Courtesy of the American Machinist
CUTTING AWAY THE DECKS
Oxygen and acetylene generators can be seen on top of after-turret.
Things move with a rush now, for all these arrangements are made ahead of time, and as soon as the workmen are sure that the parts in the mould are redhot the heating aperture is carefully plugged with fire sand and the thermit is ignited. From a mere pinch to half a teaspoonful of the ignition powder is put into a little hollow in the thermit so that the heat may be communicated at once to as much of the thermit as possible. This is then set off with a storm match. The workman quickly withdraws his hand, slams the lid on to the crucible and gets out of the way of flying sparks.
There is a hiss, a puff of white smoke, a blinding glare from the hole in the top of the crucible, and that is all, beside a few sparks, to indicate that a heat second only to that of the sun is being generated within.
One cannot help but marvel at the wonders of science as this inconceivable heat is being produced, the process is seemingly so simple, so easily handled, and so accessible for all kinds of work where steel welding is necessary.
Half a minute to a minute (according to the amount of thermit used) after the match has been applied a workman holding at arm's length a long tool called a "tapping spade" gives a few upward knocks to the little metal pin extending down from the closed pouring aperture. He jumps back for the heat is enough to set his clothes afire, even at a considerable distance, and a few flying particles of the molten thermit would inflict a serious burn.
Down through the little hole the thermit, that a minute before had been only a coarse dark gray powder like metal filings, seemingly the last thing on earth that would catch fire, flows into the pouring gate of the mould in a steady stream of white-hot liquid steel. The white glow from the metal is brighter than any electric light. It is so intense that although the workmen wear heavy dark goggles, they shade their eyes and turn their heads away.
Now you will be wondering, if you know anything about steel and its wonderful properties, how it is that this can be good steel when it is all mixed up with the aluminum oxide or slag. The reason it is of best quality is that as soon as the reaction reduces the whole mass to a molten liquid the heavier steel, set free, as the scientists say, but as we have chosen to think of it, robbed of the aluminum, sinks to the bottom, while the lighter aluminum oxide rises to the top. Consequently the steel goes into the mould to make the weld while the slag, having risen to the top, will be found at the top of the pouring gate, and only around the outer edges of the weld.
When the pour is completed the workmen go away and leave it to cool. It is usually left over night, sometimes as long as forty hours, when the weld is a very large one.