Preservation of Wood
Timber is gradually destroyed if used under the ordinary atmospheric conditions for a long period of time. It should be noted that serviceable life of wood also depends on the species and the situation in which wood is used.
For example, sound wood was found in the Egyptian tombs. The archaeologists stated that the preservation of wood could be explained easily: the wood had been very well protected from the surrounding atmosphere. Even nondurable species would last for many years under such conditions.
The sound stumps of western red cedar stay in the forest for several centuries. But this fact is explained by the high natural durability of this species. On the other hand, scientists discovered that even the most durable timbers would last only a few years if placed in a warm, damp and badly-ventilated space.
Every engineer should know the principal causes of deterioration of wood in service. These are fingi, termites and other insects, mechanical failure and fire. Ancient Romans suggested that some chemicals should be applied to increase the resistance of timber to such agents of destruction. Such chemicals were called preservatives. One or two substances were used for this purpose in Roman times. But the wide use of wood preservatives is a development of the last hundred years.
In practice, preservatives are usually applied to nondurable timbers. The treated wood is sufficiently resistant to the agents of deterioration. Thus, there is a possibility of using a less durable and not so expensive timber instead of durable but more expensive one.
The selection of the most suitable chemical and the method of treatment are of great importance. It is necessary to understand the advantages and disadvantages of using preservatives. No preservative guarantees complete immunity. A preservative suitable in one case may be useless in many others.
Read the text attentively and answer the following questions:
1. Is timber an everlasting material?
2. What does the serviceable life of wood depend on?
3. Why did wood in the Egyptian tombs preserve so well?
4. What influences the preservation of wood?
5. What should every engineer know?
6. What did ancient Romans suggest to increase the resistance of timber?
7. Were wood preservatives widely used in Roman times?
8. What is the purpose of preservative application?
9. What do preservatives make possible?
10. Do all preservatives guarantee complete immunity?
Exercise 1. Match the English words in A with their Russian equivalents in B.
Exercise 2. Find the English equivalents to the following Russian.
постепенно; срок годности; окружающая атмосфера; непрочный; предлагать; химикаты; антисептики; обрабатывать; дорогой (о цене); вместо; подходящий; выбор; полный; случай.
Exercise 3. Choose the words from the text which have the similar meaning.
destruct; working life; solid; strength; resistant; conserve; wet; badly-conditioned; reasons; taint; to use; to raise; fungicidal treatment; non-resistant; merits and demerits.
Exercise 4. Fill in the blanks with the words from the box.
1. Foresters are the key man in ________ of forested lands. 2. Acid rains contribute to the _______ of forests. 3. Wood-destroying fungi affect the mechanical _______ of timber. 4. The two main types of insects ________ the ________ of timber are beetles and termites. 5. Natural timber varies significantly from ________ to _______. 6. The effectiveness of the preservative ________ depends mainly on the amount of preservative that is absorbed by timber and the depth to which it penetrates. 7. The natural durability of wood-based panels can also be ________ by a preservative treatment. 8. The preservatives should be non-toxic to humans and ________. 9. No ________ can guarantee complete protection.
Exercise 1. Define the functions of the verb "should" and translate the sentences into Russian.
1. It is necessary that drying should be confined to timber of one size and species. 2. Finishes should be highly durable. 3. It should be noted that drying involves the greatest expenditure of time in all the woodworking processes. 4. Wood should be coated with a transparent varnish or seal to retain the original appearance. 5. It is obviously important that the air circulation should be fairly uniform over the face of the timber pile. 6. Every engineer should know the principal causes of deterioration of wood in service. 7. Wood must be treated with preservatives lest it should deteriorate. 8. It should be remembered that natural wood resources of the world are not inexhaustible. 9. A kiln should be provided with means of controlling temperature and humidity of the circulating air. 10. It should be noted that acoustic properties of wood are of great importance in musical instruments. 11. Specialists suggested that the new method of growing trees should be used in the region. 12. Wood in the foundation of the stack should be treated with creosote or other wood preservatives.
Exercise 2. Define the functions of the verb "would" and translate the sentences into Russian.
1. It would be impossible to imagine our life without wood and wood products. 2. If there were good weather conditions, trees would grow more rapidly. 3. It would be naïve to think that current levels of air pollution will not produce a negative effect on forest ecosystems. 4. The annual rings would not be wide, if the growth conditions were not favourable. 5. A rich crop of seeds would have been gathered but for rain. 6. They hoped that the demand for their lumber would increase. 7. We were informed that lumber would be packed in accordance with
the instruction. 8. Without adhesives plywood, particle boards, furniture and
thousands of other wood products would not be possible. 9. The newspaper reported that the sawmill would be reconstructed at the end of this year. 10. If the lumber were dried carefully, it wouldn’t check and split.
Exercise 3. Read the text below and write the word which best fits each space.
Use only one word in each space.
Can you imagine what the world (1) ____ be like if there (2) ____no electricity? In fact, most of what we take for granted (3) ____ not exist. There would be no computers, TV, cinemas or stereos for our entertainment, and we (4) ____ not be able to cook and eat in the same way (5) ____ cookers and fridges. If Thomas Edison (6) ____ not invented the electric light bulb, we would now still (7) ____ using candles to see at night. The problem with this energy source (8) ____ that it uses fossil fuels – we burn coal and oil to generate electricity. Our everyday lives (9) ____ a huge amount of power, and industry even more. The damage to the environment (10) ____ increase if we continue to burn coal for energy, which
(11) ____ cause serious air pollution and increase the size of the hole in the ozone layer. Because of this danger, people (12) ____ now using other sources of fuel, such as solar, wind, and water power. It is clear that we must do all we can to save energy, because if we (13) ____ not fossil fuels (14) ____ soon run out, and our environment (15) ____ become too polluted for animal and human life to survive.
1. The dependence of serviceable life of wood on different conditions.
2. The principal causes of wood deterioration.
3. The preservation of wood.
From the earliest times man has used wood for tools and weapons, for buildings and furniture. Man quickly learnt, that the wood of one species served his needs better than that of another. Tough and elastic ash, for example, has been
used for making axe handles for thousands of years.
Valuable qualities were discovered in other timbers as well. Elm was hard to split. It made good chair-seats. The heartwood of oak would endure even in contact with damp ground. Therefore it was chosen for fence posts.
The first settlers in new England were quick to make comparisons between the native American trees and those of Europe. Many species proved to be similar, but others were new and strange. While exploring the tropics, Europeans found that there too grew many woods with exceptional qualities. Teak and mahogany were soon exported to Europe. No species could match them for strength, attractive appearance and workability.
Until recent times man had to use hand tools to fell trees and work up the wood. Machines that can work up the wood are nearly all twentieth-century inventions. If the machinery had come into general use earlier, the large amounts of timber would have been utilized more effectively and a great number of valuable species would have been saved for future generation of people.
It should be noted that properties of different species of timber are thoroughly studied. Hardwood species, for example, have a tendency to shrink more
than softwoods. Therefore softwoods are used primarily in house construction, whereas hardwoods are more popular for furniture.
The principal hardwood species, for example, are birch, alder, walnut and mahogany. Alder is without doubt one of the most important and generally used hardwoods. Its wood is known everywhere for its strength, durability and good appearance. It has always been regarded as a shipbuilding wood and is highly valued by railroads for ties and car construction.
Mahogany is one of the most popular cabinet woods because of its easy cutting quality, durability, colour and a wide range of its artistic figure.
Все материалы представленные на сайте исключительно с целью ознакомления читателями и не преследуют коммерческих целей или нарушение авторских прав. Студалл.Орг (0.011 сек.)