Expanded – threaded – driven – headed – tool-deformed – or locked-thr – Internally threaded fastener element – e.g. – nut – etc. – Multipart
Patent
1996-08-19
1998-06-30
Wilson, Neill R.
Expanded, threaded, driven, headed, tool-deformed, or locked-thr
Internally threaded fastener element, e.g., nut, etc.
Multipart
411395, 411909, 411916, 411917, 29447, F16B 3500, F16B 3708
Patent
active
057723788
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to a pre-tensioning device for a screw or similar fastening element, which is used particularly to pre-tension large screws during an assembling operation.
BACKGROUND OF THE INVENTION
It is preferred that the pre-tensioning is carried out by stretching the screw using a certain pre-calculated force before a nut is screwed tight. For performing this step, some pre-tensioning tools have been developed, of which for instance hydraulic pre-tensioning devices can be mentioned, one example being described in the Swedish publication 7701049-4, where a screw is stretched by means of hydraulic pressure and thereafter the nut is screwed down. After removing the pressure, the coupling will be tightened and the desired pre-stress will remain in the screw.
In the above-mentioned case, the streching takes place at the end of the screw to be stretched, but often also a piston-like part is placed in a hole bored inside the screw, and hydraulic pressure can be exerted on one end of the piston-like part. Here, the stretching force will be directed by the contribution of the piston directly to the screw ends, between which the pre-tensioning elongation will thus be present.
In German publication DE-OS 3733243 a piston element is used which is placed within a hole bored inside a screw and which can also be heated. In some cases, a steel rod placed within a screw is used, being heatable for instance with electric current, whereby the rod will stretch the screw to be pre-tensioned through the thermal expansion caused by the heat introduced therein. All above-mentioned methods require complicated devices and tools, which often have to be each manufactured for the respective screw size.
U.S. Pat. No. 5,248,233 discloses a releasing device for a screw coupling, employing a phase change of a shape-memory metal cylinder provided with a heating element to release a segmented nut without causing a shock effect on the structure. This patent discloses no pre-tensioning for performing a fastening operation.
U.S. Pat. No. 4,450,616 discloses a shape-memory metal disc utilizing the properties of the shape-memory metal only for ensuring the tightness. of a nut or a screw.
SUMMARY OF THE INVENTION
In the pre-tensioning device according to the present invention, most drawbacks associated with the presently known devices have been eliminated. The device according to the present invention is based on the use of shape-memory metals known as such.
The invention is based on a phase transformation occurring in the crystal structure of the shape-memory metal, effected by temperature. This phenomenon is called martensitic reaction. The shapes and volumes of pieces made of shape-memory metal alloys are recovered exactly to correspond to the original status at a relatively low temperature on heating after a deformation caused by an external force. The recovery is still complete typically after a deformation of 4-8%. The martensitic reaction starts and takes place in a quite narrow transition temperature range of typically about 20.degree. C. (range A.sub.s to A.sub.f), which can usually be fitted in a desired area within the temperature range of -30.degree. . . . +100.degree. C. On certain conditions, the martensitic reaction is crystal-lographically completely reversible. The deformations of shape-memory metals are not based on thermal expansion, but on a phase change in the crystalline structure triggered by a temperature change. The transformation takes place quickly once the transformation temperature has been attained. Because of the low transformation temperature, the heating of the piece does not require large amounts of heat.
The shape-memory metals exist as two main groups, whereof one shows a one-way shape-memory effect and the other a two-way effect. For those shape-memory metals which are based on the one-way shape-memory effect, the deformation triggered by a predetermined transformation temperature is irreversible. In the case of the two-way shape-memory effect, the deformation is revers
REFERENCES:
patent: 2571265 (1951-10-01), Leufven
patent: 3835523 (1974-09-01), Stansfield
patent: 4120230 (1978-10-01), Schutzler
patent: 4450616 (1984-05-01), Morita
patent: 4884934 (1989-12-01), Ikeda et al.
patent: 4897006 (1990-01-01), Blin
patent: 4991563 (1991-02-01), Ashley
patent: 5010949 (1991-04-01), Dehaine
patent: 5248233 (1993-09-01), Webster
patent: 5366331 (1994-11-01), Ergres
Kvaerner Tamturbine OY
Wilson Neill R.
LandOfFree
Pre-tensioning device for fastening elements and method for pre- does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Pre-tensioning device for fastening elements and method for pre-, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Pre-tensioning device for fastening elements and method for pre- will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1852622