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Mr. Shen, hello:
I am a reader of *Asian Panel & Furniture*, and I work in a wood factory in Indonesia producing solid wood furniture. Thank you for explaining the difference between traditional kiln drying and high-temperature kiln drying of wood, and for illustrating the advantages and disadvantages of high-temperature drying.
Recently, I discussed with industry professionals the feasibility of using high-temperature drying kilns for carbonizing wood, as well as the advantages and disadvantages of carbonized wood. I hope you can provide some information on methods for processing carbonized wood. Some time ago, while producing two-inch thick solid wood slab tabletops, I discovered localized bulging of the glue line at the joints. Please help analyze the cause and provide suggestions for improvement. Thank you!
Best wishes for your business!
Mr. Lin
Thank you for your letter. Based on the information you provided, here is a brief summary of the questions you raised:
01. Regarding the treatment of carbonized wood
Carbonized wood processing can be achieved by first drying undried wood at high temperatures, with coniferous species such as spruce and Scots pine being the most suitable. For high-temperature drying of broad-leaved species, it is essential to select species that are less prone to honeycomb cracking, such as poplar and rubberwood.
1. High-temperature drying of wood: The drying temperature is between 110-150 degrees Celsius. If necessary, the drying kiln can be rapidly heated to raise the required temperature inside the kiln, and then dried rapidly until no honeycomb cracks are found, and the average moisture content of the wood is 8%.
2. Wood carbonization treatment: Gradually increase the temperature of the drying kiln to 185-215 degrees Celsius. After the moisture content of the wood drops to 0%, maintain the highest temperature in the kiln for about 2-3 hours to achieve the predetermined carbonization depth.
3. Cooling and Moisture Content Treatment: Activate the kiln spray system to lower the kiln temperature to between 80-90 degrees Celsius. Adjust the moisture content of the carbonized material inside the kiln to 4%-7%.
02. Main advantages and disadvantages of carbonized wood
As shown in the table below (click the original image to enlarge).
The wooden stake in Figure 2 was light yellow before it underwent high-temperature carbonization.
Figure 3 shows light yellow timber turning brown after high-temperature carbonization treatment.
03. Producing 2-inch thick solid wood slab tabletops.
Based on your question, the reasons for the localized bulging of the spliced adhesive lines found during shipment, and suggestions for improvement, are as follows:
Figure 4 shows a 2-inch thick solid wood slab tabletop. Due to excessively high moisture content in some areas, the tabletop will continue to dry and release moisture when placed in an air-conditioned room or stored in a dry warehouse. This will cause localized shrinkage or collapse of the tabletop, resulting in bulging of the glue lines.
Hopefully, the information provided above can help resolve some issues related to high-temperature carbonized wood treatment and address the drawback of protruding adhesive lines on the desktop. This brief overview of high-temperature carbonized wood treatment information is intended to be helpful.
Mr. Shen Yuxin
Born in Kuching, Sarawak, Malaysia in 1948, Mr. Shen graduated from the Department of Forestry at National Chung Hsing University in Taiwan in 1974. After graduation, he worked for the Taiwan Forestry Bureau. From 1975 to 1995, Mr. Shen worked in the timber processing and engineered wood products industry in Malaysia, Singapore, and Borneo, holding positions such as engineering technician, production supervisor, production manager, and general manager. In 1996, Mr. Shen also joined the Asia Woodworking Group of a globally renowned chemical company as Regional Technical Service Director.
This article is selected from the May/June issue of "Asian Panel & Furniture".