Reheating for machine ability was done at 100 deg. less than the drawing
temperature, but the time of soaking is more than double. After
both drawing and reheating, the blanks were buried in lime where
they remain, out of contact with the air, until their temperature
had dropped to that of the workroom.
For straightening, the barrels were heated to from 900 to 1,000 deg.F.
in an automatic furnace 25 ft. long, this operation taking about 2
hr. The purpose of hot straightening was to prevent any stresses
being put into the blanks, so that after rough-turning, drilling
or rifling operations they would not have a tendency to spring
back to shape as left by the quenching bath.
A method that produces an even better machining rifle blank, which
practically stays straight through the different machining operations,
was to rough-turn the blanks, then subject them to a heat of practically
1,0000 for 4 hr. Production throughout the different operations is
materially increased, with practically no straightening required
after drilling, reaming, finish-turning or rifling operations.
FIGS. 24 and 25.--Roof system of cooling quenching oil.]
This method was tested out by one of the largest manufacturers and
proved to be the best way to eliminate a very expensive finished
gun-barrel straightening process.
The heat-treating required a large amount of cooling oil, and the
problem of keeping this at the proper temperature required considerable
study. The result was the cooling plant on the roof, as shown in
Figs. 24, 25 and 26. The first two illustrations show the plant as
it appeared complete. Figure 26 shows how the oil was handled in
what is sometimes called the ebulator system. The oil was pumped
up from the cooling tanks through the pipe A to the tank B.
From here it ran down onto the breakers or separators C, which
break the oil up into fine particles that are caught by the fans
D. The spray is blown up into the cooling tower E, which contains
banks of cooling pipes, as can be seen, as well as baffies F. The
spray collects on the cool pipes and forms drops, which fall on
the curved plates G and run back to the oil-storage tank below
The water for this cooling was pumped from 10 artesian wells at the
rate of 60 gal. per minute and cooled 90 gal. of oil per minute,
lowering the temperature from 130 or 140 to 100 deg.F. The water as
it came from the wells averaged around 52 deg.F. The motor was of a
7-1/2-hp. variable-speed type with a range of from 700 to 1,200
r.p.m., which could be varied to suit the amount of oil to be cooled.
The plant handled 300 gal. of oil per minute.
Previous: Plant For Forging Rifle Barrels