|
Arabic
Bengali
Chinese
English
French
German
Hebrew
Hindi
Italian
Japanese
Korean
Malay
Polish
Portuguese
Spanish
Turkish
Ukrainian
Vietnamese|
ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Wood work
Encyclopedia of radio electronics and electrical engineering / Ham Radio Technologies 2.1. The choice of wood species due to the purpose of the product, its shape and the expected appearance. Wood has a layered fibrous structure, and its properties are largely determined by the cut plane. There are three main cuts: transverse, or end (across the fibers), radial - along the axis of the trunk and tangential - also along the trunk, but not in the axial plane. It should be borne in mind that the bars and boards of the radial cut are less susceptible to warping. Below are brief characteristics of the main types of wood most widely used in amateur practice. Pine - the most widely used type of commercial timber. Its advantages are lightness and sufficiently high strength, its disadvantages are knotty, resinousness and the difficulty of decorative finishing. Pine is used for products that are going to be pasted with veneer of valuable species (clauses 2.8, 2,10), for finishing with textured paper (clause 2.12), and for parts that do not require finishing (for example, bases, internal binders and auxiliary bars of cases, cases). Ale inferior in strength to pine. Its advantage is the uniform white, long-lasting wood color. Spruce has a lower resin content, therefore it is better than pine for gluing and finishing. Spruce speaker boards perform better than those made from pine. Birch homogeneous in structure, durable and very well off. Thanks to the white color, it is easily asked even in the most delicate tones. It is trimmed in walnut, mahogany and ebony. The disadvantage of birch is deformation under the influence of variable air humidity. Alder has a uniform structure, soft, very well processed, as well as finishing in walnut, mahogany, stained maple. Beech - viscous and rather hard wood, but barks significant shrinkage and strongly warps. Beech veneer has a beautiful texture, is easily finished and is widely used for veneer of pine and spruce products. Oak - hard and durable wood. It is used for the manufacture of the most critical parts that carry significant mechanical loads. The red pattern and color make it possible to use oak for finishing front panels. Bog oak, which has a dark color, is especially valued. To obtain a smooth surface, careful processing is necessary - coating with filling compounds (clause 2.9) followed by polishing, however, waxing (clause 2.14) and varnishing (clause 2.15) are considered the main processing of oak parts. 2.2. Drying - wood consists in the evaporation of moisture from its surface and the movement of moisture from the thickness to the surface. The first process proceeds faster than the second, especially when drying blanks of large cross section. Atmospheric drying (in the open air) continues for many months. Drying chambers and forced modes (in industrial conditions) significantly speed up drying, but even in this case boards with a thickness of 50 mm 11 with a moisture content of 60.% are dried to a moisture content of 12% for at least 5 days. In addition, during forced drying modes, internal stresses arise in the wood, therefore, the process is accelerated only so that these stresses do not exceed the tensile strength (tensile strength) of the material, and cracking and warping are within the permissible limits. In the open air, wood can be dried to a moisture content of 20-25%, depending on the season and weather. However, wood products that will be used or stored in residential areas should have a moisture content of 10-12%. Therefore, the manufacture of wood products must begin after drying, and it is best to dry it in blanks cut along the contour with a supply of material for shrinkage. Such blanks take up less space and dry faster. At the same time, they should not be placed near heating or heating appliances. The best place for drying blanks in a mezzanine apartment. When marking blanks, it should be remembered that the shrinkage of wood along the fibers is about 0,1, in the radial direction - 3-5, in the tangential direction - 6-10%. 2.3. ornamental material - for amateur work is quite diverse. At the disposal of the master can be boards and bars from various types of wood, plywood and chipboard, parquet board. The latter is suitable, for example, for the manufacture of decorative structural elements and critical components and parts that carry mechanical loads. Even a tare plate in the skillful hands of a master can find a new life. Ornamental material is chosen depending on the purpose and type of product, acceptable methods of processing and finishing. First of all, it is necessary to take into account not only the mechanical properties of the material, but also the color and tone of the wood. True, the methods of processing and finishing make it possible to change the color and tone by imitation (clause 2.10) or bleaching (clause 2.11). It is better to choose boards with a radial cut (less prone to warping), with a dense arrangement of annual rings, well dried. (Aged wood, such as boards from old furniture that has been in a room with normal humidity for several years, is even less susceptible to warping.) 2.4. Hole drilling - perform with special drills: transverse drilling - center, the so-called perks, and longitudinal - spiral. The drill is fixed in a brace or drill with a low number of revolutions. To ensure that the exit of a large-diameter hole during drilling is clean (without chips), it is better to first make a through hole with a drill two or three times smaller in diameter, then, having drilled a hole with a drill of the desired diameter to half the depth, turn the part over and continue drilling, but on the other side . You can drill in one go, but in this case, in order to avoid chipping the wood at the exit of the drill from the through hole, the part must be pressed tightly against the auxiliary board, preferably with clamps. The wood of the auxiliary plank should be denser. It is convenient to drill holes with a diameter of more than 25 mm using a circular jig, followed by milling the edges (clauses 5.12, 5.32). 2.5. Bonding parts - the most common way to connect wood parts. Many adhesives are suitable for this. However, preference is given to wood glue, PVA glue and casein glue (clauses 4.1, 4.10, 4.14), in particular casein glue - when gluing parts with pressing. The main requirement for adhesive joints of parts is strength, and often invisibility of the connection. The latter is especially important when the finish is completed with a transparent coating (clauses 2.9, 2.13-2.15). When staining wood, the glue line should take on the same color as the wood. Usually, wood dyes are dissolved in water, so the glue in this case must be water-based. The invisibility and strength of the connection are achieved only if the parts to be glued are tightly fitted. Flat planes or straight edges are jointed. When the planes cannot be jointed, proceed as follows. Align one of the planes and cover with dry paint or stroke with a soft pencil. Then they impose it on the second plane, press it and rub the planes with light friction; paint marks convex places that are cut off with a chisel, remove cycles or other tools. Repeated processing ensures that the colored spots are evenly distributed over the entire gluing plane. After that, the dye is removed with a soft rubber band or light scraping. The connection on glue is often supplemented with a connection on spikes or screws (clause 2.6). In cases where it is impossible to provide a minimum gap between the surfaces to be glued, it is advisable to use adhesive pastes (clause 4.12). 2.6. Joiner's connections of details - (knitting) are very diverse in execution. Wood pieces can be connected with spikes, screws or even nails. Knitting most often does not exclude the connection on the glue, but complement it. A thorn is that part of the part that is included в a corresponding hole made in another part articulated with it. The connection of two parts, for example bars, can be end, when both bars are connected by ends, or middle (tee), when the end of one bar is connected to the middle part of the other. The spike can be integral with the part or be inserted, it can pass through another part through or enter it to a certain depth. Knitting with spikes is varied. On fig. 2.1 shows corner ties, the most common type of joinery. Overlay half a tree - the simplest connection, but not strong enough and requires additional fastening with dowels (round-section plug-in spikes), screws or nails. To perform the overlay, cut off 1/2 of the thickness of the bar. Through direct single spike - very common. The thickness of the spike is 1/3 of the thickness of the bar. Through direct double spike - slightly stronger than a single stud connection. The thickness of the tire is 1/5 of the thickness of the bar. Dovetail spike - it is advisable when the connection is working on a break. The narrow part of the spike is 1/3, and the wide part is 3/5 of the thickness of the bar. Direct deaf (single or double) thorn - used where it is necessary to hide the end sides of the spikes on the front side of the product. Plug-in spikes (dowels) - strong enough, but requires good trimming of the bars and precise drilling or chiseling of nests. "On the mustache" adjoining- not strong enough and requires very careful trimming of the bars with additional fastening, for example, a "kerchief". The "kerchief" is put on glue, sometimes it is strengthened with nails or screws.
Rice. 2.1. Corner knitting of bars; a-half-tree overlay; b- through straight single spike; a-through straight double spike; G- spike "dovetail"; d-direct deaf single spike; e- plug-in spikes (dowels); f-"on. mustache "adjoining; s-" on the mustache" with a plug-in spike; and- "on the mustache" overlay;To- "on the mustache" with plug-in spikes (dowels); l- "on the mustache" with a through spike; m - "on the mustache" with a secret spike "On the mustache" with a plug-in spike - may have one or - several spikes on the glue. The thickness of the spike depends on the thickness of the bars. In miniature designs, the spike can be made of veneer. "On the mustache" overlay- does not have high strength. The thickness of the lining is 1/2 the thickness of the bar. "On the mustache" with plug-in spikes, (pins) - requires accurate trimming of the bars and precise drilling or chiseling of sockets. "On the mustache" through or hidden spike - stronger, but also requires precise trimming of surfaces. Spikes are made with a thickness of 1/3 to 1/5 of the thickness of the bars. The main types of tee knitting are shown in Fig. 2.2. For strength, the spikes of these matings can be additionally fastened with dowels. If the parts of the connection with force enter one into the other. then they are knocked down by striking with a hammer or mallet. In order not to crush the wood, enclose a safety bar or board. The walls of the body (case) can be connected using bars, placing them in the inner cavity of the corner. More often this method is used to connect plywood walls. A bar of rectangular or triangular cross-section is glued to the walls and, if necessary, fastened with screws or nails, often nails without caps. In amateur practice, it is sometimes possible to get by with an adhesive joint, reinforcing it with screws. To prevent plywood from chipping at the edges when screwing in screws, you should first drill holes in it according to the diameter of the screws and countersink if the screw has a countersunk head. Holes are drilled in the bar to half the depth of screwing with a drill of the appropriate diameter.
Rice. 2.2. T-bar knitting: a- half a tree;b- half a tree "paw"; at- trapezoidal overlay; g-deaf frying pan; d - straight single spike; e- plug-in spikes (dowels)
Rice. 2.3. Joining chipboard parts 2.7. Joining particle board parts (DSP) causes certain difficulties. Since this material crumbles easily at the edges, carpentry joints are not suitable here, and additional parts made of wood or metal have to be used to ensure a strong connection. One of the ways to obtain a strong and tight non-separable connection of parts is based on the use of screws and epoxy glue. Screws are screwed into the end of one of the parts to be joined at a distance of 30-50 mm from one another. Under the screws, holes are pre-drilled with a diameter of 1-1,5 mm smaller than the diameter of the screw. The thread of the screws is lubricated with epoxy glue before screwing. Holes of such a diameter and depth are drilled in the second part in appropriate places so that the heads of the screws of the first part can easily enter them. Now it remains to fill the holes in the second part with epoxy glue, generously smear the surfaces to be joined with the same glue, fold (as shown in Fig. 2.3) and compress the parts, providing a right angle between them. Excess glue must be removed and the knot must be kept for a day at room temperature. Using this method, it is convenient to make boxes (for example, for acoustic systems) from polished chipboard, as well as from thick plywood or boards, since the method is simpler than spiked and does not violate the decorative integrity of the material. 2.8. Veneering - gluing a product or parts of a wood product with veneer - thin, slender sheets of valuable wood. All tears, potholes, pinches and dents on the veneered surface must be sealed with inserts using glue. The smallest of these defects can be filled with adhesive putty (Table 4.1 and Section 4.12). After sealing, the surface must be leveled and sanded. To prevent cracks from forming in the veneer after gluing, it is necessary to seal (cover) all spiked joints and end surfaces with planks, stickers or "kerchiefs" while preparing the product. For large veneered areas, veneer with a large pattern is chosen, for small ones - with a small one. The veneer is cut according to a paper pattern with a sharpened shoe knife using a metal ruler. The cut pieces are sanded from the inside with a coarse-grained sandpaper and the cracks are puttied with adhesive putty. The prepared veneer, after aligning the edges, which should converge at the joints, is folded edge to edge according to the dimensions of the veneered part and glued with paper tape 20-25 mm wide. In order for the edges of the veneer to be pulled together, the paper is impregnated with water before sticking, and when sticking, it is carefully smoothed. Veneering is carried out in a room with an air temperature of 25-30 °C. The surface of the veneered part and the inner side of the veneer are smeared with carpentry glue, and after 8-10 minutes the veneer is applied to the veneered surface and rubbed with a smooth bar or a flat carpenter's hammer. It is good to grind the veneer with an iron heated to 50-60 ° C. Rub along the lines of the veneer texture from the middle to the edges. Emerging bubbles must be immediately eliminated, for which the veneer in the defective place is moistened with water, cut and glue is injected under it with a pipette or syringe, and then this place is smoothed with an iron. Chips and tears are patched by color and texture. Dents are moistened and ironed with a hot iron until a smooth surface is obtained. After one and a half, two hours of drying at a temperature of 25-30 ° C, the paper strips that connected the pieces of veneer should be removed. 2.9. Surface preparation for a clear finish comes down to sanding, delinting, priming to fill the pores to get a smooth and clean surface, reduce varnish absorption and prevent the formation of air bubbles under the varnish coating. Grind straight sections of the product surface with a sandpaper wrapped around a wooden bar, curved sections with sandpaper, in which soft rubber of the desired shape is wrapped, and holes or rounded chamfers with sandpaper wrapped around a wooden stick. Small details and hard-to-reach places are sanded with sandpaper folded in several layers and rolled into a tight tube. The movement of the skin must be directed along the fibers, otherwise deep scratches remain on the sanded surface, which are difficult to eliminate. Grinding is carried out by successively reducing the grain size of the skin.
To achieve a particularly clean surface, the removal of the pile with moisture is repeated. After that, a filler is rubbed into the surface of the product or it is primed. Wax dissolved in turpentine (clause 2.14) or special fillers produced by the industry, for example, KF-2, KF-3, liquid wax (in aerosol packaging), etc., can be used as a filler. A number of specific requirements are imposed on soils: should fill the pores well, not hide the grain of the wood, dry quickly, be water resistant and be diluted with a solvent. The simplest soil can be prepared according to the following recipe (in mass parts): natural drying oil - 35-55, turpentine-7-10, desiccant-5-7, ground chalk with a dye of the desired tone - 40-50 for large-pore rocks and 15-20 for the small ones. You can also prime with wood powder (very fine sawdust), mixed with liquid wood glue with the addition of a dye to match the color of the product. Instead of wood glue, you can use other liquefied adhesives, for example, BF-2 with alcohol or PVA with water, and chalk or talc with the desired dye as a filler. When using adhesive primer, the pile can not be removed, as it sticks and dries to the surface of the wood. After the primer or filler dries, the surface to be treated is finally polished. Table 2.1 Aqueous solutions for imitation of valuable wood
2.10. Imitation valuable wood species is usually carried out by impregnating the wood surface with an aqueous or alcoholic solution of various stains, aqueous solutions of aniline dyes, or special chemical compositions - aqueous solutions of various substances (Table 2.1). For processing wood "under mahogany" you can also use a mixture of black and red ink (the required proportion should be selected empirically). Imitation of walnut wood can be obtained by treating wood with an alcohol 2% iodine solution. Alder, elm, ash, beech, cedar, birch, cherry and pear lend themselves well to “mahogany look”, birch, oak, maple, hornbeam, apple tree, plum and cherry “under ebony” finish, alder “under walnut” , birch, linden and beech.
The paint is better fixed on the wood if a little (up to 3%) wood glue is added to the solution. When processing coniferous wood, it is recommended to first clean it from resin deposits, and then rinse it with 10% sodium hydroxide solution, gasoline, turpentine, alcohol or 10% sodium chloride solution. It is possible to finish metal cases with plywood veneer. Here is one of the technological methods. A smooth, flawless sheet of organic glass with a thickness of about 3 mm and other dimensions, 30-50 mm larger than that of the largest wall of the case, is thoroughly washed from dust and dirt, dried, lubricated with Vaseline on one side and wiped dry. In this case, the vaseline remains in the micropores of the glass. Then the sheet is placed on a flat horizontal surface with the greased side up and some amount of prepared epoxy glue is poured onto it. The glue is carefully spread over the glass with a layer of 1-1,5 mm and a veneer sheet cut with some allowance is applied with the front side on it. All air bubbles from the adhesive layer are carefully removed by squeezing them out to the edges. Bubbles are easy to detect by viewing the package from the side of the glass. Then the veneer is covered with a thin layer of epoxy glue and a case is placed on top - one of its sides. The case before this operation must be thoroughly cleaned of dust and grease. After 6-7 hours the organic glass is removed. To do this, a sheet of glass is carefully folded from one edge, and it gradually moves away from the layer of hardened glue. The surface is smooth, with a mirror finish. Glue streaks along the edges are cut off with a file immediately, without allowing it to completely harden (after a few days it will become brittle and will chip off during processing). After that, the next side of the case is processed. 2.11. Whitening wood is carried out to reduce the intensity of color, remove stains, etc. A good bleaching solution can be prepared in the following composition (in mass parts): bleach-8; crystalline soda-1; water-35. Before use, the solution must be allowed to settle.
You can use a 15% aqueous solution of hydrogen peroxide with the addition of ammonia in such an amount that the composition has a strong smell of ammonia. The surface of the wood is moistened with this composition and left for several days, after which it becomes completely white. After such bleaching, the surface of the wood does not require any kind of washing. 2.12. Textured paper finish on which one or another drawing is applied by typographic method, it is convenient for decorative processing of the outer panels of the cases. The industry produces two types of such paper: self-adhesive (the adhesive layer is protected by a film that must be peeled off before gluing) and ordinary, which is pasted like wallpaper. For gluing ordinary textured paper, a paste is used (clauses 4.20, 4.21). The paper is smeared twice, at intervals of 3-5 minutes, so that it is evenly and well saturated, then when it dries, it will stretch well. The surface of the panel must be smooth, cracks and potholes must be carefully puttied. Otherwise, the irregularities will be very noticeable through the paper. It is necessary to align the paper by pressing it with a clean, dry cloth, but not smoothing it, since the pattern on some types of wet paper can be smeared. After drying, the paper is varnished. However, when applying varnish, air bubbles almost always appear on the surface of the paper, making it rough after the varnish has dried. This can be avoided if, before varnishing, the glued paper is dried for 8-10 hours, and then covered with an even layer of a solution of PVA glue (p. 4.1) in water (ratio 1: 1). After 30-40 minutes, the glue solution will dry, forming an almost imperceptible transparent polyvinyl acetate film on the paper. After another 2-3 hours, the panel can be varnished (NTs-228 or other). The varnish spreads very well and, after drying, forms a mirror surface, which practically does not require further processing. If you do not prime with an aqueous solution of PVA glue, then after applying the varnish, another defect is possible; some grades of paper, especially light colors, become transparent. In this regard, the requirements for cleanliness and uniformity of the pasted surface are increasing. 2.13. Polishing - wood is a process of multiple application of the thinnest layers of polish - 6-10% shellac solution in ethyl alcohol on its surface. Shellac polish has high polishing properties, and the film formed on the surface of the wood is light-resistant, elastic and sufficiently resistant to scratches. Polishing is carried out with a wool swab wrapped in a clean, stretched (to reduce lint separation) linen cloth, which does not leave fibers on the polished surface, unlike wool and cotton cloth. Shellac polish (carefully filtered) is poured into the swab and a test smear is made on some auxiliary surface. The trace from the smear should be thin, without bubbles, instantly drying. Otherwise, you need to remove excess polish from the swab by wiping the auxiliary surface with it. The polishing process consists of a series of successive operations: priming, first, second and third polishing and polishing (degreasing) - degreasing and final leveling of the surface.
To obtain an even coating, there are techniques developed by practice for conducting a tampon over the treated surface. On fig. 2.4 shows examples of the rational course of the tampon at various stages of polishing. Traces (lasas) left by the tampon should overlap evenly. The separation of the swab from the surface should be sliding, with pressure gradually decreasing towards the edge of the part in order to avoid dark spots from excess polish. Priming is carried out with a thicker polish - 10%. The tampon is led evenly (Fig. 2.4, a) at a calm pace. The primed product is dried for 3-5 days in a room where the temperature is not lower than 18-20 "C. At the same time, it is necessary to protect the product from dust, especially in the initial period of drying - until "drying from dust", i.e. until the surface of the coating a film is formed to which the dust will no longer stick.Then the surface is polished with a fine-grained sandpaper or pumice powder, powdering them with a damp linen cloth. The first and second polishing is carried out with a more liquid polish - 8%. The course of the tampon is shown in fig. 2.4, b. Movements are faster than when priming. Each layer is also dried for 3-5 days. The third polishing is carried out as shown in Fig. 2.4, e, At a very fast pace and even more liquid polish - 6%. Drying time 3-5 days. If the tampon does not slide well during polishing, then 2-3 drops of linseed and sunflower oil are applied to the work surface. The polishing is done as shown in Fig. 2.4, g, with a clean swab moistened with alcohol, preferably with the addition of Vienna lime. In this case, the lacquer film is not only degreased, but also leveled. It takes considerable skill and dexterity to achieve an even finish when polished in this way. Polishing in a simplified way is less laborious and allows obtaining a coating of quite satisfactory quality. A polish solution (10-12%) is applied to the prepared surface with a spray gun as evenly as possible. In order for No. to run, the surface to be polished must be in a horizontal position. 4-6 layers are applied at intervals of at least 2-3 hours. Each layer is applied to the surface in a direction perpendicular to the previous one. The last layer is dried for 3-5 days and then all irregularities are removed from the surface with a fine-grained sandpaper. Polished with a wooden block wrapped in a piece of cloth. Surface Rubbed with GOI paste or razor straightening paste, moistened with sunflower oil and polished evenly with light pressure to a mirror finish. To see the quality of polishing, the control area of the surface is periodically wiped with a linen cloth. At the end, the cleaned surface is wiped with a swab moistened with alcohol with quick movements without pressure, and after 2-3 days the surface is finally rubbed with a dry, clean swab. 2.14. waxing, i.e., applying wax pastes to the surface of the wood, followed by polishing, is the best type of wood finishing for large-pore wood species (oak, beech, etc.). Wooden structures look beautiful, where waxed and polished details are skillfully combined. The waxed surface emphasizes the texture of the wood well. The soft and delicate sheen gives the waxed surface an extremely beautiful look. Wax pastes do not require pre-priming, as they themselves are good fillers and adhere firmly to the wood surface. Beeswax (ceresin, paraffin) is melted with moderate heating. Turpentine or a mixture of turpentine with gasoline nom is heated in a separate bowl in a "water bath", using an electric stove with a closed spiral. In small doses with vigorous stirring, hot wax is poured into heated turpentine or its mixture with gasoline, stirred until a homogeneous mass is formed and allowed to cool to room temperature. Keep in mind that beeswax based paste gives better coverage than ceresin or paraffin based paste. The surface is prepared in the same way as for a transparent finish (clause 2.9), i.e. cleaned, polished and freed from pile. If necessary, the part is painted in the appropriate color (clause 2.10), The resulting paste is applied to the surface evenly with a brush or a brush with hard hair. The temperature of the paste should be no higher than 20-25°C, as at higher temperatures dark spots may form on the surface of the wood. Dry overnight at room temperature. Then polish with a cloth until a uniform sheen appears. At the beginning of polishing, the cloth slides with difficulty due to wax sticking, the surface becomes dirty and ugly. As the wax is rubbed and leveled, the cloth begins to slide more easily, the surface is cleared of dirt and becomes smooth and shiny. At the end of polishing, the part is put to dry (2-3 days), after which it is wiped with a clean soft cloth. In order to make the glossy finish more resistant, a layer of shellac polish with the addition of wax paste can be applied to the waxed surface, having previously dissolved 5-7% of the paste in the polish. 2.15. Varnishing wood can be done with alcohol, oil or nitrocellulose varnishes. Lacquered parts look a little worse than polished or waxed ones. Before varnishing, the surface is prepared for a transparent finish (clause 2.9). Varnishing with alcohol varnishes carried out with a swab made of woolen cloth wrapped with stretched linen cloth. Alcohol varnish is poured inside the swab. The best varnish is shellac. The varnish is applied to the prepared surface along the wood fibers evenly without streaks. The drying time of the first layer is 3-4 hours, after which it is polished with a fine-grained sandpaper without pressure. Remove dust from the surface with a damp sponge or rag. The dried first layer of varnish is covered with a second layer, having previously diluted the varnish with alcohol by 10%. The second layer is also dried for 3-4 hours, then polished with pumice powder and water (a damp linen cloth is powdered with powder). Sand with light circular motions without pressure, so as not to remove the varnish. After removing the dust, apply a third layer of the same consistency as in the second coating. A day later, they are polished with GOI paste using a linen swab moistened with kerosene. The surface is then wiped with a clean cloth. Varnishing with oil varnishes not much different from alcohol varnishing. The best varnishes are based on copals (natural or artificial resins). Each layer of oil varnish is dried for 2 days. The varnish is applied with a bristle brush evenly, without streaks. After drying, the first layer of varnish is sanded with a fine-grained sandpaper with light pressure along the wood fibers. Dust is removed from the surface and a second layer of varnish is applied. The dried second layer is polished with pumice powder applied to a slightly moistened felt or cloth. Dust is removed and the surface is wiped with a clean soft cloth. The third coat of varnish is applied and sanded in the same way as the second. The dried surface is polished with a pad of linen stretched fabric. The swab is moistened with alcohol and dripped onto it with linseed or sunflower oil. Polishing is done with smooth movements so that each subsequent trace of the tampon slightly overlaps the previous one (see Fig. 2.4, d). Polishing is repeated 2-3 times. Remove traces of oil with a soft, clean cloth. Varnishing with nitrocellulose varnishes It is more convenient to produce with a spray gun. You need to work in a well-ventilated area at an air temperature of at least 18-20 ° C. The parts to be varnished must be well dried, otherwise nitro-lacquers do not adhere very well to the surface. The varnish is applied in an even layer without streaks. Each subsequent layer is applied in a direction perpendicular to the previous one. Dry each layer (first, second and third) for about an hour. After drying, each layer of varnish is sanded with a fine-grained sandpaper with a little pressure. The fourth layer of varnish is dried for a day and then sanded with sandpaper with an even finer grain size, wetting the surface with kerosene or gasoline. The sanded surface is wiped dry with a soft cloth. Then polished with a swab from linen stretched fabric, moistened with a mixture of solvent (for example, No. 646) and ethyl alcohol in a ratio of 1: 1. You can apply another technological method when working, for example, with NC-228 nitrocellulose varnish. On the surface prepared for a transparent finish, 8-10 layers of nitro-lacquer are applied with a wide hair brush with a hair length of about 20 mm. Layers are applied with an interval of 30-40 minutes. The last layer is dried for at least a day. Then the coating is cleaned with fine-grained sandpaper wrapped around a flat bar until a smooth matte surface is obtained. Another thin layer of varnish is applied to the cleaned surface with a brush and immediately after it - a layer of solvent No. 646 (or No. 647) and dried for several hours. The surface with this method of varnishing is almost mirror-like. 2.16. Coating with epoxy resin (adhesive) It is not much inferior in appearance to polyester lacquer coating, which is widely used in industrial conditions for finishing furniture and cases for radio equipment. The process consists of the following operations. Having removed flaws (scratches, etc.) on the case panel and cleaned the surface, place the panel in a horizontal plane and fill it with an even layer of a pre-prepared mixture of resin and hardener. When preparing pa- For coating, grinding the surface is not required. The thickness of the resin layer is 1,5-2 mm. Air bubbles must be carefully removed by piercing them with a needle. After -7 hours the coating will harden. After exposure for 2-3 days in air, the panel is ground and polished. First, they use coarser sandpaper, and then switch to fine-grained sandpaper. The paper must be fixed on a flat wooden block. During processing, the panel is watered. Polishing is done with any polishing paste using a piece of felt. The resulting coating is sufficiently heat-resistant, not afraid of moisture and organic solvents. If you want to get a thinner coating, the resin should be warmed up before adding the hardener by lowering the jar with it into water heated to a temperature of about 30 ° C. It is also possible to add a little acetone (up to 10%) or thinner for nitro paints to the resin before introducing the hardener and carefully (so that bubbles do not form), mix thoroughly. 2.17. Painting finish wood consists in coating its surface with oil or enamel, less often nitrocellulose paints. In amateur In practice, it often becomes necessary to make a wooden case for any device, a case for storing parts, or other boxes and boxes that do not require careful finishing. In such cases, a paint finish is quite enough. Under the painting finish, wood with defects (potholes and holes from knots) can go, which are sealed and puttied. It is desirable to prime the surface before puttying. The soil is chosen depending on the future coverage. As a primer for oil paint, natural drying oil, heated to 60-80 ° C, is successfully used. It can be primed with the same paint as the main coating, but diluted with drying oil (in a ratio of 1: 1). The surface dried after priming is puttied, choosing, based on specific conditions, ready-made putty or preparing it according to one of the recipes given in Table. 4.1. The wood is puttied completely, that is, over the entire surface. The putty is applied with a spatula (preferably with a metal spatula 0,3-0,6 mm thick), tilting it at an angle of 60-75 ° to the surface. The mass of putty must be pressed so that it fills all the cracks and grooves. You should not try to putty deep irregularities at a time. A putty layer of more than 1 mm not only dries for a long time, but also does not hold well. Therefore, deep potholes are puttied 2-3 times, allowing each layer to dry. After the putty dries, the surface must be cleaned with an emery cloth and wiped from dust. Then the surface is primed again with a continuous layer. It is desirable that the putty and primer match the color of the future coating. The primed surface should dry for 2-3 days. Matte areas of the surface should be covered with a second layer of soil, and the irregularities should be puttied again and cleaned with sandpaper. When the primed surface acquires a uniform glossiness, you can start painting. With uneven glossiness, the binder from the paint layer will be intensively absorbed into the wood, weakening the strength of the coating. For the same reason, priming is necessary before applying oil putty. When staining, you should remember the basic rules. Mix the paint thoroughly before use and filter through 2-4 layers of gauze. The paint should only cover the bottom of the brush. The brush during work should be held as perpendicular to the surface as possible. Apply the paint as thinly as possible, in wide stripes, shading it first in one direction, then in the other. If the paint does not cover the surface well, then it must be applied 2-3 times in a thin layer after the previous layer has dried. It is impossible to apply a new layer of paint on a wet one, as this leads to breaks in the coating and the formation of irregularities on the painted surface. For better preservation of the surface painted with oil paint, it is coated with oil varnish, which also gives the coating a shine. Before applying the varnish, the painted surface should be dried well. If the work is carried out in a non-residential premises, then in the summer they dry for at least 6, in the winter - at least 12 days. During this time, volatile substances completely evaporate from the oil paint, which adversely affect the strength and gloss of the varnish film. Immediately upon completion of work, the brush should be washed off the paint. Usually, the brush is washed 2-3 times in an appropriate solvent (after oil paint, it can be washed in kerosene), squeezed out and tightly wrapped with a strip of newspaper in 2-3 layers: then the hair will not shaggy after drying. Brushes during a break in work can be kept in a vessel with water. 2.18. Removing old oil paint without damaging the wood, it can be done by applying a 2% solution of caustic soda to the window surface. The paint softens and is easily removed with blunt scrapers. For the same purpose, you can use a solution of 200 g of laundry soap in 400 ml of turpentine Or alkaline paste. The basis of the alkaline paste is caustic soda (caustic soda) - 7-18% of the total mass of the prepared composition. For viscosity, quicklime (15-35%) and chalk (5-10%) are added to the paste. Others 73-37.% makes up water. Pasta can be prepared without lime: caustic soda - 20% and starch - 5% or caustic soda - 7% and chalk-13%. Pasta is prepared by first dissolving caustic soda in water heated to 40-50 ° C. The paste is applied in a thin, even layer over the entire surface and kept for 1,5-3 hours. After removing the alkaline paste and paint, the surface should be washed well with warm water and soap and dried. These pastes can also be used to remove oil paint from metal surfaces. 2.19. Removal of old clear coats When repairing wooden structures, it is sometimes necessary to remove their old coating. The vast majority of coatings can be easily removed with special compositions; with Igom, labor-intensive operations such as sanding or scraping are excluded. The wax coating can be easily removed if the surface is wiped with a cloth moistened with hot turpentine. Polishing can be removed by wiping the surface with a rag soaked in alcohol, or even better, with a mixture of alcohol and 25% aqueous ammonia in a ratio of 2: 1. Oil varnish is well removed with a mixture of turpentine and a 25% aqueous ammonia solution in a ratio of 2: 1. For the same purpose, you can apply a solution of caustic soda (3,5 mass parts) in water (10 mass parts), heating this composition to 80 ° C. Nitrolacquer is removed with an appropriate solvent or a mixture of solvent (or acetone) and alcohol in the ratio 1:1. Did you know?. 2.20 To smoothly plan a knotty board with a planer, you must first break the surface layer of each knot with a hammer. Softening the wood fiber will result in a cleaner (no burrs) surface. 2.21 If the plywood sheet is moistened with water along the cut line, there will be fewer chips and the edges will be smoother. 2.22 Spikes, grooves, slats can be cut with a hacksaw for metal by placing two blades on it. The width of the cutout will be determined by the distance between the canvases. 2.23 A crack does not form on the edge of the board when a nail is driven in, if the wood in this place is pre-compacted with a metal punch. Or you can completely grind off the tip of the nail, then it will not crush the fibers of the wood, but will also punch a hole in it. 2.24. It is possible to make a round cross-section stick for spikes (dowels) (item 2,6) or other plug inserts without a lathe. It is enough to take a metal plate with a hole of the appropriate diameter, put it, for example, on the jaws of a vise and “drive” a slightly pointed stick through the hole with a hammer. 2.25. To hammer a small nail in a hard-to-reach place, and even at a certain angle, when it is difficult to “bait” the nail and make the first blow with a hammer, you can use a piece of plasticine. The same problem can be solved with the help of a metal tube and a rod (the rod is slightly longer), sticking a nail with a plasticine head to the end of the rod and directing it through the tube to the right place. 2.26. Screws and nails rubbed with soap or lubricated with vegetable oil will more easily penetrate even the hardest wood. 2.27 If the length of the screw is less than the thickness of the part to be fastened, the screw can be "drowned" by drilling a hole in the part to the desired depth along the diameter of the screw head and a through hole for the screw itself. 2.28. A screw that has long been screwed into wood is easier to unscrew if it is heated by pressing against the head, for example, the tip of an electric soldering iron. 2.29. If the screw connecting the parts scrolls when screwed in, it can be fixed by first inserting one or more matches on glue into the hole. 2.30. You can countersink a hole for a countersunk head of a screw with a semicircular head of a screw clamped in a drill chuck. The countersink is more even than when using a drill. 2.31 The quality of the paint brush depends mainly on the type of hair. The best are made from pig spinal bristles, the second-rate ones are made from a mixture of bristles and horsehair, the lowest grades are made from horsehair. Brushes made from nylon fiber substitutes are cheaper, but cannot be compared with natural ones. 2.32 When choosing a brush, you need to pay attention to the length of its working part. If the hair is too long, the paint can neither be shaded nor, moreover, put in an even layer. A brush with short hair will peel off the paint when shading, leaving traces. Only in the case when the length of the working part of the brush is equal to its diameter, the elasticity of the hair and the pressure of the hand are easily balanced and the uniformity of the application of the paint layer is achieved. 2.33 If the brush is made with a length of hair exceeding the diameter of the bundle, in no case should it be cut. The working part is usually "shortened" by tying it with harsh threads or twine. This makes the brush more durable, because the strapping can be shortened as the brush wears. So that the strapping does not slip (the brush will taper towards the end when strapping, since there is free space inside the working part), you can put a cork (wooden or rubber) of the same diameter as the handle and the same height as the intended strapping inside the working part; . 2.34 To paint a small surface, it is not necessary to dirty the brush. You can use a piece of foam rubber, and in order not to stain your fingers, clamp the foam rubber and a bracket bent from a strip of tin. The same "brush" is convenient to apply inscriptions through a stencil. 2.35 After working with PF varnish, the brush can be put in water if there is no organic solvent at hand. After a day, the varnish, although it will harden, will be loose and easy to remove from the brush with warm water and soap.
2.37 Mixed paint with film residues may not be filtered. It is enough to pour the paint into a shallow jar, lower a piece of nylon stocking there and dip the brush into the paint right through it. The fabric on the edge of the jar can be fixed with a rubber ring. If the paint is nitrocellulose based, you need to use gauze. 2.38 So that the oil paint does not dry out during storage and that a film does not form on it, you need to put a circle of thick paper on the surface of the paint and fill it with a thin layer of drying oil. 2.39 The density of the prepared paint can be estimated by dropping one drop of paint on a piece of clean, dry glass and placing the glass vertically (it is convenient to use a bottle). Paint of normal density flows down the glass by 35-50 mm. Strokes of paint of this density, left by the brush, should spread completely in a few minutes after application. Author: tolik777 (aka Viper); Publication: cxem.net
Artificial leather for touch emulation
15.04.2024 Petgugu Global cat litter
15.04.2024 The attractiveness of caring men
14.04.2024
▪ New waste disposal technology on the International Space Station ▪ Emotions differ by complexion ▪ Current behaves like a liquid ▪ Inequality creates the world's problems
▪ Telephony site section. Article selection ▪ article Smoking incense. Popular expression ▪ article Who were the Aztecs? Detailed answer ▪ Wonzu article. Legends, cultivation, methods of application ▪ article Sweep frequency generator. Encyclopedia of radio electronics and electrical engineering
Home page | Library | Articles | Website map | Site Reviews
www.diagram.com.ua |
See other articles Section 
Latest news of science and technology, new electronics:
All languages of this page