Sandblasting off powder coat will take a long time especially on large items. Physical sanding will take much longer than that. Taking it to a sandblasting shop would probably be more cost than you want and doing it yourself a pain because you likely don't have a containment cabinet let alone one large enough to fit a roll bar.
Powder coat is usually commercially removed either by cooking it off in a high heat oven (around 1000F) or dipping it in a solvent bath of some sort. If you want to DIY this those won't be options for you but there are some gel like strippers that you can brush on let sit and then scrape off the loosened powder coating. It will take a few applications and scrapes to get most of everything but you will probably need to do some spot abrasive work on stubborn areas . Over here auto restoration suppliers such as Eastwood will carry a line of these and perhaps you can find some products on Amazon. I don't know what you can get in the EU as you may have different environmental regs and such.
Your powder coat issues aren't with that process but more likely with poor workmanship (probably prep) from whoever did your cages initially. You might still want to look into a good powder coat shop as some of those have the heaters or solvent pools on site because that is part off their powder coating prep process. You may find that doing both at one place is cheap enough for you compared to the hassle and assorted costs of doing it yourself.
I sandblast a fair number of things either in my cabinet in the garage or in my outdoor “containment cabinet”
which is a spray shelter. It works but is far from ideal. Iv'e blasted items that were powder coated and it definitely takes more time and effort.
I agree that poorly done powder coating is usually the problem. I think that’s sometimes the case with after market companies that want to get things out the door at competitive prices. Some of the black steel wheels for example, although many of those are probably just painted. Good powder coating shops can usually do a much better job.
I used to send heavy steel items like frames, axles (stripped), suspension components wheels, etc. to a company for shot blasting. Their containment cabinet was about the size of 2 auto paint booths end to end. It had a conveyor belt running through it and the doors at each end were like the vertical plastic strips you see at some car washes. It was unmanned and there were blast nozzles aimed at the belt at various angles. Everything was loaded on the belt and sent through. It came out the other end, was flipped over and sent back to where it started. It took about 20 minutes and everything was totally stripped of paint and rust. This was back in the 70s and 80s. A load was about $150-$200 which was well worth it.
I also used to send a lot of things to Redi-Strip. Watching car bodies go in the chemical dip tanks and then come out was pretty interesting. They’re still around but with fewer outlets. I believe there is only one in Canada (Vancouver). I think their process now involves more blasting and less dipping, no doubt for environmental reasons.
