Standard DTI FAQs
You try your best but it appears too difficult to properly compress the DTI bumps, even though the ironworkers sit on the bolts for 20, 30, or more seconds?
Previous editions of the RCSC specification stated that bolts should be tensioned in about ten seconds or less. It is true that impacting tools will cause the nuts to overheat during prolonged impacting. Overheating the nuts causes them to deform and may lead to stripping, galling, or seizing completely, followed by either the bolt breaking or the wrench breaking. Leaving an impact tool run for more than 20 or 30 seconds is not recommended.
Instead, the cause of the high torque resistance should be discovered and remedied. Remember, DTI's do not change the frictional resistance of the bolt hardware. They act like simple mechanical load cells compressing only as much as the bolt develops tension, and the DTI's therefore react independently from the torque resistance of the bolt and nut.
If you are experiencing the problem above, one or more of the following is occurring:
- your wrench needs more turning power - see recommended wrench capacity and make
- the bolt/nut combination has too high a friction factor* - adding lubrication on the bolt threads and the nut face will help.
- the bolt is too long and the nut has bottomed out on the thread root - get a shorter bolt, or add flat washers.
- the bolt threads are damaged - get a new bolt.
- the nut is too soft and has heated up and deformed during impacting - use 2H or DH nuts.
*Too big a friction factor can be caused by many things, for example:
- The storage conditions for the bolts and nuts have allowed them to deteriorate. Open kegs with water standing in them, bolts lying in the mud, etc. are typical examples. Click here for info on bolt storage
- The nut is dried out and needs lubricating-add some kind of lube on the threads AND on the face of the nut.
- The fit between the nut and the bolt is bad because of zinc thickness or incorrect nut overtapping.
- The flat washer ahead of the nut has been hot dipped zinc coated and is very rough.
- You have mixed rough types of coatings on the galvanized hardware - hot dipped nuts on mechanically galvanized bolts, for instance, are not allowed by ASTM A325.
- Too much time has passed between removing the bolts from their kegs and tightening them.
- The flat washers are hot dipped galvanized and are "dishing" into the bolt hole - see the advisory on this web site.
