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MMD > Archives > January 2007 > 2007.01.23 > 07Prev  Next

Quality of Materials & Testing Materials
By Mark Kinsler

> Can you tell us how to test pneumatic cloth?  Is there a way to
> know for certain that the pneumatic cloth I buy today will last
> longer than two or three years?

This is always a difficult topic, but there are some steps that can be
taken.  Industry -- the profit-making kind -- deals with these sorts of
issues on a daily basis.  That's why they began an organization called
the American Society for Testing of Materials, if I've got it right,
or ASTM.

So the first thing someone should do is to go have a look at the ASTM
literature to see if anyone has ever worked out testing standards for
rubberized fabric.  While you're at it, you'd want to see how adhesives
for wood are tested as well.  And leather, and felt, and all the other
materials used in these instruments.  ASTM has been around for a long
time, so perhaps player-piano manufacturers contributed to its data base.

> We all know how much work is involved in restoring a player and the
> sickening feeling it is to discover that all the work done will have
> to be done over again because of materials that we thought were the
> best are failing.

Yep.  Happens in many other pursuits as well.

> Why is it pneumatic cloth that dates from 1929 is excellent quality,
> still in use and not leaking, while pneumatic cloth I purchased in
> 1994 leaked like a sieve in less than five years?  (Both cloths are
> in use, in the same piano, under the same conditions.  The very old
> cloth is excellent.  The new cloth deteriorated in a very short time
> and had to be replaced)

Contamination, substituted ingredients, mixing and fabrication issues,
and/or bad luck.  Might have been made on a day that was humid, or not
humid -- things like that.  Maybe the cloth had sizing on it that
happened to be incompatible with one of the components of the rubber
mix.  Maybe the curing temperature was wrong.

> What happened to the old formulas for making good rubber cloth?
> Why can't those old formulas be found and used today?

The cloth from 1929 might have been an anomaly, and the rest produced
that year might have fallen apart fifty years hence.  Organic
composites are exceedingly complex, and we just have to do our best.

> I paid enormous prices for what I thought was the best pneumatic cloth
> available that is now worthless.  When I applied the "new" pneumatic
> cloth on various bellows, it tested tight and worked for awhile.  Then
> something happened.  The rubber slowly turned hard and crumbled.

Maybe outgassing from some other substance in the shop.

> How can this phenomenon be predicted by early testing?  Does one
> have 75 years to test the quality of rubber cloth?

There aren't any miracles in the realm of artificial time just yet.
The chemical reactions of deterioration are exceedingly slow and
unpredictable.  So we make our best guesses by trying to accelerate
matters by exercising our samples in atmospheres containing high levels
of ozone and various sorts of organic aerosols, at elevated or reduced
temperatures, under ultra-violet light, and under very moist or very
dry conditions.

> There was no guarantee when I purchased the cloth.  Why not hold the
> manufacturers responsible for quality?  Perhaps if we all get together
> and insist on a guarantee, or refuse to buy the materials, the
> manufacturers would be more careful in producing higher quality.

Somehow I doubt that the amount of rubberized cloth used in instrument
restoration would make much of a dent in anyone's profits one way or
another.  Besides which, there's no reason to believe that everyone
isn't doing his best at present.

Consider the people who build materials for aircraft.  Airplanes used
to be made with glued, wooden frames and lacquered cotton, all of which
are pretty mission-critical.  They worked out testing procedures for
these, and for fuel, and tires, and a thousand other materials over the
years.  Start with ASTM, or other industrial testing resources, and go
from there.

Mark Kinsler

(Message sent Tue 23 Jan 2007, 18:37:56 GMT, from time zone GMT-0500.)

Key Words in Subject:  Materials, Quality, Testing

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