pad welding cast iron fits

[clay87]

Does anyone have a weld procedure for pad welding register fits on cast iron or cast ni-resist pump bowls/casings?

 

[1gibson]

Strip weld (1 pass 90* relative to face) in 4 or 8 equally spaced locations depending on diameter, then remachine.

Obviously, only one side of each mating pair can be repaired this way.

You may be able to roll or otherwise deform the material (knurl?) to avoid welding...

 

[clay87]

Thanks for the reply. My main question is regarding the process not the pattern. Typically welding/brazing cast iron requires significant preheat which we would want to avoid for obvious reasons. We don't want to introduce a crack in the base metal.

 

[inginear3]

It isn't preferred to ever weld a cast iron pump component. We would try to stock cast steel replacements. What are you trying to repair? You could machine new from bar stock depending on the component.

However, I have been in a pinch before and welded CI with Ni-Rod. The high preheat is required to prevent the cracking. I would recommend a 500 - 600F preheat. At my company, we would use tracing and wraps to maintain it during the weld process. If you start to lose the preheat, the cast iron will crack. After each pass, a person could choose to peen with ballpeen hammer to relieve stresses. We then slow cool it. Drop the tracing down to 250/300F and let cool. Then remove and cool in still air to ambient.

Another reason for the preheat and slow cool is to keep the welds soft. If you cool to fast and avoid the cracking, the part will be so hard that you can't machine it OR it can crack during machining process.

Cast iron welding is an art. There aren't many guys out there that can do it well. It takes lots of practice.

I hope that helps. I learned it the hard way!

 

[clay87]

Thanks. I understand the issues with welding CI. The parts I refer to are very expensive and large castings (diffusers, bowls) and we often have them braze-repaired at a casting repair specialty shop using proper preheat. I am only referring to the practice of applying a few small stitch welds about 1" in length as gibson described above. This is a common pump repair activity performed by major pump repair companies. We'd like to do this in house but we don't have a process or procedure to do so. My hoe is that these very small welds (with minimal preheat) do not adversely affect the base metal. We are currently welding some samples that we can test.

 

[inginear3]

We've tried pad welding just like you describe on cast iron bowls. It doesn't matter the size of the weld. They crack unless you follow the proper preheat and cool down.

Have you thought of machining a ring to shrink on the part to reclaim the fit? We have done that before in lieu of welding on the cast iron.

I have brazed locating pads but only on non critical components. The issue with brazing them is that you are not tying into the parent material. A braze can pop loose during machining or even worse during assembly.

 

[clay87]

We have sleeved these fits before on smaller parts. We have also thermal-sprayed (arc-wire) and added machinable ceramic coatings (belzona) to restore the fits. Pad welds would by far be the easiest.