Freshly cut wood is not used in production and construction, as it contains a large amount of moisture. Such a tree is called wet. To improve its mechanical and physical characteristics, a drying chamber for lumber is used. In the process, biological resistance increases, the strength index increases, and other qualities of wood improve.
The concept of wood moisture
The percentage of the weight of the liquid contained in the mass of completely dry wood of a certain volume is called absolute humidity. The percentage of the mass of removed water (determined by two weighings) to the initial weight of the wood is called relative humidity.
The degree of suitability for use is determined taking into account the indicator of relative humidity. The value indicates the readiness of the material for gluing, shrinkage, with a value of over 30% there is a danger of the development of a fungal infection.
Depending on the indicator, wood is divided into categories:
- wet - with a relative humidity of more than 23%;
- semi-dry - within the range from 18 to 23%;
- dry - with a moisture value of 6 to 18%.
Natural wood drying
With this method of removing moisture, a drying chamber for lumber is not used, the liquid evaporates under the influence of atmospheric air. Dry the material under a canopy located in a draft. The sun's rays unevenly heat the outer and inner layer of the tree, which leads to the appearance of deformations and cracks.
If a drying chamber for sawn timber is not equipped on the site, the attic room, ventilated shed, and an equipped canopy are well suited for drying. The material is stored in a stack, the first layer must be laid on supports with a height of at least 50 cm from any durable material. The rows of lumber are laid with dried slats, all subsequent boards and logs are placed above the previous workpieces so that vertical air wells appear.
Sawed along the logs and finished boards are laid with the inner side up to reduce the size of the deformation. For the same purpose, a stack of wood is pressed from above by a heavy load. Due to the formation of cracking at the ends of the workpiece during drying of the material, the length of the workpiece is selected 20-25 cm longer than the intended part.
The ends of the lumber are carefully treated with oil-based paint, drying oil or hot bitumen to prevent cracks. Before stacking, the trunks of logs are cleaned of bark to reduce the likelihood of propagation of tree bugs. Removing moisture from a tree in a natural way is considered economical.
Solar wood dryer
The second way, the cost of which quickly pays off, are drying chambers for lumber. The drawings for the manufacture are quite simple, you only need to understand the principle of operation of such a device. The camera is an assembled plywood or metal container, the roof of which is made of transparent materials.
The calculation of the size of the glazed surface of the roof is done depending on the total horizontal area of all lumber laid for drying. The area of the transparent coating should be one tenth of the total surface of the boards. The roof of the building is pitched, the slope depends on the geographical position of the terrain.In the northern cold regions, where the sun does not rise high above the horizon, the roof slope is made steep. The southern sun heats the gentle cover well.
How to make a drying chamber for lumber?
The building frame is made of metal or timber treated with an antiseptic under pressure. The walls and floors of the chamber are made of moisture-resistant materials, the fencing is insulated with mineral wool or rigid foam boards. The inner surfaces of the walls are treated with water-repellent compounds, aluminum powder is applied to them, then painted black.
Fresh air blowers should not contain blades made of plastic fusible materials. If the drying chamber for lumber is not used constantly, then the room is used to dry herbs, vegetables, berries or a seasonal greenhouse. After laying all the wooden workpieces for drying, a distance of about 30-40 cm should remain between the stack and the wall on all sides.
Drying wood in artificial conditions
When removing moisture in a natural way, relative humidity indicators of about 18% are obtained. To improve the value, lumber drying is used in drying chambers, where the temperature, forced air supply rate and its humidity are regulated.
Basic equipment for dryers
Whatever type of forced wood drying chamber is used, standard equipment groups stand out for everyone.
Transportation equipment is designed for loading and unloading logs or boards into the drying room. It includes machines and mechanical devices for storing blanks in a stack or package, and raises and lowers lumber.
The thermal equipment of the chamber serves to raise the temperature of the indoor air in the chamber and consists of many systems that determine the interconnected work of the production and transfer of heat. These include heat transfer tanks, heaters, pipes for the passage of steam or hot water, devices for removing condensate, shut-off valves and control devices.
Fuel is gas, liquid fuel. For small amounts of work, a drying chamber for lumber on wood is equipped. The heat carrier is saturated steam, water, gas obtained from the combustion of the furnace, and organic fillers of the system having a high boiling point. Widely used electric heaters, where the energy of the current is converted into a thermal component.
The circulation equipment is designed for organized movement of air masses in the room of the drying chamber. Elements of the system are fans, injectors and joint installations of these elements. To increase the drying efficiency of wood, the automation of the drying chamber for lumber is used.
Drying chamber guard
To isolate the wood from the environment, a camera enclosure is installed, which consists of a floor, ceiling, walls and intermediate partitions. Partition requirements:
- must not let steam through;
- fences should have low thermal conductivity;
- must have a long service life.
Fences are made separately from various building materials or prefabricated with a set of typical metal elements.
The first type of cameras has a longer life, but differs in a longer commissioning time, which is not always justified. Prefabricated metal frames are mounted quickly, they are equipped with control and thermal devices, but steel is subjected to the destructive effect of wet and thermal conditions.
The principle of vacuum drying
After laying the wood in the stack, the chamber door is sealed and the drying process begins. Using automatic devices, part of the air is removed from the chamber until an internal pressure of 8-10 bar is created.Thanks to this scientific approach, the moisture released from the wood moves faster from the center to the outer fences of the chamber, thereby ensuring uniform and high-quality drying. This is how vacuum drying chambers for lumber work.
Making a drying chamber yourself
Private developers dry the wood in the courtyard, for this a drying chamber for sawn timber is equipped with their own hands. Its device will require a large room, a heat source and a device for distributing air between the drying packages of wooden blanks.
You can, of course, purchase used drying chambers for lumber, but the degree of wear is not always able to be determined correctly, it is much more profitable to do the arrangement of a room for drying wood. This is an opportunity to get excellent results at a low cost.
Construction stages
You will need material for the frame, usually metal racks from a corner or channel, a wooden beam is used after thorough treatment with an antiseptic. As a wall coating, metal sheets, moisture-proof plywood panels, profiled rolled products are used. Thermal insulation is carried out using mineral moisture-resistant cotton wool, polystyrene foam.
Before starting construction, determine the location of one or more dryers, which serves as a plan for the construction of a concrete foundation. The base is made for structural stability and even load distribution on the ground. If a ready-made railway container is taken for the camera, then four columnar foundations are made at the corners of the car.
The frame is assembled from metal by welding or bolted joints. When the device is checked, the verticality and horizontalness of the building level, trying to clearly observe the geometric dimensions. After fixing the frame in the mounting position, they proceed to sheathing the outer walls, simultaneously inserting doors and ventilation windows.
The heat-insulating layer of the floor, walls and ceiling should be at least 12-15 cm, the base is isolated from moisture by a rolled material. After that, the camera is checked for leaks. For laying the first layer, stationary supports made of metal or wood are placed. They install a heat source, usually a powerful fan heater, arrange it so that the direction of hot air is parallel to the lying boards.
Wood drying is a prerequisite for obtaining high-quality raw materials. The construction of a house or the manufacture of fillings of openings from wet lumber is fraught with distortions and violation of integrity. In order to perform work with wood without problems, you need to take seriously the removal of excess moisture from the material.
