Tapping-bar

The Encyclopedia of Founding (1892)

A pointed iron bar for removing the clay bott when it is desired to let metal out of the cupola. A set of bars for this purpose should include, first, a scoop-shaped tool about 3 feet long, with which to remove all superfluous clay from the orifice of the tap-hole before the final impression is made, with a longer one having a point, the idea being to clean all the clay out of the spout with the scoop before the stream is permitted to run, and thus prevent its being carried down into the ladle. Besides these it is always prudent to have another of larger dimensions, made of steel and drawn to a square point; this should always be ready, along with a good sledge, in case the plug should congeal and require to be driven in. A large bar of common iron is useful, at times, for a through opening out of the hole during protracted heats. See BOTT-CLAY; TAPPING-HOLE; CUPOLA. Tapping-hole is the hole provided at the bottom of the furnace through which the molten metal is allowed to run at intervals during the operation of melting. Ordinarily, for the cupola, it is made new, along with the spout, for every cast. When it is time to form this hole, a round bar from 1 to 2 inches diameter, according to dimensions of cupola, is thrust into the burning fuel at the breast, taking care that it rests solid on the bottom, after which the breast-hole is rammed with sand and the bar withdrawn. The above is a general view of this operation, but it is well to observe some of the special features connected with it more particularly. In the first place, a short hole is always best, there being then less danger of the metal congealing in the tap-hole; this is accomplished by reducing the brickwork of the lining inside the cupola at this part, and the length may be still further reduced by widening the orifice at the front until not more than 4 inches of straight hole remains. This of course brings the bott end of the molten plug nearer to the molten iron inside the cupola, and thus prevents freezing. If the outer edge of the tap-hole be made slightly funnel-shaped for about 2 inches in, there will be less difficulty in pressing in the bott than is experienced when the hole is parallel all the way through. This is all-important where all the metal the cupola will hold is allowed to gather in the bottom before it is tapped. An important feature in the bricked spout is that it provides a safe abutment for the breast, making it impossible for the inside pressure to force it back. If the cupola-daubing, tempered with fire-sand, be used in immediate contact with the bar when the tap-hole is being formed, and for the bed next the spout also, all possibility of slag forming at the tap-hole is obviated, the substances composing this daubing being too refractory to melt at that temperature. Let the first bott always be a long one, reaching well into the tap-hole, for reasons above described, and in order that it may be easily taken out when it is desired to make the first tap; make a hole through the bott, after it has been formed on the stick, and fill it with common black sand off the floor; by the time this has been pressed well into the tap-hole there remains little but sand to be removed-an easy operation. See TAPPING-BAR; BOTT-CLAY; CUPOLA; BREAST; SPOUT.