From: REMOVE_THISdwilkins@means.net (Don Wilkins)
Newsgroups: rec.crafts.metalworking
Subject: Re: Tell me about vapor degreasers...
Date: Tue, 07 Jul 1998 17:00:56 GMT

On Tue, 07 Jul 1998 00:30:12 GMT, joe@restoresource.com (Joe Way)
wrote:

>How do these work? Would it be practical/economical to build one? or
>does anyone have one for sale (cheap)?


There are a number of designs but one rather simple way is a rather
deep tank containing the degreasing solvent. The bottom is heated to
boil the liquid but the tank is deep enough so that (theoretically)
the vapor condenses before it reaches the top. Most have an auxiliary
exhaust system to remove the stuff that doesn't behave
"theoretically".

Now when you suspend the piece to be degreased into the vapor the
solvent condenses on the piece and the resultant liquid runs off the
piece and back to the liquid in the tank, hopefully taking the crud
with it. Once the piece reaches the temperature of the vapor phase the
amount of condensate is minimal. In fact when you pull the piece out
it probably will be dry.

This method has the advantage over just dipping the piece into hot
cleaning solvent in that the condensed liquid on the piece should be
substantially pure solvent where as the liquid in the tank contains
all the junk stripped off from prior material.

There can be some problems with these degreasers for the unwary. Some
of those chlorinated solvents have a nasty habit of polymerizing and a
product of that polymerization is hydrogen chloride (anhydrous
hydrochloric acid). Initially the solvent increases in acidity and it
is important to monitor the acidity of these solvents. In addition the
reaction is catalyzed by certain acid salts such as iron or aluminum
chloride.

Now if you clean some iron or aluminum parts e.g. and introduce some
metal (turnings e.g.) into the liquid you have a potential serious
problem if you haven't monitored the acidity. When the reaction gets
going it sort of goes critical and you have a runaway reaction which
can rapidly fill the room with solvent vapor and gaseous hydrogen
chloride.

Unfortunately one of our facilities had this happen on a weekend and I
was sent to assess the damage. They made electric clocks motors. The
vaporized perchloroethylene had degreased everything in the building
and the HCl then had a clean metal surface to work on. Everything was
rusted and I mean everything. The machinists had those nice wooden
cases for their tools and the HCl gas had diffused into every drawer.
The lathes which were originally green were blue and every exposed
metal part was rusted. All of the typewriters (before PCs) in the
offices were trashed along with the entire inventory of clock parts. I
could go on but you get the picture.

They are great to use though. You just suspend the piece then raise it
up and then pull it out clean and dry. Just don't neglect the
maintenance.