Layer-by-layer method of obtaining plywood

The constantly growing demand for plywood products, increased requirements for a number of quality indicators, keep the issues of improving the technology of plywood production and reducing the consumption of raw materials urgent. Since the idea of ​​gluing rotary cut veneer plywood, the principle of assembling plywood packages has remained unchanged. However, batch bonding of plywood has a number of significant disadvantages. These include:

1. Loss of raw materials from plywood pressing. When gluing multilayer bags, pressing reaches 9-15%, which is a direct loss of wood with the existing gluing method.

2. Plywood thickness variation caused by unequal pressing of the outer and inner veneer layers. The plywood package loaded into the press gap begins to warm up from the press plates. In this case, the outer layers of the plywood sheet directly adjacent to the slabs will always have a temperature higher than the inner ones, as a result of which the peripheral layers during the regime time of gluing are pressed more against the outer ones. With the batch method of gluing plywood, there is no practical way to eliminate the defect of the thickness difference of the plywood.

3. Uneven degree of resin hardening in plywood glue layers, subsequently leading to significant warpage of the plywood sheet. Adhesive layers located closer to the heat source, due to their higher temperature, will have a greater degree of resin hardening at the same time, this will cause stress in the adhesive layers, which will lead to warpage of the plywood sheet.

4. Decrease in temperature when gluing thick plywood. Gluing thick plywood is possible only with a significant increase in time, which increases in proportion, approximately, to the square of the plywood thickness.

5. Weak corners and weak edges in plywood sheets, which are the result of shifting of veneer sheets when loading packages into the press, and the difficulty of using veneer with a false core, causing the formation of bubbles, adversely affect the quality of products.

The experiments carried out show that pressing, in the case of using the layer-by-layer method of gluing plywood, decreases more than three times and does not exceed 4% for plywood with a thickness of 15 mm, glued layer-by-layer in five steps. Considering that such a sharp reduction in the consumption of raw materials when gluing multi-layer plywood is carried out without reducing the pressure, then the use of reduced pressure can practically reduce the pressing. Consequently, the method of layer-by-layer gluing of plywood gives not only a sharp decrease in the time of plywood gluing, but also a corresponding decrease in the consumption of raw materials in the production of plywood.