iDRY Vacuum Kilns

Sponsors:

Sticker stain on maple in Nyle kiln, best schedule?

Started by Kelvin, October 31, 2007, 08:28:19 AM

Previous topic - Next topic

0 Members and 1 Guest are viewing this topic.

Kelvin

Howdy all,
I've been trying to reduce sticker stain in my white maple.  However i've just changed a bunch of my procedures at once.  I usually air dry to 20%MC than put in kiln.  I've been advised to put straight into kiln, now the Nyle manual has different temp cycle.  Do you find the best color occurs by following the temp in the book?  It says to start out at 90 degrees until 35%MC than 100 to 25% MC than 115 below 25% MC.  Is this the best for avoiding sticker stain?  We also have new stickers we dadoed to reduce contact area.  I have about 1500 bd ft in a Nyle 200 and its running at 90 degrees right now.  The wood was air dried for 2 days before being put in kiln, so basically nothing.  What do you think?  Oh, its soft maple as well.
Thanks for any help,
kelvin

ronwood

Kelvin,

When I cut maple I stand it on end for a couple of weeks under cover and then put it into the kiln. The boards should not touch on another during that time.

It appears to help and we where able to dry the maple in the kiln without sticker stain.

I believe that Scott (gentlemen with kiln) dries it on an aggressive schedule.

Ron
Sawing part time mostly urban logs -St. Louis/Warrenton, Mo.
LT40HG25 Woodmizer Sawmill
LX885 New Holland Skidsteer

David Freed

Doing what Ron said sounds like a good idea for small amounts. I buy up to a semi load at a time and don't have near enough room or time to try it.
   The temperature in the kiln is important, but in my opinion, the wet bulb depression is more important. If you aren't drying the lumber fast enough your risk of sticker stain increases. I have a Nyle L200 inside a well insulated kiln with 5 circulation fans. Most of the lumber I dry is white wood (ash, maple & poplar) that is prone to sticker stain. I get the wet bulb depression on track first, even if it means opening all the vents and letting the temperature drop.
   On a side note, I noticed in some past conversations one or more people were having trouble with their well-insulated kilns constantly overheating in the summer. I built my kiln with a well ventilated attic that I can access and work in fairly easily. In the spring I pick up all of the ceiling insulation and stack it in a corner so the ceiling is exposed to let excess heat escape during the summer. In the fall I put it all back in place. It makes controlling the temperature a lot easier.    David

Kelvin

David,
I don't have a wet bulb meter, but i check moisture content in sample pieces trying to maintain maximum MC loss everyday.  However the Nyle manual i got has two numbers in their book.  Near the front it says maximum for soft maple is 7% MC loss per day, and near the back in a Dr. Wengert article it say 13% MC loss per day for soft maple.  Do you monitor this and which, according to your experience would be acceptable?  The average green MC for soft maple is suppose to be 90%, so if i used 13% a day i could get it down in 7 days or so?  What do you think?  maybe i need to buy some more meters?  Where do you get some cheap reliable ones?  Any ideas?
Thanks for help,
Kelvin

David Freed

   First I should correct myself. Maintaining the acceptable moisture loss for the type of lumber in the kiln as you are doing is most important. I just use the wet bulb depression as a close guide to keep the moisture loss on track. You can get a wet/dry thermometer from Nyle. that's what I use. I also bought one of their super accurate beam scales to be able to use kiln samples and keep track of moisture loss that way. I guess I need someone to draw me some pictures because I couldn't get it to work right. ??? The samples never would agree with my moisture tester. Not even close. That's why I keep a close eye on the depression, use my moisture tester and sort of go by feel. I don't know why, but the depression that works for me usually isn't what the book calls for. I just learned the peculiarities of my kiln as I went along. I messed up some real nice red oak on the 2nd or 3rd load because I was following the book depression >:( :'(.
    I am not an expert by a long shot; I just know what works for me. I have only dried 4 kiln loads of soft maple and I shoot for 10 or 11% moisture loss per day. Since you saw your own lumber you might not have to deal with as much variation in starting moisture as I do. I dry primarily white ash, and the lumber I get will be anywhere from 45 to 70%, depending on the time of the year, how long the logs have been cut, etc.
   The moisture tester I use is one I bought for $100 about 20 years ago. A couple of years ago I bought a $400 "fancy" tester but it has went haywire twice on me so I just keep using my old reliable "cheapy". I can't remember the brand of either one at the moment, but they are both well known brands.
   I don't know if any of my rambling helped, but I hope it didn't confuse you. It's late and I don't always say what I think I did even when I'm wide awake. Just ask my wife. :D    David

David Freed

   I knew I couldn't think straight that late at night. One reason my kiln is tempermental is because there is no vapor barrier in the 10'x24' door. In really cold weather I can put a load of freshly sawn ash lumber in the kiln, seal it up, turn on the circulation fans and the lumber will dry down to 15% or so at close to the proper rate before I ever turn on the dryer. The door is well insulated, just not moisture sealed, even though I used 3 coats of roof coat on the plywood. It makes fantastic icicles. ;D In the summer it doesn't lose near as much moisture through the door, and that is where a lot of the play it by feel comes in. On the rest of the building I used 6 mil plastic under the plywood. I will have frost on the metal walls when it's 25 degrees outside and 125 inside.    David

bseago

Are you using good clean grooved hardwood stickers?  I run a 10,000 bf nyle controled kiln and on maple we only saw winter cut wood and don't air dy in the warmer months.

OneWithWood

Good info and discussion.  The change in MC is something I am not sure I have clear in my battered old brain.  If a schedule recommends a 7% change in MC is that a 7 point change or a 7 percent change? 
Say my calculated MC on day 2 is 25.31 and on day 3 is 21.45.  Is the change in MC 3.86 (25.31-21.45) or 15.25% ((25.31-21.45)/25.31)?
One With Wood
LT40HDG25, Woodmizer DH4000 Kiln

Kelvin

Yeah, thats a good question OWW.  I've been getting mad that i can't get more than about 4 mc points down a day at 90% kiln compressor time and 120 degrees.  Its been going 20%,16%, 12% in 24 hr incraments.  Ami i gonna get stain for going so slow?  Or is this fast?  I thought i could take it down 11% a day, so it would only take 5 days from 60%mc.  This might be an error.  Any ideas?
Thanks
kelvin

David Freed

   OneWithWood
   Most people refer to % loss as simply subtracting one reading from another, or point loss as you called it.

   Kelvin
   At moisture readings of 20% and under there is a lot less risk of sticker stain as compared to freshly sawn lumber. As to why the moisture isn't dropping faster, is there a reason you have your compressor on 90% instead of 100%? Also are you trying to vent some of the moisture? Both of these should increase the rate of loss. As an extreme example, when I dry poplar I will load about 2500 or 3000 bf in the kiln. To be able to lose 15% per day I have the compressor on 100%, all vents open and running continuously, and an lp gas heater running continuously to make up for heat lost out the vents.    Hope it comes out ok. I know I have had my share of sticker stain while learning how to stop it or at least minimize it.

                                                  David

Danny Dimm

I was told by a business that has dealt with western hardwoods for years, [birch, big leaf maple, red alder] to take the temp up to 160 first thing. That kills whatever causes the stain. Then drop it down to what ever your kilns schedule requires. It worked for me. Nyle 2000

David Freed


I hope I don't start an arguement with this response. Sticker stain is caused by the different rates of oxidation which is caused by the differences in the rate of drying between the lumber under the sticks (little airflow) and the rest of the lumber (good airflow). Oxidation is a chemical reaction. Higher temperatures actually exacerbate the problem. I would tend to believe the company that did that avoided sticker stain by following a good drying schedule after they put their lumber at greater risk by raising the temperature that high. Every source of information I have ever seen says to start out with lower temps if the lumber moisture content is above 30 or 40 percent. Dr Gene Wengert, who probably knows more about drying lumber than anyone else in the US wrote an extensive article in 1998 about the causes and cures for sticker stain. One of the factors listed for putting lumber at a higher risk for sticker stain was;  "Using kiln temperatures over 160o F, especially early in the kiln schedule." Later in the article he reiterated; "Use low kiln temperatures (110 or 120 F initially), as recommended in the schedule; never exceed 160 F, except during equalizing and conditioning".    David


Thank You Sponsors!