There are problems with the damage of wood from the felling, storage, circulation, and final use of the timber. If stored and handled poorly, the wood will crack, deform, suffer from fungal decay, insect erosion, fire damage, resulting in wood corruption and deterioration, and even loss of the original use value. In order to maintain the original quality of the wood and make reasonable use of the timber resources, it is necessary to protect the wood.
There are many factors that contribute to the corruption of wood. There are three main aspects: biological damage, physical damage and chemical degradation. The most important of these is biological decay, that is, fungal discoloration, decay and insect pests, which not only invade the logs and sawn timber during standing, storage and transportation, but also destroy the products of air-dried wood. For wood storage, this is the primary factor to consider.
(1) Reasonable storage of timber
For logs, dry storage, wet storage and water storage methods are mostly used; for sawing materials, drying methods are used.
Dry method
The dry storage method is to reduce the moisture content of wood to below 25% as soon as possible in a short period of time, so as to inhibit the growth and reproduction of bacteria and insects. The moisture content of the logs suitable for the dry storage method is generally below 80%, and the bark is peeled off as much as possible, or the bark damage has exceeded one third. When the logs are peeled, try to keep the phloem, and leave 10-15cm bark rings at both ends of the logs, and apply anti-crack coatings on the end faces, such as 10% paraffin emulsion, lime water, coal tar, polyvinyl acetate emulsion and urea-formaldehyde resin. : 70) Mixing liquid, or nail "S" nails and other measures to prevent cracking of logs. For damage and tree joints on wood, preservatives (such as zinc chloride, copper sulfate, zinc sulfate, sodium fluoride, sodium pentachlorophenol, etc.) should be applied to prevent infestation and spread of bacteria and insects.
The site where the wood is stored in the dry storage method should be selected in a place with high topography, empty position and good ventilation; when stacking, the litter, bark, wood chips and wood in the early Qing Dynasty should be kept clean; the site should be cement. The ground is better, or the coal ash gravel is flattened to prevent moisture or weeds. The principle of dry storage of rafts is to facilitate the air circulation in the raft and to make the wood dry quickly.
2. Wet storage method
The wet storage method is to maintain the high moisture content of the wood sapwood to avoid the occurrence of bacteria, insects and cracking. This method is suitable for new felling materials and water transport materials. The moisture content of raw wood sapwood is usually higher than 80%. The methods of air-drying and logs that have been affected by bacteria and insects, as well as hardwoods that are susceptible to cracking and wet mildew, are not suitable for use in areas where the southern termites are vulnerable to wetness.
Logs stored in wet storage should have intact bark or no more than one-third of bark damage. The structure of the pile is to be densely packed and piled up as big as possible. The newly cut or new river logs are immediately intensively smashed, and the logs before blaming should not be stored in the open air for more than 5 days. The logs after blaming are immediately sealed and covered with shading. In order to prevent cracking or bacterial or insect infection caused by water loss of the log section, the end face may be painted with a preservative wet paint; a layer of lime water may be applied on the paint to prevent the sunlight from melting and disappearing. If there is water source or where there is a spray device, the water spray method can be used. The water sprayed wood does not need to be covered and shaded. The water spray delay is evenly sprayed in the cold head so that each log can be wetted, and the spraying time is generally from April to September. The water spray starts within 10 days after the blame, and the first spray time is long, so that each spray is 10-20 min, 3-4 times every night.
3. Hydrotherapy
The preservation of logs is to invade the water to keep the maximum moisture content of the wood, prevent bacteria and insect damage and avoid cracking of the wood. Hydrotherapy generally uses slow-flowing rivers, lakes, reservoirs, and log banks next to the material shop to store logs, but seawater is not suitable for storing wood due to ship rafts.
The method of water storage and storage of logs includes water immersion pile method and multi-layer wood drainage immersion method. The purpose is to store the logs in water as much as possible, stack or arrange them in layers, and pay attention to the strong binding, using wooden piles, steel cables, etc. Reinforce it to prevent it from being washed away by running water or wind and waves. The part of the water that is exposed to the surface of the water should be sprayed regularly to ensure the humidity of the logs.
4. Drying of wood
The most important and effective measures for the storage of sawn timber during drying. This not only prevents the damage of discoloring bacteria and rot bacteria, but also reduces cracking and deformation, reduces the weight of wood, and enhances the toughness and mechanical strength of wood. Hardness and nail holding power to improve the surface finish of wood. Wood drying has both natural drying and artificial drying.
Natural Drying Also known as air drying, it is used to store wood in an open space. It uses air as a heat transfer and moisture transfer medium, and uses the sun to radiate heat, so that the moisture in the wood is gradually eliminated to a certain degree of dryness. Air drying requires no construction costs and large equipment investment, no heat source and power supply, and low drying cost; its process and technology are relatively simple and easy to implement. However, air drying is greatly affected by external factors, mainly climatic conditions and seasons. It is difficult to adjust or control the labor, and the drying speed is slow. Wood may be contaminated by bacteria and insects during drying, and it is difficult to kill or remove pests that have fallen into the wood during air drying. The minimum moisture content of air-dried wood is limited by the equilibrium moisture content under natural conditions, usually between 12% and 18%. In addition, the quality of air-dried wood is also affected by the stacking method and the layout of the yard.
There are many manual drying methods. At present, at home and abroad, convection heating kiln drying method is widely used. Kiln drying (or dry room) is to place the wood in a building or metal container with good heat preservation and air tightness, artificially control the temperature, humidity and air circulation direction and speed of the drying medium, and promote the wood at a certain time. A drying method that dries to a specified moisture content. The advantage of the wood kiln dry method is that the wood can be dried to any final moisture content lower than the air dryness. The drying speed is short and the cycle is short (twice times faster than air drying), the drying conditions can be flexibly adjusted, the drying quality is good, and the loading and unloading is carried out. Concentration of loading operations facilitates the automation of mechanical integration. During the kiln drying process, due to the high temperature and heat, it can kill all the pests that have entered the wood, which is a very effective insecticide method. However, the equipment and process of kiln drying is more complicated than air-drying, with large investment and high cost.
(2) Chemical protection of wood
The chemical protection of wood refers to the treatment of wood with chemicals, which can prevent the damage of wood by bacteria, insects and marine bored animals, or make the wood fire-resistant, thus effectively protecting wood, extending the service life of wood and saving wood. The purpose of the resource.
Wood preservative
Preservatives are chemical agents that protect wood from microbial hazards. In general, they can effectively prevent wood decaying agents, and can effectively prevent the damage of wood pests and marine bored animals. There are many kinds of wood preservatives, but there are not many effective preservatives. Some preservatives have a broad spectrum and are effective for organisms that are harmful to wood, but some are selective and should be selected according to actual conditions.
Commonly used wood preservatives can be broadly classified into three types, oily preservatives, organic solvent-based preservatives, and water-soluble preservatives.
(1) Oily preservative: refers to oils with sufficient toxicity and antiseptic properties. The oil preservatives commonly used in the wood preservative industry are mainly creosote oil (Krisu oil) and coal tar, the latter mainly used in combination with the former to reduce costs. Widely used in sleepers, poles, cross-arms, bridge structural materials, pile wood, seaport engineering materials, wooden ship shell materials.
(2) Organic solvent type preservative: This is a kind of organic compound with bactericidal and insecticidal effects, also known as oil-soluble antiseptic machine. The agent is an organic solvent as an infusion carrier, enters the wood, and then the organic solvent evaporates, and the agent remains in the wood. Commonly used organic preservatives are pentachlorophenol phenol, copper naphthenate, copper quinolate, organotin compounds, phenylphenol, etc., and organic solvents are mainly petroleum products. This type of preservative is widely used for anticorrosion of electric poles, sleepers, construction materials, joinery and the like.
(3) Water-soluble preservatives: Water-soluble preservatives are generally organized by a salt solution of toxic ions. It is a kind of preservative that is widely used and widely used in various countries in the world. This type of preservative uses water as a solvent, so the cost is low. The treated material is dry and has a special odor. The surface is neat and tidy. It does not affect the paint and glue, but the treated wood will swell and swell, and the processing material with higher installation size is required. After drying, it needs to be reprocessed.
There are two types of water-soluble preservatives, namely a single preservative and a composite preservative. A single preservative uses only one kind of salt as an active ingredient of toxic sterilization and insects, and its toxicity and anti-leaking performance are poor. There are fluoride, boride, arsenide, copper, sodium pentachlorophenol and alkylammonium. . The compound preservative is mixed in a certain ratio of two or more kinds of salts. In addition to the effective toxic components, some inactive ingredients also play an important role in promoting the dissolution of salts, increasing the permeability and increasing the salt. The amount of the agent in the wood, such as fluorophenol, fluorochrome and fluorochrome arsenic phenol mixture, boronic phenol mixture, acid copper chromate, ammonia arsenate copper, copper chromium arsenic mixture, copper chromium boron mixture and the like. Water-soluble preservatives are commonly used for anti-corrosion and insect-repellent treatment of construction materials, food packaging materials, living houses and furniture, and wood storage.
2. Wood insecticide
Wood insecticides or insecticides are those that can kill or prevent wood pests. In general, commonly used wood preservatives have some insect-repellent effects. Sometimes, in order to increase the preservative's ability to kill certain pests, some insecticides can be added to the preservatives.
There are many kinds of insect repellents, which can be divided into the following three categories according to the different absorption sites of the pests and insects:
The contact agent adheres to the surface of the worm and dissolves in the epidermal fat, thereby entering the body tissue, causing the insect to die, such as chlordane, organophosphorus (phoxim), synthetic insecticide and other agents.
Stomach Toxins Agents that are poisoned by the digestive system of pests, such as boride and fluoride, after the pests have been treated with the chemicals.
Fumigant The agent enters the worm through the respiratory system of the pest in a gaseous state, causing it to die, such as sulfuryl fluoride, methyl bromide, and the like.
3. Wood weathering agent
In order to improve the weather resistance of wood and improve the finishing effect of wood products, in recent years, some researchers have used an aqueous solution of inorganic compounds to treat the surface of wood. This treatment has the following advantages: 1 can prevent the degradation of wood surface caused by ultraviolet radiation; 2 improve the durability of transparent organic coatings to ultraviolet rays; 3 improve the durability of paints and dyes; 4 improve the dimensional stability of wood surfaces 5; improve the corrosion resistance of wood surface and surface coating; 6 fix the water-soluble extract in wood, reduce the discoloration of latex paint; 7 also double the surface coating of wood, no need to deal with it.
Commonly used inorganic treatment agents are: chromium trioxide, copper chromate, ammonia-soluble copper chromate and ammonia-soluble zinc oxide. Among them, three kinds of chromium oxide and ammonia-soluble copper chromate have the best effect.
4. Wood flame retardant treatment
Wood is treated with special chemicals to treat wood, so that when it encounters high temperature or open flame, it can prevent the emission of flammable gas, cut off the source of oxygen, reduce the temperature of wood, and meet the requirements of flame retardant and fire resistance.
Commonly used flame retardants are borax, zinc chloride, ammonium chloride, ammonium sulfate, diammonium hydrogen phosphate, sodium phosphate, phosphoric acid, and the like. When the flame retardant treatment is carried out, a mixture of a plurality of chemicals is often used, and the length is not short, the cost is reduced, and the effect is improved. Such as one of the flame retardants used for infusion into the interior of the wood, the formulation is: ammonium chloride 35% + ammonium sulfate 35% + boric acid 25% + sodium dichromate 5%.
5. Wood chemical protection treatment method
There are many ways to inject chemicals into wood, and different treatment methods can be selected depending on the agent, processing requirements, and processing conditions. Usually divided into two major categories of atmospheric pressure and compression.
Atmospheric pressure treatment The artificial pressure is not applied to the treated material, and the chemically infused wood is fully utilized as a capillary action of the wood, and is absorbed into the wood by capillary absorption of the wood itself under normal pressure. The effect of the atmospheric pressure treatment method is worse than that of the pressurization method, and the medicament can only stay on the surface layer of the wood, and the residual period is not long, and the effect is limited. However, such methods are relatively simple and do not require complicated, complete sets of industrial equipment, which is convenient for on-site operation. Specific methods include: brushing method, spray method, dipping method, hot cold bath method, diffusion method, fumigation method, and the like.
Pressurized treatment The wood is placed in a special closed tank, and the treatment agent is injected into the interior of the wood under pressure. It can achieve better injection depth, can control the absorption of chemicals, and has high production efficiency. It is suitable for large-volume, high-quality and difficult-to-inject wood treatment. It is the most effective and important industrial treatment method at present. The pressurization process requires some special equipment, which includes a cylindrical steel tank capable of withstanding a certain pressure, and has a can open and close tank door at both ends or at the end, and there are heating pipes, rails and anti-floating devices in the tank. . If necessary, a fully enclosed motorized tank is used for pressurized injection, as well as a storage tank, a metering tank, a liquid preparation tank, and the like. It is also equipped with pumps, air compressors, vacuum systems, control instruments and other equipment. Commonly used pressure treatment methods are full of three methods: cell method, empty cell method and vacuum method.
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