The third group of chemicals evaporates at relatively low temperatures. Therefore, chemicals of the third group absorb sufficient quantity of heat, preventing the temperature of the wood from rising to the critical decomposition point. The remaining heat is not enough to start the chemical decomposition of the wood.
Several chemicals are known to possess the properties of fire proofing. But because of high cost and such other factors as corrosion, hydroscopicity and toxicity the number of fire-retardant chemicals is not great. Only two or three of them are in wide use nowadays.
Sometimes fire - retardant paints are used instead of fire - retardant chemicals. They function as an insulating and reflecting layer. They do not prevent the chemical decomposition of wood under heating.
Fire - retardant paints have a limited practical application: they offer practically no protection in the event of an intense fire, they are not durable and they cannot be applied to timber already painted with an oil paint.
Exercises.
Ex.1: Translate the following words and remember them.
Substance, treat, treatment, mix, mixture, evaporate, absorb, quantity, property, apply, application,
timber.
Ex.2: Translate the words given below, paying attention to different suffixes and prefixes: chemistry, chemist, chemical, chemicals; compose, composition - decomposition; treat, treatment, treated; flame, flammable, inflame, inflammable, inflammation; toxic, toxicity; mix, mixture; protect, protection; effect, effective, effectively; insulate, insulating, insulation; resist, resistant, resistance; practical, practically; usual, usually, unusual.
Ex. 3: State the part of speech of the underlined words and translate the sentences.
1. Wood treated with chemicals becomes more fire - resistant and durable.
2. Some chemicals decompose under heat giving off non - inflammable gases.
3. Fire - retardant paints have a limited practical application because they offer practically no protection from an intense fire and they are not durable.
4. Some chemicals evaporate at relatively low temperatures.
Ex.4: Answer the following questions.
1. Is there any possibility to prevent wood from fire?
2. How can we make wood more fire - resistant and durable?
3. What is the function of the fireproof substances?
4. Are there many chemicals possessing the properties of fireproofing?
5. What factors must we take into account when choosing the fire retardant chemicals?
6. What is the function of the fire retardant paints?
7. Can the fire retardant paints prevent the chemical decomposition of wood under heating?
8. Have the fire retardant paints a wide practical application?
9. Do the fire- retardant paints offer considerable protection in the event of an intense fire?
10. Are the fire - retardant paints applied to timbers already painted with an oil paint?
Measures to avoid deterioration of lumber.
Freshly cut wood often contains a lot of excess water and therefore is very heavy. It is necessary that this water should be removed. At the same time a lumber manufacturer should take some measures to reduce warp and to avoid other defects.
Logs should be taken from the forest and sawed into lumber as soon as possible, particularly during warm weather. Otherwise the wood may be attacked by fungi and insects especially during warm weather when higher temperatures speed up fungus and insect activity.
At larger sawmills where a considerable supply of logs is often kept it is impossible to saw them into lumber at one. In such cases spraying with cold water to keep the logs wet will reduce splitting, staining and decay. Very often logs are stored in the pond. Storing logs in water makes it easier to sort them before sawing.
Freshly sawed lumber may also be attacked by fungi and insects. It may split too if exposed to direct sunshine. Dipping the freshly sawed lumber in a solution of toxic chemicals can protect it against attack by fungi and insects. Care should also be taken of the lumber placed in the yard for storage. There are special rules of drying lumber in piles. If these rules are followed the attack of fungi and insects will be less probable.
Another of the most common defects is splitting. This defect leads to the loss of valuable lumber of 6 to 20 per cent. Different coatings are very important for avoiding this defect. The coatings may be divided into two classes. Cold coatings are liquid at ordinary temperatures and can be applied without being heated. Hot coatings are solid at ordinary temperatures and must be applied hot. Cold coatings can be applied to logs and lumber. There are applied by brush or can be sprayed with a special device. Hot coatings such as pitch and paraffin are well suited for
small stocks of lumber. They are low in cost and have high water resistance. Hot coatings are generally applied by dipping the lumber into the pitch or paraffin.
Exercises.
Ex.1: Translate the following words and remember them.
to contain, heavy, to reduce, wet, decay, sort, pile, common, loss, different.
Ex.2: Translate the words given below, paying attention to different suffixes and prefixes: fresh, freshly; move, movement, remove; manufacture, manufacturer; possible, impossible, possibility; act, active, activity, actively; store, storage; direct, directly, direction; apply, application, applicable; special, specially, especially; value, valuable, valueless; high, highly, height; water, waterless; reduce, reduction; lead, leader, leadership; solid, solidity, solidify, solidification.
Ex.3: State the part of speech of the underlined words and translate the sentences.
1. It is necessary that this water should be removed from wood.
2. Different coatings are very important for the reduction of splitting.
3. Sometimes it is impossible to saw a considerable supply of logs into lumber at once.
4. Dipping the freshly sawed lumber in a solution of toxic chemicals can protect it against fungi and insects.
5. There are special rules of drying lumber in piles.
Ex.4: Answer the following questions.
1. Are there any measures to avoid deterioration of lumber?
2. Is the freshly cut wood heavy or light?
3. Why is it necessary to dry wood?
Уважаемый посетитель!
Чтобы распечатать файл, скачайте его (в формате Word).
Ссылка на скачивание - внизу страницы.