476 FOUNDING; FOUNDRY 



large and rartly in small pieces, of turning out from 700 to 800 tons por annum, with 

 aa establishment of 100 operatives, including some moulding boys. 



Of making the Moulds. 1. Each mould ought to present the exact form of its 

 object. 



2. It should have such solidity that the molted metal may be poured into it, and fill 

 it entirely without altering its shape in any point. 



3. The air which occupies the vacant spaces in it, as well as the carburettod gases 

 generated by the heat, must have a ready vent ; for if they are but partially confined, 

 they expand by the heat, and may crack, even blow up the moulds, or at any rate 

 become dispersed through the metal, making it vesicular and unsound. 



There are three distinct methods of making the moulds : 



1. In green sand; 2. In baked sand; 3. In loam. 



To enumerate the different means employed to make every sort of mould exceeds 

 the limits prescribed to this work. We shall merely indicate for each species of 

 moulding, what is common to all the operations ; and then describe the fabrication 

 of a few such moulds as appear most proper to give general views of this peculiar art. 



Moulding in green sand. The name green is given to a mixture of the sand as it 

 comes from its native bed, with about one twelfth its bulk of coal reduced to powder, 

 and damped in such a manner as to form a porous compound, capable of preserving 

 the forms of the objects impressed upon it. This sand ought to be slightly argillaceous, 

 with particles not exceeding a pin's head in size. When this mixture has once served 

 for a mould, and been filled with metal, it cannot be employed again except for the 

 coarsest castings, and is generally used for filling up the bottoms of fresh moulds. 



For moulding any piece in green sand, an exact pattern of the object must bo pro- 

 pared in wood or metal ; the latter being preferable, as not liable to warping, swell- 

 ing, or shrinkage. 



A couple of iron frames form a case or box, which serves as an envelope to the 

 mould. Such boxes constitute an essential and very expensive part of the furniture 

 of a foundry. It is a rectangular frame, without bottom or lid, whose two largest 

 sides are united by a series of cross bars, parallel to each other, and placed from 6 to 

 8 inches apart. 



The two halves of the box carry ears corresponding exactly with one another ; of 

 which one set is pierced with holes, but the other has points which enter truly into 

 these holes, and may be made fast in them by cross pins or wedges, so that the pair 

 becomes one solid body. Within this frame there is abundance of room for containing 

 the pattern of the piece to be moulded with its encasing sand, which being rammed into 

 the frame, is retained by friction against the lateral faces and cross bars of the mould. 



When a mould is to be formed, a box of suitable dimensions is taken asunder, and 

 each half, No. 1 and No. 2, is laid upon the floor of the foundry. Green sand is 

 thrown with a shovel into No. 1 so as to fill it ; when it is gently pressed in with a 

 rammer. The object of this operation is to form a plane surface upon which to lay in 

 the pattern with a slight degree of pressure, varying with its shape. No. 1 being 

 covered with sand, the frame No. 2 is laid upon it, so as to form the box. No. 2 

 being now filled carefully with the green sand, the box is inverted, so as to place 

 No. 1 uppermost, which is then detached and lifted off in a truly vertical position ; 

 carrying with it the body of sand formed at the commencement of the operation. The 

 pattern remains imbedded in the sand of No. 2, which has been exactly moulded upon 

 a great portion of its surface. The moulder condenses the sand in the parts nearest 

 to the pattern, by sprinkling a little water upon it, and trimming the ill-shaped pirts 

 with small iron trowels of different kinds. He then dusts a little well-dried finely- 

 sifted sand over all the visible surface of the pattern, and of the sand surrounding it ; 

 this is done to prevent adhesion when he replaces the frame No. 1. 



He next destroys the preparatory smooth bed or area formed in this frame, covers 

 the pattern with green sand, replaces the frame 1 upon 2 to reproduce the box, and 

 proceeds to fill and ram No. 1, as ho had previously done No. 2. The object of this 

 operation is to obtain very exactly a concavity in the frame No. 1, having the shape 

 of the part of the model impressed coarsely upon the surface formed at the beginning, 

 and which was meant merely to support the pattern and the sand sprinkled over it, 

 till it got imbedded in No. 2. 



The two frames in their last position, along with their sand, may be compared to 

 a box of which No. 1 is the lid, and whose interior is adjusted exactly upon the en- 

 closed pattern. 



If we open this box, and after taking out the pattern, close its two halves again, 

 then pour in melted metal till it fill every void space, and become solid, wo shall 

 obviously attain the wishod-for end, un<l produce a piece of cast iron similar to the 

 pattern. But many precautions must still bo taken before we can hit this point. Wo 

 must fiwt lead through the mass of sand in tho frame Np, 1, ope or more channels for 



