15 replies to this topic

[MatsNorway]

I am looking for some info about plastics with some spring qualities. Is it called ductility? I need it for a kind of a reed valve. but first i need to find info.

The reason im asking is because i think it will be hard to make such a small part out of metal, and make it work under tiny loads.

the part will be round and max dim is 8mm +- inner dim will be 5mm +-

original idea was/is to punch it out from a sheet.

[Greg Locock]

" i think it will be hard to make such a small part out of metal, and make it work under tiny loads. "

I think Mr Rolex might disagree with you. No I don't think you mean ductility, that is how much you can stretch a material plastically (ie so it won't return to its old shape). You want the bending modulus of elasticity, or Young's modulus, usually called E in equations. For plastics and the like it varies from 40 N/mm^2 up to 10000, and if you add fillers much more than that. Steel is 210 000.

[gruntguru]

Even when operating entirely within the elastic range, you need to consider relaxation hysteresis which will preclude use of many polymers. The "complex Young's modulus" will tell you a lot about this property. Wikipedia

Edited by gruntguru, 23 December 2009 - 02:22.

[MatsNorway]

thanks guys

Greg: i didn't mean hard for rolex, but for me.

I never fully understood the E-module back at school. I guess its something fishy about the size of the numbers. unpractical or something. hard too visualize perhaps.

anyway, just checking if anyone know a material by name that i should check out.

Edited by MatsNorway, 23 December 2009 - 11:10.

[MatsNorway]

Guess i better talk to someone selling plastic.

Edited by MatsNorway, 23 December 2009 - 11:36.

[DaveW]

MatsNorway,

You have received two excellent responses to your question. They might have saved us much hassle when we tried (& failed) to design robust composite low rate, "springs" to support the dead weight of an active F1 vehicle in the early 1980's.

Edited by DaveW, 23 December 2009 - 11:54.

[MatsNorway]

MatsNorway,

You have received two excellent responses to your question. They might have saved us much hassle when we tried (& failed) to design robust composite low rate, "springs" to support the dead weight of an active F1 vehicle in the early 1980's.

Corvette got some leaf springs made out of something else than metal.

http://en.wikipedia....tte_leaf_spring

perhaps it was difficult then, possible today.

Googles on to try to find the name of the composite.

Edited by MatsNorway, 23 December 2009 - 17:38.

[JtP1]

I am looking for some info about plastics with some spring qualities. Is it called ductility? I need it for a kind of a reed valve. but first i need to find info.

The reason im asking is because i think it will be hard to make such a small part out of metal, and make it work under tiny loads.

the part will be round and max dim is 8mm +- inner dim will be 5mm +-

original idea was/is to punch it out from a sheet.

Cox .049 engine? Try Ebay for Teflon reeds.

[MatsNorway]

Cox .049 engine? Try Ebay for Teflon reeds.

hehe not quite. Teflon will do? or is it ohh magic spesiale teflon.

[Canuck]

PEEK perhaps. We use it a fair bit but I'm unclear what it is you need the material to do.

[MatsNorway]

PEEK perhaps. We use it a fair bit but I'm unclear what it is you need the material to do.

whats PEEK?

its a 1/10 Scale rc car damper prosjekt.

it will operate similar to a reed valve but it needs to be quite light in tension so it will operate at small bumps.

Edited by MatsNorway, 24 December 2009 - 11:04.

[JtP1]

whats PEEK?

its a 1/10 Scale rc car damper prosjekt.

it will operate similar to a reed valve but it needs to be quite light in tension so it will operate at small bumps.

Try Melinex if you can't get correct Teflon, it is heat proof unlike Mylar.

[cheapracer]

Boyesen (usa) have been making 'plastic' reed valves since the 70's

Edited by cheapracer, 24 December 2009 - 13:29.

[Stefan_VTi]

Your local scooter shop might sell small sheets of carbonfibre (branded 'Polini'). Over here in europe several shops carried them in thicknesses ranging from .25 to around .75mm. We used them to cut custom reeds for kart engines as well (we made our own Boyesen type reeds with different thicknesses).


http://www.treatland...eeds-0.25mm.htm

[Canuck]

PEEK
available mail-order in smaller quantities from mcmaster.com

[MatsNorway]

thanks guys

that polini stuff looks ideal.

PEEK stuff in rod shape might be good too.