Popping on Electrochemical Machining Line

Question:

We have an electrochemical machining line (cleaning steel parts with a solution of 31.45% HCl and glycerine). Parts are cleaned in rotating barrels.

Twice in the past week, the operator has heard a loud pop from the tank that is processing a load, and the acid is blown everywhere! Obviously, this is of great concern to the operator. What is happening? I suspect that hydrogen gas is accumulating over the tank and then somehow igniting, but it’s just a theory. Why is it happening? Also, why would it just have started happening? Have you ever heard of this happening anywhere else? What have others done to correct this problem? Thanks in advance. J.G.

Answer:

I am not very familiar with electrochemical machining so I can’t answer your last two questions. In response to your first two questions, I believe there could be two possibilities. One could be an arcing or shorting between the electrode and workpiece. Do you notice any evidence of this? I also think your hydrogen theory is a good one. In that type of electrochemical operation, the reduction reaction will involve hydrogen ions present in the acid, which will create hydrogen gas. I am a little surprised that you would have enough to create these explosions, though, if you have proper ventilation. As to why it is happening now, you would have to examine your process to see what has changed recently. Some questions that should be explored are: has ventilation for the area changed; are you machining at either a higher current density; or machining more surface area (either would create more hydrogen); and is there an arc source that can initiate the explosion?