Kiln Tech Needs Pointers


From original questioner:

hi, i just got a job as a kiln tech, I'm not completely unfamiliar with the kiln drying process. but i don't know the " in's and out's". is there any literature out there that would help, or do y'all have any tips? there isn't anybody there to really train me, I'm kinda being "thrown into the fire" so any help would be appreciated. BTW ill be drying treated SYP

From contributor Ge

Good have been assigned one of the easiest woods to dry.

As a first step, you need to make sure that you do not accentuate the warp by using poor stacking. Most drying books cover stacking, although with SYP you can use 24" spacing. For fast drying above 212 F, you will hear about 7/8 and 1" thick stickers, but for your job, 3/4" is fine. So, your concern is alignment and using full length stickers so that every piece is supported and so that the 4x4 (or maybe smaller) are aligned under the stickers.

Regarding the kiln, the treating organizations have some specifications wrt to maximum temperatures. So, get a copy of their regs and then call them and discuss. In fact, it is likely that they will be able to tell you what is the most common kiln procedures that they see when they visit operations to check on conformity to the rules.

Do you also have a sawmill? If so, the grading organization often times has technical support for drying.

Our industry is also quite open, so if you can find an operation near you, see if they will let you visit and discuss.

As a last resort, you can hire a consultant (such as me) to visit and analyze your process and make suggestions. But this is a bit more expensive than the previous suggestions.

As you may know, the drier you go, the more warp you will have. So, it is critical to find out what you target final MC is, especially the wettest. Then make sure that the kiln performs perfectly so that it does not over dry some pieces (and warp them) while under drying in other locations. The wood itself has enough variability in drying that we do not need to add to this with a non-uniform kiln. When measuring final MC, make sure your boss and the customer both agree on how to measure deep are the pins, meter manufacturer, insulated needles, temperature and species correction, etc.

From contributor ba

thanks, i saw your fast drying temp of 212, but we dry at a temp of 135. is there any benefit to drying at this temp? or would this be a requirement from the treater?

also how important are baffles in the kiln? i assume they are very important in regards to efficiency. our kilns have them but I'm not sure if they are being used properly.

i think i understand the stacking process fairly well. i read of a "composite" sticker, is that something worth looking into? or for treated syp does it really make a difference.

i really want to get a good grasp on the kiln. my personal (not professional) opinion is that our kilns have been running inefficiently. due to the lack of drive to improve them. the drying schedules have been the same for as long as i have known anything about them. but the treatment chemical has changed many times over the years.

From contributor Ge

Are these DH kilns?

135 F is fine.

Any durable sticker is fine. No need to get an expensive sticker, but certainly consider sticker life. Are sticks broken due to longevity or due to poor handling. Maybe a fork lift driver is doing some damage due to his handling of packs.

Usually we do not a schedule, but just lower th RH as much as possible at 135. But, it depends.

From contributor ba

they are not dh.

how much quicker is it to dry at a higher temp. what risks are there?
and would it cost less?

do you suggest a program that monitors rh and dries accordingly. or a schedule.

From contributor Ge

We are concerned about strength loss, so the lower temperatures when redrying are preferred. The chemical supplier should have info on the maximum temperature suggested.

The hotter you go, the more brittle the wood and the better chance you might over-dry. So, I like 135 F. It is slower, but energy use is not increased substantially. Of course, with limited kiln capacity, slower does mean less profit due to less annual production.

Again, the quality assurance company that gives you the labels or stamps for your treated wood should have some requirements and probably experience...that is better than hiring a specialist like me to visit.

From contributor Bi

Most companies doing kiln drying after preservative treatment (KDAT) use "time based" schedules, which generally run from 2 to 5 days. Dry bulb set points are raised from 120 to as high as 160 F. Using lower temperature, such as your 135 F max, typically results in better quality, though at the expense of somewhat lower throughput. Wet bulb control, especially initially, is very important. A 10 F wet bulb depression should result in reasonable drying rate, without excessive surface drying. Baffling is critical to quality and uniformity. Look to your chemical supplier with questions and for suggestions; many of them have guidelines in their quality manuals. Books such as Drying Hardwood Lumber and the Dry Kiln Operators Manual are good references. Participating in a drying short course is also a good idea; SPIB just held one, we are doing ours in January , as well as others around the country at NHLA and several universities throughout the year.