General requirements for drying chambers. Production of painting and drying chambers for metal structures Construction of a convective type drying chamber for wood

These drying kiln requirements include:

Aerodynamics requirements:

In drying chambers, a uniform speed of air circulation through the material must be ensured.

The speed depends on the species and thickness of the boards being dried. For thin boards made of fast-drying wood, high air circulation speed (2.0-2.5 m/s) is effective. For thick boards, and especially difficult-to-dry species, the speed can be reduced by half without reducing the productivity of the drying chambers(the quality will be higher than with a high circulation rate). Thus, in order to effectively carry out the drying process, it must be possible to regulate the air circulation speed with at least a 2-speed motor. Note that low speed is necessary when drying fast-drying rocks (drying from 18 to 20% to final moisture content).

If the drying chambers do not provide for regulation of air volume, then this process can be controlled using gaskets. However, this will inevitably lead to a 10-15% decrease in productivity.

Requirements for fencing:

Fences must be airtight.

Have reliable internal moisture insulation.

Have optimal thermal protection with a heat transfer coefficient of at least 0.3-0.4 W/m2 0C. This requirement is due not only to saving thermal energy, but also to the need to maintain drying conditions.

Requirements for thermal equipment:

- Drying chamber must have sufficient thermal power to raise and maintain the temperature at a given level.

Heaters must be made of stainless materials.

Requirements for chamber ventilation:

The ventilation of the chamber must ensure stable parameters of the supply air both in summer and in winter (the air must enter the chamber at a positive temperature). This is achieved by using air parameter recovery systems in the chambers - recuperators. When using chambers without recuperators in winter, productivity is reduced by 20-40%. The reason is that the incoming cold air not only condenses moisture (which is the reason for the increase in drying time at the first stage), but also negatively affects the quality of the drying itself. If the use of recuperators is impossible for some reason, then it is necessary to organize a forced exhaust of exhaust air in the chamber, and organize an influx from the room.

Requirements for process control and regulation systems:

The chambers must be equipped with a psychrometric climate control system. It should be noted that the worst results are shown by the UGL system - control of temperature and equilibrium moisture content of wood, which is equipped with many imported dryers. Studies have shown that the adequacy of the readings of this system is worse than that of the psychrometric one. This means that the drying regime is disrupted and, as a result, negatively affects the quality of dried lumber.

The chambers must be equipped with a system for monitoring the current moisture content of the wood, since the common division of the drying process by time brings the worst results.

The process must be controlled automatically.

In conclusion, we note that the Department of Woodworking Technologies has accumulated extensive experience in the reconstruction and development of projects for new dryers, examination of imported equipment, improvement of technologies and organization of drying shops, which can be very useful for production workers.

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According to marketing research, the number of Russian companies whose production cycle is related to wood processing has grown beyond 16 thousand. In this list you can find both large holdings and small companies and handicraft industries. Despite the differences in profile, quality of products produced and production volumes, a clearly noticeable common feature is the profitability of production. The high efficiency of capital investments in woodworking production encourages entrepreneurs not previously connected

Forestry and woodworking are one of the industries in which business efficiency most depends on the correct choice of equipment. A novice entrepreneur or manager often gets lost in the catalogs of companies that sell a huge amount of different equipment for logging and wood processing. Hand saws, sawmills, drying chambers, various machines. However, you don't have to buy it all in one fell swoop. After all, different machines are designed for certain operations.

Today, quite a lot of men are engaged in carpentry, as it is not strange for most of them this is a hobby. Of course, for carpentry you need a whole set of tools, but for more professional work you need a bench machine. It allows you to make from wood almost any thing or object that will later serve as decoration or even be needed in the household.

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Mobile filter for air purification during welding, plasma and laser cutting of metals, as well as for aspiration of workplaces with “spot” dust. The filter is equipped with a pneumatic cleaning system for filter cartridges; it does not require an external compressed air supply, because pneumatic cleaning is carried out from the built-in compressor. The fan is installed in a noise-attenuating chamber.

When choosing drying equipment, it is necessary to take into account the requirements for drying quality, climatic operating conditions of the drying chambers, volumes of dried material, personnel qualifications and many other factors. It can be unequivocally stated that not any equipment, even imported, will provide an effective process for the specific conditions of a particular enterprise.

Let's consider a number of fundamental requirements for drying chambers, which should help manufacturers both when choosing drying equipment and when reconstructing existing drying chambers and building new ones.

Requirements for aerodynamics of drying chambers

In drying chambers, a uniform circulation rate of the drying agent (air) through the lumber must be ensured.
The speed of air movement through a stack of lumber depends on the species and thickness of the boards being dried:

• For thin boards made of fast-drying wood, a high circulation speed of 2.0-2.5 m/s and higher is effective, in some cases reaching up to 5 m/s.
• For thick boards and especially hard-to-dry rocks, the speed can be reduced by 2 times without reducing the performance of the chambers, and the quality will be higher than at high speed. Thus, in order to effectively carry out the drying process of difficult-to-dry rocks, it must be possible to regulate the speed of the drying agent with a 2-speed motor.

Requirements for fencing of drying chambers

The enclosures of drying chambers must be sealed, that is, there should be no unorganized heat and moisture exchange with the environment. Particular attention should be paid to the doors of the drying chamber. The door of the drying chamber must prevent heat from escaping from the chamber and must completely seal the doorway, maintaining the temperature and humidity conditions inside.

Drying chamber enclosures must have effective thermal protection (insulation) with a heat transfer coefficient of no more than 0.3-0.4 W/m² ºC.

This requirement is due to a greater extent to the need to maintain drying conditions, and not just to save thermal energy.

Requirements for thermal equipment

The drying chamber must have sufficient thermal power to raise and maintain the temperature at a given level.

Requirements for the air exchange system of drying chambers

Air exchange refers to the removal of moist air from the chamber and the simultaneous influx of fresh air into the chamber. The cross-section of the air exchange channels (supply and exhaust) is calculated depending on the volume of the material being dried.

Requirements for control and regulation systems of the drying process

Drying chambers must be equipped with a psychrometric climate control system.
The worst results are shown by the UGL system - control of temperature and equilibrium moisture content of wood. Studies have shown that the adequacy of the readings of the UGL system is worse than that of the psychrometric system, which means that the drying regime is disrupted and, as a result, negatively affects the quality.

Structurally, the UGL sensor is a plate made of limb wood or cellulose fixed between two electrodes. Based on the value of electrical resistance adjusted for temperature, the equilibrium moisture content of wood in a given climate is predicted.

The chambers must be equipped with a system for monitoring the current wood moisture content. Process regulation should be carried out automatically.

The technological process of drying lumber in batch chambers includes the following stages (operations):

1. Preparing the camera for use.

2. Formation of a drying stack of lumber.

4. Warming up the chamber and carrying out the actual drying according to the specified mode.

5. Carrying out moisture and heat treatments.

6. Conditioning of lumber (if necessary).

7. Cooling of the material and rolling out the stack.

Preparing the camera for use

Preparing the camera involves clearing it of debris and checking that the equipment is in good condition.

Check the dampers of the air exchange channels; they must completely block the channels. The chamber door must provide a tight seal. The performance of the actuators is checked, and the psychrometer and fans are also subject to inspection.

The condition of the fan unit, remote control devices and automatic temperature and humidity control are periodically checked.

Formation of a drying stack of lumber

The formation of the drying stack is carried out using an elevator.

When forming a drying stack, the following basic requirements must be met:

Unedged boards are laid in a row with their butts in different directions, alternately with outer and inner faces;

wide boards - along the edges of the stack, narrow in the middle;

the ends of the stack must be leveled;

The stack is formed from lumber of the same thickness and type;

Lay boards of lower grades on the top rows of the stack;

Inter-row spacers - calibrated, 25x40mm stack width, made of healthy coniferous wood, humidity? 18 %;

the distance between spacers in a row along the length of the stack (step) for soft coniferous species is recommended equal to 20 times the thickness of the board (W = 20 T);

The outer gaskets are flush with the ends of the stack;

To load the stack into the chamber, stackable rail carts are used.

Loading cameras

From the stack formation area, the stack is transported to the chambers using a traverse trolley: from the elevator, the stack rolls along the rails onto the traverse trolley, the traverse trolley moves to the chamber to be loaded and rolls from the traverse trolley along the rails into the chamber.

Warming up the chamber and drying

After preparing the chamber for operation and eliminating any identified faults, gradually warm up the chamber and turn on the fans.

The first technological operation after loading the chamber is the initial moisture-heat treatment (warming up) of the wood. To create the required temperature and humidity environment, coolant is supplied to the chamber and, if necessary, the valve of the humidifying pipe is opened. The air exchange channels of the chamber are closed at this time. The duration of heating of coniferous boards is within 1.5 - 2.0 hours for each cm of board thickness.

Drying parameters

After warming up, the drying parameters are set by lowering the dry temperature and increasing the difference between the dry and wet thermometers. To do this, you need to close the supply valves to the humidification pipe and slightly open the dampers of the air exchange channels in order to throw out some of the moist air from the chamber and supply fresh air into the chamber. Continue this operation until the required values ​​(indicators) of the dry and wet thermometers are established according to the drying mode.

The drying mode is selected depending on the species and cross-section of the lumber in accordance with GOST 19773-84.

To relieve stress in the wood that arises during the drying process, intermediate and final moisture-heat treatments can be carried out. At the same time, is the temperature of the environment in the chamber maintained? 8 0 C above the operating temperature. The degree of air saturation with steam must be at least 95%.

End of drying. After moisture-heat treatment, the lumber is kept for 2 - 3 hours at the parameters of the last stage of the regime to dry the surface layers.

Then the water supply to the heaters is stopped, the fan is turned off and the unit is cooled to 30 0 C, while the supply and exhaust ducts are open, and then the chamber doors are opened slightly. Cooling time within 1 hour for each cm of material thickness.

It is prohibited to roll out an uncooled stack of lumber from the chamber!

Dried lumber should be stored only in a heated room. For this purpose, the workshop has a storage area for dry lumber.

Dried lumber is rolled out onto the rail tracks from the chamber using a winch on a traverse cart and a cable block system, then packages of lumber are transported using a traverse cart to the dry lumber storage area.

For long-term storage, lumber is placed in tight bags and the ends are covered. This operation can be performed using an elevator.

Transportation of packages of dry lumber for further processing is carried out using a traverse trolley.

Wood products that meet modern requirements can only be obtained from specially selected and prepared raw materials. The humidity indicator becomes decisive in this situation. It takes a long time to bring natural material to the desired condition using the natural method. Depending on the breed, this can take up to several to several decades. If you use a wood drying chamber, the time is significantly reduced. Large production associations have been using such equipment for lumber for a long time.

For small companies, individual entrepreneurs and home craftsmen, this issue becomes relevant, since boards and timber with natural moisture are much cheaper, but they are not suitable for the production of high-quality products. Waiting for the wood to dry naturally is too long. When choosing a method of forced high-quality drying, the question arises whether to purchase ready-made chambers or make them yourself. But first of all, it is necessary to understand the theory, principles and features of this operation.

Experience has shown that the process of removing moisture from lumber will be effective if the general rules are followed. They are determined by the following criteria:

• Drying chambers must meet performance and safety standards;
• Strict adherence to drying regimes;
• Correct placement and fixation of workpieces, eliminating warping and cracking;
• Control at all stages of the operation, from preparing raw materials to unloading wood from the chamber.

If the wood dryer is made by yourself, then test drying should be carried out to ensure compliance with industry standards. This will make it possible to adjust the operation mode for a specific device. The basic parameters are the initial moisture content of the wood, the thickness of the timber, boards, and species. According to the rules of the procedure, the drying speed is determined. Deviations are not desirable. Forcing the operation by increasing the temperature will lead to changes in the color of the array and deterioration in performance.

A typical mistake is the incorrect laying of lumber. While in the wood drying chamber, the workpieces undergo structural changes and strong internal stresses arise. When laying, it is necessary to forcefully fasten the material. The boards are laid out tightly to the base and spacers between them for free air movement. Distortions and deviations from the flat plane of each workpiece are eliminated. Otherwise, drying wood can hopelessly damage the lumber. High-quality products will no longer be possible.

Forced air supply significantly speeds up the process. Drying technology has been developed by several generations of craftsmen, and the accumulated experience shows that neglect of the rules causes unnecessary costs, increased cost of the final product and a decrease in its quality.

Wood moisture content

To determine the processing mode, it is necessary to check the lumber according to basic indicators. These include species, board thickness and humidity. Drying fresh wood is more difficult. In addition to high humidity, conifers produce resin and a significant shrinkage rate. In such cases, the operation is carried out in two stages with different modes. Pre-drying to 20%, then subsequent drying to the desired value, usually 8-12%. This amount of moisture during the manufacturing process of a product is considered acceptable.

It is impossible to bring the workpiece to lower humidity values, with the exception of special cases of preparing wood with special qualities. An overdried tree begins to absorb moisture from the air, the product swells, changes its geometry until the finished structure is partially or completely destroyed. It is recommended to stop the process when the recommended values ​​are reached. A wood dryer must be equipped with humidity control devices.

Why is drying needed?

When performing construction work and in furniture production, the design and estimate documentation indicates the permissible moisture content of wood. Raw materials are brought to the required condition in drying chambers of various designs. For certain operations in construction, a humidity of 20% is allowed. Furniture is made from 8-10% solid wood. The values ​​are determined taking into account possible changes in structure and geometry during further operation. Workpieces that have not been brought to the required characteristics by drying cannot be used in production.

Wood products are mostly used indoors, where humidity is lower than natural outdoors. Significant changes in dimensions and the occurrence of stress in the product due to drying are inevitable. Cracks and warping that appear impair the appearance and performance characteristics of the finished product. It is not cost-effective to remove moisture in a natural way on an industrial scale, since the raw materials will have to be procured several years before their use. Only a dryer for boards and other lumber can quickly and efficiently remove excess moisture and make the material suitable for producing high-quality products.

Drying modes

The effectiveness of drying directly depends on the composition of the air, its humidity and temperature. It’s not worth experimenting with time and temperature without experience, as you can ruin the workpiece. The following values ​​​​of the normal drying mode for a 40-50 mm board in a convective type chamber can serve as a guide:

• Beech, maple, larch. Temperature 60°C. Drying time at humidity > 35% is at least 130 hours, at 20-25% - about 40 hours;
• Oak, ash, walnut. Temperature 50°C. Drying time at humidity > 35% is at least 255 hours, at 20-25% - 95-100 hours;
• Alder, birch. Temperature 60-65°C. Drying time at humidity > 35% is at least 90 hours, at 20-25% - 30-40 hours;
• Pine, cedar, spruce, fir. Temperature 70°C. Drying time at humidity > 35% is about 70 hours, at 20-25% - at least 30 hours.

Pre-drying of wood with excess moisture content of more than 60% is carried out in a forced mode, increasing the temperature by 10-20%. Deciduous ones can be dried at higher temperatures than coniferous ones.

DIY drying chamber

If you decide that you are making the dryer yourself, then you should know the main structural elements, their purpose and installation or construction methods. In this case, only those materials are used that can withstand the upcoming loads. Conventional building materials cannot be used. Drying chambers for lumber consist of the following elements:

A room equipped with a thermal insulation system;

Heat sources;

System of forced air supply to the processed material;

Equipment for laying workpieces;

Shipping and loading system;

Devices and tools for controlling humidity and temperature.

Various devices are used as heat sources. Electric heating elements that consume significant amounts of energy. Gas burners are considered more efficient. Sometimes boiler equipment is installed that has high efficiency indicators. The easiest way to make drying chambers for lumber is the convective type. It is difficult to independently assemble an aerodynamic or microwave structure without certain knowledge and skills.

Selection of premises

Choosing the right place for drying will guarantee the effectiveness of the design. You can use either an existing premises or a building erected specifically for this purpose. It must meet the following conditions:

• Thermal insulation. The temperature difference inside and outside the dryer is significant, and in order to maintain it at the required level, heating devices are turned on. Ideally, walls and insulation should have energy efficiency ratings similar to those of a residential building. Thermal insulation layer is made on the walls, floor, ceiling. In this case, the heating devices are turned on for a short period of time during critical temperature drops, and the rest of the time they are turned off, which significantly saves energy consumption;
• Ventilation or dehumidification of air by convection along the internal circuit. Timely removal of moisture will be the key to reducing drying time, so effective ventilation or condensate collection on a cold heat exchanger is necessary in the room. When designing a dryer, this aspect should be emphasized;
• Safety. The electrical circuit, instruments and mechanisms are taken from samples intended for operation at high humidity and temperature, for example, from equipment for the construction of saunas and baths. Fire safety requirements, protection of human health and life must become a priority.

The operating principle of the wood camera is not complicated. But it can only be implemented in a suitable room. The costs of erecting and re-equipping the chamber are one-time. If all requirements are met, then in further operation the dryer, with minimal energy and maintenance costs, is able to produce the required volume of dried wood within the stated period with the desired percentage of humidity.

Construction and installation of drying chamber equipment

There are ready-made cameras on sale with excellent performance characteristics, but their cost may not be recouped even over many years with small production volumes. The choice of small companies and individual entrepreneurs often falls on independent construction of the desired structure. The design of a convective type drying chamber is simple. You can use an existing room or building, which is equipped with the devices, instruments and mechanisms necessary to solve the problem.

It should be remembered that the connection of gas equipment must be carried out by authorized organizations. The electrical circuit is designed by a qualified electrician, taking into account the use of equipment at elevated temperatures inside the chamber. Devices, cables, fans, lighting sources are marked with markings indicating the appropriate temperature and humidity conditions of operation. The premises belong to the category with increased fire danger. Fire extinguishing systems are provided at the design stage to avoid problems with regulatory authorities. The design capacity is consistent with the resource supply capabilities. In some areas there are restrictions on the supply of gas and electricity.

Equipment

The set of equipment is small, but requires careful selection when purchasing. The design of the drying chamber, in addition to the standard set of heating element, forced air supply systems can be additionally equipped with devices that increase productivity and automation systems. Temperature sensors included in the circuit can turn on or off the heat source in a timely manner, without human intervention. The equipment for drying chambers includes a device for collecting and removing condensate. High temperature is not enough to quickly remove moisture if there is excess moisture in the air. The cold circuit effectively traps water particles on the surface and is recommended to be installed to increase productivity. Improves performance and preheating of incoming air, which does not cool the processed lumber, thereby reducing drying time.

Drying chamber operation

Maintenance of the structure, when it is assembled correctly, does not seem to be a difficult process. Drying chambers are not recommended for storing, even temporarily, any foreign objects or goods. Cleanliness is maintained inside the premises. Regular cleaning is required. Removing dust, dirt, and sawdust is necessary, since sufficiently powerful air convection inside the chamber will inevitably lead to foreign substances entering the heat sources, which will reduce their performance, and in the case of using electric or gas heating elements, to the risk of fire. Regular inspection of all structural elements is carried out: thermal insulation, ventilation, heat sources.

A classic woodworking production line necessarily has a wood drying section. Is this section perhaps the most difficult in the entire technological chain? from a tree growing in the forest to a finished product. Even firewood needs to be dried before burning.
At the same time, as experience shows, many enterprises are faced with serious problems.

High demands are placed on the quality of lumber drying. At the same time, in addition to visible drying defects (cracks, warping, etc.), which directly affect the cost of products due to an increase in the consumption rate of lumber, moisture quality indicators play an important role.

Fulfillment of such high requirements is possible only with a comprehensive solution of organizational, technical and technological elements of drying.
In this section we will look at drying techniques.

When choosing drying equipment, it is necessary to take into account the actual specification, drying requirements, climatic operating conditions of the dryers, drying volumes, etc. Efficient and technologically advanced equipment will conserve and save scarce and expensive raw materials.

Therefore, we can safely say that not any equipment (even imported) is capable of providing an effective process for the specific conditions of a particular enterprise.

In this regard, it is possible to formulate a number of fundamental requirements for drying equipment, which should help production workers both when choosing new drying equipment and when reconstructing existing chambers.

These requirements include:

Aerodynamic requirements:
The chambers must ensure a uniform air circulation rate throughout the material. Theoretically, the required speed depends on the type and thickness of the boards being dried. For thin boards made of fast-drying wood, a high air circulation speed is required (2.0-2.5 m/s). For thick boards, and especially difficult-to-dry species, the speed could be reduced by half without reducing the performance of the chambers. However, this increases the spread of humidity throughout the stack.
The quality will be higher with a high circulation speed with periodic cessation of circulation, which will also save heat and electricity.

Requirements for fencing:

• fences must be airtight;

  have a reliable internal vapor barrier;

  have optimal thermal protection with a heat transfer coefficient of no more than 0.5 W/m 2 *°C.

These requirements are determined not so much by saving thermal energy, but by the need to maintain drying mode parameters.

Requirements for thermal equipment:

• the chamber must have sufficient thermal power to ensure that the temperature rises and maintains at a given level;

  heaters must be made of stainless materials.

Requirements for chamber ventilation:
The ventilation of the chamber must ensure stable parameters of the drying agent both in summer and winter.

Requirements for process control and regulation systems:

• chambers must be equipped with a psychrometric system for monitoring the parameters of the drying agent;

  cameras must be equipped with a remote control system for the current wood moisture content;

  the automation system must have manual and remote control by regulatory bodies;

  the automation system should signal the degree of opening of the regulatory bodies;

  process regulation must be carried out automatically.

The difficulty lies, first of all, in controlling the drying process. If the processes occurring in wood during drying have been studied more or less well, then the problem of managing them remains relevant today. It should be noted that the worst results of all drying agent parameter control systems are shown by the UGL system of temperature and equilibrium wood moisture control, which is equipped with many imported drying chambers. Studies have shown that the adequacy of the readings of this system is worse than that of the psychrometric one. This means that the drying regime is disrupted and, as a result, negatively affects the quality of dried lumber.

So, what is a modern drying chamber?
More than 90% of the world's drying chambers are stationary structures equipped with fans, devices for directing flow, heating and controlling air humidity.

The temperature inside such a chamber usually, depending on the stage of the drying process, ranges from 40°C to 100°C. Moreover, the temperature and humidity of the air in the chambers are controlled by automatic systems, which include devices for measuring the parameters of the drying agent in the chamber and the parameters of the moisture state of the wood. Controlling the drying speed is designed to minimize or completely eliminate defects caused by drying.

Heat sources in modern chambers are usually hot water, electricity or steam. The use of electricity to heat dryers is very limited due to its high cost. It is usually used when no other heat sources are available. The use of steam is also limited due to the high cost of equipment and fittings, as well as difficulties in dealing with government inspections.

The air flow in the chamber is formed by fans installed in special channels. The direction of the air flow is periodically changed to ensure uniform drying of the entire stack.

In order to control the air humidity in the chamber, and ultimately the rate of drying of wood, supply and exhaust ventilation and a humidification system are used. All these devices are controlled by an automatic control system for environmental parameters. It can maintain the necessary environmental parameters in the chamber without human intervention. Such systems allow you to document the entire drying process and carry out primary quality control.

Control of the drying process must be correct, fairly simple, easy to install and, if possible, must take into account the variety of initial data (type of wood, its initial humidity and temperature, etc.) and emergency situations.

In conclusion, we note that the Uraldrev-SKM company has accumulated extensive experience in the reconstruction and development of projects for new dryers, improving the technology and organization of drying shops, which can be very useful for production workers.

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