Wednesday, June 07, 2006
Corrosion! It has probably already started!
When your beautiful kit arrives for any VANS aircraft, you need to think about when you are going to get the (usually) blue plastic off. It certainly protects the aluminium from minor scratches but it encourages corrosion. Let me explain.
Kaiser makes the aluminium and VANS buy it from them. Each sheet is labelled as to its specification of grade and thickness. You will see this written on the metal in blue ink. When I first started building, I found it very hard to get the ink off with a typical de-greasing agent. The thing you need to know is that it is very easy with water. (Put one drip of soap - not detergent - into a large bucket of warm water and the writing just wipes away with a damp sponge. Remember to dry the metal off afterwards. The fact that it wipes away so easily with water is a clue to an insidious problem which has caught many out. Being water-soluble, the writing is hygroscopic to some extent. This is probably not a problem in the dry heat of Arizona, but in the humidity of the English climate, a kit left in a normally unheated garage will by the end of one or two years show mild corrosion underneath the plastic when you remove it. This has to then be polished out, with red Scotch Bright, before you can etch prime the metal.
Therefore, my advice is:
1) Get the plastic off parts as soon as possible after they arrive if there is writing underneath the plastic. (If its a flat pack you might assemble it first. If it is a QB, I think it is the first job.)
2) Wash off the blue writing with clean water.
3) Etch prime (or alodine) to protect it.
You can just see the blue writing on the ally. No corrosion this time but I had it on the -9A and had to work hard to get rid of it.
I did approach VANS on this issue 6 months ago. The first answer said "....Have not heard of that before but will research it and see what comes up." which was rather disappointing since it was much discussed from time to time on the builder group web sites. As of yesterday the comment has moved on to ".... Steve, I was working on this thru our Kaiser rep and have spoken to him several times about it with no definitive answer from Kaiser. We
have since seen several instances of minor corrosion on the lettering
of the sheets (now that we're looking)...only the lettering...odd."
From our point of view as builders, the solution is easy. Don’t use a water soluble ink! Kaiser might view that differently.
Postscript dated 23 June.
Today I was preparing some 2024-T3 sourced not from VANS but elsewhere, and made I think by Alcan. It was interesting to note that the spec printing was mostly on the plastic, and when I tried to remove it from the aluminium in the few places it occured, it was not water soluable. It wiped away with a touch of MEK!
Kaiser makes the aluminium and VANS buy it from them. Each sheet is labelled as to its specification of grade and thickness. You will see this written on the metal in blue ink. When I first started building, I found it very hard to get the ink off with a typical de-greasing agent. The thing you need to know is that it is very easy with water. (Put one drip of soap - not detergent - into a large bucket of warm water and the writing just wipes away with a damp sponge. Remember to dry the metal off afterwards. The fact that it wipes away so easily with water is a clue to an insidious problem which has caught many out. Being water-soluble, the writing is hygroscopic to some extent. This is probably not a problem in the dry heat of Arizona, but in the humidity of the English climate, a kit left in a normally unheated garage will by the end of one or two years show mild corrosion underneath the plastic when you remove it. This has to then be polished out, with red Scotch Bright, before you can etch prime the metal.
Therefore, my advice is:
1) Get the plastic off parts as soon as possible after they arrive if there is writing underneath the plastic. (If its a flat pack you might assemble it first. If it is a QB, I think it is the first job.)
2) Wash off the blue writing with clean water.
3) Etch prime (or alodine) to protect it.
You can just see the blue writing on the ally. No corrosion this time but I had it on the -9A and had to work hard to get rid of it.
I did approach VANS on this issue 6 months ago. The first answer said "....Have not heard of that before but will research it and see what comes up." which was rather disappointing since it was much discussed from time to time on the builder group web sites. As of yesterday the comment has moved on to ".... Steve, I was working on this thru our Kaiser rep and have spoken to him several times about it with no definitive answer from Kaiser. We
have since seen several instances of minor corrosion on the lettering
of the sheets (now that we're looking)...only the lettering...odd."
From our point of view as builders, the solution is easy. Don’t use a water soluble ink! Kaiser might view that differently.
Postscript dated 23 June.
Today I was preparing some 2024-T3 sourced not from VANS but elsewhere, and made I think by Alcan. It was interesting to note that the spec printing was mostly on the plastic, and when I tried to remove it from the aluminium in the few places it occured, it was not water soluable. It wiped away with a touch of MEK!
