| Here are five methods, any one or all of which may be used to learn thenature of common castings which might confuse the welder. | ||||
| No. | Test. | Malleable Iron. | Cast Steel. | Cast Iron. |
|---|---|---|---|---|
| 1 | Outside Appearance. | Generally smooth and free from all sand, weighs about same as cast iron. | Rough surface with sand in evidence, weighs much more than cast iron. | Surface fairly smooth but generally shows some sand. |
| 2 | Cross-section Test. | Ring of bright steel crystals outside, with darker iron crystals inside. | Large, bright, luminous, silver crystals. | Fine, uniform, dark gray, crystals. |
| 3 | Emery Wheel Test. | Few steel sparks and then iron sparks from interior. | Bright, luminous sparks that break in falling. | Dull red sparks that do not break. |
| 4 | Chisel Test. | Surface will curl and interior break off. | Will curl before breaking. | Will chip off. |
| 5 | Torch Test. | Gives way before flame and delivers few sparks. Metal becomes porous. | Gives forth bright sparks that break in falling. | Gives no sparks except where there are impurities. |
Fig. 43.
(68) The metal in the filler-rod should be the same in practically all cases as the metal to be welded. There are few exceptions to this rule, but the principal one is that of malleable iron. The cast iron in the rods is of a very good grade and generally much better than the piece to be worked upon. To permit the ready flow of the rod and eliminate oxidation, as much as possible, three per cent of silica is generally used in the casting of filler-rods for cast iron welding. Piston rings and other scrap iron should not be used for filler-rods, as they contain many impurities such as core-sand, dirt, grease, etc., which will ruin the weld. It is disheartening to see some operators attempt to economize on the filler-rod. It is not an uncommon sight to see several dollars’ worth of gas and the same amount of the welder’s time, together with a few cents’ worth of filler rods all lost, and the operator’s reputation ruined. This, because an attempt is made to save the few cents involved in the filler-rods by substituting a rod of a very poor grade.
(69) A flux is not used, as many suppose, to cement the filler-rod to the metal. It is used purely as a cleansing agent and may be likened to the acid used in soldering. It does not act on the metal until the latter has reached the melting-point, but then it starts to break up the oxides and clean the surface. This action permits the metal to flow together more readily. A cast-iron flux is always used in welding cast iron, to break up the oxide, because the cast iron itself will melt before the oxide and no matter how hot the metal is it will not flow together as long as this oxide is present.
(70) To obtain the best results, reliable fluxes should always be used. Occasionally an accident will happen to the flux can, when the operator is on some isolated job and a substitute flux must be obtained at once. Equal parts of bicarbonate of soda (cooking soda), and carbonate of soda (ordinary washing soda), may be purchased from any grocery in the powdered form and mixed together thoroughly. This will tide the welder over until he can return to the shop and replenish his supply.
Fig. 44.—Whenever Possible, the Beginner should “V” His Work, and Complete His Weld from One Side only. On heavy work, however, it will be necessary to “V” out from both sides, as is here shown.
(71) The flux is generally applied by means of the filler-rod. One end is heated and dipped in the flux; enough will adhere to break up part of the oxides, on the ordinary-sized job. The flux is carried to the work, which should be at the melting-point and introduced between the flame and the metal. Oxides will break up immediately and the metal will flow together, but it must be remembered that the flux has no action on cold or moderately heated metals. The flux as has been explained is used to clean the metal and break up the oxides. To the oft-repeated question, how often should the flux be applied, answer is made as follows: As often as it is necessary to clean up the metal and break up the oxides. All fluxes should be kept in airtight containers when not in use, to keep their chemical contents in the very best condition and it is best to use only a small quantity of flux on the welding table at one time.
(72) Oxy-acetylene welding is purely a fusing process and the most important points to remember in executing a weld are, to eliminate the entire crack in the fracture and to add the filler-rod without changing the character of the metal. On thin pieces of metal it is possible to depend upon the force of the flame to entirely penetrate to the depth of the crack but on work three-eighths of an inch thick or over, it is well to “V” out or remove some of the surface metal around the crack in order to get down to the bottom. By “V-ing” we mean to chip or grind off each edge at an angle of approximately 45 degrees, so that the opening will form an angle of 90 degrees where the two pieces come together, with the crack at the bottom portion of the “V.” This should NOT be ground down to a knife edge, for it will readily burn up. It is preferable to leave about one-eighth inch along the line in order that the pieces will fit together and the proper alignment may be obtained. If two pieces of cast iron have been prepared in this manner the neutral flame of the welding torch is brought down in such a manner that the tip of the cone just licks the metal. The heat is not applied directly to the line of weld to start with, but rather to the surrounding part. This is done in order to get the entire locality in a condition which will not withdraw too much of the heat from the line of the weld, once the fusing is begun. If it is found that the tip will not produce enough heat to bring the metal to a red heat in a fairly short time, a larger tip should be used.
