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FOUNDING; FOUNDRY 



Wo shall illustrate the mode of fabricating loam moulds, by a simple case, such as 

 that of a sugar-pan. Fig. 992 is the pan. There is laid upon the floor of the foundry 

 an annular platform of cast iron, a, b, Jig. 993 ; and upon its centre c, rests the lower 



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extremity of a vertical shaft, adjusted so as to turn freely upon itself, while it makes 

 a wooden pattern ef,fig. 994, describe a surface of revolution identical with the inter? 

 nal surface reversed of the boiler intended to be made. The outline e g, of the pattern 

 is fashioned so as to describe the surface of the edge of the vessel. Upon the part 

 a, d, 6, d,fiff. 993, of the flat cast-iron ring, there must next be constructed, with bricks 

 laid either flat or on their edge, and clay, a kind of dome, h i k, fig. 994, from two to 

 four inches thick, according to the size and weight of the piece to be moulded. The 

 external surface of the brick dome ought to be everywhere two inches distant at least, 

 from the surface described by the arc cf. Before building up the dome to the point 

 i, coals are to be placed in its inside upon the floor, which may be afterwards kindled 

 for drying the mould. The top is then formed, leaving at i, round the upright shaft 

 of revolution, only a very small outlet. This aperture, as also some others left under 

 the edges of the iron ring, enable the moulder to light the fire when it becomes neces- 

 sary, and to graduate it so as to make it last long enough without needing more fuel, 

 till the mould be quite finished and dry. The combustion should be always extremely 

 slow. 



Over the brick dome a pasty layer of loam is applied, and rounded with the mould 

 ff> e,f; this surface is then coated with a much smoother loam, by means of the con- 

 cave edge of the same mould. Upon the latter surface, the inside of the sugar-pan is 

 cast ; the line e g having traced, in its revolution, a ledge, m. The fire is now kindled, 

 and as the surface of the mould becomes dry, it is painted over by a brush with a mix- 

 ture of water, charcoal -powder, and a little clay in order to prevent adhesion between the 

 surface already dried and the coats of clay about to be applied to it. The board g cf 

 is now removed, and replaced by another, g' e' f',fig. 995, whose edge ef f describes 

 the outer surface of the pan. Over the surface cf, a layer of loam is applied, which 

 is turned and polished so as to produce the surface of revolution e'f, as was done for 

 the surface ef; only in the latter case, the line e' g 1 of the board does not form a new 

 shoulder, but rubs lightly against m. 



The layer of loam included between the two surfaces ef, ef f is an exact represen- 

 tation of the sugar-pan. When this layer is well dried by the heat of the interior fire, 



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it must be painted like the former. The upright shaft is now removed, leaving the 

 small vent-hole through which it passed to promote the complete combustion of the 

 coal. There must bo now laid horizontally upon the ears of the platform d d, fig. 993, 

 another annular platform p q, like tho former, but a little larger, and without any 

 cross-bar. The relative position of these two platforms is shown in fig. 997. Upon 

 the surface e' f fig. 996, a new layer of loam is laid, two inches thick, of -which tho 

 surface is smoothed by hand. Then upon tho platform p g,fy. 997, a brick vault is 

 constructed, whose inner surface is applied to tho layer of loam. This contracts 

 strong adherence with the bricks which absorb a part of its moisture, while tho coat of 

 paint spread over the surface c'/, prevents it, from sticking to the preceding layers of 

 loam. The brick dome ought to be built solidly. 



