And its a clear finish you’re putting onto bare metal I take it?
Probably the most tenacious adhesion you’d get to metals would epoxy finishes and you’d maybe look at vendors for marine applications. Polyeurathane I’m more familiar with as a wood finish and the acid-cat finishes I’ve used were also formulated for wood – tough stuff though, typically used for floors and bar-tops. By comparison Powdercoat is only ‘tough’ in terms of it being a resilient material but its not firmly adhered to the metal.
With something like car wheels an other aspect is that you’re hand-painted finish forms part of the bead and seal for the tyre – alloys are leaky enough without the additional lumps and bumps of brush-stokes – so you maybe need something to create a very thin film when applied. – Some polyurethane finishes for wood, for instance, are made to be wiped on with a cloth rather than brushed on.
That said non of your applications are especially ‘tough’ you just need something ‘suitable’ – in all those applications what people typically use is ‘paint’.
I forget what the stuff was now but I bought paint (which they’ll also sell as clear lacquer) formulated for metal coating from Smith and Rodgers in glasgow a few years back.
They make and develop their own paints and finishes as well as source and supply all kinds of specialist stuff and their advice and products are as specific as you could hope for- and they’ll recommend and blend for your particular applications – (the even let a friend of mine name a new product line they’d developed to meet her specification)
So if you told them you what you want in terms of what material its going on to – how clear, matt, gloss it needs to be, whether its for brush/roller/spray application or whatever and they’d mix up a tin to suit.