MECCANO Posted July 15, 2014 Share Posted July 15, 2014 Guys i was having a nose at a defender on the weekend, that had been fitted with a brand new galvanised chassis a few years ago. I noticed a small crack (40mm long) in the rear cross member. It was located on the bottom edge, in a plate that reinforced the cross member welded to the rail. The crack was central in the plate and hadn't propagate from an edge. It seem slightly bulged outwards, and i wondered if it was a result of trapped air during the galvanising process? Has anyone else seen anything like this? A quick google suggests galvanising can be quite distructive some times! Cheers Chris Quote Link to comment Share on other sites More sharing options...
garymorris Posted July 15, 2014 Share Posted July 15, 2014 Usually if air is trapped, the sealed piece will blow/explode/split big time , I don't think it would cause a crack like your on about Quote Link to comment Share on other sites More sharing options...
MECCANO Posted July 15, 2014 Author Share Posted July 15, 2014 Cheers, thought it sounded unlikely. i guess another viewing is in order. Should have taken a picture! Quote Link to comment Share on other sites More sharing options...
bill van snorkle Posted July 15, 2014 Share Posted July 15, 2014 Doesn't hot dip galvanising cause Hydrogen embrittlement to all but low carbon steels ? Quote Link to comment Share on other sites More sharing options...
Jon White Posted July 16, 2014 Share Posted July 16, 2014 More likely trapped corrosion, possibly where someone has had a used chassis galvanised. I've even seen one someone has had galvanised but hasn't bothered to straighten a couple of bent brackets first! Jon Quote Link to comment Share on other sites More sharing options...
CwazyWabbit Posted July 16, 2014 Share Posted July 16, 2014 Depends on where you get the galvanising done Jon, I've had a few bits galvanised that went in straight and came out bent, not warped but bent at 90 degrees to where they should have been. Then you worry about wrecking the galv when straightening, there are some rough ar$e galv companies out there. Quote Link to comment Share on other sites More sharing options...
MECCANO Posted July 16, 2014 Author Share Posted July 16, 2014 Thinking about it, the chassis number was present on the rail. I didn't think new chassis tended to come with any identity. If so then it could be the original that's been dipped. Quote Link to comment Share on other sites More sharing options...
Jon White Posted July 17, 2014 Share Posted July 17, 2014 Correct - replacement chassis dont come stamped so there is probably your answer. Quote Link to comment Share on other sites More sharing options...
studmuffin Posted July 17, 2014 Share Posted July 17, 2014 I think most Hot Rolled sheet used for chassis these days are con-cast low carbon Bill. People like Richards probably use sheet that is picked and oiled which removes mill scale and impurities from the surface. I understand for galvanising that a higher silicon content is the main cause of poor adhesion. Funnily enough most fabricators leave steel parts outside and open to the elements and have told me that a little light surface rust helps the zinc adhere, but I don't know if heavy trapped rust could cause the problem. Barry Quote Link to comment Share on other sites More sharing options...
bill van snorkle Posted July 19, 2014 Share Posted July 19, 2014 I think most Hot Rolled sheet used for chassis these days are con-cast low carbon Bill. People like Richards probably use sheet that is picked and oiled which removes mill scale and impurities from the surface. I understand for galvanising that a higher silicon content is the main cause of poor adhesion. Funnily enough most fabricators leave steel parts outside and open to the elements and have told me that a little light surface rust helps the zinc adhere, but I don't know if heavy trapped rust could cause the problem. Barry Thanks for clarifying Barry. I got the impression from a comment by 'Deranged' on his Series 2a build that LandRover chassis steel may have been a couple of grades up from mild steel. I have noticed chassis cracks in some areas on a couple of LandRover Australia built 6x6 vehicles that I surmised was due to stresses cause by the hot dip galvanising process. These chassis are fabricated from mainly standard size RHS provided by BHP steel, which may have a higher carbon content. Quote Link to comment Share on other sites More sharing options...
studmuffin Posted July 20, 2014 Share Posted July 20, 2014 Bill, I don't want to get into full anorak mode but I have never been able to determine the actual steel grade used in any LR chassis except that I would suspect that military chassis used higher tensile grades. Logically Series chassis from the 40`s/50`s/60`s would probably have used the grade of steel most easily available at the time( bearing in mind that supplies were restricted and on long lead times in Britain during this period). Either way the chassis steel would almost certainly have a higher carbon content but perhaps a less consistent chemical structure spread over the cast. In layman terms that means that Series chassis might well have been a higher tensile strength and a harder surface than general steel produced worldwide today but subject to more impurities within the structure. In other words it may be a bit stiffer but may suffer fatigue from unrestricted chemicals within the steel matrix. Either way 70 years ago Land Rover probably used any old steel sheet/plate that they could lay their hands on, and looking at Puma chassis probably still do. Ok -- I went into anorak mode Barry Quote Link to comment Share on other sites More sharing options...
bill van snorkle Posted July 20, 2014 Share Posted July 20, 2014 I know we are getting off track a little here Barry, but I read many years ago in a 4wd book authored by a Jack Jackson, who did overland tours throughout Africa etc, that series 1-2A chassis stood up much better to harsh conditions than Series 3 chassis that required extra reinforcement before being up to the task. It may have been due to material spec, or possibly due to the S3 construction method of 2 pressed channel section forming the box and stress from the pressed corners. Quote Link to comment Share on other sites More sharing options...
Cheesy Posted July 21, 2014 Share Posted July 21, 2014 I dont think that we have anoraks down this end of the world but the chassis "stiffness" is independent of the grade of steel used, it is dependent on sectional properties. Back to topic kind of, when I had my series 2 certified here I had to fix cracks in the chassis around the front shackle bush tube, apparently most of them he had seen had cracked there and wasnt overly concerned about how they were welded up (didnt need a welding ticket) Quote Link to comment Share on other sites More sharing options...
studmuffin Posted July 25, 2014 Share Posted July 25, 2014 Don't want to go even further off topic, but the steel grade is integral to the chassis structural design. Otherwise they would make them out of play dough. For example Military chassis are made from high tensile grades particularly to give them a higher tensile resistance to torsional loading. The point I was making is that contaminants in the steel can result in de-laminations causing rips or flakeing of the surface. This may be the problem the problem the original poster is seeing and every steel maker in the world occasionally suffers from this problem. Just a thought Barry Quote Link to comment Share on other sites More sharing options...
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