Veneer Drying Research Articles

Development of a logical model for controlling the veneer drying process

One of the ways to improve the quality and volume of woodworking products is to increase the level of automation of production, which requires a clear formalization of the description of the behavior of the corresponding technological processes. In the article, on the basis of automatic programming, a logical model of the automatic control system for drying veneer in a multi-zone conveyor belt has been developed, which allows to increase the safety and efficiency of the process.

Prediction of Optimum Veneer Drying Parameters with Artifi cial Neural Networks for Production of Plywood with High Mechanical Properties

Veneer drying is the manufacturing process in the plywood industry that most affects energy consumption and panel properties such as bonding and bending. Therefore, the veneer drying temperature and moisture content should be accurately adjusted. Moreover, the determination of veneer thermal conductivity is as important as these two parameters and the thermal conductivity values should also be specifi ed when forming the drying programs. This study aimed to predict the optimum values of the veneer drying temperatures, moisture content and thermal conductivity, which gave the best mechanical properties, by artifi cial neural network (ANN) analysis. Poplar (Populus deltoidesI-77/51) and spruce (Picea orientalis L.) veneers and urea formaldehyde (UF) resin were used in the production of plywood. The thermal conductivity of veneer and the bonding, bending strength and elasticity modulus of the panels were tested by the relevant standards. The most accurate and reliable prediction models were obtained by analyzing the experimental data with ANN. The optimum veneer drying temperature, moisture content and thermal conductivity values that gave the best values for all three mechanical properties were 149 °C, 6.2 % and 0.02668 W/mK for poplar and 116 °C, 4.4 % and 0.02534 W/mK for spruce.

Predicting unit energy consumption during industrial veneer drying via data-driven approaches

Veneer drying usually consumes a significant amount of energy including heat and electricity. The soaring energy price as well as the substantial social-environmental concerns regarding energy use have urged veneer manufacturers to adapt and become more efficient in energy consumption. Different from the physics-based methods commonly seen in the literature, this research embraced a data-driven approach to analyze and predict unit gas and electricity consumption during industrial veneer drying. Both linear regression and random forest (RF) algorithms were deployed for prediction. Based on cross-validation evaluations, the RF model with all explanatory variables slightly outperformed two linear models regarding almost all accuracy metrics, although linear models had the advantage of providing an easy-to-interpret solution.

Transitioning to data-driven quality control in industrial veneer drying: a case study

Transitioning to data-driven quality control in industrial veneer drying: a case study

Modelling of a continuous veneer drying unit of industrial scale and model-based ANOVA of the energy efficiency

Drying, a crucial step in process engineering aimed at producing optimal product moisture content, has evolved over time from batch processing methods to continuous processing alternatives. Continuous drying methods offer uniform moisture content of the product at lower operational cost. In this study, a continuous veneer drying model was developed based on mass and energy balances. The simulated veneer dryer is a semiautomatic machine designed to maximise the drying process efficiency via control mechanisms such as the veneer transport rate, fan speed, opening angle of the inlet and outlet dampers, and radiator temperature. In the dryer, veneer plates are conveyed horizontally through the number of connected chambers where hot air is blown transversely. The optimal drying process is dynamically maintained via the Proportional–integral–derivative controllers, manipulating the rate of the damper lids opening, that are connected to the sensors monitoring the air properties in the chambers of the drying unit. The model-based sensitivity analysis ANOVA was carried out for energy optimisation purposes. The analysis outcomes indicated that radiator temperature, initial moisture content of veneer sheets and conveyor speed are the most influential parameters affecting the drying rate. Automatic control of damper lids provides optimal temperature and moisture content of drying environment at lower energy costs.

Modelling of a Continuous Veneer Drying Unit of Industrial Scale and Model-Based Anova of the Energy Efficiency

Modelling of a Continuous Veneer Drying Unit of Industrial Scale and Model-Based Anova of the Energy Efficiency

Charphy Impact of Medium Molecular Weight Phenol Formaldehyde (MMwPF) Plywood

Plywood is a wood product frequently utilized in building as part of concrete formwork systems. In the concreting process, plywood formwork needs to be strongly made to withstand the pressure subjected by the wet concrete as well as the impact. To reduce the dependency on solid timber as plywood, oil palm stem offers alternative materials. There are four main weaknesses of oil palm stem (OPS) as a material for plywood manufacturing; high variations in density and moisture content (MC), high water absorption and high surface roughness. Therefore, this study modified the drying and treatment process of OPS veneer. The veneer was predried by using roller presser for removing a large amount of water and later treated with medium molecular weight phenolformaldehyde (MMwPF) to bond together parenchyma tissue, cell wall, and a lumen for much uniform density and better surface bonding. The Charpy impact of OPS plywood developed in this study denoted as PTA was investigated. These properties were compared with the properties of another two types of commercial OPS plywood denoted as PTB and PTC which were manufactured using OPS veneer with tropical hardwood veneer for face and back veneer and control plywood denoted as PTD which was manufactured using 100% tropical hardwood veneer. The results showed that PTA has the highest mean value of energy and strength for both notched and unnotched Charpy impact.

Optimization of Veneer Drying Temperature for the Best Mechanical Properties of Plywood via Artificial Neural Network

The drying of veneer is an essential part of the veneer-producing process to aid the gluing during the manufacture of the plywood and laminated veneer lumber. Determining the optimum veneer drying temperature without decreasing of mechanical properties is also very important from industrial viewpoint. Due to the high drying costs, increased temperatures are being used commonly in plywood industry to reduce the overall drying time and increase capacity. However, high drying temperatures can alter some physical, mechanical and chemical characteristics of wood and cause some drying-related defects. In this study, it was aimed to predict the optimum drying temperature for alder and scots pine veneers via artificial neural network modelling for optimum mechanical properties. Therefore, mechanical strength values of plywood panels manufactured from alder and scots pine veneers were dried at temperatures of 110, 130, 150, 170, 190 and 210°C. Shear strength, bending strength and modulus of elasticity of the plywood panels were experimentally determined according to EN 314-1 and EN 310 standards. Then, the mechanical strength values based on veneer drying temperatures are subjected to prediction by artificial neural network modelling. As a results of this study, the optimum drying temperature values were obtained as 165, 162 and 161°C in Scots pine plywood and 190, 195 and 196°C in alder plywood, for best shear strength, bending strength and modulus of elasticity values, respectively.

Effect of veneer drying process on some technological properties of polystyrene composite plywood panels

The aim of study was to determine the effect of veneer drying process on some technological properties of polystyrene composite plywood panels. For this reason, 2 mm-thick rotary cut veneers were obtained from beech (Fagus orientalis, Lipsky), Alder (Alnus glutinosa subsp. Barbata) and Scots pine (Pinus sylvestris L.) logs. The veneers obtained from three different wood species were divided into two groups to produce polystyrene composite plywood (PCP) and traditional plywood. While PCP was produced both air dried (at 20 °C) and oven dried (at 110 °C), the veneer sheets for production of traditional plywood were dried at 110 °C until reaching 7 % equilibrium moisture content. Two different types of polystyrene with high density (30 kg/m3) and low density (16 kg/m3) were used as bonding material for PCP panel production. The urea-formaldehyde adhesive was used as a bonding material for traditional plywood panels. Bonding shear strength, bending strength, modulus of elasticity and density of plywood and polystyrene composite plywood panels were investigated. It was found that the technological properties observed in the study of composite plywood panels manufactured with natural dried veneers gave similar results compared to those of composites produced with technical dried veneers.

Results of experimental researches into process of oak veneer drying in the solar dryer

A new design of solar drying plant with the active solar energy system is developed. It is proposed to use the K1-102 automated control system to diagnose the key parameters of air exchange in the solar dryer and to predict the intensity of heat exchange processes of oak veneer drying. This allows increasing the technological and power efficiency of the process of oak veneer drying in the solar dryer 2 times. The regularities of the influence of the physical parameters of the environment and weather-dependent factors on the heat, mass, and moisture exchange processes of oak veneer drying in the solar dryer are determined. Estimation of energy, kinetic and dynamic parameters of the oak veneer drying process is given. The duration of the drying process in the solar dryer is experimentally determined. Performance characteristics of the drying object are investigated, depending on the set technological tasks (heating or drying) under standard insolation and meteorological conditions. It is found that it is necessary to regulate air exchange, moisture release, rational moist coolant removal, solar energy flow in relation to the predicted changes in the minimum and maximum variation peaks of weather-dependent factors. This is important for intensifying the oak veneer drying processes and reducing the specific power consumption of the drying process due to solar energy. The obtained results can be used in the development and improvement of technical means of oak veneer drying, to improve the technological and power efficiency of the process

Effects of hot air and microwave drying on kinetic rate and mechanical property of oil palm veneer

This research was studied, the hot air and microwave drying of Oil Palm Veneer (OPV). The oil palm trees at 27 years of age were collected from a plantation in Chumphon. They were processed into a dimension of 80 x 150, 1 mm (thickness) and initial moisture 345 % (db.). The chamber of oven is size of 500 x 1,000 x 1,000 mm3. It had an electrical heater at maximum power output of 5,000 watts, air speed of 2.1 m/s and the microwave power level of 1,000-4,000 watts. The final moisture content reached 10±2% (db). The results were showed that while OPV drying with the hot air condition used temperature about 50, 70 and 90 °C reached the target value within 70, 32 and 16 min respectively, the microwave condition used to power about 2,000 and 3,000 watts reached the target value within 62 and 34 min, combined condition used hot air 50 °C with microwave power level 2,000 and 3,000 watts, hot air 70 °C with microwave power level at 2,000 and 3,000 watts and hot air 90 °C with microwave power level 2,000 and 3,000 watts reached the target value within 24, 20, 14, 10, 10 and 8 min respectively. Moreover, drying with hot air and microwave on high power revealed the tensile stress and shear properties increased. However, the hot air at 70, 90 °C combines with the microwave power level 2,000 watts were better than mechanical properties of hot air at 70, 90 °C combines with microwave power level 3,000 watts. The results showed the drying of hot air at 90 °C combine with the microwave power level at 2,000 watts, mechanical properties of OPV dried tensile stress at 1.9447 MPa, shear stress 19.0286 MPa, which used of energy 39 kWh, its surface was cracked burns. Therefore, the drying hot air only conditions at 90 °C can be recommended for mechanical properties, tensile stress 1.8229 MPa, shear stress 18.4472 MPa, used of energy 21 kWh, which was OPV suitable and cost optimality.

Análisis del proceso de ablandamiento de trocería de encinos para la producción de chapa para madera contrachapada (triplay)

Un uso potencial de los encinos es la producción de madera contrachapada (triplay), para lo cual se requiere definir las condiciones más adecuadas del calentamiento de la madera, del rebanado o torneado de las trozas, del secado de la chapa y del ensamble del tablero. En este trabajo se determinaron los parámetros óptimos del proceso de ablandamiento de la madera para la producción de chapa para madera contrachapada utilizando dos trozas por especie de: Quercus candicans, Quercus laurina y Quercus rugosa. De estas trozas se generaron los Aflitches@ o cuadrados, que se calentaron en un tanque metálico, a través de serpentines con aceite térmico y usando agua como medio termoconductor a la madera. En cada cuadrado se insertaron dos termopares para medir el gradiente de temperatura durante el calentamiento. Dos de los cuadrados (Q. candicans y Q. laurina), se procesaron a 60 OC, otros dos (Q. candicans y Q. rugosa) a 65 OC y los dos últimos (Q. laurina y Q. rugosa) a 70 OC. En general, la chapa de Q. candicans y Q. laurina, fue de mejor calidad en cuanto a textura, grietas pequeñas y uniformidad de coloración. La chapa de Q. rugosa presentó variación en la coloración, con manchas café-oscuras, seguramente por el ataque de bacterias al arbolado, además de pequeñas perforaciones en las chapas generadas en la parte más externa de la troza, debido a grandes dimensiones de los rayos. Se considera que la temperatura de corte en el rango de 60 a 75O C, es adecuada para procesar encinos. En cuanto al tiempo de calentamiento utilizado en este estudio, de 50 a 65 horas, se recomienda usarlo como referencia, por considerar que las prácticas y equipos de ablandamiento cambian de una fábrica a otra. Respecto al veteado de la chapa fue muy uniforme en su estructura, aún cuando Q. candicans y Q. laurina son de porosidad circular; esta característica no se manifestó en el veteado de Acatedral@, que es el más demandado por el usuario final de madera contrachapada.

Estimating birch veneer (Betula pendula Roth) moisture content using infrared technology

The potential of infrared (IR) technology in estimating the moisture content (MC) of birch (Betula pendula Roth) veneer was investigated. A total of 56 birch veneer sheets (42 × 130 cm2) were dried with a convective type laboratory-scale veneer dryer at drying times ranging from 1 to 6 min at 1 min intervals. After drying, IR data were recorded and the veneer sheets were sawn into 100 × 100 mm2 pieces. IR data were averaged over the same area and then the true MC and density values were assessed gravimetrically. The dependency between temperature and MC was found to be non-linear and between temperature and density there was no dependency. The relationship between temperature and MC was modeled with a neural network and a Gaussian model. Both model types gave similar results. At a true MC below 10 %, the root mean square error of prediction (RMSE) was 1.5 % for the 100 × 100 mm2 pieces and 1.2 %, for the larger veneer sheets, whereas at higher MC (above 10 %), the RMSE increased to 2.6 % for the 100 × 100 mm2 pieces and 1.9 % for the sheets. It was observed that the IR measurement should be taken within 5 s, since after that the RMSE increased rapidly. Based on the results of this study, it was concluded that veneer MC can be estimated with reasonably good accuracy using IR technology.

Analýza tvarové stálosti vodovzdorných překližek

The paper analyses causes of disorders of the shape stability of water-resistant plywoods produced by an important producer in the CR. Deformations of plywoods are caused by many reasons, such as wood structure (the course of wood fibres), plywood construction (the construction balance as for size and material regularity), the moisture of processed veneers and boards, glue spread, actual pressing process, the storage and climatization of finished plywoods. Basic technological parameters affecting the shape stability of plywoods were analysed, such as parameters of the hydrothermic pre­pa­ra­tion of raw material, parameters of veneer drying and the moisture of peeled veneers after drying as well as pressing parameters. At the conclusion, recommendations to improve the shape stability of plywood sheets are presented.

Internal diffusion transfer of moisture during birch veneer filtration drying

The technology of veneer production is a multistage, energy intensive and the drying stage is characterized by the highest energy costs. The authors proposed a filtration drying of packed birch veneer, which allows maximizing the heat agent drying potential, and, respectively, compared with the existing equipment, reducing energy costs for the drying process and ensuring high quality of dried veneer. The moisture transfer phenomena during packed veneer drying are defined as laws of both the external diffusion and internal diffusion processes. The solution of the differential equation of internal diffusion for a thin plate of finite sizes for the boundary conditions of the first type is given, on the basis of which the internal moisture diffusion coefficient from the veneer sheets is defined and its dependence on temperature is determined. The dependencies, given in the paper make it possible to predict the dependence of the filtration drying process of packed sliced birch veneer and at the design stage of a new drying equipment to establish economic feasibility of the process modernization.

Effects of plasma treatment and sanding process on surface roughness of wood veneers

An ideal veneer surface is crucial for good panel properties in plywood manufacturing. The aim of this study was to compare plasma treatments and sanding (mechanical) processes with respect to the surface roughness of veneers. Rotary-cut veneers with a thickness of 2 mm from Scots pine (Pinus sylvestris) logs were used as material. After rotary peeling, veneer sheets were dried at 110 °C in a veneer dryer. Veneer sheets were divided into 4 main groups. The surfaces of the control veneer sheets were left untreated. Two different grits of sandpaper, 80 and 180, were used for sanding the surfaces of veneers. Plasma treatment was applied to the last veneer group with 3 different gases (oxygen, nitrogen, and ammonia) and 3 different plasma times (1 min, 5 min, and 15 min). The Mitutoyo Surftest SJ-301 instrument was used to determine surface roughness of samples. Average roughness (Ra), mean peak-to-valley height (Rz), and maximum roughness (Rmax) parameters were measured to evaluate the surface roughness of the samples based on DIN 4768. It was found that the smoothest veneer surfaces were obtained with the sanding processes. Surface roughness values (Rz) of veneer sheets sanded with 180 grit sandpaper were lower than those of veneers sanded with 80 grit sandpaper. Compared with the plasma treatment in terms of surface roughness, plasma-treated veneers had higher Rz values. It was also determined that Rz values were the lowest in the veneers treated with nitrogen plasma. Additionally, the surface roughness values of Scots pine veneers treated with ammonia plasma were a little higher than those of veneer sheets treated with oxygen plasma. The effect of plasma treatment time on surface roughness was not found to be statistically significant.

Prediction of the optimum veneer drying temperature for good bonding in plywood manufacturing by means of artificial neural network

Veneer drying is one of the most important stages in the manufacturing of veneer-based composites such as plywood and laminated veneer lumber. Due to the high drying costs, increased temperatures are being used commonly in plywood industry to reduce the overall drying time and increase capacity. However, high drying temperatures can alter some physical, mechanical and chemical characteristics of wood and cause some drying-related defects. In this study, it was attempted to predict the optimum drying temperature for beech and spruce veneers via artificial neural network modeling for optimum bonding. Therefore, bonding shear strength values of plywood panels manufactured from beech and spruce veneers dried at temperatures of 20, 110, 150 and 180 °C were obtained experimentally. Then, the intermediate bond strength values based on veneer drying temperatures were predicted by artificial neural network modeling, and the values not measured experimentally were evaluated. The optimum drying temperature values that yielded the highest bonding strength were obtained as 169 °C for urea formaldehyde and 125 °C for phenol formaldehyde adhesive in beech plywood panels, while 162 °C for urea formaldehyde and 151 °C for phenol formaldehyde in spruce plywood panels.

Wettability of Hybrid Poplar Veneers with Cold Plasma Treatments in Relation to Drying Conditions

Veneer overdrying is a primary cause of poor plywood glue bond quality due to surface inactivation and its effect on glue transfer and penetration. The goal of this work is to investigate the feasibility of using atmospheric cold plasma to treat overdried hybrid poplar (Populus hybrids) veneers to improve wettability and plywood glue bond (shear) strength. The effectiveness of the plasma treatment using three veneer drying conditions, air drying, oven drying, and overdrying, were compared. It was found that the cold plasma treatment significantly enhanced veneer surface wettability under all three drying conditions. Compared to untreated controls, instantaneous surface contact angles of treated veneers decreased the most under the overdried condition, followed by the oven-dried and air-dried conditions, regardless of whether glycerin or urea formaldehyde (UF) was used. After a 5-s treatment, overdried veneers achieved complete wetting with both droplets. The results demonstrated that the atmospheric cold plasma was the most effective one to treat overdried poplar veneers to achieve the smallest contact angle, leading to the highest plywood glue bond (shear) strength. However, further research is still needed to understand the mechanism of the cold plasma treatment on veneers under different drying conditions.

Dimensional Stability of Fire-Retardant-Treated Laminated Veneer Lumber

Test of fire-retardant-treated (FRT) laminated veneer lumber (LVL) indicated moisture gain under adsorption and moisture loss under desorption conditions. The moisture content of FRT specimens increased considerably under adsorption conditions compared with control specimens, while it was not found to be a significant difference under desorption conditions. The statistical findings revealed that impregnation with chemical salts had significant effects on the expansion properties. Fire-retardant treatment also had meaningful effects on the swelling properties. However, the expansion and swelling properties of the LVL were not affected significantly by the veneer drying temperature. Generally, equilibrium moisture content of LVL decreased with increasing veneer drying temperature. The interactions between fire-retardant chemicals and veneer drying temperature were also found to be insignificant.

Variations in Bending Strength and Modulus of Elasticity of Spruce and Alder Plywood after Steaming and High Temperature Drying

Veneer logs are generally heated in hot water or steam prior to the cutting process in veneering and plywood manufacturing. For economical reasons, the veneers should be dried quickly and without damage. High temperatures shorten drying times. Besides the benefits of log steaming and quick drying of veneers at high temperatures, these processes can be effective on some mechanical, physical and chemical properties of wood. In this study, the effects of the steaming process on logs and veneer drying temperatures on bending strength and modulus of elasticity (MOE) of plywood panels manufactured from spruce and alder veneers were investigated. For this aim, some parts of both wood species logs were steamed for 12 hours before veneer manufacturing while some parts were used unsteamed. Unsteamed and steamed groups of spruce and alder veneers were dried at 20°C, 110°C and 180°C temperatures. The effect of the steaming process on bending strength and MOE was different depending on the wood species. Bending strength and the MOE values of spruce plywood panels increased while both strength values of alder plywood panels decreased after the steaming process. The highest bending strength and MOE values were obtained at 110°C for alder and at 180°C for spruce plywood panels.