uenching tank in front of its door is shown in Fig. 108.

These tanks are covered with plates while charging the furnace
and the cold castings are placed in a moderately cool furnace.
Since some of these steels must not be charged into a furnace where
the heat is extreme but should be brought up to their final heat
gradually, there is little discomfort during the charging process.
When quenching, however, from a temperature of 1,800 deg. to 1,900 deg.,
it is extremely unpleasant in front of the doors. The swinging
shield is here adapted to give protection for this work. As will
be noted it is hung a sufficient distance in front of the doors,
that it may not interfere with the castings as they come from the
furnace, and slide down into the tank.

To facilitate the work, and avoid the necessity of working with
the bars outside the edges of the shield, the slot-like hole is
cut in the center of the shield, and through this the bars or rakes
for dragging out the castings are easily inserted and manipulated.
The advantage of such a swinging shield is that it may be readily
moved from side to side, or forward and back as occasion requires.

FURNACE DATA

In order to give definite information concerning furnaces, fuels
etc., the following data is quoted from a paper by Seth A. Moulton
and W. H. Lyman before the Steel Heat Treaters Society in September,
1920.

This considers a factory producing 30,000 lb. of automobile gears
per 24 hr. The transmission gears will be of high-carbon steel and
the differential of low-carbon steel, carburized. The heat-treating
equipment required is:

1. Annealing furnaces 1,400 to 1,600 deg.F.
2. Carburizing furnaces 1,700 to 1,800 deg.F.
3. Hardening furnaces 1,450 to 1,550 deg.F.
4. Drawing furnaces 350 to 950 deg.F.

All of the forging blanks are annealed before machining, about
three-quarters of the machined gears and parts are carburized,
all the carburized gears are given a double treatment for core and
case, all gears and parts are hardened and all parts are drawn.

The possible sources of heat supply and their values are as follows:--

1. Oil 140,000 B.t.u. per gallon
2. Natural gas 1,100 B.t.u. per cubic foot
3. City gas 650 B.t.u. per cubic foot
4. Water gas 300 B.t.u. per cubic foot
5. Producer gas 170 B.t.u. per cubic foot
6. Coal 12,000 B.t.u. per