Why is veneer dryer hot but not drying

Before we talk about this problem, let's take a general description of theveneer dryer.

The veneer dryer is a continuous veneer drying device, and each veneer dryer includes a drying section and a cooling section. The drying section is mainly used to heat the veneer, and the water evaporates. It circulates through the hot air to discharge water from the veneer. Generally, the length of the cooling section is fixed, and the length of the drying section is varied according to the customer's required capacity. The longer the length of the drying section, the higher the amount of the dried veneer and the higher the amount of heat consumed. . The cooling section blows the external normal temperature wind to the veneer through the fan. The cooling of the veneer can eliminate the stress inside the veneer and make the veneer flat. On the other hand, the veneer surface layer and the core temperature gradient can be used to evaporate a part of the water. In order to obtain the final moisture content of the veneer that meets the needs of the product.

Below we talk about the main factors affecting the drying of veneers:

1.Effect of drying medium

The hot air temperature is an important factor affecting the drying speed of the veneer. As the temperature increases, the evaporation rate of the surface of the veneer increases, and the speed of moisture movement inside the veneer also accelerates accordingly. Usually, the veneer dryer uses a high temperature of 100-200 ° C to dry the veneer to accelerate the evaporation of water. Under the action of high temperature, as the water inside the veneer evaporates, there is a large amount of water vapor inside the dryer. The relative humidity of the circulating air is large. When the water vapor is saturated, the veneer can no longer evaporate water to the hot air. The vent hole should be opened to reduce the relative humidity of the air (the relative humidity of the air is too high to reduce the drying speed. If the relative humidity of the air is too small, the heat will be lost. Generally, the relative humidity of the air in the dryer is 10-20%).

The wind speed of hot air has a great influence on the drying time. When the wind speed exceeds 2m/s, it has little effect on the irritating speed. If the wind speed continues to increase, the power consumption will increase, and the increase of the fan motor load will affect the life of the motor and accelerate the aging of the equipment. Therefore, the hot air wind speed required by our veneer dryer is 1-2m/s, but for the jet veneer dryer, the jet airflow must have sufficient speed to effectively destroy the critical layer on the surface of the veneer. In order to accelerate the evaporation of water, the faster the better, the wind speed is generally 15-20m / s.

2. Impact of the veneer itself

The material used for the veneers is different and the drying time required is different. The higher the material density of the veneer (usually referred to as hardwood), the greater the moisture resistance in the low moisture content range, and the slower the drying speed of the veneer. At the same time, the structure of the single-plate material also has an effect on the drying speed. For example, the ash having a density of 0.69 g/cm3 has a large ring hole and a rough material, so that the water conductivity is strong, so the evaporation time is fast.

The initial moisture content of the veneer, the final moisture content required by the customer, and the thickness of the veneer all have an effect on the drying time. The higher the initial water content, the lower the final water content, the longer the drying time is required. The thicker the veneer is, the longer the time of moisture transfer inside the veneer during evaporation, and the longer the veneer will dry.

Through the above description, I believe that you have a preliminary understanding of the dryer. Let's look at the customer's problem now: Why is my veneer dryer heated but not dry? We analyze this problem according to the above description:

1、The hot air temperature does not reach the standard of drying of the veneer, so that the moisture inside the veneer does not completely evaporate. In this case, it is necessary to increase the steam temperature, check whether the boiler is running normally, whether the temperature is raised to the required temperature, or check the gas pipeline for damage.

2、The relative humidity of the air inside the dryer is too large. At this time, check if the dryer system is running normally.

3、Whether the hot air speed is up to standard. The wind speed does not reach the same level and cannot be completely dried. At this time, it is necessary to check the hot air fan system, whether the motor is running normally and is damaged.

4、The operation of the cold air zone is not normal, which will make the surface of the veneer retain moisture and cannot be volatilized, resulting in the final moisture content of the veneer not meeting the standard. At this time, it should be checked whether the cold air zone is running normally and whether the air cooler motor has a shutdown phenomenon.

5、The speed of the veneer in the dryer is too fast, so that the moisture inside the veneer does not evaporate. At this time, the single board transmission system should be checked to reduce the transmission speed.

6、Check whether the material, initial moisture content and thickness of the veneer match the working parameters set by the dryer. If it does not match, it is necessary to reset the working parameters of the dryer.

7、The high-quality veneer peeling machine also has a certain influence on the drying effect of the single-plate dryer. If the thickness of the veneer produced by the veneer production line is not uniform, the moisture content of each part of the veneer after drying is different, which will eventually affect the subsequent gluing process and hot pressing process. Under normal circumstances, the hot press cannot be solved. Plywood quality defects due to different moisture content in various parts of the veneer.

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