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

Fatigue Tests
It has been known for fifty years that a beam or rod would fa...

Open Hearth Process
The open hearth furnace consists of a big brick room with a l...

Sulphur
SULPHUR is another element (symbol S) which is always found i...

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

An Automatic Temperature Control Pyrometer
Automatic temperature control instruments are similar to the ...

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

High Speed Steel
For centuries the secret art of making tool steel was handed ...

Rate Of Cooling
At the option of the manufacturer, the above treatment of gea...

Molybdenum
Molybdenum steels have been made commercially for twenty-five...

William Kelly's Air-boiling Process
An account of Bessemer's address to the British Association w...

Oil-hardening Steel
Heat slowly and uniformly to 1,450 deg.F. and forge thorough...

Preventing Carburizing By Copper-plating
Copper-plating has been found effective and must have a thick...

Process Of Carburizing
Carburizing imparts a shell of high-carbon content to a low-...

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

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

High-carbon Machinery Steel
The carbon content of this steel is above 30 points and is ha...

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

Annealing Method
Forgings which are too hard to machine are put in pots with ...

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



Highly Stressed Parts






Category: APPLICATION OF LIBERTY ENGINE MATERIALS TO THE AUTOMOTIVE INDUSTRY

The highly stressed parts on the Liberty engine consisted of the
connecting-rod bolt, the main-bearing bolt, the propeller-hub key,
etc. The material used for parts of this type was selected at the
option of the manufacturer from standard S. A. E. steels, the
composition of which are given in Table 11.

TABLE 11.--COMPOSITION OF S. A. E. STEELS Nos. 2,330, 3,135 AND 6,130

Steel No 2,330 3,135 6,130
Carbon, minimum 0.250 0.300 0.250
Carbon, maximum 0.350 0.400 0.450
Manganese, minimum 0.500 0.500 0.500
Manganese, maximum 0.800 0.800 0.800
Phosphorus, maximum 0.045 0.040 0.040
Sulphur, maximum 0.045 0.045 0.045
Nickel, minimum 3.250 1.000
Nickel, maximum 3.750 1.500
Chromium, minimum 0.450 0.800
Chromium, maximum 0.750 1.100
Vanadium, minimum 0.150

All highly stressed parts on the Liberty engine must show, after
heat treatment, the following minimum physical properties: Elastic
limit, 100,000 lb. per square inch; elongation in 2 in., 16 per
cent; reduction of area, 45 per cent; scleroscope hardness, 40
to 50.

The heat treatment employed to obtain these physical properties
consisted in quenching from a temperature of 1,525 to 1,575 deg.F., in
oil, followed by tempering at a temperature of from 925 to 975 deg.F.

Due to the extremely fine limits used on all threaded parts for
the Liberty engine, a large percentage of rejection was due to
warpage and scaling of parts. To eliminate this objection, many
of the Liberty engine builders adopted the use of heat-treated
and cold-drawn alloy steel for their highly stressed parts. On
all sizes up to and including 3/8 in. in diameter, the physical
properties were secured by merely normalizing the hot-rolled bars
by heating to a temperature of from 1,525 to 1,575 deg.F., and cooling
in air, followed by the usual cold-drawing reductions. For parts
requiring stock over 3/8 in. in diameter, the physical properties
desired were obtained by quenching and tempering the hot-rolled bars
before cold-drawing. It is the opinion that the use of heat-treated
and cold-drawn bars is very good practice, provided proper inspection
is made to guarantee the uniformity of heat treatment and, therefore,
the uniformity of the physical properties of the finished parts.

The question has been asked many times by different manufacturers, as
to which alloy steel offers the best machineability when heat-treated
to a given Brinell hardness. The general consensus of opinion among
the screw-machine manufacturers is that S. A. E. No. 6,130 steel
gives the best machineability and that S. A. E. No. 2,330 steel
would receive second choice of the three specified.

In the finishing of highly stressed parts for aviation engines,
extreme care must be taken to see that all tool marks are eliminated,
unless they are parallel to the axis of strain, and that proper
radii are maintained at all changes of section. This is of the
utmost importance to give proper fatigue resistance to the part
in question.





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