5. Classification of Timber for Drying

Section 1.

PRE- TEXT EXERCISES

1. Check up if you read these words correctly:

degrade [di'greid], refract [n'fraekt], particularly [ pa'tik.ju.lo.li], ironbark [aisn.bcrk], rapid [raep.id], apply [a'plai], kiln [kiln], upon [э'роп], humidity [hju:'mid.i.ti], oak [эик], inch [mt J], adjust [o'djASt], assume [o'sju:m], longitude [’lon.d3i.tju:d], measure ['тез.or], lumber [km.bor], yield [ji:ld], unusable [An'ju:.zo.blJ

2. Give the initial forms of the following words:

proneness, highly, dimensions, the smallest, unusable, occurred, rarest, known, made, seventeenth.

3. State to what parts of speech the following words belong:

discovery, particularly, structural, suitable, humidity, saturation, useless, rarest, moisture, poisonous, oxidize, reddish

4. Arrange antonyms in pairs and translate them:

a) large, minimize, left, complex, frequently, variable, benefit, equality, wide, important;

b) constant, simple, seldom, maximize, inequality, small, narrow, right, unimportant, disadvantage

5. Translate the following word-groups into Russian:

highly refractory woods; moderately refractory woods; non-refractory woods; the dimensions of the wood; tangential and longitudinal dimensions; the initial moisture; the saturation vapor pressure of water; the moisture gradient; this is not an issue

6. Check if you remember the following verbs:

to split, to crack, to show, to care, to depend, to develop, to apply, to divide, to find, to express, to solve, to reduce, to use

7. Compare the following pairs of words and translate them:

danger - dangerous; correspond - correspondent; signify -significance; clean - cleanness; measure - measuring; cover -recover; care - careful; aim - aimless; open - opening

TEXT A

CLASSIFICATION OF TIMBERS FOR DRYING

The timbers are classified as follows according to their ease of drying and their proneness to drying degrade:

Highly refractory woods: These woods are slow and drying to dry if the final product is to be free from defects, particularly cracks and splits. Examples are heavy structural timbers with high density such as ironbark1, blackbutt2, southern blue gum3 and brush box alcohol4. They require considerable protection and care against rapid drying conditions for the best results.

Moderately refractory woods: These timbers show a moderate tendency to crack and split during seasoning. They can be seasoned free from defects with moderately rapid drying conditions (i.e. a maximum dry-bulb temperature of 85 °C can be used). Examples are Sydney blue gum5 and other timbers of medium density, which are potentially suitable for furniture.

Non-refractory woods: These woods can be rapidly seasoned to be free from defects even by applying high temperatures (dry-bulb temperatures of more than 100°C) in industrial kilns. If not dried rapidly, they may develop discoloration (blue stain) and mould on the surface. Examples are softwoods and low density timbers such as Pinus radiate6.

The rate at which wood dries depends upon a number of factors, the most important of which are the temperature, the dimensions of the wood, and the relative humidity. Simpson and Tschernitz have developed a simple model of wood drying as a function of these three variables. Although the analysis was done for red oak, the procedure may be applied to any species of wood by adjusting the constant parameters of the model.

Simply put, the model assumes that the rate of change of the moisture content M with respect to time t is proportional to how far the wood sample is from its equilibrium moisture content Me, which is a function of the temperature T and relative humidity h:

dM _ M - Me dt_ - - т _ _ where I is a function of the temperature T and a typical wood dimension L and has units of time. The typical wood dimension is roughly the smallest value of (Д-- Де,/10) which are the radial,

tangential and longitudinal dimensions respectively, with the longitudinal dimension divided by ten because water diffuses about 10 times more rapidly in the longitudinal direction (along the grain) than in the lateral dimensions. The solution to the above equation is:

Where Mo is the initial moisture content. It was found that for red oak lumber, the "time constant" Z was well expressed as:

Ln

т =-----—

a + 6ftat(r)

where a, b and n are constants and Р»л(г) is the saturation vapor pressure of water at temperature T. For time measured in days, length in inches, and Psat measured in mmHg, the following values of the constants were found for red oak lumber.

a = 0,0575

b = 0,00142

n= 1,52

Solving for the drying time yields:

T a + 6psat(T) n^Wo-Afe/

For example, at 150 deg F, using the Arden Buck equation, the saturation vapor pressure of water is found to be about 192 mmHg. The time constant for drying a 1 -inch-thick (25 mm) red oak board at 150 deg F is then T = 3.03 days, which is the time required to reduce the moisture content to 1/e = 37% of its initial deviation from equilibrium. If the relative humidity is 0.50, then using the Hailwood-Horrobin equation the moisture content of the wood at equilibrium is about 7.4%. The time to reduce the lumber from 85% moisture content to 25% moisture content is then about 4.5 days. Higher temperatures will yield faster drying times, but they will also create greater stresses in the wood due because the moisture gradient will be larger. For firewood, this is not an issue but for woodworking purposes, high stresses will cause the wood to crack and be unusable.

[from http://en. wikipedia. org/dki/Vood_drying#Classification_of_ timbers _Jbr_drying ]

NOTES

  • 1. Blackbutt is known as Eucalyptus pilularis. It is a common and dominant tree of the myrtaceae family native to southeastern Australia.
  • 2. Ironbark is a type of eucalyptus tree which has deep lines on the stem.
  • 3. Southern Blue Gum is known as Eucalyptus globules. Southern Blue Gum is an Australian native hardwood species.
  • 4. Brush box is an Australian tree that has evergreen foliage and is cultivated for shade.
  • 5. Eucalyptus saligna, known as the Sydney blue gum, is a large Australian hardwood (flowering) tree.
  • 6. The Monterey Pine, Pinus radiata, family Pinaceae, also known as the Insignis Pine or Radiata Pine is a species of pine native to the Central Coast of California.

ASSIGNMENTS

  • 1. Explain the title of the text A.
  • 2. Describe the scheme given below.

Classification of timbers for drying

Highly refractory woods

Moderately refractory

Non-refractory woods

3. Make up sentences based on the text:

the time to reduce the lumber; to be free from defects; for the best results; show a moderate tendency; the typical wood dimension; to create greater stresses

4. Give the English equivalents of the following:

надежная защита; условия сушки; развивать обесцвечивание; зависеть от ряда факторов; постоянные параметры; характерный размер дерева; продольное направление; поперечные размеры; относительная влажность

  • 5. Translate from Russian into English:
  • 1. Следует отметить, что понижение температуры высушиваемого материала при удалении из него влаги позволяет повысить безопасность процесса.
  • 2. В настоящее время налажен выпуск вакуумных камер для сушки древесины.
  • 3. Процесс сушки складывается из последовательно чередующихся стадий нагрева древесины и ее вакуумирования.
  • 4. На стадии нагрева материал обдувается горячим воздухом при атмосферном давлении.
  • 5. Использование горячего воздуха на стадии прогрева древесины возможно лишь в комбинации с насыщенным паром.
  • 6. По мере удаления влаги из древесины температура материала становится равной температуре среды.
  • 7. Удаление влаги из материала может происходить как при температуре выше точки кипения воды, так и при температуре, на несколько градусов ниже этого значения.
  • 8. В этот период температура древесины повышается, что сопровождается испарением влаги с ее поверхности.
  • 6. Retell text A in short.
  • 7. Summarize the principal ideas of all the three texts of the unit 4 and unit 5.

Section 2.

REVISION GRAMMAR EXERCISES

  • 1. Translate the sentences into Russian paying attention to Participle II in the function of attribute.
  • 1.

a) The device produced great voltage.

b) The device produced was powerful.

c) The device produced in the laboratory was portable.

2.

a) The component parts used high power.

b) The component parts used were of new type.

c) The component parts used for vacuum chambers are interconnected.

3.

a) The experiment required great accuracy.

b) The experiment required will be carried out soon.

c) The experiment required in order to compare theoretical results must be prepared carefully.

4.

a) The article published new experimental data.

b) The article published is not interesting.

c) The article published in the scientific magazine will be discussed.

5.

a) Data estimated the cost of the system.

b) Data estimated were used in designing the new system.

c) Data estimated by a computer were of great importance.

2. Change the following constructions into attributive clauses and translate them.

Model: the papers on sale - the papers which are on sale

the book under review, the data in question, the house under construction, places of interest, the problem in question, the method of interest, the article under review

  • 3. Translate into English, using the modal verb can (could).
  • 1. He может быть, чтобы они уже сделали эту работу. Они приступили к ней только вчера.
  • 2. Не может быть, что он все еще делает эту работу. Его часть работы была очень незначительной.
  • 3. Неужели он так равнодушен к этому изобретению?
  • 4. Не может быть, чтобы он выбрал эту профессию против своей воли.
  • 5. Неужели эта статья такая скучная? А я слышал, что статьи этого ученого привлекают всеобщее внимание.
  • 6. Не может быть, чтобы он плохо перенес путешествие.
  • 7. Неужели он овладел этим труднейшим искусством? Он, должно быть, очень терпелив.
  • 4. Think of some good questions for the following answers.
  • 1. By means of computers.
  • 6. No doubt.
  • 7. Nowhere.
  • 8. It is suitable.
  • 9. Circular.
  • 10. In the rocky canyon.
  • 2. Extremely talented.
  • 3. I’m afraid he’ll object to it.
  • 4.1 don’t agree with you.
  • 5. Some cracks in the structure.

Section 3.

CONTEX

The context of any word consists of the words surrounding it -within the same sentence, in another sentence or even within the entire paragraph.

The context determines which meaning of the word is intended by the writer. So the meaning you select for a word must fit in the context.

EXERCISES

  • 1. Two meanings are given for the word in bold type in each sentence. Decide which meaning fits:
  • 1. The timbers are classified as follows according to their ease of drying.

a) trees that are grown so that the wood from them can be used for building;

b) a long piece of wood used for building, especially houses and ships.

2. The temperature is almost eighty degrees, the humidity in the low thirties.

a) The relative humidity of the air is the amount of water that is present in the air compared to the greatest amount it would be possible for the air to hold at that temperature;

b) a measurement of how much water there is in the air.

3. The wooden floor had cracked and split in the heat.

a) to (cause to) divide into two or more parts, especially along a particular line;

b) to form cracks.

4.1 spoke to an aid worker who had recently returned from the field.

a) an area of land in which you are working or studying;

b) an area of land, used for growing crops or keeping animals, usually surrounded by a fence.

5. Crude oil is used as the raw material for making plastics.

a) cloth which can be used to make things such as clothes;

b) a physical substance which things can be made from.

6. Under what conditions do plants grow best?

a) the particular state that something or someone is in;

b) the physical situation that someone or something is in and affected by-

7. Chemists now often use platinum laboratory ware for their experiments.

a) a test done in order to learn something or to discover whether something works or is true;

b) to try something in order to discover what it is like or find out more about it.

8. One of the properties of copper is that it conducts heat and electricity very well.

a) a quality in a substance or material, especially one which means that it can be used in a particular way ;

b) an object or objects that belong to someone.

9. Many fertilizers contain nitrogen compounds.

a) something consisting of two or more different parts;

b) a chemical that combines two or more elements.

10. Under certain conditions the output signal will be distorted.

a) to make an undesired change in waveform;

b) give a false account of.

2. Give as many equivalents of the words “to amplify” and “to connect” as you can.

Section 4.

CHECK YOUR PROGRESS

  • 1. What is context?
  • 2. What is the role of context in comprehending the new words?
  • 3. Describe the text of this unit and compare it to the texts of the previous units.
  • 4. What do the formulas in the text describe?
 
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