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PHOSPHORUS is an element (symbol P) which enters the metal fr...

Tool Or Crucible Steel
Crucible steel can be annealed either in muffled furnace or b...

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

Pyrometers For Molten Metal
Pyrometers for molten metal are connected to portable thermoc...

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

It is considered good practice to quench alloy steels from th...

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

Forging High-speed Steel
Heat very slowly and carefully to from 1,800 to 2,000 deg.F....

Chromium when alloyed with steel, has the characteristic func...

The crankshaft was the most highly stressed part of the entir...

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

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

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

MANGANESE is a metal much like iron. Its chemical symbol is M...

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

Correction For Cold-junction Errors
The voltage generated by a thermo-couple of an electric pyrom...

Manganese adds considerably to the tensile strength of steel,...

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

The Effect Of Tempering On Water-quenched Gages
The following information has been supplied by Automatic and ...

Double Annealing
Water annealing consists in heating the piece, allowing it to...

Connecting Rods


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.


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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