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"Removal and treatment of corrosion on magnesium castings on helicopters"



2002

We currently having a plating shop at our facility for plating aluminium parts with alochrome and magnesium parts with chromate by dipping into vats. The plant is moving to a new facility and we are not taking the plating shop with us. I therefore require alternatives to the dipping process that are easy to use and can be integrated into the manufacturing environment. I have found some pens that we have trialled containing alochrome (similar to paint pens) and these appear to work well on aluminium parts but the test results were not good when the pens were used on magnesium parts. Are there any equivalent pens available containing magnesium chromate or does anyone know of any alternative methods.

Charles Willday
- Hemel Hempstead, England, U.K
^


2005

Q. Hi there, I'm a Heli Engineer currently involved in restoring a Sud Aviation Super Frelon to flying condition after 10 years of standing outside in the elements. No mean feat, I promise!

As I expected, I have encountered areas of corrosion on the magnesium castings. (Gear boxes mostly) These parts are HUGE so immersion is not an option. I would appreciate some help on products and procedures for local repairs and treatment. The corrosion is mostly light surface corrosion, but there is also some pitting. During my military career we used to grind the affected area down to clean metal then treat with a selenious acid type wash. We also used a product called FRAMALITE if memory serves correctly. I do have service manuals detailing treatment schemes, but these date back to 1967 so I'm hoping there has been some progress in this field that could simplify my task!

Mac d [last name deleted for privacy by Editor]
heli base - Cape Town, South Africa
^


2005

A. Hi Mac

I'm not sure of any ground breaking developments in corrosion treatment for magnesium. We have always treated our magnesium transmission cases with chromic acid

Steve P [last name deleted for privacy by Editor]
- Nelson
^


2005

Q. Hi Steve, can you clue me in as to the process involved. Can it be used for local repair without removing the component from the aircraft?

Thanx Bud,

Mac d [returning]
- Cape Town, South Africa
^


2005 2005

A. Hi Mac
Use a solution of 10% chromic acid, i.e., 10 parts water 1 part chromic acid. We dress out as much of the corrosion as possible using a very fine rubber abrasive wheel. Use a cotton swab or fine paint brush to apply the acid solution. Let stand for 5-10 minutes,but do not let the solution dry.Rinse thoroughly to remove all traces of acid.As you know,most of the corrosion will be on split lines,bolt holes and studs,which makes dressing out near impossible in which case you will have to remove or kill the corrosion by acid treatment alone. Follow up by applying a chromate or epoxy primer. AS for doing this procedure while still bolted to the helicopter best of luck.I have found the best way and the proper way is through removal of the affected components.

Steve P [last name deleted for privacy by Editor]
- Nelson, New Zealand
^


2005

A. Try the old Selenious acid mix from the Rolls royce TSD 594 , we use it on most of the Pratt and Allison parts for touch-up .

Dave Brackenridge
aerospace plating - Germiston, South Africa
^


2005

Q. Thanx Dave, I'm looking for an ALTERNATIVE to selenious acid, but what is the recipe for your potion anyway?

Mac d [last name deleted for privacy by Editor]
- Cape Town, South Africa
^


2005

A. Gentlemen, non-chromate local treatments for magnesium exist and are already in use in military aircraft industry. Probably they will also be in use in commercial aircraft when this industry return to magnesium. The treatments applied by spaying or brushing. They belong to OXSILAN MG family. Please contact Chemetall Oakite, or another Chemetall subsidiary in your country.

Ilya Ostrovsky
Germany/Israel
^


March 2, 2012

A. Hi there. Magnesium components could be saved by using the cold gas dynamic process.

Ionel Botef
- Johannesburg, South Africa
^


sidebar 2005

Hey Mac,
Did you have the shop in benoni heliport many years back?

gary joseph
Gary Joseph
Johannesburg,
South
Africa

^


2005

Hi Gary, Not me on that one. Closest would be while I was building a turbine test bed for Allison C series turbines at NAC Rand in '94.

I need a locally available product to treat these casings, any suggestions? Selenium Nitrate is prohibitively expensive.

Ta Boet.

Mac d [last name deleted for privacy by Editor]
- Cape Town, South Africa
^


2005

Sorry Mac, I do not have a clue.

gary joseph
Gary Joseph
Johannesburg,
South
Africa

^


February 11, 2008

Hi Mac, great to hear that you still in RSA, hope you get your problem sorted, if you do please contact us. I am always busy restoring old things!
Best regards

Piet le Roux
- Bloemfontein, Free State, South Africa
^

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