Liberty Motor Connecting Rods

: The Working Of Steel

The requirements for materials for the Liberty motor connecting rods

are so severe that the methods of securing the desired qualities

will be of value in other lines. The original specifications called

for chrome-nickel but the losses due to the difficulty of handling

caused the Lincoln Motor Company to suggest the substitution of

chrome-vanadium steel, and this was accepted by the Signal Corps. The

rods were according
y made from chromium-vanadium steel, containing

carbon, 0.30 to 0.40 per cent; manganese, 0.50 to 0.80 per cent;

phosphorus, not over 0.04 per cent; sulphur, not over 0.04 per

cent; chromium, 0.80 to 1.10 per cent; vanadium, not less than 0.15

per cent. This steel is ordinarily known in the trade as 0.35 carbon

steel, S. A. E., specification 6,135, which provides a first-rate

quality steel for structural parts that are to be heat-treated.

The fatigue resisting or endurance qualities of this material are

excellent. It has a tensile strength of 150,000 lb. minimum per

square inch; elastic limit, 115,000 lb. minimum per square inch;

elongation, 5 per cent minimum in 2 in.; and minimum reduction

in area, 25 per cent.

The original production system as outlined for the manufacturers

had called for a heat treatment in the rough-forged state for the

connecting rods, and then semi-machining the rod forgings before

giving them the final treatment. The Lincoln Motor Company insisted

from the first that the proper method would be a complete heat

treatment of the forging in the rough state, and machining the

rod after the heat treatment. After a number of trial lots, the

Signal Corps acceded to the request and production was immediately

increased and quality benefited by the change. This method was

later included in a revised specification issued to all producers.

The original system was one that required a great deal of labor

per unit output. The Lincoln organization developed a method of

handling connecting rods whereby five workmen accomplished the

same result that would have required about 30 or 32 by the original

method. Even after revising the specification so as to allow complete

heat treatments in the rough-forged state, the ordinary methods

employed in heat-treating would have required 12 to 15 men. With

the fixtures employed, five men could handle 1,300 connecting rods,

half of which are plain and half, forked, in a working period of

little over 7 hr.

The increase in production was gained by devising fixtures which

enabled fewer men to handle a greater quantity of parts with less

effort and in less time.

In heat-treating the forgings were laid on a rack or loop A,

Fig. 14, made of 1-1/4-in. double extra-heavy pipe, bent up with

parallel sides about 9 in. apart, one end being bent straight across

and the other end being bent upward so as to afford an easy grasp

for the hook. Fifteen rods were laid on each loop, there being

four loops of rods charged into a furnace with a hearth area of 36

by 66 in. The rods were charged at a temperature of approximately

900 deg.F. They were heated for refining over a period of 3 hr. to

1,625 deg.F., soaked 15 min, at this degree of heat and quenched in

soluble quenching oil.

In pulling the heat to quench the rods, the furnace door was raised

and the operator pulls one of the loops A, Fig. 15 forward to

the shelf of the furnace, supporting the straight end of the loop

by means of the porter bar B. They swung the loop of rods around

from the furnace shelf and set the straight end of the loop on

the edge of the quenching tank, then raise the curved end C,

by means of their hook D so that all the rods on the loop slide

into the oil bath.

Before the rods cooled entirely, the baskets in the quenching tank

were raised and the oil allowed to partly drain off the forgings,

and they were stacked on curved-end loops or racks and charged into

the furnace for the second or hardening heat. The temperature of

the furnace was raised in 1-1/2 hr. to 1,550 deg.F., the rods soaked

for 15 min. at this degree of heat and quenched in the same manner

as above.

They were again drained while yet warm, placed on loops and charged

into the furnace for the third or tempering heat. The temperature of

the furnace was brought to 1,100 deg.F. in 1 hr., and the rods soaked at

this degree of heat for 1 hr. They were then removed from the furnace

the same as for quenching, but were dumped onto steel platforms

instead of into the quenching oil, and allowed to cool on these

steel platforms down to the room temperature.