UV stabilized plastic spring material selection

[MattPolaris]

Can someone suggest a material for me please...

I need to make a small 50mm long flexible leaf spring that is used outdoors (UV stabilized/resistant) and it has to be a thermoplastic (injection molded/formed) with a life of 2 years+.

I have been researching this material choice for a few weeks now, but so far a clear winner has eluded my thinking.

To date:
1) ABS - cost effective, drawback is only black seems to be UV stabilized (variable colour is critically important - it's part of a safety mechanism)

2) HDPE - not so cost effective - not sure if it can be UV stabilized

3) Polypropylene - again black and not as well suited to spring characteristics

I have tested ABS and this is suitable in all respects except the UV resistant colour - anyone know if it can be UV stabilized and colour pigmented say orange , green or left as white.

Would very much appreciate anyone with experience giving me their input.

 

[Demon3]

If ABS works only you need more UV stability then try ASA (e.g. Luran S from BASF or similar like Geloy from GE). It has the exact same mechanicals as ABS only the rubber impact modifier used is intrinsically UV stable. You can get it in any color you want or color it yourself. It's used for exterior auto parts like grilles and mirror housings. Costs double ABS though.

PP and PE can be stabilized well enough to last for 2 years even without carbon black. Speak to a competent supplier like Borealis.

The cheapest and easiest solution is PVC though. Really cheap, good mechanicals and very UV stable. That's why it's used for siding.

Chris DeArmitt PhD FRSC CChem

 

[patprimmer]

ABS is very poor to UV and only moderately OK as a spring.

PP and HDPE are also fairly poor to UV and really bad as springs.

All can be UV stabilised and coloured to a wide variety of colours.

Very bright colours tend to fade quickly and certain UV stabilisers can kill the glowing effect from some very bright colours, but your colour/stabiliser supplier will be onto that if you ask.

ABS is more expensive than HDPE, so your relationship re costs seems a little ummm strange.

By far the best thermoplastic spring is acetal, but it's also fairly crappy re UV. It is used extensively as the plastic return springs in keyboards and ball point pen mechanisms.

For a reasonable UV and easy improvement via stabilisation and good spring characteristics, I would look at nylons and polyesters and maybe polycarbonate, depending on a whole bunch of other considerations not yet mentioned. Nylon can be difficult with fluro colours but bright non fluro is OK.

Nylons and polyesters are used extensively in car under bonnet, car exterior load bearing like roof racks and door handles and mirror housings and street light and outdoor domestic lighting housings and bodies.

Glass fibre can increase stiffness.

ASA has very similar properties to ABS except it has very good resistance to UV.

Acrylic has exceptional UV and colourability and is quite rigid and can be reasonably springy over a short deflecton, but is brittle. It is used extensively in outdoor signs and car tail lights and weathershields and aircraft windows.

Regards
Pat
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[MattPolaris]

Thanks for the detailed responses Dem and Pat

PVC would perform ideally except that I was thinking to stay away from it, apparently some people think it's
not that easy to injection mold (chlorine gas + stainless steel molds + high wear/maintenance requirements)

acetal sounds like it maybe a good choice - see if I can get some for testing and specs
and I have some polyester resin which is easy to mold with.

thanks a mill... & I owe you guys a virtual beer