Analysis of board moisture in wood based panels production

Producers of wood based panels need to control and optimize the manufacturing process. There are also industry and official standard requirements to measure several process parameters like for instance board moisture.

The EN 312 standard requires board moisture to be measured with the EN 322 method after each 8 hours of production. Each formaldehyde test with EN 120 also requires determination of board moisture according to EN 322 to correct the perforator value to 6,5 % moisture. The EN 322 standard method takes 24 hours to complete.

The Near Infrared Reflectance (NIR) technique is particularly suited for measurement of moisture in board samples.  Recent advances in instrumentation and calibration technology that have enabled stable and precise measurements.

DA 7250 NIR Analyzer

The DA 7250 is a new full-spectrum, NIR instrument designed for use in process environments. Using novel diode array technology it performs a multi-component analysis in only 6 seconds with no or little sample preparation required.

During these 6 seconds, a baseline is collected, noise monitored, wavelength accuracy is standardized, and a large number of full spectra are collected.

DA 7250 for board moisture factory production control

The EN 322 method can be replaced with the DA 7250 board moisture measurement using the procedure described in EN 326-2.

This gives several advantages, 

  • Short analysis time
  • Automatic documentation of results, no risk for typing errors
  • Save personnel resources
  • No limitation in oven capacity
  • The EN 120 uncorrected value can be moisture corrected directly after it is measured using the DA 7250 moisture measurement

The company Byggelit i Sverige AB has been testing board moisture with a DA 7200 (the previously generation to the DA 7250) parallel to their EN 322 moisture determination for a year. The NIR results has tracked the EN 322 values well all the time and Byggelit i Sverige AB are now planning to replace the EN 322 test procedure with the DA 7200 for their board moisture testing.

Experimental

Several hundred samples from wood-based panel mills were collected. The samples were analyzed on multiple DA 7200 and DA 7250 analyzers following the procedure described in the “DA 7250 Quick Guide v1.0 appendix EN moisture testing”. With this procedure the board samples are cut in pieces and measured from the edge as shown in the picture.

Reference analyses were performed by the mills according to EN 322.

A calibration was developed by Perten Instruments, with the following statistics: 

Parameter

Number of samples

Range

R

Board moisture

~ 500

3,8-9,4 % dry based

0,96

The DA 7250 results are very accurate when compared to the results from the reference method.

 

 

 

 

 

 

 

 

 

 

 

 

Figure 1. Cross validation results for the board moisture calibration is shown in the graph above.

Validation results from one particle board mill is shown in the graph below.

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 2. 33 validation samples showed an SEP of 0,34 % moisture, R= 0,96, Slope=0,97

The difference between the DA 7250 and the reference method is in the same magnitude as typical differences between two different labs.

In summary it is concluded that the DA 7250 can replace the EN 322 method to analyze wood based panels for board moisture. The ease-of-use and accuracy make it ideal for use at wood based panel production sites worldwide.