Hi Earl, Thanks for such an imformative post, it's greatly appreciated, I frequently need straightening out, (smile's). It will teach me not to assume. Kind regards Roger At 11:41 PM 6/10/98 -0400, you wrote: >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 > > Roger Jolly Balwin Yamaha Piano Centres. Saskatoon/Regina. Canada.
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