Target size adjustments

[TILLAMOOK]

Target size adjustments: I assume I should narrow my lumber's moisture content standard deviation, and increase my average kiln-dried moisture content as much as possible before attempting to decrease my target size in the sawmill; correct?

[MichaelM]

I suppose this also depends on the current target size.  If you have no skip at the planer, than there might be some opportunity without any changes at the kiln. 

The gains you are thinking of would be important.  1% MC might get you 0.003" or  little more.

[HencoV]

I am not sure about the rest of the world, but over here (South Africa), the kilns are often the anus of the sawmill. Everybody knows about it, and it's importance, but don't pay much attention to it...until it stops working..http://www.kilndrying.org/Smileys/default/shocked.gif

It hardly ever happens that someone working at a mill cares enough about it to make it their passion and interest to study the kilns, identify issues and try to resolve it. The controls are good....set to manufacturers specs and left at that. Management has enough other issues on their plates to take care of.

The mere fact that Tillamook asks this question, shows he will get it right. With the right focus and control you can reduce wet dimensions...after all else has been optimized

Following is an extract from an article I wrote for the September issue of WoodSA & Timber times magazine. www.woodsa.co.za

The article is about upgrading and optimizing kilns. Figures were supplied by the sawmills themselves:

Case study 1:

•   6 x Hot water single air flow direction progressive kilns
•   No additional capital outlay on kilns, fans, heaters or boilers
•   Raw material: Mill cuts 90%, 3.1m long class A logs (5”-7” dia.)
•   Product: Finger jointed Structural timber

Volume throughput through kilns:
•   Before optimizing by Timbersoft – 37 m3 /day (15679 board ft)
•   After optimizing – Up to 55 m3 /day (23307 board ft)   
•   Volume through kilns up by ± 48%

Quality Improvements
•   Zero downgrade on drying defects, grading on inherent defects only
•   Finger Joint production per shift has increased by 28% due to less handling as a result of more straight & flat pieces coming from the kilns
•   Although FJ production has increased, glue usage has decreased due to less joints per 6.6m length

This has led to a profitability increase of ± 15% per m3 produced

Case study 2
•   7 Steam kilns including 2 TFDesign kilns
•   Mill produces mainly structural timber (38mm), but also some 25mm and 50mm
•   ± 400m3 per day intake  (169510 board ft)
•   No additional capital outlay on kilns, fans, heaters or boilers

Before optimization by Timbersoft
•   Kilns was the bottleneck with stacks sometimes staying in front of the kilns for up to 6 weeks

After optimizing
•   Bottleneck converted to a vacuum. Wet mill cannot keep up with kiln production
•   Mill can increase production by ± 20% without adding additional kilns or boilers
•   Grading has become a lot easier due to the fact that drying defects has decreased substantially.
•   The vacuum created by the kilns has enabled the mill to improve production planning

This has led to a profitability improvement of ± 10% /m3

Case study 3

•   Upgrading a Bollmann kiln
•   Mill has 2 x Windsor single track kilns and 2 Bollmann double track kilns
•   In volume per kiln, the 2 Windsors take about a 1/3, while the Bollmanns take about a 1/3 each
•   The study was conducted over a month, grading  all 154600 pieces coming from these 4 kilns
•   Of the 154600 pieces graded, 45% came out of the Timbersoft controlled Bollmann
•   Total drying defect figure for the sample out of the 3 kilns not controlled by Timbersoft was 16.9% while the Bollmann with Timbersoft controls produced only 1.6% defects
Getting the basics right, and keeping it there, coupled with managing the conditions inside the kiln optimally can lead to FASTER drying with LESS drying defect

[GeorgeCulp]

Standard deviations and average mc's are all good markers for change, yet in the end the highest average mc you will be able to attain will be governed by what percentage of your volume you will allow to be over your maximum allowable mc. If you allow 10% to be above the max that will allow a higher average mc than if you allow 5%, and that will allow more than if you allow 0%.

One thing though....if you, for example, will allow 10% of your volume to be over 19% (assuming for this example that is what you stamp your lumber), then if all 10% lies between 19% and say 22% that will mean one thing versus if the 10% volume lies between 19% and 26% that will mean another.

Just another way to view things. Good luck.