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Written by Durrell Armstrong
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There are basically three grades of the rubberized bellows cloth used in player pianos; the heaviest for the bottom pumps; the lightest for the 88 or so "key" bellows, then a medium grade for everything else. The everything else would include the pneumatic motor that turns the music roll and its governor bellows which keeps the speed running the same tempo, no matter how slow or fast the pumping. Then you have an automatic tracking bellows on some players which keep the roll running straight. If there are any bellows to operate the soft, loud, or mandolin function, these also use the medium grade cloth.
The medium grade of cloth is usually the same as the lightest cloth doubled to itself, with the rubber in the middle, with one side dyed a color. The lightest cloth just has an airtight coating on one side.
The heaviest, pump cloth is always a combination of two types of heavy cotton, with the rubber in the middle. The outer layer of cloth is the heavier of the two, referred to as a "drill" cloth, and which is dyed some color. The inner cloth is a cotton "twill" cloth which has been bleached and a light fuzz raised on the cotton, from a brushing action. Even though no one will see the side that will be glued, it must be bleached. The reason is that to use, what the industry calls, "greige goods", which is neither dyed or bleached, but instead a dirty, slightly yellow color, it would be disaster when you tried to glue it. Cotton shrinks when water hits it. When it has been dyed a color or bleached, the process takes out most of the shrinkage. But if two layers of cotton were joined together, with one of them still able to shrink from the water content of the glue, it would want to curl away from the glued edge of the bellows board almost immediately.
The "fuzzing" of the glue side of the pump cloth will store up more of the glue and make it easier to work with, because it won't slip around as easily or slip back to the corner where there is resistance to turning and a loop might develope. There can be too much fuzzing-- so much that the cloth soaks up all of the glue that you can lay on the edge of the bellows board, with none left over to go completely through the weave of the cotton and bond with the rubber layer.
The rubber used to produce the various grades of bellows cloth in the 1920's, and before, was and still is referred to as Natural Rubber. This was before the age of synthetics. Substitutes, such as Neoprene did not have a track record to verify its longevity. Some form of Neoprene compound was used as a rubber substitute in the making of replacement bellows cloth until well into the 1960's, when even the best grades of Neoprene, were shown to have a life expectancy of no more than thirty years. At this time, some of the original material, which was now going on fifty years, was still holding up. In the final summation, it could be proven that Natural Rubber could last longer than any synthetic substitute. As with the Neoprene coatings, there were different grades of quality, with the lasting grades always costing more.
By 1950, the quality of the Neoprene coatings used in making replacement bellows cloth had sunk to an all-time low. With such poor quality, it quite often was better to leave the original material in place rather than replace it with a product that had a life expectancy of one or two years. This was largely the result of indifferent suppliers, more interested in profit and competition with others, who asked for the cheapest coating of Neoprene. Of course, the manufacturers cooperated by loading the Neoprene coating down with clay filler and making the cheapest product possible.
In the early 1950's, Player Piano Co., of Wichita, KS went into business with the motivation of improving the quality of bellows cloth and tubing, simply to fulfill their own needs for lasting restorations. With a surplus of custom made bellows cloth, evolving as a supplier, rather than a user, was inevitable.
In the late 1970's, Player Piano Co. was the first supplier to switch to using the best grade of Natural Rubber in all types of bellows cloth. Examination of the bellows cloth used by Aeolian Company was of particular interest, because there were many examples of Aeolian products around (now fifty to sixty years old) exhibiting the Natural rubber was still "live". Other examples of other player actions produced in the 1920's had shown that the Natural Rubber coating was crystallizing or had become totally hard. What had Aeolian done differently? It seems that in their quest for excellence, Aeolian had been willing to spend more money in the coating of their bellows cloth. Specifically, it was in the cost of the "Plasticisors" that were added to the sap of the rubber tree. Permanent plasticisors cost four times as much as the cheaper types of additive.
Natural Rubber is recognized in the industry as having a better "hand". The term of the "hand" refers to the feel of the rubber as being soft and without undue resistance to folding. The hand is determined by what is called the "durometer" of the rubber. Durometer is the scale of the softness to hardness. All rubber must be cured after it is applied to the fabric. This is done by heat. Before the curing heat is applied, the substance is like chewing gum: sticky and without much recovery from stretching. The application of heat allows the metamorphosis into rubber. Rubber can be over-cured or under-cured. Just the right amount of heat for the product has to be predetermined.
The total thickness of the lightest pneumatic cloth is in the range of .007" to .009" (three sheets of ordinary writing paper that you type letters on, would be equivalent to a thickness of .009") The total thickness would depend upon the thickness to the cotton cloth to start with. If Nylon fabric were used instead of cotton, the total finished thickness could be brought down to .005" using the thinnest nylon cloth to start with.
Thickness of pneumatic cloth also is determined by the method in which the rubber is applied to the cloth. If it is "calendered" it means that the rubber coating is applied to the cloth by being transferred by a roller, such as ink is transferred by the rollers on a printing press. If the spreading method is used to apply the rubber to the cloth, it means that the cloth passes under the reserve of rubber and in effect works like a squeegee, which can be regulated down to the barest minimum, but still resulting in an airtight coating.
The best method used to make pneumatic cloth is to use the machine known as the spreader. This method eliminates pinholes, presuming that a fine weave, first class quality of cloth is being used.
As the pneumatic cloth is wound up from the spreader, the rubber coating is uncured and sticky, so it must be dusted with corn starch to keep it from sticking to the back side of the previous round of cloth. Remember, that at this stage, the uncured rubber is still soft and malleable, and so it leaves a cloth imprint into the surface of the rubber coating, although it will not stick because of the dusting. This is actually an advantage in the finished product because it allows a better glue bond at the lap-over on the hinge end of the pneumatic. If the surface of the rubber coating were to be perfectly flat and shiny, the glue could not adhere as well without this roughness of the cloth imprint. Goods could be produced without the need for the dusting with the corn starch, but the material would have to either pass between heated rollers to cure before winding, or else have a plastic insert inter-wound, to separate the surface of the uncured rubber from the cloth until it could be heat cured. In this case, after the curing, the plastic liner is simply backed out of the roll of the cloth, but it leaves a slick finish to the rubber. The corn starch cannot be scrubbed off the rubber coating after curing. Even though an uneven dusting of the corn starch, can be unsightly, it doesn't affect the quality of the rubber.
The wear factor in the use of polyurethane coating in place of Neoprene or Natural Rubber was actually due to the Nylon fabric that was coated (with products named "Numalon", "Bilon", or "Polylon"). While a Polyurethane coating is cheaper than Neoprene or Natural Rubber, it is unstable unless it has just the right cure to prevent the composition from breaking down and the catalyst from working out; in this case, the coating looses its elasticity and gets gummy, although the weave of the nylon cloth doesn't break down, and holds it together. The wear and aging factor of nylon cloth as compared to cotton, is about ten times as durable as cotton. So a Nylon pneumatic cloth, coated with the best grade of Natural Rubber would result in the best material possible.
Player Piano Co., Inc. of Wichita, KS now has the Nylon pneumatic cloth available. It sells for less than half the price of traditional cotton pneumatic cloth. But for the purists that must use only the hot hide glue, Nylon pneumatic cloth cannot be used; it takes a special plastic or PVC-E glue.
This article was written specifically for the Player-Care web domain and may not be duplicated or used without the express written permission of John A Tuttle. Sadly, Durrell Armstrong passed away suddenly during the Christmas Holidays in 2008. He was a dear friend.
Want more information about gluing nylon cloth with hot hide glue, as well
as some of the differences between animal glues seldom mentioned? Read these
articles by Craig Brougher.
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