Flexible use of furniture material drying standards

Author: Ai Ye Wang Mu Fenghu

Abstract: In the dry production of furniture materials, the rational use of drying standards is directly related to the drying quality and drying cycle. In the text

The multi-stage drying reference and the drying gradient reference in the moisture content drying reference are examples of how to properly and flexibly adjust and apply the dry reference according to the actual conditions of the dried wood.

Keywords : furniture materials; drying benchmark

Wood drying is a key part of the production of wooden furniture. The drying standard is an important part of the dry production of wood. It directly affects the dry quality and drying cycle of the wood. The wood drying standard is simply referred to as a dry basis, or as a drying program. It is the relationship between the reasonable drying medium temperature and the relative humidity I or the equilibrium moisture content corresponding to the wood moisture content or drying time of each stage in the drying process.

Currently, drying standards commonly used in wood drying production are moisture content drying standards and time drying standards. The time drying standard is based on the moisture content drying standard. There is no water drying standard. There is no time drying standard. Because the moisture content drying benchmark determines the temperature and humidity parameters of the drying medium according to different moisture content stages, the degree of quantification is high and accurate. Follow the process. Therefore, the moisture content drying standard is generally used in wood drying production. Moisture drying standard is based on wood

The moisture content in the material is divided into drying standards for each drying stage, which is further divided into a multi-stage moisture drying standard, a three-stage moisture drying standard, a dry gradient basis, and a wave and semi-fluid drying standard. Multi-stage moisture content drying benchmark and third-order

Segment moisture content drying standard is suitable for wood drying with wood thickness less than 80mm. For drying equipment, it is suitable for manual controlled drying equipment, suitable for semi-automatic or fully automatic control drying equipment, with certain universality; wave type The semi-fluctuation drying standard is suitable for drying wood with a thickness of more than 80 mm. For drying equipment it is suitable for drying equipment with manual or semi-automatic control: the drying gradient reference is suitable for drying equipment with automatic detection and computer control, especially in countries) This drying standard is often used for bgl-in drying equipment. The so-called dry gradient refers to the ratio of the average moisture content of the dried wood to the equilibrium moisture content of the drying medium. This is a special gradient definition for wood drying, not a gradient definition in the strict sense. The purpose of introducing this definition is mainly to facilitate the determination of the automatic control parameters in the wood drying process and to facilitate the automatic control of the drying medium to achieve automatic control of the wood drying process. The drying gradient can intuitively reflect the speed at which the wood dries.

current. Most of the wooden furniture manufacturers in China have a certain amount of drying equipment. Among them, there are domestically produced drying equipment imported from abroad. Since the thickness of the sawn timber used in the production of wooden furniture is less than 8Omm, this paper only analyzes how to use the multi-stage moisture content drying benchmark and the drying gradient benchmark in the wood drying production.

1 Flexible use of multi-stage moisture content drying benchmark

The dry basis has a soft hardness, and the soft hardness of the dry basis refers to the strength of evaporation of moisture from the wood in a dry medium in a certain state. When the tree species, specifications and -B conditions of the wood are the same, the temperature difference between the dry and wet bulbs is large and the airflow

A dry reference with a faster cycle speed is a hard reference, and vice versa is a soft reference. The same dry basis, for thinner softwoods, may be harder for thicker hardwoods. The wood is thus damaged: wood that is important for use may be hard, and wood that is not important for use may be soft. In the process of using a certain drying standard, when the temperature and humidity conditions of a certain moisture content stage in the benchmark are performed, if the moisture content of the wood falls too fast, and the dry quality problem occurs, the temperature and humidity of the drying standard at this stage are indicated. The condition is excellent. The opposite is softer. Under the same conditions, drying the wood with a hard datum is shorter than drying the wood with a soft datum. So how to use these drying benchmarks flexibly is related to dry quality and drying cycle.

China's forestry industry standard "Technical Regulations for Sawn Timber Kiln Drying" (LY / T1068-92) recommended a total of 41 multi-stage moisture content drying benchmarks for 17 groups: the appendix of the "Wood Drying" (2nd Edition) textbook is listed in the appendix More than 10 multi-stage moisture content drying benchmarks: Some imported drying equipment specifications also give a certain number of multi-stage moisture drying benchmarks. These drying benchmarks are now available in domestic related companies "N-to universal reference and application. Now take the 35mm thickness of eucalyptus sawn timber as an example. The multi-stage drying benchmarks for reference are shown in Table 1, A, B, and C. And D. A dry basis hardness is higher than B, and so on. That is, A is the hardest dry basis, D is the softest dry basis, and B is a hard dry basis, and C is a dry BY. Benchmark.

For operators who are just beginning to contact wood drying production, they should try to refer to a relatively soft drying benchmark. For example, you can first refer to D or C which selects the dry basis. Do not directly select the dry reference A to prevent dry quality problems. For operators with a certain experience in wood drying production, reference can be made to the choice of drying standard C or B. If the drying quality is relatively high, the drying standard C can be selected: If the drying quality is required to be normal, and the moisture content of the wood is to be dried to the required value within the specified time, then the drying standard B can be selected. . For operators with rich experience in wood drying production, the drying standard A can be selected when selecting the wood drying standard, and the drying time can be relatively shortened.

Of course, the above situation is not absolute. It is most important to use the dry benchmark reasonably and flexibly. If the operator can observe the state of the dried wood frequently during the drying process of the wood and adjust the drying reference conditions reasonably according to the actual situation, it can sum up the dry basis suitable for the dry production of the wood of the enterprise, which guarantees the enterprise's The quality of wood drying is extremely beneficial to improve the economic efficiency of enterprises. The key to rationally and flexibly applying and adjusting the drying benchmark is to analyze the characteristics and laws of the dried wood. For example, the four levels of drying standards in Table 1 can be used to dry 35 mm thick eucalyptus sawn timber. For the sake of safety, the drying standard c can be selected. When the wood is dried to a certain moisture content stage, the wood does not have dry quality problems, but the drying speed is extremely slow. This indicates that the dry reference process strip at this stage is relatively soft. Refer to Table 1 for drying reference B. The dry baseline process conditions in the middle water phase stage adjust the dry baseline process conditions being performed. For example, when the actual moisture content of the wood is 23%, the process bar in the drying reference C with a moisture content stage of 25 to 20% is performed, the dry bulb temperature is 60 °C, and the dry and wet bulb temperature difference is 10 °C. If at this stage the wood does not come out during the drying process

Now that the quality of the drying problem is very low, the drying speed is extremely slow. It is considered that the dry bulb temperature is increased and the dry and wet bulb temperature difference remains unchanged. The basis for the increase in the dry bulb temperature can be referred to the dry bulb temperature value in the same moisture content stage in the dry reference B. The process condition for the same moisture content stage in Drying Reference B is a dry bulb temperature of 65. C The wet and dry bulb temperature difference is 10%. C. It is considered that the dry bulb temperature is increased from 60 ° C in the dry reference C to 65 in the dry reference B. C Increased dry bulb temperature by 5 °C may result in hard drying of the reference process conditions and lead to drying quality problems. The dry bulb temperature can be taken from 60 at this time. C is increased to 62-63 C, and the temperature difference between dry and wet bulbs remains unchanged. In this way, the drying speed can be appropriately increased, and the problem of dry quality can be ensured. If the wood drying process can be carried out smoothly during the execution of this dry reference process condition, it is reasonable to demonstrate that the adjusted dry reference process conditions are performed in the next drying cycle. The drying standard thus concluded is a dry reference process suitable for the company to dry the saw timber of this tree species. It should be noted that if the dry quality of the dried wood is observed after the dry bulb temperature is increased, the dry bulb temperature should be immediately lowered to the original state, indicating that it is not suitable to raise the dry bulb temperature. However, at this time, it is considered to increase the drying speed by appropriately increasing the temperature difference between the wet and dry bulbs. This is also a means for adjusting the drying reference process conditions.

Table 2 is a multi-stage drying benchmark suitable for 35mm thick eucalyptus sawn timber summarized in the actual production process of wood drying. The basis for the reference is the dry references B, C and D in Table 1.

2 Flexible use of dry gradient datum

Dry gradient datums are typically used in automatic control or wood drying equipment with a microcomputer automatic control system. The dry gradient datum is essentially derived from the multistage moisture content drying benchmark. For example, the four levels of drying benchmarks in Table 1 can be converted to dry gradient benchmarks by calculation as shown in Table 3.

As can be seen from Table 3, when the dry bulb temperature is constant, the value of the drying gradient G is large, and the drying reference process conditions are hard. It indirectly reflects the large IJ of the dry or wet bulb temperature difference value or the equilibrium moisture content value of the drying medium. Therefore, using a dry gradient reference wood drying equipment, the operator can easily and flexibly use the dry gradient reference if he understands and masters the adjustment and flexible application of the multi-stage drying reference. Some foreign-introduced drying equipment provide users with relevant dry gradient benchmarks for reference. Taking the 35mm thick eucalyptus sawn timber as an example, the dry gradient reference is shown in Table 4.

It can be seen from Table 4 that the foreign related drying standards are softer than the domestic related drying standards. The drying cycle is generally long. This provides a large space for the operator of the dry coal plant to flexibly adjust the drying reference depending on the state of the dried wood. For example, when using Drying Benchmark A in Table 4, the actual moisture content of the dried wood has reached a ball temperature equal to 55 ^. C and dry gradient are equal to 2.4. However, if it is observed that the dry wood does not have dry quality problems and the drying speed is slow, you can increase the dry bulb temperature (such as increasing to 58 C) or increase the drying gradient (such as increasing to 2.6 or .27). The method adjusts the drying baseline conditions at that stage to speed up the drying process. The dry bulb temperature and drying gradient at each stage of the entire drying standard can be adjusted according to the above principles according to the specific conditions of the dried wood. If the operator can flexibly adjust the drying standard according to the characteristics of the drying equipment and the state of the dried wood in the wood drying production, the drying speed can be improved and the drying cycle can be shortened under the premise of ensuring the dry quality, so as to fully exert the effect of introducing the drying equipment. It has very positive practical significance.

It is extremely important to ensure the quality of the drying in the dry production of furniture. Under the premise of ensuring the quality of drying, minimizing the drying cycle will be the basic principle of dry production of wood. Therefore, the rational and flexible use and adjustment of the drying standard in the drying process of furniture materials has important positive significance for improving the production process rules of enterprise wood drying, exerting the drying production capacity of wood, and improving the product quality and economic benefits of enterprises.