Views: 4 Author: Site Editor Publish Time: 2019-08-08 Origin: Site
Heating of logs with steam is one of the most important processes during the veneer manufacturing. The main function of steam heating is to soften veneer log temporary and making it more plastic, pliable, more readily peeled, and improving the quality and quantity of material recovered from the log. Steam heating is more efficient than water heating in terms of its safety aspects and shorter heating time.
Some of the other advantages of steam log heating include decrease in energy use during the peeling, reducing cracks on the veneer due to knife checks, improve tensile strength, and produce veneers having small colour variations. Surface characteristics, uniform thickness of veneer, and bonding quality for plywood manufacture are influenced by steaming temperature and duration between steaming and peeling processes. Above benefifits can also be reached by determining the optimum steaming temperature, steaming time as function of wood density and log diameter.
Gupta and Bist found that the optimum heating temperatures of logs for obtaining higher shear strength of plywood varied by wood species. In a previous investigation, quality of veneer obtained from Canadian pine and Norway spruce logs was also influenced by the temperature of the logs during the peeling. Another study showed that surface roughness and the quality of the veneer obtained from logs harvested following heavy rainy days were better than those of harvested duringdry times in summer .
In the same study, it was also reported that Douglas logs left in the rain for 13 days after harvesting produced veneer with smoother surface. A specialist stated that optimum peeling temperature of Douglas fifer logs ranged from 49 degree centigrade to 60 centigrade to have veneer with better quality. In general peeling temperature of the softwood logs are lower than that of hardwood logs due to their higher density. Currently there is no comprehensive information about the quality of veneer and plywood manufactured from spruce logs peeled at different temperature levels. Therefore, the main objective of this work is to determine the influence of two different log temperatures on surface roughness, wetability, and colour variation of the veneer sheets. Shear strength of the experimental plywood panels made from veneer samples was also evaluated as function of log temperature to provide an initial data to plywood manufacturers to enhance the overall quality of the final product.