There is cast iron and then there is cast iron

I am making a stand for my bench grinder and have made a reasonable start. Well at least I have bought most of the material from the
local scrap yard. The very bottom is a truck brake drum. Bolted to that is a car disk brake. Next is a piece of 6 inch steel pipe that will be welded to the car disk brake. And on the top will be a steel plate welded to the pipe. The steel pipe is about a foot too long right now. The bottom three pieces weight 140 lbs. The plate I still have to find.
Now my questions are: I am assuming the car disk brake is a pretty good grade of cast iron, maybe nodular iron. Anyone know. Can I nearly treat it as if it is steel? Or do I need to use a weed burner on it to heat it before welding. I am planning on using some monel rod ( because i have a bunch of monel rod on hand ) and a stick welder and not weld the entire circumference of the six inch steel pipe. Instead just weld three beads about 3 inches long. So would have 9 inches of bead whereas welding the entire circumference would be a bit more than 18 inches. I plan on welding with the pipe vertical and using three bits of 1/8 inch welding rod to space the pipe away from the car disk brake to allow for shrinkage of the weld bead. Or would it be better to just use two bits of welding rod each side of where I am going to put the first bead and have the pipe leaning away from the side where the bead is going?
Normally I would just go ahead and weld it, but I need to wire brush the parts. And the parts are each heavy enough as is. So will wait until they are wire brushed before welding the disk brake to the pipe.
So any comments?
Dan
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snipped-for-privacy@krl.org wrote:
(...)

I welded some 1/2" HRS bars to a car brake disk to make a support for a small oil container.
It is a lot more patient than I am and will empty that container over the funnel for *weeks*!
It worked a treat without preheating or any special handling.
--Winston
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Because I too have a simular need for a grinder stand; I am curious to read about welding the steel pipe to the brake disk. and brake drum My thoughts, prior to reading about welding to the brake disk, would be to weld a plate or flange to the pipe and then bolt the pipe to the brake drum, forgetting the disk. Please let us know how your welding of these dissimilar metals turns out.
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I am bolting the auto disk brake to the truck brake drum. But will be welding the pipe to the auto disk brake. I think your idea of welding the pipe to a steel plate and bolting that to the drum is a good way to go. I just did not find any suitable plate at the scrap yard.
I looked on the internet and found that disk brakes are grey iron. So now am thinking about using the weed burner to preheat the disk and peening the weld bead as it cools. I think the monel welding rod ought to work well on the cast iron. Not as well as pure nickel rod, but I bought a can of welding electrodes with an unreadable label for $5. And it turned out to be monel welding rods. Should get this done in a day or so.
Also looking on the internet , I found that phosphoric acid is used by dairies and one can buy a gallon of it for $12 at Tractor Supply Corp. So will be using some of that to kill the rust.
Dan
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Congrats on a great deal.
Sell the monel stuff, it is worth a lot of $$$$$$.
i
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snipped-for-privacy@krl.org wrote: ...

I have used phosphoric acid for rust removal and I was not impressed. First, it is twice the cost of muriatic acid; second, it is at least half the speed; and then it doesn't keep as long - something precipitates out of it & it loses strength.
Don't worry about muriatic eating away the steel as well the rust - it is a very slow process (eating the steel is slow, eating the rust is very fast). I've left stuff in it overnight with no apparent dissolution.
Bob
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Phosphoric acid is best on steel. Cast iron is consumed to much and it depletes the acid faster and can leave deep pits.
On steel it is good to flash coat.
One can rinse in water with phosphoric but have to go baking soda with HCL. HCL also attacks body parts and clothes.
Martin
On 6/14/2011 7:30 PM, Bob Engelhardt wrote:

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Martin Eastburn     Jun 14, 10:41 pm ".... One can rinse in water with phosphoric but have to go baking soda with HCL. HCL also attacks body parts and clothes."
Ditto on that. Never used HCL for rust applications but enough times in strong drain cleaner to lose a few pairs of pants. That stuff is insidious. You thought your gloves were clean and dry but then you go and do your laundry a few days later and find that it looks like a Doberman puppy was making out with your favourite pair of jeans.
slightly OT: Question about the rust treatment process: I have some dime sized spots, that were presumably started by stone chips, on the leading edge of my hood that I'd like to tackle. Is it necessary to get out the sand blaster, or can I use some of the Permatex anti-rust gel(pink stuff) I have lying around and forego the sandstorm ? I've used it to clean nasty bolts and old auto parts, but always washed off after and a little bit of rust returning was never a concern. But for Auto body where I want to repaint and have it stay blister free? Sand then treat, then wash, then prime and paint?
suggestions?
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Too late. I have already bought the phosphoric acid. And have used it today. The cost is close to the same. At Tractor Supply Co the muriatic acid is $5 a gallon but is 20 %. The phosphoric is about 30 %. I diluted a little of the phosphoric acid to about 10 % and used a paint brush to slather it on. And then pulled out some more rusty metal and put some on that. And then some on the iron thing my wife bought to put out in the lawn. The speed might be a problem in the winter, but today in the sunshine it was fast enough in that I put it on a lot of stuff. I did have a problem with the pipe. It has some sort of coating on the outside that is hard to get off. Paint thinner and lacquer thinner do not cut it.
The nice thing about phosphoric acid is you end up with iron phosphate on the steel which is a good base for painting. Or you can dissolve zinc in it and then you end up with zinc phosphate ( even better ).
Dan
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Well I welded the disk brake to the steel pipe today. I started to use the monel rod, but was using my AC welder and it did not like the monel rod. So I switched to some stainless welding rod made by Hobart that likes AC. I did not preheat but did run short beads. I think it is okay, but I would not use it in a high stress situation.
Dan
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Stainless is a great job. You will be just fine.
i
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Ignoramus9757 wrote:

I used plain old ER70-S2. It worked perfectly well. http://www.weldfabulous.com/Filler-Metals/Cut-Length-Weld-Rod-36-in/ER70S-2/Weldcote-Metals-ER70S-2-116-p7633985.html
--Winston
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You will be totally fine with monel rod, or stainless, or even 6013, assuming that you preheat. This is a very low stress application.
i
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