Tableros de partículas y de fibras (I parte)

Wood Processing and Particle Board Manufacturing

Introduction to Wood Processing

• The transition from water to wood signifies a shift towards utilizing natural resources with minimal technological intervention, focusing on cost-effective energy resource optimization in particle board and fiberboard production.

• The constant movement of machinery in the yard illustrates the dynamic nature of the industry, where logs are processed without strict requirements for diameter or shape, allowing even previously discarded materials to be utilized.

Log Preparation and Bark Removal

• Residual materials from other industries, such as sawmill waste, are also processed; smaller pieces that cannot be used for lumber are now valuable inputs.

• Bark removal occurs through mechanical impact within a large metal cylinder, emphasizing the need to eliminate bark efficiently to prevent energy wastage during drying and maintain product quality.

Chipping Process

• Conveyors transport debarked wood to chippers that convert it into chips suitable for further processing.

• Hydraulic cylinders adjust chipper openings based on log dimensions; chips are then screened for size before being sent to additional grinding processes.

Particle Size Reduction

• Chips undergo further fragmentation in hammer mills, producing particles ranging from fractions of a millimeter up to 30 millimeters in length.

• Wet particles are stored in silos prior to drying, which is conducted using hot air circulation that keeps particles suspended and promotes uniform drying.

Drying and Classification

• Post-drying moisture content is reduced to between 3% and 6%, followed by classification where fine dust is removed via cyclones while larger particles are filtered out using screens.

• All by-products, including dust and small residues, are repurposed as fuel for drying processes or cogeneration plants for electricity production.

Adhesive Application and Board Formation

• Dried particles are mixed with adhesive (commonly urea-formaldehyde), which is atomized onto them before they enter the forming line.

• The process begins with fine particles forming one side of the board followed by coarser layers distributed evenly with assistance from comb-like devices.

Pressing Process

• A final layer of fine particles completes the board structure; metal detectors ensure no foreign objects compromise safety during manufacturing.

• The formed mat undergoes cold prepressing before entering a continuous press where heat consolidates the adhesive bond over several minutes.

Finalization of Boards

• After pressing, boards still warm pass through cooling sprays before being cut into specified sizes using traveling saw blades.

Proceso de Desfibrado y Fabricación de Tableros

Desfibrado Termomecánico

• Las sestillas destinadas a fabricar tableros de fibras, conocidos como DM, son transportadas para ser desfibradas utilizando un proceso termomecánico.

• Se inyecta vapor a presión (hasta 10 kg/cm²) en un diquector, elevando la temperatura entre 180 y 190 grados centígrados, lo que reblandece la madera para facilitar el desfibrado.

Eficiencia del Sistema

• Este sistema es considerado el más efectivo y de mayor calidad; las instalaciones europeas suelen utilizar discos de 46 pulgadas con una producción diaria de 300 toneladas.

• También se utilizan discos más grandes (54 pulgadas), alcanzando producciones de hasta 600 toneladas por día.

Adhesivos y Secado

• Sobre las fibras húmedas se añaden adhesivos y aditivos como ceras y parafinas antes del secado, asegurando su incorporación adecuada.

• El secado se realiza a temperaturas que no superan los 180 grados centígrados para evitar el fraguado prematuro del adhesivo.

Formación del Tablero

• Una vez secas, las fibras son transportadas a la formadora donde se proyectan sobre una cinta hasta alcanzar la dosificación necesaria para el espesor programado.

• La manta de fibras con cola sin fraguar es preprensada en frío antes de dirigirse a la prensa; los colores indican propiedades específicas: rojo para resistencia al fuego y verde para humedad.

Prensado Final