The process of moulding works in sand is essentially the same both for brass and iron castings; but the very great magnitude of many of the latter gives rise to several differences in the methods: it will suffice however to advert to the more important points in which the two practices differ, or to those which have not been already noticed; I shall therefore commence with a few remarks upon the flasks and the sand.
In the greater number of cases the iron-founder moulds and casts his works horizontally, with the flasks lying upon the ground; frequently the top part only is lifted; and in the largest works the lower part of the flask is altogether omitted, such pieces being moulded in the sand constituting the floor of the foundry; in these cases the position of the upper flask is denoted by driving a few iron stakes into the earth, in contact with the internal angles of the lugs, or projecting ears of the flasks.
The sand would drop out of such large flasks, if only supported around the margin; they are consequently made with cross-bars or wooden stays a few inches asunder, which, unless the entire flask is made of wood, are fixed by little fillets cast in the solid with the sides of the iron flasks. A great number of hooks in the form of the letter S, but less crooked at the ends, are driven into the bars, and both the bars and hooks are wetted with thick clay water, so that the sand becomes entangled amidst them, and is sustained when the flask is lifted. Some flasks require the force of either two or several men, who raise them up by iron pins or handles projecting from the sides of the flask . they are then placed upon one edge, and allowed to rest against any convenient support whilst they are repaired, or they are sustained by a prop.
The very heavy flasks are lifted with the crane, by means of a transverse beam and two long hangers, called clutches, which take hold of two gudgeons in the centers of the ends of the flask; it can be then turned round in the slings, just the same as a dressing-glass, to enable it to be repaired.
The modern iron-founder's flasks are entirely of iron, and do not require the wooden stays, as they are made full of cross ribs nearly as deep as the flask itself, and which divide its entire surface into compartments four or five inches wide, and one to two feet long. On the sides of every compartment are little fillets, sloping opposite ways, so as to lock in the small bodies of sand very effectually. When these top flasks are placed upon middle flasks without ribs, as in moulding thick objects, the two parts are cottered or keyed together, by transverse wedges fixed in the steady pins of the flask; lifters or gaggers are then placed amidst the sand, these are light T shaped pieces of iron, wetted and placed head downwards, the tails of which are largest at top, so as to hold themselves in the sand, the same as the key-stone of an arch is supported. The gaggers are placed at various parts to combine the sand in the two flasks, and they fulfil the same end as the iron hooks and nails driven into the wooden stays of the old-fashioned flasks.
The bottom flask or drag, has sometimes plain flat cross ribs two inches wide, (like a flat bottom with square holes,) that it may be turned over without a bottom board; and unless the flasks have swivels for the crane, they have two cast-iron pins at each end, and one or more large wrought-iron handles at each side, by which they may be lifted and turned over by a proportionate number of men.
The sand of the iron-founder is coarser and less adhesive than that used by the brass-founder; much of the former kind, used about London, is procured at Lewisham. The parting sand is the burned sand which is scraped off the castings; it loses its sharp, crystalline character from being exposed to the red heat. The facing-sand is sometimes only about equal parts of coal-dust and charcoal-dust, ground very fine; at other times, either old or new sand is added, and for large thick works a little road-drift is introduced. All these substances get largely mixed with the sand of the floor, and lessen its binding quality, which is compensated for by occasional additions of new sand, and by using more moisture with the sand; as before extracting the patterns, the iron-founder wets the edges of the sand with a sponge, which has sometime a nail tied to it to direct the water in a fine stream; for heavy works a watering pot is used.
The green-sand moulds, are made as in the brass-foundry, of the ordinary stock of old moist sand; these are often filled as soon as they have been made.
The dry-sand moulds, are made in the same manner, but with new sand containing its full proportion of loam; these moulds are thoroughly dried in a large oven or stove, and then black-washed or painted, with thin clay water containing finely ground charcoal; this facing is also thoroughly dried before the moulds are poured.
The loam moulds, which arc much used for iron castings and somewhat also for those of brass, are made of wet loam with a little sand, ground together in a mill to the consistence of mortar; the moulds are made partly after the manner of the bicklayer and plasterer, as will be explained: the loam moulds also are thoroughly dried, black-washed, and again dried, as from their greater compactness they allow less efficient escape for the vapour or air, and therefore they must be put into the condition not to generate much vapour when they are filled.
Iron moulds are also employed for a small proportional number of works which are then called chilled castings; these were referred to at pages 258 and 259; and occasionally the methods of sand casting and chilling are combined, as in some axletree-boxes, which are moulded from wooden patterns in sand, and are cast upon an iron core. To form the annular recess for oil, a ring of sand, made in an appropriate core-box, is slipped upon the iron mandrel, and is left behind when the latter is driven out of the casting.