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polymer equivalent to a bi-metallic strip?
2

polymer equivalent to a bi-metallic strip?

polymer equivalent to a bi-metallic strip?

(OP)
Hi all, Is there a commercially available all polymer/plastic equivalent to a bi-metallic strip? I am looking for something that could be integrated in an injected moulded product. It needs to be reasonable cheap.
Many thanks in advance for any advice or leads.  

RE: polymer equivalent to a bi-metallic strip?

I have not seen it, but it should be easy. Mould a strip in GF whatever polymer suits with direction of flow along the strip.

Overmould with same polymer but no glass fibre.

It will certainly bend toward the glass filled side when heated.

Regards

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RE: polymer equivalent to a bi-metallic strip?

The principle of the bimetallic strip requires two things. A difference in coefficient of thermal expansion between two materials and modulus or stifness of the materials to generate useful forces. So as Pat suggested, glass fiber (or carbon fiber, or metal wire or strip) in plastic will create warpage with temperature change. However, if the plastic is not stiff enough it may creap or deform in other ways.   

RE: polymer equivalent to a bi-metallic strip?

(OP)
Hi all , great help, thanks for that. Is there a polymer or combination strip that will bend with moisture. I am thinking of the fortune fish material ( cellophane I think), but something more robust and repeatable?  

RE: polymer equivalent to a bi-metallic strip?

In principle you could use a material that swells in water, like a nylon, and a material that does not swell, but you would need to check what will overmold to what.

It would have a very slow response rate as (depending on a number of factors) it takes hours or even days to absorb enough to swell noticeably. This probably makes it unworkable in the real world.

A glass filled nylon on one side and an unfilled on the other might work. Nylon 6 is probably best as it absorbs most water.

Re water or temperature, re material choice, a lot depends on other factors  

Regards

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RE: polymer equivalent to a bi-metallic strip?

(OP)
hello Pat .Again very Useful Thanks . What is your background /role ? is it permissible to have your contact details? Opticsman

RE: polymer equivalent to a bi-metallic strip?

My original training was in textiles technology and I ran a colour and wet processing lab, but I have worked since 1977 in Engineering Plastics in technical marketing and product management roles.

I am a committee member of PIMA (Plastics Injection Moulders Association).

http://www.pima.asn.au/home.asp

Regards

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RE: polymer equivalent to a bi-metallic strip?

Pat's approach is a good one. I would not choose glass fiber though as the filler. Each layer is basically a spring and the one spring has to expand more than the other one, thus bending the second spring. If you put glass fiber in then one spring is much stiffer than the other so that the unfilled polymer will not be able to bend it. Therefore I would use a filler that does not increase modulus much. Examples are CaCO3 (chalk) and glass spheres. Or, if you do use glass fiber then make that layer only 1/4 the thickness of the unfilled nylon layer.

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RE: polymer equivalent to a bi-metallic strip?

Demon3

You are correct. Although the glass fibre severely reduces expansion due to moisture absorption, it also increases modulus to an unworkable extent.

Co-extruded films with nylon/tie layer/PE curl a lot on moisture absorption, but are probably to thin for your purposes. It may be possible to make them very thick by the so called film casting process where melt is extruded onto a set of rollers then pressed to size by the rollers as they freeze.

The costs of samples by this process will be high.

If it is thick enough to have the required rigidity, it will have a VERY slow response rate.

Regards

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