Coeff of Linear Thermal expansion

[NCL]

Hi all,

 

I'm new to the forum and I'd like to thank everyone in advance for any assistance they may give.

 

I''m currently working as a reseach & design engineer for a capacitor manufacturer, but I'm fairly new to the job.

 

I need some help with the thermal coefficient of unreinforced polybutylene terephthalate. The data sheet gives 2 ratings, 63 E-6/K (parallel) and 77 E-6k (normla)

 

Does any know the difference between the two ratings? I would also like to know how to interpret this information.

 

If I want to find out how much the material is going to expand at a certain temp, how do I use these figures. I've tried wikipedia but it's all a bit of a headache !!

 

Anyone got an easy explanation?

 

thanks in advance

 

NCL

[timo]

I have no idea. I am not an engineer. My daily work is not even remotely related to real-world applications. But to throw in some spontaneous idea: judging from the long name of the stuff and the terms "parallel" and "normal": are you possibly talking about a long polymer in the form/phase in which the polymers are semi-randomly distributed but arranged roughly in parallel, i.e. something like liquid crystal (not necessarily with liquid-like positions)? In that case, the two values might be the expansions in the direction parallel to the orientation of the polymer chain and the two spacial directions perpendicular to this orientation axis. Just a guess, but maybe you can judge if it's helpful to you or not.

[swansont]

As with timo, I'm guessing that if the material is not isotropic you could have different coefficients for different directions, parallel to some axis and normal to it. I don't know what property of the material distinguishes the two directions.

[John Cuthber]

I don't know much about bolybutylene terphthalate, but I do know about a bit about polyethylene terphthalate (PET)

PET, in thin sheets, is better known as mylar. It's commonly used as a dielectric in capacitors so I guess that's the sort of thing we mean.

As for the expansion coefficients I presume they mean parallel to the sheet and perpendicular to it.

If you had a big stack of sheets of this stuff 1 metre square and 1 metre high and heated it up by 1 degree the stack would get 77µm taller, and 63µm wider and deeper (front to back).

Does that help?