480 



FOtJNDING; FOUNDRY 



_ This mould, executed in baked sand, consists of three pieces; two of which, absolutely 

 similar, are represented, Jig. 1000, at p q, the third is shown at r s. The two similar 

 parts p q, present each tho longitudinal half of the nearly cylindrical portion of the 

 1000 1001 outer surface of the gas retort ; so that when they aro 



brought together, the cylinder is formed ; r s contains 

 5 in its cavity the kind of hemisphere which forms the 

 * bottom of tho retort. Hence, by adding this part of 

 the mould to the end of the two others, the resulting 

 apparatus presents, in its interior, the exact mould of 

 the outside of the retort ; an empty cylindrical portion 

 t t, whose axis is the same as that of the cylinder u u, 

 and whose surface, if prolonged, would be everywhere 

 distant from the surface u u, by a quantity equal to 

 the desired thickness of the retort. The diameter of 

 the cylinder t t is precisely equal to that of the core, 

 which is slightly conical, in order that it may enter 

 , r easily into this aperture t t, and close it very exactly 

 when it is introduced to the collet or nock. 



The three parts of the mould and the core being 

 prepared, the two pieces p q, must first be united, and supported in an upright position, 

 then the core must be let down into the opening 1 1, fig. 1001. When the plate or disc 

 o o of the core is supported upon the mould, we must see that the end of tho core is 

 everywhere equally distant from the edge of the external surface u u, and that it does 

 not go too far beyond the line q q. Should there be an inaccuracy, we must correct it 

 by slender iron slips placed under the edge of the disc o o ; then by means of a cast- 

 iron cross, and screw bolts v v, we fix the core immovably. The whole apparatus is 

 now set down upon r s, and we fix with screw bolts the plane surface q q upon r r ; 

 then introduce the melted metal by an aperture z, which has been left at the upper 

 part of the mould. 



When, instead af the example now selected, the core of the piece to be cast must go 

 beyond the mould of the external surface, as is the case with a pipe open at each end, 

 the thing is more simple, because we may easily adjust and fix the core by its two cuds. 

 In casting a retort, the metal is poured into the mould set upright. It is important 

 to maintain this position in the last two examples of casting ; for all the foreign 

 matters which may soil the metal during ?ts flow, as the sand, the charcoal, gases, 

 scoriae, being less dense than it, rise constantly to the surface. The hydrostatic 

 pressure produced by a high gate, or fi 11 mg-in aperture, contributes much to secure 

 the soundness and solidity of the easting. This gate piece being superfluous, is 

 knocked oif almost immediately after, or even before the casting cools. Very long, and 

 somewhat slender pieces, are usually cast in moulds set up obliquely to the horizon. 

 As the metal shrinks in cooling, the mould should always be somewhat larger than the 

 object intended to be cast. The iron founder reckons in general upon a linear shrink- 

 age of a ninety-sixth part ; that is one-eighth of an inch per foot. 



Melting of the cast iron. The metal is usually melted in a cupola furnace, of which 

 the dimensions are very various. Fig. 1002 represents in plan, section, and elevation, 

 one of these furnaces of the largest size ; being capable of founding 5 tons of cast iron 

 at a time. It is kindled by laying a few chips of wood upon its bottom, leaving tho 

 orifice c open, and it is then filled up to the throat with coko. The fire is lit at c, and 

 in a quarter or half an hour, when tho body of fuel is sufficiently kindled, the tuyere 

 blast is set in action. The flame issues then by the mouth as well as tho orifice c, 

 which has been left open on purpose to consolidate it by the heat. Without this pro- 

 caution the sides, which are made up in argillaceous sand after each day's work, would 

 not present the necessary resistance. A quarter of an hour afterwards, the orifice c is 

 closed with a lump of moist clay, and sometimes, when the surface is to contain a 

 great body of melted metal, the clay is supported by means of a small plaso of cast 

 iron fixed against the furnace. Before tho blowing-machine is set a-going, the open- 

 ings, g g g had been kept shut. Those of them wanted for the tuyeres are opened in 

 succession, beginning at tho lowest, the tuyeres being raised according as the level of 

 the fused iron stands higher in the furnace. The same cupola may receive at a time 

 from one to six tuyeres, through which tho wind is propelled by the centrifugal action 

 of an excentric fan or ventilator. It does not appear to be ascertained whether thoro 

 bo any advantage in placing more than two tuyeres facing each other upon opposite 

 sides of the furnace. Their diameter at the nozzle varies from 3 to 5 inches. They 

 are either cylindrical or slightly conical. A few minutes after the tuyeres have begun 

 to blow, when the coke sinks in the furnace, alternate charges of coke and pig-iron 

 must bo thrown in. The metal begins to melt in about 20 minutes after its intro- 

 duction ; and successive charges arc then made every 10 minutes nearly; each charge 



