Provide – veneering
Urea-formaldehyde adhesives are commonly used for veneering. The prerequisite for obtaining a good adhesive mass is the precise weighing of the components, maintaining the correct order of their introduction to the mixture and careful mixing. The adhesive mass is prepared in this way, that approx 1/3 the amount of water provided for in the recipe, and then, constantly stirring, the filler is gradually poured in. Everything is mixed until a homogeneous mass is obtained. Only then can the rest of the water be gradually added, and finally pour in the hardener solution in portions. Rye flour or unroasted ground gypsum can be used as fillers. The filler must be sieved before use. Hardeners can be used differently. For cold gluing, the BM-10 hardener is used, hot - hardener MZ or MG. Each of the hardeners should be dissolved in water before use. The solution must be prepared a few hours in advance, or the day before, that all ingredients dissolve. It is unacceptable to use a hardener in the form of a dry substance.
For veneering- U-70 adhesive resin is recommended for veneering larger planes, BZ-70 adhesive resin for veneering narrow planes and facing boards. Warm bone adhesives can also be used for veneering. They are inconvenient to use due to the need to be heated to a certain temperature, quick distribution and pressing of the plate. When gluing larger surfaces, the glue may gel before the board is pressed together.
In order to speed up and facilitate the work, several plates are pressed at once. The compacted stack should start and end with a flat weight plate 4-6 cm thick. Paper is put between the veneered elements, it can be newspaper, so that they do not stick together in the event of an adhesive leak. The veneered elements are arranged in pairs, face side facing you (drawing).
Drawing. Completing layers for veneering – provideowaniu.
Do not reuse the same paper dividers. Leaked and hardened glue can because, when reusing paper, leave permanent, indented mark in the veneer.
The load plates must be at least o 2 cm larger than the dimensions of the veneered elements. They can be 2 or 3 chipboards glued evenly. When veneering- in the veneering of elements longer than the load plates, the following procedure should be followed. First, glue the surface minimum 5 cm smaller than the loading plate. Apply the veneer and the loading plate and press them together. After the glue has hardened, lift the veneer as close to the sticking point as possible, we coat the rest of the element with glue, we press the plate and squeeze. Veneering- So veneering is two-stage.
Pressure on the load plates can be exerted by a screw press, and in its absence, carpentry clamps. The latter method is time consuming but effective. However, both the crossbars and the clamps must be quite close to each other.
After the glue has hardened and the press is released, the elements are air-conditioned. They are stacked with spacers evenly placed above each other. The thickness of the spacers must be at least equal to the thickness of the elements. There must be at least three of them in a layer, in order to prevent deformation of the elements during the drying process. Air conditioning period, so drying in stacks, it should not be shorter than 1-2 weeks.
The paper adhesive tape is removed as soon as the elements are removed from the press. This treatment is best done with a cloth or sponge moistened with water. Within 1-2 minutes of rubbing, the tape should peel off the veneer.
Exact dimensions of veneered- veneered elements are the basis of a well-made floor covering. Because there is usually a shortage of format saws, on which exactly two sides of the board can be trimmed, this operation must be performed on replacement machine tools as follows: one long side of the element is planed on the planer. Originally left behind 2 cm reserve is enough for finishing and alignment of the sides. Then the other side is cut exactly to the width on a circular saw with a longitudinal guide. The workpiece width is set on the circular saw guide. It must be less by 1 mm from the nominal dimensions, because after veneering the sides there will be more 2 X 0,8 mm, and after the final sanding it will remain 1 mm for veneer.
Then the length of the plate is shortened, also on a circular saw with a transverse guide. Use a well-sharpened saw with a small tooth pitch for cross cuts. So that the fibers are not pulled out when cutting, support the end of the element with a wooden lath.
For veneering the visible side planes, the same veneer as before is used. Veneer strips are cut with a veneer knife. The width of the strip should be about 6 mm greater than the thickness of the element. There is a reserve of approx 20 mm. The glueing of the veneer strips is carried out in a similar way to the front planes.
After the glue has hardened, the protruding pieces of veneer are cut off with a veneer knife. When sanding parts on a belt sander, the protruding scraps of the veneer may not be cut off.
Sometimes the sides of the elements are covered with wooden strips. It is old, laborious way, requiring more high-quality wood and therefore rather abandoned at the moment. Moreover, when gluing with strips, there is a risk of unnecessary emphasis of the transition from the glued board to the strip, especially when the wood is not dry enough.
The thickness of the batten is generally 10 mm, and the width is, as a rule, about 2 mm greater than the thickness of the veneered board. After sticking the strip, the stock will be flattened or ground down. Only after the strips are glued, both front surfaces are veneered.