Expanded – threaded – driven – headed – tool-deformed – or locked-thr – With means to indicate application of predetermined... – Including gauge means
Patent
1995-01-09
1996-12-17
Wilson, Neill R.
Expanded, threaded, driven, headed, tool-deformed, or locked-thr
With means to indicate application of predetermined...
Including gauge means
411916, 73761, 116DIG34, F16B 3102, G01L 500
Patent
active
055846270
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention relates to a load indicating fastener which is adapted to indicate loads to which it is subjected in use.
It is desirable that applied fasteners should be properly tightened to designed load levels in order to ensure that secure joints are achieved by the use of the fasteners. Torque wrenches are commonly used for tightening fasteners such as bolts to pre-determined loads. They measure applied effort and are subject to friction so that the fastener loads they produce may not be as accurate as they might be. Fasteners have been proposed which indicate when desired loads have been applied to items but such fasteners have tended to be expensive and/or complicated to install.
One form of load indicating fastener is known from French Patent No. 1,477,006 in which a graduated wire or strip is fixed at one end in an internal bore of a stud. Elongation of the stud under tensile stress is measurable against the fixed scale of the strip to provide an indication of applied load. In this arrangement it is difficult to accurately read the small elongation against the scale.
Another form of fastener is disclosed in UK Patent Application GB 2,212,284 in which a stem fixed at one end to the shank of a bolt carries an electrical contact at its other end. Extension of the shank under an applied load draws the electrical contact towards an axially facing surface of the bolt. The variation in capacitance between the electrical contact and the surface may be used to provide an indication of the bolts extension and, hence, the applied load. Alternatively, completion of an electrical circuit between the electrical contact and the surface may indicate that a predetermined load has been applied. This system has been found to be complicated and expensive to implement with the required degree of accuracy. In addition, it does not provide a visual indication of applied load.
SUMMARY OF THE INVENTION
The present invention aims to provide a load indicating fastener which indicates applied loads effectively and may be manufactured at reasonable cost.
According to the present invention a load indicating fastener is provided which comprises a body having an abutment which is moved by the changing length of the body under an applied load, and load sensing means comprising an element disposed in the direction in which a load is applied to the body when the fastener is in use characterised in that the element is of elongated U-shape, a first limb of the U providing an anchorage part which is rigidly anchored to the body, the closed end of the U providing a bearing part which bears on the abutment so as to move with the abutment relative to the anchorage part in response to a load applied to the body, and a second limb of the U having an indicator at its outer end which responds to movement of the bearing part and registers the applied load related to that movement on a scale.
The fastener may be in the form of a bolt or a stud, but it may possibly take other forms. In the form of a bolt the body of the fastener comprises a head and shank which may be of substantially standard form. Similarly in the form of a stud the body comprises a shank which may be of substantially standard form. In either case the load sensing means responds to change in the length of the shank under applied loads. Conveniently the scale is at the bolt head or end of the stud shank where it can be seen readily when the fastener is in use.
The load sensing means responds to changes in the length of the body as the fastener is being secured and when the fastener has been secured for use. Thus as the fastener is being secured the applied loads will be registered on the scale which will indicate when a required working load has been applied. When the fastener has been secured any change in the load at which it was set for use will be indicated at the scale.
Actual load figures may be indicated on the scale; loads in terms of fractions or percentages of a maximum load that should be applied may be represented, or just one requir
REFERENCES:
patent: 2995033 (1961-08-01), Stifano, Jr.
patent: 3060731 (1962-10-01), Adise
patent: 5102273 (1992-04-01), Stanage
patent: 5222849 (1993-06-01), Walton
Ceney Stanley
Hirst John A. B.
Ceney Stanley
Wilson Neill R.
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