iDRY Vacuum Kilns

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bow and honeycomb

Started by jimF, March 30, 2004, 05:17:24 AM

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jimF

Old3dogg,
you say you "control both bow and honey comb with schedules. DB,WB,and chamber pressure. "  What do you do different with the DB, WB, and pressure for honeycomb and bow prone species as compareed to species not prone to it.?  
What do you do different for lumber as compared to squares?.
.

jimF

Also, what heat source do you use?

old3dogg

Lower DB/WB = lower CP.
Most of the species I dry are prone to HC and bow.
I can make a ton of water at 100/95 in a vac kiln.
But like Den says.You put a bowed peice of wood in a vac kiln you get a bowed peice of wood out of a vac kiln.
No dry kiln or method of drying in the world is going to dry without defects.
Mike.

old3dogg

Oh yea.I use hot water as a heat source.

jimF

How is it applied?  Through pipes in contact with the wood?  Intermittent vacuum?

old3dogg

With heating plates made from aluminum[holy crap I think I spelled that right!] I pull a steady vacuum.

Den Socling

Mike,

lower temperature = lower chamber pressure because you aren't overwhelming the vac system. DanG it! Remember what I told you. Push too hard and the vapor will make the chamber pressure go up. When the chamber pressure goes up, the boiling point goes up. When the boiling point goes up, wood temperature goes up. When wood temperature goes up, degrade goes up.

Are you using the pressure controllers I built or did you go back to timers. Timers are easier in you system but they will ALWAYS be slower.

Den

Tom

 :D :D I even understood that. :D  Must have shook loose some old used-up brain cells and exposed a couple of new ones. ;D

old3dogg

Den.
I under stand the pressure control but what do I do when the weather gets warmer?
I lose CP due to warm weather even if I dont increase temp.
Mike.

Den Socling

Mike,

A drying schedule is good if it can be followed everytime time you start a kiln charge. If you can't you need to change the schedule.

Your cooling towers will give you water temperature low enough to maintain a safe chamber pressure as long as 1) you are not drying too fast and 2) you don't have more wood in the chamber than the vacuum/cooling system can handle.

So, you find chamber pressure and heating water temperature combinations that work. Then, you may need to watch the size of the load.

Den

old3dogg

Den.
So you are saying that I shouldnt stuff the kilns full?Doesnt this start to argue with the economics of a vac kiln then?
A few years ago I quit putting those half layers in the kilns and boy did I catch holy heck for losing a whole 500 BFT.
On another note.I did by pass those pain in the butt radiators on top of the kilns which gave me a lot better control of the cooling and WB control.

Den Socling

Mike,

The original vac pumps on your kilns were ridiculously small. I replaced them with the Nash because you had the Nash sitting there unused. Nobody did any calculations to see if they matched your needs.

When I design a new kiln, I look at quantity, species and desired drying rate. From this I can calculate the CFM requirements of the vac pump. Since you already have the pumps, you have to adjust quantity or rate.

Den

old3dogg

So I need to make different drying schedules for everyday of the week?
I have my computer program set up to compensate for the the WB temp which may vary depending on drying rate or the outside temp.
I cant put different amounts of wood in a vac kiln because one day it is 60 and the next day it is 45.
On another note.I only have 4 Nash pumps in operation.The other 4 are Kinneys.Someday I will have to tell you the story of how I bought the $14,000 SS pump for $7000.
Mike.

Den Socling

No. You need schedules that can be followed almost every day of the week. On that day that you can't keep the chamber pressure down, reduce the drying rate.

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