Wood and the technology of wood drying (Древесина и технологии сушки древесины). Учебно-методическое пособие

-wood consists of;

-it is common to classify;

-conversely.

4.Divide the text into logical parts and find the topical sentences of each part.

5.Write a short summary of the text.

6.Retell the text: a) in short; b) in details.

7.Read text B. Dictionaries are allowed.

TEXT B

WATER CONTENT

Water occurs in living wood in three conditions, namely:

(1)in the cell walls,

(2)in the protoplasmic contents of the cells, and

(3)as free water in the cell cavities and spaces. In heartwood it occurs only in the first and last forms. Wood that is thoroughly airdried retains 8–16% of the water in the cell walls, and none, or practically none, in the other forms. Even oven-dried wood retains a small percentage of moisture, but for all except chemical purposes, may be considered absolutely dry.

The general effect of the water content upon the wood substance is to render it softer and more pliable. A similar effect of common observation is in the softening action of water on paper or cloth. Within certain limits, the greater the water content, the greater its softening effect.

Drying produces a decided increase in the strength of wood, particularly in small specimens. An extreme example is the case of a completely dry spruce block 5 cm in section, which will sustain a permanent load four times as great as a green (undried) block of the same size will.

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The greatest strength increase due to drying is in the ultimate crushing strength, and strength at elastic limit in endwise compression; these are followed by the modulus of rupture, and stress at elastic limit in cross-bending, while the modulus of elasticity is least affected.

[from http://en.wikipedia.org/wiki/Wood#Water_content]

8.Retell text B in short.

9.Give the main points of text B in three sentences.

10.Summarize the general ideas developed in both texts of the unit.

11.Prepare to take part in the competition:

“Main Characteristics of Wood”.

12. Translate into English:

1. Для древесины основными и наиболее важными являются следующие свойства:

–механические: прочность, твёрдость, эксплуатационные характеристики, технологические характеристики, износостойкость, упругость;

–физические: внешний вид (текстура, блеск, окраска), влажность (усушка, коробление, водопоглощение, гигроскопичность, плотность), тепловые (теплопроводность), электрические (электропроводность, электрическая прочность).

2. Древесина является материалом с неодинаковыми свойствами по направлениям относительно волокон. Так, например, усушка вдоль волокон меньше, чем поперёк волокон. Различны также, в зависимости от направления волокон, влагопроводность, паропроницаемость, звукопроводность и некоторые другие характеристики.

3. Прочность древесины — это способность сопротивляться разрушению под действием механических нагрузок. Различают

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прочность на сжатие и растяжение по направлениям приложения

сопротивляться износу, то есть постепенному разрушению её поверхностных зон при трении. Износ боковых поверхностей больше, чем торцовых; износ влажной древесины больше, чем сухой.

5. Влажность древесины. Различают абсолютную и относительную влажность древесины.

6. Абсолютная влажность древесины — это отношение веса содержащейся в древесине влаги к массе абсолютно сухой древесины, выраженное в процентах.

7. Относительная влажность древесины — это отношение веса содержащейся в древесине влаги к весу сырой древесины, выраженное в процентах.

8. Влажность древесины определяется следующим образом. Измеряется масса пробы влажного материала, измеренная проба высушивается в сушилке при температуре 100—105 °С, затем происходит повторное взвешивание, но уже сухого материала. Разница между массой влажного и сухого материала и определяет количество воды, содержащейся в образце.

Section 2.

REVISION GRAMMAR EXERCISES 1. Open the brackets using the correct tense form:

1.The scientists (to develop) these new units from the beginning of the year to the end of March.

2.They (to test) these new units for the repeaters for some weeks.

3.We (to work) in the lab from 5 till 7 o’clock.

4.The teacher (to ask) the students a lot of questions.

5.He (to determine) the main properties of the substance.

6.Nobody (to fail) in this examination yesterday.

7.You (to fly) to Paris this time tomorrow!

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8.I hope Bill (to finish) the report by eight.

9.I (to look) for a flat for a long time when I first (to come) to Paris.

10.We (to treat) the sick people, but I don’t want to go there again.

2. Translate the following sentences paying attention to the verbs in the Passive Voice.

1.Our group was joined by some new persons.

2.The lecture will be attended by all the students.

3.The experiment was watched with great interest.

4.The letter will be answered at once.

5.The delegation was joined by a group of students.

6.The message must be sent immediately.

7.He said that the experiment had been completed by the end of last month.

8.The work on the apparatus is being finished.

9.The work was being done all the day yesterday.

10.What question are being discussed now?

11.Several attempts have been made recently to produce artificial rain.

3. Translate the adverbial clauses and say what they express.

1.I’m going to work on this lesson until I’ve learned it.

2.Give this message to John if you see him.

3.If my children spoke to me that way, I would be angry.

4.If you had told me you were coming, I would have prepared dinner for you.

5.This book is so long that I can’t finish it today.

6.I brought an umbrella because I thought it might rain.

7.The better I got to know him, the less I liked him.

4. Define simple sentences, compound, and complex sentences.

1. His mistake was obvious.

That the driver could not control his car was obvious.

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The driver could not control his car and it was obvious to everybody.

2. The truth is unknown.

The truth is that he was very shy.

The truth is unknown but he wants to find it out. 3. Everyone could see that.

Everyone could see that he was frightened.

Everyone could see that but nobody knew what is to be done. 4. I often see my old school friends.

I often see friends who were at school with me.

I often see my old school friends and I always feel young with them.

5. I met George twenty years ago.

I met George when I was at school.

I met George twenty years ago and we became friends.

Section 3.

VOCABULARY GROWTH

Any vocabulary consists of words and meanings. As your vocabulary grows, two things happen:

-you add new words;

-you add new meanings to familiar words.

Your reading vocabulary doesn’t stand still. It continues to grow as long as you have new experiences. You meet new words in your studies, newspapers, books. Of course, you have to do more than just meet them. To improve your vocabulary, you have to make an effort. What is the effort? You have to give your attention to new words and new meanings and try to figure out what they refer to.

EXERCISES

1. In each pair of the sentences the same word is in bold type. Decide whether its meaning is the same in both sentences.

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1.

a)He gathered some wood to build a fire.

b)Mahogany is a hard wood and pine is a soft wood.

2.

a)In the shallow waters of the Gulf of Mexico, oil rigs attract shoals of fish, and fishermen too.

b)The human body is about 50% water.

3.

a)Dictionaries are usually printed on thin paper.

b)The border guards stopped me and asked to see my papers.

4.

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

b)We value herbs for their taste, but we forget that they also have medicinal properties.

5.

a)The city needs to attract more industry.

b)The strike seriously reduced coal deliveries to industry.

6.

a)The wood extractives are fatty acids, resin acids, waxes and terpenes.

b)Vinegar is an acid.

7.

a)This man is a well-known public figure.

b)In Figure 1 the wire is not joined all the way round, but the circuit is complete.

8.

a) Hang the clothes up to dry.

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b) The fruit is dried in the sun.

2. Fill in the blanks with the following words:

difference, medium – dense, particularity, softwood, oil, fatty, density

1.The … of wood varies with species.

2.Mahogany is a … hardwood that is excellent for fine furniture crafting.

3.It is common to classify wood as either … or hardwood.

4.The … between hardwood and softwood is reflected in the composition of the constituent lignin.

5.The extraction of these organic materials from wood provides tall

…, terpentine, and rosin.

6.Drying produces a decided increase in the strength of wood, … in small specimens.

7.The wood extractives are … acids, resin acids, waxes and terpenes.

Section 4.

CHECK YOUR PROGRESS

1.What does any vocabulary consist of?

2.How does your vocabulary grow?

3.What are the new words and meanings you added to your vocabulary working at this unit?

4.What is your opinion of the information contained in the texts of the unit?

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Unit 3

Section 1.

PRE-TEXT EXERCISES 1. Check up if you read these words correctly:

weight [weɪt], sealed [siːld], capillary [kəˈpɪl.ər.i], liquid [ˈlɪk.wɪd], equation [ɪˈkweɪ.ʒən], pressure [ˈpreʃ.ər], ambient [ˈæm.bi.ənt], capillary [kəˈpɪl.ər.i], equilibrium [ˌiː.kwɪˈlɪb.ri.əm], shrink [ʃrɪŋk], tangent [ˈtæn.dʒənt], longitude [ˈlɒn.dʒɪ.tjuːd], transverse [trænzˈvɜːs], redistribute [ˌriː.dɪˈstrɪb.juːt], diffuse [dɪˈfjuːz], gradient [ˈgreɪ.di.ənt], impermeable [ɪmˈpɜː.mi.ə.bl]

2. Give the initial forms of the following words:

felled, forces, required, normally, expressed, contained, capillaries, longitudinal, tangential, redistribute, dries

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

freshly, furthermore, characteristics, fraction, ambient, mechanical, radial, transverse, significantly, accompany, suggested, evidence

4. Translate the following word-groups into Russian:

a large amount of water; the rate of exchange; give off moisture in the form of vapour; the ambient space; the largest-sized capillaries; drying history of wood; a gradient of wood moisture; the drying of impermeable hardwoods; the flux of moisture

5. Check if you remember the following verbs:

to attract, to take, to require, to bound, to form, to calculate, to mention, to express, to remain, to swell, to transverse, to relate

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

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regular – regularity; similar – similarity; popular – popularity; viscose – viscosity; stable – stability; to communicate – communicative; to imitate – imitative; to regulate – regulative; to demonstrate – demonstrative; to attract – attractive

TEXT A

WOOD–WATER RELATIONSHIPS

The timber of living trees and freshly felled logs contains a large amount of water, which often constitutes over 50% of the woods' weight. Water has a significant influence on wood. Wood continually exchanges moisture or water with its surroundings, although the rate of exchange is strongly affected by the degree wood is sealed.

Wood contains water in two forms:

Free water: The bulk of water contained in the cell lumina is only held by capillary forces. It is not bound chemically and is called free water. Free water is not in the same thermodynamic state as liquid water: energy is required to overcome the capillary forces. Furthermore, free water may contain chemicals, altering the drying characteristics of wood.

Bound or hygroscopic water: Bound water is bound to the wood via hydrogen bonds. The attraction of wood for water arises from the presence of free hydroxyl (OH) groups in the cellulose, hemicelluloses and lignin molecules in the cell wall. The hydroxyl groups are negatively charged electrically. Water is a polar liquid. The free hydroxyl groups in cellulose attract and hold water by hydrogen bonding.

Vapor: Water in cell lumina in the form of water vapour is normally negligible at normal temperature and humidity.

Moisture Content of Wood

The moisture content of wood is calculated by the formula:

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Here, is the green mass of the wood, is its oven-dry mass (the attainment of constant mass generally after drying in an oven set at 103 +/- 2 °C for 24 hours as mentioned by Walker et al., 1993). The equation can also be expressed as a fraction of the mass of the water and the mass of the oven-dry wood rather than a percentage. For example, 0.59 kg/kg (oven dry basis) expresses the same moisture content as 59% (oven dry basis).

Students in the United Kingdom would recognise this formula written as

Where the wet weight is the weight of the original 'wet' sample and the dry weight being the weight of the sample after drying in an oven. Moisture contents being expressed as a percentage.

Equilibrium Moisture Content

Wood is a hygroscopic substance. It has the ability to take in or give off moisture in the form of vapour. Water contained in wood exerts vapour pressure of its own, which is determined by the maximum size of the capillaries filled with water at any time. If water vapour pressure in the ambient space is lower than vapour pressure within wood, desorption takes place. The largest-sized capillaries, which are full of water at the time, empty first. Vapour pressure within the wood falls as water is successively contained in smaller capillaries. A stage is eventually reached when vapour pressure within the wood equals vapour pressure in the ambient space above the wood, and further desorption ceases. The amount of moisture that remains in the wood at this stage is in equilibrium with water vapour pressure in the ambient space, and is termed the equilibrium moisture content or EMC (Siau, 1984). Because of its hygroscopicity, wood tends to reach a moisture content that is in equilibrium with the relative humidity and temperature of the surrounding air. The EMC

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