Part 17 (1/2)
The process of welding whichwith aluminum is known as the Thermit process and was perfected by Dr Hans Goldschmidt The process, which is controlled by the Goldschmidt Thermit Company, makes use of a mixture of finely powdered aluminum with an oxide of iron called by the trade nanition powder, such as bariuen fro a rees Fahrenheit After the reaction, which takes from 30 seconds to a minute, the molten metal is drawn from the crucible on to the surfaces to be joined Its extreme heat fuses the metal and a perfect joint is the result
This process is suited for welding iron or steel parts of coe size
_Preparation_--The parts to be joined are thoroughly cleaned on the surfaces and for several inches back from the joint, after which they are supported in place The surfaces bethich theon the size of the parts, but cutting or drilling part of thethe entrance of new metal, the effects of contraction of theadjacent parts or by forcing the ends apart edges and jacks The amount of this last separation must be determined by the shape and proportions of the parts in the sa which heats the parts to apoint
Yellohich has been warmed until plastic, is then placed around the joint to for the space between the ends and being provided with vent holes by i a piece of stout cord, which is pulled out after the wax cools
A retaining ure 55) made from sheet steel or fire brick is then placed around the parts This mould is then filled with a round fire brick and one part fire sand These h water so that they will pack Thisthe space between the walls and the wax, and is packed hard with a rammer so that the material forms a wall several inches thick between any point of the mould and the wax The mixture must be placed in theprogresses
[Illustration: Figure 55--Thers are provided through thismaterial by the insertion of wood or pipe fors will lead from the lowest point of the wax pattern and is used for the introduction of the preheating fla leads fro into the preheating gate at a point about one inch fros, called risers, are then provided froh points of the wax pattern to the top of theat the top in a shallow basin The molten metal comes up into these risers and cares for contraction of the casting, as well as avoiding defects in the collar of the weld After the ate patterns are tapped lightly and withdrawn, except in the case of the metal pipes which are placed at points at which it would be i_--The ends to be welded are brought to a bright red heat by introducing the flaate The torch asoline or kerosene, and not crude oil, as the crude oil deposits tooof other adjacent parts to care for contraction is done at this ti flaradually increased The ill ate by re the flame at intervals for a few seconds The heat is continued until the ht to the red heat required This leaves a ate should then be plugged with a sand core, iron plug or piece of fitted fire brick, and backed up with several shovels full of the ure 56--Thernesia stone; _B_, Magnesia thimble; _C_, Refractory sand; _D_, Metal disc; _E_, Asbestos washer; _F_, Tapping pin]
_Thermit Metal_--The reaction takes place in a special crucible lined with nesia tar, which is baked at a red heat until the tar is driven off and theshould last fro ends at the botto carries a h which the molten steel passes on its way to the mould It will usually be necessary to renew this thi is closed before filling the crucible with ther a steure 56) This pin, _F_, is placed in the thi and exposing about two inches The top of this pin is covered with an asbestos, washer, _E_, then with another iron disc _D_, and finally with a layer of refractory sand The crucible is tapped by knocking the stem of the pin upwards with a spade or piece of flat iron about four feet long
The charge of ther a few handfuls over the refractory sand and then pouring in the balance required The amount of therhed before and after filling _the entire space that the thermit will occupy_
This does not mean only the wax collar, but the space of the ates filled ax The nu ive the number of pounds of thermit to be used To this quantity of theranese, 1 per cent nickel thers
It is necessary, when more than 10 pounds of ther 3/8 inch diameter by 1/8 inch thick with the powder in order to sufficiently retard the intensity of the reaction
Half a teaspoonful of ignition powder is placed on top of the thernited with a storm match or piece of red hot iron The cover should be immediately closed on the top of the crucible and the operator should get away to a safe distance because of the metal thatabout 30 seconds to ato rise to the top of the crucible, the tapping pin is struck from below and the molten metal allowed to run into theas possible, preferably over night, so as to anneal the steel in the weld, but in no case should it be disturbed for several hours after pouring After reh the ates and knock these sections off
No part of the collar should be removed unless absolutely necessary
CHAPTER IX