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I was reading about Hailun piano on pianopricepoint.com last night and one of the "innovations" they talked about was the aluminum keybed. However, it came to me as a surprise that nobody else in the 200+ years of piano making has thought about using metal for the keybed. Well, maybe somebody has thought about it, but it obviously was not widely implemented across the industry. If the plate can be made with cast iron, why wasn't the keybed made with metal too? Is it because there is no direct benefit? Is it because there are some drawbacks? Or is it because it was too technically difficult or too expensive?

It may have been done for the ultra-light weight pianos that the Germans made for their Zeppelins in the 1930's. There was a lot of aluminum in them, IIRC.

Wow. Would love to read or hear more about these pianos!

I would think that aluminum would be too sensitive to temperature changes for that use, no?

Wood expands about 3x10^-6 m/m K parallel to the grain (and about 30 across the grain), whereas aluminium has a temperature expansion coefficient of about 20 to 22x10^-6 m/m K, depending on the alloy.

Read on...

Hardman grands had cast iron frames for their keybeds.

That would make wood a more anisotropic material than aluminium (provided that the Al part is processed so that it is in a stressless state), but does a fraction of a millimeter over a meter long part make a difference in a keybed?
Or is it a matter fabrication speed/tighter tolerances, perhaps?
Or is it (in)sensitivity to humidity?

I would think aluminum, or any other metal that won't rust, will be less sensitive to humidity than wood, and that is why Hailun chose to use aluminum in their keybed. My question is why metal keybed has not been more widely adopted by other piano manufactures? For example, I would expect somebody to come up with a keybed made with titanium, which is both lightweight and strong.

Actually, aluminum (aluminium) corrodes very quickly (essentially instantaneously, hence arc welding must be done in a non-oxygen atmosphere) in the presence of oxygen. It needs to be anodized and sealed from air. Airplane maintenance is heavily biased toward corrosion inspection and prevention, for example. I have old (40-50 years) aluminium capacitors and brackets that are heavily pitted and covered in oxide residue.

That being said, a keybed would have to be sealed and electrolytic action, caused by the interaction of dissimilar metals eliminated. I am thinking about guide bolts.

Hailun is the only and first to use a light weight keybed. This is in their HU1P and HU5P models. Some benefits from this are the keybed will never shrink and never expand- most importantly it will never warp which would make it ideas for areas with strong climate changes.

It's the opposite-it's actually very ideal for areas with strong temperature changes. I've done some research on this and the keybed never shrinks or expands-it will never warp. It makes for more accurate and better playing over the years.

Yes, but it also depends on the alloy. It's been a few years, but IIRC the things I made from 6061-T6 in the machine shop did just fine without anodizing in a home environment. But on a boat in salt water, fuggedabout aluminum. Get a scratch in the anodized coating, and it's toast. The miserable thing is it swells up as it corrodes, so it's a bear to get rid of.

So, the aluminum piano was OK for Zeppelins, U-boats not so much....

Yet another materials science question...

Cast aluminum makes a great platform for a key bed. I believe others have tried this innovation on uprights, but execution matters.

When aluminum oxidizes, the outer layer looks dull almost immeadiately. If you ever see freshly cut aluminum, it shines if only briefly. This is exactly on prout's point about its use for aluminum welding, but doesn't relate to the use of an aluminum solid. In other types of welding, aluminum is included as a deoxidizer because it oxidizes faster in the alloy than the other metals required, effectively buying time for the welder .

When iron oxidizes, the rust creates small cracks in the iron surface that continuously eat away at the metal below. Active agitation accelerates this, but unless the iron is otherwise protected, it rusts and breaks down continuously in the presence of oxygen. Throw a car door in the ocean and it will rust away in hours. However, when aluminum oxidizes the outer layer becomes a thin skin of aluminum oxide (the dull aluminum) that seals the aluminum solid beneath. If it is not agitated by chemicals or abrasions, then the aluminum actually stops rusting.

More material science...

Other properties definitely depend on the alloy, but cast aluminum expands and contracts evenly, but in very small amounts at varying room temperatures, but would not be affected by humidity. Laminate wood expands and contracts unevenly (depending on grain, glue, etc) and while less affected by humidity than solid wood, it is still affected. Over time in a stressful environment, the laminate will show more variance and potential problems (twisting, warping, sagging, de-lamination) for the piano's performance.

In the Hailun HU-1P & HU-5P, the cast aluminum key bed offers numerous, small benefits to durability and performance. I don't see any drawbacks to its use in the design (unless you're trying to attach an external fallboard lock ). I would call it evolutionary, not revolutionary, and a well thought out application of a material.

Since this application is tied to the rest of the piano that is still sensitive to changes, the benefit is by a matter of degrees, but it is of benefit.