Solid wood flooring is usually made of hard broad-leaved tree villages, and medium and high-grade real flooring is mainly made of high quality imported materials. A more reasonable production method is to first process the logs into semi-finished products of floor slabs at the place of origin, and carry out wax sealing at the end of the board to prevent end cracking, and then sell them to the floor processing factory for artificial drying, and then process them into finished flooring.
Artificial drying is an important part of ensuring the quality of solid wood flooring. The purpose of drying is mainly to stabilize the wooden floor shape, so that it will not shrink, swell and deform in the future use, and also improve the processing performance, performance and durability of the solid wood floor. The key to the quality of the drying is that the final moisture content must reach an equilibrium moisture content slightly below the environment of use. It is about 10% to 12% in the south of China, about 8% to 10% in the north, and about 6% to 8% in the northwest, and it must be dry and ensure that the non-warping, cracking and drying stress are basically relieved.
Dry quality and drying cost are generally mutually restricted, but with reasonable drying equipment, reasonable drying process and proper operation, the drying cost can be ensured while minimizing investment and drying costs. .
Due to the variety of wood drying methods and drying equipment, the products sold in the market are mixed. To help the wood flooring enterprises to purchase the drying equipment reasonably, this article is written for the reader's reference.
1 Common wood drying methods and their applicable conditions
Commonly used wood drying methods include: steam heating, conventional drying, furnace gas heating, conventional drying, hot air drying, dehumidification drying, vacuum drying, and conventional drying of hot water and high temperature water circulation heating in recent years. The appropriate drying method must be selected according to the dry characteristics and requirements of the real floor, as well as the size and conditions of the company.
1.1 Steam heating conventional drying
The method is a conventional drying method for drying wood by using a saturated water vapor having a gauge pressure of P <= 0.4 MPa and heating the drying air in the crucible by a heater to dry the medium. The advantage is that the process parameters are easy to control, the drying quality is generally good; the temperature and humidity can be adjusted in a wide range, and various materials can be dried; and the heat can be concentrated and the application is relatively common. The disadvantage is that steam boilers are needed, and the investment cost is high; the method mainly utilizes the latent heat of vaporization of steam, and the condensed water is often not used, resulting in waste and increased cost. It is mainly suitable for the production of large-scale or ready-made steam for use, especially for dry softwood and soft hardwood or thin plate. For medium and small wooden flooring companies, this method is not suitable for expensive steam boilers.
1.2 furnace gas heating conventional drying
This is a conventional drying method for wood that is heated directly or indirectly with burning wood. Drying of the directly heated furnace gas will blacken the wood and cause fire, so it is almost never used. There are many ways to dry the indirect heated furnace gas: 1 Simple fire type: The stove and the furnace gas pipeline are arranged in the underground of the fire room, and the material pile is placed in the fire chamber, which is naturally circulated and dried by the hot and humid air flow. This is a relatively primitive method of drying the soil, often causing the wood to bake or fire. It is not recommended. 2 small furnace oven type: This is a small dryer with a wood waste burning furnace and its furnace gas pipe and simple fan on the side of a metal shell similar to a container, which can hold 2 to 5 cubic meters of wood. The drying method also has safety hazards, which are easy to roast wood or fire, and the air circulation is unreasonable and the drying is uneven. It is not recommended. 3 Modern furnace gas indirect heating and drying kiln: There are furnace gas heating tube sets with reasonable design and arrangement. The other configurations are the same as those of general drying kiln. In the case of such a kiln designed by experts, safety and reliability are guaranteed. The special burners of this type of kiln can be located outside the kiln or in the kiln. The former is relatively safer, but the cost and heat loss are relatively high.
Furnace gas heating conventional drying does not require a steam boiler, and uses wood waste energy, low investment costs, and low drying costs. However, it is difficult to adjust the temperature and humidity, and the quality of drying is not easy to guarantee. If the design of the drying kiln is not good, it is also easy to bake wood and fire. For medium and high-grade solid wood flooring, this drying method should be used with caution.
1·3 hot air drying
The hot blast stove for heating is located outside the kiln, and is connected to the drying kiln by inlet and return pipes. The air drying medium is heated by the return air duct to the hot blast stove outside the kiln, and then sent back to the kiln by the air blower, which is a conventional drying of the air flow double cycle. The shortcomings of this method are low heat utilization rate; large power consumption; uneven distribution of temperature and humidity fields in the kiln, difficult adjustment of process parameters, slow and uneven drying speed; easy return to the return air duct and blower; small capacity of the drying kiln The output is higher than the cost. It is not recommended.
1.4 Dehumidifying and drying
The method of drying the wood by gradually dehumidifying and drying the air drying medium in the kiln by using a dehumidifier field called a heat pump. The dehumidifier can only work in the set temperature range to have the dehumidification effect. The working temperature of the ordinary dehumidifying dryer does not exceed 55C, and the working temperature of the medium temperature dehumidifying dryer does not exceed 65 C. The advantage of this method is that the use of electrical energy is not polluted; it is easy to operate, and the drying quality is generally good. The disadvantage is that the use of electric energy drying has high cost; the drying time is long and the productivity is low; the dehumidifier is prone to failure, the maintenance cost is high, and the service life is short; there is no humidity control device, and the drying stress cannot be eliminated. Since the drying power mainly relies on lowering the relative humidity of the drying medium instead of increasing the temperature, the effect is more obvious in the high moisture content stage or in the dry and dry tree species, but not in the low moisture content stage or the dry and difficult dry species. However, drying dry tree species by this method or when the water content is high, it is too slow to dry, sometimes causing wood mold. Wood flooring companies are advised not to use unless the production is low and there are special requirements for environmental protection.
1·5 vacuum drying
The dried wood is placed in a sealed container, and after preheating, the air in the container is taken out to dry the wood under a certain negative pressure condition. The method is quick to dry and the quality of drying is not easy to guarantee; the load of the dryer is small, the equipment is complicated, the investment cost is high, and the electric energy is used, and the drying cost is high. Only a small amount of difficult villages, when using conventional drying time is too long, vacuum drying is feasible. General wood flooring companies do not recommend it.
1.6 Conventional drying of hot water or high temperature water circulation heating
This method was developed by the author in 1996-1997 and was manufactured and operated by Nanjing Yunsong Drying Equipment Co., Ltd. It has become a very popular wood drying method in China, especially suitable for small and medium-sized enterprises. . The hot water circulation heating adopts an improved heat pipe normal pressure steam and water boiler matched with the drying kiln, and can burn the processing residue such as wood chips, shavings or block wood waste. The hot water with t=95-100CC is used as the heating medium for circulating heating. The reasonably designed heating system can make the drying temperature reach 70-75 °C. This is the proper drying temperature range for hardwoods. The atmospheric pressure steam with P=0～0.04MPa can meet the process requirements of the humidity control treatment. Semi-automatic control of temperature and humidity and automatic detection of moisture content. The hot water has high heat content, stable temperature, easy control of the process, and guaranteed drying quality. The atmospheric pressure hot water boiler has low cost, is safe and reliable, and is easy to operate. Hot water circulation heating not only saves water but also recovers hot water waste heat, and simplifies soft water treatment equipment. The use of wood waste energy, not only waste utilization, greatly reduces drying costs, but also greatly reduces environmental pollution. In short, the method has the advantages of both steam heating and furnace gas heating, and at the same time discards the shortcomings of both, and is the most ideal drying method for solid wood flooring and furniture materials, especially suitable for small and medium-sized enterprises.
The high temperature water circulation heating adopts the B grade wood waste heat pipe hot water boiler, the hot water circulation system operates under the pressure of gauge pressure P=0.3MPa, and the water temperature is controlled t<=115°C, the drying temperature in the kiln can reach 95°C. Suitable for dry softwood and soft hardwood. The key to this method lies in the pressure-preserving measures of the system. It must be ensured that the saturation temperature of the hot water is about 30 °C higher than the actual temperature to avoid cavitation of the circulating hot water pump.
2 How to choose the type of drying kiln
The types of wood drying kiln mainly include upper fan type, end fan type and side fan type. The kiln type is different, and its structural characteristics and applicable conditions are also different.
2.1 Upper fan type drying kiln
Fans and heating and temperature control equipment are placed above the kiln. If the equipment is arranged horizontally and the longitudinal direction of the airflow is reversible, it is a kiln-type upper fan type kiln for forklift trucks. The piles are horizontally mounted. It is suitable for drying in whole villages with uniform length of wood and no more than 3m. If the wood is too long or has different lengths of burrs, the equipment should be arranged longitudinally, and the airflow should be horizontally reversible and the locomotive type kiln type fan kiln is placed on the railcar. The upper fan type kiln has good circulation effect and uniform drying, and is the most widely used kiln type. The loading capacity of the forklift kiln is usually 50 cubic meters to 100 cubic meters, and the kiln is too large to make the wood dry unevenly. The loading capacity of the rail car kiln can range from 80 m cubic meters to 200 cubic meters, depending on the length of the kiln. For the drying of solid wood floor billet, because the wood is short and the pile is small, it is reasonable to choose a forklift kiln type fan type kiln with a loading capacity of about 60 cubic meters, which can ensure better drying effect and economic effect.
2.2 End fan type drying kiln
Ventilation equipment and heating and humidity control equipment are installed at the rear end of the kiln, and the airflow is reversibly reversible before and after the airflow. The kiln is used to dry the real floor slab, and the kiln can be installed by a forklift, but the longitudinal direction of the wood must be consistent with the longitudinal direction of the kiln. The length of the kiln drying room should not exceed 6m. The load can be 30 cubic meters to 70 cubic meters. Compared with the upper fan type kiln, the kiln has a simple structure and convenient maintenance, but the floor space is large and the drying uniformity is poor. Suitable for smaller companies.
2·3 side fan type kiln
The fan and the heating and humidity control equipment are installed on the side of the kiln, and the next lateral unidirectional circulation or the lateral one-way circulation is performed on the airflow, and the wood is longitudinally loaded into the kiln. The disadvantages of this type of kiln are uneven drying, low energy utilization and large floor space. This type of kiln has been used less frequently, but can be designed as a small experimental kiln. It is not recommended. 3 Other matters to be aware of when purchasing drying equipment
3.1 should pay attention to brand, reputation and service
Wood drying equipment is one of the main equipments for the production of solid wood flooring, and its quality directly affects product quality and production costs. Like other commodities, wood drying equipment also has many counterfeit and shoddy products. The current drying equipment market is coexisting with large and small companies and family workshops and couples. Some drying equipment suppliers know nothing about wood drying technology. They only use the hoist to imitate other people's products, but they don't know their structural principles and key technologies. They also cut corners and shoddy materials, so that the performance of the equipment is not guaranteed, and there are security risks. It is not able to provide reasonable drying technology, good technical training, technical consultation and after-sales service. To ensure the quality of drying, to avoid or reduce the loss of reduction, and to reduce the cost of drying, in addition to good drying equipment, there must be a reasonable drying process and correct operation. Therefore, brand equipment with professional involvement of wood drying experts, research and development capabilities, good reputation and good service should be selected.
3.2 Pay attention to equipment configuration and performance quality
The price of the drying kiln is directly related to its equipment configuration and performance quality. Should pay attention to the following issues: 1 should use precision cast twisted airfoil blade reversible cast aluminum fan, with H-class insulation of high temperature motor, the performance parameters and number of fans should be calculated through the gas flow rate of the pile Not less than 2 m/s, the total width of the pile through which the airflow passes shall not exceed 5 m. 2 The heater should be a rolled bimetallic finned tube, preferably a steel-aluminum composite finned tube. The heating system should be configured so that the drying temperature meets the process requirements: the drying temperature of hot water heating should be at least 70C, the heating of high temperature water should be at least 90C, and the heating of steam should reach 100C. The piping system should not accumulate water when it is not working. The boiler shall have a safety permit, and there shall be dust removal and descaling measures. The boiler for burning wood chips shall have measures to prevent the grate from overheating, and prevent the wood chips from leaking from the bottom of the furnace from burning out the grate. 3 The steaming system does not accumulate water, the steaming pipe is evenly distributed, and the inlet and exhaust devices should have airtight measures to ensure that the cooling and moisturizing are sensitive, uniform and reliable. 4 The drying kiln should be able to ensure airtightness, heat preservation, corrosion resistance and crack resistance. Steel or color steel plates or galvanized sheets cannot be used for interior equipment such as ceilings, inner walls, kiln doors or intake and exhaust devices. Do not use polystyrene composite color plates to make kiln doors or kiln bodies. 5监测 The monitoring and control of internal temperature, humidity and wood moisture content should be sensitive and reliable. The electrical and drying process control system and each actuator must be designed reasonably, reliably and durable. All wires in the kiln are made of high temperature resistant wires.
3·3 Determination of the number of drying kiln
Once the drying kiln has been selected, the number of drying kilns required can be estimated as follows:
Drying kiln quantity = drying cycle X monthly output (cubic meters) / 30 × per kiln solid material (m3)
The drying time of the real floor slab varies with the tree species and the initial moisture content, which is about 6 to 12 days, and can take an average of 9 days. The auxiliary time for loading and unloading the kiln is 1 day, that is, the drying cycle averages about 10 days.
In the actual volume of the drying kiln, the actual material volume of the standard material must be converted into the actual volume of the floor blank. If the actual volume of the drying kiln is calculated according to the scm thick edge board, for 2. Zcm thick floor blanks are 2. When the scm is thick, the correction factor of the actual volume is (2.2 + 2.5) / (5 + 2.5) = 0.63.
Weng Wenzeng (Nanjing Forestry University)
Water-saving Makeup Cotton
Water-Saving Makeup Cotton,Makeup Cotton,Dry Wet Cotton Pads,Wet Cotton Pad
COTTONWHISPER (TAIZHOU) DAILY PRODUCTS CO.,LTD , https://www.zjcosmeticpuff.com