Metal working – Method of mechanical manufacture – With testing or indicating
Patent
1986-11-06
1988-09-27
Moon, Charlie T.
Metal working
Method of mechanical manufacture
With testing or indicating
29446, 295251, 81 5738, B23Q 1700
Patent
active
047731460
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method and apparatus for tensioning groups of studs. It is particularly applicable to the tensioning of the studs used for securing the covers on nuclear power reactors.
Nuclear power reactors are normally opened up and closed down about once a year for refuelling. The operation is hazardous because of the high levels of gamma radiation in the pit containing the reactor pressure vessel. These radiation levels may be of the order 200 milli-rems per hour. In many countries, the level of radiation to which workers can be subjected is limited by law. In the United Kingdom, for example, the limit is 2 rem per annum. Thus it can be seen that each worker can only operate in the pit of the reactor pressure vessel for about 10 hours per year.
The cost of each man-rem exposure is therefore very high and considerable cost savings could be achieved if the number of man hours taken at the high radiation level during refuelling could be reduced.
900 MW to 1500 MW pressurised water reactors typically have 54 studs of from 6 inch (15 cm) to 71/2 inch (19 cm) diameter securing the cover for the reactor pressure vessel. These studs are usually tensioned and de-tensioned during refuelling using three or four manually-operated single stud tensioners. The tensioning and detensioning operations have to be performed on the 54 studs according to a prescribed pattern in order to avoid damaging the seal between the cover and the reactor vessel. In the hot environment the operation is laborious and time consuming.
According to the present invention in a first aspect there is provided a method of tensioning a group of studs to a predetermined strain, comprising the steps of: strain is outside a predetermined tolerance range; predetermined tolerance range in step by amounts and in directions corresponding to the amount and direction in which the strain deviates from the predetermined value;
According to the present invention in a second aspect there is provided a tensioning device comprising a tension bar adapted to be screwed on a stud, and mounted for rotation in a thrust block, hydraulic means for tensioning the tension bar by way of the thrust block, and support means for transmitting the reaction to a workpiece, characterised in that the tension bar is accommodated in a bore in the support means.
According to the present invention in a third aspect there is provided a tensioning device including stud tensioning means and working nut rotating means in which the working nut rotating means includes a dog clutch ring, the dogs of the dog clutch ring being resiliently mounted.
According to the present invention in a fourth aspect there is provided a method of forming a channel between two surfaces comprising locating two lengths of elastomeric material spaced apart and side by side in grooves across at least one of the surfaces, compressing in a longitudinal direction lengths of elastomeric material in bores communicating with the grooves to cause the lengths of elastomeric material to shorten and expand laterally to form seals between the two surfaces, thus defining the channel between the lengths of elastomeric material in the grooves.
Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings of which:
FIG. 1 shows a vertical section through one of the stud tensioners of a multi-stud tensioner in accordance with the invention;
FIG. 2 shows a fragmentary plan view of the multi-stud tensioner of FIG. 1;
FIG. 3 shows a vertical section on an enlarged scale of the clutch and transducer control of the multi-stud tensioner of FIGS. 1 and 2;
FIG. 4 is a plan view of the clutch and transducer control of FIG. 3;
FIG. 5 is an exploded perspective view of the clutch of the multi-stud tensioner of FIGS. 1 and 2;
FIG. 6 is a perspective view from below of a dog-clutch of the multi-stud tensioner of FIGS. 1 and 3;
FIG. 7 is a cross-section of a detail of the dog clutch of FIG. 5 on the line VII--VII;
FIG. 8 is a diagram of a pneumatic proximity detector;
F
REFERENCES:
patent: 2866370 (1958-12-01), Beach
patent: 4047456 (1977-09-01), Scholz
patent: 4162573 (1979-07-01), Payne
patent: 4179786 (1979-12-01), Eshghy
patent: 4224843 (1980-09-01), Heiermann et al.
patent: 4375123 (1983-03-01), Ney
patent: 4413396 (1983-11-01), Wallace et al.
Moon Charlie T.
Pilgrim Engineering Developments, Ltd.
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