GB2179459A

GB2179459A - Indicating tightness of fastening device

Info

Publication number: GB2179459A
Application number: GB08520640A
Authority: GB
Inventors: Stanley Ceney
Original assignee: Rotabolt Ltd
Current assignee: Rotabolt Ltd
Priority date: 1985-08-17
Filing date: 1985-08-17
Publication date: 1987-03-04
Also published as: GB8520640D0

Abstract

An indicator (16) for indicating the strain to which a bolt is subjected is interposed between an end face (12) of the bolt and a head (15) of a pin (13), the shank (14) of the pin being secured in a bore in the bolt, so that on tightening the bolt extends, and the pin head (15) is moved away from bolt end face (12). The indicator (16) may comprise fulcrumed levers (17,21) acted on by a compression spring (22). The indicator (16) is viewed through a window (24) in a cover (23). Alternatively, the indicator may be a sleeve slidable on the bolt neck, and there is a single pivoted lever. <IMAGE>

Description

SPECIFICATION Fastening device and method of using same From a first aspect, the present invention relates to a fastening device having indicating means for indicating when the device has been tightened to a predetermined load. A known fastening device of this kind has the form of a hollow bolt or stud and a pin lying partly inside the bolt or stud with one end portion of the pin anchored inside the bolt or stud. An opposite end portion of the pin has a head which lies near to an end face of the bolt or stud and an annulus is trapped between the head of the pin and this end face.

The relative positions are set during manufacture so that, when the bolt or stud is unstressed, the annulus can be turned freely relative to the bolt or stud; whereas when the bolt or stud has been tightened to provide a predetermined load, the annulus is gripped firmly between the head of the pin and the end face of the bolt or fastener.

The known fastening device hereinbefore described provides only an indication that a predetermined load has not been achieved or has been achieved.

One object of the present invention is to provide an arrangement which gives an indication of the degree to which a predetermined load has been exceeded or of the degree to which the actual load is lower than the predetermined load.

According to a first aspect of the invention, there is provided a fastening device comprising respective parts which undergo relative movement when the device is tightened and indicating means for indicating the relative position of said parts, wherein the indicating means comprises an indicating element which is movable relative to said parts, and a mechanism having a velocity ratio less than unity for magnifying relative movement of said parts and for transmitting the magnified movement to the indicating element.

The preferred fastening device comprises an elongated, hollow member and a pin lying at least partly in the hollow member, said parts being first end portions of the hollow member and of the pin respectively.

Alternatively, said parts may both be parts of a single member which undergoes strain when the fastening device is tightened.

According to a second aspect of the invention, there is provided a method of using a threaded fastener wherein the relative position of respective parts of the fastener is indicated during tightening by indicating means which magnifies the relative movement of said parts.

Two examples of fastening device embodying the first aspect of the invention and which are used in a method according to the second aspect of the invention will now be described, with reference to the accompanying drawing, wherein: Figure 1 shows a bolt in side elevation with certain parts in axial cross-section; and Figure 2 shows a similar view of an alternative bolt.

The bolt shown in Fig. 1 comprises a first end portion formed with a male screw thread and a second end portion constituted by a head 11 formed with flats, in the usual way.

The head 11 of the bolt is hollow, defining a bore which is coaxial with the thread 10 and which extends into a shank of the bolt from an end face 12 of the head.

The bolt of Fig. 1 further comprises a pin 13 having a shank 14 disposed partly in the bore defined by the head 11 and a head 15 which lies outside the head 11. The shank 14 is anchored, at its end portion remote from the head 15, in the bore defined by the bolt, for example by an interference fit or by a screw threaded connection.

There is interposed between the head 15 of the pin and the end face 12 of the bolt an indicating means for indicating the position of the head 15 relative to the end face 12. It will be understood that, during tightening of the bolt, the shank thereof is subjected to tensile stress whereas the pin 13 is not subjected to any significant stress. The shank of the bolt therefore stretches relative to the pin and the separation between the head 15 and the end face 12 is reduced accordingly.

The indicating means comprises an indicating element in the form of a pointer 16 and a lever mechanism for transmitting to the pointer relative movement of the head 15 and end face 12. In the example illustrated, the lever mechanism comprises two levers disposed on opposite sides of the shank 14 of the pin. A first of the levers, 17, has one end portion 18 engaged with the head 15, a fulcrum 19 bearing on the end face 12 and a second end portion 20 engaged with a first end portion of the second lever 21. This lever has a fulcrum bearing against the head 15 and carries the pointer 16 at its other end. A spring 22 acts between the end face 12 and the lever 21 to maintain the levers in contact with each other and to urge the pointer in a direction away from the head 11 of the bolt.

The lever mechanism and the pin 13 are enclosed by a cover 23 which, in the example illustrated, is mounted on the head 11. As shown, the cover may be a press-fit in an annular groove provided in the head 11. In the cover, there is provided a window 24 through which the pointer 16 can be observed. This window may be an aperture in the cover or may be formed of transparent material. Reference marks, preferably a scale, are provided on the cover 23 at or adjacent to the window 24 to facilitate reading of the position of the pointer 16.

The scale or other reference marks are pre ferably marked on the cover after the lever mechanism has been assembled with the pin 13 and the remainder of the bolt, so that a datum mark on the cover coincides with the pointer when the device is unstressed. As the bolt is subjected to tensile stress during tightening, the pointer 16 moves towards the end face 12 and such movement can be observed by the user. Typically, the cover may be marked with the datum position, with the position which the pointer will occupy when the fastener is subjected to the design load and with the position which the pointer will occupy when the fastener is subjected to a load which is equal to the yield strength of the bolt.

The number of levers incorporated in the indicating means may differ from two. Furthermore, there may be provided duplicate levers, each acting between the head 15 and the end face 12 at one side of the axis of the bolt, the duplicate levers co-operating with a common lever which transmits motion to the pointer to compensate for differences which may occur in the movement of the duplicate levers, for example owing to divergence from a coaxial relation between the pin 13 and the shank of the bolt or to slight curvature of the shank of the bolt.

In the device illustrated in Fig. 2, parts corresponding to those hereinbefore described with reference to Fig. 1 are indicated by like reference numerals with the prefix 1 and the preceding description is deemed to apply, except for the differences hereinafter mentioned.

The device of Fig. 2 comprises a sleeve 125 which is carried on the shank of the bolt adjacent to the head 111 thereof. A mid-portion of the sleeve has a thin wall 126 so that the sleeve defines an annular channel having a mouth which faces away from the axis of the bolt. In this channel, there is provided indicating means for indicating relative movement of opposite end portions 127 and 128 of the sleeve.

The indicating means may comprise a lever mechanism arranged substantially as is the lever mechanism illustrated in Fig. 1. However, a somewhat modified lever mechanism is illustrated in Fig. 2. Thus, the fulcrum 119 is provided on a bracket 129 which is fixed with respect to the end portion 127 and extends towards the end portion 128 of the sleeve.

The end portion 120 of the first lever is received in a bifurcated end portion of the second lever.

The sleeve 125 is embraced by a cover which is fixed with respect to the end portion 127 only and in which there is provided a window, through which the pointer 116 can be seen during tightening of the bolt.

As the bolt is tightened, the sleeve 125 is subjected to compressive stress and the separation between the end portions 127 and 128 is reduced. This relative movement of the end portions is transmitted, with magnification, to the pointer 116.

It will be noted that the device of Fig. 2 can be formed by assembling with a known, standard bolt, a sleeve 125 carrying the indicating means.

It will be understood that each of the levers may curve around the axis of the bolt, so that relatively long levers can be confined within a moderate radius. In a case where two levers acting in series are used, the magnification may be by a factor of 350. Such a lever mechanism enables an indication which is clear to the naked eye of relative movements of one or two thousandths of one inch to be obtained.

The indicating means may further comprise a guide for guiding the levers and restraining movement of the levers other than the intended rocking of the levers. The guide may be a metal pressing which provides a fulcrum for each lever and is secured to the face 12, in the example of Fig. 1, and to the end portion 127, in the example of Fig. 2.

The features disclosed in the foregoing description, 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

1. A fastening device comprising respective parts which undergo relative movement when the device is tightened and indicating means for indicating the relative position of said parts, wherein the indicating means comprises an indicating element which is movable relative to said parts, and a mechanism having a velocity ratio less than unity for magnifying relative movement of said parts and for transmitting the magnified movement to the indicating element.

2. A device according to Claim 1 comprising an elongated, hollow member and a pin lying at least partly in the hollow member, said parts being first end portions of the hollow member and of the pin respectively.

3. A device according to Claim 1 wherein said parts are parts of a single member which is subjected to strain, when the fastening device is tightened.

4. A device according to Claim 2 wherein the pin has a head lying outside the hollow member and said mechanism is interposed between the head of the pin and an end face of the hollow member.

5. A device according to Claim 4 wherein said mechanism includes a plurality of levers arranged to act one upon another.

6. A device according to Claim 1 comprising a bolt and a sleeve on the shank of the bolt, said parts which undergo relative move ment being respective parts of the sleeve and said mechanism being carried by the sleeve.

7. A device according to any preceding Claim further comprising a cover which covers said mechanism and which defines a window for the indicating element.

8. A method of using a threaded fastener wherein the relative position of respective parts of the fastener is indicated during tightening by indicating means which magnifies the relative movement of said parts.

9. Any novel feature or novel combination of features disclosed herein or in the accompanying drawing.