Tuesday, May 18, 2010

Transport of metal during welding-Part 1

Prof. Olshanskii suggested that I should examine what forces were responsible for driving the molten metal from the front of the pool to the back of the pool where the metal solidifies.
To visualise the flow of metal during welding I did some ingenious experiments. In a stainless steel plate of 10mm thick a hole of 2mm dia was drilled. Wires of copper,titanium,tantalum etc were embedded tightly in to these holes.A full penetration Electron beam weld passed over these metals embedded in the stainless steel.The welds were sectioned along the axis of the weld.The specimens were polished and etched to reveal the distribution of these tracer metals. The tracer metals had moved over a distance 6 to 8 mm in a direction opposite to the direction of welding. The concentration of the tracer metals along the depth of the weld and along the length of weld was measured using an electron micro probe analyzer.The maximum concentration was found at the top of the weld.

We were at a loss to explain how the metal could move such long distances considering that the dimensions of the electron beam welds are generally small.We searched entire literature to see whether any body had come across such a phenomenon. We could not find any thing similar to us.We realised that we have stumbled upon a new phenomenon. Finally my professor decided to consult one of the top class Physics Professor who was working in the same institute, that is, Moscow Power Engineering Institute. My professor took me to the Physics Professor and made me explain my experiments and also show him the results obtained till now. The Physics professor thought for some time and told me that I should look for "Thermocapillary Effect" and suggested that I should read a book on physics which was in the library. The meeting ended and we came out. I was disappointed with the meeting and I told my professor so. Then he told me something which I have not forgotten and which is helping me even now. He told me " I talked to several professors and all of them suggested that he is the right person to guide us. You may take a long time to find out the right person to consult. Once you have found him follow his advice implicitly. You jolly well go to library and read that book" I went to the library and read the book suggested by the Physics Professor. Indeed the back word movement of the metal could be explained by thermocapillary effect which will be the subject of next blog.

1 comment:

  1. sir, my name is arvind..iam about to join BHPV vishakapatnam....incidentally i happened to find your blog...very interesting and very informative...

    ReplyDelete