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General Discussion / Re: Brown Stain in Ponderosa Pine
« Last post by HencoV on November 30, 2016, 07:32:51 AM »
Comments on you schedule and process graph regarding Brown stain. Not always 100% scientific or in line with literature, but my observations and opinion based on experience on kiln control none the less. Use it… or not

In short -kiln brown stain is formed when extractives like proteins and sugars accumulate at the evaporation front below the surface of a board. These extractives caramelise above certain temperatures (Somewhere around 50+oC/ 122+ oF) forming the brown stain…often highlighted when varnish is applied to the plained surface. Brown stain does not affect the strength of the timber.

Looking at your schedule, it is evident that the compiler of this schedule was attempting to create a  “soft” drying condition. Also seeing that the brown stain is an issue, I am assuming you are drying for appearance grade.

Looking at your process graph and schedule, the following observations:

Heat up and spray: You are not using a spray for humidification. This is possibly neutralized by the very slow heat up phase. Though not necessarily bad, I would use a wet steam spray to humidify the air inside the kiln, at least up to the first time I start venting. You can probably reduce you drying time considerably if you use a spray/humidification during the heat up phase, instead of relying on the woods moisture to supply sufficient humidification

Venting: During the first 15 hours of your drying cycle, your vents are 100% open for ± 40% of the time.  Even though this is at a low temperature and high EMC (±15.9%), this could already force the evaporation front deeper into the timber, setting you up for a barrier where the extractives gets stuck later, and creating an insulating “dryer” outer layer which will reduce energy transfer to the centre of the board and reduce your drying rate…requiring more energy to dry the timber.

I am not a fan of proportionate / modulating vents. Even though it makes more sense from a control point of view to control the WB more accurately, it comes at a cost of constantly loosing pressure, air flow and energy transfer through the stack. I compare it to trying to inflate a tyre with a huge gash in the sidewall…pressure never really increases enough to keep the tyre inflated. Same applies for the pressure differential over the fans and between the constantly open vents. (but this is a title for a complete study on its own)

Air flow, Wet bulb and Main steam:  Your process graph shows an avg WB reading that fluctuates every time the fans changes direction. Your WB avg line should follow the vent set point arc. It looks like it varies by ± 5 Deg F from around 50 hours into the process in each direction. I don’t trust the WB value. It indicates that there is possibly an air flow issue between forward and reverse, or one of the probes making up the average giving a very low or high reading .

The fact that the vent position does not change much/ enough to get the WB avg onto a less fluctuating arc, tells me that the logic controlling the vent is not reactive enough. (Control not sensitive enough to WB temperature changes, dead band too wide, hysteresis error or PID loop not tuned properly.)  I don’t believe in using average values for this most critical part of drying. At each wet bulb, measure and record the air flow over it, with all doors and vents closed and fans running, in both fans forward and reverse directions. Identify the probe with the highest and most constant air flow in both directions and use only that probe for WB control and venting.

Your main steam valve on the other hand, opens more in the one direction than the other. This indicates better air flow (more energy uptake/demand) in one direction than the other. It could also indicate a baffle problem or loose panel or faulty probe in the direction where main steam closes more ..you need to investigate. You will probably find that one or all the stacks on one track have a slightly higher MC% or even patchy drying.  If your proportionate vent control was good, the vent position would be “more” open in the direction that the main steam is “more” open to compensate for more moisture coming off the timber..again indicating a problem with the venting control.
Ok?

With that out the way, is there a fix for brown stain?

 I believe that by understanding the dynamics of your kiln, and applying some common sense, one can reduce, if not overcome the problem of brown stain.  Everybody I have come across who had a problem with brown stain, opted for the “softer” drying schedule route as you have, very few have achieved what they set out to do, and if they succeeded , they were not 100% sure how. No published schedule is a perfect fit for the next kiln. Even two identical kilns don’t react the same to the same schedule due mainly to variables like different air flow, heat transfer and venting capacity &strategy. These should be balanced and within the safe schedule limits that the specie you try to dry can handle. I regard published schedules  as the “safe” starting point. 

The key is to attempt to keep the evaporation front as close to the surface as possible. In other words, match the vent set point with the evaporation rate. Try the following with your kiln:

Set the proportionate venting to be as sensitive as possible.

Phase:   DB at end of Phase:   WB/Vent  Set point:   Spray SP:   Hours
1.          165 Deg F   :                       145:                 142:      8:
No venting until WB SP is reached, increase DB until 165 at 8 hours
When the vent close to more then 40%, go to Phase 2 WB/Vent SP
2.          165                             141                 No Spray
When the vent close to more than 40%, go to Phase 3 WB/Vent SP
3.          165                             138                          No Spray
When the vent close to more than 40%, go to Phase 4 WB/Vent SP
4.          165                             135                          No Spray
When the vent close to more than 40%, go to Phase 5 WB/Vent SP
5.          165                             131                         No Spray
When the vent close to more than 40%, go to Phase 6 WB/Vent SP. This should be around 25% MC
6.          165                             127                         123

Stay on this SP until you reach desired MC%

Note: The 40% position limit is just a guess. If you study the way your kiln react to these setting, you may find that you may need a higher or lower value as indication for when you need to increase the WB depression.

Good luck.
2
General Discussion / Re: Brown Stain in Ponderosa Pine
« Last post by robshow on November 28, 2016, 11:26:41 AM »
Here is the schedule we use on 6/4 shop.
3
General Discussion / Re: Brown Stain in Ponderosa Pine
« Last post by HencoV on November 23, 2016, 11:22:26 PM »
If you can, post a screenshot of the process graph for one batch..showing set point and actual values
4
General Discussion / Re: Brown Stain in Ponderosa Pine
« Last post by robshow on November 23, 2016, 05:17:47 AM »
Thanks for the reply.
Not sure how to answer the first question, do you want me to describe BD WB and time at each step.
Air flow is average of 725.
5
General Discussion / Re: Brown Stain in Ponderosa Pine
« Last post by HencoV on November 23, 2016, 02:06:22 AM »
Hi Robshow,

What is your current kiln schedule? Also what air speeds do you get on the exit side?
6
General Discussion / Brown Stain in Ponderosa Pine
« Last post by robshow on November 22, 2016, 02:08:25 PM »
Could anyone suggest a schedule that you are using for limiting brown stain?
Recently i have researched the issue and attempted to adjust some schedules but have not seen any difference.
We use double track LSI kilns with line shaft fans 100' and also double track Wellons with cross shaft fans 66'.
The Brown stain occurs in both types on kilns in shop 5/4, 6/4, 8/4 (worst in the 8/4)
Im getting ready to use a schedule that is published in the book KILN-DRYING WESTERN SOFTWOODS by Edwin Knight,  it states that it is a 6/4 schedule that will limit brown stain.
Any suggestions?
7
Dry Kiln Maintenance / Re: To map or not to map that is the question
« Last post by GeorgeCulp on November 22, 2016, 08:30:37 AM »
IMHO - kiln charge mapping is excellent AFTER all known variables are dealt with - fans pitched correctly and all fans pitched the same, rpm of all fans the same or are some belts slipping badly (if you don't have polychain), baffle system in excellent condition, stacking the way it should, etc., etc., etc.
In other words, eliminate all the variables that you know of then start the mapping otherwise you wont  know where to look for the problem.
Putting everything back "in spec" usually fixes a lot of issues.
8
Dry Kiln Maintenance / To map or not to map that is the question
« Last post by TILLAMOOK on November 18, 2016, 08:54:03 AM »
Possible mapping advantages – pin pointing a location inside the kiln where you consistently find either a wet area or dry area,  which may confirm what you already suspect/know regarding a bad trap, steam valve or baffle, or poor air flow and air leaks (poor seals in kiln doors) etc.  Also, as a research tool to do kiln baselining.

Possible mapping disadvantage – If there is not an efficient method, set of procedures or the correct equipment, time used mapping could better be used for repair and maintenance on kilns.  In other words the kilns are not yet in good enough shape to benefit from mapping. Problems evaluating data (not enough time or understanding how to use it), not familiar with statistical significance,  possible inaccurate map because of out of order units (may show a wet area in the wrong location).

9
Training / Events / Re: How to Dry Lumber for Quality & Profit Workshop
« Last post by MichaelM on November 14, 2016, 02:33:14 PM »
Thanks, I just logged on to post something about this workshop and it's already there.
Mike M.
10
Training / Events / How to Dry Lumber for Quality & Profit Workshop
« Last post by admin on November 14, 2016, 11:11:16 AM »
How to Dry Lumber for Quality & Profit Workshop

December 12-14, 2016

The purpose of this course is to provide a basic understanding of wood and how to dry it.  Practical, up-to-date information will be provided on wood properties and how wood dries.  You’ll learn how both steam-heated and dehumidification kilns are made, operated and maintained, and how to create and modify kiln schedules for different species.  Drying to meet the European quality standards and heat treating standards will also be discussed.

What to expect…
Information will be presented by university practitioners and researchers, consultants, and industry representatives using multimedia and laboratory exercises.  Lunch with manufacturers’ representatives will help you appreciate the range of equipment available.  You will receive printed materials dealing with different aspects of the course.

If you are involved with lumber drying and its management and want practical, hands-on training and knowledge, this course has something for you.

The Registration Fee Includes:
The conference registration fee of $775.00 includes all course materials, refreshment breaks each morning and afternoon as well as lunch on Tuesday and Wednesday. For online registration, please click here.

Conference Fees & Cancellation Policy:
Cancellation requests need to be made in writing via email no later than 5:00 pm (PST) on Friday, November 23, 2016 in order to receive a refund (minus a $50.00 administrative fee).  Refunds will not be made for cancellation requests after 5:00 pm (PST) Friday, November 23, 2016.  (Substitutions may be allowed)

The College of Forestry reserves the right to cancel courses.

Lodging and Directions:

Lodging:
Attendees are responsible for all hotel reservations.  At the following hotels, please mention that you are with the How to Dry Lumber for Quality and Profit Workshop upon booking to access the group rate.

Hilton Garden Inn:  There a select number of room available at the Hilton Garden Inn-Corvallis, at a special group rate of $122.00 per night plus tax.  Call 541-752-5000 to make your reservation by phone or to book online go HERE.  Let them know you are attending the Lumber Drying Workshop at OSU.  Reservations must be made before November 20, 2016 to access the group rate.

Other accommodations can be found by visiting the Corvallis Tourism Site.

Parking:
Richardson Hall has very limited parking space.  All visitors must have parking permits displayed in your car while parking on campus.  You may pre-purchase you parking permit by using this website.  If you will be staying at the Hilton Garden Inn complimentary parking is available in their parking lot.  OSU operates a shuttle around campus that picks up very near to the Hilton Garden Inn.

Go HERE for a parking map.  Parking Questions can be directed to 541-737-2583.

Getting to OSU:
All workshops will be held in Richardson Hall 107- Oregon State University Campus. 

Sign in starts at 7:30, Monday, December 12.  The workshop will end about 2:30, Wednesday, Dec. 14.

For Further Information about the program, please contact Mike Milota at mike.milota@oregonstate.edu or 541-737-4210.
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