Although the advantages offered by the gas-fired furnace for carburizing have been generally recognized in the past from points of view as close temperature regulation, decreased attendance, and greater convenience, very little information has been published regarding the consumption of gas for this process. It has therefore been a matter of great difficulty to obtain authentic information upon this point, either from makers or users of such furnaces.
In view of this, the details of actual consumption of gas on a regular customer's order job will be of interest. The "Revergen" furnace, manufactured by the Davis Furnace Company, Luton, Bedford, England, was used on this job, and is provided with regenerators and fired with illuminating gas at ordinary pressure, the air being introduced to the furnace at a slight pressure of 3 to 4 in. water gage. The material was charged into a cold furnace, raised to 1,652°F., and maintained at that temperature for 8 hr. to give the necessary depth of case. The work consisted of automobile gears packed in six boxes, the total weight being 713 lb. The required temperature of 1,652°F. was obtained in 70 min. from lighting up, and a summary of the data is shown in the following table:
| Cubic Foot Per Pound of Load | Total Number of Cubic Foot | |
|---|---|---|
| Gas to raise furnace and charge from cold to 1,652°F., 70 min. | 1.29 | 925 |
| Gas to maintain 1,652°F. for 1st hour | 0.38 | 275 |
| Gas to maintain 1,652°F. for 2nd hour | 0.42 | 300 |
| Gas to maintain 1,652°F. for 3rd hour | 0.38 | 275 |
| Gas to maintain 1,652°F. for 4th hour | 0.42 | 300 |
| Gas to maintain 1,652°F. for 5th hour | 0.49 | 350 |
| Gas to maintain 1,652°F. for 6th hour | 0.49 | 350 |
| Gas to maintain 1,652°F. for 7th hour | 0.45 | 325 |
| Gas to maintain 1,652°F. for 8th hour | 0.45 | 325 |
The overall gas consumption for this run of 9 hr. 10 min. was only 4.8 cu. ft. per pound of load.
THE CARE OF CARBURIZING COMPOUNDS
Of all the opportunities for practicing economy in the heat-treatment department, there is none that offers greater possibilities for profitable returns than the systematic cleaning, blending and reworking of artificial carburizers, or compounds.
The question of whether or not it is practical to take up the work depends upon the nature of the output. If the sole product of the hardening department consists of a 1.10 carbon case or harder, requiring a strong highly energized material of deep penetrative power such as that used in the carburizing of ball races, hub-bearings and the like, it would be best to dispose of the used material to some concern whose product requires a case with from 0.70 to 0.90 carbon, but where there is a large variety of work the compound may be so handled that there will be practically no waste.
This is accomplished with one of the most widely known artificial carburizers by giving all the compound in the plant three distinct classifications: "New," being direct from the maker; "half and half," being one part of new and one part first run; and "2 to 1," which consists of two parts of old and one part new.
SEPARATING THE WORK FROM THE COMPOUND
During the pulling of the heat, the pots are dumped upon a cast-iron screen which forms a table or apron for the furnace. Directly beneath this table is located one of the steel conveyor carts, shown in Fig. 43, which is provided with two wheels at the rear and a dolly clevis at the front, which allows it to be hauled away from beneath the furnace apron while filled with red-hot compound. A steel cover is provided for each box, and the material is allowed to cool without losing much of the evolved gases which are still being thrown off by the compound.