In order readily to understand the two remarkable properties of malleability and ductility, which are now turned to such good account in almost every branch of the mechanical arts, it will be convenient to think of the malleable or ductile metals, such as lead, tin, copper, 'wrought iron, and steel, as substances that can be moved about like dough, that can be spread out as with a roller, that can be elongated by drawing out with the hands, that can be squirted through a hole by presssure like macaroni, or even that the dough can be pushed or gathered back again into its original mass of dough—that is, if proper means are employed to perform the operation gently, and this may be done without breaking the continuity of the particles of which the mass is composed. Such a statement may well seem fabulous, but it will be my province now to enumerate many things in connection with metal l!I)uch more wonderful tha:n what I have said regarding the ough, and even more strange than the change in dough when overtaken by the biscuit state from the baking process. It is difficult to understand the possibility of the malleable and ductile properties without fully realizing that theirparti- cles are fluid, in a certain sense, and that this is due to the molecular arrangement, not so fluid, as water, tar, or bitumen, but still a fluid which will flow in obedience to sufficient pressure, and just as those fluids require time when acted upon by gravity, so the metals require greater time and more force than gravity, the rate of flow being determined by the nature of the metal, the softer metals requiring less pressure and flowing faster than the harder; and in the case of steel the flow is extremely slow, but with pressure, time, and patience, it also may be overcome and made to flow gently into any shape or form while in the solid condition. For a number of years the flowing property of the softer solid metals, such as lead and tin, has been taken advantage of very extensively, in the squirting of pipes and otherwise ; and for thousands of years the malleable and ductile metals have been under treatment by man, and a vast number of facts have thus been accumulated ; but it is due to M. Tresca, of Paris, to say, that he has done more-,-' p^haps, than any other man in regatd to the investigation of the natural laws by which the flow of solids is governed under varying cir- cum stances, and the most interesting point of all is the great similarity that exists between Ihe flow of solid metal and that of the flow of water—that in the flow of solids from an orifice there are the same converging currents, eddies, and that the qnantity of metal issuing is dependent on the same conditions as water when issuing from orifices of different arrangement, and only differs in degree. From time immemorial man has been familiar with gold as a flowing metal, both as malleable and ductile. It is in consequence of these properties that gold may be beaten into leaves so thin that it takes two hundred and ninety thousand to make one inch in thickness, or it can be drawn into a wire so fine that an ounce weight would extend a distance of fifty miles. The flowing action which takes place in - coining a sovereign or other coilil is very apparent. This process is not the mere stamping which it is generally considered to be, but the particles of the gold have really to flow in the same manner as a liq uid, from one part of the die to another, in order to fill up the deeper recesses of the die from from the shallow part of the space, and so form the perfect coin from the rush of gold penetrating everywhere. As, however, gold is not one of the most common metals of applied mechanics, its presence in the workshop is less seldom met with than some of the others which have bsen already enumerated. The metals lead and tin are both malleable and ductile ,biit their ' malleability, or spreading-out property, is much greater than !their ductility, or drawing property ; and both being eoft, and having the flowing property in a pre-eminent degree, they can thus be squirted or rolled to any extent, or into any form of pipe or sheet, so that the want of ductility is scarcely felt, The diagram (Fig. 1) will explain the nature of apparatus which is employed to squirt these metals when in the solid state. It is a powerful syringe filled with solid metal, with pressure o;]. the piston varying according to the dimensions ; in some the force required is two thousand tuns. In the earlier machines the arrangement was exactly the same as in an ordinary syringe, as shown in Fig. 1, but it was found that the fluid pressure ofthe metal within the syringe created. such an inordinate amount of friction upon the inner surface as to rapidly wea',' out the several parts; but by a slight modification, more in accordance with sound principles, the defect has been obviated. In the arrangement shown in Fig. 2, the piston contains the orifice, and in pressing against the upper surface of the metal, causes it to remain in a state of rest within the containing vessel; but as fluid pressure is equal in every direction, the solid finds the -orifice as a point of less resistance, hence it flows outward in a continuous stream, thereby avoiding the friction of the solid lead within the cylinder. It will thus'be observed that a rod of lead or tin can be squirted of any form or dimensions, depending on the die or orifice. In the Royal Arsenal may be seen lead thus squirted into continuous- rod, and then wound upon reels like yarn. to be again unwound and made into bullets by self-acting compressing machinery ; but the whole of the several processes are entirely due to the flowing property. Man's mechanism is very subordinate, may. be varied to any extent as cir-, cum stances may require, Pipes are made with the same facility as rods, by the mere insertion of a steel pin, the size of the required bore, placed in the bottom of the cylinder, and exactly in the center of the orifice, thus forming an annular space through which the metal flows outward as a continuous pipe ; or, by making this pipe of sufficiently large diameter, and then cutting it open by a stationary knife as it leaves the machine the pipe becomes a sheet of lead, which, by means of suitable rollers, may be wound on a reel as a long web of sheet lead, or the sheet lead may .be rolled out by rollers. In both ways the same mechanical work has to be done ; the respective friction is a disputed point. A very singular result was obtained by an attempt to squilt brass pipes, which are - extensively used as steam boiler tubes and for gasfitting purposes. This brass consisted of 60 parts of copper and 40 parts of zinc, and of various other proportions, but, singular to relate, the pipes so squirted were zinc rather than brass; the most of the copper remained in the vessel and refused to flow. We are not to infer from this that the copper would not flow, but rather that the union between the zinc and the copper was less than the pressure necessary to make the copper flow ; the mixture may have been more mechanical than chemical, or the temperature may have been such as to have had the zinc too near its melting point. Whatever is the explanation, the subject is well worth further experiment. In any such operation, the nearer the lead or other metal is to the liquid state, the easier it is accomplished ; but it must be solid. Lead or tin may be rolled out to any extent, either singly or both combined, or with a thin coating of tin or other metal upon one or both sides of the lead, so as to have a deaden substance, but yet covered with a tin surface, perhaps not thicker, if so thick, as the leaf called tinfoil, thus combining economy, with scarcely any disadvantage, for many purposes. A beautiful illustration of the flowing property of tin is shown in the manufacture of the German capsule, in which the paint for artists is made up for sale and use. A button of tin, as in Fig. 3, is laid in the recess of a die in a :(iy press ; a corresponding punch or die, a little smaller, is then brought down upon it with a smart blow, thus leaving, from the difference of dimensions, an annular space between them, when the metal at once squirts upward like water, but at a velocity much faster than the eye can follow, thus converting it into a perfect capsule. The form of the punch and die depends upon tho article to be made, but. in all provision has to be made for the admission of the atmosphere on the removal from the dies. From these remarks it will he seen that, by understanding a few of the natural properties of these metals, how com” pletely they are under man'^ control, and, by knowing the simple laws, he can modify the apparatus in thousands of different ways, in order to produce whatever may be required.
Malleability and Ductility of Metals
This article was originally published with the title "Malleability and Ductility of Metals" in Scientific American 21, 22, 341 (November 1869)