Prepping a fan blade for paint?

dotcentral · Post by **dotcentral** » October 20, 2007, 6:52 pm

Can this be safely done? No sandblasting, but will sanding it with medium grit do anything to weaken it? I'd like to paint it while I have it off the truck.

Alan Mclennan · Post by **Alan Mclennan** » October 20, 2007, 7:04 pm

Only with the motor turned off :rotflmao:

I m sorry just had to say it

Alan,

Phil · Post by **Phil** » October 20, 2007, 8:20 pm

Airplave remover, paint stripper, wire wheel, prime and paint
Rustoleum #7777

ripsnorter · Post by **ripsnorter** » October 20, 2007, 8:48 pm

maybe I'm not aware of something that I should be, but I wouldnt have a problem with bead blasting a fan.

blackagatha · Post by **blackagatha** » October 21, 2007, 12:35 am

Bead blasting it may not have any effect, or it could kill it... I've heard of "shot peening" resulting from blasting, which makes the metal hard and brittle. Could cause the blades to come loose, perhaps. Or nothing ever happen, it's hard to tell.

Yeah. Airplane Remover.
Remove all the airplanes from your truck....

That is the stupidest label I've ever seen.
It should read "Paint Remover"

Logically, you would think ok, it's Aircraft stripper... But it says DO NOT USE ON AIRCRAFT.... WTF MATE???

It does work pretty well though.

dotcentral · Post by **dotcentral** » October 21, 2007, 8:15 am

Well, it has some rust on it, which I'd like to remove. Or at least clean up. I think I'll try scuffing it with something like sand paper or a green scuff pad to knock the worst of it off before painting it.

Guess I didn't exactly ask the first time, but would a light hand sanding do anything to weaken the fan?

Truckfarmer · Post by **Truckfarmer** » October 21, 2007, 9:17 am

"shot-peening" actually is not destructive to metal but actually strengthens it. The iron shot being blasted actually removes stresses incurred during certain types of machining. It helps align the molecules for a stronger piece.
Where I work, we manufacture fuel injectors for diesel engines. All of our injector tips are glass bead shot to remove burrs and to strengthen the tips after grinding the seats.

36truck · Post by **36truck** » October 21, 2007, 3:32 pm

Doccentral no sanding will not hurt your fan.

The Big M · Post by **The Big M** » October 23, 2007, 3:05 pm

Truckfarmer wrote:"shot-peening" actually is not destructive to metal but actually strengthens it. The iron shot being blasted actually removes stresses incurred during certain types of machining. It helps align the molecules for a stronger piece.
Where I work, we manufacture fuel injectors for diesel engines. All of our injector tips are glass bead shot to remove burrs and to strengthen the tips after grinding the seats.

Yup. Shot peening leaves a residual "layer" of compressive stress on a piece, which would actually be beneficial on a rotating component like a fan. It replaces tensile stresses with compressive stresses, which reduces the tendency for a piece to crack, thereby increasing fatigue life (tensile stresses will open cracks on the surface, compressive stresses will close them). Though I'm not sure bead or sandblasting would actually result in a measurable peening effect...

blackagatha · Post by **blackagatha** » October 23, 2007, 3:38 pm

I dunno. All I really know is that I've heard that if you do it wrong, blasting sheetmetal can make it Hard and brittle. Most common scenario-somebody blasts the paint off of their car, uses the wrong medium, too high pressure or something screwy, and induces a crack after a few months of driving.

If haardening done properly, or for the correct application a hardened part is a good thing. BUT...

Like Heat tempered stuff... Getting a chunk of steel nice and orange-hot for an hour or so, then dumping it in a pot of oil will make it extremely hard, but brittle as all hell. They have to re-heat it and let it cool very slowly to regain its impact/bend-break resistance.

On an injector, being hard and brittle wouldn't matter- there are no twisting forces or impacts. A fan- even if a rigid model, is constantly being tweaked by aerodynamic forces. Hardened in the wrong way and brittle would be very bad...

The Big M · Post by **The Big M** » October 23, 2007, 4:46 pm

Perhaps shot-peening is used on injectors to increase wear resistance?

As for sandblasting a large body panel, I can see a ham-fisted operator being overly aggressive and inducing stresses in the panel. Particularly if it gets thinned and warped at the same time. Add that to the existing stresses present from the initial forming of the piece (especially on compound curves) and I can foresee problems.

My main concern with sandblasting a fan would be thinning of the metal or warpage, which could throw the assembly out of balance, more so than hardening. Peening typically only affects the outer layers of a piece (depends on the thickness, of course). I expect it could be done safely, given the proper conditions.

Anyway, that's neither here nor there, since the original question was about hand-sanding. Go for it, or take Heavy Hauler's advice. Either way you shouldn't hurt it.