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Steel Making

There is no mystery or secret about the proper annealing of d...

Instructions For Working High-speed Steel
Owing to the wide variations in the composition of high-speed...

Critical Points
One of the most important means of investigating the properti...

Using Illuminating Gas
The choice of a carburizing furnace depends greatly on the fa...

Heating Of Manganese Steel
Another form of heat-treating furnace is that which is used ...

Correction For Cold-junction Errors
The voltage generated by a thermo-couple of an electric pyrom...

Heavy Forging Practice
In heavy forging practice where the metal is being worked at...

Annealing Of High-speed Steel
For annealing high-speed steel, some makers recommend using g...

Highly Stressed Parts
The highly stressed parts on the Liberty engine consisted of ...

Temperatures To Use
As soon as the temperature of the steel reaches 100 deg.C. (...

Mushet And Bessemer
That Mushet was "used" by Ebbw Vale against Bessemer is, perh...

Alloying Elements
Commercial steels of even the simplest types are therefore p...

Application To The Automotive Industry
The information given on the various parts of the Liberty eng...

Effect Of A Small Amount Of Copper In Medium-carbon Steel
This shows the result of tests by C. R. Hayward and A. B. Joh...

Annealing Work
With the exception of several of the higher types of alloy s...

Judging The Heat Of Steel
While the use of a pyrometer is of course the only way to hav...

Piston Pin
The piston pin on an aviation engine must possess maximum res...

Although it is possible to work steels cold, to an extent de...

Impact Tests
Impact tests are of considerable importance as an indication ...

The Pyrometer And Its Use
In the heat treatment of steel, it has become absolutely nece...

Rate Of Cooling


At the option of the manufacturer, the above treatment of gear
forgings could be substituted by normalizing the forgings at a
temperature of from 1,550 to 1,600 deg.F. The most important criterion
for proper normalizing, consisted in allowing the forgings to cool
through the critical temperature of the steel, at a rate not to exceed
50 deg.F. per hour. For the two standard steels used, this consisted in
cooling from the normalizing temperature down to a temperature
of 1,100 deg.F., at the rate indicated. Forgings normalized in this
manner will show a Brinell hardness of from 177 to 217. The question
has been repeatedly asked as to which treatment will produce the
higher quality finished part. In answer to this I will state that
on simple forgings of comparatively small section, the normalizing
treatment will produce a finished part which is of equal quality to
that of the quenched and annealed forgings. However, in the case of
complex forgings, or those of large section, more uniform physical
properties of the finished part will be obtained by quenching and
annealing the forgings in the place of normalizing.

The heat treatment of the finished gears consisted of quenching
in oil from a temperature of from 1,420 to 1,440 deg.F. for the No.
X-3,340 steel, or from a temperature of from 1,500 to 1,540 deg.F.
for No. 6,140 steel, followed by tempering in saltpeter or in an
electric furnace at a temperature of from 650 to 700 deg.F.

The question has been asked by many engineers, why is the comparatively
low scleroscope hardness specified for gears? The reason for this is
that at best the life of an aviation engine is short, as compared with
that of an automobile, truck or tractor, and that shock resistance
is of vital importance. A sclerescope hardness of from 55 to 65
will give sufficient resistance to wear to prevent replacements
during the life of an aviation engine, while at the same time this
hardness produces approximately 50 per cent greater shock-resisting
properties to the gear. In the case of the automobile, truck or
tractor, resistance to wear is the main criterion and for that
reason the higher hardness is specified.

Great care should be taken in the design of an aviation engine
gear to eliminate sharp corners at the bottom of teeth as well
as in keyways. Any change of section in any stressed part of an
aviation engine must have a radius of at least 1/32 in. to give
proper shock and fatigue resistance. This fact has been demonstrated
many times during the Liberty engine program.

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Previous: Gears

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