Machineability





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

ground.



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.





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