Archived posting to the Leica Users Group, 2006/01/14
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]To be honest Frank, I do not know how it is protected or if it is alloyed with something to stabilize it. I have never noticed any significant corrosion. Here is a quote off of Gene Berg's site: > All VW cases are "pickled" when new. Pickling is a preservative > that leaves the case colored. This color varies from gold to green. > It is not to be removed as it is meant to protect the magnesium > from corrosion. Amusing anecdotes about burning VW cases: http://www.thesamba.com/vw/forum/archive/index.php/o-t--t-59597--.html I particularly like the one about the chap who ignited his case while welding and then threw the burning cases into a pool! More general VW magnesium case info: http://www.clubvw.org.au/all_about_magnesium.htm John Collier On 14-Jan-06, at 2:12 AM, Frank Dernie wrote: > Well John the note I wrote a few dozen messages ago looks redundant > now! Is it the crankcase shell which is magnesium? How is it > protected? > With standard potassium dichromate coating a racing car magnesium > gearbox casing can be corroded beyond repair within a year if in > storage. Magnesium water pump casings were lasting one or two races > (1000 miles or so) before being too badly corroded to reuse. We do > still have magnesium pump housings on most engines, nowadays > machined from solid on NC machines, but they still require a > passivator in the water otherwise they would be corroded through > within an hour or two running. Nowadays the life of an engine is > 1200km then most of it is scrap so the short life of mag parts is > no longer an issue (if you think that is bad it used to be 400km > before the rules changed). > Sheet magnesium was banned from use in racing cars following the > death of Piers Courage in a magnesium chassis de Tomaso at a Grand > Prix in the early 70s (the car was being run by Frank Williams but > before my time) if I remember correctly the minimum thickness of > magnesium permitted in the rules is 3mm, though I haven't looked in > years. AFAIK only cheaper racing cars use magnesium for important > parts any more, and then probably only the gearcasing as it is > probably the cheapest lightweight case, but not very stiff or > strong. I haven't designed a magnesium hub carrier since the late 70s. > Frank