Rasp
The rasp differs from the file in that the teeth protrude separately, thus making a surface much more suitable for filing cores than does the chisel-cut teeth of an ordinary file.
Ratio of Fuel to Iron.--Ratio of fuel to iron means the proportion of fuel burned to melt a given quantity of iron, as 1 to 5, or 1 to 12,--indicating that five pounds of iron is melted with an expenditure of one pound of fuel in the first instance, the latter indicating that twelve pounds is the quantity of iron melted with the same amount of fuel. Any attempt to formulate absolute rules to be observed by the cupola-man at all foundries alike must assuredly result in extreme disappointment, as nearly every place has its own special needs and requirements, which can be successfully met only by intelligent observation and persistent effort on the part of the cupola-man or his superiors. For this reason comparisons relating to the economics of melting iron at different foundries are of no real value, disappointment and loss being sure to attend any attempt to appropriate the systems of others, which may in all probability have been founded on experiences diametrically opposite to our own.
Any conceit we may have indulged in because of our ability to melt iron at the ratio of 1 to 10 for the line of castings we produce must be forever dissipated when we discover that the exceedingly low temperature of such iron would render it utterly valueless for the light castings produced by our neighbor, who for this reason must necessarily use more fuel to meet his case successfully. The foundry melting a standard gray pig with first-class scrap should undoubtedly melt its iron down with greater regularity and with much less fuel than where perhaps unwieldy and promiscuous scrap with a slight admixture of pig is the iron charged.
Quality of fuel affects results perhaps more than anything else; if poor, a greater amount must be used to obtain the requisite quantity of carbon. This, of course, increases the bulk between charges and requires extra time for its consumption; while the superfluous, impure substances, as slate, etc., yield a viscous slag, which interferes in no small degree with the regular process of melting, retarding it always. Even when all other things are favorable, the pressure of blast and care bestowed on apparatus will always exert an influence for better or worse proportionate to the amount of intelligence brought to bear upon such important details. Leaky pipes and fitful and uncertain blast mean extra fuel and delay in melting operations. Construction of the cupola and its location, with reference to adverse wind currents and draught, is sufficient in some instances to mar effectually the best efforts of the cupola-man, interfering, as it does, with the first efforts to ignite the fire, and thus precluding all possibility of an evenly-burned stock--a forerunner sometimes of endless subsequent vexations and delays. The unfairness of comparing the performance of cupolas laboring under these and kindred disadvantages with others of faultless construction and suitable location will be apparent.
The wastefulness attending melting small heats in cupolas designed for more extended operations is made plain by the following: Suppose a 44-inch cupola is employed for a heat of 12,060 pounds, the amount of fuel used, including bed, being 2140 pounds: the ratio would be 1 fuel to 5.63 iron melted. Now increase the heat by six additional charges of iron to 37,440 pounds, maintaining the same ratio of fuel between the charges as before: this gives 4960 pounds total fuel used, and the ratio is now 1 to 7.53. These are only a few of the things to be considered when comparisons are made. It may be a subject for remark that such a firm is melting iron with a much lower ratio of fuel to iron than another, and much annoyance is caused by this undisputed fact; but all this would perhaps be modified if careful investigation were instituted. Possibly this distinguished firm is melting carefully selected irons of the same mixture every day without deviation all the year round--a state of things eminently conducive to perfect practice; while those with whom they have been compared are, owing to the numerous and sometimes unpleasant changes in the nature and quality of the castings made, compelled to change their mixtures often, and more than once during the same heat sometimes.
Means for rapid transit, or close proximity of the cupola to the moulds which are to be poured, will favor metal of a low temperature being melted, thus allowing a diminished ratio of fuel. But if facilities for conveying are limited and the moulds far removed, it is incumbent that hotter metal be provided to compensate for the extra time occupied in handling. This increased temperature can only be obtained by increasing the ratio of fuel. The preceding represents in some measure a few of the reasons for the high ratio of fuel to iron as necessitated in foundries which are unfavorably circumstanced as described; still, without doubt, there is considerable waste of fuel almost everywhere, that might be remedied if rigid investigation by qualified practitioners were established. Cupolas now yielding unsatisfactory results at many places might be changed to the best of their kind if those who work them were compelled to learn the importance of placing every charge of fuel and iron in the cupola systematically and precise. This, of course, can only be done by the cupola-man who knows that in order to retain the heat within the cupola and not have it wasted up the stack more than ordinary attention must be paid to a favorable disposition of the materials charged, and, further, that to insure regularity in both speed and fluidity every pound of such material should be carefully weighed. By this means alone can be pursue a course of safe experimental practice, the results of which if carefully noted will furnish him with all the knowledge essential for supplying metal from his cupola at all times the exact temperature demanded, and without fear of disappointment. No reliance can be placed on any method of melting that does not include a correct proportioning of the fuel and iron at every charge.
Besides this, it is incumbent on the cupola-man that he carefully observe the action of his tuyeres, changing the form from time to time, raising or lowering them, increasing or diminishing their number; or, if the tuyeres be continuous, trying the effect of a gradual contraction or expansion from their original width. Expansion of tuyere area with no increase in wind-pressure will soften the blast while contracting them will have the effect of creating a cutting blast if original wind-pressure is maintained. By observing results from these several changes, as well as increasing and decreasing wind-pressure in the blast-pipes, he may arrive at the very best practice possible for the cupola he manages, and the ratio of fuel may be reduced intelligently to the lowest possible rate consistent with the actual requirements of the foundry. Much, if not all, of the annoyance and loss consequent on melting inferior irons, which include large quantities of the meanest machinery, stove-plate scrap, etc., in cupolas of moderate capacity may be obviated by a persistent adoption of the fluxing method. Usually, when large proportions of such iron are melted in the cupolas above mentioned, the heat is short-lived and unsatisfactory; but if a suitable flux is used, the dirt in the iron intimately associates with it and forms a thin liquid slag, which, by means of a slag-hole placed a short distance below the tuyeres, can be run off at pleasure, and so continue the melting uninterruptedly for an indefinite space of time. See CUPOLA.