Bell and basin system
GRABE Metallkonstruktion in Herne
Prior to the invention being made by PAUL Wurth, the customary system which was used was that of a bell and throat armour: a double-bell closing device with rotary hopper. The blast furnace is sealed gastight by two bells which are mounted one above the other, whereby the rotary hopper is mounted above the top (small) bell and can be rotated by any angular values which are required. This ensures that the material (burden and coke) is evenly distributed on the small bell – and that in every desired spot on the circumference of the top.
In the case of blast furnaces which work with counter-pressure, the double-bell closing device has frequently been improved and expanded. Closing devices are now available which have three and even four bells and numerous sealing flaps but even this does not solve the real problem. The blast furnace construction and especially the top-closing device have grown to such a considerable extent that it is imperative that the designers will have to tread new paths.
One route which is being taken by GRABE is the redesigning of the heavy cast bells with light and wear-resistant steel constructions. This has the following advantages when compared to a cast design:
considerable reduction in the weight
greater flexibility with the execution
lengthened serviceable life due to targeted surface-layer welding
shorter delivery times and reduced manufacturing costs
Perfection in wear protection
A top quality and an ideal welding speed are not a matter of course – only the best automatic welding machines can meet these demands and at the same time be so flexible that they can be quickly converted to another process.