Qualifying / Testing Wax Thermostats

[jnelson33]

Hello all! We have samples of a new wax thermostat we are looking to integrate into our product line and I believe it would be wise to test these separately (outside of the products they are to be used in) prior to them being implemented. We also test customer products and would sometimes need to determine when a wax thermostat is bad for a warranty claim. The wax thermostat is similar to pic provided here.

This has to be simple and cheap as my boss loathes testing anything, especially components from overseas, even if these thermostats are being installed in paramount applications, even when this system will be useful for faster warranty claims. We are given a sheet like is provided here. I want to validate their preload suggestion and thermostat activation at 55C, or whatever temperature we are testing.

I am thinking about a simple system that uses 2 plates, 3 rods, a spring and a heated container. I will also design and laser mark what is essentially a ruler / scale to see if the suggested preload and suggested springs equate to the force outputs.

This of course means I need to do some spring selection work so that it's reliable, but does the concept seem to be simple and effective enough? Has anyone done this for their job at one point and can lend a helping hand? Does anyone have a simpler suggestion for testing this type of product?

 

[MintJulep]

It will be sensitive to the uniformity of the surrounding temperature. Your concept will create a non-uniform temperature. You could add a stirrer.

It will be sensitive to rate of temperature change.

Extension stroke and load and temperature all seem likely to be time variant, with no obvious requirement stated to assess the "vs. time" part of the observed performance.

Use a compression spring and keep it dry, just because easier.

Just use a lever hinged at one end rather than spending the time to try and get a plate to go up and down without binding.

Are you sure the thing is immune to being immersed in water?

 

[jnelson33]

Thanks for your input MintJulep; I tend to design stuff on the side of overbuilt but simple with these budgets here haha.

I did understand that I'd have this non-uniformity in the reservoir's fluid temp as well, but I would just stir every now and again to make sure it was a better average temperature in that reservoir. I would also have to bias the heating element far enough away too..already getting more complex.

This is an overseas supplier so they supply jack-diddly in terms of product data, even when asked: I am not sure how reactive their wax is like you're getting at. Our current elements tend to activate smoothly with little impulse to the fluid itself.

"Versus Time" isn't really so important, only whether it activated at the advertised temperature range (or within the tolerance) for our customers. My boss previously set up the system so that we're always just testing the new thermostats on the devices they'd be used in. Nothing beats real life testing like that I suppose; the engineer inside me just wants to make sure the thermostat is actually working as advertised by itself first since it's a new thermostat series.

I like your hinged idea for sure as it would accomplish the same thing and be simpler I think. My rods were going to be very loosely fit since precision in X/Y isn't so important there but it's still more parts over your concept I think.

We run our current thermostats in engine oil primarily, water is fine as well, our FL tap water will just corrode/discolor the brass.

 

[IRstuff]

I would suggest using a dead weight, rather than a spring, since the dead weight can be measured more accurately and more repeatably and is not subject to thermal variations.

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[jnelson33]

Our precision doesn't really require that, and it wouldn't allow me to have a progressive force increase like the compression spring would. It's more important to have the right preload and not exceed the vendor's published maximum force as well.