CN114311201B - A wood high-frequency hot-press drying method - Google Patents

Abstract

The invention discloses a high-frequency hot-pressing drying method for wood, which comprises the following steps: s1, heat treatment of wood before pressing: heating the wood to be dried to a certain temperature C; s2, boosting and maintaining pressure: placing the wood subjected to heat treatment in the S1 into a hot press, applying unit pressure P1 to the wood through a pressing plate of the hot press, and keeping for a certain time T1; s3, pressure reduction and pressure maintaining: reducing the unit pressure P1 applied by the pressing plates to 0.1-0.12 MPa and keeping for a certain time T2, and simultaneously establishing a high-frequency electric field between the pressing plates through a high-frequency generator; s4, pressurizing and slowly releasing pressure: when the moisture of the wood in the pressing plate is reduced to 20% or below 20%, removing the high-frequency electric field, applying unit pressure P2 to the wood through the pressing plate, keeping the unit pressure for a certain time T3, and then slowly reducing the unit pressure P2 to 0.1-0.12 Mpa; s5, stacking and preserving: opening the hot press to take out the wood stack for curing; the drying cycle is short, the dried wood has stable performance, the wood drying shrinkage is controllable, and the drying cost and the processing cost can be saved.

Description

A wood high-frequency hot-press drying method

technical field

The invention relates to the technical field of wood drying, in particular to a wood high-frequency hot-press drying method.

Background technique

In the process of wood product processing, the drying and stress treatment of wood is an indispensable link, and it is the premise to ensure the production of qualified wood products. If the drying and stress treatment is not good, the wood products processed in the later stage are prone to deformation and cracking. At present, the wood drying technology in the industry mainly includes:

1. Natural drying and aging treatment. This method is mainly due to the long drying period and the large area occupied by the site, which is affected by weather factors. The moisture content and internal stress of the product are not balanced. Wood is less expensive to dry.

2. Kiln drying method. This method of drying wood mainly uses steam or heat transfer oil to transfer heat energy to dry wood. High energy consumption and high output. Reasonable control of the drying standard can get the ideal drying effect and drying efficiency. Higher skill requirements for dryers.

3. High-frequency vacuum negative pressure drying method. This method is suitable for drying precious tree species, but the energy consumption is high and the application range is relatively narrow.

Contents of the invention

In view of this, the present invention aims at the deficiencies in the prior art, and its main purpose is to provide a wood high-frequency hot-press drying method, which has a short drying cycle, stable wood properties after drying, controllable shrinkage of wood, and can save Drying costs and processing costs.

To achieve the above object, the present invention adopts the following technical solutions:

A wood high-frequency hot-press drying method, comprising the following steps:

S1. Heat treatment of wood before pressing: heating the wood to be dried to a certain temperature C by boiling water or microwave heating;

S2. Boosting pressure and maintaining pressure: place the heat-treated wood in S1 into a hot press, apply a unit pressure P1 to the wood through the platen of the hot press and keep it for a certain period of time T1, and the unit pressure P1 is 2-2.5Mpa;

S3. Pressure reduction and pressure maintenance: reduce the unit pressure P1 applied by the pressure plate to 0.1-0.12MPa and maintain it for a certain time T2, and at the same time establish a high-frequency electric field between the pressure plates through a high-frequency generator;

S4. Pressurization and slow pressure release: When the moisture content of the wood in the press plate drops to 20% or below, the high-frequency electric field is removed, and at the same time, the unit pressure P2 is applied to the wood through the press plate and maintained for a certain period of time T3. The unit pressure P2 is 2 ~2.5Mpa, and then slowly reduce the unit pressure P2 to 0.1~0.12Mpa;

S5. Stacking health preservation: when the unit pressure P2 on the wood in S4 drops to 0.1-0.12MPa, turn on the hot press and take out the wood stacking health preservation.

As a preferred solution, in step S1, the temperature C is 85-95°C.

As a preferred solution, in steps S2-S4, the temperature of the pressing plate is 180-190°C.

As a preferred solution, a medium or electric heating tube for heat conduction is provided inside the press plate, and the medium is saturated steam or heat conduction oil.

As a preferred solution, in step S2, the time T1 is 25-35 seconds.

As a preferred solution, in step S3, the time T2 is 170-190 seconds.

As a preferred solution, in step S4, the time T3 is 55-65 seconds.

As a preferred solution, a liner is provided on the contact surface between the pressing board and the wood.

As a preferred solution, in step S3, the frequency of the high-frequency electric field is 5000-18000 Hz.

Compared with the prior art, the present invention has obvious advantages and beneficial effects. Specifically, it can be seen from the above technical scheme that it mainly uses a high-frequency hot press to dry the board, and the drying cycle is short and the material property is stable after drying. 1. The drying shrinkage of wood is controllable, and corresponding templates can be made according to the shape of the final product, which can improve the material yield and reduce the processing process to a certain extent. Combining conventional wood drying and sheet metal accessories forming and processing together can save drying costs to a certain extent. and processing costs.

In order to more clearly illustrate the structural features and functions of the present invention, the present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments.

Description of drawings

Fig. 1 is a pressure curve diagram of the pressurization and heating process of the embodiment of the present invention.

Detailed ways

In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer" etc. The indicated orientation or positional relationship is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the invention and simplifying the description, rather than indicating or implying that the indicated position or element must have a specific orientation or be constructed in a specific orientation. and operation, and therefore should not be construed as limiting the invention.

In the description of the present invention, it should be noted that unless otherwise specified and limited, the terms "installation", "connection" and "connection" should be understood in a broad sense, for example, it can be a fixed connection or a detachable connection. Connected, or integrally connected; it may be mechanically connected or electrically connected; it may be directly connected or indirectly connected through an intermediary, and it may be the internal communication of two components. Those of ordinary skill in the art can understand the specific meanings of the above terms in the present invention depending on the specific circumstances.

A wood high-frequency hot-press drying method, comprising the following steps:

S1. Heat treatment of wood before pressing: heat the wood to be dried to a certain temperature C by boiling water or microwave heating; heat-treat the dry wood by high-temperature cooking and microwave heating, the purpose of which is to pass high-temperature and high-humidity treatment , so that the main component of wood, wood fiber, is softened, increasing the toughness of wood fiber, and avoiding the splitting of wood caused by compressive stress and blasting force of water removal. The duration of heating and heat preservation treatment is determined by the initial moisture content and density of wood;

S2. Boosting pressure and maintaining pressure: place the heat-treated wood in S1 into a hot press, apply a unit pressure P1 to the wood through the platen of the hot press and keep it for a certain period of time T1, and the unit pressure P1 is 2-2.5Mpa;

S3. Pressure reduction and pressure maintenance: reduce the unit pressure P1 applied by the pressure plate to 0.1-0.12MPa and maintain it for a certain time T2, and at the same time establish a high-frequency electric field between the pressure plates through a high-frequency generator;

S4. Pressurization and slow pressure release: When the moisture content of the wood in the press plate drops to 20% or below, the high-frequency electric field is removed, and at the same time, the unit pressure P2 is applied to the wood through the press plate and maintained for a certain period of time T3. The unit pressure P2 is 2 ~2.5Mpa, and then slowly reduce the unit pressure P2 to 0.1~0.12Mpa;

S5. Stacking health preservation: when the unit pressure P2 on the wood in S4 drops to 0.1-0.12MPa, turn on the hot press and take out the wood stacking health preservation.

In this embodiment, in step S1, the temperature C is 85-95°C. In step S2, the time T1 is 25-35 seconds. In steps S2-S4, the temperature of the pressing plate is 180-190°C. In step S3, the time T2 is 170-190 seconds, and in step S3, the frequency of the high-frequency electric field is 5000-18000 Hz. In step S4, the time T3 is 55-65 seconds.

The press plate is equipped with a medium or electric heating tube for heat conduction, the medium is saturated steam or heat conduction oil; the contact surface between the press plate and the wood is provided with a lining net, one is to facilitate the removal of water, and the other is to prevent wood from separating out Carbonization sticks to the hot platen.

During the S2 pressurization process, the wood to be dried is heated by contact, and the wood density tends to be balanced. Most of the free water in the wood and the bound water in the wood fiber cells are quickly released under the dual effects of pressure and temperature. The remaining moisture is close to vaporization and quickly breaks through the balance point of the coexistence of soda and water, so it needs to be discharged in time. Therefore, the rapid decompression and low-pressure maintenance make the passage of moisture smooth when it is discharged, and prevent wood from bursting. In the S3 process, the heat of the hot-pressed plate can only act on the surface of the wood through contact conduction in a short time and the heat transfer to the core layer is slow. During this process, a high-frequency electric field is applied, and the frequency is adjustable between 5000 and 18000HZ, so that the wood The water molecules in the high-speed friction generate heat, vaporize and discharge. The last stage of high temperature and pressure holding makes the lignin, cellulose, hemicellulose, tannin, polysaccharide and other encrusting substances in the wood under high temperature and high pressure, use the remaining moisture in the wood to participate in the action to produce cross-linking, and finally plasticize and shape the wood , so that the wood material and density tend to be stable. The pressure release speed is slowed down during the final unloading, so as to avoid the explosive release of residual gas caused by sudden pressure changes and damage to wood tissue. After slowly releasing the pressure, open the pressure plate and take out the wood stack for health preservation. This method can dry many types of wood.

The above descriptions are only preferred embodiments of the present invention, and do not limit the technical scope of the present invention in any way, so any minor modifications, equivalent changes and modifications made to the above embodiments according to the technical essence of the present invention are still valid. It belongs to the scope of the technical solutions of the present invention.

Claims (9)

1. The high-frequency hot-pressing drying method for the wood is characterized by comprising the following steps of:

s1, heat treatment of wood before pressing: heating the wood to be dried to a certain temperature C in a water boiling or microwave heating mode;

s2, boosting and maintaining pressure: placing the wood subjected to heat treatment in the S1 into a hot press, applying unit pressure P1 to the wood through a press plate of the hot press, and keeping the unit pressure P1 for a certain time T1, wherein the unit pressure P1 is 2-2.5 Mpa;

s3, pressure reduction and pressure maintaining: reducing the unit pressure P1 applied by the pressing plates to 0.1-0.12 MPa and keeping for a certain time T2, and simultaneously establishing a high-frequency electric field between the pressing plates through a high-frequency generator;

s4, pressurizing and slowly releasing pressure: when the moisture of the wood in the pressing plate is reduced to 20% or below 20%, removing the high-frequency electric field, applying unit pressure P2 to the wood through the pressing plate, keeping the unit pressure P2 at 2-2.5 Mpa for a certain time T3, and then slowly reducing the unit pressure P2 to 0.1-0.12 Mpa;

s5, stacking and preserving health: and when the unit pressure P2 to the wood in the S4 is reduced to 0.1-0.12 MPa, opening the hot press, taking out the wood, stacking and preserving.

2. The high-frequency hot-pressing drying method for the wood as claimed in claim 1, wherein: in step S1, the temperature C is 85-95 ℃.

3. The high-frequency hot-pressing drying method for the wood as claimed in claim 1, wherein: in the steps S2 to S4, the temperature of the pressing plate is 180 to 190 ℃.

4. The high-frequency hot-pressing drying method for the wood according to claim 3, characterized in that: a medium or an electric heating tube for heat conduction is arranged in the pressing plate, and the medium is saturated steam or heat conduction oil.

5. The high-frequency hot-pressing drying method for the wood as claimed in claim 1, wherein: in step S2, the time T1 is 25 to 35 seconds.

6. The high-frequency hot-pressing drying method for the wood as claimed in claim 1, wherein: in step S3, the time T2 is 170 to 190 seconds.

7. The high-frequency hot-pressing drying method for the wood as claimed in claim 1, wherein: in step S4, the time T3 is 55 to 65 seconds.

8. The high-frequency hot-pressing drying method for the wood as claimed in claim 1, wherein: and a lining net is arranged on the contact surface of the pressing plate and the wood.

9. The high-frequency hot-pressing drying method for the wood as claimed in claim 1, wherein: in step S3, the frequency of the high-frequency electric field is 5000-18000 Hz.

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