For DRIVERS, MECHANICS & FOREMEN.
Page 25
If you've noticed an error in this article please click here to report it so we can fix it.
!A PRIZE OE TEN SHILLINGS ü awarded each week to the sender of the best letter which we publish on this page, all others are paid for at the rate of a penny a line, with an allowance for photographs. All notes are edited before being published. Mention your employer's name, in confidence, as evidence of good faith. Address, D., M. and F., "The Commercial Motor." 7-15, Bosebery Avenue, London, E.G. 1.
• Lamps Alight.
On Saturday, November 8th, light your lamps at 4.51 in London, 4.49 in Edinburgh, 4.45 in Newcastle, 4.58 in Liverpool, 4.57 in Birmingham, 5.1 in Bristol, and 5.41 in Dublin.
Words of Wisdom to Would-be Welders.
The sender of the following communication has been awarded the 103. prize this week.
[2,0281 " Foreman" (Manchester) Writes :—" In the -commercial motor industry the most important side of welding is that which has to do with the welding of aluminium. Now although, as a matter of fact, when you know how' to handle it, aluminium is one of the easiest of metals to weld, it nevertheless calls for such special treatment that experts in the weld ing of iron and steel are frequently confounded the first time they are confronted with a job involving the manipulation of this metal. A little knowledge o7 the fundamental metallurgical properties—not a areal deal—and some little experience of the special handling of the blow-pipe, the rest is mostly commonsense.
1," First, as regards the blow-pipe. It is. particularly essential, when dealing with aluminium, that the apparatus be in good order. See that the tubing is sound, and securely fixed; make Sure that the regulator on the oxygen cylinder is in proper working .order, and that the flow of gas is even, and not subject to fluctuations. Both the .oxygen and acetylene must be as free from impurities as possible, and it is most inadvisable to commence operations unless an ample bupply of gas is available ; to stop in the middle of a weld on acc,ount, of a shiortage is fatal. 'Use a blow-pipe of the right capacity for the job. One consuming 50 litres (1.76 cubic ft.) or even 25 litres (0.88 cubic ft.) of acetylene per hour can be used satisfactorily when welding aluminium s:A. in. in thickness, whereas aluminium in. thick requires a blowpipe consuming 700 to 800 litres (24.7 to 26.2 cubic ft.) per hour.
" The selection of the flux is important. Aluminium is never found 'without a coating of -oxide 'on the Metal, and the principal function of the flux is to cause the oxide to dissolve at the same temperature. at which the aluminium melts. As the melting point of aluminium LS 675 degrees Centigrade, and that of dxide of aluminium is 3,000 degrees Centigrade, the importance of the flux may be rather more than dimly "realized. It is essential' to use only the correct amount of flux. It may not be thrown on to excess as is customary when brazing copper or brass. The best way to apply it is from the end of thewelding rod. This can be arranged if the rod be first slightly warmed in the flame of the blow-pipe, and then dipped into the flux, which will readily adhere to the rod, So used, it will be found that the flux will readily flow ahead of the flame, dissolving the oxide • and preparing the metal for the welding. When the weld to be executed is a vertical one, and the work canaet be held so as to bring it to the horizontal, it will be better to use a paste flux.. "Thorough and careful preparation of the work is very necessary. The edges of the metal, and the sur face round the break? . must be scrupulously clean, otherwise the impurities which' may remain will set up disintegration of the weld and ultimately it will fail.
"Some of the preliminaries depend to a large ex tent upon the thickness of the material to be welded. The work of joining thin sheets, for example, is considerably facilitated if the edges are turned up, or flanged. In such a. case the depth of flange should slightly exceed the thickness of the metal. When the metal exceeds in., or even equals that amount, the edges must be bevelled to such an extent that the width of the top of the yen which is formed when the edges are together is at least equal to the thickness, of the metal itself. The bevelling should he continued right to the bottom edge of the metal in order to ensure its being melted right through. When welding metal in. thick or more, try to arrange that the welding rod and the edges of the metal -melt simultaneously. The welding rod should be of a diameter about equal to the thickness of the parts to he welded, and in practice it is found that welding rodsexceeding in. in diameter are inadvisable.
"When actually performing the operation be very careful not to allow cavities to be formed in the line of the weld ; they diminish the strength of the joint c-onsiderably. An experienced welder displays his scgrby raising, or removing, the flame immediately fusion has taken place and the weld is complete, thus ensuring a, complete weld, and avoiding therisk of burning the metal.
"Alter the work is completed, the, joint, and the surrounding metal must be thoroughly cleaned, first by brushing and afterwards by washing in warm water ; this is necessary in order to remove absolutely any traces of the flux, which would otherwise most certainly corrode the metal round the joint, with possibly serious consequences. It is also necessary to relieve the metal from any internal strains which generally result from the heat to which it has been subjected. This is usually effected by a dual process of cold hammering and annealing. The lines of the weld, and the metal round about are first gently but thoroughly hammered, the casting, or whatever it is, should then be gradually heated to a temperature of about 450 to 480 degrees Centigrade. This has the effect of rearranging the molecules of the metal, and results in homogeneity throughout the weld. When possible, the reheating should be carried out in a special oven., and particular care must be taken not to exceed the upper of the two temperatures named, as aluminium softens at 500 degrees Centigrade to such an extent that it may collapse, or at least deform, under its own weight. " Two more points. When a job has to be carried out which necessitates the introduction of a new piece of metal between the edges of a break, it is essential that the new metal should have the same chemical composition and physical properties as the old. Finally, do not expect good results if the weld is carried out in a dilatory manner-. Welds in aluminium must be expeditiously made from the moment when fusion first takes place : that is to say, the rate at which the work proceeds must be even and fast. This is best achieved by making complete and adequate preparations beforehand, so that no time is lost in the actual welding owing to having to delay matters a little to reach for come accessory not previously placed within reach."