setting pitch

[Don_Lewis]

Pitch setting has to take into account what you will be doing with the lumber. If you are making a piece of pine furniture or flooring and sanding it a lot, the temperature under the sanding belt will be hot enough to quickly load the belt.  160F is the accepted temperature for that use of the lumber (not the air) for about 24 hours. The time depends on air temperature though.

[Don P]

I'd like to understand this well enough to simplify it. I've understood pitch to be sorta like crude oil. If you had a tower to condense the volatiles as the were driven off there would be a range of by products that condense at different levels. If I'm anywhere close there must be a list of what is driven off at each temperature level. Is there a point, short of amber, where it is truly "dried up"? I guess the analogy would be, does it ever become thermosetting instead of thermoplastic?

[brdmkr]

I thought Tom's explanation sounded a little like tempering metal.  Once metal is tempered, as I understand it, it will not loose its temper until it is heated above the temper temperature.  Also sounds somewhat like frational distillation as mentioed above.  Either way, sounds like if pine is exposed to temperatures above that used to set pitch, it may weep.

[beenthere]

Interesting thread, and some of it is even understandable.  Thanks Tom.
 

[Ianab]

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Is there a point, short of amber, where it is truly "dried up"? I guess the analogy would be, does it ever become thermosetting instead of thermoplastic?
I dont think so, if you take your piece of kiln dried pine and get it REALLY hot, like on a fire, the pitch will start running out again.
I think the crude oil analogy is a good one, crude oil is usually a waxy sort of sludge, if you let all the naptha and petrol evaporate out it will 'set', but it can still be melted if you warm it up. Heat it and take out the kerosene / diesel weight components then you have bunker oil that is a solid at room temp. One step more is tar, pretty much a solid, but even than it will melt in the sun on a really hot day.

Cheers

Ian

[Den Socling]

Jim,

I'm sure that there are bonds between compounds that affect boiling point but don't you agree that Tom's explanation is basically correct? Guess what happens to 'pitch' in a vacuum chamber. I've taken pine that was dried to a max of 140'F in a vac chamber and heated pitch pockets to 190 and they stayed solid.

Den

[jimF]

Tom's explaination is the first step to understand what is going on.  But there is a strong interaction beteewn the pure chemicals in the mixture.  The remaining mixture will melt and flow at a temperature lower than the maximum temperature at which it was previously exposed to.

When it is exposed to the maximum temperature also influences how effective the "setting" process is.  If performed early in the drying cycle(when the MC is high) it is more effective than later (when the MC is low) because water is part of the mixture and it's boiling point also influences the boiling point of the mixture.