BRAZING.
After the drop forgings or stampings are carefully finished by hand or machine, they are carefully cleaned to remove any scale or oil. The tubes having been cut to a proper length, are then closely fitted into the open joint of the forging or stamping connection. In order, however, to hold them securely in place they are pinned through. They are then taken to the brazing furnace. This furnace consists of an open stand, about three feet high, covered with fire brick, pumice stone or coke the purpose of which is to retain the heat. The heat is produced by a mixture of atmospheric air and gas or gasoline, which is controlled by the operator, and supplied by a blower or fan. The flame is applied directly to the joint which is to be brazed by a steel tube, resembling a Bunsen burner, and uses about nine parts of air and one of gas. The combustion or air and gas in the brazing apparatus is about the same mixture as is used in a gas engine. The joint having been brought to the necessary heat, which must in a large measure be left to the judgment and experience of the operator, powdered borax is applied first, the object being to remove any oil or other foreign substance which might interfere with the uniting of the two metals. The borax on being applied flows almost like water. The spelter is then applied, producing a flux, and owing to the expansion of the connection and the tube it readily flows between the joints. The whole operation after the required heat is obtained usually occupies five or six seconds, the object being to secure a joint as rapidly as possible, provided the brazing metal is equally distributed. The gas is then shut off. The supply of air is continued only in order to rapidly cool the joint, the object of this being to prevent the flux from disintegrating and losing its position in the joint. If a brazing has not been rapidly and properly cooled the jar and vibration which the frame receives when in use on a bicycle is apt to cause particles of the flux used in brazing to become loose and rattle in the tube. Necessarily under this operation what might be termed a congregation of scale and the brazing flux is gathered on the outside of the joint. This is afterwards removed by the use of sand blast or pickle, and last, but not least, by hand filing.
WORKING DRAWING DROP FRAME MODEL. ([See Page 52].)
What is known as “brazing spelter” is really a misnomer, and should be called brazing solder. Spelter is the crude product from which refined zinc results. Brazing solder is a combination of copper and spelter first cast into slabs or ingots, then placed into large mortars and pounded by a heavy pestle by hand, and, strange to say, that in all our recent developments in metal work no method can be found to supersede this method of manufacture, as this is the original method of making it.
There are altogether about eight grades of brazing solder, ranging from what is known as the coarse long grain to extra fine grain.
The first result of the pounding operation is the coarse long grain which comes out almost in shreds; by further pounding the shreds are produced, and the result is the fine long grain. From this operation comes the rough grain, the first being coarse long grain, the next medium, then fine and finally extra fine. The proportion of extra fine long grain to the other coarser grades or varieties is only about ten per cent. of the total, consequently making the latter grade the highest in price. The various grades are separated by sifting through a sieve. The running qualities of this solder are affected by the larger or smaller proportion of copper used in the composition. The more copper used the more heat required to melt it, the reverse being the case where more spelter than copper is used.
On bicycle frame work where the surface is largely exposed, the coarse varieties can be successfully used, but for the fine work where little heat can be used, and where the tubing is of extremely light gauge the extra fine grade, which is known also as the quick running solder, gives the best results.
Wire spelter, which comes in coils, has become very popular on account of its lessened cost, its cleanliness, and also because it is not so wasteful as loose spelter, and can be conveyed directly into the joint by the operator as soon as it has reached the melting point.
EAGLE
DROPPED FORGED
FLUSH JOINT.
Another method that is somewhat new is known as liquid brazing, which is nothing really but a special treatment of the joint plunged into molten spelter, and out of which the joint comes surprisingly free from scale, a cleaning by a wire brush being about all the after treatment necessary. The process is a secret one, and the surrounding joints are covered with what is known as the anti-flux, so that the spelter will not adhere there, but joints to be united, of course, are covered with a liquid flux as in the old way.
The makers of the Union produce their flush joints by using what they call pocket brazing. This mode requires the forming of a series of pockets in the projecting ends of the brackets, which may be oval, circular or of any desired shape, although the oval has been found the most convenient. Before the tubing is completely fitted over the bracket arm the pockets are filled with flux, and immediately upon the application of the heat the brass begins to flow and with astonishing evenness, so much so, in fact, that when after cooling, joints are cut out, the brass is found as uniformly distributed as if laid on with a brush. Moreover, no considerable amount of brass flows out of the joint and no filling is necessary. Less heat is required for the reason that the brass is placed where necessary and the parts need not be dangerously heated to cause the brass to flow in. The pocket corrugations are found to stiffen the machine to a marked degree. Taken all in all it is a sure, clean and highly ingenious braze.