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Re: Bolt Tightening - Turn of the nut method

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I would reconsider the last statement in this reply   "A similar situation prevails in case of two sets  of flanges of same material but of different thickness. For the same T.O N the bolt tension will be higher
in the case of thicker flanges"
.
 
Actually since the T.O.N. method imposes a fixed change in length to the bolt, occuring over the grip length, it follows that the shorter the grip length the greater the bolt tension.  As a result, the governing specification indicates that greater nut rotation is required to achieve the specified minimum bolt tension as the grip length increases.
 
Mark D. Anderson PE
----- Original Message -----
Sent: Monday, October 08, 2001 7:35 PM
Subject: Re: Bolt Tightening - Turn of the nut method

 

Christopher Wright wrote:

> If the "Turn of Nut" method is adopted for monitoring the bolt tension is it
> not right to say that the turn indicates the compression of the flanges
rather than
> tension in the bolt ?
Do a free body diagram of the unloaded bolt. The internal tension in the
bolt is balanced by equal and opposite forces an the bolt head and nut.
These forces are in turn carried into the flanges and reacted by equal
and opposite external forces on the flange which produce internal flange
compression equal to the external forces. The flange compression
therefore equals the bolt tension.

Christopher Wright P.E.    |"They couldn't hit an elephant from
chrisw(--nospam--at)skypoint.com        | this distance"   (last words of Gen.


Chris,
Thanks.
The forces are definitely in equilibrium , no doubt.
What I have in mind is a little different.
Suppose we consider two sets of flanges one made of steel
and the second one  made of aluminum. For the same amount of turn of  nut
the bolt tension will be higher in the first set flanges. The compression in the flanges
will be equal to bolt tension in both the cases.

A similar situation prevails in case of two sets  of flanges of same material but of
different thickness. For the same T.O N the bolt tension will be higher
in the case of thicker flanges.
Your views please.
Regards  ..  raghavan