Re: [Phys-l] rust?

[Brian Whatcott <betwys1@sbcglobal.net>]

At 11:44 AM 1/10/2008,  Anthony Lapinski, you wrote:

> I have a old metal garden sprinkler with several parts. I am trying to
> unscrew the base, but it is stuck. Maybe rust or other particles have made
> the screw threads very tight. Does anyone know of a liquid/chemical that
> might dissolve the rust/particles and loosen the opening to free these two
> pieces? I have tried WD-40. Also used vinegar. No luck. I might need a
> stronger acid, but I obviously don't want to dissolve the metal too much!

Let me introduce you to the pantheon of rust remedies.

A first pass could well be an aerosol spray of the nut loosener kind.
" PB Blaster" is one such. It comes in a yellow Aerosol can.

The next escalation is to spray with this liquid daily,
for several days, then try to tighten a joint, before attempting
 to loosen.

Another approach is a concentrated vinegar solution saturated with
table salt. The item to be derusted is immersed. This is an aggressive
 approach, so it needs watching.

There are proprietary liquid formulations which are said to remove
 rust innocuously. I am not completely convinced.

Then, for the most recalcitrant of joints, there is the brutal
oxy-acetylene torch.

A method that is much safer, and universally found effective
on rusty steel,   might be called "reverse anodizing" or
 electrolytic derusting. It is in use by conservators.

A plastic bowl which can immerse the object for treatment is
prepared (ideally) with water containing a table spoon of
washing soda,  or 'sugar soap' (= sodium phosphate etc)
 though baking soda, even lye have also been used,
 at a rate of a tablespoon per  gallon of water.

A battery charger is rigged with the positive lead to a stainless
 or iron electrode, the larger the better in order to surround
the object.

The object to be derusted is connected to the negative lead,
and left for three to twelve hours. The rust is reduced, and
may leave a dark deposit which can be wiped off.
 If the metal is completely oxidized, it will not magically
 return however. The rust free areas are not attacked,
in general, but a shiny steel surface often results.


Brian Whatcott    Altus OK    Eureka!