Wood as a natural construction material lesson notes. Lesson summary on technology: “Wood as a natural structural material. "Wood as a natural structural material"
DURING THE CLASSES
greetings,
checking students' readiness for the lesson,
communicating the lesson plan to students
III. Presentation of new material.
1. History of the creation of sewing machines.
People have been sewing with hand stitches for many centuries, and they have never abandoned the idea of speeding up their work. The first project known to us sewing machine dates back to the end of the 15th century. It is attributed to Leonardo da Vinci .
In 1755, German Karl Weisenthal invented a sewing machine that used a needle with an eye in the middle. This machine copied the principle of manual stitch formation. And the design that is widespread now has developed in general outline only by the 50s of the 19th century.
In 1844-1845, the American Elias Howe, who is considered the father of sewing machines, using the operating principle of Walter Hunt's machine (he invented a needle with an eye on a pointed end and a shuttle device), made a number of improvements in it and created a stable working lockstitch sewing machine. He managed to obtain a patent for a new machine that worked at a speed of 300 stitches per minute, while the needle moved horizontally, and the stitched fabrics were located in vertical plane and could only move in a straight line, and soon several more such sewing machines were made, each of which replaced the labor of five tailors.
In 1850-1851 Through the efforts of the Americans Alain Wilson and especially Isaac Merite Singer, the sewing machine was brought almost to its modern form.
Besides manual drive the machines were equipped with a foot drive, which freed up the tailor's hands. For the lower thread, a shuttle with a built-in bobbin similar to the Hunt and Howe shuttle was used.
From the USA, sewing machines began to be imported to Europe and Asia, and in 1877 they appeared in Japan. The most widely used machine was Isaac Singer's machine.
Since 1870, the Singer company opened its branch in Russia. In the town of Podolsk near Moscow in 1900, the company founded a factory that assembled sewing machines from parts delivered from abroad.
The creators tried to decorate the first cars with intricate drawings and carvings. A car was considered beautiful if it was richly decorated, decorated with cast ornaments and had a compositional design with a center in the middle of the ornament.
At the beginning of the 20th century, the so-called bottle shape of the sleeve of household sewing machines came into fashion. This form, in combination with a decorative cast table, was introduced by the Singer company and turned out to be so rational and perfect that it is still preserved in a number of countries in the simplest straight stitch machines, decorated with decorative ornaments.
2. Types of drives.
Drive unit – This is a device that drives the stitching mechanisms. cars .
Types of sewing machine drives: Manual; Foot; Electric drive.
3. The design of a sewing machine with an electric drive.
(Demonstration by the teacher of the structure of a sewing machine; students are offered cards - pictures Appendix 1, which they paste in their notes and indicate the parts of the sewing machine).
1 – platform.
2 – sleeve stand.
3 – sleeve.
4 – shuttle mechanism.
5 – toothed rack (for advancing fabric).
6 – switch.
7 – reverse lever (for fastening).
8 – seam selector (types of figured stitches and straight stitch lengths).
9 – flywheel.
10 – winder device (winding thread onto a bobbin).
11 – rod (for a spool of thread).
12 – adjuster for the width of curly stitches.
13 – needle bar position regulator.
14 – thread guide.
15 – upper thread tension regulator.
16 – thread take-up lever.
17 – needle bar.
18 – thread guide on the needle bar.
19 – needle.
20 – foot
Rules for working with a sewing machine.
Students are explained the rules of organization and safety precautions for working with a sewing machine, then they paste “Memos” into their notes (Appendix No. 2)
Memo.
Check the fabric for needles and pins.
Sit upright at the sewing machine with the pedal pushed up.
There should be nothing unnecessary on the table.
Check the seam adjusters.
Check the operation of the sewing machine at idle speed (turn the handwheel by hand).
Check the quality of the stitching (raise the foot, place a piece of fabric folded in half, lower the needle, foot, make the first two stitches, turning the handwheel towards you; then press the pedal).
If the stitching is not of good quality, check the threading or adjust the thread tension.
Correct sitting position at the sewing machine
Students are explained the rules for sitting when working at a sewing machine, then they paste “Memos” in their notes. (Appendix No. 3)
Memo.
“How to use a sewing machine”
You need to sit straight behind the machine, on the entire surface of the chair, slightly tilting your head and body forward;
the chair should be positioned so that the needle is directly in front of you;
the distance between the worker and the machine should be 20 - 30 cm;
the legs should rest with the entire foot on the floor or stand;
Do not lean close to the moving parts of the machine;
need to be monitored correct position hands
VI. Lesson summary.
What new did you learn in the lesson?
What drives do you know now?
What does a sewing machine consist of?
How to sit behind the car correctly?
VII. Homework.
Compose a crossword or rebus on the structure of an electric sewing machine.
Wood - natural construction material. Lumber and wood materials. Graphic representation of wood parts: Plywood and fiberboard.
Goals: familiarize students with wood as a structural material, with types of lumber and wood materials; teach to identify samples by appearance tree species; cultivate a caring attitude towards wood and wood.
Tools and equipment: table “Wood structure”; collection of wood species samples; set of wood lumber, veneer, plywood, fiberboard, chipboard;
During the classes
Wood is a natural construction material. It is obtained from the trunks of felled trees various breeds. The following tree species are distinguished: deciduous (oak, birch, linden, aspen, beech, etc.), and coniferous (spruce, pine, cedar)
Let's look at the structure of wood:
A tree consists of a root (1),
trunk (2),
branches (3),
leaves or needles (4).
The tree trunk has a thicker (butt) part at the base and a thinner part at the top. The top of the trunk is covered with bark. The bark consists of an outer cork layer and an inner bast layer. The main part of a tree trunk consists of wood. In turn, the wood of the trunk consists of many layers, which are visible in the section as growth rings. The age of the tree is determined by the number of growth rings.
Loose and soft center the tree is called the core. The medullary rays extend from the core to the bark in the form of light shiny lines. They have different colors and serve to conduct water, air and nutrients into the tree.
Cambium is a thin layer of living cells located between the bark and wood. Only from the cambium does the formation of new cells occur.
Wood species:
Pine- coniferous species. Soft. Impregnated with resinous substances. The wood is reddish in color with a pronounced texture. It is used for the manufacture of windows and doors, floors and ceilings, the construction of furniture, ships, carriages, bridges.
Spruce- coniferous species. Soft. Impregnated with resinous substances. The color is white with a yellowish tint. Used for the manufacture of musical instruments, furniture, windows and doors.
Birch- hardwood. Solid. The color is white with a brownish tint. Used to make plywood, furniture, ouds, gun stocks, tool handles, and skis.
Aspen- hardwood. Soft. The color is white with a greenish tint. Prone to rotting. Used for making matches, dishes, toys, paper.
Linden- hardwood. Soft. Color white with soft pink tint. It is used for making dishes, drawing boards, pencils, and products with artistic carvings.
Alder- hardwood. Soft. The color is white, turns red in the air. Serves as a raw material for the manufacture of plywood, dugout oud, and packing boxes.
Oak- hardwood. Solid. The color is light yellow with a brownish-gray tint and a distinct texture. On a radial section, the medullary rays are visible in the form of shiny stripes. It is used for the manufacture of furniture, parquet, cladding of valuable products, as well as in the construction of bridges and carriages.
Lumber:
Tree trunks, after trimming branches and twigs, are cut into logs. The logs are sawn lengthwise and lumber is obtained: edged and unedged boards, beams, whetstones, slabs. Lumber has the following elements: face, edge, end, edge.
Wood materials:
In addition to lumber, wood materials are also produced and used: particle boards and fiberboards, veneer, plywood, etc.
Chipboard is made on special machines by pressing chips mixed with synthetic resin.
Fiberboard is pressed into sheets of shredded wood.
Chipboard and fiberboard are used for making furniture and in construction.
Veneer is thin layers of wood. It is received at special machines
Plywood is a wood material cured by gluing together three or more thin sheets of veneer.
Stages of planning work to manufacture a product. Jigsaw technology. Safety rules when working with a jigsaw and burner.
Goals:
Educational: Introduce types of wood carving; sawing technology with a hand jigsaw along the external, internal contour; safety precautions when cutting.
Developmental: develop artistic taste and artistic creativity,
careful handling of materials and tools, patience, accuracy, attention, eye.
Career guidance: introduce the work of a wood carver.
Lesson type: combined.
Teaching method: explanatory and illustrative.
Visual aids: board, posters, templates, handouts, tools and accessories for cutting, crafts and products.
>>Technology: Wood is a natural construction material
A tree consists of a trunk, roots, branches, leaves or needles. Trees with foliage are called deciduous, and those with needles are called coniferous. Deciduous species are birch, aspen, oak, alder, linden, etc., coniferous species are pine, spruce, cedar, fir, larch, etc. A tree is called larch because, like deciduous species, it sheds its needles in the winter.
Wood as a natural structural material obtained from tree trunks when sawing them into pieces.
The tree trunk has a thicker part at the base and a thinner part at the top. The surface of the trunk is covered with bark. The bark is like clothing for a tree and consists of an outer cork layer and an inner bast layer (Fig. 8). The cork layer of bark is dead. The bast layer serves as a conductor for the juices that nourish the tree. Main inner part The tree trunk is made of wood. In turn, the wood of the trunk consists of many layers, which are visible in the section as growth rings. The age of the tree is determined by the number of growth rings.
The loose and soft center of the tree is called the heartwood. The medullary rays extend from the core to the bark in the form of light shiny lines. They have different colors and serve to conduct water, air and nutrients inside the tree.
The core rays create the pattern (texture) of wood.
Cambium- a thin layer of living cells located between the bark and wood. Only from the cambium does the formation of cells and the annual increase in thickness of the tree occur. "Cambium - from the Latin "exchange" ( nutrients).
To study the structure of wood, three main sections of the trunk are distinguished (Fig. 9).
Cut 1, running perpendicular to the core of the trunk, is made end-to-end. It is perpendicular to the growth rings and fibers.
Cut 2 passing through the core of the trunk is called radial. It is parallel to the annual layers and fibers. Tangential cut 3 runs parallel to the core of the trunk and is some distance away from it. These sections reveal various properties and wood drawings.
Wood species are determined by their following characteristic features; texture, smell, hardness, color.
Pine-coniferous breed. Soft. Impregnated with resinous substances. The wood is reddish in color with a pronounced texture. It is used for the manufacture of windows and doors, floors and ceilings, furniture, in the construction of ships, carriages, bridges.
Spruce- coniferous breed. Soft. Impregnated with resinous substances. The color is white with a yellowish tint. Used for heating musical instruments, furniture, windows and doors.
Birch- hardwood. Solid. The color is white with a brownish tint. Used to make plywood, furniture, ouds, gun stocks, tool handles, and skis.
Aspen- hardwood. Soft. The color is white with a greenish tint. Prone to rotting. Used for making matches, dishes, toys, paper.
Linden-deciduous species. Soft. The color is white with a soft pink tint. It is used for making dishes, drawing boards, pencils, and products with artistic carvings.
Alder- hardwood. Soft. The color is white, turns red in the air. Serves as a raw material for the manufacture of plywood, dugout oud, and packing boxes.
Oak- hardwood. Solid. The color is light yellow with a brownish-gray tint and a pronounced texture. On a radial section, the medullary rays are visible in the form of shiny stripes. It is used for the manufacture of furniture, parquet, cladding of valuable products, as well as in the construction of bridges and carriages.
The wood texture of the most common species is shown in Figure 10. 
The texture of wood is the pattern on its surface formed as a result of cutting growth rings and fibers. The beautiful surface of wood is said to have a rich texture. For example, walnut or Manchurian walnut wood has brown and gray colors a wide variety of shades, it is highly valued for making furniture and hunting rifle stocks from it (Fig. 10, a). A particularly valuable texture is formed by unsprouted buds (eyes) on the surface of Karelian birch (Fig. 10, b). Oak, ash, and also mahogany species growing in Africa, America, and Australia have beautiful textures (Fig. 10, c), producing red wood of various shades. Such valuable species wood is planed into thin sheets (veneer), which are glued onto valuable products.
PRACTICAL WORK
Determination of wood species from samples
1. Study the description or table of tree species.
2. Write down in your notebook the main characteristics by which wood species are determined.
3. Identify the types of wood using the samples given by the teacher.
- Wood, tree, coniferous and deciduous species, trunk, bark, core, trunk cuts (end, radial, tangential), growth rings, texture.
1. What parts does a tree consist of?
2. What types of trees do you thorn?
3. Where is wood used?
4. What do tree rings show?
5. What is wood texture called?
A.T. Tishchenko, P.S. Samorodsky, V.D. Simonenko, N.P. Shchipitsyn, Technology 5th grade
Submitted by readers from the website
Item: Technology (boys). Section “Wood processing technology. Elements of Mechanical Engineering"
Location: workshop of Sahaptinskaya secondary school
Lesson topic: Wood as a natural construction material..
Lesson type: combined.
Teaching methods: oral questioning, storytelling, demonstration of visual aids, practical work.
Literature: Textbook V.D. Simonenko.
Equipment: samples of various types of wood.
Lesson objectives:
Study with students the types of wood, structure and areas of its application.
cultivate interest in learning.
develop the ability to identify wood types by eye.
Organizational part.
Theoretical part.
Repetition of covered material.
What are the main parts? carpentry workbench?
What purpose do the front and rear screw clamps serve?
List the rules at the woodworking bench.
Explanation of new material:
Forests occupy an area of over 700 million hectares in our country. Despite such enormous forest wealth, everyone must treat the forest with care, since it significantly affects the climate, vegetation and animal world In addition, the forest is of great economic importance. Its main product - wood - is used in construction, furniture, match production, chemical industry, etc. Forest resources in our country are protected by law.
What is a tree made of?
A tree consists of a trunk, roots, branches, leaves and needles. Trees with foliage are called deciduous, and those having needles - coniferous. TO deciduous trees include birch, linden, aspen, alder, oak, etc. coniferous species– pine, spruce, cedar, fir, larch.
The top of the tree trunk, together with the branches, forms the crown.
The crown is one of the three main parts of the tree, which performs certain functions during its life. The leaves or needles of the crown absorb carbon from the air, forming organic substances in the sun that are used to build the plant body of the tree.
The other part of the tree is the roots. They can be compared to a foundation and piles that hold a tree trunk upright.
The third part of the tree is the trunk. It holds the heavy crown and serves as a conductor for nutrients coming from the roots and entering the leaves.
The trunk is the most valuable part of the tree.
Wood as a natural structural material is obtained from tree trunks by sawing them into pieces.
Trunk The tree has a thicker (butt) part at the base and a thinner part at the top. Barrel surface (Fig. 2) covered with bark(7). The bark is like clothing for a tree; it consists of an outer cork layer and an inner bast layer. Cork layer bark is dead . Bast layer(6) - a conductor of juices that nourish the tree. The main interior of a tree trunk consists of wood. In turn, the wood of the trunk consists of many layers, which are visible in the section as tree rings(4).
What can you tell from the number of tree rings?
The loose and soft center of the tree is called core (1). From the core to the bark in the form of light shiny lines extend medullary rays (2). The core rays create the pattern (texture) of wood.
Cambium (5)- a thin layer of living cells located between the bark and wood. Only from the cambium does the formation of new cells and the annual increase in thickness of the tree occur. “Cambium” comes from the Latin “exchange” (of nutrients).
(Figure 1)
Main sections of the trunk. (Fig. 2)
To study the structure of wood, three main sections of the trunk are distinguished. They reveal different properties and patterns of wood. The cut (1) running perpendicular to the core of the trunk is called end. It is perpendicular to the growth rings and fibers. The cut (2) passing through the core of the trunk is called radial. It is parallel to the annual layers and fibers. Tangential cut (3) runs parallel to the core of the trunk and is some distance away from it
(Fig. 2)
Let's look at the structure and scope.
Wood species. (Fig. 3)
They are determined by the following characteristic features: texture, smell, hardness, color.
Pine. Coniferous breed. Soft. Impregnated with resinous substances. The wood is red in color with a pronounced texture. It is used for the manufacture of windows and doors, floors and ceilings, furniture. In the construction of ships, carriages, bridges.
Spruce. Coniferous breed. Soft. Impregnated with resinous substances. Color white with yellow tint. Used for the manufacture of musical instruments, furniture, windows and doors.
Larch. The density of larch is 30% higher than that of pine. After lying in water for a long time, it becomes hard as a stone. Red-brown paint is made from the bark. Used for making houses, wheels, dishes, bridges.
Cedar. Sound breed. Cedar wood has wide white sapwood with a yellow tint and a pinkish-ocher heartwood. Used for floorboards, furniture, pencils.
Birch. Hardwood. Solid. The color is white with a brownish tint. It is used for the manufacture of musical plywood, furniture, dishes, gun stocks, and skis.
Aspen. Hardwood. Soft. The color is white with a greenish tint. Prone to rotting. Used for making matches, dishes, toys, paper.
Linden. Hardwood. Soft. The color is white with a pink tint. It is used for making dishes, drawing boards, pencils, and products with artistic carvings.
Oak. Hardwood. Solid. The color is light yellow with a brownish-gray tint and a distinct texture. It is used for the manufacture of furniture, parquet, cladding of valuable products, bridges and carriages.
(Fig. 3)
Most beautiful texture have species such as oak, ash and various types of mahogany. These rocks are planed into thin sheets - veneer, and then valuable products are glued onto them.
3. Practical work: identify wood types using samples given by the teacher.
1. Study the description and table of tree species.
2. Write down in a notebook the main characteristics by which wood species are determined.
3. Determine the types of wood using samples given by the teacher.
III. Lesson summary: verification of practical work.
IV. Homework assignment: learn definitions. 2, pp. 12-15.
The lesson plan was compiled by Ivan Evgenievich Kryukov, a technology teacher at Sahaptinskaya Secondary School.
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Wood as a construction material
Our country is the first in the world in terms of the number of forest areas, which occupy almost half of the territory of Russia - approximately 12.3 million km 2. The main part of Russia's forests, about 3/4, is located in the regions of Siberia, Far East, in the northern regions of the European part of the country. The predominant species are conifers: 37% of the forests are larch, 19% - pine, 20% - spruce and fir, 8% - cedar. Deciduous trees occupy about half the area of our forests. The most common species is birch, occupying about 1/6 of the total forest area.
Wood reserves in our forests amount to about 80 billion m3. About 280 million m3 are harvested annually. industrial wood, i.e. suitable for the manufacture of structures and products. However, this amount does not exhaust the natural annual growth of wood in remote areas of Siberia and the Far East.
Harvested timber in the form of sections of trunks of standard length is delivered by road, rail and water transport or by rafting along rivers and lakes to wood processing enterprises. There, sawn materials, plywood, wood boards, structures and building parts are made from it. During logging and wood processing, a large amount of waste is generated, efficient use which are of great national economic importance. The production of insulating fiberboards and particle boards from wood waste, which are widely used in construction, allows saving a large amount of industrial wood.
Coniferous wood is used to make basic elements wooden structures and construction parts. Straight tall trunks coniferous trees with a small number of knots make it possible to obtain straight lumber with a limited number of defects. Coniferous wood contains resins, which makes it more resistant to moisture and decay than deciduous wood.
Most hardwood species are less straight, have more knots, and are more susceptible to rot than softwood. It is almost never used for the manufacture of basic wooden elements building structures.
Oak wood stands out among hardwoods for its increased strength and resistance to decay. However, due to its scarcity and high cost, it is used only for small connecting parts.
Birch wood also belongs to hard deciduous species. It is used mainly for the production of construction plywood. Needs protection from decay.
Advantages and disadvantages of wood as building material.
Wood, like other building materials, has its advantages and disadvantages.
Advantages:
Availability of a wide, constantly renewable raw material base;
Relatively low density;
High specific strength - the ratio of tensile strength along the fibers to density: 100/500 = 0.2 (approximately equal to steel);
Resistance to salt aggression and other chemically aggressive environments;
Biological compatibility with humans and animals - timber buildings have the best microclimate;
High aesthetic and acoustic properties - the best concert halls countries are lined with wood;
Low coefficient of thermal conductivity across the fibers - a wall made of timber 200 mm wide is equivalent in thermal conductivity brick wall width 640 mm;
Low coefficient of linear expansion along the fibers - in wooden buildings there is no need to install expansion joints and movable supports;
Less labor intensive machining, the possibility of creating bent-glued structures.
Flaws:
Anisotropy of wood structure;
Susceptibility to decay and damage by wood-boring beetles;
Combustibility in fire conditions;
Change physical and mechanical characteristics under the influence of various factors (moisture, temperature);
Shrinkage, swelling, warping and cracking under the influence of atmospheric influences;
The presence of defects (knots, slanted grain and others) that significantly reduce the quality of products and structures;
Limited range of timber products.
Wood structure
As a result of plant origin, wood has a tubular layered fibrous structure. The bulk of wood consists of wood fibers located along the trunk. They consist of elongated hollow shells of dead cells (tracheids, about 3 mm long) of organic substances (cellulose and legnin).
Wood fibers are arranged in concentric layers around the axis of the trunk, which are called annual layers, because each layer grows throughout the year. They are clearly visible in the form of a series of rings on transverse sections of the trunk, especially of coniferous trees. By their number you can determine the age of the tree.
Each annual layer consists of two parts. The inner layer (wider and lighter) consists of soft early wood, formed in the spring when the tree grows quickly. Earlywood cells have thinner walls and wider cavities. Latewood cells have thicker walls and narrow cavities. The strength and density of wood depends on the relative content of late wood in it.
The middle part of coniferous wood trunks has more dark color, contains more resin and is called the core. Then comes the sapwood and finally the bark.
In addition, the wood contains horizontal core rays, a soft core, resin ducts, and knots.
Timber obtained for construction is divided into round and sawn.
Round timber, also called logs, are parts of tree trunks with smoothly sawn ends - the ends. They have standard length 3 - 6.5 m with gradation every 0.5 m. The logs have a natural truncated-conical shape. Reducing their thickness along the length is called running. On average, the runoff is 0.8 cm per 1 m of length (for larch 1 cm per 1 m of length) of the log. Medium logs have a thickness of 14 to 24 cm; large logs are up to 26 cm. Logs with a thickness of 13 cm (subtovarnik) and less are used for temporary construction structures. Depending on quality, round timber is divided into grades 1, 2 and 3.
Lumber is obtained by longitudinal sawing of logs on sawmill frames or circular saws. Lumber is divided according to the nature of processing: edged (sawn on 4 sides along the entire length); wane (part of the surface is not sawn along the entire length due to the run-off of the log); unedged (two edges are not sawn).
Lumber rectangular section divided into boards, bars and beams. The wider sides of lumber are called seams, and the narrower sides are called edges. Lumber has a standard length of 1-6.5 m with gradation every 0.25 m. The width of lumber ranges from 75 to 275 mm, thickness - from 16 to 250 mm. Based on the quality of wood and processing, boards and bars are divided into five grades (selected, 1, 2, 3, 4th), and beams into four (1, 2, 3, 4th).
Density. Wood belongs to the class of lightweight structural materials. Its density depends on the relative volume of the pores and their moisture content. The standard density of wood should be determined at a moisture content of 12%. Freshly cut wood has a density of 850 kg/m3. The calculated density of coniferous wood as part of structures in rooms with a standard air humidity of 12% is taken equal to 500 kg/m3, in rooms with an air humidity of more than 75% and at outdoors- 600 kg/m 3.
Temperature expansion. Linear expansion upon heating, characterized by the coefficient of linear expansion, in wood varies along and at angles to the fibers. The coefficient of linear expansion b along the fibers is (3 h 5) 10-6, which makes it possible to build wooden buildings without expansion joints. Across the wood fibers, this coefficient is 7 to 10 times less.
The heat capacity of wood is significant; the heat capacity coefficient of dry wood is C = 1.6 KJ/kg єС.
Another valuable property of wood is its resistance to many chemical and biological aggressive environments. She is chemically more resistant material than metal and reinforced concrete. At ordinary temperatures, hydrofluoric, phosphoric and hydrochloric (low concentration) acids do not destroy wood. Most organic acids do not weaken wood at ordinary temperatures, so it is often used for structures in chemically aggressive environments.
Mechanical properties wood is characterized by: strength - the ability to resist destruction from mechanical influences; rigidity - the ability to resist changes in size and shape; hardness - the ability to resist the penetration of another solid body; impact strength - the ability to absorb work upon impact.
Wood is an anisotropic material, so its strength depends on the direction of the forces applied to the fibers. When forces act along the fibers, cell membranes work in the most favorable conditions and wood shows the greatest strength.
The average tensile strength of pine wood without defects along the grain is:
Tensile - 100 MPa.
When bending - 80 MPa.
Under compression - 44 MPa.
When stretched, compressed and sheared across the fibers, this value does not exceed 6.5 MPa. The presence of defects significantly (by ~30%) reduces the strength of wood in compression and bending, and especially (by ~70%) in tension. The main unacceptable defects of wood are: rot, wormholes and cracks in chipping zones in joints.
The most common and inevitable defects of wood are knots - overgrown remains of former tree branches. Knots are acceptable with limited defects.
The duration of the load significantly affects the strength of wood. Under unlimited long-term loading, its strength is characterized by a long-term resistance limit, which is only 0.5 of the strength limit under standard loading. Wood exhibits the greatest strength, 1.5 times higher than short-term strength, under the shortest shock and explosive loads. Vibration loads, causing stress to change in sign, reduce its strength.
The rigidity of wood (its degree of deformability under the influence of a load) significantly depends on the direction of action of the loads in relation to the fibers, their duration and the moisture content of the wood. Stiffness is determined by the elastic modulus E.
For conifers along the fibers E = 15000 MPa.
In SNiP II-25-80, the modulus of elasticity for any type of wood is Eo = 10,000 MPa. E90 = 400 MPa.
At high humidity, temperature, as well as under the combined action of permanent and temporary loads, the value of E is reduced by the operating condition coefficients mв, mт, mд< 1.
Influence of humidity. A change in humidity ranging from 0% to 30% leads to a decrease in wood strength by 30% of the maximum. Further changes in humidity do not reduce the strength of the wood.
Transverse changes in humidity (shrinkage and swelling) lead to warping of wood. The greatest shrinkage occurs across the fibers, perpendicular to the annual layers. Shrinkage deformations develop unevenly from the surface to the center. During drying, not only warping appears, but also shrinkage cracks.
To compare the strength and stiffness of wood, the standard moisture content is set to 12%
B12=BW,
where b is the correction factor, for compression and bending b = 0.04.
Effect of temperature. As the temperature rises, the tensile strength and modulus of elasticity decrease, and the fragility of wood increases. The tensile strength of wood Gt at a temperature t ranging from 10 to 30 o C can be determined based on its initial strength - G20 at a temperature of 20 o C, taking into account the correction factor b = 3.5 MPa.
Gt = G20 - in(t-20).
Wood for load-bearing elements of wooden structures must meet the requirements of grades I, II and III.
Grade I wood is used in the most critical stressed tensile elements. These are individual stretched rods and boards of stretched zones of laminated beams with a section height of more than 50 cm
Cross-layered? 7%.
Total diameter of knots over a length of 20 cm d? 1/4b.
Grade II wood is used in compressed and bending elements. These are individual compressed rods, boards of the extreme zones of glued beams with a height of less than 50 cm; boards of the extreme compressed zone and stretched zone located above boards of the 1st grade in laminated beams with a height of more than 50 cm, boards of the extreme zones of working glued compressed, bent and compressed-bent rods.
Cross-layer? 10%.
Total diameter of knots over a length of 20 cm d? 1/3b.
Grade III wood is used in less stressed medium laminated compressed, bent and compressed-bent elements, as well as in lightly critical elements of decking and sheathing.
Cross-layer? 12%.
Total diameter of knots over a length of 20 cm d? 1/2b.
Construction plywood is a factory-made sheet wood material. It consists, as a rule, of an odd number of thin layers - veneers. The fibers of adjacent veneers are located in mutually perpendicular directions.
SNiP II-25-80 for the design of wooden structures recommends the following types waterproof plywood as construction:
1. FSF grade plywood, glued with phenol-formaldehyde adhesives. This plywood is produced:
Made from birch wood (5- and 7-layer, 5 - 8 mm thick or more).
Made from larch wood (7-layer, 8 mm thick or more).
Sheets of plywood with a thickness of more than 15 mm are called plywood boards. The shear strength of plywood in a plane perpendicular to the sheet is approximately 3 times higher than the strength of wood when chipped along the grain, which is its important advantage.
The modulus of elasticity of birch plywood along the grain is 90%, and across it is 60% of the modulus of elasticity of wood along the grain. The elastic moduli of larch plywood are 70% and 50% of the Eo of wood, respectively.
Banelized plywood (FBS) differs from FSF grade plywood in that its outer layers are impregnated with water-resistant alcohol-soluble resins. It has a thickness of 7-18 m. Its strength along the grain is 2.5 times, and across it is 2 times greater than the strength of coniferous wood along the grain. Used in particularly unfavorable humidity conditions.
Rotting is the destruction of wood by the simplest plant organisms - wood-destroying fungi. Some fungi infect still growing and drying trees in the forest. Warehouse mushrooms destroy timber during storage in warehouses. House mushrooms - (merilius, poria, etc.) destroy the wood of building structures during operation. wood construction plywood rotting
Fungi develop from cells - spores, which are easily transported by air movement. Growing, the spores form a fruiting body and a mycelium of the fungus - a source of new spores.
Rot protection:
1. Sterilization of wood during high-temperature drying. Warming up wood at t > 80 o C, which leads to the death of fungal spores, myceliums and fungal fruiting bodies.
2. Structural protection assumes an operating mode when the wood moisture content is W<20% (наименьшая влажность при которой могут расти грибы).
2.1. Protection of wood from atmospheric moisture - waterproofing of coatings, required roof slope.
2.2. Protection from condensation moisture - vapor barrier, ventilation of structures (drying vents).
2.3. Protection against moisture from capillary moisture (from the ground) - waterproofing device. Wooden structures must rest on a foundation (with bitumen or roofing felt insulation) above the ground or floor level by at least 15 cm.
3. Chemical protection against rotting is necessary when wood moisture is unavoidable. Chemical protection consists of impregnation with substances poisonous to fungi - antiseptics.
Water-soluble antiseptics (sodium fluoride, sodium fluoride) are colorless, odorless substances that are harmless to people. Used indoors.
Oily antiseptics are mineral oils (coal oil, anthroscene oil, shale oil, wood creosote, etc.). They do not dissolve in water, but are harmful to humans, therefore they are used for structures in the open air, in the ground, above water.
Impregnation is carried out in autoclaves under high pressure (up to 14 MPa).
Protection from grinder beetles - heating to t>80 o C or fumigation poisonous gases type hexachlorane.
It is characterized by a fire resistance limit (about 40 minutes for a beam 17 x 17 cm, loaded to a stress of 10 MPa).
1. Constructive. Elimination of conditions favorable for fires.
2. Chemical (fireproof impregnation or painting). Impregnated with substances called fire retardants (for example, ammonium salt, phosphoric and sulfuric acid). Impregnation is carried out in autoclaves simultaneously with antiseptic treatment. When heated, fire retardants melt, forming a fire retardant film. Protective painting is carried out with compositions based on liquid glass, superfluorine, etc.
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- Remember what material is called structural.
- What raw materials are paper and cardboard made from?
- Name the construction materials that are used for the production of cars, airplanes, construction of houses, manufacturing home furniture. Where are these materials made and what raw materials are used for this?
The development of modern equipment and technologies depends on the production and use of various structural materials: wood, metal, plastics, glass, etc. The use of wood has become widespread. Products made from it are used in almost all areas of our lives. This material is used to make paper, cardboard, artificial silk, plastic, furniture, building elements, musical instruments and souvenirs and many other necessary things.
All tree species are divided into two groups: coniferous and deciduous (Fig. 13).
Rice. 13. Tree species: a – coniferous; b – deciduous
Conifers have needle-shaped leaves. These include: spruce, pine, cedar, larch, fir, etc. Deciduous species are alder, linden, oak, beech, hornbeam and others (Fig. 14).
Rice. 14. Wood of various tree species: a – oak; b – linden; c – birch; g – alder; d – spruce; e – pine
Trees are used to make structural wood products. Wood materials are easy to process with various cutting tools: saws, knives, chisels, drills, files and others. Structural elements made of wood materials are reliably and firmly connected with nails, screws, and gluing. Trees are the tallest of all plants, although there are also dwarfs among them, up to several centimeters tall (Fig. 15).
Rice. 15. Tall (a) and dwarf (b) trees
Rice. 16. Tree structure
Each tree consists of three parts: root, trunk and crown (Fig. 16).
Root absorbs moisture and nutrients dissolved in it from the soil and conducts them to the trunk.
Trunk- This is the main part of the tree. It conducts water with nutrients dissolved in it from the root to the branches and leaves.
Crown – top part tree, consisting of branches and leaves. Tree leaves absorb carbon dioxide, and produce oxygen, which is why forests are called “the lungs of the planet.” They improve the condition environment By purifying the air and water, they contribute to the development of flora and fauna - all life on Earth.
Protection of Nature is an important responsibility of every person. Security in Ukraine natural resources has become one of the most important tasks, and such rare trees as Polish larch, cedar pine, chalk pine, Austrian oak, Dnieper birch and others, listed in the Red Book of Ukraine, are protected by law and prohibited for industrial use.
In our country there are forestry enterprises - specialized forestry enterprises that grow trees for industrial processing and production of wood materials. They grow different types of trees over vast areas. After a certain time, when the tree reaches industrial age, that is, it has a certain height and diameter of the trunk, it is harvested. At the same time, forestry also takes care of the renewal of forest plantations - new young trees are planted in place of cut trees.
In forestry, trees are first cut down (Fig. 17, a). Then the trunks, cleared of branches, which are called whips, are moved to the place of shipment. This process is called skidding. For skidding, special skidding tractors are used (Fig. 17, b). Then the wood is loaded and transported to a special overpass, where the logs are cut into pieces - logs. This process is called bucking (Fig. 18).
Rice. 17. Wood harvesting: a – sawing; b – skidding
Rice. 18. Bucking wood
The logs are called commercial wood, and the top of the log (where there are many knots) is called firewood (Fig. 19).
Rice. 19. Business (a) and firewood (b) wood
Rice. 20. Sawmill
To obtain wood materials, industrial wood is cut along the trunk using special machines - sawmills (Fig. 20). Enterprises that process wood are called wood processing. They also process wood waste: sawdust, bark, branches, roots. They are made from various materials: glue, rayon, paper, cardboard, wood boards, etc.
As a result of sawing industrial wood, a variety of timber lumber is formed (Fig. 21). A variety of products are made from lumber. However, in order for the product to be reliable in use, it must have an attractive appearance and a number of other qualitative characteristics, it is necessary to take into account the structural features of wood during its manufacture. It is studied through three sections of the trunk: transverse (end), radial and tangential (Fig. 22).
Rice. 21. Types of lumber
Rice. 22. Main cuts of a tree trunk: 1 – tangential; 2 – radial; 3 – transverse (end)
Rice. 23. Annual rings on a cross section of a trunk
Rice. 24. Texture of some types of wood: a – oak; b – birch; c – nut; g – hornbeam
By the cross-section of the trunk and the number of rings that are visible on it, you can determine how old the tree is, how quickly it grew, how the weather changed during its growth, etc. (Fig. 23). The cross section shows alternating light and dark rings.
The cut of wood along the trunk through the core is called radial. It shows longitudinal stripes formed as a result of tree growth. By cutting the trunk at some distance from the core, a tangential cut is obtained. On it you can see a pattern of a certain color characteristic of each tree, which is called texture (Fig. 24). It depends on the structural features of each type of wood and the direction of the trunk cut.
You will learn about other properties of wood materials from the following paragraphs of the textbook.
Laboratory and practical work No. 3. Familiarization with the texture of wood materials
Equipment and materials: carpentry workbench, samples different breeds wood, magnifying glass, set of colored pencils, ruler, chalk.
Work sequence
- Look at samples of different types of wood.
- Mark each sample with chalk.
- Compare the texture of each wood sample with the texture of the different types of wood shown in Figure 24 in the textbook.
- Explain the similarities and differences between the samples (placement and width of annual rings, wood color, smell, other characteristics).
- Based on the above properties and the pattern of the corresponding texture shown in the textbook, determine the type of wood.
- Fill out the table according to the following example:
New terms
deciduous, coniferous, root, trunk, crown, industrial wood, firewood, industrial age, whip, log, bucking, texture.
Basic Concepts
- Timber - sawn tetrahedral log.
- The Red Book of Ukraine is a book that records plants and animals protected by the state and prohibited for industrial use.
- A sawmill is a device with an electric motor designed for sawing logs into lumber.
- Nutrients are substances dissolved in water that nourish the plant.
- Tree species is a set of certain characteristics and properties that characterize a tree.
- Natural resources are reserves of something in nature that can be used if necessary.
- Property, sign – a feature characteristic of something (for example, smell, color, sound conductivity, etc.).
Fixing the material
- What types of wood are classified as coniferous? To deciduous?
- What wood materials are produced at woodworking enterprises?
- What is wood texture called?
- What is the structure of a tree?
- What types of lumber do you know?
- Describe the role of forests in human life.
- How do green spaces improve the natural environment?
- What trees in your region are listed in the Red Book of Ukraine?
Test tasks
1. Coniferous species belong
- And the birch
B pine
In alder
G oak
D e l
E hornbeam
2. Lumber belongs to
- And the whip
B timber
In deck
G board
D all of the above
E none of the above
3. What are decks made from?
- And the tables
Used lumber
In the chairs
4. They belong to deciduous trees
- And maple
B eel
In aspen
G pine
5. What is the name of the natural pattern on the treated surface of wood?
- And the structure
B longitudinal stripes
B texture
G sapwood
