TOOLING
Engineer Build Maintain
How to preserve mold performance
A better understanding of what
the latest mold coatings can do
can make your customer
relations invulnerable.—Steven
J. Bales, edited by Carl Kirkland
If there is one common thread binding
good relations between moldmakers
and molders, it’s the need to continuously preserve, and even enhance or improve, a mold’s performance. This thread
is what helps create a valuable partnership
to maintain customer loyalty and perpetuate a mutually profitable alliance.
One effective way to solidify that
thread is for moldmakers to more clearly
understand the importance of using the
correct mold coating. It’s no longer just
a question of using nickel or chrome.
There are other smart options available.
First, rest assured that there is still a
place—and there probably always will be a
place—for hard chrome and electroless
nickel in the plastics tooling industry.
However, with the growing field of new
molding materials being used today, it naturally follows that new coatings have either become available or soon will be
available that are designed to help take
mold performance to a new level, as
shown in the chart on p. 36.
Some of these newer molding materials and compounds can be brutal on a
mold. In addition to glass and mineral
fillers, we now regularly deal with rice
hulls, wood fibers, metal powders, flame
retardants, and other additives, to name
just a few. Add to these the frequent occurrence of outgassing and moisture acidity, and your very expensive tools are in
for a beating.
Hard chrome vs.
diamond chrome
The first step in choosing the best coating
for your mold is to assess your needs.
What kind of material is being molded?
What kind of tool steel is being used?
How intricate are the parts being molded? How many cycles do you expect the
mold to perform between scheduled
maintenance? What are the tolerances
expected?
Hard chrome may be the answer if
you are molding very intricate parts using
glass-filled materials. Its main advantage is
that it offers a tough 72 Rockwell C
hardness and is applied at a very low temperature, providing excellent protection
from abrasion, plus moderate corrosion
protection. Hard chrome also gives you
the ability to achieve any SPI finish.
Hard chrome can be costly, though,
especially if the parts you’re molding are
very intricate and detailed, because it requires the construction of an anode to apply it. The more intricate the part, the
longer and more involved the anode construction. This also means a higher price.
An alternative could be a newer nickel-cobalt alloy, a unique alternative that
does not require an anode to apply it,
This chromium-matrix
diamond composite coating
provides a high dispersion of
nanometer-sized, spherical
diamond particles.
thereby rendering it a
cost-effective alternative
to hard chrome. Also, because it has electroless
properties, it plates more
uniformly. And the cobalt
gives the mold good abrasion resistance at 62
Rockwell C hardness.
So what is the best choice? It depends
on the percentage of glass in the molding material you’re running. You have
to decide which matters most: abrasion or
corrosion protection.
Another new alternative
For very high-wear conditions that even
hard chrome and nickel-cobalt can’t effectively protect, consider an even newer coating product called diamond-chrome. With a Rockwell C hardness of
85-plus, this chromium-matrix diamond
composite coating provides a high dispersion of nanometer-sized, spherical diamond particles (see photo, above). These
diamond particles give this coating its impressive ability to offer superior abrasion
protection.
A noted benefit is that diamond-chrome does not compromise the integrity of the tool as do similar products on the
market, because it is applied at a very low
temperature—about 130°F. Also, diamond-chrome will plate all commonly
used tool steels, even when they are heat-treated, nitrided, or prehardened.
It’s easily strippable by using reverse
electrolysis in a caustic solution and it can
be deposited in any controlled thick-
