Publisher's Synopsis
This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1914 Excerpt: ... electric furnace are the crucible and electrodes. The crucible has been found to have a life of from 1200 to 1800 hours at a temperature of 2350 degrees F., and up to 3000 hours at lower temperatures. This is much longer than with muffle furnaces, which is probably due to the absence of the destructive influence of the gases of combustion, and to the fact that the crucible does not transmit the heat from the outside to the inside. The most sensitive part of the electrodes is that which projects over the level of the bath, and which is protected by exchangeable tips. These tips have a life of from 400 to 800 hours, and the cost of their replacement is as low as fireclay for other furnaces. The amount of salts lost by evaporation and waste under ordinary working conditions in a furnace 8X8X11 inches amounts to a little more than one pound for ten hours' continuous operation. coming in contact with the hot tool has a tendency to crack it, so that it becomes necessary to dry the air before it enters into the nozzles. It has also been found that it is absolutely impossible to cool a cutter which has a very heavy body and fine teeth in the air blast, as the heat from the central portion is not extracted fast enough, and therefore does not permit a sufficiently rapid cooling of the teeth to insure proper hardening. For this reason, some firms have adopted a method of cooling the cutters from the hardening heat of 2370 degrees F. to a temperature of about 1100 degrees F. by quenching in an electrically heated salt bath. After having been cooled to about 1100 degrees F. in the bath, the cutters are allowed to cool down slowly in the air, and the whole process has the advantage of being cheap and reliable as well as effecting a considerable saving in time. The ease ...
