Search Images Maps Play YouTube News Gmail Drive More »
Sign in
Screen reader users: click this link for accessible mode. Accessible mode has the same essential features but works better with your reader.

Patents

  1. Advanced Patent Search
Publication numberUS3696412 A
Publication typeGrant
Publication dateOct 3, 1972
Filing dateOct 19, 1970
Priority dateOct 19, 1970
Publication numberUS 3696412 A, US 3696412A, US-A-3696412, US3696412 A, US3696412A
InventorsSwanson Roger I
Original AssigneeDake Corp
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Method and means for indicating tension
US 3696412 A
Abstract
In a method and means for indicating tension on bolts, screws and the like, a plastic member of flowable material having a plurality of relatively thin copper wires embedded along each edge is utilized. The member has an annular cutout portion permitting it to be inserted between any two bearing surfaces of a threaded fastening joint with the bolt passing through the cutout portion. When the point is tightened to pre-load below yield, the plastic material flows or is extruded until the joint contacts the wire. Subsequent tightening to the desired minimum proof load will shear the wires and material to indicate that minimum proof load has been reached. The plastic strip material also serves as a lubricant to reduce the amount of torque required to reach minimum proof load and a portion is extruded into the core of the joint to act as a lock and seal. In one embodiment, the wires form a pair of leads which may be connected in an electric circuit so that when the joint is tightened to pre-load below the plastic range, there is sufficient extrusion of the plastic material to establish electrical contact between the joint and edge wires to close the electrical circuit, activating an electrical signal to indicate that pre-load has been reached.
Images(2)
Previous page
Next page
Claims  available in
Description  (OCR text may contain errors)

United States Patent Swanson [451 Oct. 3, 1972 METHOD AND MEANS FOR INDICATING TENSION [72] Inventor: Roger I. Swanson, Butler, Pa.

[73] Assignee: Dake Corporation, Grand Haven,

Mich.

[22] Filed: Oct. 19, 1970 [21] Appl. No.: 81,819

[52] US. Cl. ..340/42l, 73/88 F, 85/62, 174/117 F, ZOO/61.08 [51] Int. Cl. ..G08b 21/00 [58] Field of Search ..340/42l, 213 R; 174/] 17 R, 174/117 F, 117 AS; ZOO/61.08, 61.19; 73/88 E, 88 F, 94; 85/62 [56] References Cited UNITED STATES PATENTS 2,626,303 1/1953 Link ..l74/l 17 AS 3,469,492 9/ 1 969 Dahl ..85/62 2,648,833 8/1953 Wilson et a1 ..340/421 2,503,141 4/1950 Stone ..340/421 3,132,204 5/1964 Giellerup ..174/117 R 3,153,974 10/1964 Canning ..73/88 F 3,495,907 2/1970 Rogers ..73/88 F Primary Examiner-David L. Trafton Attorney-Price, Heneveld, Huizenga & Cooper 7] ABSTRACT In a method and means for indicating tension on bolts, screws and the like, a plastic member of flowable material having a plurality of relatively thin copper wires embedded along each edge is utilized. The member has an annular cutout portion permitting it to be inserted between any two bearing surfaces of a threaded fastening joint with the bolt passing through the cutout portion. When the point is tightened to pre load below yield, the plastic material flows or is extruded until the joint contacts the wire. Subsequent tightening to the desired minimum proof load will shear the wires and material to indicate that minimum proof load has been reached. The plastic strip material also serves as a lubricant to reduce the amount of torque required to reach minimum proof load and a portion is extruded into the core of the joint to act as a lock and seal. in one embodiment, the wires form a pair of leads which may be connected in an electric circuit so that when the joint is tightened to pre-load below the plastic range, there is sufficient extrusion of the plastic material to establish electrical contact between the joint and edge wires to close the electrical circuit, activating an electrical signal to indicate that pre-load has been reached.

44 Claims, 12 Drawing Figures PATENTEDUBIS I972 S.696,412

sum 1 or 2 11+ FIG.\

us SI [III Illl

FIG. 5

INVENTOR. 2065/? 1 5/1/4445? PAIENIEDnm 3 m2 3.696.412

sum 2 or 2 FIG. 8

IIIITIIIII ll FIG. 9

FIG."

METHOD AND MEANS FOR INDICATING TENSION BACKGROUND OF THE INVENTION This invention relates to threaded fasteners. and, more particularly, to a fastener tension indicating system that will provide a signal at various levels of load tensioning in a threaded joint.

It is well recognized that a key to a successful product is many times directly related to the success in properly tightening a threaded joint to maximum tension load. Too little or too much will in either event result in failure and the objective is lost. In addition, in mass production, material costs in the way of quantity and size of bolts, nuts, tools, etc. can often represent the difference between commercial success or failure.

With the advent of power tools, many prior and existing proposals have used torque as the standard for measuring "bolt tension. Although it is theoretically feasible under ideal conditions to measure the torque applied to a fastener and thereby accurately arrive at the desirable tension, there are so many variables in actual practice such as the quality of threads, galling, foreign matter, etc. that it has proven to be unreliable as a standard for bolt tension. Where it is still used, it is common to specify bolts larger than required for the assembly and utilize less than their maximum tension. While this reduces the chances of over stressing the bolt, it also results in higher costs.

With the advent of high strength bolts, and in view of the unreliability of torque as a measure of tension, the trend has been to obtain higher tensile loading in the fastener, and draw the bolt up to minimum proof load and beyond. Thus, other methods have been devised to indicate bolt tension such as strain washers, strain gauges, bolt stretch and others. However, all have proven to be too costly or impractical.

SUMMARY OF THE INVENTION To achieve a successful assembled product, there are several areas of major concern. To begin with, the product must be designed to withstand the stresses and strains of the work load. Thus, an economical fastener system must be designed that will pre-stress the assembly above the work load without loosening or failing. From a commercial standpoint, an economical method and tools for assembly and inspection must be established to insure the proper pre-stressing of the assembly.

Therefore, it is a principle object of this invention to provide a method and means for indicating when minimum proof load or desired bolt tension is reached in a threaded joint at a cost well below today's unreliable methods.

It is also an object of this invention to provide a method and means for indicating when the joint has been tightened to pre-load before minimum proof load is reached.

It is a further object of this invention to additionally provide such benefits as, the reduction of required torque to achieve proper joint tension; a seal; a bonding to resist rotation if the joint relaxes; and a method and means which is not only convenient and easy to handle by an unskilled operator, but, in fact, will reduce the amount of handling required thereby increasing overall production.

For achievement of these and other objects, a tension indicating tab of flowable material is provided having a center cutout portion and means of substantially greater hardness than said material embedded along each edge. With the tab positioned between two bearing surfaces in the joint, tensile loading is provided. The tab is deformable and extrudable so that when minimum proof load is achieved, the tab is completely sheared off between the bearing surfaces.

Preferably, the means embedded along each edge is comprised of a wire to provide a pair of leads connected to an electrical circuit which when closed operates an electric signal. The tab is positioned so that the wire means is partially interposed between the two bearing surfaces and when the joint is tightened to a pre-selected pre-load, the tab is partially extruded in, around and out of the joint area until electrical continuity is established between the wire means and joint thereby closing the electrical circuit to actuate the signal. Further tightening of the joint causes complete shear of the tab and wire means between the bearing surfaces thereby opening the electrical circuit to indicate minimum proof loading. The flowable characteristics of the tab acts as a lubricant thereby reducing the amount of torque required to establish a positive joint and in addition acts as a sealant and bond to resist rotation should the joint relax. To increase production and reduce handling, a plurality of tabs may be collated into a continuous strip.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a plan view of the tension indicating tab proposed by this invention;

FIG. 2 is an end view of the embodiment shown in FIG. 1 taken in cross section along line II-II in FIG. 1;

FIG. 3 is a schematic view of the tab as shown in FIG. 1 connected to an electric circuit;

FIG. 4 is an enlarged view of a portion of the nut shown in FIG. 3;

FIG. 5 is a cross-sectional view of a fastening joint embodying the present invention prior to stressing the joint;

FIG. 6 is a cross-sectional view similar to FIG. 5 with the joint tightened to a predetermined pre-load;

FIG. 7 is a cross-sectional view of the joint shown in FIGS. 5 and 6 with the joint tightened to the desired tensile load;

FIG. 8 is a cross-sectional view of an alternative embodiment of the present invention showing a washer collated to a tab similar to the one shown in FIG. 1;

FIG. 9 is a cross-sectional view of a washer for use as an alternative embodiment of the present invention;

FIG. 10 is a plan view of the washer and tab shown in FIG. 8 collated into a continuous strip providing a plurality of washers and tabs;

FIG. I] is a cross-sectional view of an alternative embodiment of this invention showing the collation of a plurality of threaded bolts mounted in tabs forming a continuous strip; and

FIG. 12 is a schematic current diagram of a power fastener tool connected to an electrical circuit in communication with the tension indicating tab.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In order to design a product which will withstand the stresses and strains of the work load, the designer must analyze the structure, determine static and dynamic stresses, and design with an adequate factor of safety. The designer knows that if the joint is fastened and held at a load greater than the fluctuating load on the bolt, the fastener will not fail or loosen in operation. Not infrequently, the average designer is concerned with the modulus of elasticity (30 X for steel. Therefore, for each thirty thousand PSI stress of a fastener, there will be 0.001 inch elongation of the fastener per inch of grip or portion elongated. At 90,000 PSI, elongation will be 0.003 inch/inch regardless of the size of fastener.

To illustrate the importance of elongation or bolt stretch, if the grip is only one-half inch, at 90,000 PS], the stretch is only 0.0015 inch; and at one-quarter inch grip, 0.0075 inch. Thus, even though the fastener is tightened to pre-load, the one-quarter inch grip joint will lose all of its load if the joint relaxes 0.00075 inch. Once the joint loses its clamp load, dropping below the fluctuating load of the assembly, the fastener will loosen further or be stressed and eventually fail from fatigue.

The problem thus is to obtain a joint that will not relax and a fastener that will be stretched to the maximum amount. As indicated in the Background of the Invention, torque has been used as a measure of bolt tension. However, it is well-known that if torque is used, it is most difficult to obtain 75percent of the bolt minimum proof load. Tests have been made on a 36-24 SAE 8 bolt with various lubricants that indicated variations of to 74 lb. ft. of torque to obtain 7,100 pounds tension. Other tests show the nut to gall and weld on a 36-10 bolt having 1,000 lb. ft. torque and zero tension. Needless to say, the ideal fastener joint with maximum stretch cannot be obtained with torque.

As an alternative to torque, the Research Counsel on Riveted and Bolted Structural Joints permitted oneturn of-the-nut-from-hand-tight method of pretensioning structural bolts. This made sense as a 1 inch 8 bolt will stretch 0.] in one-turn-of-the-nut on a rigid joint. However, the problem was, and still is; when is the joint snug, and how can one indicate the start of tensioning. With todays higher tensile bolts (120,000 PSI) even one-half turn may cause the bolt to fail in tightening. In response to the many problems encountered in the art today, which remain unsolved, the present invention has been developed, and will indicate and prove maximum tension at a cost below todays unreliable methods.

Referring now to the drawings in detail, FIGS. I and 2 show a tension indicating tab 10 preferably comprised of a flowable plastic such as polyethylene and having enlarged edge portions 12 and 14. The tab includes an arcuate cutout portion 16 which permits clearance of a threaded bolt when the tab is inserted in the joint between two bearing surfaces. While cutout 16 is shown having a circular shape, it will be appreciated that various other shapes could be used, and indeed preferred in certain applications, the essential requirement being that the minimum diameter of cutout 16 be large enough to permit insertion of the threaded bolt. Embedded in each enlarged edge portion of the tab is a wire 18 and 20, preferably multistrand copper although other materials such as aluminum, soft steel, etc. may also be used so long as the material is substantially harder than the flowable material of the tab and it yields under tension prior to the joint, usually comprised of steel.

One reason that a wire such as copper is preferred is because of its good electrical characteristics since in many instances, wires 18 and 20 are connected to an electrical circuit as shown in FIG. 3. When a predetermined load is applied to the joint, the flowable material partially deforms and extrudes to establish electrical continuity between wires 18, 20 and the joint. This closes circuit 80 and the electrical source 82 activates signal 84 to indicate the predetermined load level.

FIG. 5-7 show a particular fastening joint comprised of two members 22 and 24 joined together in positive fashion by a threaded bolt 26 having a standard hex head 28, bolt 26 being threaded into a hex nut 30 with a washer 32 interposed between the nut 30 and member 24. In this embodiment, the tension indicating tab is shown interposed between nut 30 and washer 32. It will be appreciated, that the indicating tab is operable between any two bearing surfaces such as washer 32 and member 24; bolt head 28 and member 22; or in fact the joint itself. Subsequent embodiments discuss and show some of the alternative uses of tab 10, however for purposes of this embodiment, the tab is interposed between nut 30 and washer 32.

Turning to FIG. 4, hex nut 30 is shown having a preferred configuration wherein an external tapered surface 34 and internal tapered surface 36 is provided with the bearing or seating surface 38 lying therebetween. The tapered surfaces 34 and 36 are described in terms of chamfer, there being an external chamfer angle a and an internal chamfer angle b. The chamfer of nut 30 is provided to facilitate the extrusion of the tab and wires as the nut is tightened. The chamfers provide easy flow of the plastic tab as the nut is tightened to permit flow of the plastic internally toward the core 37 of the nut and external thereof. In part, the plastic acts as a lubricant reducing the amount of torque required to tighten the nut to pre-load and the desired load; and in addition, the flow internally towards the core 37 creates a bond in the core between the nut 30 and bolt 26 as shown in FIG. 7 so that should the joint relax, the bonding resits rotation of the bolt. Furthermore, the plastic at the core acts as a sealant to weatherproof the joint.

Preferably, the internal chamfer angle b is less than the external angle a and it has been found that a 10 and 45 relationship provides good lubricating, bonding and sealing as well as reliable tension indicating characteristics. The ideal bearing surface 38 of nut 30 is to maintain a stress area at least equal to the stress area of the bolt. The outside bearing diameter shown at 39 (at the start of the outer chamfer) in FIG. 4 is preferably less than the outer diameter of the nut and the inside diameter shown at 41 (at the start of the inner chamfer) should be large enough to gather the wires inward as the joint is tightened. The smaller outside bearing diameter permits use of a smaller fastener and also will reduce the torque radius and therefore reduce the torque required to tighten the joint.

OPERATION The operation of tab will now be described in detail with reference to the embodiment shown in FIGS. 5-7, it being understood that the tab can be used in conjunction with an electric responsive device or not. In either use, tab 10 is inserted between the bearing surface 38 of nut 30 and the external bearing surface of washer 32. The outer periphery of cutout 16 should be relatively close to edge portions 12 and 14 so that at least a portion of wires 18 and 20 are positioned directly between bearing surface 38 of nut 30 and washer 32. The nut may be finger tightened so that there is physical contact between the tab, nut and washer (as shown in FIG. 5) prior to mechanical tightening of the joint.

Preferably, wires 18 and 20 are connected in an electrical circuit with an electrical source and signal connected in series. The circuit will be open at the onset since there is no electrical continuity between wires 18 and 20. When used in conjunction with an electrical responsive device as diagramatically disclosed in FIGS. 3 and 12, the nut or bolt is mechanically tightened to achieve a desired pre-load, generally in the vicinity of 10 to 50 percent minimum proof load. At pre-load, there is partial deformation or extrusion of the enlarged edge portions 12 and 14 so that electrical continuity is established between wires 18 and 20 and the joint as shown in FIG. 6. Once electrical continuity is established between wires 18 and 20 an electric circuit 80 or 90 such as disclosed in FIGS. 3 and 12 is closed. In the example of FIG. 3, the electric signal 84 indicates to the operator or tool that pre-load has been reached. In the example of FIG. 12, the electric circuit also controls the operation of the tool.

At pre-load, the bolt tension is in general below its inelastic or yield limit, although very close to it. Further tightening of the bolt will bring the bolt into its plastic range, which is beyond yield. It is in this vicinity, that the bolt reaches its proof load, and though the bolt will retain a certain amount of permanent stretch when loosened, this will not affect the strength of the bolt so long as the bolt is not stretched beyond its minimum tensile strength. Thus, it is realized that once pre-load is reached, sensitive tightening is required.

Having achieved pre-load, the operator or tool now tightens the bolt further to bring it up to minimum proof load. At minimum proof load, there is a complete shear of the plastic tab and wires. Once complete shear is obtained, the electrical circuit 80 such as the one shown in FIG. 3 is opened and the electric signal 84 ceases to operate. This notifies the operator or tool that minimum proof load has been reached and further rotation is terminated. The minimum proof load condition is shown in FIG. 7 and is characterized by the steelto-steel contact between the bearing surface 40 of washer 32 and bearing surface 38 of nut 30. If a power tool 92 and circuit 90 as shown in FIG. 12 is used, the circuit (to be described hereinafter) is designed to automatically shut the tool off at both pre-load and minimum proof load.

It will be appreciated that when it is unnecessary to determine pre-load, an electrical circuitry is not required to determine proof load. The operator then can visually ascertain proof load when complete shear of the tab and wires takes place. For this reason, the width of tab 10 should be less than the washer diameter so that the entire strip will be covered. Also, it has been found that when it is unnecessary to determine preload, there are applications wherein the wires are in and of themselves sufficient for indicating proof load at shear eliminating the necessity of any flowable material in between.

Referring now in detail to FIG. 12, an electrical circuit diagram is shown which automatically turns the power tool 92 off when pre-load and minimum proof load is reached. As override is provided in the system so that when pre-load is reached, the tool can be further operated to tighten the joint to minimum proof load. While there are multifarious circuits capable of design to automatically control the tool during fastening, the circuit shown in FIG. 12 includes an electrical source 94, an electrical signal 96, a circuit relay 98 and plurality of switches 100, 102 and relays 104, 106, 108, and 110. Leads 112 and 114 are connected to wires 18 and 20 of tab 10 and leads 116, 118 and 120 are connected to tool 92 to provide electric energy for the operation thereof. Before loading, wires 18 and 20 and hence leads 1 12 and 114 are open. With relays 104 and 108 normally open and relays 106 and 110 normally closed, the tool is activated by closing switch 102 thus providing power to the tool through leads 118 and 120. The joint is thus loaded until the plastic material is partially deformed and extruded to establish contact between wires 18 and 20 through the joint at pre-load. At this point, circuit relay 98 is activated to open relays 106 and 110 causing the tool to cease operation while at the same time circuit relay 98 closes relays 104 and 108. Further activation of the tool is achieved by closing switch 102 providing current flow through leads 116 and 120 causing the joint to be tightened to minimum proof load at which point wires 18 and 20 are served from between the joint thereby deactivating circuit relay 98 causing relays 104 and 108 to return to their normally open position thus cutting off power to the tool. Preferably, switches and 102 are arranged so that when one is open, the other is closed. Thus, when switch 100 is open and the joint is tightened to minimum proof load, the deactivation of circuit relay 98 which opens relay 104 and 108 also causes relay 106 and to return to their normally closed position. However, at this point, switch 102 is open so that the tool 92 is not reactivated. An electric signal 96 may be connected in series with the circuit relay to provide visual indication of pre-load and minimum proof loading of the joint.

In addition to providing a signal for indicating both pre-load and minimum proof load in the joint, the plastic tab 10 provided by this invention along with the embedded copper wires reduces the amount of torque up to 50 percent necessary to load the joint. That is because the plastic, in essence, operates as a lubricant in the joint thereby greatly reducing the possibility of galling caused by metal-to-metal contact. Tests have shown that the reduced friction up to cutoff (Le. preload) will permit 36 %inch SAE 5 bolt to be tensioned to pre-load (approximately 30,000 PSI) with a conventional one-half inch capacity impact wrench. This is signif'icantly smaller than generally used today. In addition, at cutoff, the contact surfaces are changed from steel, copper and plastic to steel-to-steel. At this point, the torque can double if the proper bearing area and stress is reached thereby providing a built-in brake to resist the energy output of the turning power system. This means that I percent loading can be reached at 50 percent the normal torque output and still have conventional calibrated power tools not exceeding minimum tensile load.

It has been found that a seven strand copper wire 18 and 20 provides a reliable and consistent proof load indicating tab. For one thing, the reliability of the joint is increased since seven strands of copper wire must be cut off at four points or 28 individual check points are provided. In addition, by using multi-strand copper wire, as the joint is tightened, the wire is flattened and drawn both inwardly and outwardly with some of the strands remaining between the bearing surfaces. The wire outside the fastener remains round and as the load increases, will tend to pull outward on the wire as the tab extrudes from the fastener. The copper is being severely cold worked at this point or yielded to its ultimate and will fail with little additional tension or pull. It is the use of an embedded wire which permits the tab to remain useful up to minimum proof load (for a given grade bolt) and thereby permit an accurate indication at minimum proofload.

By having an approximate 45 external chamfer angle a on the outside of the fastener nut 30, the plastic will extrude outward, tending to pull the wires free at pre-load. This can be demostrated by heating the plastic and wire to 250 F. wherein it is found that the cutoff is at a slightly higher load than when at 0 F. The reason is that the plastic will not pull on the wire as well when the plastic is hot. That portion of the plastic and wire extruded internally in the core area 37 provided by the 10 chamfer angle b forms a lock nut around the bolt shank and joint, and many joints remain secure even after the nut is removed as a result thereof. The plastic in the core will also act as a seal against the weather and elements. As a result of the features provided by the present invention, increased speed in fastener tightening is provided with a more reliable tensioning method and simple quality inspection as surance. All this adds up to total lower in place cost.

MODIFICATIONS Turning to FIG. 9, an alternative embodiment is shown to that described with relation to FIGS. 1-7 in that washer 50 is shown having the same physical bearing surface characteristics as that described with regards to nut shown in FIG. 4. That is, washer 50 is characterized by having an internal tapered surface 52, a bearing surface 54 and an external tapered surface 56. Internal surface 52 and external surface 56 characterized by chamfer angles 0 and d are similar in respect to chamfer angles a and b with regards to nut 30 shown in FIG. 4. By providing a washer having the characteristics as shown in FIG. 9, tab 10 could be inserted in the same position as shown in FIG. 5 with a flat hex nut 30 acting as one bearing surface; or in the alternative, bearing surface 54 of washer 50 could be positioned to face member 24 which would act as the opposite bearing surface for tab 10. Furthermore, it will be appreciated that any of the joint elements such as the bolt, screw, nut, washer, etc. or the joint itself could include the preferred bearing surface comfiguration.

Referring to FIG. 8, instead of providing a single tab 10 as shown in FIG. 1, tab 10 is collated with washer 32 by an adhesive or other conventional means thereby reducing the amount of handling required by the ope rator to reduce installation costs and time. In fact, several alternatives are envisioned such as that shown in FIG. 10 wherein a continuous strip of tabs and washers are collated together to further reduce handling by the operator.

Yet another alternative is shown in FIG. 1] wherein a plurality of screws or bolts 64 are shown to be premounted in a collated strip 66 so that they can be easily and rapidly screwed into each individual joint. It should be noted that the screw heads 68 are characterized by having an internal chamfer e; an external chamfer f and a bearing surface 70 similar to that described previously with regards to nut 30 and washer 50. In this embodiment, each individual tension indicating tab in strip 66 will be compressed between the bolt head 68 and one of the members to be joined.

Thus, it is appreciated from the foregoing, that a variety of independent tension indicating fastener tab or collated strips may be provided depending on the particular application envisioned. In addition, the bolt, nut or washer can be collated with the strip to cut down on handling time and packaging thereby providing yet more economy in the setup and tightening of the joint.

Other alternatives envision the use of more than two wires so that an indication can be registered of more than one tension level prior to shear. It is also possible that the compression media be of such a mixture of suspended conducting particles that when subject to a given load, the conducting particles will conduct and complete the circuit. An example of this is gallium antimonide which has an electrical output when subject to pressure.

Although several alternative embodiments have been shown and described, it will be obvious to those having ordinary skill in this art that the details of construction may be modified in a great many ways without departing from the unique concepts presented. It is therefore intended that the invention is limited only by the scope of the appended claims rather than by particular details of construction shown, except as specifically stated in the claims.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows.

l. A method for indicating load tension in a threaded fastener joint comprising the steps of:

providing a tab of flowable material having means of substantially greater hardness than said material embedded along each edge and means defining a cutout to permit passage of a threaded member therethrough;

positioning said tab between two bearing surfaces in said joint so that a portion of said embedded means is between said bearing surfaces; and tightening the threaded fastener to apply a tensile load to the joint of sufficient magnitude to deform and extrude the flowable material and embedded means to completely shear the tab when the predetermined load has been applied.

2. The method according to claim 1 wherein said means embedded along each edge is wire-like.

3. The method according to claim 1 wherein said means embedded along each edge is metallic.

4. The method according to claim 2 wherein said wire-like means is metallic.

5. The method according to claim 4 wherein said metallic wire-like means is connected to an electric circuit having an electric source and signal so that when said joint is tightened to a predetermined tensile load of less magnitude than that required to shear said tab, said flowable material is partially deformed and extruded to establish electrical continuity between said metallic means and joint closing said electric circuit to actuate said signal.

6. The method according to claim 1 wherein said means embedded along each edge is of sufficient hardness in relation to the strength of said joint to permit said joint to be tightened to minimum proof load prior to shear of the tab and sufficiently soft with relation to the strength of said joint to permit complete shearing of the tab prior to the joint being tightened to its ultimate breading point.

7. The method according to claim 6 wherein a plurality of said tabs are collated into a continuous strip to facilitate mass production and reduce installation time and handling.

8. The method according to claim 6 wherein one of said bearing surfaces is characterized as having an internal and external chamfer to permit deformation and extrusion of said material and metallic means inwardly around the core of said joint and outwardly away from the fastener, said inwardly extruding portion forming a bond to restrain said joint from rotation should said joint loosen, and further forming a seal to weatherproof said joint after tightening.

9. The method according to claim 8 wherein said one bearing surface is formed on a nut.

10. The method according to claim 8 wherein said one bearing surface is formed on a bolt or screw.

ll. The method according to claim 8 wherein said one bearing surface is formed on a washer.

12. The method according to claim 8 wherein said internal chamfer is of less angular magnitude than said external chamfer, and said flowable material provides a lubricant in said joint reducing the amount of torque required to tighten said joint to shear at which point the torque increases due to the increased friction in the joint.

13. The method according to claim 8 wherein a fastening element means is collated onto each tab in said strip to further reduce handling and installation time.

14. The method according to claim 13 wherein said element means is comprised of a plurality of screws or bolts.

15. The method according to claim 13 wherein said element means is comprised of a plurality of nuts.

16. The method according to claim 13 wherein said element means is comprised of a plurality of washers.

17. A fastener construction comprising, in combination: at least one member with an opening and a fastener element including a shank extending through said opening; a shoulder-like means associated with said shank, said member and shoulder-like means providing two opposed bearing surfaces; a tab of flowable material having means of substantiallygreater hardness than said material embedded along each edge, and means defining a cutout portion through which said shank is extended so that when said tab is positioned between two bearing surfaces in said fastener construction with a portion of said embedded means aligned between said bearing surfaces, and said fastener construction is tightened to a predetermined load, the tab will become deformed and extruded at said predetermined load, to completely shear the material and embedded means when said predetermined load has been reached.

18. The combination according to claim 17 wherein said means embedded along each edge is wire-like.

19. The combination according to claim 17 wherein said means embedded along each edge is metallic.

20. The combination according to claim 28 wherein said wire-like means is metallic.

21. The combination according to claim 17 wherein said means embedded along each edge is of sufficient hardness in relation to the strength of said fastener construction to permit said fastener construction to be tightened to minimum proof load prior to shear and sufficiently soft with relation to the strength of said construction to permit complete shearing of said tab prior to said construction being tightened to its breaking point.

22. The combination according to claim 20 wherein said metallic wire-like means is comprised of a malleable electric conducting wire connected to an electric circuit having an electric source and signal so that when said fastener construction is tightened to a predetermined tensile load less than minimum proof load, said flowable material will partially deform and extrude to establish electrical continuity between one of said bearing surfaces and said wire to close said circuit and actuate said electric signal.

23. The combination according to claim 21 wherein one of said bearing surfaces in abutment with said tab is characterized as having an internal and external chamfer to permit extrusion of said material and metallic means inwardly around the core of said fastener construction and outwardly away from the fastener construction, said inwardly extruded portion forming a bond to restrain said fastener construction from rotation should said construction loosen, and further forming a seal to weatherproof said construction.

24. The combination according to claim 23 wherein said internal chamfer is of less angular magnitude than said external chamfer and said flowable material provides a lubricant in said fastener construction to reduce the amount of torque required to tighten said fastener construction.

25. The combination according to claim 17 wherein said shank includes a head, and one of said bearing surfaces between which said tab is positioned is formed by the head portion of said shank.

26. The combination according to claim 17 wherein one of said bearing surfaces between which said tab is positioned is formed by a nut threadable on said shank.

27. The combination according to claim 17 wherein one of said bearing surfaces between which said tab is positioned is formed by a washer.

28. The combination according to claim 17 wherein one of said bearing surfaces between which said tab is positioned is formed by said one member.

29. The combination according to claim 17 wherein said fastener element is adapted to tighten said fastener construction, and the bearing area of said opposed bearing surfaces is substantially equal to the cross-sectional bearing area of said fastener element.

30. The combination according to claim 29 wherein one of said bearing surfaces in abutment with said tab is characterized as having an internal and external chamfer to permit extrusion of said material and metallic means inwardly around the core of said fastener construction and outwardly away from the fastener construction, said inwardly extruded portion forming a bond to restrain said fastener construction from rotation should said construction loosen, and further forming a seal to weatherproof said construction.

31. The combination according to claim 30 wherein said internal chamfer is of less angular magnitude than said external chamfer and said flowable material provides a lubricant in said fastener construction to reduce the amount of torque required to tightensaid fastener construction.

32. A fastener construction comprising, in combination: at least one member with an opening and a fastener element including a shank extending through said opening; a shoulder-like means associated with said shank, said member and shoulder-like means providing two opposed bearing surfaces: a continuous strip of flowable material having means of substantially greater hardness than said material embedded along each edge, and means defining a plurality of openings spaced along said strip, said openings permitting passage of a threaded member therethrough so that when one of said openings is positioned between two bearing surfaces in a fastener construction with a portion of said embedded means aligned between said bearing surfaces, and said fastener construction is tightened to a predetermined tensile load, the strip will become deformed and extruded at a predetermined load to completely shear the material and embedded means when said predetermined tensile load has been reached.

33. The combination according to claim 32 wherein said embedded means is of sufficient hardness in relation to the strength of said fastener construction to permit said fastener construction to be tightened to minimum proof load prior to shear of the strip and sufficiently soft with relation to the strength of said fastener construction to permit complete shearing of the strip prior to the fastener construction being tightened to its ultimate breaking point.

34. The combination according to claim 33 wherein said embedded means along each edge is comprised of a malleable metallic wire-like means connected to an electric circuit having an electric source and signal so that when said fastener construction is tightened to a predetermined tensile load of less magnitude than that required to shear said tab, said flowable material is partially deformed and extruded to establish electrical continuity between said metallic means and fastener construction closing said electric circuit to actuate said signal.

35. The combination according to claim 32 wherein a plurality of fastening element means are collated onto said strip to further reduce handling and installation time, each of said fastening element means being aligged with one of said OPCHlIFS.

The combination accor mg to claim 35 wherein said element means is comprised of a plurality of screws or bolts.

37. The combination according to claim 35 wherein said element means is comprised of a plurality of nuts.

38. The combination according to claim 35 wherein said element means is comprised of a plurality of washers.

39. A fastener construction having at least two bearing surfaces and a tension indicating device comprising at least one element including metallic means embedded in a flowable solid material, said element being positioned between said two bearing surfaces in said fastener construction so that when said fastener construction is tightened to a predetermined tensile load said element including said metallic means will become sufficiently deformed and extruded to completely shear said element including said metallic means, thereby indicating that said predetermined load has been reached.

40. The construction according to claim 39 wherein said metallic means is wire-like.

41. The construction according to claim 39 wherein said flowable solid material is deformed away from said metallic means embedded therein at a second predetermined tensile load less than said first predetermined tensile load whereby at least one of said two bearing surfaces are in physical contact with said metallic means when said second tensile load is reached.

42. The construction according to claim 41 wherein said metallic means is comprised of an electrical con ducting material.

43. A method for indicating load tension in a threaded fastener joint comprising the steps of:

providing a tab of flowable material having metallic means of substantially greater hardness than said material embedded along each edge and means defining a cutout to permit passage of a threaded member therethrough;

positioning said tab between two bearing surfaces in said joint so that a portion of said embedded means is between said bearing surfaces; and

tightening the threaded fastener to apply a tensile load to the joint of sufficient magnitude to partially deform and extrude said flowable material to establish electrical continuity between said metallic means and joint.

44. A method according to claim 43 wherein said metallic means is wire-like and connected to an electric circuit having an electric source and signal so that when said joint is tightened to a predetermined tensile load to establish electrical continuity between said wire-like means and joint, said electric circuit closes to actuate said signal.

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US2503141 *Nov 12, 1946Apr 4, 1950Gerotor May CorpStress indicator for bolts or studs
US2626303 *Mar 16, 1950Jan 20, 1953Link Le Roy JPerforated ribbon mounting for electrical conductors
US2648833 *Apr 5, 1951Aug 11, 1953Winfred E WilsonMeans for measuring tension in bolts
US3132204 *Jul 27, 1962May 5, 1964 Electrically conductive pressure sensitive adhesive tapes
US3153974 *Apr 26, 1961Oct 27, 1964Western Electric CoMethod of and device for indicating a predetermined pressure exerted by a fastener
US3469492 *Jul 11, 1967Sep 30, 1969Standard Pressed Steel CoPre-load indicator
US3495907 *Feb 1, 1966Feb 17, 1970Donald E RogersIndicating means
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US3945704 *Mar 28, 1974Mar 23, 1976Kraus Robert ADevice for detecting an applied compressive load
US4365577 *Dec 8, 1980Dec 28, 1982Heinrich Edgar WFloat module combination
US4738438 *Dec 22, 1986Apr 19, 1988Nabeya Iron & Tool Works, Ltd.Machine vise with clamping force detector
US5291789 *Jul 17, 1989Mar 8, 1994Rotabolt LimitedLoad indicating
US6734364Feb 20, 2002May 11, 2004Commscope Properties LlcConnecting web for cable applications
US7152907 *Aug 23, 2002Dec 26, 2006Brose Fahrzeugtelle Gmbh & Co Kg, CoburgMotor vehicle sub-assembly
US7543729 *Nov 1, 2007Jun 9, 2009Tyco Healthcare Group LpSurgical fastener applying apparatus with controlled beam deflection
US7699205Jan 23, 2009Apr 20, 2010Tyco Healthcare Group LpSurgical fastener applying apparatus with controlled beam deflection
US8011552Mar 18, 2010Sep 6, 2011Tyco Healthcare Group LpSurgical fastener applying apparatus with controlled beam deflection
US8292149Aug 2, 2011Oct 23, 2012Tyco Healthcare Group LpSurgical fastener applying apparatus with controlled beam deflection
US8696275 *Jan 4, 2012Apr 15, 2014Applied Bolting Technology Products, Inc.Creep limiting direct tension indicating washer
US8701961Sep 24, 2012Apr 22, 2014Covidien LpSurgical fastener applying apparatus with controlled beam deflection
US20130170921 *Jan 4, 2012Jul 4, 2013Applied Bolting Technology Products, Inc.Creep Limiting Direct Tension Indicating Washer
US20130322988 *Jun 4, 2012Dec 5, 2013Manoj HandaTorque-Indication Crush Washer
Classifications
U.S. Classification340/668, 411/548, 200/61.8, 73/761, 174/117.00F
International ClassificationG01L5/24, F16B31/02, F16B31/00
Cooperative ClassificationG01L5/243, F16B31/028
European ClassificationG01L5/24B, F16B31/02W