A method for hot pressing and dehumidifying three-layer bamboo oriented strand board

Abstract

The present invention discloses a method for paving and hot-pressing moisture removal of bamboo oriented strand board, comprising the following steps: S1, sorting bamboo shavings; S2, paving to form a slab; S3, rolling the surface bamboo shavings along the length direction to form filamentous cracks, paving the surface layers of the slab on both sides, and then covering them with wood veneer; S4, hot pressing. By providing surface shaving cracks and covering them with veneer composite, the present invention forms channels in the surface layer. These channels allow moisture to be effectively discharged through the channels formed by the cracks during the hot pressing process, aided by the arrangement of the internal shavings and the hot pressing temperature control method. This avoids the problem of blistering and debonding of the slab caused by the explosion of moisture due to pressure release.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application is a divisional application based on the Chinese patent application with application number 2022113819241, application date: November 7, 2022, and invention name: "A method for hot pressing and dehumidification of bamboo oriented strand board". Technical Field

[0003] The invention relates to the technical field of bamboo material processing, in particular to a method for paving and hot-pressing moisture removal of bamboo oriented strand boards. Background Art

[0004] Oriented strand board is made by processing wood into particles with a specific shape and paving them in a directional manner. Due to its large particle structure, the bending resistance of the wood chips is fully utilized, so the produced boards have good physical and mechanical properties and processing performance. Oriented strand board has gradually replaced multi-layer boards and blockboards and become the main material for building decoration.

[0005] Bamboo is China's most advantageous forestry resource. In recent years, the country has continuously advocated the transformation and upgrading of the bamboo industry and promoted the development of bamboo building materials. Currently, existing technologies are able to produce bamboo shavings of specific specifications to replace wood shavings, thereby preparing bamboo oriented strand board (OSB). Since bamboo fibers have a longitudinal structure, the prepared bamboo shavings are sliced along the growth direction of the bamboo. The bamboo shavings are in long strips, making full use of the fiber's bending resistance. In order to pursue high static bending and high elastic modulus, the density of bamboo oriented strand board will reach above 900g / cm³, the internal density of the board is high, and the compression ratio is relatively large.

[0006] The production process of bamboo oriented strand board is: flake acquisition → drying → glue mixing → laying → pre-pressing → hot pressing → cooling and forming → thickness determination and sanding → trimming → packaging. In the whole process, hot pressing is the key process. The main issues involved are the effects of hot pressing temperature, pressure and time on moisture content, uniformity, thermal curing and stability. If not handled properly, it will cause problems such as debonding, poor gluing, board explosion and blistering of the slab. For example, the problem of venting water vapor from bamboo shavings during hot pressing will solidify the air mass in the slab if not handled properly, causing board explosion and poor gluing when opening the board.

[0007] Specifically, due to its physiological characteristics, the moisture in the vascular tubes of bamboo fiber is easily dried and discharged, and the remaining is the bound water in the bamboo fiber cells; in the shavings drying process, the moisture content of the bamboo shavings after drying is 8%±1%. If the drying is too low, the bamboo shavings will cause curling and lateral cracking, causing problems with paving and pre-pressing, especially the curling of the bamboo shavings, it will be impossible to effectively overlap the bamboo shavings, and it is easy to form gaps in the slab, which seriously affects the quality of hot pressing; therefore, during hot pressing, as the heat continues to penetrate and replace, the water vapor in the shavings will gradually precipitate, and because of the high density of the bamboo shavings, the high-temperature water vapor cannot be discharged laterally, and more often it will gather into clumps above and below. Once the slab is released, the water vapor will explode. Summary of the Invention

[0008] In order to solve at least one of the technical problems mentioned in the background technology, the purpose of the present invention is to provide a hot pressing and dehumidification method for paving bamboo oriented strand board, so as to solve the problems of blistering, debonding, uneven slabs and poor gluing of the slab caused by the high density of the bamboo oriented strand board slab and the density inside the slab, which makes it impossible to discharge water vapor, and the uneven density of the paving.

[0009] To achieve the above object, the present invention provides the following technical solutions:

[0010] A method for paving bamboo oriented strand board with hot pressing and moisture removal comprises the following steps:

[0011] S1, bamboo shavings sorting;

[0012] S2, paving to form a slab;

[0013] S3, rolling the surface bamboo shavings along the length direction to form filamentous cracks, and paving them on both sides of the slab, and then covering them with wood veneer;

[0014] S4. Hot pressing.

[0015] Compared with the prior art, the beneficial effect of the present invention is that by setting surface wood chip cracks and covering them with veneer composite, channels are formed on the surface, which can allow water vapor to be effectively discharged through the channels formed by the cracks during the hot pressing process with the assistance of the internal wood chip arrangement and the hot pressing temperature control method, thereby avoiding the problem of blistering and debonding of the slab caused by the explosion of water vapor due to the release of pressure on the slab.

[0016] Furthermore, step S4 includes the following stages:

[0017] S41, pre-pressing stage: pressure is 0.5-1Mpa, and the stage maintenance time is 1-2min;

[0018] S42, pressurization stage: the pressure is 4-5 MPa, so that the slab is close to the size of the thickness gauge, and the stage is maintained for 2-3 minutes;

[0019] S43, tide discharge stage: pressure is 3-4Mpa, and the stage duration is 5-6min;

[0020] S44, pressure release stage: reduce the pressure at a rate of 1 MPa / min in the first two minutes and 0.5 MPa / min in the next two minutes until it reaches 0 MPa. The stage is maintained for 5-6 minutes.

[0021] Furthermore, in step S4, the temperature of hot pressing is 140°C-160°C.

[0022] Furthermore, in step S3, the depth of the cracks produced by the pressing roller is 5%-10% of the thickness of the bamboo shavings, and the distance between adjacent cracks is 20%-30% of the width of the bamboo shavings.

[0023] Furthermore, both sides of the bamboo shavings are subjected to roller deflagration.

[0024] Furthermore, in step S1, the bamboo shavings are screened according to length, and the screening sizes are 5-8 cm, 8-12 cm, and 12-15 cm.

[0025] Furthermore, in step S2, bamboo shavings of 5-8 cm in length are placed in the core layer of the slab, and bamboo shavings of 8-12 cm in length and bamboo shavings of 12-15 cm in length are sequentially laid outward from the core layer.

[0026] Furthermore, in step S2, the bamboo shavings are laid in a layered and staggered orientation in a horizontal and vertical alternating manner.

[0027] Furthermore, in step S2, the overlapping distance of the bamboo shavings in the length direction is 1 / 4-1 / 3 of the length of the bamboo shavings, and the overlapping distance in the width direction is 1 / 5-1 / 4 of the width of the bamboo shavings. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a schematic diagram of the process flow of the present invention;

[0029] Figure 2 Schematic diagram of the stage flow of the hot pressing process of the present invention;

[0030] Figure 3 This is a temperature curve diagram of the core layer of the slab in the hot pressing process of the present invention.

[0031] In the figure: 1. Water vapor direction; 2. Water vapor form; 3. Temperature field intensity; A. Initial state; B. Pre-compression stage; C. Pressurization stage; D. Dehumidification stage; E. Pressure release stage. DETAILED DESCRIPTION

[0032] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0033] See also Figure 1 This embodiment provides a method for paving bamboo oriented strand board by hot pressing and dehumidifying.

[0034] Oriented strand board is made by processing wood into particles with a specific shape and paving them in a directional manner. Due to its large particle structure, the bending resistance of the wood chips is fully utilized, so the produced boards have good physical and mechanical properties and processing performance. Oriented strand board has gradually replaced multi-layer boards and blockboards and become the main material for building decoration.

[0035] Bamboo is China's most advantageous forestry resource. In recent years, the country has continuously advocated the transformation and upgrading of the bamboo industry and promoted the development of bamboo building materials. Currently, existing technologies are able to produce bamboo shavings of specific specifications to replace wood shavings, thereby preparing bamboo oriented strand board (OSB). Since bamboo fibers have a longitudinal structure, the prepared bamboo shavings are sliced along the growth direction of the bamboo. The bamboo shavings are in long strips, making full use of the fiber's bending resistance. In order to pursue high static bending and high elastic modulus, the density of bamboo oriented strand board will reach above 900g / cm³, the internal density of the board is high, and the compression ratio is relatively large.

[0036] The production process of bamboo oriented strand board is: flake acquisition → drying → glue mixing → laying → pre-pressing → hot pressing → cooling and forming → thickness determination and sanding → trimming → packaging. In the whole process, hot pressing is the key process. The main issues involved are the effects of hot pressing temperature, pressure and time on moisture content, uniformity, thermal curing and stability. If not handled properly, it will cause problems such as debonding, poor gluing, board explosion and blistering of the slab. For example, the problem of venting water vapor from bamboo shavings during hot pressing will solidify the air mass in the slab if not handled properly, causing board explosion and poor gluing when opening the board.

[0037] Therefore, the present invention aims to solve the problems of blistering, debonding, uneven slabs and poor gluing of bamboo oriented strand boards caused by high slab density and compactness inside the slab when the density is designed to be above 900 g / cm³, as well as uneven density during paving, and provides a method for dehumidifying bamboo oriented strand boards during paving. The method solves the problem of uneven slab paving and the problem of water vapor exhaust during hot pressing, avoids the problems of blistering, debonding, board explosion and the like through process adjustment, and improves the efficiency of the hot pressing process.

[0038] Specifically, the present invention proposes a paving method, in which the bamboo oriented strand board has a multi-layer, 3-layer or 5-layer structure, and the bamboo shavings have a length of 5-15 cm, a width of 0.8-3 cm, and a thickness of 0.6-1.2 mm; the bamboo shavings are obtained by cutting a bamboo tube of a fixed length in the longitudinal direction, using a rotary cutting and thickness-fixing technology. Because the width is the radial wall thickness and chordal layer thickness of the bamboo tube, there will be shavings of different widths, but the distribution is relatively uniform; at the same time, due to the different curvatures of the bamboo tube and the existence of bamboo nodes, the bamboo tube will be in an unstable state during cutting, and the obtained bamboo shavings will vary within a certain range, and there will be decomposition in the length direction, but the thickness uniformity is relatively consistent.

[0039] Specific implementation: bamboo shavings of different lengths are screened and sorted according to lengths of 5-8cm, 8-12cm, and 12-15cm, and then laid in layers according to different lengths. The laid shavings are layered and staggered in orientation, specifically in a horizontal-vertical-horizontal staggered structure, with short shavings in the inner core layer and long shavings on the surface, which can better utilize the bending and tensile properties of bamboo; and the shavings of each layer are overlapped in the paving direction, that is, the length direction, at 1 / 4-1 / 3 of the length, and in the width direction at 1 / 5-1 / 4 of the width.

[0040] Due to its physiological characteristics, the moisture in the vascular tubes of bamboo fiber is easily dried and discharged, and the remaining is the bound water in the bamboo fiber cells; in the shavings drying process, the moisture content of the bamboo shavings after drying is 8%±1%. If the drying is too low, it will cause curling and lateral cracking of the bamboo shavings, causing problems with paving and pre-pressing, especially the curling of the bamboo shavings, it will be impossible to effectively overlap the bamboo shavings, and it is easy to form gaps in the slab, which seriously affects the quality of hot pressing; therefore, during hot pressing, as the heat continues to penetrate and replace, the water vapor in the shavings will gradually precipitate, and because of the high density of bamboo shavings, the high-temperature water vapor cannot be discharged laterally, and more often it will gather into clumps above and below. Once the slab is released from pressure, the water vapor will explode, causing the slab to be scrapped.

[0041] In order to avoid the above-mentioned water vapor explosion problem, the present invention proposes a dehumidification method. Specifically, the sorted bamboo shavings are first obtained according to the above-mentioned method, and the surface bamboo shavings are selected and roller-flashed along the length direction to form filamentous cracks on the surface of the bamboo shavings. The treated bamboo shavings are laid on the surface of the slab, and then a piece of wood veneer is added respectively; the depth of the cracks fluffed by the roller is 5%-10% of the thickness of the bamboo shavings, and the adjacent cracks are 20%-30% of the width; the bamboo shavings are subjected to double-sided fracturing treatment.

[0042] The fracturing bamboo shavings are laid on the surface of the slab according to the above method, and a wooden veneer with a thickness of 1.2-1.8mm is laid. This treatment can maintain a specific air cavity structure formed between the bamboo surface shavings and the veneer surface. As the slab is heated, water vapor will seek a channel for exhaust.

[0043] The slab is then hot pressed. The present invention proposes a hot pressing method, which is divided into four stages: a pre-pressing stage, a pressurizing stage, a moisture removal stage, and a pressure release stage. The hot pressing temperature is 140°C-160°C.

[0044] The difference between bamboo and wood is that the material is relatively hard overall and has a low heat transfer coefficient. It takes longer to heat than wood to soften and plasticize. Therefore, according to the high-strength performance indicators of the product, the hot pressing time and pressure need to be maintained, specifically:

[0045] The pre-pressing stage is 0.5-1Mpa, which compresses the bamboo shavings to slowly level the curled or unevenly laid parts of the slab. The time is 1-2 minutes.

[0046] During the pressurization stage, the pressure is directly and rapidly increased to 4-5 MPa, so that the slab is close to the size of the thickness gauge. This stage is the key to slab forming. While quickly compressing the slab, heat conduction is enhanced to improve heat conduction efficiency. The time is 2-3 minutes;

[0047] During the dehumidification stage, as the slab temperature gradually reaches the design temperature and the bamboo material gradually softens, the slab volume gradually shrinks. When it reaches the thickness gauge, the slab is in a stable state of heat and pressure, and the pressure is controlled at 3-4 MPa. When the slab is completely within the thickness gauge range, the thermal field of the slab reaches uniformity, and the moisture is completely vaporized by heat. The steam at the edge of the slab is directly discharged, and the steam inside moves horizontally or up and down. When it moves to the surface, it is discharged through the air cavity. The time is 5-6 minutes.

[0048] During the pressure release stage, the slab will have a certain volume rebound as the pressure is released after hot pressing. At the same time, since part of the water vapor in the slab will be discharged, the pressure reduction in the pressure release stage is step-by-step, decreasing by 1Mpa / min in the first 2 minutes and 0.5Mpa / min in the next 2 minutes until it drops to 0Mpa, and the time is 5-6 minutes.

[0049] Figure 2 The changes in water vapor direction 1, water vapor form 2, temperature field intensity 3, and the changing process of slab hot pressing are indicated.

[0050] During the hot pressing process, the surface pressure rises first in the initial stage, and is initially greater than the core pressure, and then the core pressure rises sharply and exceeds the surface pressure; the time it takes for the core temperature to reach 100°C is almost equal to the equilibrium period before the core pressure begins to rise; the greater the density of the board, the more stable the pressure, the greater the maximum pressure of the surface and core layers, and the later the time of occurrence; the higher the moisture content of the slab, the shorter the duration of the short equilibrium period; in the rapid pressure increase section, the pressure of the slab with a high moisture content rises faster, and the maximum value of the core pressure is large; in the vaporization section, the higher the density, the greater the core pressure, and the higher the vaporization temperature; in the pressure reduction stage, the core pressure is always greater than the surface pressure, and the pressure of the slab with a high moisture content is always greater than that of the slab with a low moisture content.

[0051] The steam pressure at the center of the slab is divided into three sections: the partial pressures of water vapor and air both increase, and the total pressure gradually increases; the water vapor partial pressure increases to a stable state, the air partial pressure decreases, and the total pressure first increases to a peak value and then slowly decreases; the water vapor and air partial pressures both decrease slowly, and the total pressure slowly decreases.

[0052] Example 1

[0053] The above-mentioned paving method is used, wherein the bamboo oriented strand board has a three-layer structure, with 5-8 cm long strands placed in the core layer and the other two types placed in the surface layer; the above-mentioned moisture removal method is used for treatment; and the above-mentioned hot pressing method is used for hot pressing; details are shown in Table 1.

[0054] Example 2

[0055] The above-mentioned paving method is adopted, wherein the bamboo oriented strand board has a five-layer structure, with layers 1-5 from bottom to top, 5-8 cm long strands are placed in the core layer, i.e., the third layer, 8-12 cm long strands are placed in the second and fourth layers, and 12-15 cm long strands are placed in the surface layers, i.e., the first and fifth layers; the above-mentioned moisture removal method is adopted for treatment; and the above-mentioned hot pressing method is adopted for hot pressing; details are shown in Table 1.

[0056] Table 1 Result data of Example 1 and Example 2

[0057]

[0058] Among them, the temperature of the core layer of the slab during hot pressing is detailed in Figure 3 , indicating the temperature change curves under the initial state A, pre-compression stage B, dehumidification stage C, and pressure release stage D.

[0059] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the invention can be embodied in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as illustrative and non-restrictive, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations that come within the meaning and range of equivalents of the claims be embraced therein.

Claims

1. A method for paving and dehumidifying three-layer bamboo oriented strand board by hot pressing, characterized in that: The following steps are involved: S1, bamboo shavings sorting; the bamboo shavings are screened by length, and the screening sizes are 5-8cm, 8-12cm, and 12-15cm; S2. Paving to form a slab; placing 5-8 cm long wood chips in the core layer, 8-12 cm long wood chips and 12-15 cm long wood chips in the surface layer respectively; S3, rolling the surface bamboo shavings along the length direction to form filamentous cracks, and paving them on both sides of the slab, and then covering them with wood veneer; S4, hot pressing, the hot pressing temperature is 140 ℃ -160 ℃; Step S4 The following stages are included: S41, pre-pressing stage: pressure is 1Mpa, and the stage maintenance time is 1-2min; S42, pressurization stage: the pressure is 5 MPa, so that the slab is close to the size of the thickness gauge, and the stage is maintained for 2-3 minutes; S43, tide discharge stage: pressure is 4Mpa, stage maintenance time is 5-6min; S44, pressure release stage: reduce the pressure at a rate of 1 MPa / min in the first two minutes and 0.5 MPa / min in the next two minutes until it reaches 0 MPa. The stage is maintained for 6 minutes.

2. The method for paving and hot pressing moisture removal of three-layer bamboo oriented strand board according to claim 1, characterized in that: In step S3, the depth of the cracks produced by the pressing roller is 5%-10% of the thickness of the bamboo shavings, and the distance between adjacent cracks is 20%-30% of the width of the bamboo shavings.

3. The method for paving and hot pressing moisture removal of three-layer bamboo oriented strand board according to claim 2, characterized in that: Both sides of the bamboo shavings are roller-fluffed.

4. The method for paving and hot pressing moisture removal of three-layer bamboo oriented strand board according to claim 1, characterized in that: In step S2, the bamboo shavings are laid in a layered and staggered orientation in a horizontal and vertical alternating manner.

5. The method for paving and hot pressing moisture removal of three-layer bamboo oriented strand board according to claim 4, characterized in that: In step S2, the overlapping distance of the bamboo shavings in the length direction is 1 / 4-1 / 3 of the length of the bamboo shavings, and the overlapping distance in the width direction is 1 / 5-1 / 4 of the width of the bamboo shavings.

Images