Characterizing the Roughness of Southern Pine Veneer Surfaces

A reduction in the quality and diameter of southern pine veneer logs has led to a higher proportion of rough veneer surfaces. In the near future, the need to monitor and control veneer surface roughness in plywood production will be essential to maintain plywood quality and reduce production costs. A roughness index is needed that is highly correlated with veneer surface roughness (specifically toughness that is caused by the machining process) and yet is obtainable in real time (at production speeds). Veneer samples (12 inches square) were visually classified into three roughness classes; rough, intermediate, and smooth. A stylus tracing technique was used to obtain surface profiles from ten randomly selected veneer samples from each roughness class. Both the back (loose side) and front (tight side) were traced for each sample. Five indexes describing the frequency and amplitude of veneer surface profiles were calculated and evaluated for their ability to distinguish the veneer surface roughness classes (rough, intermediate, and smooth) and veneer side (tight and loose). Eight levels of roughness grade (0 to 0.01 inch on the amplitude scale) were filtered from the profiles to observe the effects on the five indexes. Results show that the frequency index was the only index able to distinguish all three roughness classes when a roughness grade of 0.002 inch was filtered from the profile. The other four indexes that described the amplitude or a combination of the amplitude and frequency were able to distinguish between the rough and smooth and rough and intermediate roughness classes. Roughness grade filtering had little effect on improving the sensitivity of the other four indexes in distinguishing all three roughness classes. All indexes were able to distinguish the tight and loose veneer faces. As expected, the loose side was significantly rougher than the tight side. In terms of simplicity and accuracy, the frequency index shows the greatest potential for use in the production environment.

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