Expanded – threaded – driven – headed – tool-deformed – or locked-thr – With means to indicate application of predetermined... – Including gauge means
Patent
1992-04-16
1993-07-13
Wilson, Neill R.
Expanded, threaded, driven, headed, tool-deformed, or locked-thr
With means to indicate application of predetermined...
Including gauge means
411916, 73761, 116212, 116DIG34, F16B 3102, G01L 500
Patent
active
052267652
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to load-indicating fasteners.
The invention relates in particular to fasteners, such as bolts or studs, which in use are subject to tensile loading. It is often important to ensure that the fastener is tightened to a predetermined loading. It is known to use the stretching of the fastener which occurs under tensile loading to give an indication when the appropriate loading has been reached.
2. Description of Related Art
European patent EP 0 049 537B describes a load indicating fastener having a shank with an axially extending bore which receives a gauge pin anchored at its inner end to the shank and protruding outwards beyond an end face of the fastener, with an indicating member rotatable on the protruding part of the gauge pin and arranged so that the indicating member is free to rotate when the fastener is unstressed but when the fastener is subject to a predetermined tensile loading is held against rotation by contact with the end face of the fastener.
The gauge pin and indicator member are usually set with an initial gap between the indicator member and the end face of the fastener such that the gap is closed when the fastener is subjected to the predetermined loading and the end face bears against the indicator member sufficiently to prevent its being rotated by hand.
A difficulty which can arise in use of the fastener described in EP 0 049 537B is that to ensure that the fastener is not over-tightened, the operator has to check the indicator member at frequent intervals during tightening. This problem is particularly acute when the fastener is tightened using a power tool. Moreover, after the fastener has been tightened, there is nothing to indicate whether the fastener has been over-stressed.
SUMMARY OF THE INVENTION
It is an object of this invention to provide a load indicating fastener which avoids this problem.
The present invention consists in a load indicating fastener comprising a body having a shank which is subject to tensile loading in use, the body having a bore which extends axially from an end face of the body into the shank and which receives a gauge pin anchored at its inner end to the shank and protruding outwards beyond the end face of the body, an indicating member rotatable on the protruding portion of the gauge pin and arranged so that the indicating member is free to rotate when the shank of the fastener is unstressed but when the shank is subject to a predetermined tensile loading is held against rotation by contact with the end face of the body, characterised in that the gauge pin has an axially extending bore, and the fastener further comprises a second gauge pin which is received within the bore in the first gauge pin and is anchored at its inner end and protrudes outwards beyond the outer end of the first gauge pin, and a second indicating member which is rotatable on the protruding part of the second gauge pin, the second indicating member being free to rotate when the shank of the fastener is unstressed or subject to the first predetermined loading, but being held against rotation by contact with another part of the fastener when the shank is subject to a second predetermined tensile loading greater than the first predetermined loading.
The second gauge pin and indicator member can be set so that the second indicator member is held against movement when the tensile loading reaches a maximum desired value. Thus, in use, if the second indicator member cannot be rotated, the operator will know the fastener has been overtightened. Moreover, the state of the fastener can subsequently be easily checked, by simply checking both indicator members. If the fastener is at the correct tension, the first indicating member will be held against rotation whilst the second will rotate freely. If neither member can rotate, this will indicate that the fastener has been overtightened. If both indicator members rotate freely this will indicate that the fastener requires retightening.
In one form of the invention,
REFERENCES:
patent: 4636120 (1987-01-01), Brandsberg et al.
patent: 4927305 (1990-05-01), Peterson, Jr.
RotaBolt Limited
Wilson Neill R.
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