CN106881755A - Method for densifying wood/bamboo by hot pressing combined with steam spraying method and densifying wood/bamboo - Google Patents

Abstract

The invention discloses a method for densifying wood/bamboo materials by a hot-pressing combined steam jet method, which comprises the following steps: the method comprises the following steps of (1) additionally arranging high-pressure-resistant high-temperature-resistant breathable metal plates on an upper pressing plate and a lower pressing plate of a hot press with steam spray holes, enabling smooth surfaces of the breathable metal plates to face outwards to be in contact with pressed wood/bamboo, heating the upper pressing plate and the lower pressing plate to 160-220 ℃, and keeping the temperatures of the upper pressing plate and the lower pressing plate in subsequent steps; placing the wood/bamboo with the water content of 8-30% on a lower pressing plate of the press; rapidly closing the upper pressing plate and the lower pressing plate, stopping closing when the upper pressing plate contacts the pressed wood/bamboo and exerts certain pressure, and starting high-pressure steam for steam injection; slowly closing the upper pressing plate and the lower pressing plate, performing steam injection at the same time, stopping closing the pressing plates when the thickness of the pressed wood/bamboo wood is compressed to the required thickness, maintaining the pressing plates in the original position, and performing steam injection at the same time; stopping the steam injection, starting the air suction function of the small holes on the upper pressing plate and the lower pressing plate, and discharging the excessive moisture and the extract gas.

Description

Method for densifying wood/bamboo by hot pressing combined with steam spraying method and densifying wood/bamboo Bamboo

technical field

The invention relates to the field of material preparation, in particular to a method for densifying wood/bamboo by hot pressing combined with a steam spraying method and densifying wood/bamboo.

Background technique

In the wood product industry, high-strength wood raw materials have always been pursued by people, but high-strength wood raw materials are always limited in natural resources and expensive. Therefore, wood scientists try to increase the density of wood through the process of wood densification, and turn low-density, resource-rich and cheap low-density wood into high-density, high-strength wood. There are many reports of wood densification in historical literature (Fang et al. 2011, 2012a, 2012b, 2012c; Boonstra and Blomberg 2007; Fukuta et al. ; Inoue et al.1993b; Inoue et al.2008; Ito et al.1998b; Kamke 2006; Kollmann 1936; Kollmann et al.1975; Navi and Heger2004; Seborg et al.1945). There are also many patents on wood densification ( Sears, 1900; Walch and Watts, 1923; Oleheimer, 1929; Brossmannes, 1931; Esselen, 1934; Olson 1934; Huang Rongfeng et al. 2011, 2013). However, due to various defects, the industrial application of densified wood is still very limited. These processes mainly include chemical methods and mechanical methods. The main drawbacks of chemical methods include:

1) The natural characteristics of wood cannot be guaranteed;

2) Affect the recycling or natural degradation of wood, causing pollution to the environment;

3) The cost is higher.

Therefore, from the perspective of environmental protection, physical and mechanical methods are more in line with today's environmental protection concepts. The major deficiencies of existing international mechanical methods include:

1) The process is complicated and takes a long time;

2) At present, the methods in several laboratories mainly engaged in wood densification in the world are mostly limited to small-sized test materials;

3) Dimensional springback caused by mechanical densification of wood;

4) Some use high-temperature treatment (190-230 degrees Celsius) and long enough time to reduce the dimensional rebound. High-temperature and long-term treatment will damage the mechanical properties of wood, especially the surface of wood, often causing partial carbonization, or causing deep color and The shades vary widely, often rendering compressed wood unusable at all.

5) The use of high-temperature steam can alleviate some of the problems mentioned in 4) above, but because the wood is under the high pressure of the hot-pressed iron plate, it is difficult for the steam to act evenly (or even impossible) on the pressure surface of the pressed wood, especially when the wood is pressed When the pressure surface is large.

6) Some hot presses have steam injection holes on the hot iron plate (my previous experiment) which can alleviate some of the problems mentioned in 5) above, but the steam still cannot be evenly distributed to the surface of the pressed wood, and the wood is in the Under high pressure, it will protrude into the spray hole, causing many bumps on the surface of the compressed wood.

All of the above problems limit the commercial application of compressed wood to varying degrees and in different aspects. Therefore, it is necessary to continue to explore how to solve these problems.

Bamboo is one of the important renewable biological resources on the earth. It has a short growth cycle and quick growth. It has been widely used in recent years. Bamboo has high mechanical strength, and its elastic modulus per unit density is comparable to that of steel. However, the density and mechanical strength of bamboo in the transverse direction (from bamboo green to bamboo yellow) and vertical direction (from the base of the vertical bamboo to the tip) The difference is very large, which leads to the high non-uniformity of density and mechanical strength inside the composite engineering board made of raw bamboo, which cannot be compared with steel, which greatly restricts the utilization of raw bamboo. In addition, due to the arc shape of the bamboo wall, a large amount of bamboo raw materials are wasted in order to obtain regular bamboo strips in the bamboo chip processing process. Although ordinary recombined bamboo can obtain high-density and relatively uniform boards, this type of product requires a large amount of sizing, which is extremely environmentally unfriendly. The above-mentioned problems can be overcome by the physical and mechanical densification of bamboo, new high-strength products can be manufactured, and a new direction for the utilization of bamboo can be opened up. .

Contents of the invention

The object of the present invention is to provide a kind of method and the densification wood/bamboo wood of hot pressing combined with steam injection steaming method, simplify technological process, reduce process time; Improve the color consistency of wood/bamboo wood after densification , to prevent carbonization of wood/bamboo; to improve the uniform distribution and penetration of steam on compressed wood/bamboo to reduce the moisture rebound of compressed wood/bamboo; to improve the surface properties of densified wood/bamboo (to eliminate the damage caused by steam injection holes) surface bumps) to reduce springback.

In order to achieve the above object, the technical scheme that the present invention takes is:

The method for compacting wood/bamboo by hot pressing in combination with steam jet steaming method comprises the following steps:

S1. Install high-pressure-resistant and high-temperature-resistant breathable metal plates on the upper and lower platens of the hot press with steam injection holes. The smooth side of the breathable metal plate faces outwards and contacts with compressed wood/bamboo, and heats up the upper and lower platens to 160- 220°C, and maintain the temperature of the upper and lower platens in the subsequent steps;

S2, placing wood/bamboo with a moisture content of 8% to 30% or wood/bamboo that has been pre-softened by high-temperature saturated steam on the lower platen of the press obtained in step S1;

S3. Quickly close the upper and lower pressure plates, and stop closing when the upper pressure plate touches the compressed wood/bamboo and exerts a certain pressure (the purpose is to prevent the pressured wood/bamboo from moving during steaming), and open the high-pressure steam to the compressed wood/bamboo The upper and lower sides of the bamboo are steamed;

S4. Slowly close the above-mentioned upper and lower pressing plates, spray and steam at the same time, and stop closing the pressing plates when the thickness of the compressed wood/bamboo is compressed to the required thickness;

S5. After the pressing plate is stopped and closed, it remains in the original position, and steaming is carried out at the same time;

S6. Stop steaming, and turn on the suction function of the small holes on the upper and lower pressure plates to discharge excess water and the extract gas produced by wood/bamboo due to high temperature. After 1 to 2 minutes, stop the suction function, and the small holes on the pressure plate The ventilation channel is naturally unblocked, so that the pressure inside and outside the pressure plate is consistent, and the upper and lower pressure plates are opened to take out the compressed wood/bamboo.

The hot press used for wood/bamboo densification in the step S1 has steam spray holes and has the function of air suction and exhaust.

The air-permeable metal plate adopts a sintered filter net, and the surface in contact with the compressed wood/bamboo is relatively flat and smooth and can effectively transmit steam.

The present invention also provides the densified wood/bamboo produced by the above-mentioned method of densifying wood/bamboo by hot pressing combined with steam injection.

The present invention has the following beneficial effects:

Simplifies the process and reduces the process time; improves the color consistency of the wood/bamboo after densification, prevents carbonization of the wood/bamboo; improves the uniform distribution and penetration of steam on the compressed wood/bamboo to reduce the pressure of the compressed wood/bamboo Moisture absorption rebound; improve the surface performance of densified wood/bamboo (eliminate surface bumps caused by steam spray holes), reduce rebound.

Description of drawings

Fig. 1 is the schematic diagram of the densification process of the embodiment of the present invention;

In the figure: preprocessing (T ₀ ～T ₁ ), compression (T ₁ ～T ₂ ), and postprocessing (T ₂ ～T ₃ ).

Fig. 2 is a schematic structural view of the upper pressing plate and the lower pressing plate in the embodiment of the present invention.

Fig. 3 is a schematic diagram of the connection structure of the upper pressing plate, the lower pressing plate and the air-permeable metal plate in the embodiment of the present invention.

detailed description

In order to make the objects and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the examples. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention.

Figure 1 is a schematic diagram of the densification process, and the densification equipment used is an all-in-one machine for spraying, steaming and hot pressing. ), sealing equipment can be installed around the hot pressing plate (which can improve the compaction efficiency). All densification processes can be completed on the same equipment at one time, or pre-processing and post-processing can be processed separately in other equipment. The function of pretreatment is to soften the wood/bamboo before heat pressing, which is convenient for heat pressing. The role of post-treatment is to shape and dry the wood/bamboo after heat pressing, to prevent or reduce the rebound of compressed wood/bamboo. The high-pressure and high-temperature steam in the hot-pressing process also has the function of softening and setting, and can prevent or reduce the carbonization of wood/bamboo at high temperature. Carbonization not only greatly reduces the mechanical properties of compressed wood/bamboo, but also causes the color of wood/bamboo to become darker. Blackening makes compressed wood/bamboo unusable. The steam spraying in the whole process can also make the inside and outside of the pressurized material heat up rapidly at the same time, and the temperature difference between the inside and the outside is small. The whole process is controlled by computer software, and the program of the whole process is set in the computer (including the temperature of the hot plate, the distance, when the hot plate opens and closes, the speed of the hot plate opened and closed, the steam pressure, when to start and stop spray steam, when to absorb steam, etc.), after putting in the wood/bamboo that needs to be densified, the entire softening, hot-press steaming, post-processing and other processes will run automatically.

During the hot pressing process, due to the strong pressure, the wood/bamboo at the corresponding part of the steam spray hole will often protrude and be stuffed into the steam spray hole because it is not in contact with the press plate, thus greatly affecting the distribution and distribution of steam on the compressed wood/bamboo. penetration. In order to solve this problem, a high-strength, high-pressure, high-temperature, corrosion-resistant, and breathable metal plate (sintered filter, made of 316L or 304 stainless steel) was added to the surface of the upper and lower hot pressing plates (Figure 3). The interconnected fine gaps allow the steam to completely pass through the metal plate, so that the steam can be evenly distributed to all parts of the compressed wood/bamboo. The contact surface of the alloy air-permeable board and the hot-pressed board does not require high smoothness and flatness, and the side that is in contact with the pressed wood/bamboo requires smoothness, so that the final densified wood/bamboo surface is very smooth. Example of the present invention The air-permeable metal plate used in has fully met such requirements. This invention not only greatly improves the uniform distribution of steam on the compressed wood/bamboo, improves the softening and setting effect, but also prevents the carbonization of the surface of the compressed wood/bamboo and the problems of inconsistent color, which are the problems of hot-pressed wood/bamboo in the past. problems that are difficult to overcome.

Specific embodiments of the present invention are as follows:

S1. Install a high-pressure, high-temperature, and high-temperature breathable metal plate (sintered filter) on the upper and lower pressing plates of the hot press with steam injection holes. The smooth side of the mesh faces outward (in contact with the compressed wood/bamboo), and the pressing plate Raise the temperature to 160-220°C.

S2. Place wood/bamboo with a moisture content of about 8% to 30% (or pre-softened wood/bamboo) on the lower platen of the press (comprising a breathable metal mesh, hereinafter referred to as the platen). Pre-softened wood/bamboo can be softened by high-temperature saturated steam. The specific operation is to put the wood/bamboo into a sealed tank and inject saturated steam at 160 to 200 degrees Celsius for softening. The softening time depends on the size of the wood/bamboo. It can be several minutes to ten minutes.

S3. Quickly (within 30 seconds) close the hot pressing plate to reduce the moisture loss of wood/bamboo caused by high temperature. When the bamboo moves), it stops closing and turns on the high-pressure steam to steam the upper and lower sides of the compressed wood/bamboo. The purpose of this process is to soften the pressure with high-temperature steam to facilitate subsequent compression. The time depends on the pressure wood/bamboo The thickness of the bamboo and the species, as well as the steam pressure and the temperature of the hot-pressed plate can be adjusted within a few minutes to tens of minutes. For example, 4mm poplar and 3.5mm thick maple need to 5 minutes or so. This process is called preprocessing in this paper, see preprocessing (T ₀ ˜T ₁ ) in FIG. 1 . This process can save or reduce time if the pressed wood/bamboo is softened before being put into the press.

S4. After the softening treatment, the hot pressing plate continues to close slowly (the closing speed can be adjusted according to the compressed wood/bamboo of different tree species, and it can also be closed, pause, continue to close, and then pause... The purpose is to let the pressure Wood/bamboo has a certain period of time to relieve the internal compressive stress, which can play a role in fixing compression and reduce the compression rebound in the later stage), and steaming is carried out at the same time. When the thickness of the compressed wood/bamboo is compressed to the required thickness, stop the closing of the pressing plate. This process is a compression process, see the compression (T ₁ ~ T ₂ ) in Figure 1, the time depends on the compression rate, the thickness of the compressed wood/bamboo and the tree species, and it can be several minutes to tens of minutes. For example, under the steam pressure of 200 degrees Celsius and 550KPa on a hot-pressed plate, it takes about 7 minutes for 4mm poplar wood to be pressed to 2mm and 3.5mm thick maple wood to be pressed to 2.4mm.

1) After the press plate stops closing, it remains in place, and steaming is carried out at the same time. The purpose is to relieve and release the internal stress of the compressed wood/bamboo, play a role of fixed compression, and prevent and reduce the rebound of the compressed wood/bamboo. This process is called post-processing in this article, see post-processing (T ₂ -T ₃ ) in Figure 1 , and the time can range from a few minutes to tens of minutes. Under the steam pressure of 200 degrees Celsius and 550KPa on the hot-pressed plate, 4mm poplar wood is pressed to 2mm and 3.5mm thick maple wood is pressed to 2.4mm, and the time required for post-processing is about 10 minutes.

2) Stop steaming, and open the suction function of the small holes on the pressure plate to discharge excess water and the extract gas produced by wood/bamboo due to high temperature. This process only takes 1-2 minutes, and then the suction function is stopped, and the small hole ventilation channel on the pressure plate is naturally unblocked, which means that the air pressure inside and outside the pressure plate is consistent. Open the pressure plate, take out the compressed wood/bamboo, and the compressed wood/bamboo at this time The moisture content is very low, and there is no need to dry it later.

Fig. 3 is installed on the upper and lower hot pressing plate 1, high temperature resistant, high pressure, corrosion resistant and breathable metal plate 2, the breathable metal plate 2 is respectively connected with the upper and lower hot pressing plate 1 through screws or welding at 4 corners, and the breathable metal plate 2 The sintered filter is used, the rough surface is in contact with the hot-pressed plate with spray holes, and the smooth and flat surface is the compressed wood/bamboo contact surface. Steam can easily pass through this plate. If it is installed by screws, the height of the screws must be lower than the height of the gas-permeable metal plate.

The above is only a preferred embodiment of the present invention, it should be pointed out that for those of ordinary skill in the art, without departing from the principle of the present invention, some improvements and modifications can also be made, and these improvements and modifications should also be It is regarded as the protection scope of the present invention.

Claims (4)

1. the method for hot binding steam spraying method compacted wood/bamboo wood, it is characterised in that comprise the following steps：

S1, install high pressure resistant high temperature resistant Vented metal plate, Vented metal plate additional on the upper lower platen of the hot press of carrying vapour spray orifice It is smooth face outwardly, contacted with over-topped/bamboo wood, and upper lower platen is warmed up to 160-220 DEG C, and in subsequent step always The temperature of lower platen in holding；

S2, by moisture content 8% to 30% timber/bamboo wood or by the timber/bamboo wood of high temperature saturated vapor pre-softening It is placed on the press lower platen obtained by step S1；

Lower platen on S3, quick-make, stops closing when top board touches over-topped/bamboo wood and effect has certain pressure Close, and open high steam and the upper and lower surface of over-topped/bamboo wood is steamed；

S4, above-mentioned upper lower platen is slowly closed, steam is carried out simultaneously, when the thickness reduction of over-topped/bamboo wood is to required thickness Stop pressing plate closure when spending；

S5, pressing plate are maintained in the original location after stopping closure, and steam is carried out simultaneously；

S6, stopping are steamed, and open the air suction function of aperture on upper lower platen, and discharge excessive moisture and timber/bamboo wood are because of high temperature And the extract gas for producing, then stop suction function, and the aperture venting channels on pressing plate are naturally unimpeded so that inside and outside pressing plate Air pressure is consistent, lower platen in unlatching, takes out over-topped/bamboo wood.

2. such as the method for the hot binding steam spraying method compacted wood/bamboo wood in claim 1, it is characterised in that described It is used for the hot press of timber/bamboo wood densification in step S1 with steam-injection hole, and with the function of air-breathing exhaust.

3. such as the method for the hot binding steam spraying method compacted wood/bamboo wood in claim 1, it is characterised in that described Vented metal plate is compared flat smooth and can effectively be passed through steaming using sintering screen pack, and the face contacted with over-topped/bamboo wood Vapour.

4. the method institute of the hot binding steam spraying method compacted wood/bamboo wood as described in any one in claim 1-3 Obtained compacted wood/bamboo wood.