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Author Topic: SYP kiln drying dilemma - (question for the experts)  (Read 843 times)

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Offline btulloh

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SYP kiln drying dilemma - (question for the experts)
« on: July 08, 2018, 08:18:01 AM »
So I put this short load of SYP in the kiln last Monday, right off the saw, but the logs had been sitting around for a while before I sawed them.  Cut a sample board and dried some moisture samples and determined the MC to be right about 40%.  Seemed a bit low, but the logs had been sitting around for a while.  (Pretty good shape, a little blue towards the outside, no borers.)

I ran with the doors open and just fans for a day and a half and then decided to close the doors and get the heat going.  The MC was at 30% at that point.  The weather was strange all week (most of you had the same - hot and really humid).  Mostly sunny every day, but some clouds floating around.

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As the week went along the stack dried and this morning it averages 9% MC.  Great.  Sort of.

I'd like to get the temp up to 140 ish for a day and today has the right weather forecast to make that happen.  Yesterday was mostly cloudy with occasional sun and the kiln got up in the high 120's anyway.  MC went from 12 to 9%.  I should take the load out today, but I'd really like to run the temp up but don't want to end up at 6% mc.  

After all that explanation, the question is this:  If you over-dry SYP and then let the MC go back to equilibrium, does the machinability come back or is it forever stuck in the brittle mode?
HM126

Offline YellowHammer

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Re: SYP kiln drying dilemma - (question for the experts)
« Reply #1 on: July 08, 2018, 04:52:09 PM »
Gene and others may have a different answer, but in my experience, once its over cooked, it stays over cooked.  6% is right at the edge.  5% and youll know it.  Rehydrating doesnt help because you cant force the moisture back into the cell walls, only into the areas where unbound water was present.  

If you burn the beans, then the beans stay burned even if you put water on them.  Their physical properties have irreversibly been altered, no matter how good the chef.

I have personally seen some hardwood lumber that was virtually ruined by severe overdrying, resulting in boards that chipped out when planing and were abnormally cupped, twisted and bowed.  

That being said, which is more important to you, setting the pitch in pine or having boards that may have machinability issues?
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Offline btulloh

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Re: SYP kiln drying dilemma - (question for the experts)
« Reply #2 on: July 08, 2018, 06:16:22 PM »
That makes sense, YH.  I don't really like burnt beans.  I had the doors open today to keep the beans happy.  Tomorrow is going to be another good day for sun, so I may try to run the temp up for a while, depending on what the MC is in the morning.  Otherwise I'll just take the beans out of the oven.

I overcooked some SYP a while back and did not like the results, although it all came out in the wash.  It was probably around 6% mc.  The only machining was to run through the planer (byrd head) the cut shiplap with a chamfer.  Just too brittle for my taste.  It sounded like I was running bakelite through the planer.

Thanks for the feedback.  I'm going to consider that definitive.

===

I did get some good data collected during this run and I'll be posting it pretty soon.  Hopefully a few people will find it interesting.  I'm still going through it, and I find it interesting.  Running this load during extremely humid weather seems to have had an impact on how the kiln runs.  (Blinding glimpse of the obvious.)  I hope to get it posted in the next couple days.  
HM126

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Re: SYP kiln drying dilemma - (question for the experts)
« Reply #3 on: July 09, 2018, 08:51:59 AM »
Checking the load this morning after leaving the doors open for 24 hours.  Back to 12% now, by pin meter and sample weight.  Being new at this, I don't know if that's because it's returning to EMC that quickly or because of surface moisture picked up because we were below the dew point temp for 7 or 8 hours.  In any event it looks like I can close the doors and run the temp up today without burning the beans.
HM126

Offline GeneWengert-WoodDoc

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Re: SYP kiln drying dilemma - (question for the experts)
« Reply #4 on: July 09, 2018, 11:25:50 PM »
A lot of syp is dried at 240 F, which does over-dry much of the wood creating cup, increasing other warp, and creating some machining defects.  So, commercially, the lumber in the kiln is put in a shed for three days or so outside, to allow the driest pieces to regain some moisture.  It does not help warp, but because the knives are in the outside of the wood, it does help (not perfect) machining, as the outside was maybe 4% MC and is now closer to 12% MC.

Are you using a pin meter with insulated needles?  This would allow you to get shell and core readings.  I am not sure if your readings are an average.  Perhaps they are not uninsulated?

It would be rare for a solar kiln to reach 150F with the fans running.  The wetter lumber would use the energy for evaporation of water.  If you are that hot, why isnt the wood using this heat?
Gene - Author of articles in Sawmill & Woodlot and books: Drying Hardwood Lumber; VA Tech Solar Kiln; Sawing Edging & Trimming Hardwood Lumber. And more

Offline btulloh

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Re: SYP kiln drying dilemma - (question for the experts)
« Reply #5 on: July 09, 2018, 11:27:52 PM »
Great weather today for solar kilns.  Closed the vents and the kiln was between 140 and 150 degrees for four or five hours.



 

 

HM126

Offline btulloh

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Re: SYP kiln drying dilemma - (question for the experts)
« Reply #6 on: July 09, 2018, 11:31:15 PM »
I'm using un-insulated pins.  I don't have any insulated pins.  

I did prepare I kiln sample.  Perhaps I should cut it and test the core.  

It will be interesting to see what the reading is in the morning after running the temps up today.
HM126

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Re: SYP kiln drying dilemma - (question for the experts)
« Reply #7 on: July 09, 2018, 11:59:27 PM »
Are you using a pin meter with insulated needles?  This would allow you to get shell and core readings.  I am not sure if your readings are an average.  Perhaps they are not uninsulated? It would be rare for a solar kiln to reach 150F with the fans running.  The wetter lumber would use the energy for evaporation of water.  If you are that hot, why isnt the wood using this heat?


Gene, the readings are an average of 8 or so readings taken from various boards in the stack.  The variation is a shade over +/- 1.0 degr.

Today the kiln was up between 140 and 150 for most of the afternoon.  The stack is fairly dry, starting at 12% this morning.  The vents were open just a crack both top and bottom.

Like you've said before, measuring the temp in solar kiln depends on where you measure it.  I have a sensor in the collector area (level with the bottom of the fans) and a sensor near the stack where the air exits.  I am curious about the differential, as both the temp and rh should be affected by evaporation.  Of course the exit air is mostly recirculated, so that differential may not always be a lot especially with the vents almost closed.  Here are a slice of today's data:  (not sure how it will turn out in a post, but ...)


         
Amb TempFAmbient rHCllctrTempFClltr rHCllcrDewPtStack Temp FStack rHStackrHExpctdIncr rH Tc TsFan1Fan2TimeDateSmplTmp
78.944.0103.057.585.198.565.765.8-0.14.5ONON11:40:0007-09-201894.8
79.143.0106.956.688.2102.464.264.7-0.54.5ONON11:50:0007-09-201898.6
80.143.0110.655.991.3106.162.963.8-0.94.5ONON12:00:0007-09-2018102.4
81.041.0114.154.893.9109.661.362.4-1.14.5ONON12:10:0007-09-2018106.0
81.938.0117.553.696.3112.959.561.1-1.64.6ONON12:20:0007-09-2018109.5
82.736.0120.853.098.9116.058.760.7-2.04.8ONON12:30:0007-09-2018112.8
83.336.0123.852.1101.1119.057.559.5-2.04.8ONON12:40:0007-09-2018115.8
83.738.0126.550.9102.8121.856.257.9-1.74.7ONON12:50:0007-09-2018118.7
84.334.0129.149.8104.5124.454.956.6-1.74.7ONON13:00:0007-09-2018121.6
84.531.0131.749.2106.4126.854.156.2-2.14.9ONON13:10:0007-09-2018124.0
85.533.0134.047.9107.6129.052.854.8-2.05.0ONON13:20:0007-09-2018126.5
86.136.0136.247.0108.9131.051.654.0-2.45.2ONON13:30:0007-09-2018128.8
87.035.0138.145.9109.8132.950.652.6-2.05.2ONON13:40:0007-09-2018130.8
87.633.0139.844.9110.6134.549.551.6-2.15.3ONON13:50:0007-09-2018132.9
87.832.0141.544.2111.6136.148.750.9-2.25.4ONON14:00:0007-09-2018134.7
87.932.0143.043.5112.3137.447.950.3-2.45.6ONON14:10:0007-09-2018136.2
87.836.0144.342.8112.9138.747.449.4-2.05.6ONON14:20:0007-09-2018137.8
88.629.0145.442.1113.3139.746.648.7-2.15.7ONON14:30:0007-09-2018139.2
88.931.0146.241.2113.3140.445.747.8-2.15.8ONON14:40:0007-09-2018140.6
88.932.0147.140.7113.7141.245.147.3-2.25.9ONON14:50:0007-09-2018141.8
88.132.0147.540.1113.5141.844.446.4-2.05.7ONON15:00:0007-09-2018142.8
87.530.0148.039.5113.4142.243.945.8-1.95.8ONON15:10:0007-09-2018143.7
86.831.0148.239.1113.2142.643.345.1-1.85.6ONON15:20:0007-09-2018144.5
86.330.0148.238.7112.9142.842.744.4-1.75.4ONON15:30:0007-09-2018144.8
86.033.0148.138.2112.3142.842.243.7-1.55.3ONON15:40:0007-09-2018144.9
86.233.0148.238.2112.4142.841.943.8-1.95.4ONON15:50:0007-09-2018144.7
86.132.0147.537.7111.3142.641.342.7-1.44.9ONON16:00:0007-09-2018144.4
86.632.0147.237.5110.9142.240.942.6-1.75.0ONON16:10:0007-09-2018143.8
86.630.0146.637.2110.1141.940.541.9-1.44.7ONON16:20:0007-09-2018143.3
86.131.0145.936.8109.1141.239.941.5-1.64.7ONON16:30:0007-09-2018142.6
85.729.0144.836.8108.2140.739.740.9-1.24.1ONON16:40:0007-09-2018141.9
85.232.0143.436.7106.8139.839.440.3-0.93.6ONON16:50:0007-09-2018141.2
84.934.0142.436.6105.9138.939.140.1-1.03.5ONON17:00:0007-09-2018140.4
84.838.0141.036.6104.7137.938.739.7-1.03.1ONON17:10:0007-09-2018139.6
84.438.0139.436.6103.3136.738.439.3-0.92.7ONON17:20:0007-09-2018138.6
84.136.0138.036.7102.1135.738.339.0-0.72.3ONON17:30:0007-09-2018137.5
84.135.0136.436.8100.8134.538.038.7-0.71.9ONON17:40:0007-09-2018136.5
83.939.0134.736.899.3133.137.938.4-0.51.6ONON17:50:0007-09-2018135.3
I'm going to put the spreadsheet up here as soon as I re-check my rH to dewpoint calcs
HM126

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Re: SYP kiln drying dilemma - (question for the experts)
« Reply #8 on: July 10, 2018, 08:20:56 AM »
The humidity readings don't seem right.  There may be a problem with the humidity sensors, but I have no way to check them at the moment.  I have extra temp sensors in the kiln to implement wet-bulb readings, but I haven't gotten my hands on any wicking yet.

HM126

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Re: SYP kiln drying dilemma - (question for the experts)
« Reply #9 on: July 10, 2018, 09:17:46 AM »
Avg mc this morning by pin reading: 7.9%  
Sample mc by weight: 8.67%   
Core mc of sample: 7.8%
HM126

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Re: SYP kiln drying dilemma - (question for the experts)
« Reply #10 on: July 26, 2018, 08:21:52 AM »
Just to put the tail end on this topic, this load came out a little crispy.  I need to get the timing better for running the temp up at the end.  Of course it's a little tricky waiting for a good solar day with a load that's already at the target mc.  Learning curve.  I  wouldn't want to learn this with something more valuable.  
HM126

Offline YellowHammer

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Re: SYP kiln drying dilemma - (question for the experts)
« Reply #11 on: July 26, 2018, 08:52:25 AM »
Burned the beans? ;)

It happens.  Youll get the timing, just takes a few runs.  Everybody does it.  
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