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Repairing the Cupola

The first duty of the cupola-man, after the refuse of the previous day has been carefully picked for whatever iron and unburnt fuel may be found, is to chip out the cinder and scoria from the inside of his cupola and ascertain what damage has been done to the walls. Now, good tools for this operations are an absolute necessity, as the more pounding required for the loosening of this adhering dirt, the more will the brick lining be loosened--a result to be avoided if possible. For this operation the cupola-man should be supplied with an adequate set of steel-pointed chisel-bars, large and small, and these, along with steel pick-hammers of suitable dimensions, should be kept sharp and of proper temper. When tools of this class are supplied there will be no difficulty in chipping out in such a way as to jar the bricks but little, and leave the surface clean and ready for the daubing, and in much less time than it takes to do it in the slipshod way it must inevitably be done where perhaps only a sledge-hammer is used. The chief object in repairing is to maintain as near as possible the original shape of the cupola. Except at the melting zone, just above the tuyeres, this may be accomplished fairly well; but at that point there will be, owing to the intense heat and force of the blast a decided tendency of the bricks to waste away; and it is just here where the judgment and skill of the cupola-man is put to the test, as by proper management a lining may be preserved almost indefinitely. By careful observation it may be seen which parts are being acted upon the most. Follow up at these parts with thin coats of daubing (see DAUBING), and use no more than will adhere firmly to the wall, without fear of its being prematurely loosened by the intense heat. The bad effects from using too much daubing of any kind may be understood when we consider that most of this drying must take place immediately the heat is intensified by the admission of the blast; the front of the patching dries at once, and the rapidly formed steam should find an outlet at the brickwork behind; failing this it naturally forces off the daubing, which falls over on the stock, the result being that the regular action of the cupola is interfered with to the extent of changing the direction of the blast and preventing the iron as it melts from falling direct to the bottom; by this means some iron finds its way into the tuyeres, some lodges around them and solidifies, ultimately choking the orifice altogether. Thin daubing, well rubbed on, will never fall away if made of the correct ingredients. When it has been thought necessary to insert new bricks at parts, as well as to rub on more daubing than usual, light up a little earlier in order to dry it out with a more gentle heat. Better a little extra expense in fuel than run the risk of a bad heat. See DAUBING; CUPOLA.