welding a hole in lower case

[37fordtruck]

I took the lower case of a 770 to have a hole welded and now I have problems. The hole was sand blasted on both sides to clean it and it welded real good except for one or two pin holes. When I took it back to get them welded the case began to cook impurities out of the metal. What can be used to clean this so that the pin holes will weld?

[Technical Support]

A better welder that actually does it the right way.