A vacuum drying device and drying method for wood beams

Abstract

The present invention discloses a vacuum drying device and method for wood planks. The core is that an expandable interlayer cavity is provided between the inner wall of an airtight processing container and the wood planks. The interlayer cavity serves as a buffer layer for the air pressure difference during negative pressure drying processing, and can offset the pressure of an atmospheric pressure formed on the outer wall of the processing container by the normal pressure of the external air after a vacuum state is formed inside the container. At the same time, a resistive heating plate arranged on the inner wall of the interlayer cavity, under the control of a sensor and a temperature controller, heats and insulates the air inside the interlayer cavity by heat convection. The heat energy generated is then transferred to the outer layer of the wood planks through the inner wall of the interlayer cavity by heat conduction, thereby ensuring that the wood planks maintain a physical indicator of 50°C, which is higher than the water vapor phase temperature under a vacuum state. Such a device and method have the comprehensive advantages of low equipment cost and maintenance cost, high internal space utilization of the equipment, and simple operation, and can replace expensive vacuum kettles.

Description

Technical Field

[0001] The present invention relates to the technical field of vacuum drying, in particular to a vacuum drying device and a drying method for wood and wooden planks. Background Art

[0002] Wood planks are a crucial raw material in furniture processing and production. Undried wood planks typically have a moisture content exceeding 25%, significantly lower than the 5%-8% moisture content requirement for the wood processing industry. Wood planks generally require drying before use. Conventional drying methods include atmospheric pressure drying and vacuum drying.

[0003] Atmospheric pressure drying generally uses a drying chamber as a processing container for the wood planks. Hot air or steam is then applied to increase the ambient temperature inside the processing container. The temperature difference between the ambient temperature of nearly 100°C and the original temperature of the wood planks accelerates the evaporation of the internal moisture, ultimately achieving the purpose of drying the wood planks. Its disadvantages include: a long processing cycle, generally taking several weeks or even months; wood planks of different species or with significantly different thicknesses cannot be mixed in the same processing batch; otherwise, it is difficult to set their temperature control curve parameters and processing cycle; and the peripheral processing temperature of nearly 100°C increases the risk of wood plank deformation due to the uneven transmission of thermal expansion and contraction.

[0004] Vacuum drying generally utilizes the physical indicator of the vapor phase temperature of water under a vacuum state, and uses a metal vacuum kettle as a processing container for wood planks to carry out vacuum drying. This is a processing method that aims to reduce the risk of thermal deformation of wood planks by using a preheating temperature of about 50°C, and to create an external environment that reduces the moisture vapor phase conditions. Its disadvantages are: First, in order to balance the atmospheric pressure of one atmosphere (i.e. 1Kgf / cm²) that the outer wall of the vacuum kettle needs to withstand after a vacuum is formed inside, the vacuum kettle has to adopt a cylindrical structure with the most uniform pressure distribution and the highest pressure resistance as its processing container, and is made of a relatively expensive steel structure. Therefore, its cost and maintenance costs often discourage potential users. Second, an unusable space of about 40% is naturally formed between the circular end face design that can achieve the best pressure resistance and the square end face for the best wood plank stacking effect, and this ratio will not improve as the cylindrical structure is enlarged (see Figure 1 ). Third, when vacuuming, the vacuum kettle can only measure temperature using a radiant heater, which makes it difficult to detect the actual heating results. This makes it difficult to control the subsequent temperature at 50°C, and the temperature can easily exceed or fall below the control range of 50°C. Therefore, the existing technology needs to be improved and enhanced. Summary of the Invention

[0005] The purpose of the present invention is to overcome the shortcomings of the existing vacuum drying technology for wood beams, and to propose a vacuum drying device and drying method for wood beams that reduces the cost and maintenance cost of an airtight processing container, increases the available processing space inside the container, and ensures uniform heat preservation and no deformation during the processing of the wood beams.

[0006] The purpose of the present invention is achieved through the following technical solutions: a vacuum drying device for wood beams, comprising: a processing container for placing wood beams, a vacuum pump for generating vacuum negative pressure, an air compressor for generating positive pressure, a resistive heating plate for generating heat, a sensor for detecting air temperature, and a temperature controller, characterized in that: the airtight processing container is made of insulation material, and its internal space is rectangular, the wood beams are placed on the bottom surface of the processing container, and a flexible expandable and contractible interlayer cavity is provided on the inner walls and upper inner walls of the processing container. The interlayer cavity is divided into an outer layer and an inner layer, and the inner cavity is between the inner and outer layers. The outer layer is tightly adhered to the inner wall of the processing container without any gap. The interlayer cavity serves as a buffer layer for the air pressure difference during negative pressure drying processing. The inner layer of the interlayer cavity will airtightly wrap the wooden planks placed on the bottom of the processing container. Its enclosed space is connected to a vacuum pump, and the inner cavity of the interlayer cavity is connected to an air compressor. The vacuum pump evacuates the airtightly wrapped wooden planks, and the air compressor inflates and pressurizes the inner cavity of the interlayer cavity. The resistive heating plate is arranged in the inner cavity of the interlayer cavity, and electricity is turned on to heat the gas in the inner cavity of the interlayer cavity, and then the wrapped wooden planks are kept warm at 40-60℃ through the inner wall of the interlayer cavity by heat conduction.

[0007] Furthermore, the airtight processing container is assembled from insulating composite building materials or composite panels, such as flame-retardant plywood, silicate board, aluminum-plastic board, or other common insulating materials. The interlayer cavity is made of elastic and thermally insulating rubber or silicone sheeting, adapted to the inner wall dimensions of the rectangular processing container. The outer layer of the interlayer cavity is tightly attached to the inner wall of the processing container by gluing or screwing.

[0008] The air compressor inflates and pressurizes the inner cavity of the interlayer cavity to maintain the air pressure at 1.1-1.3Kgf / cm².

[0009] A vacuum drying method for wood beams, characterized by:

[0010] A. Preheat the wood to 50°C, stack them neatly on the bottom of the processing container, seal the container, and completely cover the inner walls and upper inner walls of the container with the interlayer cavity to form an airtight seal.

[0011] B. Before starting the vacuum pump to vacuum dry the wood, first start the air compressor to inflate the expandable interlayer cavity with positive pressure. The air pressure is 1.1-1.3 kgf / cm², so that the interlayer cavity is fully inflated and fills all the remaining space between the inner wall of the processing container and the wood being dried. The interlayer cavity acts as a buffer layer for the air pressure difference during the negative pressure drying process, which can offset the pressure of one atmosphere of external air on the outer wall of the processing container after the vacuum state is formed inside the processing container.

[0012] C. Then start the vacuum pump used to lower the gas phase temperature of the wood beams and perform vacuum drying. As the wood beams gradually enter the vacuum state, the inner wall of the interlayer cavity will expand slightly again, and the air compressor needs to continue to start to inflate and maintain pressure. After the enclosed space of the interlayer cavity wrapping the wood beams forms a vacuum state, the sensors and thermostats placed on the inner wall of the interlayer cavity start working to maintain the internal temperature at 50°C. The resistive heating plate is controlled to be on / off according to the measured temperature inside the interlayer cavity being lower than / higher than 50°C, and the moisture inside the wood beams is continuously vaporized and extracted.

[0013] The inner cavity of the sandwich cavity has pressurized air that can circulate naturally. The air in the inner cavity of the sandwich cavity is heated by a resistive heating plate, and the heat energy is then transferred to the outside of the processed wood beams through the inner wall of the sandwich cavity in the form of heat conduction, thereby keeping the overall temperature of the wood beams higher than its gas phase temperature in a vacuum state.

[0014] The core of this technology is that a flexible expandable and contractible interlayer cavity is provided between the inner wall of the airtight processing container and the wood beams. The interlayer cavity serves as a buffer layer for the air pressure difference during negative pressure drying processing, thereby offsetting the pressure of an atmospheric pressure formed on the outer wall of the processing container by the external air after a vacuum state is formed inside the processing container. At the same time, the resistive heating plate arranged on the inner wall of the interlayer cavity, under the control of the sensor and the temperature controller, heats up the air inside the interlayer cavity by heat convection. The heat energy generated is then transferred to the outer layer of the wood beams through the inner wall of the interlayer cavity by heat conduction, thereby ensuring that the wood beams maintain a physical indicator of 50°C, which is higher than the vapor phase temperature of moisture in a vacuum state. A vacuum pump is used to draw vacuum to create a vacuum state for the wood beams, and the vaporization rate of moisture is accelerated by lowering the vapor phase temperature of moisture, thereby ultimately achieving the purpose of drying the wood beams.

[0015] The advantages of the present invention are: 1. The rectangular space inside the airtight processing container can be designed and manufactured into a shape that is most suitable for square stacking of wooden beams, so that the proportion of available space is increased to more than 80%. 2. Through the expandable and contractible interlayer cavity, the pressure resistance of the processing container is changed from preventing inward deformation to preventing outward deformation, and the pressure resistance requirement is reduced to 0.2 kgf / cm². In this way, the manufacturing materials and production methods of the airtight processing container have great flexibility, and composite building materials and composite panels with less high compressive strength requirements can be used, such as flame-retardant plywood, silicate board, aluminum-plastic board and other general insulation materials, which greatly reduces the cost. 3. The interlayer cavity with expansion and contraction properties is made of rubber or silicone sheets with good elasticity and thermal insulation properties according to the size of the inner wall of the container, which is low in cost and has low maintenance or replacement costs. 4. The resistive heating plate, temperature sensor and temperature controller placed on the inner wall of the interlayer cavity are all conventional components, easy to obtain and low in price. 5. Compared with the vacuum drying method of vacuum kettle, the present invention can achieve the same processing purpose and effect, and can use the rectangular space structure to improve the processing volume rate of the container while reducing the cost and maintenance cost of the container. The drying time is short and the deformation of the wood beams is small, which can replace expensive vacuum kettles. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a schematic diagram of the spatial placement of a traditional cylindrical vacuum kettle for vacuum drying of wooden beams.

[0017] Figure 2 It is a structural schematic diagram of the present invention.

[0018] Figure 3 yes Figure 2 Schematic diagram of the cross-section structure.

[0019] Figure 4 This is a schematic diagram of the enlarged sandwich cavity.

[0020] Explanation of reference numerals: 1-processing container, 2-wooden beam, 3-sandwich cavity, 31-inner cavity of the sandwich cavity, 4-resistive heating plate, 5-temperature sensor, 6-temperature controller, 7-vacuum pump, 8-air compressor. DETAILED DESCRIPTION

[0021] In order to make the objectives, technical solutions and advantages of the present invention more clear and explicit, the present invention is further described in detail with reference to the following embodiments.

[0022] See also Figure 2-Figure 4The vacuum drying apparatus of this embodiment comprises: an airtight processing container 1, which is generally a rectangular parallelepiped; a flexible expandable and contractible interlayer cavity 3; a resistive heating plate 4; a temperature sensor 5; a temperature controller 6; a vacuum pump 7; and an air compressor 8. The airtight processing container 1 is assembled from thermally insulating aluminum-plastic panels, while the interlayer cavity 3 is made of elastic and thermally insulating rubber corresponding to the inner dimensions of the processing container 1.

[0023] The internal space of the processing container 1 is rectangular. A flexible expandable and contractible interlayer cavity 3 is arranged between the inner walls of the four sides of the processing container 1 except the bottom surface and the upper inner walls and the wood beams 2 to be dried and processed. The interlayer cavity 3 is divided into an outer layer and an inner layer. There is an inner cavity 31 between the inner layer and the outer layer. The outer layer of the interlayer cavity 3 is tightly adhered to the inner wall of the processing container 1 without a gap. The interlayer cavity 3 serves as a buffer layer for the air pressure difference during negative pressure drying processing. Before inflation and pressurization, a gap of 0.1-0.2 meters is generally left between the inner wall of the interlayer cavity 3 and the stacked wood beams 2. After the processing container 1 is sealed, the inner layer of the interlayer cavity 3 will wrap the wooden beam 2 in a sealed manner, and its sealed space is connected to the vacuum pump 7. The inner cavity 31 of the interlayer cavity is connected to the air compressor 8. The vacuum pump 7 evacuates the sealed wooden beam 2. At the same time, the air compressor 8 inflates and pressurizes the inner cavity 31 of the interlayer cavity. The resistive heating plate 4 is arranged on the inner wall of the inner cavity 31 of the interlayer cavity. When electricity is turned on, the gas in the inner cavity 31 of the interlayer cavity is heated, and then the wooden beam 2 is kept warm at 40-60°C through the inner wall of the interlayer cavity 3 by heat conduction.

[0024] The drying method is as follows: first, the wood planks 2 are preheated to 50°C. When the vacuum drying device is in a standby state, the expandable interlayer cavity 3 is in a contracted state without positive pressure. The wood planks 2 to be dried are stacked and placed in the processing container 1. After they are properly stacked, the air compressor 8 is immediately activated to inflate the interior of the interlayer cavity 3. As the air pressure increases, the air pressure inside the interlayer cavity 3 reaches 1.2 kgf / cm² and the interlayer cavity 3 is in an expanded state, filling all the remaining space between the inner wall of the processing container and the wood planks being dried. The vacuum pump 7 is then activated to evacuate the enclosed space, gradually placing the enclosed wood planks 2 in a vacuum state, causing the vapor phase temperature of the moisture in the enclosed space to drop from 100°C under normal pressure to approximately 35°C in a vacuum state, thereby causing the moisture inside the wood planks 2, which have been preheated to 50°C, to vaporize and be discharged.

[0025] In order to maintain the processing temperature of the wooden beam 2 at 50°C, the resistive heating plate 4 is started, and the temperature sensor 5 is responsible for transmitting the temperature information of the inner cavity 31 of the interlayer cavity to the temperature controller 6 through the signal line, which is responsible for controlling the on and off of the resistive heating plate 4.

[0026] It should be understood that the application of this patent is not limited to the above examples. For ordinary technicians in this field, equivalent improvements or changes can be made based on the above description. All these equivalent improvements and changes should fall within the scope of protection of the claims attached to this patent and will not be repeated here.

Claims

1. A vacuum drying device for wood beams, comprising: a processing container for placing the wood beams, a vacuum pump for generating negative vacuum pressure, an air compressor for generating positive pressure, a resistive heating plate for generating heat, and a sensor for detecting air temperature and a temperature controller, characterized in that: The airtight processing container is made of thermal insulation material, and its internal space is rectangular. The wood planks are placed on the bottom surface of the processing container. The inner walls around the processing container and the upper inner wall are provided with a flexible expandable and contractible interlayer cavity. The interlayer cavity is divided into an outer layer and an inner layer. There is an inner cavity between the inner layer and the outer layer. The outer layer of the interlayer cavity is tightly combined with the inner wall of the processing container without a gap. The interlayer cavity serves as a buffer layer for the air pressure difference during negative pressure drying processing. The inner layer of the interlayer cavity will airtightly wrap the wood planks placed on the bottom surface of the processing container. The enclosed space is connected to a vacuum pump, and the inner cavity of the interlayer cavity is connected to an air compressor. The vacuum pump evacuates the airtightly wrapped wood planks, and the air compressor The inner cavity of the interlayer cavity is inflated and pressurized, and a resistive heating plate is arranged in the inner cavity of the interlayer cavity. Electricity is applied to heat the gas in the inner cavity of the interlayer cavity, and then the wrapped wooden beams are kept warm at 40-60°C through the inner wall of the interlayer cavity by heat conduction; the airtight processing container is assembled with insulating composite building materials; the interlayer cavity is made of rubber or silicone sheets with good elasticity and thermal insulation properties according to the inner wall size of the rectangular processing container, and the outer layer of the interlayer cavity is tightly fitted to the inner wall of the processing container by gluing or tightening screws; the air compressor maintains the air pressure of the interlayer cavity at 1.1-1.3Kgf / cm².

2. The vacuum drying method implemented by the vacuum drying device according to claim 1, characterized in that: A. Preheat the wood to 50°C, stack them neatly on the bottom of the processing container, and seal the container. The inner walls around the container and the upper inner wall are completely covered with the interlayer cavity to form an airtight seal. B. Before starting the vacuum pump to vacuum dry the wood, first start the air compressor to inflate the expandable interlayer cavity with positive pressure. The air pressure is 1.1-1.3 kgf / cm², so that the interlayer cavity is fully inflated and the inner layer of the interlayer cavity fills all the remaining space between the inner wall of the processing container and the wood being dried. The interlayer cavity acts as a buffer layer for the air pressure difference during the negative pressure drying process, which can offset the pressure of the external air pressure on the outer wall of the processing container after the vacuum state is formed inside the processing container. C. Then start the vacuum pump used to lower the gas phase temperature of the wood beams and perform vacuum drying. As the wood beams gradually enter the vacuum state, the inner wall of the interlayer cavity will expand slightly again, and the air compressor needs to continue to start to inflate and maintain pressure. After the enclosed space of the interlayer cavity wrapping the wood beams forms a vacuum state, the sensors and thermostats placed on the inner wall of the interlayer cavity start working to maintain the internal temperature at 50°C. The resistive heating plate is controlled to be on / off according to the measured temperature inside the interlayer cavity being lower than / higher than 50°C, and the moisture inside the wood beams is continuously vaporized and extracted.

3. The vacuum drying method according to claim 2, wherein The inner cavity of the sandwich cavity has pressurized air that can circulate naturally. The air in the inner cavity of the sandwich cavity is heated by a resistive heating plate, and the heat energy is then transferred to the outside of the processed wood beams through the inner wall of the sandwich cavity by heat conduction, thereby keeping the overall temperature of the wood beams higher than the gas phase temperature under its vacuum state.

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