Wood and its properties = Древесина и ее свойства. Учебное пособие

temperatures as low as 120 ° C (250 ° F). In this range, wood gradually degrades or pyrolyzes. Pyrolysis is chemical breakdown caused by heat. If the temperature is raised above 200 ° C (392 ° F), rapid pyrolysis occurs. Pyrolysis accelerates between 260 and 350 ° C (500 and 680 ° F). At these temperatures, flammable gases are evolved. When heated in the presence of oxygen, these gases can either ignite from an ignition source such as a flame and they can self - ignite if the temperature becomes high enough. Above about 270 ° C (520 ° F), the rate of heat produced will be greater than the heat required to generate the gas and the fire will support itself. In a burning piece of wood, the carbon char left after the volatile gases are driven off tends to increase in thickness with time but at a decreasing rate. Because wood and char are good thermal insulators, the rate of heat transfer to the interior wood decreases as the char thickens. Eventually, the heat transferred inward may not be sufficient to produce and drive off flammable gases. If this occurs, the flame will die and unless there is an outside source of heat, the piece will gradually cool. Because of this self - insulating behavior, heavy members such as glue - laminated beams or solid - sawn timbers provide excellent fire resistance. Improved fire resistance ratings for light - frame buildings can be obtained by use of gypsum board on both sides of walls and on ceilings. Where a greater level of fire resistance is needed, wood members can be treated with fire retardants. The impregnation of wood with fire retardants is used commercially to reduce surface flammability by reducing the production of flammable gases. Wood so treated tends to char and decompose but does not support. Commonly used fire retardants incorporate combinations of organophosphates, boron, polyphosphates, and urea; 35 -80 kg m - 3 (2.2 - 5.0 lb ft - 3) are required for proper protection. Many fire retardants can be leached from the wood by water, so their use must be restricted to interior applications. Some nonleaching fire retardant treatments are, however, available for exterior applications such as wood shingles. Early fire retardants such as zinc chloride and ammonium sulfate often resulted in treated materials being more hygroscopic (i.e., more prone to absorb moisture) than normal wood at low humidity. The newer systems have a lower impact on hygroscopicity and are less corrosive. The three major model building codes permit fire retardant - treated lumber to be used in many building systems, which can then be rated as noncombustible, exposed wood roof systems, and interior wall and ceiling paneling in buildings requiring a relatively low flame - spread rating.

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[From: Shmulsky R., Jones P. D. Forest Products and wood science / R. Shmulsky, P. D. Jones. – US : Willey-Blackwell, 2011. – P. 244]

5. Read the following statements and define whether they are true or false according to the text.

1.Pyrolysis is chemical breakdown caused by heat.

2.When heated in the presence of oxygen, these gases can either ignite from an ignition source such as a flame and they can self - ignite if the temperature becomes low enough.

3.In a burning piece of wood, the carbon char left after the volatile gases are driven off tends to increase in thickness with time but at a increasing rate.

4.Where a greater level of fire resistance is needed, wood members can be treated with fire retardants.

5.The impregnation of wood with fire retardants is used commercially to reduce surface flammability.

6.Many fire retardants can`t be leached from the wood by water.

7.The use of fire retardants must be restricted to interior applications.

8.Early fire retardants such as zinc chloride and ammonium sulfate often resulted in treated materials being more hygroscopic.

9.The three major model building codes permit fire retardant - treated lumber to be used in many building systems, which can then be rated as combustible.

10.Nonleaching fire retardant treatments are available for exterior applications.

6. Give the English equivalents for the words and word combinations given below and memorize them.

Горючие газы, быстрый пиролиз, огнестойкость, уплотнение древесного угля, источник воспламенения, присутствие кислорода, внутреннее применение, обработанная древесина, теплопередача, объединение комбинаций, общее применение, ламинированный брус.

7. Give the Russian equivalents for the words and word combinations given below.

Rapid pyrolysis, fire retardants, low humidity, lower impact, interior wood,

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wood roof systems, char, ammonium sulfate, volatile gases, chemical breakdown, carbon dioxide, carbon monoxide, nonleaching fire.

8. Fill in the gaps.

1.Water vapor is driven off along with carbon ……and ……..monoxide.

2.Flammable gases are………..

3.The rate of heat produced will be greater than the heat required to

…………..and the fire will support itself.

4.When heated in the presence of oxygen, these gases can either ignite from an ignition source such as a flame and they can self -

………………..enough.

5.The heat transferred inward may not be sufficient to produce and drive off ………….gases.

6.The flame will die and unless there is an……………, the piece will gradually cool.

7.Heavy members such as glue - laminated beams or solid - sawn timbers provide excellent………………...

8.The impregnation of wood with fire retardants is used commercially to reduce …………….by reducing the production of flammable gases.

9.Commonly used fire retardants incorporate combinations of organophosphates, boron, ………………, and urea are required for proper protection.

10.When wood is heated above about 100 ° C (212 ° F)

…………….occurs.

9. Translate the following sentences from Russian into English.

1.Горючие газы улетучиваются при температурах до 120 ° C (250 ° F).

2.В данном диапазоне, древесина постепенно ухудшается.

3.Многие виды защиты от огня могут вымываться из древесины водой, поэтому их применение должно быть ограничено до внутреннего применения.

4. Обычно используемые антипирены включают комбинации фосфорорганических соединений, бора, полифосфаты и мочевины.

5.Некоторые невымываемые антипирены доступны только для внешнего применения , такие как черепица.

6.Ранние виды защиты от огня, такие как хлорид цинка и сульфат

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аммония часто приводили к тому, что обработанные материалы становились более гигроскопичными.

7.Новейшие системы имеют меньшее воздействие на гигроскопичность и менее коррозийны.

8.Основные модели строительных норм разрешают применение огнезащитных средств так, что обработанная древесина может быть использована во многих строительных системах и может получить оценку, как негорючая.

9.Древесину обрабатывают, как правило, таким образом, что она обугливается, разлагается, но не поддерживает воспламенение.

10.Деревянные крыши, и внутренняя обшивка стен и потолка в зданиях, требуют относительно низкого уровня воспламенения.

10. Translate the following phrases.

Присутствие кислорода, rapid pyrolysis, теплопередача, laminated beams, ламинированный брус, carbon dioxide, уплотнение древесного угля, fire retardant, внутренние стены, volatile gases, молекулярное разложение laminated beams, пар воды, combinations of organophosphates, хлорид цинка, presence of oxygen, термоизоляторы.

11. Check yourself with the following questions.

1.When does molecular decomposition occur?

2.What temperature does decomposition occur slowly at?

3.What conditions does rapid pyrolysis occur under?

4.When are flammable gases evolved?

5.What are considered to be good thermal insulators?

6.What conditions can laminated beams or solid - sawn timbers provide excellent fire resistance?

7.Can you name commonly used fire retardants?

8.Why does the use of many fire retardants have to be restricted to interior applications?

9.What kind of early fire retardants were used?

10.What kinds of fire retardants are popular nowadays?

12.Make a summary of the text.

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UNIT 7

WOOD PRESERVATIVES

1. Read the following words and state what Russian words help to guess their meaning.

Preservatives, pine, stem, vacuum, lumina, penetration, retention, oilborne, amount, application, species, timber, cell, deterioration, excess, sequence, tank, hazard, millwork, sapwood, whitewoods, maple, birch, cottonwood.

2. Check up if you remember the following verbs.

To include, to remove, to present, to incise, to involve, to increase, to allow, to preserve, to release, to fill, to force, to export.

3. Match the following word combinations.

4. Read and translate the text into Russian.

TREATING PROCESS.

Throughout history, many methods of applying wood preservatives have been devised. Examples include painting wood ships with pine rosin, using the capillary action of freshly felled trees to treat stem butts, and boiling fence posts in oil. To some extent, these methods are still used in

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various parts of the world. Most modern treating processes involve the use of differential pressure to force preservative into wood. Wood is commonly placed in a vacuum/pressure retort where preservative can then be added and a scheme of vacuum and or pressure applied. With oilborne preservatives, the preservative and the wood are often heated for the purpose of lowering liquid viscosity and increasing penetration. A vacuum can be pulled prior to introduction of the preservative to remove air from cell lumina, allowing greater retention of treating chemicals. Many different vacuum pressure–time cycles are used depending on the species, the type of preservative, and the amount to be retained in the wood. Some treating cycles are intended to leave the cell lumina filled with preservative for applications where the hazard of deterioration is high, such as bridge timbers and railroad ties. These are termed full cell processes. In empty cell processes, an attempt is made to remove excess preservative once it has

been forced to the desired depth within the wood. Picture 1 illustrates the pressure – time sequence used in the pressure - treating tank for one type of empty cell process, that is, the Reuping process. These latter processes are typically used for lumber as well as distribution and transmission poles. Species vary greatly in their resistance to penetration by preservatives, although the sapwood of almost all species is readily penetrated. Species

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that are very difficult to treat (called refractory), such as inland -or mountain - type Douglas fir and white oak, are frequently incised to form passages for the preservative to penetrate more deeply into the wood. Incising machines puncture the surface of wood with chisel - shaped points that expose end grain up to a depth of 2.5 cm (1.0 in.). Currently, nonpressure preservation methods are used commercially, but these methods are applicable primarily for wood that will be used under conditions presenting only a mold or stain hazard or moderate decay hazard. Nonpressure methods include vacuum, brushing, dipping, and soaking. Dipping, soaking, and vacuum application of preservatives and water - repellents is used extensively to protect millwork such as windows and for bright whitewoods (maple, birch, and cottonwood) for high - value export.

[From: Shmulsky R., Jones P. D. Forest Products and wood science / R. Shmulsky, P. D. Jones. – US : Willey-Blackwell, 2011. – P. 248]

5. Read the following statements and define whether they are true or false according to the text.

1.Most modern treating processes involve the use of differential pressure to force preservative into wood.

2.Wood is commonly placed in a vacuum/pressure retort.

3.The preservative and the wood are often heated for the purpose of lowering liquid viscosity and increasing penetration.

4.A vacuum can be pulled prior to introduction of the preservative to remove air from cell lumina.

5.Some treating cycles are intended to leave the cell lumina filled with preservative.

6.Species vary greatly in their resistance to penetration by preservatives, although the sapwood of almost all species isn`t readily penetrated.

7.Currently, nonpressure preservation methods aren`t used commercially.

8.Nonpressure methods include vacuum, brushing, dipping, and soaking.

9.Species that are very difficult to treat (called refractory), such as inland - or mountain - type Douglas fir and white oak, are frequently incised to form passages.

10.Many methods of applying wood preservatives have been devised.

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6. Give the English equivalents for the words and word combinations given below and memorize them.

Временная последовательность, вакуумное применение, проходы для консервантов (сохраняющие древесину средства), консерванты для применения, желаемая глубина, наполненный консервантами, белый дуб, чистка, пропитка, погружение в раствор.

7. Give the Russian equivalents for the words and word combinations given below.

Nonpressure preservation, cell lumina, vacuum, brushing, dipping, soaking, mold or stain hazard, expose end grain up to a depth, moderate decay hazard, bright whitewoods, chisel - shaped points, distribution and transmission poles, commonly placed, increasing penetration, treating cycles, cell processes, greater retention, oilborne preservatives.

8. Fill in the gaps.

1.Most modern treating processes ………….of differential pressure to force preservative into wood.

2.With oilborne preservatives, the preservative and the wood are often heated for the purpose of lowering ………….and increasing penetration.

3.Nonpressure methods include vacuum, ……., ………., and soaking.

4.Currently, …………preservation methods are used commercially, but these methods are applicable primarily for wood.

5.Species vary greatly in their resistance to penetration by preservatives, although …………………………………is readily penetrated.

6.Incising machines puncture the surface of wood with chisel - shaped points that …………end grain up to a depth of 2.5 cm (1.0 in.).

7.These latter processes are typically used for lumber as well as

………….and ……………………poles.

8.These methods are applicable primarily for wood that will be used under conditions presenting only a ……….or …………hazard or moderate decay hazard.

9.Inland -or mountain - type Douglas fir and white oak, are frequently incised to form passages for the preservative

………………………………the wood.

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10. Examples include painting wood ships with pine rosin, using the capillary action of freshly felled trees to………………….., and boiling fence posts in oil.

9. Translate the following sentences from Russian into English.

1.На протяжении всей истории были разработаны методы применения средств по сохранению древесины.

2.Большинство современных процессов обработки включают в себя использование дифференциального давления, для усиления действий по сохранению древесины.

3.Древесину помещают в вакуумную колбу.

4.Консервант и древесину часто нагревают с целью снижения вязкости жидкости и увеличения проникновения.

5.Вакуум может быть вытянут до введения консерванта, чтобы удалить воздух из клеточных просветов.

6.Данный метод позволяет дольше удерживать химические вещества, сохраняющие древесину.

7.Виды сильно различаются по их устойчивости к проникновению консервантов, хотя заболонь почти всех видов проникает довольно легко.

8.Виды, которые очень трудно поддаются обработке, такие как ели Дугласа и белого дуба, часто надрезают с образованием проходов для консерванта, чтобы проникнуть глубже в древесину.

9.В настоящее время, методы без давления сохранения используются в промышленных масштабах, но эти способы применимы в первую очередь для древесины, которая будет использоваться в условиях, представляющих плесень или пятна или среднюю степень опасности гниения.

10.Методы без давления включают вакуум, чистку щетками, промачивание, погружение.

10. Translate the following phrases.

Nonpressure methods, вакуумный реторт, resistance to penetration, sapwood, снижения вязкости жидкости, moderate decay hazard, удалить воздух из клеточных просветов, stem butts, столбы электропередачи, penetrate more deeply, смола сосны, capillary action, дифференциальное давление, liquid viscosity, антисептики древесины, used extensively.

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11. Check yourself with the following questions.

1.What are the examples of wood preservatives include?

2.What do most modern treating processes involve?

3.What is the purpose of the preservative and the wood being heated?

4.What is the use of removing air from cell lumina?

5.What do nonpressure methods include?

6.Is the sapwood of almost all species readily penetrated?

7.What kinds of species are very difficult to treat?

8.What conditions are nonpressure preservation methods used under?

9.Where is the hazard of deterioration high?

12. Make a summary of the text.

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