I was once having a conversation with a fellow …. I’m not sure of the subject … it is likely that we were talking about the storage temperature of B-stage pre-preg  ….

I suppose some of you want definitions here …. Pre-preg stands for pre-impregnated …. Nope  … it is NOT artificial insemination  ….I’m  talking about composites  …. fiberglass, graphite  …. carbon fiber …. etc

One of the methods of producing carbon fiber stuff is to pre-impregnate the carbon fiber with resin … the resin  becomes the matrix ….

they take a woven sheet of material and apply the resin …. The resin is formulated so that it is ready to cure … fiber plus resin makes pre-preg …. the pre-preg is then cooled ….  way cooled …  the cold environment stops the curing process.

You take the pre-preg out of the freezer … you let it thaw  …  you mold or form it into whatever shape you want it  … then you cure the product.

The stuff is typically cooked in an autoclave for the final cure …. Sometimes it is cured by ultraviolet light  … or some other method ….

In this example the first stage is making the fiber …. The second stage is adding the resin … the third stage is curing

The final product can be produced in stages …. So the B-stage is the second stage …. B-staged pre-preg can be made in a multitude of shapes and sizes  …. It can be woven …. It can be made like tape with the filaments aligned …. It can be made with chopped fibers  … it can be made into whatever shape the customer desires ….

Frozen pre-preg is wonderful stuff  ….  This process allows you to procrastinate …. You can do stage one and stage two and then throw the stuff into a forty below freezer  … then you take a nap  … you can leave the pre-preg in the freezer till you are ready to use it …. By keeping the stuff real cold it increases the shelf life …. it can stay in the freezer  a long time …. The molecular movement and chemical reactions are slowed down when it’s real cold  … kind of like cold tar … according to the comparisons I have heard, cold tar is real slow …. The colder temperature gets the slower the tar gets  …. Eventually it gets so cold that the tar stops moving … that is the motion zero point ….  then it goes into negative numbers …. even colder and the tar slowly starts moving backwards … uphill  … by forty below it is going so fast backwards that your freezer just slips into the twilight zone  … do the math you will see … to verify that tar actually behaves in this way I guess that I would need a cold tar slowometer  … does anyone have a slowometer that I can borrow?

So how cold is forty below …. I have experienced forty below in a freezer … I might have met forty below one miserable night in Wyoming …. I have slept in an igloo when the outside temperature was around 25 below   …. I have fought to start a car when it was 20 below … all of these experiences were  too cold  ….  Way below way cool  … the cold did terrible things to my body … forty below is better to avoid than to describe.

Back where we started …back to the conversation with that guy …. I said we stored the pre-preg at forty below …. He asked whether that was forty below  Fahrenheit or forty below Centigrade  … I answered “forty below is forty below … you can chose your scale” ….  The fellow was exasperated …. He didn’t think I was funny ….. I had to explain that forty degrees below zero is the one point where the Centigrade and the Fahrenheit scale are the same number …. forty below zero   ….  So to one and all I say “forty below is forty below” … I also say “forty below is real cold and should be avoided  … avoid it just like you avoid pain and disease and the IRS”

 

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