Cast ironvs. Steel was Prowler V6

[Greg Hermann]

>Greg,
>    All points well taken but a few contradictions. If the steel part is so
>much stiffer why does it have a harder time tampening tortional vibes.

This happens this way because cast iron has much more "hysteresis" than
steel when it is deformed and then allowed to return to its undeformed
shape.--Not saying that there is any permanent deformation in the iron part
after it is loaded and unloaded, but that a significantly higher portion of
the strain energy that was put into deforming the part is converted to heat
when the part resumes its unloaded shape with an iron part. This conversion
to heat is where the vibration damping property of iron comes from.

This property is why massive iron castings are used for things like machine
tool beds--there is less likeihood of tool chattering than there would be
with a steel bed because of the iron's vibration damping properties. A
machine tool is clearly designed for stiffness and stability, and ends up
being FAR stronger than it needs to be once these primary design concerns
have been addressed, and, of course, weight is of no serious concern in the
case of a machine tool.

And properly surface hardened steel has equally good, probably slightly
better, wear properties than cast iron. For instance, lathes such as Lodge
& Shipleys, which have particularly massive bed castings are regarded as
_VERY_ desireable units--extremely rugged, durable, and exceptionally
accurate tools.

>Ductile essentially means "bendable without breaking." It is for this reason
>all your points hold true.

Another thing which lots of folks overlook about stiffness--besides the
fact that the elastic modulus of cast iron is about 50 to 66% that of
steel, depending on alloy--is the fact that virtually all steels have about
the same elastic modulus_regardless_ of alloy _or_ of state of heat
treatment! You gain hardness and strength, and lose ductility with a harder
state of heat treatment of a given steel part, but you _do_NOT_ gain any
stiffness by going to a fancy alloy or by heat treating a steel part!!

Ponchos do have a rather massive cranks, big crank pins, lots of "overlap",
so prolly not much crank deflection, and I will stand corrected that the
block failures in them may just be due to inadequate webs.

Regards, Greg