Cable tie

Abstract: The cable tie (10) includes an elongate strap (14) and a head (12) having an aperture (22) therethrough for insertably accommodating the strap. A locking barb (24) is movably supported in the head and is engagable with the strap in a manner which permits insertion of the strap thereinto and prevents withdrawal of the strap therefrom. The strap includes a strap body (15) and plural protrusions (36) extending from the strap body. The barb is engagable with the protrusions of the strap upon insertion. Upon an attempt to withdraw the strap, the barb digs into the strap body to prevent withdrawal of the strap from the head.

Description: FIELD OF THE INVENTION: The present invention relates generally to ties used to bundle an article or a group of articles. More particularly the present invention relates to a cable tie having an improved strap design which facilitates securement of the strap in the head of the cable tie. BACKGROUND OF THE INVENTION: Use of cable ties to bundle or secure a group of articles such as electrical wires or cables is well known. U.S. Patent No. 3,102,311 is an early example of straps used for such purposes. Known cable ties of conventional construction are elongate members having a head at one end, a tail at the other end and a longitudinal strap therebetween. The strap is wrapped around a bundle of articles and the tail is inserted through an aperture or passage in the head. The head of the cable tie typically includes a locking element which is engagable with the body of the strap so that when the tail is pulled through the head aperture, the locking element secures the strap body in the head. Advances in cable tie construction have taken many forms and shapes. However, since the initial introduction of cable ties, the development of self-locking devices carried in the cable tie head have taken basically two divergent paths. One approach has been to form an integral one-piece plastic cable tie where the locking element is formed integrally with the head of the cable tie. An example of an integrally formed one-piece cable tie is shown in U.S. Patent No. 3,965,538. One advantage of such an integrally formed one-piece cable tie is that the tie exhibits relatively low insertion force. That is, it is relatively easy to insert the tail of the tie through the head aperture. An integrally formed flexibly supported pawl forming the locking element facilitates such ease of insertion. A further example of a one-piece cable tie is described in US-A-4092765; this cable tie comprises an elongate tie strap having a head at one end, a tail at the other end and a generally planar strap body therebetween, the head having an aperture therethrough for insertion of the tail therein permitting passage of the strap body through the aperture in a first direction, a locking barb movably supported by the head and extending into the aperture for engagement with the strap body upon movement of the strap body in a second direction opposite said first direction to prevent withdrawal of the strap body from the aperture, the barb and strap having complementary serrations for providing grip. A second distinct approach used to form cable ties has been the use of a cable tie having a metallic barb embedded into the cable tie head at an acute angle with respect to the inserted tail. The metal barb permits insertion of the cable tie strap through the head aperture but bites into the strap upon an attempt to withdraw the strap therefrom. An example of a cable tie having such construction is shown and described in U.S. Patent No. 3,186,047. As the metal barb of the cable tie actually bites into the inserted tail preventing withdrawal, cable ties of this construction exhibit high long-term pull-out resistance. This results in the cable tie having good loop tensile strength over time which is an important criteria in the selection and use of cable ties. A further example is shown in US-A-3457598. The cable tie art has also seen attempts to obtain the benefits of both an integrally molded one-piece cable tie and those of the two-piece cable tie having an embedded metallic barb. One such attempt at a multiple piece cable tie is seen in U.S. Patent No. 5,121,524 where the cable tie is formed to have a head including a hingedly mounted pawl which holds a metallic barb therein. The pawl is flexibly rotatably movable within the head upon insertion of the strap. The metal barb supported by the pawl bites into the strap upon attempted withdrawal of the strap. A further example of the combination of the two technologies is shown in U.S. Patent No. 5,193,251 where the head of the cable tie includes a metallic barb supported on a cantilevered platform. The platform is deflectable upon insertion of the strap through the aperture to permit ease of passage therethrough. The barb is positioned for biting insertion into the strap upon an attempt to withdraw the strap from the aperture. While the cable ties shown in each of these patents attempts to provide the advantages of both types of cable tie technology, there is still a need to provide a cable tie which exhibits high long-term loop tensile strength as well as low strap insertion force. SUMMARY OF THE INVENTION It is an object of the present invention to provide an improved cable tie of the type including an elongate strap, a head at one end thereof and locking means in the head for securing the strap therein. It is a further object of the present invention to provide a cable tie having an improved strap which facilitates easy insertion of the strap into the head and prevents withdrawal of the strap from the head. It is a still further object of the present invention to provide a cable tie having a locking barb movably supported by the head of the cable tie and strap body having a plurality of protrusions extending for engagement with the locking barb. The interaction between the protrusions on the strap body and the locking barb facilitates easy insertion of the strap while preventing withdrawal thereof. According to the invention, there is provided a self locking cable tie comprising an elongate tie strap having a head at one end, a tail at the other end and a generally planar strap body therebetween, said strap body having a given strap thickness, said head having an aperture therethrough for insertion of said tail therein permitting passage of said strap body through said aperture in a first direction, a locking barb movably supported by said head and extending into said aperture for biting engagement with said planar strap body upon movement of said strap body in a second direction opposite said first direction to prevent withdrawal of said strap body from said aperture, said barb being positioned with respect to said aperture so as to create a passage of dimension not substantially less than said strap body thickness, a multiplicity of barb engagement protrusions extending from said planar strap body for engagement with said barb upon movement of said strap in said first direction, said barb engagement protrusions being longitudinally and transversely spaced from one another, said strap protrusions together with said strap body providing a thickness which is greater than the dimension of said strap body passage, so that said barb is caused to engage said protrusions and thereafter said strap body upon movement of said strap body in said second direction. Means are preferably provided for flexibly supporting the barb to the head. The flexible supporting means may be integrally formed with the head and supports the barb for rotative flexible movement therewith. The flexible supporting means may include a hingedly mounted pawl extending from the head for pivotally supporting the barb or may include a cantilevered platform extending from the head for deflectably supporting the barb. BRIEF DESCRIPTION OF THE DRAWINGS: Figure 1 is a bottom plan view of an improved cable tie of the present invention. Figure 2 is a side elevational view, partially in section of the cable tie of Figure 1. Figure 3 is an enlarged transverse cross-section of the strap of the cable tie of Figure 1. Figures 4 and 5 are cross-sectional showings of the head of one embodiment of a cable tie of the present invention shown in insertion position and withdrawal position, respectively. Figures 6 and 7 are cross-sectional views of the head of a further embodiment of the cable tie of the present invention in insertion position and withdrawal position, respectively. Figure 8 is a cross-sectional view of the head of a still further embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS: Referring to Figures 1 and 2, a cable tie 10 of the present invention is shown. Cable tie 10 is typically an elongate molded plastic member which is used in a manner which is well known in the art to wrap around a bundle of articles such as electrical wire or cable (not shown). Cable tie 10 may be molded from a high strength plastic such as nylon or polypropylene and is suitable for both indoor and outdoor use. Cable tie 10 has a head 12 at one end thereof, a depending strap 14 extending from head 12 and a tail 16 at the end opposite of head 12. In the present and illustrative embodiment head 12 is formed as an integral portion of cable tie 10. However, in certain applications cable tie 10 may be constructed in a manner where head 12 is formed separately from strap 14. Head 12 of cable tie 10 includes a central passage 22 therethrough which insertably accommodates tail 16 and strap 14 therein. Central passage 22 is defined by an upper wall 23 against which tail 16 may be inserted. Cable tie 10 further includes a metallic locking barb 24 supported in head 12 which engages strap 14 after it has been coiled around the bundle of articles to lock strap 14 in place around the bundle. The barb 24 of the embodiment of Figures 1 and 2 is preferably formed of stainless steel and includes a knife-like tail engagement portion 24a extending into passage 22. The barb 24 further includes a mounting portion 24b which is supported on a flexible support hinge 26 which is molded integrally with head 12. Flexible support hinge 26 permits insertion of tail 16 through passage 22 by deflecting in a cantilevered manner to permit passage of tail 16 and strap 14 therethrough. The passage of strap 14 is shown by phantom lines in Figure 2. Common in barb type cable ties of the prior art, the barb is positioned in the head such that it engages the strap upon insertion in order to provide biting engagement with the strap upon an attempt to withdraw the strap. While providing superior withdrawal strength, this engagement also has the tendency to increase the force necessary to insert the strap into the head. Referring specifically to Figures 1-3, an improvement in strap body design facilitates easy insertion of strap 14 through passage 22 of head 12. Strap 14 generally defines a planar strap body 15 between a pair of opposed elongate planar surfaces 30 and 32. Strap body 15 is constructed so that the thickness, as measured between opposed planar surfaces 30 and 32, is not substantially greater than the distance between wall 23 defining passage 22 and the distal extent 24c of barb 24 (Figure 1). Thus, upon insertion of strap body 15 through passage 22 (arrow A, Figure 2), the strap body is not in substantial engagement with barb 24. Preferably the dimension of strap body 15 between surfaces 30 and 32 is selected so there is no engagement between barb 24 and strap body 15. However, manufacturing tolerance may not preclude slight engagement therebetween. This slight engagement would not significantly increase the force necessary to insert strap 14 into passage 22. As there is at most only slight engagement between strap body 15 and barb 24 upon insertion, strap 14 is further modified as described hereinafter so that upon an attempt to withdraw strap 14 from passage 22 (arrow B, Figure 2), the barb 24 will still bite into strap 14 securing the strap 14 in passage 22. Strap 14 includes a pattern of protrusions which extend from surface 30 along the width of strap body 15. A series of first protrusions 34 are positioned in two pairs of transversely spaced longitudinally extending rows along each lateral edge of surface 30. Protrusions 34 extend a short distance above surface 30 and are provided primarily to contact the bundle of wires or cables (not shown) when strap 14 is wrapped therearound. This frictional engagement between protrusions 34 and the wire bundle prevents the strap from rotating or revolving around the bundle during securement. A series of second protrusions 36 are more centrally located and as shown in Figures 1 and 3 are arranged in three longitudinally extending transversely spaced rows along a central longitudinal strip 15a. The protrusion may be transversely aligned or may be arranged in staggered fashion. In addition to frictionally engaging the wire bundle in a manner similar to that of protrusions 34, protrusions 36 are constructed to have a height measured from surface 30 which is substantially greater than the height of protrusions 34. With reference to Figure 2, it can be seen that the height of protrusions 36 is constructed such that the height, d 1 of protrusions 36 plus the thickness, d 2 of strap body 15 between surfaces 30 and 32, is greater than the distance, d 3 (Figure 2) between wall 23 of passage 22 and the distal extent 24c of barb 24. Also, distal extent 24c is constructed to have a width which engages protrusion 36 along strip 15a. Thus, upon insertion of strap 14 into passage 22, protrusions 36 engage distal extent 24c causing generally rotational deflection of barb 24 on cantilevered surface 26 in a clockwise direction as viewed in Figure 2. Upon an attempt to withdraw strap 14 from passage 22 (arrow B), protrusions 36 catch distal extent 24c rotating barb 24 in a counter-clockwise direction and forcing distal extent 24c into biting engagement with strap body 15 preventing withdrawal of strap 14 through passage 22. Thus, in the embodiment shown in Figures 1 and 2 of the present invention, low insertion force of strap 14 through passage 22 is achieved by spacing the distal extent 24c of barb 24 from opposed passage wall 23 a distance not substantially less than the thickness of strap body 15 measured between surfaces 30 and 32. Further, sufficient pullout resistance and loop tensile strength is provided by the biting engagement of barb 24 with strap body 15 which is facilitated by the engagement of distal extent 24c with protrusions 36 upon an attempt to withdraw strap 14 from passage 22. Referring now to Figures 4 and 5, the present invention may be practiced with reference to a further embodiment thereof. Figures 4 and 5 show generally the head portion of a cable tie which has been modified from the configuration shown in Figures 1 and 2. Cable tie 110 includes a head 112 and a strap 114. Strap 114 includes a strap body 115 having opposed planar surfaces 130 and 132 with protrusions 136 (shown in phantom) extending from surface 132, protrusions 136 being similar to protrusions 36 shown in Figure 3. A passage 122 through head 112 permits insertion of strap 114 therethrough in the direction of arrow A. An upper passage wall 123 engages surface 130 of strap 114 upon insertion of strap 114 through passage 122. Head 112 is modified to include a pivotally mounted pawl 140 formed integrally with head 112. Pawl 140 supports metallic barb 126 which is secured therein such that distal extent 126a lies within passage 122. In a manner similar to that described above with respect to cable tie 10, distal extent 126a of barb 126 is positioned such that upon insertion of strap 114 in the direction of arrow A, distal extent 126a engages protrusions 136 extending from strap surface 132. As with cable tie 10, barb 126 is positioned such that the distance between distal extent 126a and passage wall 123 is not substantially less than the strap thickness measured between surfaces 130 and 132 so as to provide ease of insertion of strap 114 through passage 122. In that regard, head 112 of cable tie 110 includes integrally molded pawl 140 which supports barb 126 for flexible rotative movement within head 112. Pawl 140 includes a pawl body 142 attached to head 112 by a thin flexible hinge 144. Hinge 144 permits rotative movement of pawl body 142 and barb 126 supported thereby within head 112. Pawl body 142 includes an upper portion 146 adjacent barb 126. The upper portion 146 provides structural support for barb 126 and positions barb 126 for engagement with strap body 115. Upper portion 146 includes an upper planar surface 146a which extends into passage 122. Surface 146a is positioned from passage wall 123 a distance which is greater than the strap body thickness measured between surfaces 130 and 132 together with the distance of extending protrusions 136. Thus, upon insertion of strap 114 into passage 122 in the direction of arrow A, both strap body 115 and protrusions 136 are out of engagement with surface 146a. Thus, the only resistance to insertion of strap 114 is the light engagement of distal extent 126a of barb 126 with protrusions 136. The construction of pawl body 142 together with its attachment to head 112 by flexible hinge 144 permits low force insertion of strap 114 through passage 122 of head 112. Pawl body 142 further includes a rearwardly directed shoulder 148 separated from head 112 by an undercut 149. As will be described further hereinbelow, shoulder 148 and undercut 149 serve as a stop, preventing overrotation of pawl 140 in a counter-clockwise manner upon an attempt to withdraw strap 114 from passage 122. Referring now to Figure 5, attempted withdrawal of strap 114 from passage 122 of head 112 is shown. As strap 114 is attempted to be withdrawn in the direction of arrow B, distal extent 126a of barb 126 catches against protrusions 136 extending from of strap body 115. Once such engagement is established, pawl 140 rotates in a counter-clockwise direction embedding the distal extent 126a of barb 126 into strap body 115. Further movement of strap 114 in the direction of arrow B is prevented by the biting engagement of barb 126 with strap body 115. Further, upon counter-clockwise rotation of pawl 140, surface 146a of pawl 140 wedges strap 114 against passage wall 123 providing further frictional retention of strap 114 in passage 122. Thus, in addition to preventing withdrawal of strap 114 by the biting insertion of barb 126 into strap body 115, resistance against withdrawal is enhanced by the wedging engagement of surface 146a with strap 114. Over-rotation of pawl 140 in the counter-clockwise direction, which could result in over insertion of barb 126 into strap 114 or breakage of flexible hinge 144, is prevented by the collapsing of hinge 144 and the engagement of shoulder 148 with surface 112a of head 112. This provides a mechanical stop preventing over rotation of pawl 140. Referring now to Figures 6 and 7, a further embodiment of the present invention is shown. Cable tie 210 of Figures 6 and 7 is substantially similar to cable tie 110 shown in Figures 4 and 5. In this embodiment pawl 240 is modified so that the upper portion 246 is extended to provide an upper surface 246a which engages protrusions 236 of strap 214 upon insertion of strap 214 into aperture 222 in the direction of arrow A. In addition to the engagement of distal extent 226a of barb 226 with protrusions 236 of strap 114, upper surface 246a also provides frictional engagement against protrusions 236a upon insertion of strap 214 in the direction of arrow A. Upon an attempt to withdraw strap 214 from head 212 in the direction of arrow B, as shown in Figure 7, further engagement between strap 214 and the barb/pawl combination is achieved thereby increasing the tensile strength of the tie. Upon movement of strap 214 in the direction of arrow B, barb 226 bites into strap body 215 in a manner similar to that shown and described with respect to Figure 5. Also, upper surface 246a of upper portion 246 engages strap body 215 to provide an increase in frictional resistance by the wedging action upon movement in the direction of arrow B. In situations where greater loop tensile strength is required, the design shown in Figures 6 and 7 provides such increase in tensile strength while only minimally increasing the insertion force required to insert strap 214 through passage 222. A still further embodiment of the present invention is shown with respect to Figure 8. In this embodiment, barb 326 is embedded into head 312 of cable tie 310 adjacent surface 312a. A flexible barb support 340 is positioned adjacent barb 326. Barb 326 may be constructed in a manner described above to have a distal extent 326a which engages protrusions 336 of strap 314 upon insertion of strap 314 through passage 322. Barb support 340, positioned adjacent barb 326, includes a distal portion 341 which extends into passage 322 for engagement with protrusions 336 of strap body 314 upon insertion thereof. The barb support 340 is flexibly constructed having a thin flexible hinge 343 and a tapering body extending toward distal portion 341, so as not to overly increase the insertion force of tie 310. Thus upon insertion (arrow A), barb support 340 easily deflects permitting passage of strap 314 therethrough. As with the embodiment shown with respect to Figures 4 and 5, upon withdrawal of strap 314 from head 312 (arrow B), barb 326 digs into strap body 315. Barb support 340 frictionally wedges strap 314 to provide increase withdrawal force resistance and loop tensile strength. In the embodiment shown in Figure 8, barb 326 is embedded into head 312 at an end 314b opposite distal extent 326a. It has been found that in known ties having a similarly embedded barb upon attempt to withdraw the strap from the head, breakage of the barb at the point where it is embedded into the head may occur. This incidence of breaking may be caused by over flexing of the barb in the direction of arrow B. In this embodiment of the invention, a pawl support 340 supports barb 326 along nearly the entire length thereof. Such support prevents over flexing of barb 326 in the direction of arrow B. This support would tend to lessen the incidence of breakage of barb 326. In addition, and as similarly described with respect to the embodiment of Figures 4 and 5, over-rotation of the barb support 340 is prevented upon withdrawal of the strap 314 from the head 312 along the direction of arrow B. This over-rotation prevention is effected by the collapsing of hinge 343 and the engagement of shoulder surface 340a on barb 340 with inner surface 312a of head 312. Such engagement provides a mechanical stop for over-rotation of barb support 340. As set forth hereinabove, the present invention seeks to provide a barb flexibly positioned within a cable tie head such that a distal extent of the barb is spaced from the opposed passage wall a distance which permits the substantially unimpeded insertion of strap body through the passage in the cable tie head. In this regard it is desirable to space the distal extent of the barb from the passage wall a distance which is greater than the thickness of the strap body but less than the thickness of the strap body plus the extending protrusions. Thus upon insertion, the distal extent of the barb engages the protrusions and not the strap body. However in practice controlling such tolerances is difficult. Therefore the present invention contemplates forming a cable tie where the distance between the distal extent of the barb and the opposed passage wall is not substantially less than the thickness of the strap body as measured between the opposed surfaces. By controlling the positioning of the barb so that there is no more than insubstantial engagement of the distal extent of the barb with the strap body upon insertion of the strap into the head, a cable tie having an extremely low insertion force will be provided without sacrificing pullout resistance (loop tensile strength). Various changes to the foregoing described and shown structures would now be evident to those skilled in the art. Accordingly, the particularly disclosed scope of the invention is set forth in the following claims.

Claims: A self locking cable tie (10; 110; 210; 310) comprising: an elongate tie strap having a head (12; 112; 212; 312) at one end, a tail (16) at the other end and a generally planar strap body (14; 114; 214; 314) therebetween, said strap body having a given strap thickness; said head (12; 112; 212; 312) having an aperture therethrough for insertion of said tail therein permitting passage of said strap body through said aperture in a first direction; a locking barb (24; 126; 226; 326) movably supported by said head and extending into said aperture for biting engagement with said planar strap body upon movement of said strap body in a second direction opposite said first direction to prevent withdrawal of said strap body from said aperture, said barb being positioned with respect to said aperture so as to create a passage of dimension not substantially less than said strap body thickness; a multiplicity of barb engagement protrusions (36; 136; 236) extending from said planar strap body for engagement with said barb (24; 126; 226; 326) upon movement of said strap in said first direction, said barb engagement protrusions (36; 136; 236) being longitudinally and transversely spaced from one another, said strap protrusions together with said strap body providing a thickness which is greater than the dimension of said strap body passage, so that said barb is caused to engage said protrusions and thereafter said strap body upon movement of said strap body in said second direction. A cable tie of claim 1 wherein said locking barb (24; 126; 226; 326) has a barb width for engagement with a central longitudinal strip of said planar strap body. A cable tie of claim 2 further including a multiplicity of lateral protrusions (34) extending from said planar body on either edge of said longitudinal strip, said lateral protrusions having an extent less than that of said barb engagement protrusions (36; 136; 236). A cable tie of any one of claims 1 to 3 wherein said barb (24; 126; 226; 326) is a metallic member. A cable tie of claim 4 further including means for flexible supporting said barb to said head. A cable tie of claim 5 wherein said flexible support means includes a cantilevered platform (34) extending from said head deflectably supporting said barb. A cable tie of claim 5 wherein said flexible support means includes a pivotally mounted pawl (140; 240) extending from said head pivotably supporting said barb.

Inventors: WELLS PETER M, WELLS, PETER M.
Applicants: THOMAS & BETTS CORP, THOMAS & BETTS CORPORATION (A TENNESSEE CORPORATION)
Application year: 1995
Main classification: B65D63
IPC codes: B65D63