Roger, et al:
At 03:56 PM 06-06-98, the following was written:
>Hi Newton,
> You are quite correct in saying that the volitiles evaporate
>quicker with the use of acetone, however you are refering to the free
>acetone molecules, and not the very complex polymer that you have created
>by melting the keytop STUFF?? The attached molecules of the polymer are the
>ones that take a long time to be given off. Since acetone is an alcohol,
>and is hydroscopic, the RH conditions will have a significant effect on the
>rate of curing, hence that is why we notice such dramatic effects in this
>region.
I'm afraid I'm going to reap the reward opposite to being hygroscopic on
this one, but here goes, as a chemist I can't resist replying:
Acetone is not an alcohol. It is a simple ketone with the formula, CH3-C=O
|
CH3
that is sometimes called "the universal solvent" because it both dissolves
and dissolves in so many other chemicals. It is not hygroscopic. What
really happens when another chemical dissolved in acetone is applied to
hammerfelt is that the acetone evaporates so rapidly this evaporation lowers
the temperature of the acetone not yet evaporated to below the dew point of
the water in the surrounding air. This causes airborne water molecules to
condense on its surface. And, acetone and water being infinitely soluble in
one another, this water dissolves in the acetone--you might notice
indication of this happening by observing a whitish opalescence on the
surface of the solution. By the time the remaining acetone evaporates (It's
more volatile than water.) the wool may have absorbed enough water to remove
press--release press, if you will.
> To correct you on a minor point, laquer thinner is also an alcohol, and
>is also hydroscopic, and there fore is effected by moisture, and is not
>impervious, as Steinway may claim.
Chemically, lacquer thinners generally tend to belong to the chemical class
of esters, but in practice may be a complex solution of many chemicals, e.g.
toluene, xylene, maybe even higher ketones and other chemicals. They are
not hygroscopic as a whole but may evaporate rapidly, which would lead to
the same cooling effect as acetone, although they likely will not evaporate
quite so rapidly. Anyway, the effect is *somewhat* the same: they pull
moisture to the surface, and this moisture may be captured by the wool.
Laquer solvents may cause less of a problem than acetone, however, since
they are not water soluble. There will be a blushing problem though, for
instance, if a wood surface is being coated in a high humidity environment.
> Ask any refinisher.
> My practice of always dry ironing after all voicing, helps to over come
>some of the hydroscopic activity
> I think it is the climatical conditions,
Yes, high humidity ambient conditions do tend to exacerbate the moisture
gathering problem. And something else: wool and some other textile fibers
show the property of hysteresis. It's a bit hard describing this in words,
but I'll try since its effects may be encountered by those encountering
moisture effects on wool. When damp wool, for instance, that is dried by
taking the ambient relative humidity from very high to very low, and water
in the wool is plotted vs. the lowering relative humidity this curve does
not follow the same path as when the same wool is dried bone dry and then
gradually brought up in water content by raising the relative humidity of
the surrounding air. You have to overdo the drying or wetting to get back to
where you started.
In the situation we're dealing with now this phenomenon means that, when a
hammer has attracted moisture from the air because it's been chilled below
the dew point of the moisture in the surrounding air, and this moisture has
been absorbed by the wool, provided the temperature and relative humidity
remain unchanged, there will likely be much more moisture in the hammer
after all the acetone is gone than before the "juicing." This added water
will not evaporate unless the air becomes much dryer or the temperature is
raised a notable amount.
The hammer maker probably used heat in gluing/pressing the hammer. This
removed mosture and added a more or less durable press. Earlier, the felt
maker had added also added press to achieve the thickness dimensions and
hardness the hammer maker specified at given distances from, say, the bass end.
The more the water gathered in "juicing" and the more the press in the
hammer (Treble hammers have received much more press to achieve their higher
density--read that "specific gravity"-- than bass hammers.) the more the
percentage swell release that can be expected. If one dries the hammer
after "juicing," it may help under some conditions, especially if press is
reapplied, but it is also possible that too much press has been lost by then
to be replaced by simple ironing
and the press reapplied will be too little. Also, the rapid drying, if
there has been much "juice" added, may well cause the "juice" to migrate
toward the side of the hammer that is being rapidly dried making it
harder/crustier. At this point it must be admitted though that keytop
material is likely to be thermoplastic and ironing can activate it to hold
the wool down in place.
A nasty cycle can develop. Press is lost, more "dope" is applied because
the hammer has become too soft, more water is attracted, more press is
released (along with the resiliency undoped wool provides), more dope is
added...and so on. Finally, the hammers are in effect treble keytops:
really wool-reinforced keytop material!
Sorry if I put you to sleep, folks. That's what happens when you jostle a
chemist/textile chemist. Let me sleep next time.
I await the steam!
Regards,
Earl Dunlap
Bacon Felt Co., Inc.
Earl S. Dunlap, Jr.
Technical Director
Bacon Felt Co., Inc.
395 W. Water St.
Taunton, Mass.
dunlapes@iCi.net
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