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A Chromium-cobalt Steel
The Latrobe Steel Company make a high-speed steel without tun...

Restoring Overheated Steel
The effect of heat treatment on overheated steel is shown gra...

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

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

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

ANNEALING can be done by heating to temperatures ranging from...

The Influence Of Size
The size of the piece influences the physical properties obta...

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

Instructions For Working High-speed Steel
Owing to the wide variations in the composition of high-speed...

Affinity Of Nickel Steel For Carbon
The carbon- and nickel-steel gears are carburized separately...

Impact Tests
Impact tests are of considerable importance as an indication ...

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

This steel like any other steel when distorted by cold worki...

Hardness Testing
The word hardness is used to express various properties of me...

Care In Annealing
Not only will benefits in machining be found by careful anne...

Composition Of Transmission-gear Steel
If the nickel content of this steel is eliminated, and the pe...

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

Chrome-nickel Steel
Forging heat of chrome-nickel steel depends very largely on ...

Preventing Decarbonization Of Tool Steel
It is especially important to prevent decarbonization in such...

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

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.

Next: Crankshaft

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