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

Case-hardening Treatments For Various Steels
Plain water, salt water and linseed oil are the three most co...

Fatigue Tests
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Instructions For Working High-speed Steel
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Optical System And Electrical Circuit Of The Leeds & Northrup Optical Pyrometer
For extremely high temperature, the optical pyrometer is lar...

High-chromium Or Rust-proof Steel
High-chromium, or what is called stainless steel containing f...

The Forging Of Steel
So much depends upon the forging of steel that this operation...

Robert Mushet
Robert (Forester) Mushet (1811-1891), born in the Forest of D...

Sulphur
Sulphur is another impurity and high sulphur is even a greate...

Tempering Colors On Carbon Steels
Opinions differ as to the temperature which is indicated by t...

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

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

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

Hardening High-speed Steels
We will now take up the matter of hardening high-speed steels...

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

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

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

Heat-treating Equipment And Methods For Mass Production
The heat-treating department of the Brown-Lipe-Chapin Company...

Preparing Parts For Local Case-hardening
At the works of the Dayton Engineering Laboratories Company, ...

Carburizing By Gas
The process of carburizing by gas, briefly mentioned on page ...



Connecting Rods






Category: APPLICATION OF LIBERTY ENGINE MATERIALS TO THE AUTOMOTIVE INDUSTRY

The material used for all connecting rods on the Liberty engine
was selected at the option of the manufacturer from one of two
standard S. A. E. steels, the composition of which are given in
Table 13.

TABLE 13.--COMPOSITION OF STEELS NOS. X-3,335 AND 6,135

Steel No. X-3,335 6,135
Carbon, minimum 0.300 0.300
Carbon, maximum 0.400 0.400
Manganese, minimum 0.450 0.500
Manganese, maximum 0.750 0.800
Phosphorus, maximum 0.040 0.040
Sulphur, maximum 0.045 0.045
Nickel, minimum 2.750
Nickel, maximum 3.250
Chromium, minimum 0.700 0.800
Chromium, maximum 0.950 1.100
Vanadium minimum 0.150

All connecting rods were heat-treated to show the following minimum
physical properties; Elastic limit, 105,000 lb. per square inch:
elongation in 2 in., 17.5; per cent, reduction of area 50.0; per
cent., Brinell hardness, 241 to 277.

The heat treatment used to secure these physical properties consisted
in normalizing the forgings at a temperature of from 1,550 to 1,600 deg.F.,
followed by cooling in the furnace or in air. The forgings were then
quenched in oil from a temperature of from 1,420 to 1,440 deg.F. for the
No. X-3,335 steel, or from a temperature of from 1,500 to 1,525 deg.F.
for No. 6,135 steel, followed by tempering at a temperature of from
1,075 to 1,150 deg.F. At the option of the manufacturer, the normalizing
treatment could be substituted by quenching the forgings from a
temperature of from 1,550 to 1,600 deg.F., in oil, and annealing for
the best machineability at a temperature of from 1,300 to 1,350 deg.F.
The double quench, however, did not prove satisfactory on No. X-3,335
steel, due to the fact that it was necessary to remove forgings
from the quenching bath while still at a temperature of from 300
to 500 deg.F. to eliminate any possibility of cracking. In view of the
fact that this practice is difficult to carry out in the average
heat-treating plant, considerable trouble was experienced.

The most important criterion in the production of aviation engine
connecting rods is the elimination of burned or severely overheated
forgings. Due to the particular design of the forked rod, considerable
trouble was experienced in this respect because of the necessity
of reheating the forgings before they are completely forged. As
a means of elimination of burned forgings, test lugs were forged
on the channel section as well as on the top end of fork. After
the finish heat treatment, these test lugs were nicked and broken
and the fracture of the steel carefully examined. This precaution
made it possible to eliminate burned forgings as the test lugs were
placed on sections which would be most likely to become burned.

There is a great difference of opinion among engineers as to what
physical properties an aviation engine connecting rod should have.
Many of the most prominent engineers contend that a connecting rod
should be as stiff as possible. To produce rods in this manner in
any quantity, it is necessary for the final heat treatment to be made
on the semi-machined rod. This practice would make it necessary for a
larger percentage of the semi-machined rods to be cold-straightened
after the finish heat treatment. The cold-straightening operation
on a part having important functions to perform as a connecting
rod is extremely dangerous.

In view of the fact that a connecting rod functions as a strut,
it is considered that this part should be only stiff enough to
prevent any whipping action during the running of the engine. The
greater the fatigue-resisting property that one can put into the
rod after this stiffness is reached, the longer the life of the
rod will be. This is the reason for the Brinell limits mentioned
being specified.

In connection with the connecting rod, emphasis must be laid on the
importance of proper radii at all changes of section. The connecting
rods for the first few Liberty engines were machined with sharp
corners at the point where the connecting-rod bolt-head fits on
assembly. On the first long endurance test of a Liberty engine
equipped with rods of this type, failure resulted from fatigue
starting at this point. It is interesting to note that every rod on
the engine which did not completely fail at this point had started
to crack. The adoption of a 1/32-in. radius at this point completely
eliminated fatigue failures on Liberty rods.





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Previous: Rate Of Cooling



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