jmhannon@.................... wrote:

> George,
> Could you tell me more about the advantages of a triangular shape for the spring
> as opposed as a retangular shape.  Also I would like more info on heat treating
> the berrylium copper.
>
> Jim Hannon
>

Jim,

The optimum shape for a spring is such that all parts are subjected to the same
stress.  If you analyze a
triangular spring clamped on one side and loaded at the opposite point, the stress
is equal at all points of
the spring.  A flat rectangular spring with the same base can be loaded with the
same force, but it will
not deflect as much as the triangular.  Thus the triangular spring has absorbed more
energy with the same maximum force.

Beryllium copper is what is known as a precipitation hardened metal.  That is the
beryllium is dissolved in the copper when it is made and cooled quickly.  In this
condition it is about as soft as copper, though it is better if it is rolled
thinner, since it hardens it somewhat, and results in a higher yield strength after
heat treatiing.
The heat treating process requires that it be heated in a reducing atmosphere (or
clamped so that oxygen cannot get to the surface).  There are a variety of heat
treatments depending on how high you want the yield strength to go.  I believe that
the optimum one is around 600 deg. F for an hour.  Any experienced heat treating
shop ( specially ones who make springs) will have the proper equipment.  The
temperature is rather critical if the highest properties are to be achieved.

What happens during the heat treatent is that tiny particles of beryllium
precipitate out in the grains of copper.  This ties the copper grains together in
such a way that they cannot slide to elongate, thus leading to very high strengths.
Due to the fact that the bending modulus of copper is about 1/2 that of steel, it is
possible to store twice as much energy in a copper spring as a steel one of the same
size.

Another major advantage of beryllium copper is that the spring can be formed while
soft to an exact final
shape.  To maintain the shape is must be clamped to a piece of stainless or similar
material during the heat treatment.

George Harris


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