The new technologies, incising, moisture tolerant phenolic adhesives and steam pressing were evaluated for the manufacture of laminated veneer lumber (LVL). Both 8- and 13-ply incised spruce LVL panels were prepared using these new technologies. The results showed that both steam pressing and self-generated steam from wet face and back veneers accelerated temperature rise in the innermost glueline of 13-ply incised spruce LVL panels. This would help facilitate faster production rates for LVL manufacture. Bond quality and edge bending values were determined for the steam-pressed 8-ply and 13-ply incised spruce LVL panels. In all cases the average % wood failure was above 90% indicating excellent adhesion between the moisture tolerant adhesive and wood. The modulus of rupture and modulus of elasticity values measured for the steam-pressed incised spruce LVL samples compared very favourably with those for a commercial Norway spruce 15-ply LVL product.
A series of plywood and laminated veneer lumber (LVL) panels were prepared using veneers with higher than normal moisture contents in face and back layers. The purpose of the work was to evaluate the effects of self-generated steam on the pressing times and panel warpage. Panels made with 6% and 10% m.c. faces and backs were compared with control panels made with all dry veneer. Thirteen- ply 40 mm (1 5/8 inch) thick panels were evaluated for press times and thin 9.5 mm (3/8 inch) panels were evaluated for cupping and bowing. Normal plywood press temperatures and adhesives were used. All panels were made with incised 3.2 mm (1/8 inch) SPF veneers. The project demonstrated that substantially shorter press times and more dimensionally stable panels can potentially be made using higher moisture content outside veneers.
A series of plywood and laminated veneer lumber (LVL) panels were prepared using incised veneers in the second phase of this two year project. The primary purpose of the work was to evaluate the effects of steam injection on the pressing times. A secondary objective was to expand the study of warpage in three-ply and four-ply plywood which was begun in phase one. Thirteen-ply 40 mm (1 5/8 inch) thick panels were evaluated for press times and thin 9.5 mm (3/8 inch) and 12.5 mm (1/2 inch) panels were evaluated for cupping and bowing. Press temperatures of 150 degrees C, 175 degrees C and 204 degrees C were used with a commercial adhesive mix for the LVL study while normal plywood pressing conditions were used for the plywood. For the plywood warpage study, the effect of lathe check orientation and species mix were evaluated. The lathe check orientation had little effect while the surface veneer species had a pronounced effect on the warpage in the plywood. Steam used for injection was heated to 260 degrees C at 450 KPa (65 psi) with a super-heater. All panels were made with incised 3.2 mm (1/8 inch) SPF veneers. The project demonstrated that steam injection can shorten press times by fifty percent if incised veneers are used.
Six trials were conducted at the Department of Wood Science, UBC on the drying of "redry" and green SPF veneer using a 0.3 m3 laboratory Radio Frequency/Vacuum (RF/V) apparatus. A larger scale trial was conducted at Canfor's Eburne mill, on the drying of "redry" SPF veneer using a 60 m3 pilot plant apparatus. Results from all these trials showed there was a wide variation in the final moisture content (m.c.) of the veneers with many veneers showing low m.c. regions. This m.c. variation could pose problems for bonding with moisture tolerant phenolic adhesives. Results from the Eburne RF/V trial showed there was a species effect in drying rates and subalpine fir veneer dried at a faster rate than spruce veneer using radio frequency heating.
Steam press drying of green SPF veneers was evaluated on a 4 x 8 foot prototype steam press set up at a local plywood mill. A used industrial press has been modified into a single opening oil heated hot press with grooves machined into the upper platen. Standard green nominal 4 x 8 foot 3.2 mm (1/8 inch) thick mill veneer was dried with super-heated steam injected through 6 mm (1/4 inch) holes in the bottom platen. All veneers were incised with Forintek's patented veneer incisor. The project demonstrated that steam injection can dry green veneers three to four times faster than conventional veneer driers. From the results of this project, a study on the press drying of redry veneer was initiated and showed good potential for industrial implementation.
Unseasoned spruce heart veneer was incised and steam-press dried using platen pressures of 25, 100 and 200 psi. Three-ply plywood panels were then prepared from these densified veneers. Results showed that the stiffness values for laminated veneer lumber (LVL) made with low stiffness SPF veneer or combinations of SPF and Douglas-fir veneer can be greatly increased and meet the 2,000,000 psi MOE marketing requirement using two methods. One involves impregnating unseasoned SPF veneer with phenolic resin and the second method involves using a special lay-up of the SPF and Douglas-fir veneers. These results will greatly help in marketing LVL using western veneer species. New technology of incising, moisture tolerant adhesives and self-generated steam developed at Forintek substantially reduced pressing time by about 40% which will make the manufacture of LVL more economical.
There is a need to demonstrate how novel timber-concrete composite floors can span long distances and be a practical alternative to other traditional structural systems. Better understanding of the fire behaviour of these hybrid systems is essential. To achieve this, the fire-resistance of a timber-concrete composite floor assembly, using BC wood products, will be evaluated in accordance with
CAN/ULC-S101 . A 2 hr fire resistance rating will be targeted, as this is the current requirement in high-rise buildings for floor separations between occupancies.
The structural behaviour of this type of system will also be assessed from conducting pull-out tests of the shear connectors.
In conjunction with previous test data, the results of this test will be used to develop an analytical model to assess the structural and fire-resistance of timber-concrete composite floors. 301010618
The purpose of this study was to determine flatwise and edgewise bending strength ("MOR") and stiffness ("MOE") of spruce and pine 1.5-inch by 3.5-inch by 48-inch laminated veneer lumber ("LVL") specimens parallel to grain. The experimental spruce and pine data was pooled together to give a combined spruce-pine data set.
Appendix 1 to Forestry Canada No. 35, Contract no. 1812L007 on
lumber and laminated veneer strength.
The project objective is to provide key data on the laminating properties of Canadian wood species to assist the secondary manufacturing industry to meet domestic and international customer expectations. This is a progress report to March 31, 1999.
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.