FOUNDING; FOUNDRY 477 



the introduction of the melted metal ; and though one may suffice for this purpose, 

 another must be made for letting the air escape. The metal is run in by several 

 orifices at once, when the piece has considerable surface, but little thickness, so that 

 it may reach the remotest points sufficiently hot and liquid. 



The parts of the mould near the pattern must likewise be pierced with small holes, 

 by means of wires traversing the whole body of the sand, in order to render the mould 

 more porous, and to facilitate the escape of the air and the gases. Then, before lifting 

 off the frame No. 1, we must tap the pattern slightly, otherwise the sand enclosing it, 

 would stick to it in several points, and the operation would not succeed. These gentle 

 jolts are given by means of one or more pieces of iron wire which have been screwed 

 vertically into the pattern before finally ramming the sand into the frame No. 1, or 

 which enter merely into holes in the pattern. These pieces are sufficiently long to 

 pass out through the sand when the box is filled ; and it is upon their upper ends that 

 the horizontal blows of the hammer are given ; their force being regulated by tho 

 weight and magnitude of the pattern. These rods are then removed by drawing them 

 straight out ; after which the frame No. 1 may be lifted off smoothly from the pattern. 



The pattern itself is taken out, by lifting it in all its parts at once, by means of 

 screw pins adjusted at the moment. This manoeuvre is executed, for large pieces, 

 almost always by several men, who while they lift the pattern with one hand, strike 

 it with the other with small repeated blows to detach the sand entirely, in which it is 

 generally more engaged than it was in that of the frame No. 1. But in spite of all 

 these precautions, there are always some degradations in one or other of the two parts 

 of the mould : which are immediately repaired by the workman with damp sand, 

 which he applies and presses gently with his trowel, so as to restore the injured 

 forms. 



Hitherto it has been supposed that all the sand rammed into the box is of one 

 kind, but from economy, the green sand is used only to form the portion of the mould 

 next the pattern, in a stratum of about an inch thick ; the rest of the surrounding 

 apace is filled with the sand of the floor which has been used in former castings. The 

 interior layer round the pattern is called in this case, new sand. 



It may happen that the pattern is too complex to be taken out without damaging 

 the mould, by two frames alone ; then three or more are mutually adjusted to form the 

 box. 



When the mould, taken asunder into two or more parts, has been properly repaired, 

 its interior surface must be dusted over with wood charcoal reduced to a very fine 

 powder, and tied up in a small linen bag, which is shaken by hand. The charcoal is 

 thus sifted at the moment of application, and sticks to the whole surface which has 

 been previously damped a little. It is afterwards polished with a fine trowel. Some- 

 times, in order to avoid using too much charcoal, the surfaces are finally dusted over 

 with sand, very finely pulverised, from a bag like the charcoal. The two frames are 

 now replaced with great exactness, made fast together by the ears, with wedged bolts 

 laid truly level, or at the requisite slope, and loaded with considerable weights. When 

 the casting is large, the charcoal dusting, as well as that of fine sand, is suppressed. 

 Everything is now ready for the introduction of the fused metal. 



Moulding in baked or used sand. The mechanical part of this process is the same as 

 that of the preceding. But when the castings are large, and especially if they are tall, 

 hydrostatic pressure of the melted metal upon the sides of the mould cannot be counter- 

 acted by the force of cohesion which the sand acquires by ramming. We must in 

 that case adapt to each of these frames a solid side, pierced with numerous small holes 

 to give issue to the gases. This does not form one body with the rest of the frame, 

 but is attached extemporaneously to it by bars and wedged bolts. In general no 

 ground coal is mixed with this sand. Whenever the mould is finished, it is trans- 

 ferred to the drying stove, where it may remain from twelve to twenty-four hours, at 

 most, till it be deprived of all its humidity. The sand is then said to be baked, or 

 annealed. The experienced moulder knows how to mix the different sands placed at 

 his disposal, so that the mass of the mould as it comes out of the stove, may preserve 

 its form, and be sufficiently porous. Such moulds allow the gases to pass through 

 them much more readily than those made of green sand ; and in general the cattings 

 they turn out are less vesicular, and smoother upon the surface. Sometimes in a large 

 piece, the three kinds of moulding, that in green sand, in baked sand, and in loam, 

 are combined to produce the best result. 



Moulding in loam. This kind of work is executed from drawings of the pieces to 

 be moulded, without being at the expense of making patterns. The mould is formed 

 of a pasty mixture of clay, water, sand, and cows'-hair, or other cheap filamentous 

 matter, kneaded together in what is called the loam mill. The proportions of the 

 ingredients are varied to suit the nature of the casting. When the paste requires to 

 be made very light, horse-dung or chopped straw is added to it. 



