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Steel Making

The Theory Of Tempering
Steel that has been hardened is generally harder and more br...

Reheating for machine ability was done at 100 deg. less than ...

Quenching The Work
In some operations case-hardened work is quenched from the bo...

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

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

Silicon prevents, to a large extent, defects such as gas bubb...

Crucible Steel
Crucible steel is still made by melting material in a clay or...

Preventing Cracks In Hardening
The blacksmith in the small shop, where equipment is usually ...

Steel Worked In Austenitic State
As a general rule steel should be worked when it is in the a...

Phosphorus is one of the impurities in steel, and it has been...

Steel Can Be Worked Cold
As noted above, steel can be worked cold, as in the case of ...

Heat Treatment Of Lathe Planer And Similar Tools
FIRE.--For these tools a good fire is one made of hard foundr...

Composition And Properties Of Steel
It is a remarkable fact that one can look through a dozen tex...

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

Chrome-nickel Steel
Forging heat of chrome-nickel steel depends very largely on ...

Annealing Alloy Steel
The term alloy steel, from the steel maker's point of view, r...

Hardening Operation
Hardening a gear is accomplished as follows: The gear is tak...

Temperature For Annealing
Theoretically, annealing should be accomplished at a tempera...

Annealing Of Rifle Components At Springfield Armory
In general, all forgings of the components of the arms manufa...

Hardness Testing
The word hardness is used to express various properties of me...

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.

Next: Connecting Rods

Previous: Gears

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