"The woman is created for a man, not a man for a woman" - such a postulate ...
When designing plywood, the following rules are followed:
- the sheet of plywood should be symmetrical relative to the middle layer
- the number of layers of veneer in the plywood is usually odd.
The thickness of the veneer used for the outer layers of plywood does not exceed 3.5 mm, and the inner layers are 4 mm.
Special properties of plywood are attached through the use of various resins and varnishes.
The water resistance is distinguished by three types of plywood:
- FK - Plywood gluits a carbamide resin. Used indoors.
- FSF - Plywood gluits phenolic resin. Used both indoors and outside.
- FB. - Bakelized plywood - impregnated with a bakelite varnish, after which gluits. Used in tropical climates, aggressive environments and sea water.
According to the degree of mechanical surface treatment, Phaneur is divided into:
- NSH - unlocked;
- Sh1 - polished on one side;
- Sh2. - polished on both sides.
Plywood is also divided by type of wood, from which it is made: Birch, coniferous and combined plywood. Plywood is considered made from the breed from which its outer layers are made.
High physico-mechanical properties of birch in combination with a multilayer structure ensure the unusual strength of plywood. Evalnamed properties such as warm shades and beautiful wood structure. |
|
This type of plywood is made mainly of pine, the properties of which are not only attractive and harmonious, but also excellent strength indicators at a low weight, which is successfully used in house-building. |
|
Attractive appearance, along with an attractive price (due to alternation of layers of coniferous and birch veneer) make it possible to use plywood in furniture production, interior decoration of premises and sports halls, design solutions. |
|
The laminated surface of the plate creates high resistance to various natural and chemical conditions, which makes laminated phanener in an indispensable in production (form of a multi-sized concrete formwork, trimming and floors of vans, etc.) |
For all types of plywood, it is necessary to indicate the emission class of free formaldehyde E1 and E2 (respectively, up to 10 or 10 to 30 mg / 100g dry product).
The quality of plywood is also estimated along the strength of the durability, static bending, stretching the samples, the content of moisture, the presence, structure, bitch color, the presence of defects.
Thickness plywood sheets (plates) are produced from 4 to 40 mm.
The grades of plywood is determined by the number of bitch per 1 sq. M. The surface of the outer sheet is denoted by Roman numbers from I to IV or Latin letters "A", "B", "C" and their combinations.
| Sort I. - Practically without defects, only a few healthy controversial bitch with a diameter of up to 8mm and minor brown bodies are allowed. | |
| Grade II. - It is allowed to repair the surface of the sheet. Bounds and open defects are sealed with veneer inserts. Covered with various finishing materials and paints. | |
| Grade III - This variety includes plywood sheets discarded from grade II (BB). It is intended for the manufacture of structures hidden from external review, various special containers and packaging. | |
| Grade IV. - All production defects are allowed. The bitches are allowed in unlimited quantity, only a good gluing is guaranteed. Used for the manufacture of durable packaging and packaging. |
Physico-mechanical indicators
Standard plywood size: 1525x1525 mm
Dimensions, mm (inches): 1525x1525 (60x60), 1525x1270 (60x50), 1270x1525 (50x60), 1270x1270 (50x50), 1525x1475 (60x58), 1475x1525 (58x60), 1475x1475 (58x58), 1830x1525 (72x66), 1830x1475 (72x58) ), 1830x1270 (72x50).
Brand: FC, FSF
Thickness, mm: 3; four; five; 6; eight; nine; 10; 12; fifteen; eighteen; 21; 24; 27; thirty.
Standard Size: 1250 (1220) x2500 (2440), 1525x3050 mm
Dimensions, mm: 1250x2500, 1220x2440, 2500x1250, 2440x1220, 1525x3050.
Brand: FSF. Thickness, mm: 4.0; 6.5; nine; 10; 12; fifteen; eighteen; 21; 24; 27; 28; thirty; 35; 40.
According to SP 64.13330.2011:
3.3. The calculated resistance of the construction plywood is given in Table. 10.
Table 10.
| Type of plywood | Estimated resistance, MPa (kgf / sq. CM) | ||||
| Stretching in the sheet plane R. F.R. | compression in the sheet plane R. F.S. | bending from sheet plane R. F.I. | rocking in the sheet plane R. F.Sc. | cut perpendicular to the sheet plane R. F.Sh. | |
| 1. Plywood glued birch grades FSF varieties in / bb, in / s, bb / s | |||||
| a) seven layer 8 mm thick and more: | |||||
| along the fibers | 14(140) | 12(120) | 16(160) | 0,8(8) | 6(60) |
| 9(90) | 8,5(85) | 6,5(65) | 0,8(8) | 6(60) | |
| at an angle of 45 ° to the fibers | 4,5(45) | 7(70) | _ | 0,8(8) | 9(90) |
| b) five-layer 5-7 mm thick: | |||||
| along the fibers of the outer layers | 14(140) | 13(130) | 18(180) | 0,8(8) | 5(50) |
| across the fibers of the outer layers | 6(60) | 7(70) | 3(30) | 0,8(8) | 6(60) |
| at an angle of 45 ° to the fibers | 4(40) | 6(60) | _ | 0,8(8) | 9(90) |
| 2. Plywood glued from the larch wood of the FSF grade varieties in / explosive and BB / with a semi-layer thickness of 8 mm and more: | |||||
| along the fibers of the outer layers | 9(90) | 17(170) | 18(180) | 0,6(6) | 5(50) |
| across the fibers of the outer layers | 7,5(75) | 13(130) | 11(110) | 0,5(5) | 5(50) |
| at an angle of 45 ° to the fibers | 3(30) | 5(50) | _ | 0,7(7) | 7,5(75) |
| 3. Plywood Bakelized FSB grads with a thickness of 7 mm and more: | |||||
| along the fibers of the outer layers | 32(320) | 28(280) | 33(330) | 1,8(18) | 11(110) |
| across the fibers of the outer layers | 24(240) | 23(230) | 25(250) | 1,8(18) | 12(120) |
| at an angle of 45 ° to the fibers | 16,5(165) | 21(210) | _ | 1,8(18) | 16(160) |
Note. Estimated resistance to crumpled and compression perpendicular plane sheet for birch plywood FSF brand R. F.S.90 \u003d. R. F.Sm.90 \u003d 4 MPa (40 kgf / cm 2) and FBS brands R. F.S.90 \u003d. R. F.Sm.90 \u003d 8 MPa (80 kgf / cm 2).
In the necessary cases, the values \u200b\u200bof the calculated resistance of the construction plywood should be multiplied by the coefficients m. in, m. t, m. d, m. N I. m. And given in PP. 3.2, and; 3.2, b; 3.2, in; 3.2, g; 3.2, to these standards.
The scope of plywood depends on the characteristics of each type. One of the main parameters is the strength of plywood or resistance to destruction.
Features
This is a layered material, where veneer from various wood species alternates with adhesive composition on the base of the resin. Connecting layers into a single integer by pressing, as a result, a canvas with different properties are obtained, including stability resistance. This is due to some differences in technology, wood features and glue. Special production technology allows you to get such products that if you compare the strength of plywood and boards, then the first is more resistant to the loads, and this quality is used not only in the design of interiors, but also in construction and mechanical engineering.
Parameters defining plywood strength:
- Thickness;
- Species of wood;
- Crowded;
- Glue for production;
- Lamination.
Thickness
The standard thickness that can be products of industrial production is usually ranging from 3 to 30 mm, although the contract with a 40mm thick can be made under the contract with the enterprise. Naturally, high strength plywood will have a sheet thickness of about 20 mm and higher.
Type of wood from which veneer is manufactured
Practically any wood is used for design - coniferous and deciduous veneer that gives her different qualities. In the first case, it is used pine, larch or cedar, and the deciduous species of trees are represented mainly by birch, alder or poplar. If we evaluate the effect of the tree of wood for resistance to destruction, the advantage has a delicate plywood, its strength is higher due to the fact that the wood used for its production is more dense.
Note! Due to differences in density, even similar to the image of the canvas have a different weight. For example, with the same thickness of 21 mm, the coniferous standard size of 1.52 m per 1.52 m weighs about 32 kg, and the same sheet made from birch veneer will weigh 34.5 kg.
Crowded
The variety is determined by the number of defects on one square meter. Plywood, the tensile strength of which is quite high, should not have defects that reduce its resistance to destruction. There are only five varieties that determine the amount of defects and their size. The best is the products of elite varieties, without presence on the surface of damage, and can withstand significant loads. The products of the first and second grade can be considered sufficiently, because a small amount of defects allows it to laminate or use as a basis for finishing materials, including as a basis for floor covering.
Note! The lower the quality of the canvases, the smaller the safety margin of the strength is, therefore it is used or where there will be no heavy loads or to align the surface by another material, for example, if it is necessary to align the wooden floor in front of the finish coating, then the fourth grade sheets can be used.
Glue for production
Depending on which resins are used for the production of glue, products of the FC or FSF brand are obtained, having almost the same strength and the difference between them is manifested in how these types react to humidity. The highest strength has plywood, for which bakelite glue is used. This product is referred to as FB, FBS or BS and it can be used for almost any operating conditions.
Bakelite Sheets Boats
Lamination
Lamination when the veneer is covered with thermosetting film before gluing, allows you to create sheets having very high strength and resistance to damage. At the same time, the cost of the material is quite accessible, and the appearance allows you to use almost everywhere, because furniture from such sheets is indistinguishable from real wood, but unlike it is not afraid of high humidity.
Note! Laminated canvases may not only be dark shades. Popular and bright rich shades that are used to create original interiors.
Flexibility of material
A flexible plywood with unique properties that distinguishes it in a special appearance is particularly demand. It is indispensable to create decor elements in the interior and furniture with curved lines that cannot be created from other materials.
The high strength of the bending plywood provides wood exotic for our tree latitudes - Seb and Kuring, which, in addition to high flexibility, have good stroke resistance and are not afraid of moisture. It is made by such a canvas with a special way, having all the layers of the veneer so that the fibers are in the same direction.
What is the advantage of flexible plywood:
- High flexibility allows you to create forms where the canvas without damage can be bent to 180 o, which allows you to create elements of any form;
- The ability to process any ways that does not require acquisition to work with the material of special equipment;
- It has a smooth surface with high decorative characteristics, which allows it to be used for the manufacture of furniture, including kitchen, taking into account resistance to high humidity;
- Low density makes the material quite light and allows you to produce suspended structures that do not require reinforced fastening;
- The absence of smell and resins that distinguishes harmful to health compounds, which makes it possible to use it even for registration of children's rooms.
Recently, such material from birch veneer appeared, and such a plywood tensile strength under bending has higher than the usual specially developed technology, which almost twice reduces the density of the material.
Separation formwork element, perceiving concrete pressure and all other loads, it is plywood. The above mentioned plywood species have different values \u200b\u200bdepending on the direction of operation, both for the modulus of elasticity and for the flexural strength:
- In the floors with low requirements for the surface F - in overlaps with higher requirements for the surface F, the deflection of plywood (0 depends on the load (the thickness of the overlap), the characteristics of the plywood itself (the module of elasticity, the thickness of the sheet) and the content of the support.
Appendix 1 (Fig. 2.65) shows the charts on the main types of plywood supplied by Peri - Birch Plywood (Fin-Pry and Peri Birch) and conifer (Peri-Sprice). The diagrams are composed for a sheet thickness of 21 mm. At the same time, the dotted line is allocated areas where the deflection exceeds 1/500 span. All lines end when the strength limit is reached. The main charts are made up for standard sheets working as multiplet continuous beams (minimum three spans).
For the running size of sheets, the following variants of the step of transverse beams are obtained.
Table 2.7.
When evaluating the deflection at a good: for birch plywood, they take the same values \u200b\u200bfor the modulus of elasticity and strength limit, as for the main sheets, as it is not always known, in which direction there are a goodwear. For coniferous plywood
in which, when turning the sheet, these characteristics change dramatically.
According to the diagram (Fig. 2.65) for birch plywood with 3 or more spans, along the X axis, we find our overlap thickness value (20 cm) and determine the values \u200b\u200bfor the deflection:
For our sheet length, two options are acceptable - either 50 cm, or 62.5 cm. Let us dwell on the second version, as it gives savings by the number of transverse beams. The maximum deflection is 1.18 mm. We look into the diagram for a single-spare system. With such a scheme, a line for a span of 60 cm just on the value of the overlap thickness in 20 cm ends (plywood strength). The deflection is 1.92 mm.
From this it follows that in order to avoid inflated deformations of the problem, you should either limit the span of this kind to 50 cm, or to put the additional transverse beam (the calculated scheme of a uniformly loaded 2-touch beam has the smallest values \u200b\u200bfor the defaults, but it has an increase in relation to to multiplet schemes supporting moment).
Determination of the span of transverse beams (pitch of longitudinal beams b)
According to the transverse beams selected in the previous paragraph, check the tables in the corresponding bar. 2.11 The maximum allowable span of these beams. As already mentioned above, these tables are compiled, taking into account all the calculated cases, for transverse beams, first of all, a moment and deflection.
When choosing a step of longitudinal beams, it is necessary to consider that the extreme longitudinal beam is at a distance of 15-30 cm from the wall. An increase in this size may result in the following unpleasant results:
- increasing and unevenness of deflection on cross-beam consoles;
- Opportunities for overturning transverse beams during reinforcement work.
Reducing complicates rack management and creates a risk of scaling transverse beams from longitudinal.
For the same reason, as well as taking into account the normal operation of the end of the beam (especially when using Baok Farm), a minimum beam beam is assigned to 15 cm on each side. The actual step of longitudinal beams in no case should exceed the permissible value in Table. 2.11 and 2.12. Recall that the span in the formula for determining the moment is present in the square, and in the deflection formula even in the fourth degree (according to formula 2.1 and 2.2).
Example
For simplicity, we select a rectangular room with internal dimensions of 6.60x9.00 m. The overlap thickness is 20 cm, PERI BIRCH plywood with a thickness of 21 mm and the size of 2500x1250 mm.
The permissible value for the span of the transverse beams during their step in 62.5 cm will be found along Table. 2.11 for GT 24 beam beams. In the first column of the table we will find a thickness of 20 cm and move to the right to the appropriate step of cross-beams (62.5 cm). We find the maximum permissible value of the span 3.27 m.
We present the calculated values \u200b\u200bof the moment and deflection for this span:
- the maximum moment at the time of concreting is 5.9 kNm (permissible 7 kNm);
- Maximum deflection (single-break beam) - 6.4 mm \u003d 1/511 span.
If the longitudinal beams put in parallel to the length of the room side, we get:
6.6 m - 2 (0.15 m) \u003d 6.3 m; 6.3: 2 \u003d 3.15 m 3.27 m; 8.7: 3 \u003d 2.9 Mf Three spans with a length of beams of 3.30 m (minimum 2.9 + 0.15 + 0.15 \u003d 3.2 m). Transverse beams are less loaded - most often it is already a sign of material overpower.
In some cases, for example, if necessary, the installation of the formwork around the predetermined large-sized equipment has to be calculated by the beams. The following prerequisites should be taken into account. As the calculated scheme in the MultiFlex type systems, only a single-break hinged leaf beam without consoles is considered, since when installing the formwork and during concreting, we always have intermediate stages, where the beams work precisely according to such a scheme. For large beam spans without additional support, the loss of stability is possible already with small loads. Any formwork of overlapping after concreting should be pulled out from under the finished overlap, sometimes from a closed room, so it is desirable to limit the length of the beams (the problem of weight and maneuverability).
In the absence of values \u200b\u200bin the table, it can still be used. For example, to increase the span, you want to reduce the beam step - as a result, you must check the permissibility of the span. For example, the beams decided to put 30 cm in increments, the overlapping thickness is 22 cm. The calculated load is according to the 7.6 N / m2 table. We multiply this load on the beam step: 7.6-0.3 \u003d 2.28 kN / m. We divide this value for one step of transverse beams, which are present in the table: 2.28: 0.4 \u003d 5.7 ~ 6.1 (load on overlapping thickness 16 cm); 2.28: 0.5 \u003d 4.56 - 5.0 (load on overlapping with a thickness of 12 cm).
In the first case, we find for the thickness of the overlap 16 cm and the beam steps 40 cm. The span is 4.07 m, in the second case - the thickness is 12 cm and step 50 cm - 4.12 m.
We can take a smaller of two values \u200b\u200bminus the difference of these values \u200b\u200b(Accounting for changing the temporary load, which is present only in the calculation at the time), without losing time for long-term calculations. In a concrete example, it turns out with the exact calculation
4.6 m, and accepted 4.02 m.
