Safe foundry practice . Fig. 9. A Carrying Pot, with Shank. A great deal of harm is done by carelessness inhandling the tongs and shanks, and the life of a cruci-ble may be seriously shortened in this way. When atilting furnace is used, as many as fifty heats can oftenbe obtained from a crucible; but if the heating is infurnaces from which the crucibles must be removed bymeans of tongs, they can be used for only about fifteenheats, on an average. A crucible is soft and plastic at a white heat, andmay easily be squeezed out of shape by the pressureexerted upon it when the handles of the tongs a
Safe foundry practice . Fig. 9. A Carrying Pot, with Shank. A great deal of harm is done by carelessness inhandling the tongs and shanks, and the life of a cruci-ble may be seriously shortened in this way. When atilting furnace is used, as many as fifty heats can oftenbe obtained from a crucible; but if the heating is infurnaces from which the crucibles must be removed bymeans of tongs, they can be used for only about fifteenheats, on an average. A crucible is soft and plastic at a white heat, andmay easily be squeezed out of shape by the pressureexerted upon it when the handles of the tongs areforced together. The walls of the crucible gradually CRUCIBLES 27 become weakened by treatment of this kind, andeventually, if the crucible is not discarded, a completerupture will probably occur, with its attendant toll ofinjuries and burns. Three styles of tongs are in general use in foundries—one-pronged, two-pronged, and spade tongs. Thedifferent styles are designed for various special purposes. Fig. 10. Tongs Properly Applied to a Crucible, forRemoving it from a Stationary Furnace. and operations, but they are sometimes improperlyused interchangeably. It is essential to see that thetongs that are used are of the proper shape, and thatthey fit perfectly from the widest part of the crucible(usually called the bilge or belly), down to with-in a few inches of the bottom. They should not 28 THE TRAVELERS INSURANCE COMPANY extend to the extreme bottom, however, because thiswould make it hard to place the crucible in the the other hand, if they do not extend down farenough the crucible will be badly squeezed. Theproper use of the tongs consists in taking hold of thecrucible below the bilge and lifting it in such a waythat the least possible pressure is exerted against thecrucible walls. One-pronged tongs should be used only for liftingthe smaller-sized crucibles,—say up to size No. larger sizes two-pronged tongs should be used. Itis not uncommon to see large
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