A Primer on Rust
by: Bob Neidorff
I Hate Rust
When I lived in Arizona, my tools never rusted. Arizona is hot and dry.
Here in New England, rust is a significant problem. It is especially bad
for people who have shops in their cellars. Cellars tend to be damper than
heated rooms or garages, and dampness leads to rust.
What Is Rust?
Many materials react with oxygen to form a chemical compound that
is a combination of that material and oxygen. When iron combines with
oxygen, it forms iron oxide, or rust. Iron oxide is a larger molecule than
iron, so if iron oxidizes, it often puffs up and may even flake. This is
because the rust requires more physical space than the original iron.
Some things cause steel or iron to rust faster than others. Water will
cause iron and steel to rust. Dissimilar metals rust faster than single
metals because of electrochemical reactions, so steel rusts faster than
iron, and joints between dissimilar metals rust very quickly. Salt water
will cause rust faster than water because salt water is a better
electrical conductor. Like most chemical reactions, heat also speeds rust.
If steel starts to rust, it will puff up because iron oxide is a larger
molecule than iron. The puffing causes cracks and voids, which expose more
bare metal to the environment. So the rusting of iron can progress and is
only limited by destruction of all solid iron. Other metals oxidize, but
the oxides of some other metals are no larger than the metal themselves,
so they don't puff up or flake. For example, aluminum doesn't puff up when
it oxidizes. This helps make aluminum oxide a good protective coating,
rather than the start of rapid degeneration.
Rust is really Fe2O3, a reddish form of iron oxide. Iron has another
oxide, Fe3O2, which is sometimes called black oxide or black rust. Black
oxide is a good protection for steel. Like aluminum oxide, black oxide
molecules are the same size as iron molecules, so black oxide does not
grow or flake. Black oxide is true gun bluing and the oxide found on some
drill bits.
You can coat steel with black oxide by a careful regimen of rusting the
right amount and boiling the rusted metal in water to convert it. This is
how non-caustic gun bluing is done, and although it is tedious, it
produces very attractive and durable results after several treatments.
Is Rust Alive?
Many people say that rust lives and that you have to kill rust to
stop metal from continuing to rust. The real significance is that once
rust is formed, there is mobile oxygen in the metal, and the oxygen can
move deeper into the metal causing further rust. Techniques to kill rust
are described below. All rely on dissolving rust or converting rust into
black oxide and then coating the metal with something that inhibits the
formation of more rust.
Preventing Rust on Tools
You can discourage rust a number of ways. For my woodworking tools,
like my table saw and jointer tops, I use Automobile Paste Wax. I put it
on fairly heavily and often. It seems to work well. There are also cream
waxes, but these contain some water, so I stick with paste.
Another excellent product for protecting woodworking machinery is
Bostik Top Cote. This is a product specifically engineered for protecting
the surfaces of woodworking machinery and lubricating the working surfaces
to reduce wood-to-metal friction. As this was developed for contact with
wood, it has no additives which might interfere with wood finishing.
For machine tools, Way Lube is the right thing. Keep unpainted parts of
your lathe and mill covered with Way Lube. It's really inexpensive, often
less than $12 per gallon.
For small tools, cutting bits, and stock, it is more complex. You
really don't want to dunk a center punch in Way Lube or wax it, because
you don't want it to be slippery. You also want the best possible
protection up front, because it won't be renewed.
There are many commercial products that claim to displace moisture and
prevent rust. Some common ones are WD-40, Starrett M1, LPS-1, and LPS-3.
All come in aerosol cans, which is convenient although expensive and bad
for our environment. All leave a film of light oily stuff on the metal.
Other products are Sprayon Corrosion Supressant, Rustlick 631, CRC SP-350,
CRC SP-400, Boeshield T9, Birchwood Casey Sheath, and Rust-X. Some of
these products are petroleum based, while others seem to be wax based.
However, they all prevent rust by keeping air and water off of the metal
surface.
Not surprisingly, each product is claimed to do everything well and to
surpass every competitor. Some claim that one works better than the
others, but the real differences between these products are more related
to their uses. For example, some leave a heavier, tougher coating than
others. Some leave an easy-to-remove coating. Some are better in the
presence of salt spray. But any of them will keep rust at bay as long as
the work is well coated.
In general, I hear very good things from people about Boeshield T9 and
I get poor feedback about WD-40. Perhaps this is because WD-40 is meant to
do everything, while Boeshield T9 is specifically engineered as a
treatment for long-term storage of materials. One common complaint about
WD-40 is that it gums up mechanisms.
You can make your own rust protection coating by mixing 1 part
Anhydrous Lanolin with 5 parts Paint Thinner. Just brush it on or dip the
metal in it. You can get Anhydrous Lanolin from a pharmacy by special
order. Dillon Case Lube is a commercial rust protection made from Lanolin
and Alcohol. Many people have reported excellent results with Lanolin and
Lanolin-based rust protection products. Contrary to popular belief,
Lanolin is not perfectly safe even though it is natural. Some people have
allergic reactions to it. In addition, it can clog pores and cause
infections.
Another great technique for preventing rust is to protect the metal
with a coating of zinc. This coating process is often called galvanizing.
(Named after Luigi Galvani. Luigi Galvani is best known for experiments
making dead frog muscles contract with electrical impulses.) Zinc is more
electrochemically reactive than iron. Zinc prevents rust by oxidizing
itself instead of iron. Many of today's cars are made with galvanized
steel panels. These panels won't rust until after the paint is damaged and
the zinc corrodes through to the underlying steel. You can buy Crown 7007
Cold Galvanizing Spray and other zinc based primers in aerosol cans.
Still another technique for preventing rust is to surround the metal
with fumes from a material that discourages rust, such as Camphor
(C10H16O) or Moth Balls. Some Moth Balls are naphthalene (C10H8) while
others are paradichlorobenzene. Gun suppliers sell protective wrapping
material and blocks which prevent rust by a similar technique. For
example, Brownell's sells VPI Paper and Rust Blocks Vapor Tabs. Another
good product is Permatex In-Charge Corrosion Inhibitor, a moisture
absorber which also releases rust-protecting vapor.
Just storing your tools in a tight wooden box will discourage rust.
Wood acts as a fairly good barrier to humidity and absorbs what remains.
One person stored tools in side-by-side tool cases, one a Gerstner Wooden
Case, the other a Kennedy Metal Case. After years of storage, the tools in
the metal case showed surface rust while the tools in the wooden case were
clean.
Dust can be a good magnet for moisture, so if you can keep dust off of
your tools, you will discourage rust. A breathable canvas tarpaulin or
fitted tool cover is effective. However, avoid a cover that goes all of
the way to the floor. This will trap moisture and encourage condensation
on your tool. Instead, just cover the tool down to the bench or chip pan.
Another great way to prevent rust is to put a dehumidifier in your
shop. If your shop is a closed room or cellar, then a dehumidifier will be
very effective. A dehumidifier will not be helpful in a drafty garage, but
a garage may not be as humid as a cellar, either.
Removing Rust
When iron or steel starts to rust, it will puff up and expose clean
metal to the open air, allowing rust to continue to the depths of the
metal. If your favorite possession is already rusting and you want to
clean it or at least stop the rusting, you have a few alternatives.
There are a few products on the market which fall into the category of
organic rust converters. These products contain acid to convert rust to
black oxide and polymers which bond to rust. Instructions say to remove
all loose rust, paint on the product, and let it dry. I've used one of
these products and it did work. However, the resulting surface is black
and rough. Also, the converted rust is not durable, so this may not be the
right treatment for tools or stock. Some trade names for these products
are: POR-15, Glean Tech Rust Killer, and RustX.
Another rust treatment is to remove loose rust and coat the metal with
a product like WD-40. This fills pores and rust with a noncorrosive
substance and prevents additional rusting. Often, this is sufficient to
slow the progress of rust and leave the tool protected for future storage.
There are also techniques which remove rust. The most crude is sand
blasting or bead blasting. This is standard practice in auto body repair
shops. Sand blast will remove some good metal and will work-harden the
surface, so glass bead blasting is used for more delicate parts.
Immediately after any blasting, metal is clean and exposed, so it is
essential that some form of rust proofing goes next. In auto body work,
this is often an acid metal wash (see below) followed by self etching
primer, but could also be a coating of a product like Boeshield T9.
Sand paper and steel wool will also remove rust, but they don't get
into tiny crevices. Rubber abrasive sanding blocks like those made by
Cratex are good at removing a thin coat of rust and can also remove rust
from minute pores in the metal.
Another technique for removing rust is etching with Phosphoric Acid.
Phosphoric Acid has a unique property of dissolving iron oxide quickly
while etching iron very slowly. This means that you can leave metal in
Phosphoric Acid for much longer than necessary with very little damage.
The acid will attack bare metal slowly and will start the process of
hydrogen embrittlement, so use the minimum etch time that removes all
rust.
Another unique advantage of Phosphoric Acid is that it leaves a fine
coating of iron phosphate behind. Iron phosphate prevents rust. However,
the iron phosphate coating is not very thick and not durable. Some
additional protection is still required.
Phosphoric Acid etch will leave a hard, bright metal finish. This is
because it will etch the surface slightly, exposing new, bare metal. Often
this is desirable. It leaves an attractive surface and a surface ready to
paint. A common product which contains Phosphoric Acid is Naval Jelly. The
soft drink Coca-Cola contains Phosphoric Acid, so Coke will etch rust. But
Coke also contains carbonic acid and other nasty things. You're going to
drink that stuff?
Auto body shops treat metal with acid metal wash, a solution of
Phosphoric Acid and alcohol before painting. This removes waxes and oils,
removes slight amounts of rust that form between sand blasting and
painting, and leaves a thin protective coat of iron phosphate. One
commercial solution for this is DuPont Quick-Prep. Sherwin Williams has a
similar product called Metal Prep.
Other acids will etch rust, but not as selectively. Hydrochloric acid
can etch rust very quickly. Oxalic acid has also been used. However, if
you leave metal in these acids a bit too long, you will lose a significant
amount of metal. Also, neither acid leaves a protective film behind.
I read of using a solution of 1 part black molasses and 9 parts water
to remove rust. Perhaps this works because the molasses is slightly
acidic. The procedure is very slow. After treatment, metal starts rusting
quickly, so this is probably not a phosphoric acid treatment.
All acids contribute some hydrogen to the metal structure. This weakens
steel by a process called hydrogen embrittlement. If the metal is a
cutting tool or gun barrel, for example, this weakening can be dangerous.
One person claimed that if you bake the metal at 400F for an hour after
acid cleaning, then you can drive out the hydrogen and prevent this
embrittlement. With all acids, use rubber gloves and splash goggles, no
matter how weak the solution. When thinning acid, add acid to water. Never
add water to acid.
One more technique for removing rust is Electrolytic Rust Removal. Rust
can be electrically etched off of iron or steel in a bath of mild alkali,
such as Sodium Carbonate. Connect the rusty part to the negative terminal
of a 12V battery or battery charger and a scrap piece of steel or iron to
the positive terminal. Use one tablespoon of Sodium Carbonate per gallon
of water. This technique has many advantages. First, the alkaline solution
is much safer than some of the acids mentioned earlier. It is still a
chemical, so rubber gloves and splash goggles are recommended. Another
advantage of electrolytic rust removal is that it will have no effect on
good metal, so you can leave the work in the bath for a long time and not
damage the metal. There is no risk of hydrogen embrittlement nor of
etching unrusted metal.
Electrolytic rust removal will leave a black oxide surface, which is
the result of a process that doesn't remove any good metal at all. The
only thing removed is loose rust and embedded oxygen. If your goal is to
keep as much of the original metal behind, this is the best technique.
However, be prepared to immediately follow this technique with one of the
rust prevention procedures, such as using Boeshield T9 or VPI Paper wrap.
Guy Lautard mentioned Knorrostol in one of his popular bedside readers.
He recommended it for precision tools. This is a mildly abrasive rust
removing polish that can remove light surface rust on smooth metal
surfaces quickly. It comes as a paste in a tube.
There's another rust removal technique used for restoring chrome on old
cars and motorcycles. Rub the area vigorously with the end of an aluminum
bar. This will scrape the iron oxide off and at the same time the aluminum
dust formed will penetrate and react with the rust to form aluminum oxide
and iron. I haven't tried this myself.
Beware of Mr. Rust
Some people have a reputation for rusting everything that they
hold. These people have unique body oil. I don't know if it contains metal
salts, high moisture content, or low pH. If you have guests in your shop,
be careful about letting them handle good steel or tools. You might be the
first to discover that Uncle Bert is one of those guys with a corrosive
touch.
If you have this unique body oil, consider wearing cotton gloves oiled
with something like Breakfree CLP to keep your body oils off of tools.
Breakfree CLP is a multipurpose teflon oil designed to clean, lubricate,
and protect metal. Another approach is to wash your hands and give them a
light rub with mineral oil before handling metal.
Sources of Supply
Anhydrous Lanolin - Many pharmacists, on special order
Automobile Paste Wax - Any auto supply store Birchwood Casey
Sheath - Brownells (see below)
Black Molasses - Many grocery stores
Boeshield T9 - McMaster-Carr, Woodworkers Warehouse
Bostik Top Cote - Specialty wood tool suppliers such as
Woodworkers Warehouse
Breakfree CLP - Many gun supply shops including: Brownells
Camphor - Many large drug stores. Available as blocks and as Oil
of Camphor.
Crown 7007 Cold Galvanizing Compound - Wholesale Tool
Cratex Rubber Abrasive - Many tool dealers (MSC, Travers Tool,
Wholesale Tool)
CRC SP-350 - MSC
CRC SP-400 - MSC
Dillon Case Lube - Many gun stores. For a local dealer call
Dillon Precision at 800-762-3845.
Dupont Quick-Prep - Auto paint supply stores which sell Dupont
paint
Gerstner Tool Boxes - Many tool dealers (MSC, Travers Tool,
Wholesale Tool)
Glean Tech Rust Killer - Bomar
Knorrostol - Many tool dealers (Hammar Industrial, Kennametal,
MSC). For a local dealer, call SPI at 888-774-8200.
Moth Balls - Many hardware and drug stores.
Naval Jelly - Most hardware stores.
Permatex In-Charge Corrosion Inhibitor - Travers Tool or other
Permatex distributors.
POR-15 - RestoMotive Laboratories
Rust-X - Integrity Industries
Sherwin Williams Metal Prep - Auto paint supply stores which
sell Sherwin Williams paint.
Sodium Carbonate - Swimming pool supply stores. Ask for product
to raise water pH.
Starrett M1 - Many tool dealers (MSC, Travers, Wholesale Tool)
LPS-1 and LPS-3 - Many tool dealers (MSC, Travers, Wholesale
Tool)
Rust Blocks Vapor Tabs - Brownells
VPI Treated Paper - Brownells
Way Lube - Many tool dealers (MSC, Travers, Wholesale Tool)
WD-40 - Any department store or hardware store
Addresses
Bomar Corporation (sells
Glean Tech Rust Killer)
PO Box 80555; Baton Rouge, LA 70898
Phone: 888-264-2626
E-Mail: CyberDesn@Aol.Com
Brownells, Inc.
(gunsmithing tools and accessories dealer)
200 South Front Street; Montezuma, IA 50171
Phone: 515-623-5401
E-Mail: brownelusa@Aol.Com
Hammar Industrial Supply (local broad-range supplier)
175 Amherst St; Nashua NH 03060
Phone: 800-388-3232
Integrity Industries (makers of
Rust-X)
PO Box 5342; Kingsville TX 78383
Phone: 512-595-5561
Kennametal (sells Knorrostol)
1600 Technology Way; Latrobe, PA 15650
Phone: 800-446-7738
E-Mail: dbaldwin@kennametal.com
McMaster-Carr Supply (national
broad-range supplier)
PO Box 440; New Brunswick, NJ 08903-0440
Phone: 908-329-3200
MSC Industrial Supply
(national tool supplier)
151 Sunnyside Blvd; Plainview NY 11803-9915
Phone: 800-645-7270
E-Mail: Prod_Info@MSCDirect.Com http://www.mscindustrial.com
RestoMotive Laboratories (makers of
POR-15)
PO Box 1235; Morristown NJ 07962-1235
Phone: 800-457-6715
E-Mail: techsupport@por15.com
Travers Tool (national tool
supplier)
128-15 26th Ave; PO Box 541550; Flushing NY 11354-0108
Phone: 800-221-0270
E-Mail: Info@Travers.Com
Wholesale Tool
(national tool supplier)
12155 Stephens Dr.; PO Box 68; Warren MI 48089
Phone: 800-521-3420
E-Mail: WTMich@Aol.Com
Woodworkers Warehouse/Trendlines
(sells Bostik Top Coat)
Many Woodworkers Warehouse retail stores
Also by mail at:
Trendlines
135 American Legion Highway; Revere MA 02151
Phone: 800-767-9999
Useful Internet Web References
Auto Paint
FAQ
Electrolytic Rust Removal
FAQ
Metalworking FAQ
Model Engineer Support
Metal Web News
Credits and Disclaimer
I have taken much of the above from others, including:
- Robert Bastow
- Pete Bellas
- Kevin Eva
- Jim Hardman
- Chris Heapy
- Scot Heath
- Russ Kepler
- Ted Kinsey
- Dean Lake
- Randolph Lee
- Harry Phinney
- Keith Taylor
- Doug White
Thank you for teaching me. Forgive me if I omitted someone.
I tried to check information and test many of the above techniques and
materials. However, I have not tried every technique or product listed
here. Some may be better than others. I am not affiliated with any company
represented here.
Please use proper safety precautions when dealing with all chemicals,
machines, and other dangerous procedures.
I welcome comments, suggestions, and corrections.
Email: Bob Neidorff
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Rev: 06/30/98 |