Aluminium door frame - can this be right?

[davedee]

Our Coachman is less than a year old but I think we have a problem with the aluminium door frame; the corners,where the ali' has been rolled into a 90 degree bend, have gone a milky white colour. There are also,what appear to be,tiny hairline cracks along the outer edge of the curves.They're a little like the stress cracks sometime found in GRP.

I've queried these marks with our dealer.Response: "Yeah, they do that.It's the way they bend the aluminium.Crap isn't it!"

Have any of you noticed this problem with your vans?

Is it,in fact, a problem at all?

Your comments please.

Dave

 

[rob_jax]

Hi Dave,

Sorry to hear that. The milky white "discolouration" of the aluminium isn't too worrying - it's a surface artefact from the bending process - it is a stress mark but it shouldn't cause any problems.

But I'd be much more concerned about cracking on the outer edge of the bent aluminium - this section of aluminium has been stressed beyond it's plastic deformation limit - and those are probably stress cracks. But since the aluminium isn't under stress, they shouldn't continue to grow (unlike those in GRP panels) but they could easily become sources of corrosion and corrosion cracking...

The aluminium should have been heated sufficiently so that the bending process didn't exceed the plastic limits for the material (hot means more plasticity), but ...

Robert

 

[Lutz]

From your description it sounds as though the door frame is manufactured from anodised extruded aluminium sections. The anodised finish protects the aluminium from oxidising (going milky) but this cracks went it is bent. The answer would be to anodise after it is bent but this would push up the cost of manufacture significantly. It is only a cosmetic issue so there is no need to worry that is might turn into a serious problem. It's a cost saving exercise.

 

[davedee]

Hi Robert.

I can't actually feel the caracks; no ridges,no roughness,theali' is nice and smooth.

The cracks - if that is what they are - are approx. 2 to 6mm in length, spaced about 2mm apart and you can spot them easily or not, depending on the viewing angle,refraction and all that.

Dave

 

[Lutz]

You wouldn't be able to feel the cracks because anodising is only a few microns thick.

 

[davedee]

From your description it sounds as though the door frame is manufactured from anodised extruded aluminium sections. The anodised finish protects the aluminium from oxidising (going milky) but this cracks went it is bent. The answer would be to anodise after it is bent but this would push up the cost of manufacture significantly. It is only a cosmetic issue so there is no need to worry that is might turn into a serious problem. It's a cost saving exercise.

Many thanks,Lutz. You and Rob_jax have put my mind at rest.

Sound,knowledgable answers !

Dave

 

[davedee]

Cheers again,Lutz.

Obviously nowhere near as thick as our dealer then...heh,heh.

Dave

 

[rob_jax]

Full agreement with Lutz - if you can't feel the cracks with your finger-nail or insert a piece of paper in them - then they aren't physical "through the material" cracks

So as long as you can't detect a real crack - then it's a just damage to the anodised coating and this will be protected by a layer of Aluminium Oxide (which instantly forms when Aluminium is scratched).

Anodised Aluminium (surface coating of Aluminium Hydroxide) will easily accept colours and dyes into the surface - and some natural materials in the environment will have the same effect.

You can protect the anodised aluminium from colour changes or blotches by applying a good wax layer - like Turtle Wax paste - to all the "bare" aluminium on the caravan. That'll keep the aluminium looking fresh and new for years...

 

[KnL]

Cheers Rob & Lutz,

Noticed the same 'defect' at the corners of our Bailey aluminium door frame as well as on one of our aluminium Dukdalf chair frames.

Pleased it's nothing to worry about !

Ken.