FOUNDING; FOUNDRY 471 



tinguished by the surface of the pig of iron, which was exposed to the air during 

 cooling, being smooth, and presenting a slightly convex figure. The surfaces of Nos. 

 3 and 4 pig-iron, and of the white crystalline pig-iron (most suitable for making into 

 wrought iron) present a concave figure, and the surfaces are very irregular and pitted 

 with holes. The colour of the fracture, and the closeness of the grain, also indicate 

 the proportion of carbon in pig-iron. 



The mixtures of metal, melting temperatures of metal, &c., require the closest 

 observation on the part of the workmen and foremen who practise iron-founding, and 

 these mechanics are in the practice of observing differences so minute that they cannot 

 be appreciated by the chemist, or expressed in words. 



Machinery has enabled the modern founder, by means of railways, turn-tables, 

 travelling-cranes, and steam-power to move at will the heaviest masses without con- 

 fusion and with great expedition ; but nothing but the traditions of the factory, and 

 the constant habit of observation will enable him to conduct properly the melting and 

 casting of metal so as to arrive at certain results. 



This is proved by the constant failures of those who undertake to make descriptions 

 of castings, of which they have had no previous knowledge. 



Each branch of foundry work must be studied in detail, and we can only pretend to 

 indicate those directions in which progress has been and is being made. 



FOUNDRY. The process of iron smelting and the construction of furnaces having 

 been described under other heads, the remaining part of the business of a foundry, viz., 

 that which relates to the preparation of the moulds and moulding, will now be described. 



Moulding. The art of moulding is one of the most important processes carried on 

 in a foundry, and the success of the founder is directly proportioned to the skill 

 and ingenuity brought to bear upon the production of the patterns and the system 

 of moulding. 



Before metals can be cast into the variety of shapes in which they are wanted, 

 patterns must be prepared of wood or metal, and then moulds constructed of some 

 sufficiently infusible material capable of receiving the fluid metal, and retaining it 

 without uniting with it until it has solidified. 



A mixture of sand and loam (packed tightly into metal boxes, called flasks) is 

 generally chosen as the material for making moulds, and is employed advantageously 

 for several important reasons. 



Flasks. In modern foundries a system has been invented, by which flasks of any 

 dimensions may be constructed by means of bolting together a number of rectangular 

 frames of cast iron, so arranged as to admit of being easily connected together. 



When the particular castings for which the flask has been constructed, or rather 

 compounded, are completed, the separate pieces are unbolted, and are ready to be 

 combined in some new form appropriate to the dimensions of the pattern next to be 

 moulded in them. 



The loss of capital, &c., invested in flasks, only occasionally used, is thus saved, as 

 well as loss of time in searching for the size required. The space devoted, on the old 

 system, to the reception of flasks belonging to a foundry was very large, and this may 

 now be appropriated to other purposes. 



Sand and loam. Founders formerly used, on account of price, the description of 

 sand most accessible to them, but at the present time, the convenience and cheapness 

 of railway carriage has enabled special qualities of sand to be delivered to all parts of 

 England. 



For founding purposes sand is much improved by the admixture of coke, crushed 

 and reduced to a fine powder, and a mill for this purpose is as necessary in every 

 large foundry as those for grinding and mixing loam. 



Moulding-sand must be a mixture of a large quantity of silex and a small quantity 

 of alumina the property of the latter material being to cement the grains of silex 

 together. Loam consists of the same materials mingled in opposite proportions. 



The preparation of loam for those purposes for which sand is not adapted, is an 

 important duty in a foundry, for a great quantity of loam cores have to be made and 

 dried in proper ovens, which is a tedious operation. 



Many castings, such as the screws for steamers, are more conveniently cast in moulds 

 constructed of wet loam. These are shaped to the required form when the clay is 

 moist, and then carefully dried afterwards. 



Other castings are of such peculiar shapes that they can only be produced in moulds 

 that take in a vast number of pieces. These mo aids are then formed of a number of 

 pieces of hardened sand, held together by strips of iron or of plaster, if the sand used is 

 not coherent enough in itself. 



Compounds of silex and alumina are very infusible, and when moistened with water 

 and faced with carbonaceous matter, they are capable of receiving the most delicate 

 impressions from the patterns which the founder employs. 



