Heating green-wood prior to peeling is necessary to improve both peeling process and quality of veneer.
This study investigates optimum heating temperatures by soaking of beech, birch and spruce. Experiments have studied the influence of heating temperatures from 20 to 80 C on thickness deviations and veneer lathe checking using a pneumatic rugosimeter and image analysis of opening checks with the SMOF device (Système de Mesure de l’Ouverture des Fissures). Conclusions account for reduced heating temperatures compared to the temperatures currently in-use in the industry. Already at 50 C, positive effects of heating ensure efficient peeling process.
Low temperatures produce veneers with deeper and more spaced checks than high temperatures when checks are closer and less deep, becoming even unpredictable especially in case of spruce. These results establish the SMOF as an essential non-destructive control device to control the quality of the veneer produced at research level.; Institut Carnot, RYM-TO Doctoral School
Laminated veneer lumber (LVL) is a well-known high-performance engineered wood product suitable for structural applications. However, the peeling process can induce lathe checks of the veneer with various depth and spatial frequencies. In this study, a finite element model (FEM) is proposed to describe and to analyze the influence of veneer lathe checks on the elastic properties of LVL. Firstly, the typical lathe check depths and frequencies were determined by means of different compression rates of the pressure bar when peeling. These experimental results served as input to the model to compare the influence of check depth and frequency on the elastic behavior of an LVL beam in four-point bending. The checks were modeled as free spaces in the cross-section that can be partially filled with glue. The results show that the longitudinal modulus of elasticity is marginally affected by checking, while the shear rigidity of the LVL beam is significantly reduced in edgewise bending if checks are not glued. Gluing checks, even under consideration of a low Young’s modulus of glue, highly reduces the effect of checking on the elastic mechanical properties of LVL.
In the course of most wood machining processes, operators are usually able to detect various problems simply by hearing the sound emitted
by the process. This is especially true for wood peeling. Lathe checks formation has been identified as one of the typical situations that an experimented
peeler can detect. Poplar and beech veneer samples have been produced on a laboratory microlathe, using working conditions deliberately favourable
to checking. Forces, sound, and vibration levels were measured during the tests. The lathe check frequencies have been determined on both sound
and vibration signals using a local Root Mean Square (RMS) averaging and a peak detection algorithm. This makes possible the evaluation of lathe
checks distribution along the veneer length. The technique was validated by measuring the real veneer profile using a specific apparatus developed by
IVALSA-CNR in Trento (Italy).; The veneer characterization was realized during a short term scientific mission supported by the COST Action E35.
Experienced peeling operators are able to adjust the settings of their device by hearing the sound coming from the process. Based on this idea, a research program was undertaken to evaluate the possibility of using acoustic or vibration measurements supplying a support decision system to assist untrained operators.
The present paper deals with lathe check phenomenon which is one of the most critical defects of veneer (leading to handling difficulties, excess of glue consumption, poor veneer surface quality, etc.). Several signal processing techniques giving a spectral representation of sensors measurements are compared. Finally, an original procedure based on Power Spectral Density ratio is proposed to measure the average lathe check frequency of the veneer during the process.
Fast growing sengon (Paraserianthes moluccana) is largely rotary-cut to produce veneer
for core plywood production. In order to provide better information on veneer production
and utilization, in this study the effects of wood juvenility and veneer thickness on lathe
checks of rotary-cut sengon veneers were evaluated. Before veneer manufacturing, sengon logs were boiled at 50 oC and 75 oC for 4 and 8 hours respectively. The boiled logs were peeled to produce veneer of 1 mm, 1.5 mm, 2 mm in thickness. Lathe checks of veneers were measured on the loosed side at every 5 mm veneer length under an optical video microscope and their frequency, depth, and length were characterized. Twenty sampling points of 5 mm veneer length were prepared from each segmented ring of 1 cm width from pith to bark. Isocyanate resin adhesive were used to produce laminated veneer lumber (LVL) of 20 mm thick, which consisted of 24-ply of 1 mm veneer thick, 14-ply of 1.5 mm veneer thick, and 11-ply of 2 mm veneer thick, for glue bond and bending strength test. Results showed that wood juvenility and veneer thickness determined the frequency, depth and length of lathe checks for the sengon rotary-cut veneers. In general, the frequency of lathe checks of the veneer increases with increasing veneer thickness...