Document VjvD4akL3pdxvxY38jNYp4mR4

HOT WORKING OF METALS Fig. 27-6. Suggested method of raising bottom doors of cupola by mechanical means. equipmentThey should be closed when the air supply fails or when the melting equip ment is shut down, in order to prevent the accumulation of combustible gases m the air supply system In the cupola, the blast gate may be omitted if alternate tuyeres are opened to permit air circulation. Blast gates should be so located in rela tion to the cupola wind box that the duct volume will be kept to a minimum Motor ized dampers may be installed at centrifugal blowers so that they will close automatical ly when the air supply fails. Positive-pressure blowers should be equipped with safety valves having liberal discharge areas If these are not provided, dogging of the cupola with slag or quick dosing of the gate or damper may produce sufficient pressure in the blast pipe to burst it Every cupola should have at least one safety type tuyere, with a small channel 1V4 or 2 m below die normal tuyere Ievd. This channel has a fusible plate that will melt through should the slag and iron rise to an unsafe level Tapping out Tappmg out with safety requires stall and should be done only by eipenenced and de pendable men In "bottmg-up" the hole, the bott should not be thrust directly mto the stream of molten metal or it will cause spattering To eliminate this, place the bott immediately over the stream of metal dose to the hole and aim it down toward the hole at a sharp angle. A supply of botts ready for use should be kept within convenient reach of die man who does the tappmg When the cupola is tapped, the hack end of the tappmg bar should be held below the level of the hole, to prevent puncturing the sand bed and causing run-out through the bottom A biting spout placed with one end direedy beneath the staboruuy cupola spout and mounted on trunnions on a stand adds to safety and efficiency. It can be tilted back and forth by a foot lever The rear end of the blbng spout is closed so that when that end is tilted down it forms a reservoir to receive the molten metal from the cupola. When the supplementary spout is tilted for ward, the metal runs from it into the wait ing ladle. At the same tune more metal continues to run into the spout from the cupola. Thus the stream of metal runs from the cupola continuously, and the blbng spout acts as a reservoir between ladle loads The dag spout of the cupola should be equipped with a shield or guard to protect workers from sprays of molten slag and to form a hood to collect slag wool The slag wool is sometimes collected through a wet slagging system wherein slag is thrown off mto a water-filled container or trough and flushed away. Dropping cupola bottom When the cupola is in operation, its bot tom doors should be supported by one solid prop and two adjustable screw props (of the required structural strength) on a metal prop base set on a concrete footing or other fabricated footing of equivalent strength (Fig 27-5). Temporary supports (timbers, blocking, etc.) should be placed under the cupola bot tom doors to prevent their falling on em ployees while die metal props are being ad justed to proper height Mechanical means for raising the bottom doors of the cupola should be provided (Fig 27-6). Dropping the bottom doors of a cupola requires extraordinary care One of the best methods is to use a block and tackle with a wire rope and chain leader attached 27-13