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TC Bolts

TC Bolts

TC Bolts

General question - The wrench for tightening TC Bolts...  The socket fits over the nut, and inside the socket is another that fits over the TC spline.  The socket turns one way, but does the TC splice socket turn the other way, or does it remain stationarY?

RE: TC Bolts

It is accepted practice that all bolts be snugged up by hand before tightening with an electric gun.  In such a case the nut only turns (until the splined tip breaks off), however if this procedure is not followed and the bolt/nut is loosly installed, the bolt will also turn (in the opposite direction of the nut) untill the nut comes up snug. By not snugging the nuts up  first, a great deal of time is wasted and some of the bolts in the pattern may not be up  to torque.  A good inspector  will not allow this practice, and a good  engineer should require  pre tightening of bolt patterns before torquing.


RE: TC Bolts

I agree with EVELROD and also wanted to make the point that good inspectors and good bolt-up ironworkers make use of the proper sequence for tightening - Bolt patterns should be tightened from the inside out.

RE: TC Bolts

Your Question answered. (An extract from Tension Control Bolts Ltd literature.  Shropshire SY13 1LJ UK.)

The outer socket will rotate and tighten the nut untill the the bolt reaches the required tension. When the proper bolt tension is reached the outer socket will stop rotating and the inner socket will rotate in the oposite direction and shear the spline off.



RE: TC Bolts

Well Stuart_L,  we must clarify your extract from the TC literature to the point---the outer hex-head socket will turn to tighten the nut until the proper torque (tension) is achieved and at that point the inner splined socket will shear of the tip and rotate.  During the tightening process the inner splined shaft does not rotate normally but applies an opposite torque to the bolt, thereby holding it static (as I mentioned above, the bolt will not normally turn if it has been properly snugged up beforehand) When torque has been achieved and the splined tip has twisted off, the outer socket will stop and if power is kept on the gun, only the inner socket will rotate (to no effect).
I have used these fasteners in sizes ranging from 3/4 inch to 1 3/4 inch and the effort required to use the gun to tighten any of them was about the same (time to torque varies), very smooth, quiet and, efficient given proper preparation of the bolt patterns being tightened.  The only real short-comeing with these bolts is the fact that all bolted pieces must be fairly open to allow access to the electric gun(some of which may have a socket that can be swiveled through 45 deg. or so, but there were no extensions or universal joints available at the time I retired).  The primary reason for using this system is noise abatement and, to some degree to assure proper torque control( even though there are several cheaper alternatives available).


RE: TC Bolts

You guys are good.  Thanks for the info.  Sorry the original question didn't have an engineering application.  It was just for my own personal education.  Thanks again.

RE: TC Bolts

You are all partially correct. The tension control installation tool works like an axle differential in a car. If one wheel is on ice and the other is on pavement, the one on the ice will spin. The tool will turn whichever element (bolt or nut) has less friction. In very general terms this will always be the nut due to the fact that the nut is lubricated, has a smaller bearing area and is placed on a hardened washer (usually lightly oiled). The friction between the nut and washer is significantly less than the friction between the bolt bearing area and the structural steel. This causes the nut to rotate clockwise.

When the torque required to rotate the nuts exceeds the shear capacity of the groove at the end of the bolt, the tool will, in effect, twist the sline counter clockwise until it shears. In a properly designed bolt this happens without the bolt spinning.

RE: TC Bolts

I cannot disagree with you as you either wrote the factory handout or are reading directly from it.  Point of fact---the inner splined drive will ALWAYS turn unless the bolt is restrained by pre snugging with a wrench or by holding the head (some TC bolts have rivet heads and some have hex heads) or by preventing it turning by some other means. Often both will turn simaltaniously.  All the TC bolts that I used were lubed with a wax concoction (that was not always true, some had NO lube)and were installed in the field in all types of weather, not a shop or controlled installation. When a torque wrench is applied to a TC bolt to check for correct torque (just because the tip twists off the correct tension is NOT always garanteed) the torque setting is somewhat lower than a conventional bolt(example-3/4 in. TC will click off at approxamitly 320 to 330 lbs/ft. whereas a conventional grade 5 will do 355 to 375 approx. with a normal Skidmore setup on the impact)  We liked the TC bolts for many reasons already stated, but some of the fasteners faults include the necessity to pre tension each bolt,  the lack of a universal type socket( a 45 degree was available),no pneumatic tool only electric, the wax lube degrading on bolts that had been in storage too long, damage to the  splined tip, even a very small flaw ment the bolt could not be used and, the tips created hazards on the jobsite if they were not religiously picked up (they also hurt when dropped from high rise type structures).  Hopefully some of these problems have been corrected in the years since I retired.  I have installed or supervised the installation of TC bolts by the tens of thousands and can say that ,by and large, it is a very good system.  Quality control in the manufacture of the bolts was acceptable and failures were rare when proper care on installation was observed.  If you read some of the other threads pertaining to TC bolts you will see  some of the other real world things that the system can or cannot handle.

The original question was "---does the TC splice socket turn the other way, or does it remain stationary?"  To this my answer is directed.


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