Gentlemen best of luck in 2021 from Croatia!

My name is Mario and I work for hardwood flooring company that produces mostly laminated parquet. Main role I have is operating kilns and monitoring process of drying. Please note that I have no real education in school. Everything I know is self-taught, passed experiences from mentors and just pure trial and error method learning so be easy on me if i ask dumb questions. It will be hard to explain all the points that i would like to ask but i'll try to shorten this post as much as possible.

I operate 38 kilns of volume around 150m3. Main product we dry is white oak 3,0-3,2 cm thick / 0,5 - 2,3 m long, delivered from all around Europe. Targeted MC is 6,6% (+/- 0,6%). It is cut in 3mm lamella. Initial MC is 40% - 100%.

Technical shape of kilns is, well not perfect but that is something i can't influence. What I can do is get the better understanding in what i'm doing wrong. So let me begin:

1. Starting temperatures & EMC

Start with 27°C - EMC 19% because big difference in initial MC (40-100%). I can't influence this so must adapt.
My question is, what would You suggest for highest starting temperature? My tests with 31/33 °C resulted with white water marks at the end of production, cutting in lamellas - and that is something that must not happen.

2. Drying time FR->KD in 65 days.

It is the topic which has become more and more looked upon by every day. I understand that costs of drying are big but with all the side influences i can't find the way to shorten drying process. Either i end up with too much end cracks, white water marks, tension problems,etc...

Hope to get at least some reply so we can start the discussion. Best wishes, thank You in advance.

Here are current drying schedules i work with.

View higher quality, full size image (2560 X 1440)

View higher quality, full size image (2560 X 1440)

You might want to read DRYING HARDWOOD LUMBER, which is available on the Internet. Free

Also, I gave a webinar on oak drying, which you can get from the National Hardwood Lumber Association...go to education, then webinars and scroll to the bottom. Free.

A key point is never start a kiln at an EMC higher than the surface moisture content, especially with oak. ALSO, STARTING AT A HIGH EMC can lead to darkening.

Most steam kilns in North America have trouble operating under 40 C. What kiln do you have?

Most kilns here will not go under 5%EMC at any time. Also, most kilns use a stress relief step at the end. The final target MC here is 7% MC, so the posted schedules previous would not get the wood dry enough. Most kilns here use the wettest one or two samples to get the MC. Essentially one of the oak. Drying schedules here use a warming cycle or a heating cycle, but instead go directly to the appropriate temperature, perhaps using a ramp of 2.5 C per hour, while controlling the EMC.

The initial moisture range is extremely wide and will cause some issues, as the drier wood will not like the required EMCs for the wetter wood. Plus, such dried wood might have a low surface MC, so the EMC would be too high. The green moisture for oak is rarely above 80% MC ( oven dry basis), for higher MCs indicate a bacterial infection that can also,mean weaker wood and some bad odors.

Good day and than You for reply.

I'll surely look up for mentioned webinar & have already downloaded "Drying hardwood lumber :)

"A key point is never start a kiln at an EMC higher than the surface moisture content" - can You please explain this? For example, if starting process with material having MC=60% MC, what EMC would You recommend? I do have a problem with darkening, this would be one of my points later on in hope anyone would answer to this thread.

I use evaporation kilns, so steaming is out of equation. They were built in 2000, designed by Italian company OS PANTO. In 2017 half of them were converted to Muhlbock - Austria controlers but infrastructure was not changed.
Going under 5% EMC is not a problem. At final drying stages i go up to 65°C and under 3,5%EMC. For the reason of not trusting our sensors (cellulose plates) I bought additional instrument to measure clima in kiln, never had a problem lowering under 4%EMC.

Regarding warming cycle. I do it but more gentle. 25°C - 18%EMC - 2°C/h - 24 hours to be sure.

In last post i accidentally uploaded 2 same pictures and gave only FR_AD schedule. Here is the AD_KD now. Note that this is just formal schedule & it is changed according to conditions in kiln / material / etc.

In next few days I'll post a few more topics with pictures so You can have a "whole picture" of kilns / meterial / stock etc.

Thank You once more,
BR.

View higher quality, full size image (2560 X 1440)

View higher quality, full size image (2560 X 1440)

Do you have a pin moisture meter? This is how you measure the surface MC.

We want to start the kiln at an EMC that will not add moisture back to the lumber, as a higher EMC than the surface MC will cause the surface to swell and this swelling will cause any checks to go deeper. Also, high EMC is associated with causing stain in the lumber.

It is important to understand that discoloration occurs above 45% MC. Also, understand that checks develop a bit higher. We only make them worse at lower MCs. If there are no checks, you cannot make them worse.

So, all efforts should be directed at preventing checks in the first place and also drying at a low enough EMC to prevent discoloration. It only takes one day of high EMC to discolor the wood, although the discoloration shows up later.

Hello,

I'm watching webinar & now got the understanding of "surface MC & starting EMC connection." To be honest, it never crossed my mind to look it this way (like i mentioned, lack of real education restricts my vision :) Let me mention that I'm 31 years old and only do this for 3 years. Approximately 1 year ago i started to work "alone" as my mentor returned to Switzerland where company headquarters are located. My plan is to finish education if possible and stay in this line of work. I think this is something person needs to "love" to do rather than look it simply as a 8 hour/day job. Back to the subject...

In my equipment there are 2 brand new moisture meters, Gann H35 & Gann H85. By request company bought them, but somehow i never got used to work with them except just using them to determine "wettest sample - core" so that they can be prepared for drying process. All my decisions are made by calculating MC by oven drying method.

- MEASURING MC DURING DRY.PROCESS - maybe just to create "whole picture" .

We are using 5 samples for constant daily measuring (weighting) and 10 samples connected to cables. During drying process we unload material near the center of stack and make additional MC checks with oven drying method. I forgot to mention that kilns do not have "back door entrance" so only way to check the center of stack is by unloading and randomly picked samples (flat:quarter sawn = 40:60). These samples are marked and checked multiple times during drying. They are taken from "center" of package. Forklift lifts part of the material and board is cut from the end (40 cm at least). Then the inner part of the board is cut for core sample and cross cut sample. They are dried for 24h at 103°C in oven. All standard process. I'm attaching one of my drying protocols. It is mostly in Croatian but i don't think You will have problem understanding measurements. Vital information is translated to English so if You have time & and are willing , maybe take a look...

View higher quality, full size image (2560 X 1440)

View higher quality, full size image (2560 X 1440)