Cast iron repair

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Hi AllThe attached pictures show the pump housing of a pump used to pump acid. The housing is usually ceramic coated. What usually happens is that the coating is chipped and the acid that the pump is supposed to pump eats away the metal of the housing, which I am told is called the volute.I am from South Africa and there are no new volutes like this in the country. Delivery time for a new one is 18 weeks. As mentioned the damage is caused by acid and there are no cast pieces to weld the holes up. I used mild steel bar and plate shaped appropriately to fill the gaps. Most areas I used 309L rod and tig brazing.One area that gave me serious cracking problems was the centre area where the seal sits. Gassing, snap crackle and pop and then crack. I eventually used ac tig with 85% balance using copper rods to 'weld' in the slice of mild steel tube to form the new seal seat. Photos are not great but when I rough ground it the copper and cast have combined, no cracks and no voids. Normal service life for this part is 2 months. This one has now been running for three.Please bear in mind I am self taught welder. I used to be business analyst and due to retrenchment had to make a living some other way. So what I would like to ask is this: Given the dissimilar nature of cast and copper how have they bonded so well? Just intuitavely I think the copper is stretchy enough to prevent cracking and the cast is porous enough to bond well with the copper. I would love to get some input from the more experienced members of this forum on this repair. Attached Images
Reply:Man, that is worn out, I understand the problem with your location.  Do you have a spare where you can exchange one, wile working on the other? Is there another way to pump acid rather than a pump like that? Pretty awesome repair for being self taught! I also wonder if there are 2 part epoxy or polyurethane coatings that would extend the life of the repair.  I sent you a private message with another repair technique.Last edited by blackbart; 06-16-2013 at 04:59 PM.
Reply:Hi, many years ago, around the 60's,  I worked for CDM, Consolidated Diamond Mines of South West Africa, (Namibia), in Oranjemund, and all our big pumps were Vacseal pumps with rubber linings.....they had to deal with salt water and sand.The life of the rubber lining was varied and was dependent on the quality of the vulcanising of the rubber on the chambers, back plates and front covers.We did a weekly check on the pumps and once the rubber developed a blister it was a matter of hours before the pump blocked up with shredded rubber.Ian.
Reply:Every time my rubber got a blister I had a kid in nine months......