similar pieces not hardened. The effect of hardening is thus ascertained. 6. Forging tests. This is used for rivet rods. One end of the rod is heated to a red heat, then flattened with a hammer. If any small cracks appear this indicates red shortness. 7. Welding test. A bar one square inch in cross-section is heated to a white heat, then upset and drawn down to the original thickness with a ten-pound hammer. Neither flux nor water should be used. The bar is then tested in tension. 8. Quenching test. Heat the steel bar to a cherry red and plunge in water at 80° F. Then bend the bar around the curve 11⁄2 times its diameter. No cracks should appear on the outer part of the bar. CHAPTER IV. Shop and Mill Inspection of Iron and Steel. Shop Operations. Following are the main operations to which iron and steel are subjected in a structural shop and to which the shop inspector should pay considerable attention: Straightening, marking off and punching, second straightening, reaming, assembling, second reaming, riveting, facing, boring, finishing, fitting up, oiling, painting and shipping. The shop inspector must be provided with a set of working drawings, a bill of materials and a copy of the specifications. He must also see that all material is straight before and after punching; otherwise the riveting will be deficient, with loose rivets caused by the spring of the bent parts. The inspector should also examine the punch dies occasionally to see that the edges are sharp and unbroken and that the difference in diameters between the upper and lower dies does not exceed 1/16 in. The shop inspector must examine all dimensions of finished parts, must see that all rivets and bolt holes are in their proper places and must make sure that all field connections match. He must see that all errors are corrected at the shop. Connections to be riveted in the field may be checked by assembling the parts in the shop, or by reaming both parts in succession to the same template. Drifting should be used only for bringing pieces together preparatory to riveting. After part of the rivets are in place, drifting may injure plates and rivets by causing distortion. Pieces should be kept together preparatory to riveting by means of a sufficient number of temporary bolts. The inspector should also see that parts inaccessible after riveting are painted at least one coat of paint, and that all stiffeners fit tight and good. After riveting each rivet is tested to see that it is tightly driven and that the head is properly formed. In boring and facing the inspector must see that all pin holes are of the proper size and at the proper distance centre to centre. He must also see that the ends of pieces are properly planed to the required bevels and that the lengths of milled end pieces are correct. The shop inspector marks for identification all the pieces approved by him. This is done by causing some mark or initial to be impressed on all parts approved by means of a special inspector's hammer. A circle of red paint around the mark will make it easily to locate. ADDITIONAL SHOP AND FIELD OPERATIONS AND THEIR EFFECT UPON IRON AND STEEL. Heating. Cast iron of average quality is slightly affected by heat below 900° F. At a red heat it looses only one third of its strength. Wrought iron and steel loose no sensible portion of their ultimate strength up to about 500° F., but beyond this point the strength decreases rapidly with the increase in temperature. At 800° F., both steel and wrought iron may lose one-fifth of their ultimate strength. Welding consists in joining together two pieces of metal with the aid of heat and that of hammering, and with or without the use of a flux. Wrough iron is the easiest iron to weld at a white heat. Steel is less weldable than wrought iron and it becomes less and less capable of welding, the higher its carbon content. Cast iron is not weldable. Welding weakens the cross-section of a bar at the point of weld, and for this reason it is often specified that no welding shall be allowed in any steel that is used in main steel structures. A welded bar of steel or wrought iron may have in the weld as little as 60% of the strength of the original solid bar. Forging consists in raising a metal to a high temperature and hammering it into any desired form. The metal must not be overheated or burned. Overheating lowers both the tensile strength and the ductility. Steel is more affected by overheating and therefore requires more care than wrought iron. Either metal, however, when heated fully, should be quickly worked, as working at a cool stage is injurious. Steel or iron worked at a blue heat, or at about 600° F. becomes "blue short" or brittle, being too cold to be hammered. A simple way to tell when a bar or plate is too cold to be hammered, is to press against the metal a piece of wood or the end of the handle of the hammer. If the mark thus made on the metal will not glow, the piece must be reheated. Hardening consists in heating the metal to a red heat and then in cooling it rapidly, by plunging into oil, water, brine or molten lead. The quicker the heat is extracted the harder will the metal be. Oil extracts the heat slower than water; water extracts the heat slower than brine. Hardening increases the ultimate strength as shown by tests if the load is slowly applied. Hardening also increases brittleness. In order to make the metal tough enough for use after hardening, it has to be subjected to the operation of "tempering." Steel with 40% carbon can be hardened sufficiently to cut soft iron and maintain an edge. Tempering consists in reheating a hardened piece of metal to a certain point and then allowing it to cool by plunging it into water. When a hardened steel bar is reheated, the hardness decreases as the heat increases. In the same time various colors due to oxides appear on the surface of the steel with increasing temperature and by means of these colors, the heating may be stopped at any desired point and the corresponding hardening can thus be obtained. Beginning with the cold metal, the tempers of different colors are sometimes described as follows: Light straw Light brown or pigeon wing Dark blue Used for files, lathe-tools, etc. Used for drills, reamers, taps, etc. Used for axes, hatchets and tools. Used for springs. Both tempering and hardening cause an increase in the elastic limit and ultimate resistance, and a decrease in ductility. Both processes are generally used in making steel wire and tools, but very seldom in structural work. Annealing consists in heating a metal object throughout to a high and uniform temperature, and then allowing it to cool uniformly in the air. For annealing purposes the steel is generally heated above 1000° F. It is then allowed to cool in the air or under a muffle, or it is kept in the heating furnace, but the temperature of the same is gradually reduced. This last method gives as slow a cooling process as may be desired. The object of annealing is to make the metal uniform. in density throughout. When a piece of iron is hammered, bent, or upset, the uniform density of the metal is considerably changed at various points and internal stresses are the result. Annealing causes the various minute particles of metal to readjust themselves, thus reducing and perhaps totally excluding internal stresses. All pieces that have been hammered, bent or upset, should be annealed. Punching and Shearing. In both these operations the metal is subject to shearing forces, and therefore the effects. are practically the same. Punching and shearing in iron and steel cause an increase in the elastic limit with lower ductility and lower ultimate strength; consequently both processes injure the strength of the metal. In punching and shearing minute cracks are started at the edges of the metal. These cracks are injurious as they may extend within a short time and become dangerous before being discovered. They also reduce the ultimate strength. In the same time the disturbance caused by shearing hardens the sheared edges and this explains the loss of ductility and the increase in elastic limit. It is evident from the nature of the shearing process, that thinner plates will be less injured than heavier plates. Also, if punches, dies and shears are maintained in a sharp condition. the metal will be more cleanly cut and there will be less cracks started. The injurious effects caused by punching and shearing can be removed by annealing, reaming or drilling. For reaming and drilling, the rivet holes are punched in. smaller in diameter than the finished holes; then by means of a cutting tool or a drill 1/16 in. is removed all around the hole. In case of sheared plates remove 1/16 in. all along the sheared edges. Reaming removes almost entirely the injurious effects caused by punching or shearing and in this respect is superious to annealing. Wrought iron and soft steel are less affected by punching and shearing than the higher carbon steel. Upsetting is the operation of thickening an iron bar by hammering back against its end. Upsetting is used in making eye bar heads. The end of the bar is hammered, then flattened, and finally a pin hole is drilled through. In riveting the shank or body of the rivet is upset to fill the hole completely and then to form the new head from the remaining metal. In all cases of upsetting the metal to be upset must be heated and worked at a temperature high enough to cause a flow without bending or folding. With proper care upsetting gives satisfactory results. Caulking. When two pieces of metal are riveted together, the operation of hammering down the edges of one of the pieces in such a manner as to make them slightly penetrate into the other piece is called caulking. (Fig. 9). Caulking is an approved process in boiler and tank work and is applied to both rivets and plates, in order to secure water tight joints. For this purpose a narrow, blunt chisel-like |