AU2020286180A1

AU2020286180A1 - A dual thread fastener assembly

Info

Publication number: AU2020286180A1
Application number: AU2020286180A
Authority: AU
Inventors: Brian Davies
Original assignee: Metso Outotec Finland Oy
Current assignee: Metso Finland Oy
Priority date: 2020-01-13
Filing date: 2020-12-07
Publication date: 2021-07-29

Abstract

A dual thread fastener assembly 10 comprises a head 12 and a stud 14. The head has an axial hole 16 formed, in a lower portion, with an internal thread Th. The head 12 has an outer 5 circumferential surface with a circular cross-sectional profile. The stud is formed with first and second threads T1 and T2 which are different to each other. The thread T1 is engageable with the thread Th and the thread T2 is engageable with a thread fastening point 58. 14

Description

A DUAL THREAD FASTENER ASSEMBLY TECHNICAL FIELD

A dual thread fastener assembly is disclosed. The assembly may be well suited to applications where a head of a fastener may otherwise become locked in a recess for example due to corrosion. One of many scenarios where this may occur is when fastening a wear plate to a structure. BACKGROUNDART

It is common to protect industrial machines and structures such as for example ore chutes or bins, and haul pack buckets by fastening wear plates to their surface. One type of fastener is formed with a frusto-conical head that sits in a frusto-conical hole in the wear plate. A threaded stud extends from the head and can be attached to either a threaded hole in an underlying wall or threaded nut. The head is provided with one or more holes to enable coupling to a tool to facilitate the tightening or releasing of the fastener.

When the wear plate requires changing the tool is re-engaged with the head and operated to undo the fastener. Corrosion often occurs at the interface between the conical circumferential surface of the head and the adjacent surface of the wear plate. The corrosion may bind the head to the wear plate to the extent that the tool is unable to apply sufficient torque to unscrew the stud from the threaded hole or nut. In this instance to remove the wear plate a worker may need to access the opposite side of the fastener and cut the nut from the stud, or alternately cut a hole in the wall and then weld a patch on the wall over the hole. Accessing the opposite side of fastener is often difficult and dangerous and greatly increases both the cost of the wear plate replacement and the downtime cost of the associated machine or structure.

It would be desirable to provide a fastener that may reduce the cost impact of corroded or otherwise stuck fasteners.

The above references to the background art do not constitute an admission that the art forms a part of the common general knowledge of a person of ordinary skill in the art. The above references are also not intended to limit the application of the drive sub as disclosed herein.

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SUMMARY OF THE DISCLOSURE

In broad and general terms, the idea or concept behind the disclosed fastener assembly is to form the assembly as a combination of a head and a separate stud with two different threads. One of the threads engages the head, while the other thread engages a nut or other fastening point. One benefit of this arrangement is that when tightening or releasing the fastener assembly the friction surface area between a rotating part of the assembly and the article being fastened is substantially reduced. Therefore, substantially lower torque is required for fasting and more significantly, releasing. A further benefit, as explained in greater detail below, is that by this arrangement when releasing the fastener assembly, the stud acts as a jack applying force to the head in an axial direction of the hole.

In a first aspect there is disclosed a dual thread fastener assembly comprising: a head having an axial hole and formed with a thread Th, the head having an outer circumferential surface with a circular cross-sectional profile; and a stud formed with first and second threads T1 and T2 wherein the thread T1 is different to the thread T2, the thread T1 is engageable with the thread Th and the thread T2 is engageable with a thread fastening point.

In one embodiment the head has a first portion and a neck extending from the first portion, the head provided with a reduction in outer diameter from the first portion to the neck and wherein the neck is coaxial with the hole and provided with the thread Th.

In one embodiment a portion of the hole extending through the first portion of the head is formed with a constant diameter.

In one embodiment the portion of the hole extending through the first portion of the head has a diameter smaller than a portion of the hole extending through the neck.

In one embodiment the stud comprises, at an end accessible through the hole, one or more recesses configured to engage a tool to facilitate tightening or releasing of the assembly.

In one embodiment the recess has a polygonal or elliptical cross-sectional shape.

In one embodiment the assembly has an installation state in which the thread T1 is engaged with the thread Th and the stud is juxtaposed so that an end of the thread T2 nearest the thread T1 is spaced from the thread Th.

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In one embodiment the assembly comprises a locking system that temporarily or releasably locks the head to the stud when the stud is at least partially engaged in the head, wherein when torque is applied directly to the stud the head and the stud rotated together as a single unit.

In one embodiment the locking system is arranged to release the head from the stud to enable relative rotation between the head and the stud when a frictional force applied by contact between the outer circumferential surface of the head and a surface of a hole in which head is located exceeds a threshold level.

In one embodiment the locking system comprises: (a) an adhesive; or (b) a shrink wrap collar that extends from over a portion of the head onto the stud; or (c) one or more turns of a cling plastic film wrapped around a portion of the head and part of the stud; or, (d) an adhesive tape or paper applied about a portion of the head and a part of the stud; or (e) a settable resin/epoxy; or thermosetting plastics material.

In one embodiment the thread T1 has a smaller pitch than the thread T2.

In one embodiment the thread TI has an opposite sense to the thread T2. In this embodiment it is also possible for the thread T1 has a same pitch as the thread T2.

In one embodiment the outer circumferential surface of the head includes a tapered or frusto-conical portion.

In a second aspect there is disclosed a method of releasing a fastener assembly from a threaded engagement point where the fastener assembly has a head and stud threateningly engaged with the head and the fastening point, the method comprising operating the stud as a jack to apply a force in an axial direction to the head.

In a third aspect there is disclosed dual thread fastener assembly comprising: a head having an axial hole and formed with a thread Th; and, a stud formed with first and second threads T1 and T2 wherein the thread TI is different to the thread T2, thread T1 is engageable with the thread Th and the thread T2 is engageable with a thread fastening point.

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BRIEF DESCRIPTION OF THE DRAWINGS

Notwithstanding any other forms which may fall within the scope of the assembly as set forth in the Summary, specific embodiments will now be described, by way of example only, with reference to becoming drawings in which:

Figure 1 is a schematic representation of one embodiment of the disclosed fastener assembly;

Figure 2 is a photograph of the embodiment shown in Figure 1 in a disassembled state with a stud of the fastener assembly disengaged from a head of the fastener assembly;

Figure 3 is a photograph of an embodiment of the fastener assembly in an installation state, ready to be applied to fastener and an article to a structure;

Figure 4 is a schematic representation of a second embodiment of the disclosed fastener assembly; and

Figure 5 is a representation of an embodiment of the disclosed fastener in use fastening a wear plate against a wall of a structure.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

With reference to the drawings an embodiment of the disclosed a dual thread fastener assembly 10, comprising a head 12 and a threaded stud 14. The head 12 has an axial hole 16 and is formed with a thread Th. The stud 14 is formed with first and second threads T1 and T2. The thread T1 is different to the thread T2. The thread T1 is engageable with the thread Th. The thread T2 is engageable with a thread fastening point. The fastening point may comprise for example a nut or a threaded hole in a structure.

The head 12 has a first portion 18 and a neck 20 extending from the first portion 18. In this embodiment the first portion 18 is formed with a generally tapered outer circumferential surface. The first portion 18 is arranged so that a minimum diameter of the taper is at an end 22 near the neck 20 while a maximum diameter of the taper is at an end 24 distant the neck 20. The end 24 of the first portion 18/head 12 coincides with the free face 26 of the head 12.

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As is apparent from the drawings there is a reduction in the outer diameter of the head 12 from the first portion 18 to the neck 20. The reduction in outer diameter is in a substantially stepwise manner. Also, the neck 20 is coaxial with the hole 16. The thread Th is formed on the inner circumferential surface of the neck 20.

An upper part 28 of the hole 16 that lies within the first portion 18 of the head 12 and opens onto the surface 26 has a constant inner diameter D1. That is, the upper part 28 is formed without a screw thread. The hole 16 also has a lower or downhole part 30 that resides within the neck 20. The part 30 has an inner diameter D2 which is equivalent to the major diameter of the thread T1. The diameter D1 is less than the diameter D2.

In this embodiment the first portion 18 of the head 12 is segmented into an upper part 32 and a lower part 34. The upper part 32 runs for an axial length of about two to four times the length of the lower part 34. There is a small step increase in outer diameter between the first part 32 and the second part 34 creating a circumferential ridge or shoulder 36. When the head 12 is disposed in a tapered hole having a taper extending linearly from the lower part 34, a small annular gap is formed between the hole and the outer circumferential surface of the upper part 32. This can be filled with an anticorrosion material or grease during installation of the assembly 10.

As a result of the tapering described above, a cross-section the outer surface of the head 12 in any radial plane has a circular profile. This is to be contrasted with the head of a bolt, or nut which typically have a hexagonal profile or otherwise comprise a plurality of planar surfaces and with respect to each other to facilitate the engagement with a tool such as a spanner or socket. The head 12 is not designed to be gripped about its outer circumferential surface by a tool. Rather it is designed to progressively advance into a hole while torque is being applied directly to the stud 14. Moreover, in this embodiment the portion 18 of the head 12 has frusto-conical configuration. The largest diameter of the head 12 is at an end distant the stud 14. Due to this configuration, and as explained in greater detail below, the head 12 is able to apply a clamping force to an article being fastened by the assembly 10 to a surface.

The stud 14 has an end 38 that is accessible through the hole 16. This is at the end having the thread T1. One or more recesses (in this embodiment one recess) 40 is formed in the end 38 to facilitate engagement with a tool (not shown) for tightening or releasing the fastener assembly 10. The recess 40 may take any shape that can receive a shaft of the tool

5 17044068_2(GHMatters)P112290.AU.1 in a keyed manner. Thus, the recess 40 may have a cross-sectional shape of, for example, but not limited to, a polygon (e.g. triangle, rectangle, pentagon, hexagon, star) or ellipse.

The threads T1 and T2 on the stud 14 are different in this embodiment by way of their respective pitch. In particular the thread T1 has a smaller pitch than the thread T2. By way of nonlimiting example only, and for the purposes of ease of description the thread TI may have a pitch of 1.5 mm and the thread T2 may have a pitch of 3 mm.

When the assembly 10 is initially in use the thread T1 is engaged with the thread Th. The stud 14 is screwed into the head 12 to a point where the beginning of the thread T2 is spaced from, as distinct from hard against, the neck 20. When there is no appreciable gap between the adjacent ends of the threads T1 and T2, this spacing may be facilitated by ensuring that say at least 2-4 turns of the thread TI extend from the free end of the neck 20. This juxtaposition of the stud 14 and the head 12 is shown in Figure 3 and may be considered as the "installation state" of the assembly 10.

The assembly 10 also includes a locking system that temporarily or releasably locks the head 12 to the stud 14 when the stud is at least partially engaged in the head 12. The purpose of this is to cause the assembly 10 as a whole to rotate as a single unit in the initially stages of installation (i.e. so that there is no relative rotation between the head 1 2nad the stud 14). Therefore, on initial engagement of the assembly 10 with a fastening point, the head 12 and stud 14 rotate together. The locking system may be realised in several different forms. For example, one form of locking system may be an adhesive. In this example, prior to threateningly engaging the stud 14 with the head 12 a locking compound such as, but not limited to, "Loctite"TMadhesive may be applied to the engaging threads Th and T1. In alternate examples the locking system could be in the form of: a shrink wrap collar that extends from over at least a portion of the head (e.g. from the neck 20) onto the stud 14; or, one or more turns of a cling plastic film wrapped around at least a portion of the head (e.g. the neck 20) and part of the stud 14; or, an adhesive tape or paper applied about at least a portion of the head (e.g. the neck 20) and a part of the stud 14; or a settable resin/epoxy; or thermosetting plastics material. The locking system is arranged to release the head 12 from the stud 14 to enable relative rotation between the head12 and the stud 14 when a frictional force applied by contact between the outer circumferential surface of the head 12 and a surface of a hole in which head is located exceeds a threshold level.

The manner of use of the fastener assembly 10 is described below with the aid of Figure 5. Figure 5 shows an embodiment of the fastener 10 being used to fasten a wear plate 50

6 17044068_2(GHMatters)P112290.AU.1 against a wall 52 of a structure such as an ore chute. The wear plate 50 has a hole 54 with a tapered circumferential surface and having a configuration substantially complimentary to that of the head 12. Due to the relative configurations of the head 12 and the whole 54 when the assembly 10 is fully fastened the head 12 will be fully seated in the hole 54 and clamp the wear plate 50 to the wall 52. The wall 52 has a hole 56 in which the next 20 and stud 14 can pass. A nut 58 is welded onto the back side of the wall 52 for threateningly engaging the thread T2 on the stud 14.

• An anticorrosion compound or grease is deposited in the hole in the article (for example a wear plate) to be fastened by the fasting assembly 10.

• The assembly 10, in the installation state, (i.e. with the head 12 releasably locked to the stud 14) is inserted into the hole 54 of the wear plate 50 and the hole 56 wall. This can be done by hand or by coupling a tool such as a rattle gun or electric drill to the recess 40. In the latter instance a rod would be connected to the tool and inserted through the hole 16 to engage with and key in the recess 40.

• The assembly 10 is rotated so that the thread T2 engages the nut 58 (which in this embodiment constitutes the coupling point for the assembly 10). This reputation can be done initially by hand or with the tool mentioned immediately above.

• The assembly rotates as a single body until a stage in the tightening process where effect of the locking system is overcome and the head 12 is released from the stud 14 to the extent that they are able to rotate relative to each other. The stage will occur when the frictional force acting between the head 12 and the hole 54 in which it resides exceeds the locking strength of the locking system; so that the continued application of torque applied by the tool to the stud 14 causes the stud 14 to commenced to rotate relative to the head 12. It should be appreciated that this occurs because of the cross sectional shape of the head 12 allows it to progress into the complimentary shaped hole in the wear plate or other article being fixed to a surface, while still rotating together with the stud 14. The assembly 10 is now in a "free state".

• Further application of torque results in the stud 14 rotating relative to the head 12 which remains stationary or at least substantially rotationally stationery within the hole.

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* As the stud 14 progresses into the locking point, the head 12 is drawn toward the fastening point/nut 58 applying an ever-increasing clamping force on the article (i.e. the wear plate 50) but the rate of advancement of the head 12 is slower than that of the stud 14. More particularly because of the difference in pitch between threads T1 and T2 the head 12 is drawn toward the fastening point/nut 58 by distance D=(PT2 PT1)0/360, where

o PT2 is the pitch of the thread T2, o PTI is the pitch of the thread T1, and o 0 is the angle of rotation of the stud 14.

Thus, by way of example if the stud 14 were rotated two complete turns the stud 14 advances a total distance of 6 mm (for the case where the thread T2 has a 3 mm pitch) but the head 12 advances by only 3 mm. {(3mm-1.5mm).720/360}. So notwithstanding that the thread T1 is screwing out of the neck 20 the clamping force applied by the head 12, and the tension in the stub 14 continues to increase because the stud 14 is advancing at a quick rate than the thread t1 is disengaging from the thread Th.

• When the designated maximum torque is applied, the tool and rod is withdrawn from recess 40 and the hole 16. The end 38 of the stud 14 will stay engaged with the head 12; the end 38 residing within the neck 20 but axially spaced from the end 22. Several turns of the thread Ti will lie outside of the neck 20.

• The hole 16 inclusive of the portion 30 and the recess 40 may be filled with a sealant to prevent ingress of solid material and liquids.

• To release the assembly 10, the sealant is removed, and the tool and rod reinserted so that the rod engages and is keyed with the recess 40.

• The tool is now operated in an opposite direction to that when applying the assembly 10. This results in the stud 14 rotating and unscrewing from the fasting point. For each complete rotation of the stud 14 the thread T2 advances in an up-hole direction by a distance equal to the thread pitch, in this example 3 mm. Assume that the head 12 is corroded or otherwise stuck in the hole 54 of the wear plate 50 so that it does

8 17044068_2(GHMatters)P112290.AU.1 not turn with the stud 14. For each turn of the stud 14 the thread T2, the stud can only advance an axial distance equal to the pitch of the thread T1, namely 1.5mm into the head 12/neck 20. The shortfall in the distances, in this case 1.5mm is progressively taken up by an axial compression of the stud 14 which in turn applies a jacking or thrust force in an axial direction to the non-rotating head 12.

• This axially directed force will disengage or "pop" the head 12 from the contacted surfaces of the hole 54 in the wear plate 50.

• Now continued operation of the tool results in the thread T2 being completely disengaged from the fasting point/nut 58 so that the assembly 10 can be simply pulled out.

In the above process it should be recognised that the torque applied to the stud 14 when releasing the fastener assembly 10 does not need to be sufficient to overcome the friction and other binding forces such as resulting from corrosion between the substantial circumferential surface area of the head 12 and the hole in which it resides by way or rotating the head 12 within the hole. Measurements have indicated that an equivalent prior art fastener having an integrated head and single thread stud of the same dimensions as an embodiment of the present assembly, when stuck in a hole for example due to corrosion, requires torque in excess of 350 Newton metres to commence rotation (i.e. disengagement). Tests on an embodiment of the present assembly enable disengagement with an applied torque of around 8 Newton metres.

Figure 4 shows a second embodiment of the disclosed fastener assembly, denoted here as 10a. In Figure 4 the identical reference numbers are used to denote identical features to those of the first embodiment shown in Figures 1-3. Features of the second embodiment of the assembly 10a which are similar to those of the first embodiment of the assembly 10 are shown with the same reference numbers but with the addition of the suffix "a".

Using this nomenclature, it can be seen from Figure 4 that the only differences between the first and second embodiments 10, 1Oa is the thread T1a on the stud 14a, and the complimentary thread Tha on the head 12a. Specifically, the threads Tla and Tha are left hand threads. So, in this embodiment the threads on the stud 14a have a different sense to each other, the being a right-hand thread T2 (as in the first embodiment of the assembly 10), and a left-hand thread Ta. In this illustrated embodiment the thread T2 in this embodiment

9 17044068_2(GHMatters)P112290.AU.1 has a larger pitch (for example, but not limited to, 3 mm) than the thread T1a, which may for example of a thread of, but not limited to, 1 mm.

When the assembly 10a is used to bolt an article such as a wear plate to a surface is placed in an installation state where a gap G is formed between the end 38 of the stud 14a and the end 22 of the head 12. This coincides with a number of turns of the thread T1a being located outside of the neck 20. As with the first embodiment the head 12 and the stud 14a are releasably locked together during the initial stages of applying the fastener assembly 10a using a locking system, such as an adhesive compound, shrinkwrap, adhesive tape et cetera. This will ensure that in the initial stages of application the head 12 rotates with the stud 14a.

Towards the end of the application stage where the friction acting between the head 12 and the surface of the hole in which it is located increases there will be a differential in the rate of rotation between the head 12 and the stud 14a. This differential will be at its greatest if this frictional force holds the head 12 stationery within the wear plate as the stud 14a is rotated by the application tool. In this event the thread T2 continues to screw into a corresponding nut (not shown) while the thread T1a screws into the neck 20. (Hence the requirement for the gap G when the assembly 10a is in the initial installation state.) This in effect increases the thread pitch of the stud 14a to the sum of the pictures of Tia and T2 (in this case 4 mm).

Of course, as with the first embodiment when the assembly 10a is initially being applied an anticorrosion compound or grease may be disposed in the hole into which the head 12 is finally seated. Thereafter once the assembly 1Oa is sufficiently tight and plug or a sealing compound may be inserted into the hole 16.

When releasing the assembly 1Oa, any sealant or plug in the hole 16 is removed and a tool such as a rattle gun with an appropriate key is inserted into the hole to engage the recess 40 in the stud 14a. The tool is operated in the opposite direction to that used in the initial installation.

As the stud 14a is rotated the thread T2 winds out of its fixing point at a rate of 3 mm per rotation. Likewise, thread T1a unwinds or unscrews from the neck 20 and a rate of 1 mm per rotation. In the event that the head 12 is held within the hole due to the effects of corrosion and/or friction, the rotating stud 14a effectively operates as a jack applying in the axial force for pushing or popping the head 12 out of the hole.

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Now that embodiments have been described, it should be appreciated that the assembly maybe embodied in many other forms. For example, a non-threaded band may be provided on the stud 14 between the thread T1/T1a and the thread T2. In such embodiments the head 12 and the stud 14/14a are juxtaposed in the installation state with a portion of the non-threaded band extending from the neck 20. Also, the when the threads T1 and T2 are of a different sense they may have either the same or a different pitch.

In the claims which follow, and in the preceding description, except where the context requires otherwise due to express language or necessary implication, the word "comprise" and variations such as "comprises" or "comprising" are used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the system and method as disclosed herein.

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Claims

1. A dual thread fastener assembly comprising: a head having an axial hole and formed with a thread Th, the head having an outer circumferential surface with a circular cross-sectional profile; and a stud formed with first and second threads T1 and T2 wherein the thread TI is different to the thread T2, the thread T1 is engageable with the thread Th and the thread T2 is engageable with a thread fastening point.

2. The assembly according to claim 1 wherein the head has a first portion and a neck extending from the first portion, the head provided with a reduction in outer diameter from the first portion to the neck and wherein the neck is coaxial with the hole and provided with the thread Th.

3. The assembly according to claim 2 wherein a portion of the hole extending through the first portion of the head is formed with a constant diameter.

4. The assembly according to claim 3 wherein the portion of the hole extending through the first portion of the head has a diameter smaller than a portion of the hole extending through the neck.

5. The assembly according to any one of claims 1-3 wherein the stud comprises, at an end accessible through the hole, one or more recesses configured to engage a tool to facilitate tightening or releasing of the assembly.

6. The assembly according to claim 5 wherein the recess has a polygonal or elliptical cross-sectional shape.

7. The assembly according to any one of claims 1-6 wherein the assembly has an installation state in which the thread T1 is engaged with the thread Th and the stud is juxtaposed so that an end of the thread T2 nearest the thread T1 is spaced from the thread Th.

8. The assembly according to any one of claims 1-7 comprising a locking system that temporarily or releasably locks the head to the stud when the stud is at least partially engaged in the head, wherein when torque is applied directly to the stud the head and the stud rotated together as a single unit.

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9. The assembly according to claim 8 wherein the locking system is arranged to release the head from the stud to enable relative rotation between the head and the stud when a frictional force applied by contact between the outer circumferential surface of the head and a surface of a hole in which head is located exceeds a threshold level.

10. The assembly according to claim 8 or 9 wherein the locking system comprises: (a) an adhesive; or (b) a shrink wrap collar that extends from over a portion of the head onto the stud; or (c) one or more turns of a cling plastic film wrapped around a portion of the head and part of the stud; or, (d) an adhesive tape or paper applied about a portion of the head and a part of the stud; or (e) a settable resin/epoxy; or thermosetting plastics material.

11. The assembly according to any one of claims 1-10 wherein the thread T1 has a smaller pitch than the thread T2.

12. The assembly according to any one of claims 1-10 wherein the thread T1 has an opposite sense to the thread T2.

13. The assembly according to claim 12 wherein the thread TI has a same pitch as the thread T2.

14. The assembly according to any one of claims 1-13 wherein the outer circumferential surface of the head includes a tapered or frusto-conical portion.

15. A method of releasing a fastener assembly from a threaded engagement point where the fastener assembly has a head and stud threateningly engaged with the head and the fastening point, the method comprising operating the stud as a jack to apply a force in an axial direction to the head.

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