Re: Torque-to-Yield Meaning

["Brant M. Miller" <brant@xxxxxxxxxxxxxx>]

David -

Torque-to-yield is a way of tightening bolts that does not depend upon
achieving precise torque values to ensure that the parts being clamped by=

the bolts are held adequately tight.

A typical torque-to-yield procedure might be: (1) torque bolts (or the nu=
ts
on them, depending) to 20 lb-ft, (2) turn bolts an additional 90 deg. =

Basically, step 1 just gets the bolts snug to provide a known starting
point for Step 2.  Step 2 loads the bolts beyond their yield point - the
stress level at which they begin to stretch.  Since the clamping force wi=
ll
remain constant while the bolts are in their elastic yield range, it is n=
ot
necessary to be too precise re the additional rotation in Step 2.  It onl=
y
needs to be enough to get the bolts into yield and not so much as to brea=
k
them.

Automatic assembly systems often use torque-to-yield.  In a statistical
quality control environment, the probabililty of achieving correct
tightness is greater.

When rebuilding by hand, there is some question as to whether or not
torque-to-yield bolts should be replaced with torque-to-tight bolts.

Above is probably clear as mud.

Cheers

Brant

Date: Mon, 9 Nov 1998 10:17:38 -0800 =