CN105276930B - A kind of method for suppressing drying of wood shrinkage - Google Patents

Abstract

The present invention is a method for inhibiting drying and shrinkage of wood, comprising the following steps: 1) wood stacking; 2) decompression and vacuuming; 3) centrifugal dehydration; 4) vacuum drying; The drying tank is restored to normal pressure, and then the wood is unloaded from the drying tank. Advantages of the present invention: (1) After vacuum dehydration at room temperature and high speed, all free water in wood is quickly removed, and this process simultaneously completes wood dehydration and effectively avoids wood shrinkage caused by free water; ( 2) The integration of centrifugal dehydration and vacuum drying, under vacuum conditions, under the critical temperature of shrinkage, and in the range of high moisture content of wood, high-speed centrifugal dehydration of wood to the fiber saturation point, effectively inhibiting the dehydration caused by the removal of free water Drying and shrinking; the combination of centrifugal dehydration and vacuum drying reduces a large amount of equipment investment, saves costs, and meets the requirements of rapid production of shrinkable wood.

Description

A method for inhibiting dry shrinkage of wood

technical field

The invention relates to a method for accelerating wood drying and inhibiting wood drying and shrinkage under vacuum conditions, that is, by performing high-speed centrifugal pretreatment on wood to effectively avoid the shrinkage defects of wood in the process of dehydration and drying, which belongs to wood drying field.

Background technique

Due to my country's economic development, improvement of living standards, enhancement of aesthetic concepts and health awareness, more and more home styles tend to be more natural, green and environment-friendly, so solid wood furniture, solid wood floors and solid wood interior decoration have become preferred. However, my country's natural high-quality wood resources are in short supply. According to the state of forest resources in my country and the world, the raw materials of my country's wood products industry will be mainly planted forest fast-growing materials for a considerable period of time in the future. These materials will be gradually applied to wooden furniture, wooden floors, wooden doors and windows and other products. It is the only way to deeply and finely process these fast-growing plantations and improve their comprehensive utilization rate and added value. However, the natural forest eucalyptus, poplar and other woods planted in large areas in my country often have serious wood drying defects such as "shrinkage" during the drying process. After drying, the wood is deformed and cracked seriously, resulting in a large number of wood internal cracks. , leading to serious degradation of wood, which cannot be applied to solid wood furniture, floors and interior decoration, or even completely scrapped. So far, there are no effective drying methods and treatments aimed at avoiding wood shrinkage. Existing technologies including microwave, steam, pre-freezing pretreatment and conventional segmented drying and post-treatment can only slightly slow down or partially restore shrinkage, but cannot effectively suppress severe shrinkage during the drying process, and further Severely limit the efficient and high value-added utilization of wood such as eucalyptus and poplar.

Contents of the invention

The present invention proposes a method for inhibiting wood drying and shrinkage, the purpose of which is to rapidly dehydrate wood in the range of high moisture content by centrifugal force under vacuum conditions without causing excessive shrinkage. Medium speeds up drying without drying shrinkage.

Technical solution of the present invention: the method for suppressing dry shrinkage of wood: comprises the following steps:

1) For wood stacking, choose wood that is prone to shrinkage, process it into a board with a thickness of 25mm~38mm, stack it according to the conventional drying method and put it into a vacuum centrifugal drying tank, and close the tank door;

2) Decompress and vacuumize, turn on the vacuum pump, reduce the vacuum degree of the centrifugal drying tank, control the absolute pressure at 3.3~6.7kPa, and keep the vacuum degree in the tank for 0.5 to 1h;

3) Centrifugal dehydration, turn on the centrifuge, adjust the centrifugal speed according to different moisture content ranges, and perform rapid centrifugal dehydration on the wood. When the moisture content of the wood drops to the fiber saturation point, stop the centrifuge to effectively avoid wood shrinkage caused by capillary tension , this is because before the fiber saturation point, the free water in the wood has been removed by centrifugation, and there is no free water inside the wood, which eliminates the conditions for wood drying and shrinkage;

4) Vacuum drying, turn on the heating equipment to heat the wood, after the wood temperature rises to 35~45°C, carry out the wood drying and heat-humidity treatment, and perform an intermediate heat-humidity treatment when the moisture content drops to 20%, and the dry bulb temperature is 52°C , the wet bulb temperature is 51°C, the treatment time is 3h; when the moisture content drops to about 8%, the final heat and humidity treatment is carried out, the dry bulb temperature is 50°C, the wet bulb temperature is 47°C, the treatment time is 4h, until the wood moisture content reaches 8~10%;

5) Cool down the wood, keep the absolute pressure in the tank at 6.7~13.4kPa, let the water on the wood surface evaporate and cool naturally for 3 to 5 hours; the wood temperature drops to room temperature;

6) Wood out of the kiln: Let the vacuum centrifugal drying tank return to normal pressure, and then unload the wood from the drying tank to complete the wood drying.

Advantages of the present invention:

(1) After vacuum dehydration at room temperature and high speed, all free water in wood is quickly removed. This process completes wood dehydration at the same time and effectively avoids wood shrinkage caused by free water.

(2) Because there is no free water inside the wood, the conditions for dry shrinkage are eliminated, so there is no dry shrinkage defect in the subsequent drying process, the whole process reduces the problem of material handling, improves the drying speed of wood, and avoids dry shrinkage of wood;

(3) When the moisture content of the wood is above the fiber saturation point, the water in the wood can be quickly removed by adjusting the speed of the centrifuge, and at the same time, the shrinkage of the wood due to capillary tension can be avoided;

(4) The integration of centrifugal dehydration and vacuum drying. Under vacuum conditions, under the critical temperature of shrinkage, and in the range of high moisture content of wood, high-speed centrifugal dehydration is performed on wood to the fiber saturation point, which effectively suppresses the generation of dryness caused by the removal of free water. The combination of centrifugal dehydration and vacuum drying reduces a large amount of equipment investment, saves costs, and meets the requirements of rapid production of shrinkable wood.

detailed description

Example 1

The method for suppressing dry shrinkage of wood: comprises the following steps:

1) For wood stacking, choose wood that is prone to shrinkage, process it into a certain thickness of board, stack it according to the conventional drying method and put it into a centrifugal drying tank, and fix it with a clamp, and close the tank door;

2) Decompression and vacuuming: vacuumize the centrifugal drying tank at room temperature, the absolute pressure in the tank reaches and remains at 3.3kPa, and the wood is placed in the tank for 0.5h;

3) Centrifugal dehydration: Keep the vacuum centrifuge tank at room temperature, adjust the speed of the centrifuge according to the different moisture content ranges of wood, when the water content is 60%, the centrifugal speed is 2000r/min; when the water content is 60~50%, the centrifugal speed is 3000r/min; when the water content is 50~40%, the centrifugal speed is 5000r/min; when the water content is 40~30%, the centrifugal speed is 6000r/min. High-speed centrifugal dehydration is performed on the wood in the centrifuge tank. The free water inside the wood is removed under the action of centrifugal force and internal and external pressure difference at the shrinkage critical temperature. The wood cells are not subjected to long-term capillary tension and cannot shrink; When the rate drops to the fiber saturation point, the centrifugal dehydration is stopped, and the centrifuge stops;

4) Vacuum drying: Turn on the heating equipment, control the temperature in the drying tank at 35°C, and implement vacuum low-temperature drying on the wood. Temperature is an important factor causing wood shrinkage. The moisture content of wood is below the fiber saturation point to maintain a high vacuum in the tank , Using a lower heating temperature can make the wood dry quickly and without shrinkage; during the vacuum drying process, when the moisture content drops to 20%, perform an intermediate heat and humidity treatment, the dry bulb temperature is 52 ° C, the wet bulb temperature is 50 ° C, The treatment time is 3 hours; when the moisture content drops to about 8%, the final heat and humidity treatment is carried out, the dry bulb temperature is 50°C, the wet bulb temperature is 47°C, and the treatment time is 4h. Heat and humidity treatment to balance the stress in the wood drying process, stop drying when the moisture content drops to 8%;

5) Wood cooling: stop heating, and maintain the absolute pressure of the vacuum centrifuge tank at 6.7kPa to evaporate the water on the wood surface and cool it naturally for 3 hours; the wood temperature drops to room temperature;

6) Wood out of the kiln: Let the vacuum centrifugal drying tank return to normal pressure, and then unload the wood from the drying tank to complete the wood drying.

Example 2

The method for suppressing dry shrinkage of wood: comprises the following steps:

1) For wood stacking, choose wood that is prone to shrinkage, process it into a certain thickness of board, stack it according to the conventional drying method and put it into a centrifugal drying tank, and fix it with a clamp, and close the tank door;

2) Decompression and vacuuming: vacuumize the centrifugal drying tank at room temperature, the absolute pressure in the tank reaches and remains at 6.7kPa, and the wood is placed in the tank for 1 hour;

3) Centrifugal dehydration: keep the vacuum centrifuge tank at room temperature, adjust the speed of the centrifuge according to the different moisture content ranges of wood, the general trend is high moisture content range, low centrifugal speed, low moisture content range (above fiber saturation point), centrifugal speed high. The details are as follows: when the water content is 60%, the centrifugal speed is 2000r/min; when the water content is 60~50%, the centrifugal speed is 3000r/min; When the efficiency is 40~30%, the centrifugal speed is 6000r/min. High-speed centrifugal dehydration is performed on the wood in the centrifuge tank. The free water inside the wood is removed under the action of centrifugal force and internal and external pressure difference at the shrinkage critical temperature. The wood cells are not subjected to long-term capillary tension and cannot shrink; When the rate drops to the fiber saturation point, the centrifugal dehydration is stopped, and the centrifuge stops;

4) Vacuum drying: Turn on the heating equipment, control the temperature in the drying tank at 45°C, and implement vacuum low-temperature drying on the wood. Temperature is an important factor causing wood shrinkage. The moisture content of wood is below the fiber saturation point to maintain a high vacuum in the tank , Using a lower heating temperature can make the wood dry quickly and without shrinkage; during the vacuum drying process, when the moisture content drops to 20%, perform an intermediate heat and humidity treatment, the dry bulb temperature is 52 ° C, the wet bulb temperature is 50 ° C, The treatment time is 3 hours; when the moisture content drops to about 8%, the final heat and humidity treatment is carried out, the dry bulb temperature is 50°C, the wet bulb temperature is 47°C, and the treatment time is 4h. Heat and humidity treatment to balance the stress during the drying process of wood, and stop drying when the moisture content drops to 10%;

5) Wood cooling: stop heating, and maintain the absolute pressure of the vacuum centrifuge tank at 13.4kPa to evaporate the water on the wood surface and cool it naturally for 5 hours; the wood temperature drops to room temperature;

6) Wood out of the kiln: Let the vacuum centrifugal drying tank return to normal pressure, and then unload the wood from the drying tank to complete the wood drying.

Example 3

The method for suppressing dry shrinkage of wood: comprises the following steps:

1) For wood stacking, choose wood that is prone to shrinkage, process it into a certain thickness of board, stack it according to the conventional drying method and put it into a centrifugal drying tank, and fix it with a clamp, and close the tank door;

2) Decompression and vacuuming: vacuumize the centrifugal drying tank at room temperature, the absolute pressure in the tank reaches and remains at 4.3kPa, and the wood is placed in the tank for 0.8h;

3) Centrifugal dehydration: keep the vacuum centrifuge tank at room temperature, adjust the speed of the centrifuge according to the different moisture content ranges of wood, the general trend is high moisture content range, low centrifugal speed, low moisture content range (above fiber saturation point), centrifugal speed high. The details are as follows: when the water content is 60%, the centrifugal speed is 2000r/min; when the water content is 60~50%, the centrifugal speed is 3000r/min; When the efficiency is 40~30%, the centrifugal speed is 6000r/min. High-speed centrifugal dehydration is performed on the wood in the centrifuge tank. The free water inside the wood is removed under the action of centrifugal force and internal and external pressure difference at the shrinkage critical temperature. The wood cells are not subjected to long-term capillary tension and cannot shrink; When the rate drops to the fiber saturation point, the centrifugal dehydration is stopped, and the centrifuge stops;

4) Vacuum drying: Turn on the heating equipment, control the temperature in the drying tank at 40°C, and implement vacuum low-temperature drying on the wood. Temperature is an important factor causing wood shrinkage. The moisture content of wood is below the fiber saturation point to maintain a high vacuum in the tank , Using a lower heating temperature can make the wood dry quickly and without shrinkage; during the vacuum drying process, when the moisture content drops to 20%, perform an intermediate heat and humidity treatment, the dry bulb temperature is 52 ° C, the wet bulb temperature is 50 ° C, The treatment time is 3 hours; when the moisture content drops to about 8%, the final heat and humidity treatment is carried out, the dry bulb temperature is 50°C, the wet bulb temperature is 47°C, and the treatment time is 4h. Heat and humidity treatment to balance the stress during the drying process of wood, and stop drying when the moisture content drops to 9%;

5) Wood cooling: stop heating, and maintain the absolute pressure of the vacuum centrifuge tank at 7kPa to evaporate the water on the wood surface and cool it naturally for 4 hours; the wood temperature drops to room temperature;

6) Wood out of the kiln: Let the vacuum centrifugal drying tank return to normal pressure, and then unload the wood from the drying tank to complete the wood drying.

After vacuum room temperature and high-speed centrifugal dehydration, all the free water in the wood is quickly removed. This process completes the wood dehydration at the same time and effectively avoids the wood shrinkage caused by free water.

Because there is no free water inside the wood, the conditions for dry shrinkage are eliminated, so there is no dry shrinkage defect in the subsequent drying process, the whole process reduces the problem of material handling, improves the drying speed of wood, and avoids dry shrinkage of wood.

The invention integrates centrifugal dehydration and vacuum drying at the same time, and performs high-speed centrifugal dehydration to the fiber saturation point of wood under vacuum conditions, under the critical temperature of shrinkage, and in the range of high moisture content of wood, effectively suppressing the loss of moisture due to free water removal. The resulting drying shrinkage; the combination of centrifugal dehydration and vacuum drying reduces a large amount of equipment investment, saves costs, and meets the requirements of rapid production of shrinkable wood.

Claims (2)

1. the method for suppressing drying of wood shrinkage, it is characterized in that the method comprises the following steps：

1）Timber stacking, selection is also easy to produce the timber of shrinkage, the sheet material of thickness 25mm ~ 38mm is processed into, according to conventional drying side Method stacking is simultaneously put into traditional vacuum drying chamber, closes tank door；

2）Decompression vacuum pumping, opens vavuum pump, reduces centrifugal drying tank vacuum, and absolute pressure control is protected in 3.3 ~ 6.7kPa Hold in tank vacuum 0.5 to 1h；

3）Centrifugal dehydration, opens centrifuge, according to the interval adjustment centrifugal rotational speed of different water cut, quick centrifugation is carried out to timber de- Water, when moisture content is down to fibre saturated point, stops centrifuge work；

4）Vacuum drying, opens firing equipment and timber is heated, and Wood temperature carries out the drying of wood after rising most 35 ~ 45 DEG C, enters Row heat and wet treatment, moisture content carries out heat and wet treatment in the middle of once, 52 DEG C of dry-bulb temperature, 51 DEG C of wet-bulb temperature, treatment when being down to 20% Time is 3h；When moisture content is down to 8% or so, end of a period heat and wet treatment, 50 DEG C of dry-bulb temperature, 47 DEG C of wet-bulb temperature, treatment are carried out Time is 4h, until moisture content reaches 8 ~ 10%；

5）Timber is lowered the temperature, and it is 6.7 ~ 13.4kPa to keep absolute pressure in tank, allow wood surface moisture evaporation and natural cooling 3 to 5h；Wood temperature is down to room temperature；

6）Timber kiln discharge：Allow traditional vacuum drying chamber to recover normal pressure, then timber is unloaded from drying chamber, complete the drying of wood.

2. the method for suppressing drying of wood shrinkage according to claim 1, it is characterized in that described according to different water cut Interval adjustment centrifugal rotational speed, when moisture content is 60%, centrifugal rotational speed is 2000r/min；At 60 ~ 50%, centrifugation turns moisture content Speed is 3000r/min；At 50 ~ 40%, centrifugal rotational speed is 5000r/min to moisture content；Moisture content at 40 ~ 30%, centrifugal rotational speed It is 6000r/min.