Thin-walled vessels high quality welding is rather actual for every kind of industry, especially when such welded vessels have to work in the so-called hard conditions.

There are many various thin-walled vessels which are used in chemical and petroleum industries. Part of them belong to boilers and autoclaves (please, see our cryogenic and autoclave equipment rubric), other - to gas-holders, gas scrubbers, gas-separators and pressure equipment or to different reservoirs. If such vessels are made of sheets or tubes with thicknesses up to 3 mm from stainless steel, copper, nickel and titanium alloys, we may recommend to use our welding equipment for their producing and repair. An example of such cylindrical vessels can see be found on our site (part 1).

Below we consider an interesting application of plasma welding for manufacturing and sometimes for repair of glass and basalt melting vessels made from platinum metals as well as boilers for growing of glass monocrystals. Pictures of glass melting vessels you can see on (part 3).

Possessing more than 50% of the world platinum metals resources, Russia has a very strong and unique branch of industry-manufacturing of melting devices for glass fibre (crucibles) and basalt producing, which, in turn, is used in many important industries (aircraft, shipbuilding,etc.).

The author of this site worked in the field of crucibles plasma welding for 16 years (in the former USSR). Together with some organizations we have obtained interesting results, developing new types of glass melting vessels, their welds, methods of improving welds parameters and properties, etc. - (13), (14), (21), (28-30), (33). Nearly 100 microplasma sets were improved in this branch of industry. At the present time the amount of this equipment has drastically fallen, due to its being worn out, no longer realiable and not worthy of substitution by argon welding sets. Today producers of crucibles and boilers still are not sutisfied by existing welding equipment. Besides crucibles manufacturing there is an extremely important problem - how to repair them? The matter is that, when a crucible suddenly stops working, the glass freezed - as inside of the crucible as well as outside of it - at the damaged place, where usually a leak exists. And a freezed glass, being an isolator, stands in the way of plasma arc, prevents the welding current going through and makes it impossible to do repairing welding. Mechanical removing of the preventing glass layer is rather problematic because the walls of crucible have thicknesses 0,4-0,8 mm and their platinum based material is very soft. In order to remove the glass layer, well coupled with platinum metals, the crucibles users usually use gas flame which has too much power and leads to excessive deformations of thin-walled crucible body that reduces its working resources. In some cases the proposed set gives possibilities to melt and to shift not very thick layers of glass on the damaged surfaces and to immediately perform repairing welding. This is a good illustration for such an advantage of the proposed set - quick acting of transferred and non-transferred arc - in turn. For example, if in crucible drawplate or in a bushing one or a few (of many hundreds) calibrated orifices (dies) are spoiled, it may be possible to close them very quickly, using the proposed new set. And these faulty orifices may be even covered by non thick layer of glass or basalt. Other small damaged places in such a repair may be found during the new set's usage. Because of very high costs of platinum metals and crucibles our cheap, safe and simple sets using looks rather perspective.

The actuality of crucibles welding may be illustrated by the Document DVS Berichte, no.220. Welding and Cutting 2002. Proceedings, Conference, Kassel, 25-27 Sept.2002. Publ: 40010 Dusseldorf, Germany; DVS-Verlag, for Deutscher Verband fur Schweissen und verwandte Verfahren; 2002. ISBN 3-87155-679-3 with the name Automated microplasma and plasma welding in the glass industry and pressure vessel construction. There "a description is given of an automated installation capable of plasma welding in the manufacture of a wide variety of industrial equipment. The advantages of plasma welding are enumerated and the manufacture of spinnerets for glass fibre manufacture is described. This process, formerly done by manual TIG welding, involves the plasma treatment of thin tubes of PtRh alloy. Other industrial equipment made by this installation includes: cold gas generators for airbags, pressure vessel manufacture and tap hole welding to make ventilator components".

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