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Flange Shields For Furnaces
Such portable flame shields as the one illustrated in Fig. 1...

The Thermo-couple
With the application of the thermo-couple, the measurement of...

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

Leeds And Northrup Optical Pyrometer
The principles of this very popular method of measuring tempe...

Carbon Steels For Different Tools
All users of tool steels should carefully study the different...

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

Hardening High-speed Steel
In forging use coke for fuel in the forge. Heat steel slowly ...

Suggestions For Handling High-speed Steels
The following suggestions for handling high-speed steels are ...

Steel Before The 1850's
In spite of a rapid increase in the use of machines and the ...

A Satisfactory Luting Mixture
A mixture of fireclay and sand will be found very satisfactor...

Tungsten, as an alloy in steel, has been known and used for a...

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

Carbon Tool Steel
Heat to a bright red, about 1,500 to 1,550 deg.F. Do not ham...

Quenching Tool Steel
To secure proper hardness, the cooling of quenching of steel ...

Air-hardening Steels
These steels are recommended for boring, turning and planing...

Cyanide Bath For Tool Steels
All high-carbon tool steels are heated in a cyanide bath. Wi...

Armor plate makers sometimes use the copper ball or Siemens' ...

Separating The Work From The Compound
During the pulling of the heat, the pots are dumped upon a ca...

Heat Treatment Of Axles
Parts of this general type should be heat-treated to show the...

Placing The Thermo-couples
The following illustrations from the Taylor Instrument Compan...

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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