I have a host of mild steel parts, ranging from small lathe tools to
large JCB wheels that I would like to de-rust and - for some, - paint.
All the methods I have tried take ages, are not really effective and
leave me thinking that there must be a better way.
I have tried a hand held air blaster and a high pressure water device,
using slag, not to mention a host of angle grinder and drill based wire
and abasive wheels of one sort or another, but I remember a tank I used
to use abroad that contained - was it, phosphoric acid? For parts that
were big enough to go in the tank, it did work fairly well, except for
small springs! However, I would be willing to bet that I should risk
all sorts of official disapproval in this age of universal regulation,
by using this, even if I could find some.
What would be the cheapest and most effective solution, nowadays? Any
comments would be welcome, thanks, George.
A phosphoric acid dip works great for items you'll be painting. It leaves a
black (iron phosphate?) stain on the surface. This is the main active
ingredient in many rust preparations and rusty metal primers. I buy it as
"Lime Away" at my local Fleet Farm.
Many here swear by a solution of vinegar and table salt. Slow, but just
leave it in the bucket. be sure the part is completely immersed, it will
leave a mark at the liquid surface.
If you'd like to strip that rust off FAST, use Muratic acid. Follow quickly
with a water rinse and a dip or spritz of a base solution. I use my purple
degreaser spray bottle. if you don't cancel out that acid quickly, you get
an almost immediate thin film of rust.
There's also an electrolytic method. I don't remember the details.
Electrolysis. No question about it (and very widely and regularly
described - just search).
Electrolysis is effective, but it does take days. OTOH, you can just
leave it running unattended, so that's not a big problem. Very low
Phosphoric acid doesn't remove anything, it converts existing stable
rust into a reasonably good paint primer. Useful, but it's not a
I use muriatic acid quite a bit - it is the fastest rust remover (on the
order of minutes, depending on the severity of rust). The base rinse
isn't necessary if you do a good water rinse. The hotter the better.
The part will rust even if all the acid is rinsed off because it is so
clean - there is no oxide coating. I *immediately* dip in my wax
solution (see Iggy's thread). You can *see* it rust if it isn't protected.
One time I had a badly pitted part that I de-rusted and neutralized with
some sodium base (TSP maybe). I got rust back right away, so I
de-rusted again and it rusted again! I de-rusted a 3rd time without the
base neutralizer and it was OK. I concluded that the acid and base
reaction was making sodium chloride (table salt!) which was "sticking"
in the pits and promoting re-rust.
Wait, wait!! The above is a "line" that I have believed and repeated,
but I just had some second thoughts. If it's the clean-ness of the
derusted part that promotes rust, why don't just-machined surfaces rust
as fast? What could be cleaner that freshly cut steel? So I take it
all back about the "why" and just stick with what I do and that it works:
1. immerse in acid
2. hot water rinse (& scrub off the crud)
3. protect with wax (oil works too)
BTW - "rust removal" is probably in the top 3 FAQ's - there is a ton of
info in the archives.
1. Sandblasting/Bead blasting
Requires a HUGE amount of air (think compressor on trailer)
Free blasting makes a HUGE mess
need eye, ear protection + airline respirator for free blasting
Cabinet blasting takes up a lot of room
Owning a real sandblaster + cabinet is spendy
blasting will remove paint, rust, scale and leave bare metal
blasting is extremely effective, no limit to size of parts (entire ships!)
2. Wire brushing
Buy heavy knotted cup brush and heavy knotted disk brush for heavy rust
Running angle grinders real tough on wrists/hands (think carpal tunnel)
brushes throw wires - eye protection a must
wire brushing quickly knocks off most of rust but tough to get it all
slow to remove some paint/scale
some parts can have rust/scale/paint in areas difficult to brush
relatively low tooling cost, can address many jobs quickly
3. Acid dips
Muriatic acid dangerous to handle, potentially illegal to store (Kalifornia)
some say acid dips -> hydrogen embrittlement
must be followed by neutralizing dip, hot water rinse
disposal of chemicals tricky, can be major issue in urban environment
real hard to do large parts (truck bed?)
4. Electrolytic derusting
Simple, cheap, effective for small parts (can fit in 5 gallon bucket)
Uses garage sale auto battery charger, box of washing soda, some wiring ~ $20
Problem with reaction slowing as anode oxidizes if anode is steel
can use stainless but problem with hexavalent chrome in solution - BAD
can use graphite, high current density will erode anode over time, $$$
have heard of using lead sheet, don't know good/bad yet ???
Lots of incomplete information on Web about procedure
Optimal setting calculation MUST include surface area of part
For higher currents, using DC welder has been reported, should work fine
can be hard to do large parts (truck bed?)
can do spot EDR with carbon rod/cotton batting wetted in solution
Naval jelly - never did much for me, extremely slow/weak
"rust neutralizers" e.g. Jasco Metal Prep
Knorrostol - works really great on small parts, I use it all the time, A+++
Ive been having marvelous luck with electrolysis.
Gunner, not talking about his leg hair....
"I think this is because of your belief in biological Marxism.
As a genetic communist you feel that noticing behavioural
patterns relating to race would cause a conflict with your belief
in biological Marxism." Big Pete, famous Usenet Racist