Tension control of fasteners

• US 4,219,921 A
• Filed: 04/19/1979
• Issued: 09/02/1980
• Est. Priority Date: 04/19/1979
• Status: Expired due to Term

• Current Assignee: Rockwell International Corporation
• Original Assignee: Rockwell International Corporation
• Inventors: Eshghy, Siavash
• Primary Examiner(s): Combs, Ervin M.
• Application Number:
  US06/031,361
• Time in Patent Office: 502 Days
• Field of Search: 29/240, 29/407, 73/139, 73/761, 81/52.4 R, 81/52.4 B, 81/52.5, 173/1, 173/12
• US Class Current: 29/407.03
• CPC Class Codes: B23P 19/066 by electrical means
• CPC Class Codes: B25B 23/14 Arrangement of torque limiters or torque indicators in wrenches or screwdrivers couplings for transmitting rotation or clutches F16D; devices for measuring torque per se G01L
• CPC Class Codes: Y10T 29/49767 Determining relative number of threaded member rotations
• CPC Class Codes: Y10T 29/53687 by rotation of work part

Abstract

There is disclosed a technique for tightening threaded fasteners in which values of offset torque, initial tension rate relative to angle, final tension rate relative to angle and other joint related factors are empirically determined by instrumenting a plurality of fasteners of the type ultimately to be tightened. In one embodiment, torque and angle are monitored during tightening. Calculations are conducted, while tightening, to determine the tension prevailing in the bolt at a particular angle of advance. By using the calculated tension value and the particular angle of advance, an instantaneous position of threading advance on the tension-angle curve of the fastener is established. From this instantaneous position, it is determined how much greater angle of advance or how much torque is required to tighten the fasteners to a final desired tension value. The same technique may also be used merely to monitor tightening which is terminated by a different tightening strategy. A number of quality control procedures are conducted to determine if the fastener and the tightening tool are performing normally. In another embodiment, analog devices are utilized to convert sensed values of torque and the rate of threading advance into parameters which control tool shut off.

Claims

1. A method for tightening a joint having a plurality of threaded fasteners, comprising

contemporaneously tightening the fasteners;

measuring the torque applied to the fasteners;

suspending threading movement of the fasteners thereby allowing the joint to relax;

after all of the fasteners have suspended tightening, resuming tightening of the fasteners for a final tightening angle increment measured from a location where the measured torque is at least equal to the torque existing immediately prior to the suspension of threading movement.

2. The method of claim 1 wherein the angle increment is measured from a location where the measured torque is greater than the torque existing immediately prior to the suspension of threading movement.

3. The method of claim 1 wherein the contemporaneous tightening step comprises simultaneously initiating tightening of the fasteners toward an intermediate tightening parameter and the suspending step comprises stopping threading movement of each fastener upon attainment of its intermediate tightening parameter independent of whether other fasteners are tightening.

4. Apparatus for tightening a joint having a plurality of threaded fasteners, comprising

a plurality of powered instructable tools capable of suspending and resuming tightening of the fasteners including means for measuring torque applied to the fasteners;

means for instructing the tools to initiate tightening of the fasteners;

means for separately instructing each tool to suspend tightening of the fastener associated therewith independent of the suspension of tightening of other fasteners; and

means for instructing, upon suspension of tightening of all the fasteners, the tools to resume tightening of the fasteners for a final tightening angle increment measured from a location where the measured torque is at least equal to the torque existing immediately prior to the suspension of threading movement.

5. Apparatus for tightening a threaded fastener, comprising

means for applying torque to the fastener;

means for sensing applied torque at various angles of threading advance;

means for suspending tightening of the fastener;

means for calculating the torque applied to the fastener at an angle location adjacent to where threading advance stops; and

means for resuming tightening of the fastener for a final tightening angle increment measured from a location where the sensed torque is at least equal to the calculated torque.