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Minimizing glue dry-out and delamination in plywood. Part 1: softwood plywood

https://library.fpinnovations.ca/en/permalink/fpipub37853
Author
Xu, H.
Dai, Chunping
Chow, Gordon
Andersen, Axel W.
Date
October 2007
Material Type
Research report
Field
Wood Manufacturing & Digitalization
Author
Xu, H.
Dai, Chunping
Chow, Gordon
Andersen, Axel W.
Date
October 2007
Material Type
Research report
Physical Description
46 p.
Sector
Wood Products
Field
Wood Manufacturing & Digitalization
Research Area
Advanced Wood Manufacturing
Subject
Veneer gluing
Veneer
Plywood manufacture
Plywood
Laminate product
Gluing
Series Number
4574
W-2461
Location
Vancouver, British Columbia
Language
English
Abstract
This work provides scientific support for, and confirms, what most mills already use as rough and dirty rules of thumb as best practices for manufacturing plywood: i.e. dry veneer should be pressed when its temperature is 100°F or less; average veneer moisture can be 4 %; assembly times should not exceed 20 minutes; and glue spreads should be approximately 32 lbs. per M ft2 SGL. In addition, this report used the data generated to formulate multivariate statistical models that could be used to develop or enhance existing in-mill process control software, and/or quality procedures at member operations. This report documents the results of an extensive investigation of plywood dryout and delamination. The study included laboratory and mill tests of key manufacturing variables used in the production of phenol formaldehyde (PF) bonded plywood. Relationships between key variables and plywood quality were used to develop a statistical equation to quantify the effect of veneer moisture content, temperature, assembly time and glue spread rate on wood failure percentage. Testing methods using vacuum/pressure boil-dry-boil, and 6-cycle soak were used and a new multi-step pressing schedule was examined. The following are the main findings:
Veneer with a low moisture content (MC) level is more likely to create glueline dryout than high MC sheets when PF resin is used. Although veneer with a high MC level could minimize the occurrence of dryout, PF gluing systems accept a maximum allowable veneer MC (peak moisture) range of 6 to 8%.
Sheets having temperatures over 100°F are strongly correlated with dryout problems.
An excessively long assembly time approaching 20+ minutes could significantly affect bonding, especially when veneer or ambient temperatures are high.
Increasing glue spread rate can be used to minimize dryout caused by high veneer temperature and low veneer MC; however, a higher glue cost per M ft2 is incurred.
Flexure tests cannot be relied upon to detect bond quality as bending strength is heavily influenced by surface panel properties. During the mill study, it was learned that variations within each of the above mentioned controllable factors could not be avoided in a mill situation. Good manufacturing process control can ensure that all variables stay within ideal ranges and occurrences of dryout are minimized. The statistical models developed during this project could, possibly, be used to develop or enhance process control software. A multiple-step hot-pressing schedule, capable of improving plywood bonding properties with or without sacrificing volume recovery, was developed to minimize bond problems caused by dryout. Existing mill presses may be able to implement this approach seamlessly or after a few minor adjustments have been made. Some mills may have to peel thicker veneer to compensate for increased veneer compression associated with multi pressing and in doing so sacrifice log recovery. Pressing schedules illustrated in this study indicate that press production is not sacrificed as single or multi-step pressing time is identical for most thicknesses. Laboratory tests showed that wood failure percentage figures from a glueline shear test, a standard method for evaluating bond quality, are useful glue dry-out indicators for softwood plywood. An attempt to develop a tack strength test that could assist in evaluating dryout was unsuccessful as excessive variation was present within recorded data.
Veneers - Gluing
Lumber, Laminated veneer - Gluing
Plywood - Manufacture
Documents
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Minimizing glue dry-out and delamination in plywood. Part 2: hardwood plywood

https://library.fpinnovations.ca/en/permalink/fpipub37854
Author
Xu, H.
Dai, Chunping
Chow, Gordon
Andersen, Axel W.
Date
October 2007
Material Type
Research report
Field
Wood Manufacturing & Digitalization
the effect of veneer moisture content, temperature, assembly time, glue spread rate, and amount of catalyst
Author
Xu, H.
Dai, Chunping
Chow, Gordon
Andersen, Axel W.
Date
October 2007
Material Type
Research report
Physical Description
16 p.
Sector
Wood Products
Field
Wood Manufacturing & Digitalization
Research Area
Advanced Wood Manufacturing
Subject
Veneer gluing
Veneer
Plywood manufacture
Plywood
Laminate product
Gluing
Series Number
4574
W-2462
Location
Vancouver, British Columbia
Language
English
Abstract
An extensive investigation of plywood dryout and delamination was conducted in this study. It included laboratory tests of key variables for urea formaldehyde (UF) bonded plywood. A statistical equation was developed to quantify the effect of veneer moisture content, temperature, assembly time, glue spread rate, and amount of catalyst on wood failure percentage. The following are the main findings:
Veneer with a low moisture content (MC) level is more likely to create glueline dryout than high MC sheets when UF resin is utilized. Although veneer with a high MC level could minimize the occurrence of dryout, maximum allowable veneer MC (peak MC) is limited by other factors. UF gluing systems can employ a maximum MC range of 10 to 12%, which is much higher than the one that applies to PF resin (6 to 8%).
Sheets having temperatures over 100°F are strongly correlated with dryout problems.
An excessively long assembly time could significantly affect bonding, especially when veneer or ambient temperatures are high.
Increasing glue spread rate can be used to minimize dryout caused by high veneer temperature and low veneer MC.
In UF gluing systems, catalyst level heavily influences bonding and the extent to which dryout occurs.
Veneers - Gluing
Lumber, Laminated veneer - Gluing
Plywood - Manufacture
Documents
Less detail