Does
this all sound too complicated? Well,
take it from a person who has a bead blast cabinet and a pressure pot abrasive
blaster, electrolytic de-rusting is faster, cheaper, and easier than abrasive
blasting. I’ve had my electrolytic vat
in almost continuous operation for the past seven years. Rather than stand at the bead blasting
cabinet for days on end, my de-rusting operation keeps going while I sleep and
go on vacation.
Passivation
If
you don’t immediately prime and paint, the passivation process is something you
should do after abrasive blasting, anyhow.
So, it’s not any more work to do it as suggested, here.
If
you don’t passivate, you’ll notice some red rust forming soon after you are
done. This is what happens: Some of the rust was converted back to pure
iron, but it is in the form of very fine particles. This fine iron “dust” will almost immediately
re-rust. The passivation process removes
the last traces of rust and prevents re-rusting.
Some
people suggest using phosphoric acid for passivation. Take my word for it, if you use phosphoric
acid, you’ll eventually wind up with more rust than you started with. Been there.
Done that. Use the phosphoric
acid mixed with “salts” that is intended for the job. It doesn’t cost any more than straight
phosphoric acid; and, it is more readily found in stores.
Passivation
compounds
As
mentioned, earlier, most paint departments sell compounds made of a blend of
phosphoric acid and certain metal salts.
Sometimes they are called “metal etch” compounds. They are all very similar, but some seem to
work better than others. I prefer the
“Jasco” Metal Prep brand, however, the only place I’ve found it is in a Seattle
Home Depot. Local Home Depot stores
don’t carry it.
“Ospho”
is readily available in these parts, but in my experience it tends to remain
“sticky” instead of drying completely. Ospho
directions say that it can be used as a primer, but I have reservations about
painting on top of a sticky surface.
To
avoid the sticky surface, I apply Ospho sparingly. If the part is cast-iron I immediately wipe
off the excess with a blue paper shop towel.
If it’s steel, I’ll either blow off the excess with shop air; or, wait
five minutes and wipe off the excess.
Use eye protection and wear coveralls if you blow it off.
Another
way of preventing a too-thick layer of these passivators is to apply them, let
them “work” for a few minutes, then rinse off.
Then, immediately blow-dry with shop air.
I
have tried diluting these passivation products, but have gotten unsightly
results. The end result will be a layer
of white powder. The directions instruct
the user to brush off the excess white powder; however, I don’t have confidence
about paint sticking to it very well.
Stubborn rust
If
your rusty piece is stubborn about coming clean, finish up with either
hydrochloric acid (muriatic acid, available at your plumbing shop or hardware
store), phosphoric acid, Rust Solv, or you can abrasive blast it.
If
you use hydrochloric acid, your part will look nice for a few days, but will
soon show signs of rapid rusting all over, again. You can prevent this by following up the acid
cleaning with another day of electrolysis treatment. The electrolysis will help remove all traces
of the troublesome chlorides.
Be careful
with hydrochloric (muriatic) acid! Follow all precautions given in the introduction. As mentioned in the previous paragraph,
follow the acid cleaning with another electrolysis session. Then, passivate the part with Ospho, or the
like. If you don’t repeat the electrolysis
after using acid, you’ll wind up with rust that is worse than before. [Have you ever seen the rust caused by salt
(sodium chloride) or tractor tire fluid (calcium chloride)? Well, any remaining traces of hydrochloric
acid (hydrogen chloride) will do the same thing.]
If
you use hydrochloric (muriatic) acid, store your supply outdoors. Even in a closed container, it can rust
everything in your shop! Been
there. Done that. I keep my jug in a five gallon bucket,
outdoors.
Even
if you have to abrasive blast, you’ll find that by electrolytic de-rusting
beforehand, the time you spend abrasive blasting will be a tiny fraction of
what it usually takes. Furthermore, your
grit will stay cleaner, longer, because most of the rust was removed
beforehand. Without all the rust dust,
visibility will be much improved in your bead blasting cabinet.
More about
“waste” electrodes
Some
people will suggest using stainless steel for waste electrodes. They claim that the stainless will not be
affected. Not so. Been
there. Done that. I have proof.
It started out as a medium-gauge piece of solid material and is now a
paper-thin sheet of stainless steel that looks like a lace curtain.
You
will find that stainless steel waste electrodes will last much longer than
ordinary mild steel. However, be
prepared to deal with a poisonous waste, afterward. You’ll
eventually notice that your solution will turn yellow and the stainless steel
is disappearing. The yellow is caused by
the presence of chromate. Hexavalent
chromium is poisonous. Please don’t ruin
your property by dumping it on the ground.
Please don’t dump it down the drain.
I
am a “householder” and not a business; however, I am careful of how I dispose
of my chromate-bearing wastes. I
evaporate the solution in the summer sun until is completely dry. Then, I take the dried rust/chromate sludge
and deliver it to one of the special collections of hazardous waste. Your local landfill or state environmental
quality office will tell you the time and place.
A
much better waste electrode is graphite.
The last time I was there, Pacific Recycling at
But,
steel works very well, except that it makes for a very messy, rusty
solution. If you have to leave your part
in the vat for a long time, you’ll find that rust particles will settle out on
it, making a mess that you’ll have to brush off.
The electrolyte
As
mentioned, earlier, the purpose of the “stuff” dissolved in the water is to
make a solution that conducts electricity.
Don’t worry about recipes for your electrolyte. It’s not like baking a cake, the ingredients
are not critical.
Whatever
you use for mixing your electrolyte, it never “wears out,” but contaminants may
eventually make it unusable. For the
most part, all you need to do is replenish the water as it evaporates and is
converted to hydrogen gas. But, if the
solution gets loaded with dirt, your part may be disappointingly dirty after
electrolysis. At that point you may want
to dispose of it and mix fresh. My
electrolyte generally lasts a year, or more.
You
should cover your vat with a loose-fitting screen to keep out insects, leaves,
and pets. Do not cover tightly! You don’t want to accumulate an explosive
volume of hydrogen gas!
There’s
at least one recipe out there that calls for a heavy dose of washing soda. It would be prohibitively expensive to follow
it if mixing up a 55-gallon batch. I
find that one 3½ pound box of washing soda and an 18-ounce container of Red
Devil lye is plenty for a 55-gallon batch.
This
is a fairly “weak” solution, but with it I can easily pull maximum current on
my battery chargers if I use a foot-square waste electrode.
In
our dry climate, strong solutions are a pain.
You’ll have to deal with a white crust at the waterline of your vat and
workpiece (if it isn’t fully submerged).
Here
is one such recipe for a strong solution of one gallon:
Washing soda 10-oz.
Lye 1.7-oz.
Tri-sodium-phosphate (TSP) 3.3-oz.
Water glass (sodium silicate) 1.7-oz.
Multiply
it out and you’ll find it would require almost ten boxes of washing soda for a
55-gallon batch!
That
said, however, the strong solution may make a more effective de-ruster. Under the white crust at the waterline where
the “strength” of solution is strongest, I usually find clean, bare metal.
Difficult jobs
With a gas tank there will be
these problems:
·
Getting a big
enough “waste” electrode inside it. A
steel rod will work, but the process will take longer because it won’t have
much surface area.
·
Keeping the waste
electrode from shorting out to the tank.
I use pieces of rubber hose, wraps of rubber bands, plastic window
screen, coffee can plastic lids, wood, etc. for this. Just remember that solid barriers, such as a
plastic lid, may prevent the current from reaching the area underneath. That’s why plastic window screen works well.
·
Preventing the
accumulation of explosive hydrogen gas.
This is easy. Just make sure the
tank is completely full of solution.
·
Getting rid of
the cruddy residue. A good shaking with
the tank partially filled with water and crushed gravel does a good job.
One
job I had was to clean the rust off a cylinder wall. I poked a collar of plastic in the spark plug
hole, then poked a steel rod through that.
Then, I took a plastic lid the same size as the bore, punched a hole in
it, and slid it over the rod inside the cylinder. All these precautions keep the waste
electrode from shorting out to your workpiece.
Most battery chargers have some kind of circuit breaker to protect them,
but there’s no use of risking fire or burning up your charger. Be careful
Unsticking engines?
For
this technique to work, an electrical current must be able to “reach” the
rusted area. But, in the wee, tiny gap
between a piston and cylinder, it is unlikely to happen. Even if this area could be “wetted” with the
solution, the surrounding area will “soak up” the current and create a shield
that pretty well prevents large currents from getting down into the gap.
I’ve
found many engines to be stuck from varnish and dried out carbon. It forms such a strong barrier to the
solution that it is unlikely that electrolysis will work. That said, however, if all else fails to unstick
your engine, it’s worth a try. However, be sure to dry out the engine after
pulling it from the vat. You don’t want
to create further rusting or corrosion by leaving water in the cracks and
crevices.
Daisy-chaining
You
can clean many parts at once. The only
thing you have to make sure of is that they are all connected together,
electrically. I usually string them on a
length of bare copper wire. The copper
won’t be affected.
There’s
no problem if one doesn’t connect up, electrically. There will be no harm done. Just file off some rust, make a good
connection, and give it another day in the vat.
Lifting paint
All
but the best of paint jobs will lift off in big sheets. It will amaze you. Remember, you will probably find leaded paint
on antique machinery. If you are a
business, you’ll have to dispose of it as hazardous waste.
If
you are a homeowner, common sense applies.
Do the right thing.
Brushing off the black crud
Ordinary
wire brushes work well, but they can’t get into nooks and crannies. For this, use the small wire brushes with a
looped handle and are shaped like paint brushes. They are found at most welding supply places.
After
wire-brushing, you may want to follow up with a rubdown with a Scotchbrite pad,
followed by a rinse with water. Then,
blow dry with shop air.
Plastic barrels
The
deposit on plastic 55-gallon drums is about $25.00 so this is what most oil
distributors charge for them. D&B
Farm and Home Supply in
As
mentioned, earlier, you’ll be able to de-rust bigger items if you cut a
foot-wide slot in the side. The plastic
is flexible, so you can temporarily spread this slot to get much larger things
into the vat. I’ve de-rusted entire
engines.
Really big stuff
If
you put large items, such as buzz saw blades or flywheels, into your vat, you
can de-rust one side, brush off the crud, then put the other half and de-rust
it. There is a “however,” though. You might wind up with a visible line at the
high water mark. It’s merely a cosmetic
thing and shouldn’t show after painting.
Leftover chemicals
Any
unused acids or passivators can be stored in plastic cottage cheese or sour
cream containers. They come with a tight
fitting lid. So, you shouldn’t ever have
excess acid to dispose of. Whatever you
do, don’t dump it on the ground or throw it down the drain. Use it until it is gone.
If
you must dispose of acid, neutralize it with ordinary lime. Then, you can safely dispose of it in the
garbage.
It’s
a good idea to have lime on hand to neutralize any spills. Acid will cause serious etching of concrete,
so keep it off your floors, driveways, or sidewalks.
My favorite setup
I
cut a twelve inch wide slot the length of a plastic 55-gallon drum and laid it
in a wooden cradle. I added one box of
washing soda and a can of lye.
At
each end of the drum I’ve fastened a large waste electrode. For small jobs, I connect both to one battery
charger. For big jobs that would
overload one charger, I’ll connect one charger’s positive lead (red alligator
clip) to each waste electrode. Of
course, you should connect all negative leads (black) to the part to be
de-rusted.
What can go wrong
So,
you set up your de-rusting operation and everything seems to be going just fine: The battery charger’s ammeter shows a good,
healthy current, tiny bubbles are fizzing up from the part you’re
de-rusting. Everything looks great!
But,
a day later you take a look and there’s no current, no bubbles, and your part
is just as rusty as it ever was. What’s
wrong?
Nine
times out of ten you’ll find that you’ve got a bad electrical connection,
somewhere. If any connections to your
waste electrode got down into the solution, it’s almost certain that corrosion
stopped the flow of electricity. Just
file or sand off the gunk, make a good connection, and things will be just
fine, again.
Most
battery charger alligator clips have a rather cheesy crimped connection between
the wire and the clip. Eventually, there
will be some corrosion there and the electrical resistance will increase. When this happens, the connection will
overheat, sometimes to the point where the insulation will melt. Keep a close watch on this connection. If it starts going bad, use an awl to spread
the crimp and disconnect the wire from the clip. Use sandpaper to clean things up and
re-crimp. You may want to solder this
connection like it should have been in the first place.
You
might also want to check your waste electrode.
If you used a flattened tin can like I did the first time, it will
probably be gone! Yup, with great care I
cut both ends out of a 3-pound coffee can, figuring I had a great waste
electrode. In a day it was gone!
How long can you leave something in the
vat?
You’ll
read later on about a post drill that was left in the vat for three weeks. But, if your solution is really rusty, you
won’t want to leave your things cooking too long. The rust will settle out on top of the thing
you’re trying to de-rust. It will look
worse than when it went into the vat.
Actually, the rust won’t be fastened to your part; but, it can be a
nuisance. Sometimes, it doesn’t want to
wire-brush off.
What
you’ll want to do is remove the stain with hydrochloric (muriatic) acid. It will come off rather easily.
But,
the best thing is to not forget and leave your part in the vat too long. It won’t be damaged; it will just be a bit
harder to clean up.
Limitations
Electrolytic
de-rusting isn’t the end-all, do-all. It
has its place. There will be times when
you can’t use it. It sometimes won’t
touch the “skin” on some castings. Quite
often this is a mix of sand and gunk.
Pieces that have been badly scorched in a fire can also have a skin that
won’t come off. Don’t worry about
it. If it’s stuck that tightly, you can
probably paint right over it.
That
said, however, this process usually works very well on cast iron. It works less well on some steels. Why, I don’t know. Very often it won’t get down into rust
pits.
You’ll
hear some folks say that the process is “line of sight.” That is, only the side of the part that faces
the waste electrode will be de-rusted.
To a certain extent, this is true (more on that, later). But, you can say with 100-percent certainty
that it cannot “reach” into “shielded” places such as gas tank interiors.
Gas
tanks, carburetor bowls, and other enclosed castings present a challenge, but
they can be electrolytically
cleaned. Just wrap the waste electrode
with plastic window screen (to prevent it from shorting out), and put it into
the gas tank or whatever. Window screen,
rubber bands, wooden sticks, scraps of plastic milk jug—you name it—will come
in handy for these jobs. Just use them,
as necessary, to prevent the waste electrode from accidentally shorting out to
the workpiece.
“Line-of-sight rust” removal?
Many
electrolysis instructions will tell you that the process is
“line-of-sight.” That is, rust will only
be removed from the side of your part that faces the waste electrode.
When
I first started using this process I noticed the line-of-sight thing. In the years since, when I use
electro-de-rusting, all sides of the part come clean. The only exceptions are shielded pockets or
nooks and crannies.
I
wondered why my experience was different from others; and, I wondered why I
experienced line-of-sight then, but not now.
I think I’ve discovered the answer.
When
I first experimented with electro-de-rusting my container was a one gallon ice
cream bucket. Then, I moved up to a five
gallon bucket. Finally, I settled on
using a fifty-five gallon barrel.
Aha! That’s it!
The large barrel allows a large “field” of voltage to surround your
entire part. Thus, all sides of your
part get de-rusted all together.
Contrast
this to using a small container. There
is not enough space around your part to allow a large field of voltage to
develop.
I
can demonstrate this “voltage field” effect, easily, by moving the waste
electrode from the side to the middle of the vat. By allowing a large space around the waste
electrode, the back side of it became “electrically involved” in establishing a
connection to the solution. The same
effect occurs at the part being de-rusted.
Some success stories
Post drill #1. Found in a
junkyard. It had been in a fire and was
a total wreck. Hopeless. Every nut, bolt, and set screw was seized up,
solidly. So, I paid 15¢ a pound for it
and dropped it into my vat while I went on a three week vacation.
When
I got back every fastener came off without a struggle. Except for the flywheel which suffered some scaling,
every part cleaned up and looked as if it just came from the foundry.
Post drill #2. Found in an
antique store. As well as being rusty,
it had a half-century of hardened grease and crud one it. The whole works went into the vat for a few
days.
Every
speck of grease and loose paint floated to the top of the vat. This one cleaned up without dismantling. I only had to blow out all shafts and
bushings with air in order to dry them out and prevent re-rusting.
Feed grinder. The burrs,
shaft, and all fasteners were seized up, solidly. Into the vat it went.
Everything
came unstuck. No harm was done to the
babbit bearings. It cleaned up,
beautifully. Try doing that with a sand
blaster!
Copyright © 1998-2008, Orrin B. Iseminger
Revised -- 12/23/08