METALLURGICAL AND SHOP FURNACES.
Scientists and engineers have for many years been searching for a cheap and clean method of refining ores and bullions.
Electricity was at one time looked to for the solv ing of this problem. A great many economical re sults were obtained by the use of electricity, but to buy or generate electricity at mining camps or small shops was out of the question. For commercial use it was found to be too expensive.
From the results that are being obtained with fuel oil it will tend to prove that the fuel problem has been solved. Furnaces have been designed to meet the requirements in every case where an ore or metal is to be melted and refined. Muffle types of furnaces are used where the flame or gases would be injurious to the metal treated. For the assayer who may wish to do more than one class of work at a time, the three muffle furnace has been devised. Here he may do crucible work or melt in one muffle, scorify in the second, and cupel in the third. Or only one muffle may be used.
Some of the results obtained by mining companies were most gratifying. One report is as follows : "We have made one more melt with about the same results as we go in the test run. We use for a melt 550 lb. of precipitate, yielding about 6300 oz. metal (975 fine Au. and Ag.), 20 gal. of oil against 1000 lb. of coke at $16 per ton ; oil at 15c per gal. at the plant. The slags from the coke furnace used to run about $200 per ton, while those from the oil fur nace run between $12 and $13, which avoids retreat ment." Another report : Crucible used, Dixon No. 275.
Lbs. of precipitate and flux melted 1148 lbs.
Hrs. required to melt 20 hrs.
Amount of oil used bbls.
Number of crucibles 1 Smelting No. 1, cold furnace, 2 hr. 20 min oil 7 gals.
Smelting No. 2, hot furnace, 50 min .oil 3% gals.
Smelting No. 3, hot furnace, 45 min oil 2% gals.
Smelting No. 4, cold furnace, 2 hr. 05 min. oil 6% gals.
Smelting No. 5, hot furnace, 1 hr. 10 min. oil 4 gals.
Smelting No. 6, hot furnace, 40 min oil 2% gals.
Smelting No. 7, hot furnace, 40 min. oil 2% gals.
The slag obtained from these smelts average $40, this being very low when comparing same with old method with 50 oz. value. Precipitates charged being better than 200 fine and bullion 970. The oil used was California crude, of 24 gravity, costing 64 cents on the ground here.
From the above data one can readily see at a glance the amount of time and labor saved and the economy effected by using oil fuel.
Other mines have submitted similar reports, showing much time and labor saved, and great econ omy effected, by the use of oil fuel.
Fig. 71 shows the method of constructing a cru cible melting furnace. The size of the furnace re quired depends of course, on the size of crucibles used. The inner walls and bottom are built of a good grade of fire-brick, while common red brick may be used on the outer wall. The top may be made of arch and tapered fire-brick, held in place by an iron band. A small loop on each side of the band affords a means of raising the cover, in the center of which a small opening must be left for charging or adding flux as re quired.
Almost any type of an oil burner can be applied to this furnace, the low pressure air type being the most suitable. It will maintain a temperature of over 3000 deg. F., with a fuel consumption of only 3 gal lons of oil per hour, using air at 2 lb. pressure. Two gallons of oil will melt 100 lb. of brass scrap in about 30 minutes, and crucible steel, brass, copper, bronze, silver, gold or nickel can be melted with similar econ omy and convenience.
Fig. 72 shows a small heating furnace, that is easily made. Doors may be placed at either end. Fig. 73 shows a rivet heating furnace, which may also be used for tempering, annealing, case hardening, etc.
This type of furnace can be run 8 hours on less than 20 gal. of oil. The furnace illustrated is designed to use compressed air for atomizing, for where riveting is being done, compressed air is generally available. In operation, the furnace is first started and thoroughly heated. Then the oil is shut off and about 12 or 20 rivets are thrown in, depending upon their size. The rivets must not lie in a heap, hut be spread over the bottom of the furnace. The oil is then turned on, and in a few moments the rivets will all be heated to a uniform temperature. When they are driven they will thicken up and fill the hole, and the head and back will form squarely over the rest of the rivet. Being uniformly hot, the iron is left in good condition and the stress is evenly distributed throughout the rivet, making a good steam tight job.