Expanded – threaded – driven – headed – tool-deformed – or locked-thr – With means to indicate application of predetermined... – Axially deformable member or portion
Patent
1988-11-15
1990-03-20
Smith, Gary L.
Expanded, threaded, driven, headed, tool-deformed, or locked-thr
With means to indicate application of predetermined...
Axially deformable member or portion
411 14, 73761, F16B 3112
Patent
active
049096850
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION OF INVENTION
The present invention is concerned with screw-threaded fasteners, examples of which include bolts and studs. It is a common requirement for bolts and studs to be tightened to a predetermined load. Various proposals have been made to achieve this. These includes the use of torque wrenches for tightening and the provision, in a fastener, of means for indicating when a predetermined load has been achieved.
Known means provided in threaded fasteners for indicating when a predetermined load has been achieved are responsive to elongation of the fastener.
According to a first aspect of the present invention, there is provided a method of tightening a threaded fastener wherein a predetermined change in a diameter or other transverse dimension of the fastener is indicated or detected. Generally, threaded fasteners are elongated and have circular transverse cross sections. However, the unthreaded part of a bolt may have a transverse cross section other than circular.
The fastener preferably has indicating means so arranged as to be free to move relative to the fastener, when the fastener is subjected to stress of one value, and to be restrained against movement relative to the fastener when the fastener is subjected to a stress of a substantially different value. However, it is also within the scope of the invention for the predetermined change in a diameter of the fastener to affect the range of possible movement of the indicating means relative to the fastener.
The changes in diameter, in particular contraction, of a fastener which occur when the fastener is subjected to tension beyond its elastic limit are more pronounced than are the changes in diameter which occur when the fastener is stressed within its elastic limit. Accordingly, the invention is more readily applied to tightening of a fastener to a degree such that the elastic limit is exceeded.
According to a second aspect of the invention, there is provided a threaded fastener 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 has been attained in the fastener.
The preferred fastener is hollow, the indicating means lying at least partly inside the fastener. However, a fastener with indicating means which overlies a part of a circumferential surface of the fastener is also within the scope of the invention.
According to a third aspect of the invention, there is provided a power tool for tightening a screw-threaded fastener, the tool having control means for controlling operation of the tool and signalling means for co-operating with the indicating means of a fastener according to the second aspect of the invention and with the control means to transmit to the control means a signal indicating that said selected value of stress has been attained in the fastener.
Examples of fasteners embodying the second aspect of the invention, which are used in a method according to the first aspect and an example of a power tool in accordance with the third aspect of the invention will now be described, with reference to the accompanying drawing, wherein:
FIG. 1 shows a cross-section of a bolt in a plane containing a longitudinal axis o the bolt,
FIG. 2 shows a similar view of a stud,
FIG. 3 shows a similar representation of the combination of a further bolt and a power tool for turning the bolt; and
FIG. 4 shows a further bolt partly in diammetral cross-section.
The bolt 10 shown in FIG. 1 comprises a shank 11 having on one end portion thereof a screw-thread 12 and a head 13 at the opposite end of the shank. The threaded end portion of the shank is hollow and defines a cylindrical bore 14 which extends longitudinally of the bolt and, in the example illustrated, is co-axial with the thread 12.
Indicating means 15 is disposed in the bore 14. The indicating means is in the form of a pin having a head 16 which, as shown in FIG. 1, may be received in a recess in the end of the shank 11. The pin 15 includes a cylindrical shank portion 17 which lies r
REFERENCES:
patent: 2316720 (1943-04-01), Ramsey
patent: 3954004 (1976-05-01), Orner
patent: 3969960 (1976-07-01), Pagano
patent: 4294122 (1981-10-01), Couchman
patent: 4338054 (1982-07-01), Dahl
patent: 4525114 (1985-06-01), Hirst
Exotech Limited
Smith Gary L.
Suether Flemming
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