Re(2): [MV] Kroil?
Gordon.W.I. McMillan (gwim2@student.open.ac.uk)
Tue, 31 Aug 1999 08:00:11 +0100
Well rust is iron oxide, basically a mixture of iron and water that swells
up and packs any available volume. As I understand it the heat just
drives off the water and the powdered iron that remains has a much lower
volume, so you have some room again. You would think that the bolt and
nut would expand the same amount too, as you are heating them to the same
temperature, but in fact as most bolts are rolled or forged along their
length the expand slightly more longitudinally (boring stuff about grain
size and direction edited out ) whereas the nuts tend to expand radially.
They are different metal grades too, with the nuts typically slightly
harder to avoid another problem known as galling.
As I live in an area where all UNC and UNF stuff is non-standard I try to
salvage every fitting that I can. A typical spring shackle removal would
involve me roasting the nuts and exposed thread ends, spraying with
penetrant while hot, then a wire brush, and then run a die up the exposed
thread till it hits the nut face. How many times have you had a nut turn
off a couple of threads and then lock? and by that time it is too late to
do anything about it.
Gordon
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