Wings900 - How To Protect Your Models

The affected models still exist and I think a lot of collectors would like to know how they can take care to their models and keep them in good condition.

To start off I bought an Aeroclassics Northwest B720 through eBay Johan Chan.

Here are some photos of said model:

I first noticed this problem on a SMA KLM B737-200. I touched the stab and it broke. In this case I was able to get a spare part and able to repair it.The next case was an AC Canadian B737-200. I tried to bend the wing in a more straight position and it broke. The metal was so brittle it broke like a cookie. The same with the B720 when I touched the antenna, the front landing gear and an engine everything was broken.My advice to all owner of old AC B720 and B737-200 don’t try to bend parts in these models there is a high risk to break parts. The same with the SMA B737-200 which were made in the same factory. Collectors from old model trains like Maerklin or model cars like Matchbox or Dinky Toys know this problem well. In german it is called “Zinkpest” and in english I found the expression “zinc plague”. The affected models are mostly more than 50 years old. In Europe the producer solved the problem late in the 1950s.After some research in the internet I decided to analyse the zinc alloy of this B720 because in Europe it is impossible to find a zinc alloy in this poor quality standard.I work at a Swiss research and testing institute http://wwws.empa.ch as a mechanical engineer and I have an access to the most usual analytical process. I’m not a material engineer a buddy did that for me. For the moment we used XRF, it works with x-rays, and REM, a kind of microscope. http://34189.dynamicboard.de/file.php?url=http%3A%2F%2Ffiles.homepagemodules.de%2Fb34189%2Ff2t392p3073811n1.jpg&content=RE%3A+Zinkpest+an+Aeroclassics+Modell http://34189.dynamicboard.de/file.php?url=http%3A%2F%2Ffiles.homepagemodules.de%2Fb34189%2Ff2t392p3073811n2.jpg&content=RE%3A+Zinkpest+an+Aeroclassics+Modell http://34189.dynamicboard.de/file.php?url=http%3A%2F%2Ffiles.homepagemodules.de%2Fb34189%2Ff2t392p3073811n3.jpg&content=RE%3A+Zinkpest+an+Aeroclassics+Modell The highlighted elements are relevant. The deleted elements are errors generated by the analysis software (UniQuant) With the XRF analysis we got not a big surprise. The alloy contains a little too much aluminium and no copper. But the big surprise was in the REM. We found 11% oxygen and that is really bad. It means the metal is already heavily corroded. Inside zinc alloy oxygen is not allowed. The big problem is the process of destroying the material starts from the inside and cannot be recognized before it is too late. Once the process is started there is nothing to stop it. What can you do to prevent that with your collection? Don’t store the models in cold humid rooms like cellars. Humidity over 60% and temperature below 14°C will accelerate the process of corrosion. Don’t expose the models too often to quick temperature changes. Don’t illuminate the models with spots because they warm up the models. If possible don’t put the models in a sea water atmosphere. If you live in a beach house it is fine for you but bad for the airplane collection. The chloride (salt) destroy zinc alloy in a very short time. I don’t know for the moment if the paint will protect enough the metal or not. We do a second more accurate analysis in the REM and we look especially if there is chloride inside. If you touch the models often use gloves. The sweat of the hands contains also chloride and may help to destroy the paint. Especially the paints with metal particle like silver are sensitive to fingerprints. If you observe these simple things you will enjoy your collection for a long time. What can the manufacturer do to prevent a bad zinc alloy quality? He should buy the zinc alloy from a quality certified dealer. The manufacturer of the blanks should have a well working quality control and well skilled workers. The blanks should not be stored in sea water atmosphere or in surroundings with a high humidity.

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