THREADING INDICATING BOLT

Abstract

A threading indicating bolt comprises a shank and a head, said head defining a trailing end and said shank defining a leading end of said bolt, said shank comprising a threaded trailing portion having a thread pitch, and a threaded leading portion, said threaded leading portion having a thread start, wherein said threaded leading portion extends in the axial length of said leading portion from said thread start to the threaded trailing portion for a length (L) being three times the thread pitch of said threads of said trailing portion; and wherein a torque is needed to thread a matching nut onto said bolt; said leading portion of said bolt comprising a mechanical threading indicating element adapted to increase said torque needed to thread a matching nut onto said bolt, while said matching nut is in threaded engagement with the mechanical threading indicating element arranged on said leading portion of said bolt; said increase of said torque being in comparison to a required run-down torque when said matching nut has been threaded onto said bolt past said leading portion and onto said threaded trailing portion. A threading indicating system and a method for assembling a bolted joint are also disclosed.

Claims

1. A threading indicating bolt comprising: a geometrical central axis (A) defining an axial direction; a shank and a head, said head defining a trailing end and said shank defining a leading end of said bolt, said shank comprising a threaded trailing portion having a thread pitch, and a threaded leading portion, said threaded leading portion having a thread start, wherein said threaded leading portion extends in said axial direction from said thread start to the threaded trailing portion for a length (3P) being three times the thread pitch of the threads of said trailing portion; and wherein a torque (T) is needed to thread a matching nut onto said bolt; said threaded leading portion of said bolt comprising a mechanical threading indicating element adapted to increase said torque (T) needed to thread a matching nut onto said bolt while said matching nut is in threaded engagement with the mechanical threading indicating element arranged on said threaded leading portion of said bolt; said increase of said torque (T) being in comparison to a required run-down torque when said matching nut has been threaded onto said bolt past said threaded leading portion and onto said threaded trailing portion.

2. A threading indicating bolt according to claim 1, wherein said mechanical threading indicating element is a change of at least one thread property of at least a portion of one thread turn of said threads of the leading portion of said bolt.

3. A threading indicating bolt according to claim 1, wherein mechanical threading indicating element is a partial deformation of at least a portion of at least one thread turn of said thread of said leading portion.

4. A threading indicating bolt according to claim 2, wherein said change of at least one thread property is at least one of the following thread properties: a thread angle, a pitch, a lead, a major diameter, a minor diameter, a top radius, a bottom radius or a thread depth.

5. A threading indicating bolt according to claim 1, wherein said mechanical threading indicating element is arranged on at least a portion of the third thread turn of said bolt counting from said thread start of said threaded leading portion.

6. A threading indicating bolt according to claim 1, wherein said mechanical threading indicating element comprises an altered thread pitch of at least a portion of the threads of the leading portion.

7. A threading indicating system comprising a threaded bolt according to claim 1, and a matching threaded nut, wherein: a first torque is required when said nut is threading onto said threaded trailing portion; and said mechanical threading indicating element is a torque increasing element; and wherein a second torque is required when said nut is threading onto said threaded leading portion of said bolt and said nut is in threaded contact with said torque increasing element; and wherein said second torque is larger than said first torque.

8. The threading indicating system according to claim 7, wherein said run-down torque is decreased when said nut is threaded past said leading portion, and is determined not to be in threaded contact with said threads of said leading portion of said bolt.

9. A method for assembling a bolted joint, said bolted joint comprising the bolt according to claim 1 and a matching nut, said method comprising the steps of: detecting a change in run-down torque when threading said bolt to said nut, said change in run-down torque being above a predetermined threshold value and due to said mechanical threading indicating element, determining, based on the step of detecting said change in run-down torque, a starting point for measuring an angle from; and assembling said bolted joint by applying a torque and performing one of the method steps A and B: A. torquing said nut to said bolt until said measured angle is within an angle range; and B. torquing said nut to said bolt until said applied torque is above a predetermined torque threshold value and said measured angle is within an angle range; wherein said angle being within said angle range is indicative that said bolted joint is securely assembled.

10. The method according to claim 9, further comprising the steps of: comparing said measured angle to said predetermined angle range, and based on said comparison and if said measured angle is within said angle range: determining that said bolted joint is securely assembled.

11. The method according to claim 9, further comprising the steps of: if said measured angle is determined to not be within said predetermined angle range: determining that said bolted joint is not securely assembled; and indicating to an operator that the bolted joint is not securely assembled.

12. The method according to claim 9, wherein said step of detecting a change in run-down torque comprises detecting an increase in run-down torque resulting from said nut threadingly engaging said mechanical threading indicating element of said bolt, or a decrease in run-down torque resulting from said nut threadingly disengaging said mechanical threading indicating element of said bolt, when said nut is threading onto said bolt.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The above objects, as well as additional objects, features and advantages of the present inventive concept, will be more fully appreciated by reference to the following illustrative and non-limiting detailed description of preferred embodiments of the present inventive concept, when taken in conjunction with the accompanying drawings, wherein:

[0035] FIG. 1a shows a schematic graph of the torque as a function of rotation angle, when threading a standard nut to a bolt of a nut and bolt joint;

[0036] FIG. 1b shows a schematic graph for the torque as a function of rotation angle, when threading a standard nut to a bolt comprising a thread locking patch;

[0037] FIG. 2 shows a schematic graph for the torque as a function of rotation angle, when threading a nut to a bolt comprising a mechanical threading indicating element according to at least one embodiment of the bolt;

[0038] FIG. 3a shows a bolt comprising a mechanical threading indicating element in the form of an altered pitch according to at least one exemplary embodiment of the bolt;

[0039] FIG. 3b shows a bolt comprising a mechanical threading indicating element in the form of a partly deformed thread according to at least one exemplary embodiment of the bolt;

[0040] FIG. 3c shows an enlarged partial view of an area B in FIG. 3b;

[0041] FIG. 3d shows a bolt comprising a mechanical threading indicating element in the form of an altered thread depth, or height, according to at least one exemplary embodiment of the bolt;

[0042] FIG. 3e shows an enlarged partial view of an area C in FIG. 3d;

[0043] FIGS. 4a-4d show flow charts of a method for assembling a bolted joint, comprising a nut and a bolt, wherein the bolt comprises a mechanical threading indicating element;

[0044] FIG. 5 shows a threading indicating system comprising a threaded bolt according to the first aspect of the bolt and a matching nut.

[0045] All the figures are highly schematic, not necessarily to scale, and they show parts which are appropriate for elucidating the invention as set forth in the appended claims, other parts being omitted or merely suggested.

DETAILED DESCRIPTION OF THE DRAWINGS

[0046] Embodiments of the bolt and system will be described in more detail in the following with reference to the accompanying drawings.

[0047] FIG. 1 shows a schematic chart comprising a torque curve for a bolt comprising a mechanical threading indicating element being threaded onto a standard nut. The torque is drawn as a function of a rotation angle α when threading the nut to the bolt. By threading the nut to the bolt, either both the nut and the bolt are counter rotated or one of the nut and the bolt is fixated while the other of the nut and bolt is rotated. The torque is the torque applied by a tool to overcome the friction between the threads of the nut and the bolt in order to thread the nut and bolt together. The chart shows an ideal case when threading between the nut and the bolt where the threads of the two are lubricated in order reduce friction when threading and no initial axial loads are present i.e. the nut and bolt are not exposed to initial axial forces.

[0048] The angle α denotes the angle of rotation between the nut and the bolt. Hence one full revolution between the nut and the bolt is 360 ° or 2π. Naturally in order to assemble a nut and bolt joint, a plurality of full rotations is required. Hence the angle is larger than 360°. For example, if seven and a half rotations (7.5) are needed to assemble the bolted joint the resulting angle is 2700°.

[0049] In a point P1, the bolt enters the nut. From point P1 to a point P2, no very low frictional forces are present in the threading contact between the nut and the bolt. Hence, between the points P1 and P2, the torque is constant and approximately 0 Nm. At a point P2, the nut and the bolt have been threaded until contact, direct or indirect, is achieved between the nut, the bolt and the body being clamped between the nut and bolt. After point P2, the resistance from frictional forces in the threads of the nut and the bolt will start to build up and increase as the nut and bolt are rotated. Between point P2 and a point P3, an exponential and non-linear torque increase occurs. After point P3 and before a point P4 a linear torque increase occurs. During this linear torque increase the rotational angle of the nut and bolt will result in increased axial forces in the nut and bolt. The axial forces in turn results in normal forces which in turn results in frictional forces in the threads. Hence increased axial forces result in that an increased torque is needed to be applied in order to tighten the bolted joint. Between points P3 and P4 elastic, and no plastic, deformation is present in the nut, bolt and body being clamped.

[0050] At a point P4, the nut and the bolt start to experience plastic deformation due to the axial forces in the two. Hence, point P4 may be referred to as a yield point. Plastic deformation normally occurs in the weaker one of the nut and bolt, preferably designed and dimensioned to be the bolt.

[0051] After point P4 where plastic deformation has been initiated, the torque will start to level out. At a point P5, the torque is constant and will start to decrease slightly.

[0052] FIG. 1b shows a schematic chart comprising a torque curve when threading a bolt comprising a thread locking patch to a standard nut. A thread locking patch is a self-locking element comprised of nylon permanently bonded onto the threads of a fastener. The purpose of the thread locking patch is to prevent a bolted joint from coming loose by increasing the frictional forces between the nut, the bolt and the patch arranged there between. In other words the thread locking patch functions as a wedge between the bolt and mating nut compressing the patch and creating metal to metal contact on a surface opposite the patch. Hence, the purpose of a thread locking patch is as a means for preventing the bolted joint from coming loose due to, for instance, vibrations.

[0053] In a point P1′, the bolt enters the nut. Between entering the nut in point P1′ and a point P2′, where the patch comes into contact with the threads of the nut, the torque is constant and approximately 0 Nm. When the patch comes into contact with the threads of the nut the frictional forces, due to the smearing of the patch in the threads of the nut and the bolt, increase approximately linearly. The point P2′, indicates that the patch of the bolt has entered the nut. When the patch is smeared between the threads, the patch is moved from its original placement on the bolt and spread out on a larger portion of the bolt. The patch will thus increase the torque needed to thread the bolt to the nut or “steal torque” from the tool applying the torque to the bolted joint.

[0054] In a point P3′ the torque decreases slightly before starting to increase once more in point P4′. After point P4′ and before point P5′ a linear torque increase occurs due to increased axial forces and friction between the thread of the nut and the bolt. At point P5′, the yield point, the bolt will start to plastically deform and the torque start to flatten out. Between point P5′ and a point P6′ only minor change in torque occurs.

[0055] FIG. 2 shows a schematic graph for the torque T as a function of rotation angle α, when threading a nut to a bolt comprising a mechanical threading indicating element according to at least one embodiment of the bolt. The bolt enters the nut in a point P10 in the chart, the point being arranged in the chart origin. After the nut is threaded onto the bolt and is determined to be in threaded engagement for about 2-3 full thread turns, and a thread on the nut is in threaded engagement with the mechanical threading indicating element on the bolt, a torque increase will occur. The torque will continue to increase until the mechanical threading indicating element is in full engagement with the threads of the nut. This is shown in the chart in point P20 where the torque value flattens out into a constant torque value. From P20 an approximately constant torque is needed to thread the bolt to the nut. Point P20 may thus be used for controlling or measuring and angle from. The approximately constant torque value needed depends on the type and dimensions of the mechanical threading indicating element of the bolt.

[0056] After being constant between point P20 and a point P30 the torque is decreased due to the mechanical threading indicating element leaving the nut or coming out of contact with the nut. Since the mechanical threading indicating element is arranged on a small portion of the bolt, the decrease of torque is sudden, or almost instant, and occurs during a small angular range. When the nut is threaded completely past the mechanical threading indicating element the torque needed to thread the bolt onto the nut will be low or approximately 0 Nm. Hence, contrary to using a thread locking patch the mechanical threading indicating element will not “steal torque” from the tool applying the torque to the bolted joint when the mechanical threading indicating element is threaded past the nut. Further, the mechanical threading indicating element is fixed in position on the bolt and does not move or smear like a patch.

[0057] In a point P40 the linear torque has decreased and is approximately 0 Nm. From point P40 the torque will start to increase. However, and depending on the design of the bolt, after the decrease in torque from point P30 to point P40 the torque may remain constant and approximately 0 Nm for an angle until the bolt and nut fit snuggly. Between the point P40 and a point P60 the bolt will function as a normal bolt. This may be seen when comparing the torque curve shape between points P3 to P6 of FIG. 1 and points P40 to P60 in FIG. 2.

[0058] The length of the phase P20 to P30 of the curve in FIG. 2 may be altered depending on the mechanical threading indicating element of the bolt. For example, if the mechanical threading indicating element of the bolt is a partly deformed thread, the length of the phase will be approximately three revolutions of the bolt/nut, e.g. 1080°. As a comparison, a patch will affect the torque for more than 1080°.

[0059] Ideally point P20, the first torque increase, is used for counting or measuring an angle from, however, additionally or alternatively point P30 may be used for the counting or measuring the angle.

[0060] FIG. 3a shows a bolt 1 comprising a mechanical threading indicating element according to at least one embodiment of the bolt. The bolt 1 comprises a head 2 and a shank 3. The head 2 comprises a tool engaging interface 40 in the form of a hexagonal head. However, other tool engaging interfaces are equally usable such as torx, Phillips or Allen. The head 2 of the bolt defines a trailing end 4 of the bolt 1. At the opposite end of the bolt is the leading end 5. The shank has a cylindrical shape revolving around an axis A and extends from the head for a length Ls. The length Ls is a design parameter and may vary depending on the intended use for the bolt 1.

[0061] The shank 3 comprises a threaded trailing portion 6 and a threaded leading portion 7. The threaded trailing portion 6 is arranged between the threaded leading portion 7 and the head 2 of the bolt 1 and comprises a thread pitch 1P. The threaded leading portion 7 is arranged adjacent the leading end 5 of the bolt 1. The threaded leading portion 7 comprises a thread start 11 defining a starting point 11 of the thread of the threaded leading portion 7, being arranged adjacent the leading end 5 of the bolt 1. The threaded trailing portion 6 of may be threaded all the way up to the head 3 of the bolt 1 or there may be a non-threaded portion 60 between the threaded trailing portion 6 and the head 3 of the bolt 1. The threaded leading portion 7 comprises a mechanical threading indicating element 10 in the form of an altered thread pitch compared to the thread pitch 1P of the threaded trailing portion 6. The altered thread pitch is adapted to alter the fit between the bolt 1 and a nut being threaded onto the threaded leading portion 7. The result is that the fit will be slightly off with increased interference between the threads of the bolt 1 and a nut. This will result in larger frictional forces that need to be overcome by the applied tool torque in order for the nut to be threaded onto the bolt 1. Hence when the nut is threaded onto the bolt the increased torque is detectable and a point for counting or measuring an angle from may be determined. Only minor change to the thread pitch may be needed in order to increase the frictional forces between the threads.

[0062] The threaded leading portion 7 is arranged such that the axial length of the threaded leading portion 7 is three times 3P the thread pitch of the threaded trailing portion 6. A rule of thumb when dimensioning bolted joints is that the first three thread turns of a bolt are not to be loaded when the bolted joint is assembled. Hence, when arranging the mechanical threading indicating element 10, in the form of an altered thread pitch 10, the threading indicating application does not void or alter the structural integrity of the bolt 1.

[0063] Arranged adjacent the threaded leading portion 7 on the leading end 5 of the bolt 1 is an extended unthreaded end 8. The extended unthreaded end 8 may help guide the bolt 1 into a threaded hole or nut when assembling a bolted joint comprising said bolt 1 and a matching nut or threaded hole.

[0064] FIG. 3b shows a bolt 1′ comprising a mechanical threading indicating element 10′ in the form of an at least partly deformed thread, or threads according to at least one embodiment of the bolt. The bolt 1′ shown in FIG. 3b shares in most parts structural elements with the bolt 1 discussed in relation to FIG. 3a. However, the mechanical threading indicating element of the bolt in FIG. 3a has in FIG. 3b is replaced with an at least partly deformed thread or threads 10′. When a nut is threaded onto the bolt 1′ and is in contact with the deformed thread 10′ the result is an increased frictional force between the deformed thread 10′ and the thread of the nut. In order to detect the increased torque needed to thread the nut to the bolt only a minor thread deformation may be needed. FIG. 3c shows an enlarged view B of the deformed thread 10′. The deformed thread 10′ is shown having a width W being larger than the width of the adjacent threads of the threaded leading portion 7. Further the deformation may only be arranged to a part of a thread turn as shown in FIG. 3c or to a complete thread turn. The thread deformation 10′ shown in FIG. 3b and FIG. 3c is in the shape of a punch mark to a thread crest.

[0065] FIG. 3d shows a bolt 1″ comprising a mechanical threading indicating element 10″ in the form of an altered thread depth Dp, or thread height, according to at least one exemplary embodiment of the bolt (See detailed view in FIG. 3c). The bolt shares most structural elements with the bolts shown in FIG. 3a-3c however the mechanical threading indicating element is in FIG. 3d-FIG. 3e in the form of an altered thread depth Dp of at least a portion of a thread turn or revolution. An enlarged view of the area C in

[0066] FIG. 3d is shown in FIG. 3e. FIG. 3e shows a partial view of three threads 21-23, where the root 28 between the two threads 22, 23 has been changed such that the thread depth Dp is smaller than the normal thread depth Dn between two adjacent thread roots 21, 22. When a nut is being threaded onto the bolt 1″ the altered thread depth Dp will result in the interference between the altered thread root 28 of the bolt 1″ and the nut, thus increasing frictional forces between the nut and the bolt. Thus, increasing the tool torque needed to assemble the bolted joint. Hence the altered thread root 28, or thread depth Dp between the threads 22, 23 may be used as a mechanical threading indicating element 10″.

[0067] FIG. 4a shows a flow chart of a method for assembling a bolted joint, comprising a nut and a bolt 1, 1′, 1″ wherein the bolt 1, 1′, 1″ comprises a mechanical threading indicating element 10, 10′, 10″.

[0068] In a first step S1, a change in run-down torque when threading a bolt 1, 1′, 1″ comprising the mechanical threading indicating element 10, 10′, 10″ is detected. The change in run-down torque is due to the threads of the nut being in threaded contact with the mechanical threading indicating element 10, 10′, 10″ of the bolt 1, 1′, 1″. When a nut is being threaded onto a bolt 1, 1′, 1″ a run-down torque is needed in order to overcome the frictional forces between the threads of the nut and the bolt 1, 1′, 1″. Normally when the threads are clean and lubricated the run-down torque is low or approximately 0 Nm. However, when due to the mechanical threading indicating element 10, 10′, 10″ the run-down torque will change when the mechanical threading indicating element 10, 10′, 10″ comes into contact, or comes out of contact, with the threads of a nut being threaded onto the bolt 1, 1′, 1″. A change in run-down torque being above a predetermined torque threshold is indicative of that the mechanical threading indicating element 10, 10′, 10″ is in contact with the threads of the nut.

[0069] In a step S2, and based on the detected run-down torque change a starting point for counting or measuring an angle α from is determined. A device for measuring the rotation of the tool driving the bolt may be used for continuously measuring the rotation angle of the tool. In addition the tool may measure the torque applied to the bolt. When a torque increase above a threshold is detected, the angle from which to count or measure may be determined in an almost instantaneous manner.

[0070] In a step S3, the bolted joint is assembled by applying a torque to the bolted joint. The step of assembling the bolted joint is performed by either performing a method step A or B, referred to as step S41 or S42 in FIG. 4a. In step S41, the nut is torqued to the bolt, or vice versa, until the measured angle α is within an angle range. The angle range is predetermined and configured based on the load/clamping force and design of the bolt and the bolted joint. When the bolted joint has been assembled and is determined to be within the predetermined angle range the bolted joint may be determined to be securely assembled. In a step S42, the nut and bolt are torqued by an applied tool torque until the torque is above a predetermined torque threshold value and the measured angle is within an angle range. Hence, both the torque and the measured angle are used for determining that the bolted joint is securely assembled, and if one of the two is not within its specified range the bolted joint may be determined to not be securely assembled. In both step S41 and step S42, the counted or measured angle being within the predetermined angle is indicative of that the bolted joint is securely assembled.

[0071] FIG. 4b shows a method for assembling a bolted joint further comprising the steps of: S5 of comparing the measured angle to the predetermined angle range. Based on the step of comparing, S5, and if the measured angle is within the predetermined angle range, the bolted joint may, in a step S6, be determined to be securely assembled. Hence, when comparing the measured angle to an angle range, the measured angle may form a control value indicative of if the bolted joint is securely assembled or not.

[0072] FIG. 4c shows a method for assembling a bolted joint further comprising the steps of: if the measured angle is determined to not be within the predetermined angle range, determining, in a step S7, that the bolted joint is not securely assembled. In a step S8 an indication may be indicated to the operator of the torquing tool that the bolted joint is not securely assembled. Such an indication may be visual, audiotory and/or sensory. The indication may in addition also be logged to a computer.

[0073] FIG. 4d shows the step S1 of detecting a change in run in torque comprises: in a step S10, detecting an increase in run-down torque resulting from the nut threadingly engaging the mechanical threading indicating element of the bolt; or in a step S11, a decrease in run-down torque resulting from the nut threadingly disengaging the mechanical threading indicating element 10, 10′, 10″ of the bolt 1, 1′, 1″ when the nut is threading onto the bolt. Hence, the method may determine both the increase and the decrease in run-down torque resulting from the mechanical threading indicating element engaging and disengaging a matching threaded nut.

[0074] FIG. 5 shows a threading indicating system 1000 comprising the threaded bolt 1 shown in FIG. 3a and a matching nut 100.

[0075] The invention has mainly been described above with reference to a few embodiments. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the invention, as defined by the appended patent claims.