VGrader, Veneer Grading Optimizer, was developed at Forintek to assist mills to optimize on-line veneer stress grading operations. So far, more than 10 copies of VGrader 1.0 software have been delivered to Forintek member mills. The software can recommend the optimum grading thresholds through analyzing the properties of veneer to help mills deal with “what-if” scenarios when veneer species, log source and diameter as well as final veneer products change. By tailoring veneer grades to the market requirements of LVL/plywood products, the software serves as a useful tool to characterize specific veneer for end use and help optimize veneer on-line stress grading and products lay-up options.
During the past year, the VGrader software has been upgraded to deal with either UPT-based (ultrasonic signal propagation time) veneer stress grading or E-based (modulus of elasticity) veneer stress grading or veneer visual grading. The software has also been upgraded to accommodate UPT data either from mills or laboratory testing of veneer samples. A direct linkage between laboratorial measurement span and desired wheel-span of the on-line grading system was also setup. The current version of the software is VGrader 3.0. To help mills optimize current on-line stress grading operations, the proper procedures to find the optimum UPT thresholds were established.
The proper procedures are as follows:
1) Sample veneer sheets representative of veneer population in the mill and perform stress wave testing for sampled sheets using a portable stress wave timer. Alternatively, full-size veneer sheets can be sampled right after the on-line grading system with UPT data being recorded for each veneer sheet;
2) Measure other relevant veneer properties such as thickness, density, moisture and knots;
3) Calibrate the stress wave time (or UPT) to find its zero offset value;
4) Store all measurement data into a VGrader compatible database;
5) Use the upgraded VGrader software to examine the distribution of veneer attributes/properties such as thickness, UPT, density and MOE;
6) Derive required veneer MOE based on the performance requirements of target veneer products;
7) Establish stress grading constraints and using VGrader 3.0 to perform computerized veneer stress grading through adjusting the UPT or E thresholds and examining the change of statistical veneer MOE, densities and volume breakdown per grade until all the grading constraints are satisfied;
8) Convert the optimum set of UPT or E thresholds from the VGrader software into those used for on-line veneer grading system to perform stress grading;
9) Make veneer products and test them to validate the grading results.
An example of establishing the above procedures was also demonstrated.