WO1989005713A1

WO1989005713A1 - Tool for and a method of tightening a threaded fastener

Info

Publication number: WO1989005713A1
Application number: PCT/GB1988/001082
Authority: WO
Inventors: John Andrew Brian Hirst
Original assignee: Exotech Limited
Priority date: 1987-12-19
Filing date: 1988-12-12
Publication date: 1989-06-29
Also published as: GB8729659D0

Abstract

A tool for transmitting torque from a wrench to a nut has a socket component (10) and a sensing element (17) which projects along the interior of the socket component into engagement with the head of a pin (16) mounted in an end portion of a bolt. A spring (25) transmits torque to the sensing element so that the sensing element turns with the nut until the nut is tightened sufficiently for the bolt to grip the pin. The socket component then turns relative to the sensing element and this exposes a coloured area through a window in a sleeve (24) on the outside of the socket component.

Description

Tit le: "Tool for and a method of tightening a threaded fastener"

In GB 2, 184,509A, we have described threaded fasteners having indicating means responsive to a change in a diameter or other transverse dimension of the fastener for indicating when a selected value of stress ha s been attained in the fastener, during tightening. One example of fastener described is a bolt and nut wherein a threaded end portion of the bolt is hollow and contains a pin which, when the bolt is unstressed, is free to turn relative to the bolt but, when the bolt is stressed in tension to its elastic limit, is gripped by the bolt so that turning of the pin relative to the bolt is no longer possible. It is suggested that freedom of the pin to turn relati ve to the bolt can be checked by means of an al l en key introduced into an appropriate socket in a head of the pin.

It is an object of the present invention to provide a more convenient way of indicating when the bolt disclosed in the a foresaid pub l ished application has been stressed to its elastic limit.

According to a first aspect of the present invention, there is provided a tool suitable for use in turning a nut on a bolt and including. an output member through which, when the tool is in use for turning the nut. torque is transmitted to the nut, a sensing element arranged for at least limited turning relative to the output member about an axis defined by the output member. transmitt ing means for transmitting torque to the sensing element to turn the sensing element with the output member and indicating means for indicating when the output member turns relative to the sensing element.

The sensing element is preferably arranged to lie on the axis of the output member and adapted to co-operate in torque transmitting relation with a pin mounted in a threaded end portion of a bolt, onto which end portion a nut is to be driven by means of the tool.

The output member may define a socket to receive the nut. in which case the sensing element is preferably accessible through the socket. Alternatively, the output member may comprise a polygonal lug for receiving a separate socket component, such as is commonl y used in conjunction with wrenches. In the latter case, the sensing element may protrude beyond a free-end of the lug to enter a socket component, when the latter is fitted to the lug.

The sensing element is preferably movable along the axis of the output member relative to that member against the action of biasing means. Accordingly, as the nut is driven along the bolt the output member can advance with the nut, without carrying the sensing element along the bolt.

The indicating means may be adapted to provide a visual indication when the output member turns relative to the sensing element. A visual indication may be provided mechanically, for example by the relative movement of two components. Alternatively, the visual indication may be provided by an electrically energisable indicator. Additionally or alternatively, the indicating means may be adapted to provide an audible indication and may comprise an electrically energisable sound source.

According to a second aspect of the invention, there is provided a tool suitable for use in turning a bolt or nut and having an output member through which, when the tool is in use for turning a bolt or nut, torque is transmitted to the bolt or nut, a sensing element arranged for at least limited turning relative to the output member about an axis defined by the output member, a handle, means for transmitting drive from the handle to the output member, means for transmitting drive from the handle to the sensing element and indicating means for indicating whether or not one of the output member and the sensing element turns relative to the other.

According to a third aspect of the invention, there is provided a tool suitable for using in turning a bolt or nut and having an output member through which, when the tool is in use for turning a bolt or nut, torque is transmitted to the bolt or nut, a sensing element arranged for at least limited turning relative to the output member about an axis defined by the output member, transmitting means for transmitting torque to the sensing element to turn the sensing element with the output member and indicating means for indicating when the output member turns relative to the sensing element, wherein the sensing element has a socket suitable for receiving an end portion of a pin protruding from a bolt when the tool is used for turning the bolt or for turning a nut on the bolt.

There is also provided in accordance with the present invention a method of turning a nut on a hollow, threaded end por tion of a bolt which contains a pin arranged for turning relative to the bolt about an axis of the thread, wherein the pin and the nut are turned together relative to the bolt until the bolt is subjected to α predetermined tensile stress, as said stress is attained, the pin is gripped by the bolt to restrain turning of the pin relative to the bolt, turning of the nut relative to the bolt and the pin is continued, a signal is derived from turning of the nut relative to the pin and turning of the nut is then discontinued.

The signal may be a visual and/or audible signal provided to a person contro lling the operation of tightening of the nut. Alternatively, the signal may be applied automatically to discontinue operation of a machine which is tightening the nut.

Examples of tools embodying the present invention and which are used in a method according to the present invention wil l now be described, with reference to the accompanying drawings, wherein:-

FIGURE 1 shows an end view of a first tool;

FIGURE 2 shows a cross-section of the first tool on the line II-II of Figure 1 ;

FIGURE 3 shows a bolt and a second tool, both the bolt and the tool being shown partly in cross-section;

FIGURE 4 shows internal parts of the second tool, as viewed along on axis defined by the second tool; and

FIGURE 5 shows diagrammaticall y a cross-sect ion of the second tool in a plane containing the axis.

The tool of Figures 1 and 2 is intended for use in transmitting drive to a polygonal nut and includes a generall y cylindrical output member 10 having at one of its ends a socket 11 of a suitable size and shape to receive the nut with a sliding fit. The external surface of the member 10 is a surface of revolution about a longitudinal axis 12 of the member. The member addtionally has surfaces which are other than surfaces of revolution about this axis and which are thereby adapted to transmit torque to a further member. for example a nut. The form and disposition of these torque-transmitting surfaces is selected according to the form of a nut or other member to be driven by the too l. By way of examp le, an hexagona l socket is shown. The longitudinal axis 12 of the output member 10 coincides with an axis defined by the socket 11 . The output member is adapted to receive rotary drive from a polygonal driving lug (not shown) of a known wrench. Generall y, wrenches have a driving lug of square shape in transverse cross- section. Accordingly, the output member is provided at its end remote from the hexagonal socket 11 with a square socket 13 suitable for receiving the driving lug of a known wrench. The output . member fits onto a known wrench and transmits drive therefrom to a nut in the same manner as do known socket components used with wrenches. The output member can be used for driving a known nut onto a known bolt.

The tool illustrated in Figures 1 and 2 is intended primarily for driving a nut 9 onto a bolt of the kind illustrated in Figure 3. This kind of bolt has a hollow, threaded portion 15 to receive the nut and a pin 16 mounted in the threaded portion of the bolt. An end portion of the pin protrudes from the bolt and is adapted to engage in a torque-transmitting manner with a sensing element 17 of the tool of Figures 1 and 2. In the particular example illustrated in Figure 3, the protruding end portion of the pin has the form of an enlarged, non-circular head. A shank of the pin 16 extends into the bolt with sliding clearance so that the pin is free to turn relative to the bolt, when the bolt is unstressed. A circlip or other means may be provided to retain the pin in the bolt. The bolt is disclosed in GB 2.184,509. published 24th June 1987.

The too! illustrated in Figures 1 and 2 is hollow along its entire length. Between the hexagonal socket 11 and the square socket 13. there is a cylindrical chamber 14 which contains the sensing element 17. Between the sensing element and the square socket 13. there is fitted into the chamber a plate 18 which is fixed with respect to the output member 10 . A coiled compression spring 19 acts between the plate 18 and the sensing element 17 tourge the sensing element resiliently towards the hexagonal socket 11. The sensing element 17 has at its end adjacent to the socket 11 a recess having a size and shape which are complementary to the size and shape of the head 20 of the pin 16. One or other of the head 20 and recess 21 may be flared, to facilitate entry of the head into the recess. The sensing element lies on the axis 12.

The chamber 14 also contains a sleeve 22 which receives the sensing element 17 with a sliding fit. The sensing element and the sleeve are keyed together so that relative axial movement is permitted but relative turni ng about the axis 12 is prevented. A pin 23 extends through a hole in the sleeve and an end portion of the pin is received with clearance in an axially extending groove formed in the sensing element 17 at the periphery thereof. Co-operation between the end portion of the pin and the sides of the groove prevents turning of the sleeve relative to the sensing element about the axis 12. The pin 23 extends from the sleeve 22 in a direction away from the axis 12 through a slot formed in the output member 10 to a further sleeve 24 mounted on the outside of the output member. The pin 23 is fixed to the sleeve 24 so that this sleeve is constrained to turn about the axis 12 relative to the output member 10 with the sleeve 22 and the sensing element 17.

The sleeve 24 constitutes indicating means for indicating to a user when turning of the output member 10 relative to the sensing element 17 occurs. To this end, the sleeve 24 is formed with several windows which are spaced apart around the circumference of the output member 10 and through which corresponding parts of the external surface of the output member can be viewed. Turning of the sleeve 24 relative to the output member 10 is limited by the length of the slot in the output member through which the pin 23 extends. This slot typically subtends at the axis 12 an angle in the range 30º to 60°.

Those parts of the external surface of the output member 10 which are exposed to view through the windows of the sleeve 24, when the pin 23 is at one end of its slot, may be coloured differently from those parts which are exposed to view when the pin is at the opposite end of its slot.

Transmitting means is provided for transmitting torque between the output member 10 and the sensing element 17. In the example illustrated the transmitting means is capable of urging the sensing element into a datum position with respect to the output member 10. that datum position corresponding to occupation of one end portion of its slot by the pin 23. The particular example of transmitting means illustrated in the drawing is a torsion spring 25. One end portion of the torsion spring is attached to the sleeve 22 and the opposite end portion of the torsion spring is attached to the plate 18. During assembly of the components, the torsion spring is prestressed to ensure that the torsion spring exerts torque on the sleeve 22 in all positions of the pin 23 in its slot. This torque must be overcome in order for the output member 10 to turn relative to the sensing element 17. It will be noted that the pin 23 prevents axial movement of the sleeve 22 with the sensing element 17 and thus prevents the torsion spring 25 being affected by relative axial movement of components of the tool. When the tool of Figures 1 and 2 is used to screw a nut onto the bolt illustrated in Figure 3. the output member 10 is fitted over the nut and the sensing e lement 1 7 is urg ed by the spring 19 onto the head 20 of the pin so that a torque-transmitting relation is established between the output member 10 and the nut and a torque-transmitting relation is established between the sensing element 17 and the pin 16. Torque is then transmitted to the nut via the output member 10 from a handle or from a power fool. The nut is screwed along the bolt by the applied torque and torque is also transmitted from the handle or power tool via the spring 25 to the sensing element 17 and thence to the pin 16 so that the pin is turned with the nut. The pin 23 remains at that end of its slot to which is urged by the spring 25.

When a predetermined tensile stress, for example that stress which corresponds to the elastic limit of the bolt, is established in the bolt, the bore in which the shank of the pin 16 is disposed contracts sufficiently for the bolt to grip the pin and restrain continued turning of the pin with the nut. As turning of the nut is continued, the sensing element 17 is held against rotation by the pin 16 and the output member 10 turns relative to the sensing element. This is indicated to the operator by the appearance of differently coloured material in the windows of the sleeve 24. The operator then discontinues driving of the nut. The output member 10 is withdrawn from the nut, thereby withdrawing the sensing element 17 from the head of the pin 16. The sensing element is then turned by the spring 25 back to its initial position with respect to the output member 10.

The tool illustrated in Figures 3, 4 and 5 comprises a body 126 having a handle 127 which protrudes from and is fixed with respect to the body. An output member 110 of the tool also protrudes from the body 126 but in a direction which is perpendicular to that in which the handle protrudes. The output member 110 has external surfaces which are other than surfaces of revolution about the axis 112 of the output member. The particular example of output member illustrated in the drawing is a square lug having the same size and shape as do the driving lugs of known wrenches. The lug is mounted for turning relative to the body 126 about the axis 112 of the lug and a ratchet mechanism may be incorporated in the body to control turning of the lug relative to the body. The lug 110 is hollow and the internal surface of the lug may be a surface of revolution about the axis 112.

A sensing element 117 is also mounted in the body 126. for turning relative thereto about the axis 112 . The sensing element lies on that axis and extends through the central opening formed in the driving lug 110. The sensing element protrudes somewhat beyond the driving lug so that as shown in Figure 3, when a socket component 128 is fitted to the driving lug the sensing element can protrude into the socket component. The socket component may be a known component used with known wrenches. That end portion of the sensing element 117 which lies in the socket component may have a demountable head 129 formed with a recess to receive the head 20 of the pin 16.

The sensing element 117 is connected with the body 126 in a similar manner to that in which the sensing element 17 is connected with the output member 1 0. Thus, the sensing element is free to undergo limited axial displacement relative to the body and the output member and is urged by a coiled compression spring 119 to move along the axis relative to the body in a direction towards and into the socket component 128 . The sensing element is also arranged for limited turning relative to the body and output member and a torsion spring 125 is provided to oppose relative turning of the sensing element and body and to urge the sensing element towards a datum position about the axis 112 re lat ive to the body. The sensing element slides in and is keyed to a sleeve 122.

The indicating means provided in the tool of Figures 3, 4 and 5 differs from the indicating signalling means of the tool shown in Figures 1 and 2 in that the means of Figure 3 includes an electrically energisable light-source 130. This light-source is mounted on or in the body 126 where it will be conspicuous, during use of the tool. A battery for supplying electrical pow er to the light-source is contained in the body 126 and energisation of the l i ght-source is controlled by an electrica l switch 131. also mounted in the body and near to the axis 112.

For operating the sw itch 13 1, there is provided a rotary cam 132 which is connected with the sensing element 117 by the sleeve 122 to prevent turning of the sensing element relative to the cam but to permit axial movement of the sensing element relative to the cam.

When the tool of Figure 3 is used to tighten a nut on the bolt of Figure 3, the socket component 128 is fitted over the nut and the head 20 of the pin is received in the recess of the head 129. There is thus established a torque-transmitting relation between the handle 127 and the nut and a torque-transmitting relation between the sensing element 117 and the pin 16. The output member 110 is turned by means of the handle 127 to drive the nut along the bolt. Torque is transmitted from the handle via the torsion spring 125 to the pin 16 to turn the pin with the nut. When there has been attained in the bolt a predetermined stress such that the bolt grips the pin and prevents continued turning of the pin, continued turning of the output member 110 results in turning of that output member and of the body 126 relative to the sensing element 117 and the cam 132. The switch 131 is carried by the body around the cam 132 so that the switch is operated by the cam and the light-source 130 is energised. This provides to the user a visual signal indicating that the required stress has been attained in the bolt. The user than ceases turning of the nut and removes the tool from the nut and bolt.

It will be understood that an electrically energisable light-source and a switch for controlling the light-source may be provided in the tool of Figures 1 and 2, the switch being arranged to be operated by turning of the sleeve 24 relative to the output member 10. For example, provision may be made for limited axial movement of the sleeves 22 and 24 and the slot in the output member 10 through which the pin 23 extends may be inclined to the axis 12 so that movement of the pin along the slot causes axial displacement of the sleeve 24. The switch may be positioned in the path of travel of the sleeve. Modified in this way, the tool may be driven by a power tool, the switch being incorporated in the power tool to control operation thereof automafically.

It will be understood that, in a case where electrically energisable signalling means is provided, this may include an electrically energisable sound source for providing an audible signal to the user.

The tool of Figures 3, 4 and 5 may be modified for turning a bolt, in a case where the hollow end portion of the bolt which conta ins the pin is that end portion which includes a polygonal head of the bolt. In such a modified tool, the means for transmitting drive from the handle to the sensing element is arranged to turn the sensing element relative to the output member. For example, a ratchet mechanism of the tool may be arranged to apply torque in one direction to the output member when the handle is turned in one direction and then to apply torque to the sensing element in the opposite direction when the movement of the handle is reversed. As in the case of the tool described with reference to Figures 3, 4 and 5. the means for transmitting torque to the sensing element would be adapted to yield when the pin is gripped by the bolt, and yielding of the torque-transmitting means would operate a switch to energise the light-source.

The features disclosed in the foregoing description. or the accompanying drawings. 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, as appropriate, may, separately or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

Claims

CLAIMS:-

1 . A tool suitable for use in turning a nut on a bolt and including an output member (10) through which, when the tool is in use for turning the nut, torque is transmitted to the nut, a sensing element (17) arranged for at least limited turning relative to the output member about an axis (12) defined by the output member, transmitting means (25) for transmitting torque to the sensing element to turn the sensing element with the output member and indicating means (24) for indicating when the output member turns relative to the sensing element.

2. A tool suitable for use in turning a bolt or nut and having an output member (10) through which, when the tool is in use for turning a bolt or nut, torque is transmitted to the bolt or nut. a sensing element (117) arranged for at least limited turning relative to the output member about an axis (112) defined by the output member, a handle (127), means for transmitting drive from the handle to the output member. means for transmitting drive from the handle to the sensing element and indicating means (130) for indicating whether or not one of the output member and the sensing element turns relative to the other.

3. A tool according to Claim 1 or Claim 2 wherein the sensing element (17, 117) lies on the axis of the output member (10, 110).

4. A tool according to Claim 3 wherein the sensing element (17, 117) is movable along the axis relative to the output member.

5. A tool according to Claim 4 wherein the sensing element is urged by a resident element in one direction along the axis relative to the output member.

6. A tool according to any preceding Claim wherein the output member ( 10, 110) defines a polygonal socket and the sensing element (17, 117) is accessible through the socket.

7. A tool according to any preceding Claim wherein the transmitting means is a spring.

8. A tool according to any preceding Claim wherein the sensing element ( 17, 117) has a socket suitable for receiving an end portion of a pin.

9. A tool according to any preceding Claim further comprising means (23) for limiting turning of the output member relative to the sensing element.

10. In combination, a threaded fastener and a tool according to any preceding Claim wherein the fastener includes a bolt having a threaded hollow end portion (15) and a pin (16) mounted in the end portion of the bolt and wherein the sensing element of the tool is engaged In torque-transmitting relation with the pin of the fastener.

11. A method of tightening a nut on a hollow, threaded end portion (15) of a bolt which contains a pin (16) arranged for turning relative to the bolt about an axis of the thread, wherein the pin and the nut are turned together relative to the bolt until the bolt is subjected to a predetermined tensile stress. as said stress is attained, the pin is gripped by the bolt, turning of the nut relative to the bolt and the pin is continued, a signal is derived from turning of the nut relative to the pin and wherein turning of the nut is then discontinued.

12. Any novel feature or novel combination of features disclosed herein or in the accompanying drawings.