Hard broad-leaved trees are usually used for solid wood floors, and high-quality imported wood is mainly used for medium and high-grade solid wood floors. A more reasonable production method is to first process the logs into semi-finished floor slabs at the place of origin, and seal the ends of the boards with wax to prevent end cracks, and then sell them to the floor processing factory for artificial drying. Reprocessing into finished floors.

Artificial drying is an important link to ensure the quality of solid wood floors. The purpose of drying is to stabilize the shape of the wooden floor. It will no longer shrink, swell and deform in the future use process, and also improve the processing performance, use performance and durability of the solid wood floor. The key to drying quality is that the final moisture content must be slightly lower than the equilibrium moisture content of the use environment. It is about 10%-12% in the south of my country, about 8%-10% in the north, and about 6%-8% in the northwest region, and it must be completely dry, and ensure that it does not warp, crack and basically relieve the drying stress.

Drying quality and drying cost are generally mutually restrictive, but if there are reasonable drying equipment, reasonable drying process and correct operation, the investment cost and drying cost can be minimized while ensuring the drying quality. .

Since there are many types of wood drying methods and drying equipment, and the products on the market are mixed, in order to help wood flooring enterprises choose drying equipment reasonably, this article is specially written for readers' reference.

Commonly used wood drying methods include: steam heating conventional drying, furnace gas heating conventional drying, hot air drying, dehumidification drying, vacuum drying, and conventional drying of hot water and high-temperature water circulating heating that has become popular in recent years. The appropriate drying method must be selected according to the drying characteristics and requirements of the solid wood floor, as well as the scale and conditions of the enterprise.

1.1 Steam heating conventional drying

This method is a traditional drying method of drying wood by using saturated steam with gauge pressure P≤0.4MPa and heating the circulating air drying medium in the drying kiln by a heater. Its advantages are that the process parameters are easy to control, and the drying quality is generally good; the temperature and humidity can be adjusted in a wide range, and various materials can be dried; it can be centrally heated, and it is widely used. The disadvantage is that a steam boiler is required, and the investment cost is high; and the latent heat of vaporization of steam is mainly used, and the condensed water is often not used due to the troublesome recovery, resulting in waste and increased costs. It is mainly suitable for enterprises with large production scale or ready-made steam, especially suitable for drying softwood, soft broadleaf or veneer and other easy-drying species. For small and medium-sized wood floor enterprises, this method is not applicable because it requires expensive steam boilers.

1.2 Furnace gas heating conventional drying

This is a conventional drying method for wood heated directly or indirectly by burning waste wood. Directly heated furnace air drying will blacken the wood and easily catch fire, so indirect heating furnace air drying is almost no longer used. In the heated kang room, it is dried by natural circulation of hot and humid airflow. This is a relatively primitive soil drying method, which often damages the wood or causes fires. Not recommended. ②Small furnace oven type: This is a small dryer equipped with a wood waste burning furnace and its furnace gas pipeline and a simple fan on one side of a metal shell similar to a container, which can hold 2-5m3 of wood. This method of drying also has potential safety hazards, and it is easy to burn the wood or cause fire, and because of the unreasonable air circulation, the drying is uneven. Not recommended. ③Modern furnace gas indirect heating drying kiln: there is a furnace gas heating tube group with reasonable design and arrangement in the kiln, and other configurations are the same as the general drying kiln. Safety and reliability are guaranteed for this type of kiln designed by experts. The special combustion furnace of this type of kiln can be located outside the kiln or inside the kiln. The former is relatively safer, but the cost and heat loss are relatively high.

The conventional drying of furnace gas heating does not require a steam boiler and utilizes wood waste energy, so the investment cost and drying cost are low. However, because the temperature and humidity are difficult to adjust and control, the drying quality is not easy to guarantee. If the design of the drying kiln is not good, it is easy to damage the wood and cause fire. For medium and high-grade solid wood floors, this drying method should be used with caution.

1.3 Hot air drying

The hot blast stove used for heating is located outside the kiln, and is connected to the drying kiln by the inlet and return gas pipes. The air drying medium is introduced into the hot blast furnace outside the kiln for heating through the return air pipe, and then returned to the kiln by the blower, which is a conventional drying with double circulation of air flow. The disadvantage of this method is that the utilization rate of heat energy is low; the power consumption is large; the temperature and humidity fields in the kiln are unevenly distributed, the process parameters are not easy to control, and the drying speed is slow and uneven; The output is higher than the cost, so it is not recommended to use it.

1.4 Dehumidification and drying

It is a method of drying wood by gradually dehumidifying the air drying medium in the kiln with a dehumidifier (or called a heat pump) and heating it appropriately. The dehumidifier can only work in the set temperature range to have the dehumidification effect. The working temperature of ordinary dehumidifiers does not exceed 55℃, and the working temperature of medium temperature dehumidifiers does not exceed 65℃. The advantage of this method is that there is no pollution in the use of electric energy; it is easy to operate, and the drying quality is generally good. The disadvantage is that the drying cost of using electric energy is high; the drying time is long and the productivity is low; the dehumidifier is prone to failure, the maintenance cost is high, and the service life is short; there is no humidity control device, and the drying stress cannot be eliminated. Since its drying power mainly depends on reducing the relative humidity of the drying medium rather than increasing the temperature, the effect is more obvious in the high moisture content stage or when drying easy-to-dry tree species, but the effect is not obvious in the low moisture content stage or when drying difficult-to-dry tree species. However, using this method to dry easy-to-dry tree species or when the moisture content is high, the drying is too slow, and sometimes the wood will grow mold. It is recommended not to use wood flooring companies unless the output is very low and there are special requirements for environmental protection.

1.5 Vacuum drying

The dried wood is placed in a sealed container, and the air in the container is drawn out after preheating, so that the wood is dried under a certain negative pressure. This method dries faster, and the drying quality is not easy to guarantee; the loading capacity of the dryer is small, the equipment is more complicated, and the investment cost is high; the use of electric energy, the drying cost is high. Only for a small amount of difficult-to-dry materials, vacuum drying is feasible when conventional drying takes too long. General technical floor companies recommend not to use it.

1.6 Conventional drying of hot water or high temperature water circulating heating

This method is the first researched and developed by the author in 1996-1997, and it is a technical achievement manufactured and operated by Nanjing Yunsong Drying Equipment Company. It has become a very popular wood drying method in China, especially suitable for drying hard broad-leaved wood in small and medium-sized enterprises. The hot water circulation heating adopts the improved heat pipe atmospheric steam and water boiler matched with the drying kiln, which can burn the processing residues such as wood chips, shavings or block wood waste. With t=95-100℃ hot water as the heating medium, the drying temperature can reach 70-75℃ with a reasonably designed heating system. This is the suitable drying temperature range for hard hardwoods. The atmospheric pressure steam of P=0-0.04MPa can meet the technological requirements of humidity control treatment. It adopts semi-automatic control of temperature and humidity and automatic detection of moisture content. The hot water has high heat content, stable temperature, easy process control and guaranteed drying quality. The atmospheric pressure hot water boiler is low in cost, safe and reliable, and easy to operate. The hot water circulation heating not only saves water but also fully recovers the waste heat of the hot water, and can simplify the soft water treatment equipment. Using wood waste energy, not only waste utilization, greatly reducing drying costs, but also greatly reducing environmental pollution. In a word, this method has the advantages of both steam heating and furnace gas heating, and at the same time abandons the shortcomings of both. It is the most ideal drying method for solid wood floors and furniture, especially for small and medium-sized enterprises.

High-temperature water circulation heating adopts B-class wood-burning waste heat pipe hot water boiler. The hot water circulation system operates under the pressure of gauge pressure P=0.3MPa, and controls the water temperature t≤115℃, which can make the drying temperature in the kiln reach 95℃, suitable for Dry softwood and soft hardwood. The key to this method lies in the pressure maintaining measures of the system. It must be ensured that the saturation temperature of the hot water is about 30°C higher than the actual temperature to avoid cavitation in the circulating hot water pump.