LY/T 3224-2020Drying procedures for modified wood with resin impregnation (English PDF)

5.1 Equipment inspection

5.1.1 Check whether the operation and display of the control cabinet's instruments are normal; whether the connection of each moisture content measuring point line and the host is normal.

5.1.2 Check whether the heating valve of the heating system and the steam injection valve of the steam injection system work normally; check whether the nozzle of the steam injection pipe is blocked Plug; to ensure that there are no leaks in the heating plate and the pipeline.

5.1.3 Check whether the fan is running smoothly, repair or replace it in time if there is an abnormal response; check whether the inlet and exhaust valves are running flexibly, Whether the air tightness is good when in the closed position.

5.1.4 Check the humidity detection device. If the drying equipment uses a dry and wet bulb thermometer to measure the state of the dry medium, pay attention to the dry and wet bulb temperature the wet bulb gauze of the meter should always be kept moist. Generally, the distance between the wet bulb temperature sensor and the water level of the water tank should be 30mm-50mm.

5.1.5 Check whether the kiln body and door of the drying kiln are sealed.

5.2 Stacking and air drying

5.2.1 The modified material dried in the same kiln should have the same tree species and resin, and the resin concentration should be similar. The allowable deviation of the thickness of the board shall be the level of the modified material.

10% of the average thickness, the initial moisture content should be consistent.

5.2.2 The partitions should be made of hard and dry hard broad-leaved materials with little deformation, or made of stainless steel or aluminum alloy; the cross-sectional dimensions of the partitions should be.

(20-25)mmx(25-30)mm, thickness tolerance is +/-1mm; the length of the spacer should be compatible with the width of the stack.

5.2.3 The spacers should be perpendicular to the length of the stack, and the spacing is generally 0.3m~0.6m; the spacers of the upper and lower layers of the stack should be in the height direction it should be on a vertical line and fall on the supporting beam of the stack or pallet. The spacers at both ends of the stack should be flush with the end face of the stack.

5.2.4 The sides of the stack should be kept flush. When the lengths of the plates are different, the long plates should be stacked on the lower part and on both sides of the stack, and the short plates should be stacked on the stack.

The middle and upper part of the pile to ensure the stability of the pile; the upper part of the pile should be pressurized with heavy objects or a compression device (such as packing belt) should be used to prevent the pile the upper wood is deformed.

5.2.5 The external dimensions of the wood pile should be compatible with the structure and internal dimensions of the drying kiln. For a drying kiln with a forklift loaded kiln, if the wood pile is the width of the drying kiln is not suitable, so when the kiln is installed in the depth direction of the drying kiln, two adjacent rows of stacks must be staggered to prevent the circulating air from flowing the material Pass by. If the modified material to be dried is not enough to fill a kiln, the width of the material pile can be reduced to ensure that the material pile is loaded as far as possible along the length and height of the kiln.

Full to avoid short circuit of air flow.

5.2.6 During the stacking process, 6-9 plates must be selected at different positions of the stack for moisture content inspection. The moisture content inspection plate should be selected Straight texture, no knots, no cracks and obvious visible defects, representative plates with relatively wet, the placement of the inspection plate is in accordance with the requirements of GB/T 6491 Operation. The moisture content data in the drying process shall be tested in accordance with the GB/T 1931 gravimetric method or the electrical measurement method verified by the gravimetric method.

5.2.7 The modified material should be air-dried to a moisture content of less than 25%, and then kiln-dried. The air-drying time should be more than 1 month. Field during air-drying the local conditions and management should meet the technical requirements of LY/T 1069.

6.1 Recommended benchmark

The drying standard of modified timber refers to the corresponding drying standard of the corresponding tree species and thickness of sawn timber in LY/T 1068, and will correspond to the moisture content stage.

The temperature is lowered by 10°C and the humidity conditions remain unchanged. After trial use with reference to the drying standard, the drying standard can be appropriately optimized according to the drying quality.

6.2 Warm-up phase

6.2.1 During the preheating phase, the intake and exhaust must be closed.

6.2.2 The temperature during preheating should be slightly higher than the temperature at the beginning of the drying reference.

6.2.3 The humidity in the preheating stage should be adjusted to the difference in temperature between the dry and wet bulbs so that the equilibrium moisture content of the wood in the kiln is slightly greater than the equilibrium moisture content of the wood during air drying.

Water content, allowing a small amount of moisture on the surface of the wood to reduce the moisture content gradient and improve the stress state in the wood.

6.2.4 The preheating time should be calculated from the temperature and humidity in the drying kiln reaching the specified value. 1.5~2h/cm (plate thickness) in summer and 1.5~2h/cm (plate thickness) in winter.

The season is 2~2.5h/cm (sheet thickness).

6.3 Drying stage

6.3.1 After the modified material is preheated, the temperature of the dry and wet bulb is gradually reduced to the specified value in the corresponding drying reference stage, and the time shall not be less than 2h.

6.3.2 During the drying stage, the temperature control of the dry and wet bulb in the kiln should be operated according to the set drying standard, usually when the moisture content of the modified material drops to 15%.

Before, the drying temperature should not exceed the curing temperature of the resin.

6.3.3 During the drying process of the modified material, the spray steaming treatment (intermediate treatment) should be carried out at an appropriate time, and the humidity during treatment should be higher than the drying standard of the corresponding stage the specified balance moisture content of wood is 5%-6%, in order to reduce the moisture content gradient, so that the existing stress tends to relax, and prevent the wood from drying defects;

Generally, the spray steaming treatment time can be calculated as 1 hour per 1cm thickness.

6.4 Curing stage

6.4.1 For enterprises using high-temperature drying kilns, this stage adopts high temperature, close the inlet and exhaust ports, and the temperature in the kiln should be higher than the resin solid the melting temperature is above 5°C, and the time is generally calculated according to the thickness of 2-6h/cm.

6.4.2 For enterprises using conventional drying kilns, the highest allowable working temperature of the drying kiln can be used at this stage, and the heating time can be extended.

The way to realize the resin curing, the time is generally calculated according to the thickness of 12-24h/cm.

6.5 Final stage

6.5.1 During balance and humidity treatment, the temperature of the medium is equivalent to the temperature in the final stage of drying, and the humidity is based on the equilibrium moisture content of the wood in the kiln.

Determined at the lowest allowable final moisture content of wood.

6.5.2 The final treatment temperature can be 5-8°C higher than the final stage temperature of the drying reference or the temperature during the equilibrium treatment. Final treatment the relative humidity is determined by 5%-6% of the equilibrium moisture content of the wood in the drying kiln which is higher than the specified value of the final moisture content. Relative humidity is not up to the required high temperature when required, the temperature can be appropriately lowered.

6.5.3 The treatment time can refer to the provisions of LY/T 1068 "Sawn Timber Kiln Drying Process Regulations".

6.6 Cooling phase

6.6.1 Under normal circumstances, if time permits, it is advisable to adopt the method of "stuffy kiln" to gradually lower the temperature, that is, stop the operation of the fan in the kiln and turn off Heating and steaming the valve, and then gradually cooling.

6.6.2 Under special circumstances, if it is necessary to speed up the cooling of the wood, after closing the valve of the heater and the steam jet pipe, let the fan continue to run to enter and exhaust.

The air port was slightly open. When the temperature in the drying kiln drops to no more than 30°C above the atmospheric temperature, the kiln can be discharged. In cold areas, the temperature in the kiln can be lower than Exit the kiln at 30°C.