Q: We have an RF gluer. As you know, when we have a wet piece of wood, we tend to get some arcing and smoking, which of course, ruins current production and takes time to get back into production. So, we see two options: First, run the kilns longer to avoid wet lumber or, second, use an in-line moisture meter to eliminate the wet pieces (maybe 1 to 3 percent of a load might be wet) and then refrying these wet pieces when we collect enough for a kiln load. What do you think?
 
 
 
A: Obviously, you have done some studying and also know your equipment. So, without any background info, I will give you my thoughts.
 
 
 
The first approach is a good solution if you are drying different species or thicknesses. It may take an extra day or two in the kiln to get the correct final MC and eliminate the wet pieces. As a rough rule of thumb, I suggest that a kiln has an operating cost of $10 to $15 per day per MBF. So, two extra days in the kiln increases the cost of the incoming lumber by about $25 per MBF. In a 50 MBF kiln, that is $1250. This approach does work technically, but it can be expensive. (Rather than running the kiln an extra day or two, we might also address the cause of MC variation, which is often uneven air drying prior to kiln drying. So, money spent in the air yard to get a uniform MC for lumber going into the kiln can have a big impact on costs and gluing production too.)
 
 
 
 

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The second approach is very effective when the incoming raw material is the same from hour to hour and day to day. Stated another way, the second approach will not work well (money-wise) when there are variations in raw material (other than moisture variations). I have had several clients install in-line meters to identify wet lumber (and even give clues as to which kiln and what history may be encouraging the wide range of MC). One client reduced the end splitting problem in the wintertime to well under 1 percent after they pulled out the wet pieces from production. Although each operation will have different numbers, several clients have found that rejecting 1 to 3 percent of the pieces due to high MC is more cost effective than running the kilns for several extra days.
 
 
 
I had a client making kitchen cabinets and they were able to reduce their rejects in the wintertime to under 4 percent by pulling the wetter pieces and then holding them in storage until the summertime.
 
 
 
As a final comment, even with the first approach, an on-line meter will help in identifying the incoming MC, the variations in MC and potentially the causes of such undesired variations or high MCs so that changes can be made to improve overall processing. If you cannot afford to measure the MC of every piece with an in-line meter, there are valid ways to estimate the average MC and the variation using a handheld meter and specific sampling techniques (such as 6-Sigma, SPC, and TQM). Your local community college or Cooperative Extension Small Business office often can provide on-the-ground assistance.

 

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