Car-wheel Founding
The manufacture of car-wheel is a special branch of foundry industry, which, in all of its varied phases, demands more than ordinary attention to make good wheels at a profit. The processes of their manufacture are substantially as follows: First, a good, substantial wood pattern, or better, an iron one, with iron core-boxes in which to dry the cores. Second, a set of flasks consisting of cope, with bars to fit one inch clear of the pattern; drag, with separate perforated bottom-plate; and an intermediate chill 4 inches thick, for chilling the tread, with lugs and pins to match both upper and lower parts, and trunnions for reversing. Third, moulding and casting. Fourth, lifting from the sand red hot, and lowering into the annealing-pit, where the wheel cools gradually in about three or four days, when it is taken out, cleaned, tested, and if found sound in every particular, is pronounced a chilled car-wheel.
The "Barr" contracting car-wheel chill is described in The Machinery Moulders' Journal as follows:
The ring, which constitutes the ordinary chill, is divided into 96 sections by radial divisions. The sections or blocks are held in position by an outside ring, which is capable of being expanded or contracted, thus causing the blocks composing the chill to be moved, radially, outward or inward. By this means the expansion which occurs in the ordinary chill is entirely prevented, and the inward radial motion of the chill-blocks is such as to extend the time of contact between the chill and the contracting-wheel within, until nearly the full effect of the cooling influence of the chill is obtained. The expansion and contraction of the outside hollow retaining-ring is effected by introducing steam or water.
The operation of the chill is as follows: When the moulder is nearly ready to pour his metal, steam is turned on through the outer ring, causing it to expand, and carrying with it the chill-blocks, thus increasing the diameter of the chilling surface. When the chill becomes so warm that you can barely lay your hand upon it the steam is then turned off. The iron is now placed in position to pour, and the moment the iron enters the gate or pouring-head, cold water is passed through the ring which causes a contraction of the outside hollow sustaining ring and a consequent decrease in diameter of the chilling surface.
This chill has been in use in our foundry for the past year, and during that time our loss from chill-cracks and other causes has been 1/2 of 1 per cent, while in the old style chill the loss has been from 3 to 6 per cent. There is in fact an entire absence of chill-cracks, rough tread, and sweats, and the presence of slag almost entirely prevented. There is a decided improvement in the depth of white iron and its uniformity around the tread; the average variations in the white iron being about 1/16 inch, while in the old or solid chill I have known it to vary as much as 3/8 to 1/2 inch. The quality of gray iron, with its freedom from slag or imperfections, and the general strength of the wheel is enhanced by hotter and faster pouring, which is made possible by the use of this chill. With the old or solid chill the time consumed in pouring a chill is about twenty seconds, and with the contracting chill nine to twelve seconds.
There is only one objection to the Bar contracting chill, and that is the small ridges formed by the spaces between the chill-blocks. These we are compelled to grind off with an emery-wheel. This labor can be lessened by filling these crevices with sharp sand.
Case-hardening is the term applied to the process of converting the external surface of articles or masses of iron into steel, with the view of combining the hardness of the latter with the toughness and comparative cheapness of the former. This may be done by placing iron articles (finished, but not polished), along with animal carbon, as hoofs, leather, skins, etc., that have been partly burned to admit of being powdered, into an iron box, well luted, and subjecting them to a red heat for about half an hour, or even more, according to the depth of hard surface needed, after which plunge the contents into water.
Cast iron may be hardened on the surface by first bringing to a red heat and rolling in a mixture of saltpetre, powdered prussiate of potash, and sal-ammoniac in equal proportions, after which immerse in a bath of water which contains in each gallon, sal-ammoniac 4 oz., prussiate of potash 2 oz. Small iron articles will be case-hardened by allowing them to remain 30 minutes in a fused liquid consisting of common salt 10, prussiate of potash 1, and subsequently plunging into cold water. An iron pot will serve to fuse in. Casings are perforated iron shells, provided with prickers for carrying the loam thickness, and with means for lifting and turning over the cope part. When the form of castings is favorable to non-interference with contraction, as in some sugar-pans, crystallizing-cones, and other kindred castings, both inside and outside moulds may be swept with the spindle, closed and cast, without any subsequent ramming in the pit which necessarily attends the ordinary methods. Cylindrical casings are equally as advantageous when the quantity of castings required will warrant the outlay for making them. See BELLS; KETTLES; SPINDLE.