Method for controlling clamping load of a threaded fastener

Claim 1

A method of effecting close control of the clamping force exerted against a workpiece by a threaded fastener in which inner and outer nuts having adjacent and radially displaced workpiece engaging surfaces are threaded onto a bolt at positions spaced axially of the bolt with the inner nut relievably driven from the outer nut though a prevailing torque driving connection therebetween so that the inner nut follows tightening movements of the outer nut to maintain contact with the workpiece, and wherein the outer nut has a section rupturable in shear in a direction axial to the nut when substantially a predetermined bolt tension is developed by said tightening of the outer nut against the workpiece, said method comprising, the steps of tightening the outer nut with the inner nut following the tightening movement of the outer nut as a result of said prevailing torque connection until said section of the outer nut ruptures in shear to relieve the clamping force exerted against the workpiece by the outer nut and thereby causes the transfer of a large proportion of the last-mentioned clamping force to said inner nut, and then turning the inner nut through a predetermined angular increment of movement relative to the bolt in a direction to increase the clamping force exerted thereby against the workpiece by a predetermined amount commensurate with the relaxation of the clamping force against the workpiece.

Claim 2

A method of effecting close control of the clamping force exerted against a workpiece by a threaded fastener in which inner and outer nuts having adjacent and radially displaced workpiece engaging surfaces are threaded onto a bolt at positions spaced axially of the bolt with the inner nut relievably driven from the outer nut though a prevailing torque driving connection therebetween so that the inner nut follows tightening movements of the outer nut to maintain contact with the workpiece, and wherein the outer nut has a section rupturable in shear in a direction axial to the nut when substantially a predetermined bolt tension is developed by said tightening of the outer nut against the workpiece, said method comprising, the steps of tightening the outer nut with the inner nut following the tightening movement of the outer nut as a result of said prevailing torque connection until said section of the outer nut ruptures in shear to relieve the clamping force exerted against the workpiece by the outer nut and thereby causes the transfer of a large proportion of the last-mentioned clamping force to said inner nut, and then turning the inner nut through a predetermined angular increment of movement relative to the bolt in a direction to increase the clamping force exerted thereby against the workpiece by a predetermined amount commensurate with the relaxation of the clamping force against the workpiece.

Claim 5

A method of effecting control of the clamping force exerted against a workpiece by a threaded fastener which embodies one threaded fastener element having a portion engaging one surface of a workpiece and a pair of coacting threaded fastener elements which are each threadedly engaged with said one fastener element and are constructed and arranged with a prevailing torque connection therebetween and have portions which simultaneously engage a surface of the workpiece opposed to said one, which method comprises the steps of tightening said pair of fastener elements relative to said one fastener element and against the workpiece by the application of torque to one of the pair while the second of the pair of fastener elements is tightened by virtue of said prevailing torque connection between the fastener elements of the pair, sensing a preselected value of clamping force exerted between the workpiece and said one of the pair of fastener elements, effecting release of the force exerted against the workpiece by said one of the pair of fastener elements without changing the tightened position of the second of the pair of fastener elements relative to said one threaded fastener element when said preselected value of clamping force is reached by said one of the pair of fastener elements to transfer the clamping force exerted on the workpiece to the second of the pair of fastener elements with accompanying force relaxation resulting from said transfer, and then tightening said second of the pair of fastener elements by rotation through a predetermined angle of movement relative to said one fastener element to reestablish the value of clamping force exerted against the workpiece to approximately said sensed value.

Claim 6

A method of effecting control of the clamping force exerted against a workpiece by a threaded fastener which embodies one threaded fastener element having a portion engaging one surface of a workpiece and a pair of coacting threaded fastener elements which are each threadedly engaged with said one fastener element and are constructed and arranged with a prevailing torque connection therebetween and have portions which simultaneously engage a surface of the workpiece opposed to said one, which method comprises the steps of tightening said pair of fastener elements relative to said one fastener element and against the workpiece by the application of torque to one of the pair while the second of the pair of fastener elements is tightened by virtue of said prevailing torque connection between the fastener elements of the pair, sensing a preselected value of clamping force exerted between the workpiece and said one of the pair of fastener elements, effecting release of the force exerted against the workpiece by said one of the pair of fastener elements without changing the tightened position of the second of the pair of fastener elements relative to said one threaded fastener element when said preselected value of clamping force is reached by said one of the pair of fastener elements to transfer the clamping force exerted on the workpiece to the second of the pair of fastener elements with accompanying force relaxation resulting from said transfer, and then tightening said second of the pair of fastener elements by rotation through a predetermined angle of movement relative to said one fastener element to reestablish the value of clamping force exerted against the workpiece to approximately said sensed value.

Claim 12

A method of establishing, in a threaded bolt-type fastener, a bolt tension commensurate with the safe load limit of the bolt and fastener by utilizing therewith a pair of concentric nuts having a prevailing torque connection therebetween, as well as adjacent radially separated workpiece engaging surfaces and bolt engaging threads spaced axially of the bolt, which method comprises the steps of turning the outer nut in a tightening direction while the inner nut follows to maintain contact with the workpiece as a result of the prevailing torque connection between the nuts of the pair, tightening the outer nut until a predetermined value of bolt tension measured axially of the bolt in terms of clamping force between the outer nut and workpiece is reached, releasing the clamping force of the outer nut without changing the position of the inner nut in contact with the workpiece to transfer the clamping force to the inner nut with attendant force relaxation, and then tightening the inner nut by turning it through a predetermined angular increment relative to the bolt to reestablish the bolt tension at approximately said predetermined value.

Claim 13

A method of establishing, in a threaded bolt-type fastener, a bolt tension commensurate with the safe load limit of the bolt and fastener by utilizing therewith a pair of concentric nuts having a prevailing torque connection therebetween, as well as adjacent radially separated workpiece engaging surfaces and bolt engaging threads spaced axially of the bolt, which method comprises the steps of turning the outer nut in a tightening direction while the inner nut follows to maintain contact with the workpiece as a result of the prevailing torque connection between the nuts of the pair, tightening the outer nut until a predetermined value of bolt tension measured axially of the bolt in terms of clamping force between the outer nut and workpiece is reached, releasing the clamping force of the outer nut without changing the position of the inner nut in contact with the workpiece to transfer the clamping force to the inner nut with attendant force relaxation, and then tightening the inner nut by turning it through a predetermined angular increment relative to the bolt to reestablish the bolt tension at approximately said predetermined value.

Claim 16

A method of effecting close control of the clamping force exerted against a workpiece by a threaded fastener which initially embodies a pair of adjacent threaded fastener elements in adjacent relationship acting against one surface of the workpiece and both coacting with a third threaded fastener element which has opposed engagement with the workpiece, which method comprises the steps of tightening one of the pair of fastener elements relative to the third fastener element and against the workpiece until a predetermined sensed value of clamping force between said one fastener element and the workpiece is reached, turning the other of the pair of fastener elements to bring it into contact with the workpiece while said one of fastener elements is tightened to said predetermined sensed value of clamping force, releasing the clamping force of said one of the fastener elements without changing the position of said other fastener element to transfer the workpiece clamping load to said other fastener element with accompanying relaxation of the clamping force magnitude, and then tightening said other fastener element of the pair against the workpiece by turning through a predetermined angular increment relative to the third fastener element, which angular increment is a function of the compression characteristic of said other fastener element and said predetermined sensed value of clamping force.

Claim 17

A method of effecting close control of the clamping force exerted against a workpiece by a threaded fastener which initially embodies a pair of adjacent threaded fastener elements in adjacent relationship acting against one surface of the workpiece and both coacting with a third threaded fastener element which has opposed engagement with the workpiece, which method comprises the steps of tightening one of the pair of fastener elements relative to the third fastener element and against the workpiece until a predetermined sensed value of clamping force between said one fastener element and the workpiece is reached, turning the other of the pair of fastener elements to bring it into contact with the workpiece while said one of fastener elements is tightened to said predetermined sensed value of clamping force, releasing the clamping force of said one of the fastener elements without changing the position of said other fastener element to transfer the workpiece clamping load to said other fastener element with accompanying relaxation of the clamping force magnitude, and then tightening said other fastener element of the pair against the workpiece by turning through a predetermined angular increment relative to the third fastener element, which angular increment is a function of the compression characteristic of said other fastener element and said predetermined sensed value of clamping force.