GB2165611A - Indicating tension in fasteners - Google Patents
Indicating tension in fasteners Download PDFInfo
- Publication number
- GB2165611A GB2165611A GB08424240A GB8424240A GB2165611A GB 2165611 A GB2165611 A GB 2165611A GB 08424240 A GB08424240 A GB 08424240A GB 8424240 A GB8424240 A GB 8424240A GB 2165611 A GB2165611 A GB 2165611A
- Authority
- GB
- United Kingdom
- Prior art keywords
- fastener
- indicator
- carrier
- abutment face
- bolt
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Withdrawn
Links
- 239000000463 material Substances 0.000 claims description 3
- 229910010293 ceramic material Inorganic materials 0.000 claims description 2
- 230000000295 complement effect Effects 0.000 description 3
- 229910000831 Steel Inorganic materials 0.000 description 2
- 238000004519 manufacturing process Methods 0.000 description 2
- 238000000034 method Methods 0.000 description 2
- 239000000203 mixture Substances 0.000 description 2
- 239000010959 steel Substances 0.000 description 2
- 238000004873 anchoring Methods 0.000 description 1
- 239000000969 carrier Substances 0.000 description 1
- 238000005260 corrosion Methods 0.000 description 1
- 230000007797 corrosion Effects 0.000 description 1
- 238000005553 drilling Methods 0.000 description 1
- 239000003112 inhibitor Substances 0.000 description 1
- 230000002427 irreversible effect Effects 0.000 description 1
- 230000000670 limiting effect Effects 0.000 description 1
- 239000000314 lubricant Substances 0.000 description 1
- 238000003754 machining Methods 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 238000000465 moulding Methods 0.000 description 1
- 230000036961 partial effect Effects 0.000 description 1
- 230000002093 peripheral effect Effects 0.000 description 1
- 239000004033 plastic Substances 0.000 description 1
- 229920003023 plastic Polymers 0.000 description 1
- 238000003825 pressing Methods 0.000 description 1
- 230000002829 reductive effect Effects 0.000 description 1
- 230000000717 retained effect Effects 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- 238000011179 visual inspection Methods 0.000 description 1
Classifications
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16B—DEVICES FOR FASTENING OR SECURING CONSTRUCTIONAL ELEMENTS OR MACHINE PARTS TOGETHER, e.g. NAILS, BOLTS, CIRCLIPS, CLAMPS, CLIPS OR WEDGES; JOINTS OR JOINTING
- F16B31/00—Screwed connections specially modified in view of tensile load; Break-bolts
- F16B31/02—Screwed connections specially modified in view of tensile load; Break-bolts for indicating the attainment of a particular tensile load or limiting tensile load
- F16B31/025—Screwed connections specially modified in view of tensile load; Break-bolts for indicating the attainment of a particular tensile load or limiting tensile load with a gauge pin in a longitudinal bore in the body of the bolt
Landscapes
- Engineering & Computer Science (AREA)
- General Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Insertion Pins And Rivets (AREA)
Abstract
A pin (14) extends into and is anchored in a bore formed in a bolt (10). Between a head of the pin and a head of the bolt, there are trapped two annular members (17, 18). When the fastener is unstressed, the annular members can rotate. When the fastener is subjected to a predetermined tension, the head of the pin and the head of the bolt engage respective members with sufficient pressure to inhibit rotation. If the bolt is subjected to excessive tension, one of the annular members (17), which is brittle, fractures. <IMAGE>
Description
SPECIFICATION
Fastener
From one aspect, the present invention relates to a device, hereinafter called a device of the kind specified, comprising a hollow fastener having an abutment face in which there is an opening to the interior of the fastener, a carrier which is disposed partly inside the fastener and partly protruding through said opening and an indicator, the carrier being anchored to the fastener at an anchor position spaced from the abutment face against movement of the carrier relative to the fastener in a direction to withdraw the carrier from the interior of the fastener through said opening and the carrier having an abutment which is spaced from the abutment face of the fastener in a direction away from the anchor position, the indicator being trapped between the abutment face on the fastener and the abutment on the carrier, and the arrangement being such that, when the fastener is unstressed, movement of the indicator relative to the fastener in at least one mode is substantially uninhibited; whereas when that part of the fastener which contains the carrier is subjected to increasing stress by tightening of the fastener, the abutment face becomes pressed against the indicator to inhibit said movement.
From a further aspect, the invention relates to a device comprising a hollow fastener having an abutment face in which there is an opening to the interior of the fastener, a carrier which is disposed partly inside the fastener and partly protruding through said opening and an indicator on the carrier, the indicator being adjacent to and overlapping with the abutment face, the carrier being anchored to the fastener at an anchor position spaced from the abutment face to maintain the indicator adjacent to the abutment face and the arrangement being such that, when the fastener is unstressed, rotation of the indicator relative to the fastener is substantially uninhibited; whereas when the fastener is subjected to increasing stress by tightening of the fastener, the abutment face becomes pressed against the indicator to inhibit said movement.
Examples of devices of both of the kinds described are disclosed in EP49537A. In these examples, the fastener has a male screw thread and, in one example, is hollow along a part only of its length whilst in other examples the fastener is hollow along its entire length. In the latter cases, the carrier extends completely through the fastener and the anchor position is at one end of the fastener.
In cases where the fastener is hollow along a part only of its length, the anchor position is between the ends of the fastener. The abutment on the carrier is conveniently in the form of an integral head but may be formed separately and mounted on the carrier.
In the example disclosed in EP49537A where the anchor position is between the ends of the fastener, the carrier is fixed with respect to the fastener and the indicator is carried on a cylindrical portion of the carrier which protrudes from the opening in the fastener, the indicator having a hole within which the cylindrical portion of the carrier is received with clearance to permit rotation of the indicator relative to the carrier and relative to the fastener. In other examples, the indicator is fixed with respect to the carrier, which is received in the fastener with sufficient clearance to permit rotation of the carrier and indicator relative to the fastener. When the fasteners are unstressed, each indicator is freely rotatable relative to its fastener.When the fasteners are subjected to tension, the fasteners stretch whilst the carriers do not and the gap between the abutment face of each fastener and the abutment on the corresponding carrier or between the abutment face and the indicator, as the case may be, is reduced until the abutment face of the fastener engages the indicator under sufficient pressure significantly to inhibit rotation of the indicator. This occurs when the fastener has been stretched a predetermined amount and has therefore been subjected to a predetermined stress. By providing an appropriate clearance during manufacture, the device can be so arranged that when the stress in the fastener is below a predetermined value, the indicator can be turned easily by the fingers and, when the predetermined stress is achieved, the indicator cannot be turned by the fingers.Unskilled persons can ensure that the fastener is tightened to achieve at least the predetermined stress, without the use of special tools or measuring devices.
If the fasteners disclosed in EP49537A are over-tightened, so that they are subjected to excessive stress, this will not be readily apparent. The indicator will still be held firmly and the appearance of the device will not differ from the appearance of the device when the fastener is subjected to the intended stress. Although a person tightening the fastener can avoid excessive tightening by checking frequently the freedom of the indicator to rotate and ceasing to tighten the fastener immediately the indicator is held against rotation, another person subsequently inspecting the device cannot conveniently ascertain whether excessive tightening of the fastener has occurred.
According to a first aspect of the present invention, the indicator of a device of either of the the kinds described is so arranged that increasing the pressure to which the indicator is subjected by the abutment face of the fastener will eventually result in fracture of the indicator. Fracturing of the indicator may so change the appearance of the indicator that the change is readily apparent to anyone in specting the indicator visually. Additionally, or alternatively, fracturing of the indicator may result in loss of contact pressure between the indicator and one or both of the abutment face of the fastener and the abutment of the carrier, so that the indicator is no longer gripped and can be moved by the fingers. In this case, over stressing of the fastener can be detected by touch, rather than by visual inspection.
According to a further aspect of the invention, there is provided a device comprising a hollow fastener which is in tension and a carrier having an indicator, wherein the fastener has an abutment face and, in the abutment face, an opening to the interior of the fastener, the carrier lies partly in the interior of the fastener and protrudes through the opening, the indicator is on the protruding part of the fastener and the indicator is engaged with the abutment face of the fastener under pressure, the arrangement being such that reducing to zero the tension in the fastener reduces said pressure to zero and the indicator being adapted to fracture if said pressure is increased by increasing the tension in the fastener.
The arrangement is preferably such that fracturing of the indicator results in release of the indicator from the carrier so that the indicator can or will fall from the carrier or can readily be removed from the carrier.
The indicator may be formed in two or more parts, only one of these parts suffering fracture when the fastener is over stressed.
Alternatively, the indicator may be a one-piece element. In the latter case, it is preferred that the indicator includes a relatively weak portion which is adapted to fracture when the fastener is over stressed, without the entire indicator suffering fracture.
It will be understood that fracturing is an abrupt and irreversible change; whereas the slight deformation of the indicator of a device disclosed in EP49537A which may be caused by over stressing of the fastener of that device will occur gradually as the stress is increased, will, to at least some extent, be reversed if the stress is removed and will not be readily discernible.
In a case where the indicator comprises parts having respective different compositions, it is preferred that one of these parts be brittle, relative to the other part or parts.
An example of a device in accordance with the present invention will now be described, with reference to the accompanying drawing, wherein:
Figure 1 shows a side elevation of a fastener device; and
Figure 2 shows, on an enlarged scale, a cross-section through a part of the device.
The device illustrated in the drawings comprises a bolt 10 having a male screw thread 11 which is intended to be screwed into a complementary, threaded hole in another member (not shown), for example a nut. At the end of the bolt remote from the thread, there is a head 12 having flats in the usual manner.
The bolt 10 is partly hollow, being formed with a blind bore extending from an end face 13 of the bolt a part of the way, typically one third of the way, along the length of the bolt.
The bore is preferably cylindrical with its axis coinciding with the longitudinal axis of the bolt and the axis of the thread 11. The diameter of the bore is preferably less than one third the diameter of the shank of the bolt.
The bore of the bolt 10 is occupied by a part of an elongated carrier in the form of a pin 14. That end of the pin which is disposed in the bore of the bolt 10 is spaced somewhat from the blind end of the bore and the pin is anchored to the bolt 10 at a position near to the closed end of the bore in the bolt, so as to restrain the pin against movement relative to the bolt out of the bore. At the anchor position, the pin may be an interference fit in the bore. However, it is preferred that the pin be formed with a screw thread on an end portion disposed within the bore and that the bore be formed with a complementary female screw thread so that the pin can be screwed into the bore to the required position. A known settable composition may be used to prevent subsequent screwing of the pin along the bore.There is a small clearance between the circumferential surface of the pin and the wall of the bore along the major part of the length of the pin, so that relative longitudinal movement will not be impeded by contact between the pin and the bolt, except at the anchor position.
The pin 14 includes a head 15 at the end of the pin remote from the anchor position.
This head is spaced from the end face 13 of the bolt by an intermediate part 16 of the pin.
The device further comprises an indicator which is carried on the pin 14 and is trapped between the head of the pin and the end face 13 of the bolt. In the example illustrated, the indicator is annular and comprises two separately formed parts, namely a frangible part 17 which is immediately adjacent to the head 15 and a relatively non-frangible part 18 which is immediately adjacent to the end face 13 of the bolt.
As shown in the drawing, the infrangible part 18 of the indicator is annular and has an internal diameter considerably greater than the diameter of the intermediate part 16 of the bolt so that there is a considerable clearance between these. The indicator part 18 has a flat surface presented towards the end face 13 of the bolt and this face 13 may include a relatively raised seat 19 having a surface area which is small, as compared with the entire area of the face 13, for engaging the indicator.
The indicator carries a cover 20 which may be formed as a sheet metal pressing or as a plastics moulding, which is substantially cupshaped, and is a push fit on the peripheral surface of the infrangible part 18 of the indicator. A marginal portion of the cover extends into a recess 21 formed in the end face 13 of the bolt and there is provided in this recess an O-ring or like seal 22 which seals the cover to the bolt. The cover thus excludes moisture and foreign solid matter from the indicator and from the bore of the bolt. During manufacture, this bore and/or the cover 20 may be charged with a lubricant or corrosion inhibitor.
The relatively frangible part 17 of the indicator also is of annular form. However, the internal diameter of this part is considerably smaller than is the internal diameter of the infrangible part 18. Typically, the internal diameter of the part 17 is only slightly greater than the diameter of the intermediate part 16 of the pin. The frangible part 17 is arranged to engage the head 15. In the example shown, the head is formed with a conical seating surface 23 and the part 17 of the indicator is formed with a complementary surface which can seat on the head. It will be noted that the head 15 retains the frangible part 1 7 of the indicator in assembled relation with the pin and that the part 17 retains the relatively infrangible part 18 in assembled relation with the pin.The internal diameter of the part 18 is somewhat less than the external diameter of the part 17 so that there is partial overlap of these parts.
When the bolt 10 is unstressed, there is a small, predetermined clearance between the indicator and one of the end face 13 of the bolt and the head 15 and/or between the parts 17 and 18 of the indicator. The indicator and the cover 20 are therefore free to rotate relative to the pin 14 and relative to the bolt 10. Such rotation can easily be effected by the fingers.
When the bolt 10 is tightened, that part of the bolt which extends between the nut or equivalent and the head 12 is stressed in tension and stretches slightly. The part of the bolt lying between the anchor position and the end face 13 increases in length so that clearances initially provided are eliminated and the indicator is gripped between the seat 19 and the seat 23. When the bolt has been tightened just sufficiently for rotation of the cover 20 and indicator by hand to be prevented, a predetermined tension has been established in the bolt. If the bolt is tightened further, the indicator will be subjected to increased pressure by the seat 19 and the seat 23. It will be noted that this pressure will exert a shear force on the relatively frangible part 17 of the indicator.When a predetermined limiting stress is achieved in the bolt, the force exerted on the indicator will fracture the part 17 of the indicator. The resulting pieces will generally be free to fall from the pin 14, although they will be retained inside the cover 20.
The internal diameter of the relatively infrangible part 18 of the indicator is slightly greater than the maximum diameter of the head 15.
Thus, once the part 17 of the indicator has been destroyed, the remainder of the indicator is free for movement away from the head 12 of the bolt and completely off the pin. In some situations, the cover and indicator will fall from the pin. In situations where the cover and indicator do not fall from the pin, they can readily be lifted away from the bolt. In either case, anyone inspecting the device can readily ascertain that the indicator has been broken. This indicates that the bolt 10 has been subjected to excessive stress.
The bolt 10 is typically formed of steel in the usual manner and is then subjected to a drilling operation to form the bore and a further machining operation to form the recess 21. In other respects, the bolt may be a conventional bolt. The pin 14 is preferably formed of the same material as is the bolt 10. This avoids variations in temperature affecting clearances in the device. The relatively infrangible part 18 of the indicator is preferably also formed of steel; whereas the frangible part 17 is preferably formed of a ceramic material.
The shape and thickness of this part of the indicator can be varied in accordance with the maximum stress which is to be permitted without fracture of the indicator part.
The device illustrated in the accompanying drawing may be modified to provide a device in which the indicator is fixed with respect to the pin and the pin and indicator are rotatable relative to the fastener, when the latter is unstressed. For anchoring the pin in the bore of the fastener, there may be provided a bush, relative to which the pin is rotatable but which restrains the pin against axial movement relative to the bush, the bush being fixed in the fastener. Alternatively, in a case where the fastener has a length of only a few inches, the bore and the pin may extend completely through the fastener, an end portion of the pin remote from the indicator lying outside the fastener and bearing means for preventing withdrawal of the pin from the fastener. In a case where the indicator is fixed with respect to the pin, the indicator may be an integral part of the pin.
The features disclosed in the foregoing description, or the following claims, or the accompanying drawing, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, may, separately or in any combination of such features, be utilised for realising the invention in diverse forms thereof.
Claims (10)
1. A device of the kind specified wherein the indicator is so arranged that increasing the pressure to which the indicator is subjected by the abutment face of the fastener will eventually result in fracture of the indicator.
2. A device comprising a hollow fastener which is in tension and a carrier having an indicator, wherein the fastener has an abutment face and, in the abutment face, an opening to the interior of the fastener, the carrier lies partly in the interior of the fastener and protrudes through the opening, the indicator is on the protruding part of the fastener and the indicator is engaged with the abutment face of the fastener under pressure, wherein the arrangement is such that reducing to zero the tension in the fastener reduces said pressure to zero and wherein the indicator is adapted to fracture if said pressure is increased by increasing the tension in the fastener.
3. A device comprising a hollow fastener having an abutment face in which there is an opening to the interior of the fastener, a carrier which is disposed partly inside the fastener and partly protruding through said opening, the carrier being anchored to the fastener at an anchor position spaced from the abutment face against movement of the carrier relative to the fastener in a direction to withdraw the carrier from the interior of the fastener through said opening and the carrier having an indicator adjacent to the abutment face of the fastener, which indicator is rotatable when the fastener is unstressed, the arrangement being such that, when the fastener is subjected to increasing tension, the abutment face engages the indicator under sufficient pressure to impede rotation of the indicator relative to the fastener and the indicator being adapted to fracture if the tension in the fastener continues to increase.
4. A device according to any preceding claim wherein the indicator comprises two parts, one of which is adapted to fracture whilst the other part remains unfractured, when the fastener is subjected to increasing tension.
5. A device according to Claim 4 wherein said one part of the indicator is formed of a material which is brittle, as compared with the material of which the other part is formed.
6. A device according to Claim 5 wherein said one part of the indicator is formed of a ceramic material.
7. A device according to Claim 6 wherein the other part of the indicator is metallic.
8. A device according to any preceding claim wherein the arrangement is such that fracturing of the indicator results in release of the indicator from the carrier.
9. A device substantially as herein described with reference to the accompanying drawing.
10. Any novel feature or novel combination of features disclosed herein and/or shown in the accompanying drawing.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB08424240A GB2165611A (en) | 1984-09-25 | 1984-09-25 | Indicating tension in fasteners |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB08424240A GB2165611A (en) | 1984-09-25 | 1984-09-25 | Indicating tension in fasteners |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB8424240D0 GB8424240D0 (en) | 1984-10-31 |
| GB2165611A true GB2165611A (en) | 1986-04-16 |
Family
ID=10567251
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB08424240A Withdrawn GB2165611A (en) | 1984-09-25 | 1984-09-25 | Indicating tension in fasteners |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2165611A (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2217421A (en) * | 1988-04-09 | 1989-10-25 | Stewart Dudley Jelfs | Load indicating device |
| GB2381056A (en) * | 2001-10-16 | 2003-04-23 | James Walker Group Ltd | Tension indicating fastener assembly |
Citations (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB898026A (en) * | 1958-12-29 | 1962-06-06 | Guest Keen & Nettlefolds Ltd | Improvements in screw-threaded bolts |
| GB1079580A (en) * | 1965-01-13 | 1967-08-16 | Rotron Mfg Co | Fastener between a rotary driving member and a rotray driven member |
| GB1213734A (en) * | 1968-05-28 | 1970-11-25 | Jack Victor Haig Trigg | An improved tensile member |
| GB1269924A (en) * | 1969-11-14 | 1972-04-06 | Mac Lean Fogg Lock Nut Co | Controlled clamping load threaded fastener and method of using same |
| GB1418282A (en) * | 1974-01-03 | 1975-12-17 | Hi Shear Corp | Threaded pin-collar system with retention means |
| GB1564237A (en) * | 1976-08-09 | 1980-04-02 | Hilti Ag | Expansible dowel |
| EP0049537A2 (en) * | 1980-10-08 | 1982-04-14 | Rotabolt Limited | Fastener device |
-
1984
- 1984-09-25 GB GB08424240A patent/GB2165611A/en not_active Withdrawn
Patent Citations (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB898026A (en) * | 1958-12-29 | 1962-06-06 | Guest Keen & Nettlefolds Ltd | Improvements in screw-threaded bolts |
| GB1079580A (en) * | 1965-01-13 | 1967-08-16 | Rotron Mfg Co | Fastener between a rotary driving member and a rotray driven member |
| GB1213734A (en) * | 1968-05-28 | 1970-11-25 | Jack Victor Haig Trigg | An improved tensile member |
| GB1269924A (en) * | 1969-11-14 | 1972-04-06 | Mac Lean Fogg Lock Nut Co | Controlled clamping load threaded fastener and method of using same |
| GB1418282A (en) * | 1974-01-03 | 1975-12-17 | Hi Shear Corp | Threaded pin-collar system with retention means |
| GB1564237A (en) * | 1976-08-09 | 1980-04-02 | Hilti Ag | Expansible dowel |
| EP0049537A2 (en) * | 1980-10-08 | 1982-04-14 | Rotabolt Limited | Fastener device |
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2217421A (en) * | 1988-04-09 | 1989-10-25 | Stewart Dudley Jelfs | Load indicating device |
| GB2217421B (en) * | 1988-04-09 | 1992-09-23 | Stewart Dudley Jelfs | Load indicating system |
| GB2381056A (en) * | 2001-10-16 | 2003-04-23 | James Walker Group Ltd | Tension indicating fastener assembly |
| GB2381056B (en) * | 2001-10-16 | 2004-11-03 | James Walker Group Ltd | Fastener assembly |
Also Published As
| Publication number | Publication date |
|---|---|
| GB8424240D0 (en) | 1984-10-31 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| WAP | Application withdrawn, taken to be withdrawn or refused ** after publication under section 16(1) |