http://citycyclingedinburgh.info/bbpress/ CityCyclingEdinburgh Forum » Topic: aluminium oxide frames en Sun, 28 Jun 2026 11:43:01 +0000 http://citycyclingedinburgh.info/bbpress/topic.php?id=15536#post-201002 Mon, 05 Oct 2015 23:19:38 +0000 kaputnik 201002@http://citycyclingedinburgh.info/bbpress/ <p>Thanks to the wonders of no useful chemistry in my eduction but some quick lunchtime googling, it seems another feature of the aluminium oxide film that forms on the surface of the alloy is that it doesn't flake, blister or expand; quite the opposite from rust basically. So if you're getting blistering under the paint or around a junction with another part, it's not oxidation but some other salt of aluminium. </p> http://citycyclingedinburgh.info/bbpress/topic.php?id=15536#post-200996 Mon, 05 Oct 2015 21:33:59 +0000 chdot 200996@http://citycyclingedinburgh.info/bbpress/ <p>"there <em>is</em> a CCE metallurgist"</p> <p>We let anyone join... </p> http://citycyclingedinburgh.info/bbpress/topic.php?id=15536#post-200992 Mon, 05 Oct 2015 21:25:14 +0000 Greenroofer 200992@http://citycyclingedinburgh.info/bbpress/ <p>In a previous life I was a metallurgist (so, chdot, there <em>is</em> a CCE metallurgist). I have a doctorate in an obscure method of <a href="http://www.journalamme.org/papers_vol24_1/24147.pdf">continuously-casting aluminium</a> (I didn't write this paper...). It was a long time ago. I can't remember any of it. I now work for a major financial services company.</p> <p>The only thing I can remember is that the oxide film on aluminium forms instantaneously, and is effectively always present. Aluminium is actually quite a reactive metal, but the oxide film stops that. In foundries you have to be extremely careful not to introduce moisture into the liquid aluminium (under the oxide film, in other words) because you will get an explosive reaction.</p> <p>(This might perhaps qualify as CCE's most useless response yet by someone who ought to know to a valid question in their (former) area of expertise. [Although, to be fair, corrosion chemistry was never one of my stronger subjects]) </p> http://citycyclingedinburgh.info/bbpress/topic.php?id=15536#post-200890 Mon, 05 Oct 2015 10:54:37 +0000 wingpig 200890@http://citycyclingedinburgh.info/bbpress/ <p>A good coating of winter path-gunk is probably comparable to partial immersion in seawater.<br /> I'll see what the suite of Seafield mechanical/automotive shops has by way of aluminium-compatible varnishes. </p> http://citycyclingedinburgh.info/bbpress/topic.php?id=15536#post-200883 Mon, 05 Oct 2015 10:34:47 +0000 kaputnik 200883@http://citycyclingedinburgh.info/bbpress/ <p>I'm assuming an off-the-peg EBC alloy frame is 6061 alloy;</p> <p>From;<br /> <a href="http://www.ihpva.org/projects/practicalinnovations/materials.html" rel="nofollow">http://www.ihpva.org/projects/practicalinnovations/materials.html</a></p> <p><em>Aluminum corrodes</p> <p>Yes it does. The 6061 series of aluminum has good corrosion resistance. However, if left partially submerged in a salt water it will eventually corrode. Once aluminum is placed in an oxygen environment it builds a protective layer of oxidation. Although this layer plays havoc during any welding process, it does protect the aluminum from many outside elements. As for bicycle frames, this corrosion is benign as it possesses no threat to the structural integrity. The same cannot be said about steel. It can and will rust. If left unchecked, a rusting steel frame shall fail.</em></p> <p>From what I've read it does sound more like catalytic corrosion. Recommendations seem to be to remove the offending paint areas, feathering the edges of the good paint, and buff the corrosion out with wire wool and/or a Dremel back to the aluminium, then allow that to naturally form its protective oxide coating (won't take long if it's dry and free of salts) before priming and re-painting.</p> <p>Other option is take all the paint off the whole frame and polish it up with an aluminium polish ("Mother's" brand) as used on alloy car wheels and under the bonnet by the sort of people who like a clean and shiny engine bay. I'm not sure how frequently you'd have to polish it... </p> http://citycyclingedinburgh.info/bbpress/topic.php?id=15536#post-200866 Mon, 05 Oct 2015 09:48:16 +0000 urchaidh 200866@http://citycyclingedinburgh.info/bbpress/ <p>I *believe* you get fairly large and frightening blisters of aluminium oxide for very little loss of actual aluminium.</p> <p>I have a near 20 year old (can't believe that) Cannondale M3 frame that had blistering around the top tube, seat post and top of the seat stay. I cleaned it back to the bare metal, there was lots of white dust but it looked fine/sound underneath. I used an alu primer and a few coats of black spray to seal it back up. </p> http://citycyclingedinburgh.info/bbpress/topic.php?id=15536#post-200829 Sun, 04 Oct 2015 13:15:51 +0000 wingpig 200829@http://citycyclingedinburgh.info/bbpress/ <p>Some of mine is on the chainstays (could be steel flakes dripping off the chain) and some on the bottom of the downtube, which could be either proximity to gear wires or large amounts of wheel-splatter containing exciting winter chlorides. </p> http://citycyclingedinburgh.info/bbpress/topic.php?id=15536#post-200825 Sun, 04 Oct 2015 10:51:57 +0000 steveo 200825@http://citycyclingedinburgh.info/bbpress/ <p>My racer has similar damage on the rear triangle. It's getting replaced but I'd rather the poor thing didn't waste away.</p> <p>The last post mentioned galvanic corrosion, and that makes sense on wingpigs. The corrosion is where the alu contacts steel. Though I'm sure mine is on the chain stay. </p> http://citycyclingedinburgh.info/bbpress/topic.php?id=15536#post-200822 Sun, 04 Oct 2015 09:54:13 +0000 chdot 200822@http://citycyclingedinburgh.info/bbpress/ <p>This may or may not help (via Google). </p> <p><a href="http://www.bikeforums.net/bicycle-mechanics/157699-aluminum-frame-corrosion-advice-please.html" rel="nofollow">http://www.bikeforums.net/bicycle-mechanics/157699-aluminum-frame-corrosion-advice-please.html</a> </p> http://citycyclingedinburgh.info/bbpress/topic.php?id=15536#post-200819 Sun, 04 Oct 2015 09:47:45 +0000 chdot 200819@http://citycyclingedinburgh.info/bbpress/ <p>Why not scrape some of the corosion off and see whether there is negligible change to tube smoothness or a noticeable pit showing that quite a bit is missing?</p> <p>Check at top of seat tube for an idea of how thick tubes are. </p> <p>Unless there is a significant amount of corrosion I would regard frame as sound/safe unless tubes are especially thin. </p> <p>It's the aluminium equivalent of rust. </p> <p>Though CCE might have a metallurgist who knows that 'once corrosion starts on aluminium it just keeps going'... </p> http://citycyclingedinburgh.info/bbpress/topic.php?id=15536#post-200818 Sun, 04 Oct 2015 09:35:39 +0000 wingpig 200818@http://citycyclingedinburgh.info/bbpress/ <p>Corrosion beneath, I think. As soon as the shape of the surface is changed the crisp and inflexible paint is popping.<br /> I vaguely looked at respray costs years ago before properly checking out the costs of better frames with decent tyre clearances.</p> <p>Is the paint over the varnish primarily to protect the varnish or to avoid a diseased/blotchy appearance, which I wouldn't mind? </p> http://citycyclingedinburgh.info/bbpress/topic.php?id=15536#post-200817 Sun, 04 Oct 2015 08:00:26 +0000 kaputnik 200817@http://citycyclingedinburgh.info/bbpress/ <p>Are the lumps formed by the paint blistering? Or buildup of corrosion behind? (Or both)?</p> <p>I suppose the cost of a good strip and spray (£~70) would negate point in reusing a shedframe? </p> http://citycyclingedinburgh.info/bbpress/topic.php?id=15536#post-200812 Sat, 03 Oct 2015 21:50:43 +0000 Arellcat 200812@http://citycyclingedinburgh.info/bbpress/ <p>If it were mine, I'd carry on riding it, and stop once the chainstays had acquired non-factory designed holes. You might wire brush it all down and clean and varnish/paint those areas. </p> http://citycyclingedinburgh.info/bbpress/topic.php?id=15536#post-200803 Sat, 03 Oct 2015 18:11:07 +0000 wingpig 200803@http://citycyclingedinburgh.info/bbpress/ <p>Lumpy, on the lumpy bits. </p> http://citycyclingedinburgh.info/bbpress/topic.php?id=15536#post-200802 Sat, 03 Oct 2015 18:09:53 +0000 gembo 200802@http://citycyclingedinburgh.info/bbpress/ <p>Looks ok, how does it feel..? </p> http://citycyclingedinburgh.info/bbpress/topic.php?id=15536#post-200801 Sat, 03 Oct 2015 17:17:46 +0000 wingpig 200801@http://citycyclingedinburgh.info/bbpress/ <p>I finally had a moment to take a brush to the glagged-on guNEPNk that's been clinging to my previous previous fame since its last journey twenty-odd months ago. I'd forgotten it was so tarnished, though taking a stiff brush to it helped a bit more paint escape.</p> <p><a href="https://flic.kr/p/zpe7iz"><img src="https://farm6.staticflickr.com/5717/21922610411_16a1a8a3c4_n.jpg"></a></p> <p>Would you...</p> <p>Bin this on the grounds of unsafeness?</p> <p>Consider the appearance to be an anti-thievery device and go ahead with the plan to turn it into a singlespeed spare thing?</p> <p><a href="https://flic.kr/p/zonkDg"><img src="https://farm1.staticflickr.com/723/21912899685_a3646734f4_n.jpg"></a></p> <p><a href="https://flic.kr/p/z6KvAU"><img src="https://farm1.staticflickr.com/670/21724845220_efc216d624_n.jpg"></a></p> <p><a href="https://flic.kr/p/yru1HV"><img src="https://farm1.staticflickr.com/633/21291794543_e38e217783_n.jpg"></a></p> <p>It all sounds whole enough when tapped but the only reason for using this existing frame for such a purpose is that it's already in the shed, whereas a new one would have to be researched, bought, delivered and justified. </p>