How I learnt to operate an Electron Beam Welding Mchine

I am not going to write about what is an electron beam welding machine about which anyone can read in a standard welding text book. I am going to write how students were trained in Moscow Power Institute.

There were two electron beam welding (EBW) machines in the Department of Technology of metals where I joined for my Ph.D program under Prof. N.A.Olshanskii. One was operating at high voltage and the other was operating at a low voltage. The one operating at a high voltage was built by Prof. Olshanskii and the other was a factory built machine. New students were asked to start with the machine built by Prof.Olshanskii and after mastering the principles of operation of EBW they were allowed to go on the factory built machine. There was a reason behind this exercise. The machine with which we started to learn operation of EBW used to go out of order often as it was very old. The cathode which was a filament made of
tungsten used to burn up fast either due to our wrong handling of the machine or due to its life being over. When that happened we were supposed to take out the electron gun and replace the tungsten filament. During this process we learnt how the electron gun looks, how to make the tungsten filament, how to mount the filament and how to align the filament properly etc. All EBW machines are connected to a fore vacuum pump which is a mechanical pump and an oil diffusion pump. Whenever these pumps went out of order we were supposed to strip them open, rectify the mistakes and put them back in to operation. These exercises gave the new entrants enough confidence to handle any EBW machine. When you made mistake no one asked any questions but you were only required to set the mistake alright.This was totally different from the approach of Indian institutions.After my quota of mistakes, when Prof. had the confidence that I can handle factory built machine he allowed me to go on that machine.

There is a particular procedure for opening and closing of various valves to create vacuum. In today's machines everything is automated. In 1968 all these operation were manual. Fist you have to switch on the electric heater to heat the oil in the diffusion pump and after some time you switch on the fore vacuum pump and when the fore vacuum has reached a predetermined level you close the valves of fore vacuum pump and open the valves connected to the diffusion pump. If valves connected to the diffusion pump is opened when the valves connected to the fore vacuum pump is not closed air enters diffusion pump and oil burns and vacuum is lost.Then you have to switch off the machine, clean up the mess and put the machine back in to operation.

I will write in next blog what happened when I burnt the oil in diffusion pump.