Oxy-Acetylene Welding of Steel & Iron
There are many different varieties of steel, but from a welding standpoint they may be classified by their carbon content. Those having a high carbon content are called hard steels; those with a low carbon content, soft steels. Wrought iron may be treated the same as mild or soft steel. To be sure, there are various alloys, such as vanadium, tungsten, nickel, manganese, chromium, etc., but in general these alloys will not seriously bother us, except in special instances and we will not take them into consideration, but will keep in mind whether the steel is soft, medium or hard.
Soft or mild steel is in the widest use. More than any other metal, the welder will have to study it, since from previous understanding or training he has learned that it is the easiest metal to weld; whereas, it is by all means the most difficult and frequent failures result if the operator lacks certain elementary knowledge of it. Mild steel is very ductile-it may be hammered cold or hot without fracture, and this fact is an invitation to the careless workman to disregard the effects of expansion and contraction.
We should bear in mind, then, that while it may not break, it will bend or distort, unless we take into consideration expansion and contraction, and we are very likely to have failures or leave a strain in the weld or in some section of the article· welded, which will break while in use. Since the metal is ductile, it is not necessary at all times to preheat it in order to offset expansion and contraction, we may bend certain sections before welding, with a view of having the contraction straighten them and thus allow for contraction ; we may use water or heat resistant material, clay, etc., to LIMIT the expansion, these methods are sometimes essential, where we cannot preheat, due to size or location of the weld, but in all cases, where we may do so, the proper way is to preheat. Where we cannot do so, we will choose one of the other methods, but ALWAYS we must allow for expansion and contraction. Previously we have spoken of the danger of oxidation and de-carbonization. The oxidation, or we might say burning, of steel is very rapid, if we in any way neglect essential requirements, chiefly the proper adjustment of the torch to secure a neutral welding flame, a welding rod without injurious elements and the proper handling of the torch. De-carbonization is caused in the steels but not particularly mild steel, if we are reasonably careful. But particular care must be taken to adjust the welding flame to secure a neutral flame and to keep it neutral during the welding. Make sure you understand this.
Oxy-Acetylene Welding of steel & Iron : Preparation of the Weld
Particular care must be taken in beveling steel to see that the V is especially wide. We are not able to burn out this V with the torch, as we are sometimes able in other metals, since to do so means severe oxidation or burning. On metal under one-eighth inch no beveling is necessary.
The proper preparation will depend largely on whether we are constructing or repairing. If we are welding new sheet metal, for instance, we may butt the edges and make what is termed a “flash” weld , using no welding rod. Such a weld will naturally not be as strong as the material, since it will not be as thick.
Or we may upset the edges, and these upset edges take the place of the welding rod and melt down. As the metal becomes thicker, this is impractical, and we then bevel it. Use a welding rod approximately of the same material as the metal welded, being sure it is of the right quality, however. No flux is necessary on mild steel and torch should be held in the position previously described, particular care being given to the necessity of having the flame directed to BOTH edges of the material. Much of the mild steel welding done is impractical to preheat, and a frequent mistake of the beginner is to too quickly try and start fusion. To avoid this, we first play the torch in a gradually decreasing circle, with the end of the cone just a short distance from the surface, until the metal becomes red in the vicinity of the weld for a distance about three times as wide as the metal is thick.
Then we bring the cone down until the end of it just touches the surfaces to be joined. Note, this carefully, since steel is the ONLY metal with which we bring the cone INTO ACTUAL CONTACT. On all other metals we hold the cone a little distance away. Do not make the mistake of bringing the tip of the torch to the metal, hold the torch so that the end of the cone just LICKS the surface.
As the bottom of the bevel melts together, the welding rod is brought down until it touches that spot and a small portion of it is melted while. it is in contact with the material. Now, we fuse this small portion to the material by a short circular motion, making sure that the flame actually comes. into contact with every portion of it and that it is thoroughly fused to the material and that it has penetrated. As we finish the circular motion, we start melting the spot immediately adjoining. Unlike cast iron, steel does not remain a liquid, it solidifies almost the instant the flame is removed, and it is for this reason that we are able to weld it in a vertical or overhead position, as well as horizontal.
If there is an excess of sparks, the flame is improperly adjusted and contains an excess of oxygen. If the metal melts too rapidly and is difficult to control, the tip is too large. If it does not keep in fusion and there is difficulty in getting the welding rod material to actually fuse to the article, the tip is too small. The beginner will be troubled with the welding rod sticking to the metal-don’t attempt to pull it away; let it stay there until it is necessary to melt a portion of it in the weld.
Steel welding on a commercial scale should not be attempted until after the operator has proved to his own satisfaction that the weld is strong by welding together mild steel plates of one-eighth to one-quarter inch, sawing them through the weld to make sure that the material is really bonded and testing them by bending back and forth. The practice of twisting several pieces of wire together to form a welding rod is not a good one, since this exposes more surface to oxidation or burning and for the same reason have the rod in contact with the material welded as it is added to the weld, so the article will prevent burning by its. ability to conduct the heat away from the rod.
In welding two pieces of unequal thickness, we must bear in mind suggestions previously given, that the large piece requires more heat than the smaller one, and that care must be used to cool equally to prevent strains.