Brazing Cast-iron.
—Although it has been dogmatically asserted both that cast-iron can and cannot be brazed, it may be stated that the general results of attempting this process are so indifferent as to warrant the conclusion that this process cannot be recommended. In brazing, one of the conditions essential to success is that the metal to be brazed and the spelter should unite to form an alloy just where the brazing occurs, and that this should take place spontaneously. This actually happens when brazing copper, brass, wrought-iron, etc., but not in the case of cast-iron. If, however, the reader desires to experiment in this direction, the following hints may be useful. First of all, remove all dirt and grease from the cast-iron, and then chemically clean it by immersion in hydrochloric acid, afterwards well rinsing it in clean cold water. A mixture of borax and water and spelter should now be applied where the brazing is required, and gentle heat then brought to bear on it until the water is evaporated. The heat should now be increased until the casting is red hot in the neighbourhood of the brazing; and some workers claim that at this juncture the best results are obtained by dusting the red hot cast-iron liberally with boric or boracic acid powder. A hard spelter should be used in preference to a readily fusible one, otherwise the spelter would be fused much too soon, and before the casting is raised to a sufficiently high temperature.
An experienced worker who believes that it is possible to make a sound joint in cast-iron by brazing, states that he has brazed articles with equal parts of borax and boracic acid. The chief difficulty is the flux. He has tried one called “Ferroment,” which seems to give good results. The first casting brazed with it was 3 in. wide and 5⁄8 in. thick, and this casting at the time of writing had been in work six months for fifteen hours per day. This same worker prefers to roast borax before use, as it stops on the work better. Also, when a deep, wide joint is being dealt with, he finds it an advantage to smear on a little clay underneath and the side, as should the joint get slightly hotter in one part the spelter will run through and make an unsound joint. The heat required to braze cast-iron varies somewhat with the spelter used. If brazing by means of a smithy fire, the spelter will show a blue flame when it starts to run, and the article must then be removed from the fire. In using a blowpipe or blowlamp, the blue flame does not show, and one has to look for the spelter melting, and see that it flows well along the joint before removing the flame. Spelter which has been kept in stock a good time may not flow well. The worker in question prefers brazing wire to grain spelter, as by means of warming the end of the wire and dipping in the flux (which will adhere to the hot wire), it may be put just where desired. He collects all the soft brass turnings from his lathe and uses them for brazing.
Another worker has stated that those who have a forge of any kind will find the following an effective method of repairing an iron casting. A flux may be made of chlorate of potash 4 oz., boracic acid 1 lb., and carbonate of iron 3 oz. These should be mixed well together and pounded. The parts to be brazed together should be carefully cleaned by scraping them, and brought to a bright-red heat. Then apply the flux and spelter and increase the heat.
Still another worker says that in brazing cast-iron, if powdered soda is used instead of borax, the result will be a perfect joint.
CHAPTER XI
Welding Iron and Steel under the Hammer
Iron and steel can be joined by heating until they become plastic and then consolidating the two members of the joint by hammer blows, the work being supported on an anvil. Correct heat and cleanliness are the chief requisites. The “welding heat” corresponds with that temperature at which the metal is in a state of partial fusion on the surface. The better the quality of the iron, the higher the temperature it can stand without being burned and ruined. Iron at a welding heat gives off dazzling sparks, whereas ordinary cast steel is only an intense yellow, but few sparks being evolved. Sufficient lap for the proper making of the joint must always be allowed. When heated in a perfectly clear fire, the metal may need no treatment prior to hammering; but otherwise it may be necessary to sprinkle sand or some special flux over the work. At the proper moment the iron is transferred to the anvil, and the union of the two members of the joint immediately effected; delay means an imperfect joint. In lifting the work out of the fire, remove it vertically and so as not to collect particles of dirt on it. Keep a switch of brushwood at hand for removing adhering matter.