Monday, May 25, 2009

The Plastic Piano #1 - PVC

I went to my customer's house prepared to tune her piano.  She had warned me that some notes weren't working, usually not a big deal.  As soon as I opened the piano and looked inside, I could see the problem.  There were shards of a yellowish white plastic all over the place.  Oh no, plastic action parts!

To be fair, there's nothing wrong with plastic action parts if they're made correctly - the same can be said of wooden parts.  This piano, a beautiful console made in 1957, had action parts made of PVC, and I'm sure the parts worked well for a time.  Now the plastic had begun to disintegrate, and the parts would have to be replaced.

PVC, polyvinyl chloride, is usually referred to simply as vinyl.  It is one of the most widely used plastics.  It can be molded into things like pipes, it can be made into shiny cloth, and it can be bonded to fabric for use in upholstery, mimicking leather.  The properties of vinyl chloride had been investigated as early as the late 19th century, but it wasn't until the 1930's that a commercially viable plastic was developed.  PVC is quite rigid and brittle, and requires the addition of various plasticizers and stabilizers.  Vinyl combined with cellulose acetate (another plastic) as a plasticizer is what replaced lacquer for making phonograph records, starting in the 40's.  Vinyl without plasticizers is what is molded into rigid shapes, like pipes for plumbing, and siding and flooring for houses.

Rigid PVC should have been perfect for replacing wooden parts in a piano action.  The plastic parts were molded in the same shape as the wooden ones, and installed the same way.  The most common plastic parts were flanges, which are the hinged ends of many action parts and are attached with screws to various rails.  In some actions, backchecks, jacks, and damper levers were also made of PVC.  The only parts that were not made of plastic were the parts that are glued to each other.  PVC parts can be bonded together (using the solvent methylethylketone, or MEK, often called PVC glue), but I guess this was not viable for the action manufacturers.  I did see a Lindner piano, made in Ireland, probably in the 60's, whose action was entirely of plastic.  Even the keys were plastic, made of sheets of PVC glued into long hollow rectangles.

The problem with PVC, as with many other plastics, is outgassing.  The various additives that give vinyl its different characteristics slowly evaporate out of the plastic.  Over time, some plastic becomes more brittle, or shrinks, or becomes discolored, or, in the case of PVC, spontaneously disintegrates.  The technology behind the additives is almost more important than the technology behind the plastic resin itself.  When PVC was used for piano actions, the technology for stabilizing rigid PVC must have been in its infancy.  It was not foreseen that the outgassing would proceed so quickly, that the actions would start to fall apart in a couple of decades.  Modern PVC could be used with no problem, but now the piano industry won't go anywhere near it, and modern plastic action parts are made of other plastics.

The solution is simple, but costly.  The parts must be replaced.  PVC spinet elbows are replaced with acrylic ones, but other parts are replaced with wooden ones.  The parts are readily available because of the demand.  Sometimes not all of the PVC is falling apart, so apparently the outgassing varies from batch to batch.  For instance, in the case of the console I'm working on, the jacks and backchecks are completely shot, they crumble at a touch, but the hammer flanges and damper levers are fine.  They're not the least bit brittle.  I won't replace them for now, but I have warned the owner about the possible need for replacement in the future.

There has been one other use of vinyl in pianos.  Some of the more crazy and delightful console and spinet case designs from the 40's and 50's used vinyl upholstery fabric in addition to the more traditional wooden veneer.  It's found on the sides and top, and Wurlitzer was the main culprit.  The vinyl is usually embossed with the classic leather grain, and my favorite example used a white-with-brown-spots cowhide pattern.

Vinyl imitation leather has also been used to replace the leather on the ends of bridle straps, the straps that connect upright hammers to the wippens.  Over time, the leather disintegrates (not to mention the strap itself), but the vinyl holds up for much longer.  The only disadvantage is that it stiffens up over time and can rattle against the bridle wire.  It also becomes harder to remove from the wire.  I'll have more to say about the use of artificial leather and suede in pianos in a later post.

Related website:
The Plastics Historical Society