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

Temperature Recording And Regulation
Each furnace is equipped with pyrometers, but the reading an...

Carbon-steel Forgings
Low-stressed, carbon-steel forgings include such parts as car...

Introduction Of Carbon
The matter to which these notes are primarily directed is the...

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

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

The Modern Hardening Room
A hardening room of today means a very different place from ...

Non-shrinking Oil-hardening Steels
Certain steels have a very low rate of expansion and contract...

Bessemer Process
The bessemer process consists of charging molten pig iron int...

Connecting Rods
The material used for all connecting rods on the Liberty engi...

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

Detrimental Elements
Sulphur and phosphorus are two elements known to be detrimen...

Hardening
Steel is hardened by quenching from above the upper critical....

Short Method Of Treatment
In the new method, the packed pots are run into the case-har...

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

S A E Heat Treatments
The Society of Automotive Engineers have adopted certain heat...

Furnace Data
In order to give definite information concerning furnaces, fu...

Protectors For Thermo-couples
Thermo-couples must be protected from the danger of mechanica...

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

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



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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