gas, and second, to relieve strains, due to uneven expansion and contraction of the part being welded. Great care should also be used to see that all castings cool slowly after welding, as many a good weld has been spoiled by too rapid cooling. A box of lime

or ashes should be provided in which to bury the casting so it will cool slowly.

Method of Preheating.-Where city gas of some kind, together with compressed air, are both obtainable in the shop we recommend very highly a preheating blow pipe using this fuel. It makes an ideal outfit and in fact will be found just as efficient as the other preheaters herein shown, and will answer any and all purposes

Fig. 456.-Examples of Defective Cylinders that Were Repaired by Autogenous Process. Cylinder Flange at the Left was Repaired at a Cost of $7.50; Cracked Crown and Water Jacket at the Right Repaired at a Cost of $12.

to which the oil burning preheaters might be applied. Of course, where fuel gas and air are not both obtainable in one shop we recommend the oil burning outfit shown, although they are slightly higher in price, but, as stated above, where the shop is so situated as to be fortunate enough to have both compressed air and fuel gas of some kind the gas preheating torch will be found to be very satisfactory, as the first cost, and also the cost of maintenance, is low. The furnace or muffle is then built of fire brick to a suitable

size for the particular part we are about to weld. A removable cover is used of asbestos board or sheet metal.

After the welding has been done, the object should be heated again in a similar manner as the preheating was done and then allowed to cool off slowly in the muffle. This is necessary to prevent cracking due to the local expansion and contraction, caused by the local heat of the welding flame. This method is also useful in obtaining a softness of the material in the weld. This method of handling welding of cast iron will prove a saving of from 30 to 50% of the cost of gases used for welding. There is nothing particularly difficult in the handling of the welding flame in connection with welding cast iron, but it should be borne in mind in welding of heavy sections, that the fractured portions should be tapered out in order that the welding can be commenced at the center of the section, building up as the welding proceeds. A flux is necessary for use in welding cast iron and will be found to make the metal flow more readily and at the same time, flux out the sand, dirt, grease, etc. Be sure that the sides of the fracture are in molten condition before filling material is added.

Welding Aluminum.-The welding of aluminum requires considerable skill and experience before successful work can be expected on intricate parts. The manner of making the weld is slightly different from that used with welding of cast iron, due to the fact, that when aluminum is heated, an oxide film is formed, which prevents the metal running together and forming a suitable weld. To overcome this, the aluminum filling rods must be inserted into the molten aluminum, which is being welded, and moved about rapidly, something similar to puddling, in order to break up this oxide film and allow the aluminum to run together. A flux has also proven of advantage in this connection, where before, practically all of this work was done without the use of a flux. A larger tip is necessary for welding a section of aluminum than would be required for the same section of steel or cast iron. This is due to the fact that aluminum conducts heat away very rapidly. With the proper size tip in use, it is necessary to melt a considerable portion of aluminum, which is being held in shape by the fire clay Porm. Now the extra metal can be added from the filling rod and

stirred or puddled with this rod to break the oxide film which forms when aluminum is melted. A flux has been provided for use in this connection and will be found very valuable for breaking up this film. In fact, by using this flux, bosses can readily be built up at any desired point. This is something that could not be done before a flux for welding aluminum came into general use.

All precautions should be taken to have the work securely fastened or harnessed, for instance, when welding a hole in the

side of a crank case, it is customary to clamp a shaft, which approximates the size of the bearings (plus, of course, the thickness of the cast metal bearings, which would melt out when preheating,) into the crank case bearing supports, in order to insure perfect alignment of the bearings. Angle irons are bolted to the flanges where connection is made to the other half of the crank case in crder to insure perfect alignment of this part.

It is good practice to place a sheet of paper on the inside of the case next to the crack to be welded. This paper prevents the fire clay from getting into the crack. Upon this is placed fire clay in plastic condition which is held in place by means of asbestos fiber. This makes a light backing or mold for the case and can be easily handled without fear of the mold or core being so heavy as to break down the case when heated for welding. This mold should be large enough to cover sufficient area around the crack so that the aluminum will not break down.

Aluminum parts must always be preheated and handled in a similar manner as automobile cylinders, as outlined before, with the exception that aluminum, of course, should not be heated to such a high temperature, on account of the fact that within 50 degrees C. of the melting point, the metal is very brittle and without strength. It is customary to heat up these cases thoroughly until they will melt half and half solder in wire form. This temperature is about right to prevent cracking occurring on account of expansion and contraction and at the same time, the aluminum will possess sufficient strength so that with ordinary handling no trouble is experienced with alignment or failure of the part.

Welding Malleable Iron.-Parts of malleable iron are handled in much the same manner as cast iron parts in preparation for welding. It is customary to re-enforce the malleable iron weld as much as possible by building up the section at the fracture. The filling material used is usually nickel steel in the bottom of the weld, finishing the top surface with cast iron rod. The latter runs better and makes a smoother finish.

In some instances you may find that the fracture will be through a tapped opening, in which case, it will be necessary to cape this portion out entirely, making a much larger opening than the hole itself and then filling this with cast iron, using the same precaution in welding cast iron to have this portion soft. Wherever the union is made between filling material used and the malleable iron, you will find this so hard that it will be impossible to drill or machine in any way except by grinding.

In some cases in making repairs on malleable iron parts, it is even necessary to strap these parts by means of wrought iron or