Ordnance experts and military men generally have lately been much interested in a new method of making projectiles. This is the Electric Welding Process, used by the American Projectile Company of Lynn, Mass., and from the success so far achieved, it certainly seems that an important step in advance has been made in the manufacture of steel shell.
The American Projectile Company was organized a little more than a year ago to engage in the practical manufacture of all kinds of projectiles, and having been given contracts by both the navy and army, have, since that time, equipped their shops with the necessary special plant and are now, after a great deal of experimental work, manufacturing on a regular business basis.
All ordnance experts well know the tedious and difficult processes at present used in producing the different kinds of forged steel projectiles. Steel castings for this purpose having long since been abandoned on account of the difficulty in obtaining the desired results and the expense of the castings themselves, it has been, up to the present time, a question of high grade and expensive armor-piercing projectiles and ordinary cast-iron ones for common use. It has been rendered possible, by the invention of electric welding, and is now one of the aims of the American Projectile Company, to produce a forged steel shell at about the same price as it now costs to manufacture the common cast-iron projectile. This is accomplished in the following manner:
1. Hollow Steel blooms are cast and from them is rolled out a thick-walled tube, having the approximate finished dimensions of the body of the shell. This is then cut into suitable lengths, and to the short blanks thus made are joined, by electric welding, the head and base of the projectile, which have been previously formed in suitable dies. After this is done, the only machining necessary is turning to gauge on the outside, cutting the rotating band-score and the fuze thread and seat. This projectile is afterwards hardened, and thus is produced in this very cheap manner a thoroughly efficient wrought-steel shell. It will be understood that this is not the high grade armor-piercing shell, but a shell that can be used very efficiently against armor of moderate thickness, and will in other respects fulfill the offices of the common shell, at the same time costing no more than the cast-iron now in use. This, of course, is a very important feature, as it will enable the Government, without any additional cost, to fill the magazines with this much better grade of shell, which may, in time of peace, be used for target practice, etc., and still be on hand for efficient service in case of war. The company are now filling two large contracts for the navy for shell of this character—one for 30-pound projectiles for the 4" rapid-fire gun and the other for 6" common shell.
Figure 1 illustrates the formation of this projectile, although in this illustration the midships section of tubing should be longer and the head and base pieces proportionately short. To understand the simplicity of the welding operation, it must be understood that it is only necessary to place these three pieces in contact, one above the other, in an electric welding machine designed for the purpose, and by means of the electric current, which is passed from one pole to the other through the joint which is to be made, the metal at this point is quickly heated to a welding heat, and being kept in close contact by mechanical pressure, so unites at this point as to become homogeneous and equally strong with the rest of the metal. The surplus metal, or burr, formed by the pressure, is mainly forced upwards and is removed in the operation of trueing the body of the shell. The operation of electric welding is so simple that it requires no expert to operate the machine, as any intelligent man can be taught in a very short time all that is necessary to produce a weld impossible in any other way. Furthermore, it is feasible to weld the highest carbon steels, steels that are absolutely unweldable by any other process, one to another, or to weld a high carbon to a low-grade steel, or even to wrought-iron. The importance of this in projectile manufacture will be understood when it is seen that the head of a projectile may be made of high grade expensive steel, and as much of the balance as desired of cheaper, softer material. One who understands the difficulties of obtaining a perfect weld when the metal has to be heated in the blacksmith's fire, will fully appreciate the great advantage obtained by this method, where the metal stands fully exposed to view in the open air and comes in contact with no impurities whatever, where the heat can be checked at any desired moment by the simple movement of a lever, and regulated as easily as the turning off or on of steam or air pressure.
These remarks apply to the ordinary operations of welding, but of course there are many forms which are practically impossible to the smith, and among them the tubular sections used in the manufacture of projectiles. The following will illustrate the strength of a weld of high carbon steel:
A six-pounder armor-piercing shell, fired at a recent test, slapped or "key-holed" slightly on striking the plate. It, however, passed through a 4-inch iron plate whole, and when recovered it was found to be slightly bent directly at the region of the weld. The snap, as the shell straightened itself in the plate, had been so great that the square head of a brass plug, which was screwed into the fuze-hole, had actually been broken short off by the blow, leaving the threaded portion in the hole. Of course, this great strain, as shown by the bend, came directly on the section in which the weld was located, and this showed not the slightest sign of fracture.
The armor-piercing projectiles of this size are being manufactured in two pieces, as shown in figure 2, and in section in figure 3. In this case no tubing is used. Figure 4 shows one of these projectiles that has been fired through a 4-inch armor-plate. One of the marked peculiarities of these armor-piercing projectiles is the following:
The head section is hardened uniformly all over; the base section is not hardened at all. When the two pieces are joined by the electric welding, one of the features of which is limiting the heat to a short distance on either side of the joint, the shell is placed with a portion of the head in cold water, and thus the heat from the weld draws the temper gradually toward the point, thus leaving the base unhardened, and from it tapering to the necessary hardness at the point. Aside from this simple method of drawing the temper gradually toward the point, it will be seen that the hardening of the head alone is a very much less difficult operation than heating and hardening the whole projectile; also, that temper-cracks and other defects may be very easily distinguished in this portion of the shell before the base is welded on. This is considered one of the very important features covered by the patents of this company.
Another style of projectile now being manufactured is the shrapnel, for the army 3.2-inch field-piece, illustrated in section in figure 5 and in detail in figures 6, 7, 8, 9 and 10—figure 6 being the head forging, figure 7 the tubular midships section, figure 8 the steel diaphragm and central tube, forming, respectively, the powder chamber and the passage from the point fuze to it; figure 9 the base forging, showing the shoulder on which the diaphragm rests, and figure 10 the copper rotating band, which is afterwards shown pressed on the shell in figure 5. The method of making this shrapnel is as follows:
The base piece and tube, figures 9 and 7, are placed in contact in the welding machine and joined together, forming a deep cup; while the weld is still hot, the diaphragm and tube are dropped into it so that the former rests on the shoulder of the powder chamber. The weld is then lightly swaged, thus locating the diaphragm firmly in place. Next the head forging is placed in contact with the open end of the tube and with the small central tube passing into the fuze-hole. This is then similarly joined by an electric weld. Afterwards the upper end of the small tube is crimped over a slight shoulder in the bottom of the fuze-hole. The outside of the shrapnel is then turned to gauge. A small hole is drilled in the head, communicating with the interior cavity; through this the shrapnel is filled with the necessary bullets; next the matrix is poured in, and finally the hole is closed by a small plug which is screwed into place. Before the case is filled with the bullets and matrix it is hardened to give increased rigidity to the thin walls and to increase the number of fragments into which the case will burst. In trial, these shrapnel have given most excellent results.
So far, the largest shell being manufactured by the American Projectile Company are the 6-inch naval common shell above referred to. These weigh, empty, 94 pounds, and have an outside diameter of 5.96 inches, with a thickness of wall of 0.95 of an inch. It is expected, in the near future, that the company will undertake the manufacture of very much larger projectiles, as the only limit seems to be the possibility of obtaining the necessary tube, and arrangements are now being made to have this produced of the necessary dimensions to make as large as 12-inch shell.
It is believed that projectiles of the character described in the beginning of this article will be peculiarly adapted for use in mortar service against deck armor, etc., as they will have all the advantages of armor-piercing projectiles for penetrating that thickness of armor, and can be produced at a fraction of the cost of the more expensive missiles.
In conclusion, a brief description of one of the welding machines may be interesting. Figure 11 shows one devoted to small size projectiles, such as the 6-pounder armor-piercing and common shell. It stands high from the ground to enable the operator's helper to place and remove the shell being operated on from beneath. After placing the separate pieces of the shell in the machine from the under side, a movement of the hand-lever in front of the operator throws in a set of hydraulic contacts through which the electric current passes to the portions of the shell they enclose. This current is obtained by transforming the primary current of 200 volts and about 250 amperes into a current of ½ a volt and consequently enormous quantity. The current is perfectly controlled by a switch, operated by a foot-lever and in connection with a reactive coil. To carry this great current, heavy copper castings are necessary, which are kept cool by water-jackets and a continuous circulation of water. These water connections, for cooling and for pressure purposes, are shown by the numbers of pipes and tubes at the top of the machine. To give the necessary pressing together when the shell is at the welding heat, another hydraulic cylinder is provided. This is controlled by a lever conveniently placed. After the weld is finished, the assistant quickly carries the shell to a small hammer, where the burr is lightly swaged. It is then placed, head downward, in a shallow vat, to keep the temper from drawing out of the point.
The general construction of all the welding machines is extremely simple, the only thing requiring any particular care being to insure proper electrical contacts on the shell. This cut is taken from a photograph, and shows the operator holding the freshly-welded shell on its jig. This will give an idea of the local limit of the heat after the weld has been made.
In welding larger projectiles, another style of machine is used. This is illustrated by Figure 12. In this case the parts to be welded are placed upon the head of an hydraulic ram, which moves them upward into position as shown. The electric connection in this case is also made by hydraulic plungers in electrical connection with the induction coils, and they are caused to move in or out by means of a valve operated by the T-shaped handle shown near the top. A foot-lever actuates the switch, as in the smaller welding machine and a hand-lever shown on the right of the machine controls the upward pressure. The work at present being done by this machine is a section of eight square inches per weld, the operation being completed in 3 ½ minutes.
In describing the tubular shell of the 4-inch type it should have been stated that these projectiles have already been successfully tried against thin armor and have exceeded in results what was expected of them.
A great number of special machines and appliances necessary for making this business a practical and financial success have been designed by Lieutenant William Maxwell Wood, U.S.N., who is also the inventor of this system of manufacturing projectiles.