Using Phosphoric Acid

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After much googling and reading, I've decided that I'm going to use a solution of 85% phosphoric acid mixed 1:1 or 1:2 with water on the 3x3 tubing I'm using for a new welding bench...it's reclaimed structural steel that's been out in the weather, pretty rusty, inside and out.Took a wire wheel to it, basically did nothing but polish it to a nice brown...hence my plan to use the acid to convert the rust.   My question is the vessel used....I was just going to build a long narrow box, line it with heavy plastic and dunk away, as the longest piece is 68" long...I've also read you can just cover large pieces with paper towels dampened in the solution and cover with plastic so it doesn't evaporate prematurely....finally, read a thread on here about using a length of 6" sewer pipe capped at both ends and rolling it around...any thoughts?thanks,Steve
Reply:Would an old bath tub work?If you don't want to stand behind our Troops, feel free to stand in front of them.
Reply:Sanding belt.You don't give us a pix but I assume this is all some type of pipe whatever long.One way is take a belt sander fairly coarse grade of belt (like 24 or 36 but maybe at least 40 grit) and flip it on its back, roll or rotate the pipe over the belt. Actually goes pretty quick, gives a good clean result, can finish with whatever grade needed. I prefer the belt sander down and me rolling the pipe on it if that is what is to be cleaned.Got an old heavy steel U beam that I have been using to cut up for various things. Same basic problem, lots of corrosion, rust, old thick paint. Belt sander blows thru it without much trouble. Nice and shinny in the end. I start with 24 grit good industrial grade belt. Makes short work of it. Good grade of belt lasts a long time.If you want to do it inside, put in gravel / sand mix plug both ends and shake / roll it by some means.
Reply:Number 1) 85% is way stronger than needed. What is the right amount is an endless debate but 85% isn't needed to get the job done. Fine if you want to buy that amount but it'll work okay down to around 14%. Some say 4% but that's way too much work for me. The guys that go 4% also spend hours baby setting and re-wetting the stuff to get resultsNumber 2) Unless it is way way cheaper using off the shelf phosphoric etchers, many of the metal preps and prep 'n primes already have some additives in there to aid not only in the wetting out but in staying wetter longer. Maybe a guy could buy smaller amounts of each and mix them?Most of those metal preps and prep 'n primes can be cut fairly thin for working directly with rust. One thing about treating with phosphoric is that while it needs to be wet to work, it also needs air to work. Putting something in a bath isn't necessarily the best for results. I've soaked pieces for a week and noticed no addtional benefits beyond what you get when you pull it out of the bath and the drying/conversion process begins.You need it to be wet long enough to penetrate the deepest rust plus allow time for conversion but it really needs exposure to some air. The thinner the concentration below the longer it needs to be wet naturally. That'e where the additives help. They keep it wetter longer while allowing for the conversion. Don't be spilling any on your concrete floor.Last edited by Sandy; 11-14-2011 at 11:27 PM."The things that will destroy America are prosperity at any price, peace at any price, safety first instead of duty first, the love of soft living and the get rich quick theory of life." -Theodore Roosevelt
Reply:Ive found no better way to remove rust than with a spooge tank. Its fast, almost free. takes very little elbow greese  I use any kind of wooden frame or plastic pipe or old tank that I can find. I lay a peice of plastic in it to hold the liquid bath. I arange a few pieces of rebar in it to hook up to the positive end of a battery. Then I hang what ever I want to derust in the tank by a wire or to grounde to the negative end of the battery.  Then You start the magic.  Fill a bucket with hot water and dump in a 1/2 cup of clothes washing soap , any kind will do, powdered is best. pour in tank. be careful . You dont want the positive rods to touch the negative part. Keep ading the water soap mix till the part is covered. Hook a battery charger up to the battery to keep it charged and go play with something.  The rust will electricaly be removed in short order. but the rebar will get a thick coat on it and it will have to be rinced off from time to time.   Almost any mixture will work.   Mac
Reply:Originally Posted by Tool MakerIve found no better way to remove rust than with a spooge tank. Its fast, almost free. takes very little elbow greese  I use any kind of wooden frame or plastic pipe or old tank that I can find. I lay a peice of plastic in it to hold the liquid bath. I arange a few pieces of rebar in it to hook up to the positive end of a battery. Then I hang what ever I want to derust in the tank by a wire or to grounde to the negative end of the battery.  Then You start the magic.  Fill a bucket with hot water and dump in a 1/2 cup of clothes washing soap , any kind will do, powdered is best. pour in tank. be careful . You dont want the positive rods to touch the negative part. Keep ading the water soap mix till the part is covered. Hook a battery charger up to the battery to keep it charged and go play with something.  The rust will electricaly be removed in short order. but the rebar will get a thick coat on it and it will have to be rinced off from time to time.   Almost any mixture will work.   Mac
Reply:Electrolysis worked well for me.http://weldingweb.com/vbb/showthread.php...t=electrolysisIf you don't want to stand behind our Troops, feel free to stand in front of them.
Reply:Why not just grind where you need to weld, spray it with some rusty metal primer, & paint?That seems like an awful lot of work.Buy American, or don't whine when you end up on the bread line.
Reply:Originally Posted by WeldingMachineWhy not just grind where you need to weld, spray it with some rusty metal primer, & paint?That seems like an awful lot of work.
Reply:Originally Posted by CosmicRamblerSanding belt.You don't give us a pix but I assume this is all some type of pipe whatever long.One way is take a belt sander fairly coarse grade of belt (like 24 or 36 but maybe at least 40 grit) and flip it on its back, roll or rotate the pipe over the belt. Actually goes pretty quick, gives a good clean result, can finish with whatever grade needed. I prefer the belt sander down and me rolling the pipe on it if that is what is to be cleaned.Got an old heavy steel U beam that I have been using to cut up for various things. Same basic problem, lots of corrosion, rust, old thick paint. Belt sander blows thru it without much trouble. Nice and shinny in the end. I start with 24 grit good industrial grade belt. Makes short work of it. Good grade of belt lasts a long time.If you want to do it inside, put in gravel / sand mix plug both ends and shake / roll it by some means.
Reply:Sometimes "free" isn't very free.  :-/JoeMiller 140 Autoset (2010)Miller Syncrowave 250 (1996)
Reply:Originally Posted by shepdogSorry for lack of pics...it's 3x3 sqaure tube and 4x3, all 1/8" wall.  Tried every angle grinder attachment under the sun, including 24 grit sanding disk, knotted wire cup, grinding wheel....taking a loooong time to get anywhere.
Reply:I'd use a rust removing disc like the the norton rapid strip. There are a couple other manufacturers as well, other than the nortons, but these are available at the home despot and OSH. Just be sure to wear long sleaves, gloves, and eye protection, because little bits tend to fly off. One disc should clean about 40' of 3x3 square tube. Attached ImagesIan TannerKawasaki KX450 and many other fine tools
Reply:I agree that a belt sander would make short work of this.  But either a wire wheel or a flap disc should be able to take it down to bare metal.  Your description of 'glazed brown' is confusing to me.  If you wipe it with a cloth dipped in acetone, is it still not shiny metal?  If the brown is not just the dust from the rust you're seeing on the metal, then you might need a fresh wire wheel.Jack OlsenMy garage website
Reply:A-yup, the general problem with anything rotary that is aggressive enough too really give results is you tend to wind putting more unwanted marks / damage in it.With that belt sander I can turn that beam I showed up on edge and completely grind out all those bases where the railings have been cut off  in nothing flat while completely cleaning the edge down shiny flat in no time with no unwanted extra damage. Just switching belts allows you very good control to whatever finish desired. Cheap and fast with the right results possible.
Reply:The metal is somewhat pitted, but I'm not getting to shiny metal with the wire cup or the 24g sanding disk unless I'm right on the edge or really dig at a section...I'll grab some photos tonight (new iphone!)
Reply:Belt sander it is then...I'll give it a go tomorrow night!  Jack thanks for the tip on wiping with acetone, I'll see what happens.  Wiping my hand over it though, not much of the brown patina comes off....
Reply:Go by your local auto paint supply store and pick up a gallon of rust mort or something like it. It is premixed and ready to use, Or a product like rust seal makes a good base primer and converts the rust. It turns black.
Reply:Originally Posted by fortyonethirtyI'd use a rust removing disc like the the norton rapid strip. There are a couple other manufacturers as well, other than the nortons, but these are available at the home despot and OSH. Just be sure to wear long sleaves, gloves, and eye protection, because little bits tend to fly off. One disc should clean about 40' of 3x3 square tube.
Reply:Originally Posted by WeldingMachineWhy not just grind where you need to weld, spray it with some rusty metal primer, & paint?That seems like an awful lot of work.