sooo I brought this cargo frame to a company to get it sand blasted and powder coated. It had already been coated once and then I had to change some stuff at a later point and so it was still coated in parts.
Having been there before I thought it was cheapest (and usually working), to just blast it where it was welded and everywhere else just lightly and then just have it coated over.
So I brought it to a company who agreed to try. They then called me saying they tried to remove all of the coating but it did’t work. they did not charge me anything for trying (and even blasting some small parts) and I brought the frame to another company who removes coatings in the oven. They heated, sand blasted (lightly I suppose) and recoated the frame. when I picked it up I STILL didn’t even notice (don’t ask how that’s possible), but as soon as I got home I realised the damage (see pictures)
Now both parties obviously say that it wasn’t them. So I need to know how something like that could even happen. Company number 2 said that long and heavy blasting can lead to red hot steel…
I would personally think it was the first one, also from the extremely defensive way they reacted, the fact they didn’t charge me for anything and some other minor clues..any ideas?
That is absolutely bizarre looking damage. To me it looks like buckling, which I guess in theory could happen if the tubes were REALLY hot and then forcefully blasted with air/medium. It also depends on what blasting medium they use if it’s something very aggressive.
I personally have sandblasted dozens of frames in several different industrial setups (no heat involved, various mediums) and have never ever done or seen damage like this.
It could also have potentially been manhandled in a shop while it was hot in a manner than caused the tube to buckle and they don’t want to admit it. Even in a really large blasting cabinet it can be kind of a pain to wrestle a frame around, so if it was hot and it got stuck in a corner or flipping it around or whatever and it got wrenched on I could see this happening. I had a powdercoater cause some clamping damage on a frame that they “swear was there when I dropped it off” while I have photos proving otherwise. Unfortunately it happens and it’s always a risk when finding new finishers.
Also, as much as this is a total bummer, it’s kind of the least-bad tube location it could happen. Pretty easy fix, you could probably even get away with a sleeved replacement of the damaged section vs. an entire tube replacement.
Thank you so much for your reply! Ok that kind of confirms what I thought: the tube must have been very hot. Too hot for it to happen when they removed the coating, right? What do you think about company no2‘s claim that if you try long and hard enough (and with a hard medium I guess), steel can go red hot from blasting? I mean no1 said they tried and failed, maybe someone who just wasn‘t used to thin walled tubes just went loco on them? That would be my best guess..
Its a very sturdy tube as well
At what point would you say it‘s most likely to have happened? And as for company no 2, I paid them 400€, you think it‘s justified to demand I be refunded because they ignored the damage? I mean I didn‘t notice it (assuming it was there) somehow. But they say they did..
And yeah its kind of an „easy“ replacement but still, it‘s work for me, logistics as I am spending summer in another coty and have to squat someone elses workshop, coating is fucked..
I can’t imagine a typical sandblasting medium making a tube go red hot unless, maybe they are using a steel shot? But that is more intended for heavy industrial application. I guess it depends what the company typically works on. I would ask what their blasting medium is.
Without any pictures or proof it would be a hard go to get your money back. If the second company did blast it with steel shot, I would say that’s poor practice as they should know it wouldn’t be appropriate for something thinner wall, but again if you can’t prove it wasn’t damaged when it was dropped off you’re out of luck.
Is it for you or a customer? If you, I’d just ride it. It is unlikely to ever break there. Put an ironic bumper sticker over it so you don’t have to look at it.
If the whole frame was blasted, and this damage is from the blasting, I’d be very suspicious about the condition of the other tubes as well even if they look undamaged.
I’ve absolutely seen that in enclosed media-recycling blasting cabinets where the media isn’t replaced, like ever. It’s surprisingly common for media recycling cabinets to only get new media to replace what falls out. Think of it like a sanding belt that’s gone dull, eventually it’ll do more heating than cleaning, right? Blasting media does the same when it’s gone blunt from overuse, not to mention diluted with blasting crap as well. Ignore that long enough, eventually enough blasting junk will build up to sustain combustion in the media tray and force a maintenance event.
If you find a shop that replaces cabinet media frequently, make note. If they do a bit of cleaning inside the thing when they do, you’ve found a unicorn.
Is it definitely deformed steel and not delaminating powder coat? Maybe from a poorly cleaned surface? Since the first company said they had trouble removing prior coating, that could be a clue.
That’s an insane amount of damage if the tube is actually buckled. Since that area is already a lost cause, I might take a wire wheel to a portion of it to find bare steel and see what happened.
Well, what a lovely piece of modern art. I have some clients for metal sculpture who would probably be interested in using this technique so I would love to know what the process is!
Based on your story I suspect the first shop too. But here is a little more information that might help you come to a conclusion. As someone who has had lots of frames sandblasted, painted and powder-coated over the years, and also knowing lots more people who do this, and doing sandblast myself, and knowing painters, and doing powder coating myself too, oh yeah also a professional blacksmith…
No normal sandblast cabinet set-up would cause damage like that. If one of the shops has a sandblast room where the guy goes inside in a duct-taped re-enforced spacesuit-looking costume and uses a sandblast nozzle that looks like a fire hose that would be the most likely source of damage.
Powder coating happens between 350 and 400 F usually which is not nearly hot enough to weaken metal and allow deformation
If one of the paint removal attempts used a burn-off oven there is a chance your metal got red hot for a time (in which case the mechanical properties of your steel tubes may have been altered somewhat, probably not critically if they opened the oven and took it out right away but possibly softened if the oven remained closed after burn-off and the the frame was left to cool slowly). I’m not exactly sure what temperature a burn-off oven usually gets run at, maybe someone could chime in with that information. For example, if aluminium is safe to burn paint off then steel wouldn’t be getting red hot at that temperature, although you would still see some small change in your cromoly’s mechanical properties.
Nobody would be putting a still-hot cargo frame inside a sandblast cabinet. It would be too difficult to handle and would melt the rubber gloves in the cabinet. It’s also hard to imaging someone trying to sandblast a red-hot bicycle frame that just came out of a burn-off oven. Anyway, the tubing is so thin that it would almost certainly stop being red hot (stop being at the magical temperature for plastic deformation) within thirty seconds of coming out of the oven so there really isn’t time in that scenario to get it from the oven, into the sandblast room, suit up and start blasting it before it cools down and regains a lot of its strength.
