Oxy-acetylene welding manual

by Lorn Campbell

Part One.—STEEL WELDING

(83) The term “steel,” as used in the following pages, unless otherwise specified, will be the term applied to wrought-iron and low-carbon steels. High-carbon and alloyed steels are to be considered only in advanced work and will therefore not be deemed a topic of interest to the beginner in laying his foundation.

(84) The welding of steel is much more difficult than cast iron on account of the many points which must be observed. In cast iron the metal is brought to a molten state and may be worked in that condition for some time without any apparent change in the characteristics of the metal. A flux is used to break up the oxide or scale and the metal will flow very easily. The flux is necessary because the oxide has a higher melting-point than the iron itself. When working on steel, it will be observed that just the reverse is true, that its oxide has a lower melting-point than the steel and consequently no flux or cleaning powder is necessary when working upon it.

(85) A large quantity of steel kept in a molten condition by the flame acting upon it is very easily influenced. The same area is not kept in a molten condition as with cast iron. The heat does not hold to the vicinity of the weld nearly so much as in cast iron because of the greater conductivity of the metal. If the flame is removed, the molten metal will set almost immediately. This means that the flame must be in contact with the metal at all times. It must be a strictly neutral flame or else one of the two gases will be introduced into the weld and its strength will be materially affected. The size of this flame must be such that too great an area will not be covered, yet enough must be covered to keep the metal along the line of the weld in a molten condition. If a carbonizing flame is used, one which has an excess of acetylene, such as was shown in [Fig. 23], much carbon will be taken up by the metal, producing a brittle weld. If the flame is oxidizing, that is, contains an excess of oxygen which is noticed by the shortening of the flame and an accompanying hissing sound, [Fig. 25], the metal will burn and a white foam will appear on the weld like a milky white glue. This tends to weaken the weld. This same effect will be in evidence if too large a tip is used. On the other hand if the tip is too small not enough heat is obtained and the oxides and other impurities which may be present will not be allowed to float to the surface but will be trapped in the weld.

(86) The filler-rod used on steel should be as near the same grade, if not better than the metal to be welded and should be very low in its carbon content. A pure grade of soft iron wire or mild steel will make a very good filler-rod for ordinary purposes. The size of this filler-rod is very important, for it should fuse at the same time as the metal being worked upon, and unless it does this the weld will not be satisfactory. If the filler-rod is too large it will not be at the fusion point when the work is, and will not fuse with it. If the rod is brought to a melting-point the work will have too much heat and will burn. On the other hand, if the filler-rod is too small, it will burn up before the work is at the fusion point, or in other words, the work will still be too cold when the rod is melted.

(87) There are many different methods of executing a steel weld, and it has been noted that very few experienced welders handle their steel in the same manner. Most of these methods are very difficult to learn and can be perfected only after years of practice. However, a simple method which will produce results is thought the most advisable for the beginner. A careful examination and study of this point has brought out the following method, which is very easily picked up and which dispenses with most of the torch movements that are generally advocated by the old time welders.

Fig. 57.—Preparing and Heating Steel before Welding.

(88) When welding two pieces of steel bars, the cross-section of which will measure one-half inch by three inches, they are beveled off and prepared in the manner illustrated in [Fig. 57], either by means of a chisel, file, or by the use of a grinding wheel. About an eighth of an inch of the original stock is left on the bottom side and the angle formed from these two places when brought together, should be 90 degrees. When the pieces have been prepared and placed in the position shown in the illustration, the neutral flame is then brought down at right angles to the plane of the metal, so that the end of the cone will just lick the surface. It is moved up and down upon each side of the part to be welded until each piece is brought to a red heat, for a distance of at least one inch back. The position of the torch during this operation can be seen in [Fig. 57]. From this time on, the operator should work as rapidly as possible, for the quicker the fusion of the metal is brought about, the less oxide or scale will appear and a better weld will result. The description of this process may take some length but the actual fusion not nearly so long.

Fig. 58.—In Welding Steel, the Beginner Should Fuse His Pieces together along the Bottom with the Torch Flame, Adding no New Metal. The Metal on Both Sides of the Torch Flame is Melted together until a Small Pool of Molten Metal Appears, then the Torch is Twisted Smartly away, as Shown by the Arrow, and the Metal Allowed to “Set” for an Instant before Proceeding along the Line of Weld.

Fig. 59.—Method of Adding “Filler-rod” in Welding Steel. Note that the Rod is Worked behind the Flame.

(89) When the red-hot stage is reached, the neutral flame is brought down to the very lowest part of the “V” at the side nearest the operator and held there until the metal has melted and is about to collapse. The flame is then quickly twisted away for just a second to let the metal set. Perhaps this operation will fuse about one-half inch or less along the bottom of the “V.” This same operation is repeated along the line of weld until the whole piece is fused along the bottom. It will be noted that no filler-rod has as yet been used. After the last portion has been fused, the flame is brought back to the starting-point and played not only on the bottom, which has already been fused, but on the sides of the “V” as well, bringing an area of about one inch in diameter to a molten condition. The tip of the welding torch is held in a vertical position all this time to introduce as much heat into the weld as possible. During this operation the filler-rod, which should measure three-sixteenths or one-quarter inch in diameter, is picked up by the operator’s free hand and its end brought near the heat of the flame so that it may be warmed and will not chill the metal when introduced into the weld. When the melted metal is running freely, the tip of the welding torch is slowly inclined in the direction of the part to be welded and is advanced along the “V-ed” out portion at this angle as rapidly as the metal can be made to melt. This position is shown in [Fig. 59]. It will be noted that as the flame advances along the line of the weld the molten metal will mount up behind it of its own accord, providing the metal is in a molten condition, when the flame passes over it. During this period the filler-rod is stirred into the molten metal in a circular movement which should be in back of the torch as much as possible. This means that the torch comes in contact with the filler-rod but very little and the rod is melted, not by the flame, but by the molten metal of the piece being welded. It will be noticed at times, when too much metal has been welded and the torch is not advancing rapidly enough, that some of the molten metal will run ahead of the flame, into that part of the “V” yet to be fused, and to the unwary student this will be looked upon as a safe place to add his filler-rod. However, when the piece is broken and the cross-section of the weld examined, it will be found that in this part of the weld, the metal has only been laid on and not fused. The beginner should watch this operation and see to it that this molten metal is not permitted to run ahead of his torch, an act which he can overcome by the proper manipulation of his filler-rod, which really governs all the melted metal behind the flame. If not enough metal has been added to fill in the “V” to the proper thickness, this operation can be repeated until enough metal has been added. By practicing this method the student can be taught to execute a very successful weld and reinforce it all in one operation without any chance of burning his filler-rod or lapping his metal. More practice is required to successfully weld steel than most other metals and the beginner should not be discouraged if it takes him some time to conquer this metal. It should be forcibly impressed on the student that the metal must be in a molten condition before the filler-rod is added, or else it will stick and prevent his working readily and in addition will produce a very faulty weld. Fusion is the thing to bear in mind for without it success cannot be expected.

Fig. 60.—This Method of Adding the “Filler-rod” when Welding is not Recommended for the Beginner.

(90) While outside appearances should not be considered as a prime requisite, when beginning it is always well to add more metal than is really necessary in order to reinforce the weld as much as possible. It cannot be expected, however, that a steel with the same cross-section as the original will possess the same properties and be as strong, for a weld is only a casting unless treated otherwise and the steel or wrought iron used in the specimens is of rolled stock. If too much metal has been added and dressing down is necessary, the student will find that by using a slightly oxidizing flame the surplus metal can be burnt away very rapidly and a very good-looking job can be executed much more rapidly than if a neutral flame were used. It is well to remember, however, that this is used only in dressing off pieces and in places where the strength of the weld is not to be jeopardized.

(91) When advancing in steel work, it will be noticed that the same provision for contraction and expansion is not considered in as great proportions as on cast iron, and the reason is quite evident. In cast iron we find the metal is very brittle and will not give without breaking, whereas on steel it is more ductile and will twist and bend before breaking. This does not mean, however, that the important points of expansion and contraction are to be neglected in steel work, for they are very important, as we shall see later on.