPER AND A PLURALITY OF GENERALLY WEDGESHAPED JAWS OPERATING AS A SET JOINTLY MOVABLE AXIALLY IN SAID BORE INTO CONVERGING RELATION, SAID JAWS EACH HAVING AN ARCUATE EXTERIOR SURFACE FOR ABUTTING ENGAGEMENT WITH THE WALL OF THE BORE AND AN INTERIOR SURFACE GRIPPING THE STRAND UPON CONVERGENCE OF THE JAWS, SAID INTERIOR SURFACES, WHEN IN GRIPPING RELATION WITH THE STRAND, LYING ON A COMMON, SUBSTANTIALLY CYLINDRICAL SURFACE, THE EXTERIOR SLANT SURFACE OF A LONGITUDINAL PORTION OF EACH JAW EXTENDING INWARDLY FROM THE SMALLER END OF THE JAW A DISTANCE OF SUBSTANTIALLY ONE-THIRD TO ONE-HALF OF THE AXIALLY-MEASURED LENGTH OF THE JAW HAVING A TAPER, MEASSURED WHEN THE JAWS ARE NOT CONVERGED INTO SAID GRIPPING RELATION, WHICH IS OF SOME ANGLE GREATER THAN THE TAPER OF THE BORE, THE REMAINDER OF SAID EXTERIOR JAW SURFACE MEASURED IN THE SAME MANNER, HAVING THE SAME TAPER AS THE BORE, ALL TAPERS BEING REFERRED AS ACUTE ANGLES TO THE COMMON LONGITUDINAL AXIS OF THE BORE AND JAWS WHEREBY, WHEN THE JAWS ARE FULLY CONVERGED, THE SAID EXTERIOR JAW PORTIONS ARE DEFORMED RADIALLY OUTWARDLY INTO ABUTTING RELATION WITH THE WALL OF THE BORE.

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