Expanded – threaded – driven – headed – tool-deformed – or locked-thr – Tensioned along the longitudinal axis by a coaxial force...
Patent
1999-02-24
2000-06-20
Saether, Flemming
Expanded, threaded, driven, headed, tool-deformed, or locked-thr
Tensioned along the longitudinal axis by a coaxial force...
411 14, 73761, F01B 2500
Patent
active
060770082
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to preloaded bolts and more particularly to hydraulically preloaded bolts subjected to high preloads, and more specifically it provides a safety device for such preloaded bolts.
For locking different elements to each other it is well known to use bolt and nut joints. It furthermore is well known to stretch such bolts axially before the nuts are tightened, whereby the bolt joint will have internal stresses preventing the nut from being untightened during operation.
Bolt joints of this kind are used, for example, as casing bolts for securing the casing of steam and gas turbines to the pressure vessel. Such applications require large preloads and the bolt joints will be subjected to very high tensile stresses particularly during the mounting and preloading operations, and this means that there always is a risk that the bolts during mounting and preloading will develop crack formation, which in some cases also may result in bolt rupture.
Breaking tests may show that the heavy nut and bolt fractions, which part from the rest of the bolt, at such a breakage will be thrown several tens of meters up in the air for a vertically positioned bolt. This of course presents a large and serious risk for damages to material and injuries to personnel.
The purpose of the present invention is to provide a safety device for such preloaded bolt joints, by which the risk for such damages and injuries is substantially reduced, and for accomplishing this the safety device according to the invention has been given the features defined in the accompanying claim 1.
Hereinafter the invention will be further described with reference to a non-limiting embodiment illustrated in the accompanying drawing.
FIG. 1 shows in a longitudinal cross section a bolt joint provided with a safety device according to the invention.
FIGS. 2-4 are enlarged detail views from FIG. 1.
FIG. 1 shows in a longitudinal cross section a fraction of a first element 1, e.g. a pressure vessel wall, and in which is provided a threaded blind hole 2, wherein is screwed in the threaded free end of a bolt 3. The shank 4 of the bolt 3 extends with clearance through a through-bore 5 in a second element 6, e.g. a casing for the pressure vessel.
A thrust washer 7 is arranged in an annular recess 8 in the second element 6 encircling the through-bore 5 thereof. This thrust washer 7 serves as a support for a nut 9 which is tightened on the threaded end of the bolt 3 projecting from the second element 6 and the thrust washer 7. In the free end of the bolt 3 there is provided a threaded tapering centric recess 10, in which is screwed in a threaded tapering portion 11 of a connecting piece 12 having at its opposite end a cylindrical threaded portion 13 and forming part of a hydraulic device intended for stretching the bolt 3 for creating therein a desired preload. Between the unthreaded part 12 and the threaded part 13 of the connecting piece is provided an adaptor 12a. This device incorporates a distance collar 14 arranged to enclose the nut 9 while resting with its lower end surface against the thrust washer 7. This distance collar 14 has a slotted opening 15 for allowing a tool 16 to reach the nut 9 for tightening it during assembly. The hydraulic device further incorporates two substantially annular members 17, 18 forming a hydraulic cylinder in which is arranged a hydraulic piston 19, rigidly connected to the threaded end portion 13 of the connecting piece 12, and also the earlier mentioned adaptor 12a, rigidly connected to the end portion 13 and serving as a second hydraulic piston. A connector 20 is provided in the piston 19 and connected to a duct 21 for supply of hydraulic pressure fluid to the space between piston 19 and the hydraulic cylinder 18, whereas another connector 20a is provided in the wall of the annular member 17 for supply of hydraulic pressure fluid to the space between the adaptor 12a and the member 17. Both connectors are preferably fed with pressure fluid of the same pressure simultaneously. Another connector 22 is connected
REFERENCES:
patent: 2316720 (1943-04-01), Ramsey
patent: 2562831 (1951-07-01), Stone
patent: 2995033 (1961-08-01), Stifano
patent: 3844533 (1974-10-01), Markiewicz et al.
patent: 4185504 (1980-01-01), Exner
patent: 4927305 (1990-05-01), Peterson
Ovaka Couplings AB
Saether Flemming
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