Упражнения

Упр.1. Найдите в тексте английские эквиваленты данных слов и словосочетаний:

1. Редуктор, 2. горючий газ, 3. резак, 4. вентиль горелки, 5. безинжекторная горелка, 6. мундштук, 7.газовый баллон, 8. манометр, 9. давление в баллоне, 10. однокамерный редуктор, 11. корпус, 12. входной штуцер, 13. шланговое соединение, 14. регулировочный вентиль, 15. разгерметизация

Упр. 2. Вставьте нужное слово:

1.The main disadvantage of single-stage regulators is that you must constantly … the regulator. 2. Fuel gas regulators are basically of the same … . 3. … shows the level of pressure in the gas cylinder. 4. The most common … used for cutting torches is acetylene. 5. In … the oxygen comes out of a small nozzle under pressure and drags the fuel gas along with. 6. The mixing chamber with … is set at 90º. 7. The double stage regulator is similar… to the one stage one. 8. The total pressure … takes place in two stages. 9. Dirt in the connections may be … into the valve seats and damage them. 10. Mechanisms of a regulator are enclosed in a suitable …

Упр. 3. Переведите на АЯ:

1. Горючий газ и кислород смешиваются в смесительной камере. 2. Ацетилен в смеси с кислородом дает пламя высокой температуры. 3. В инжекторной горелке кислород подается под давлением и увлекает за собой горючий газ. 4. Смесительная камера устанавливается под углом 90º к корпусу горелки. 5. Если в смесительной камере горелки газы просто смешиваются, ее называют однокамерной. 6. Редукторы устанавливают на баллоны с горючим газом и кислородом. 7. Редуктор снижает давление газа, выходящего из баллона, в соответствии с необходимостью для выполняемой работы. 8.Давление регулируется вручную поворотом регулирующего вентиля. 9. Манометр показывает давление в баллоне, когда вентиль открыт. 10. Детали редуктора помещены в соответствующий корпус.

Unit 20. GAS HOSES AND VALVES

Flexible hoses that connect from the regulators to the torch and carry the fuel gas and oxygen must be strong, non-porous, light and flexible enough to make the torch movement easy. They must be made to withstand internal pressures that can reach as high as 100 psig. The rubber used to make these hoses is specially treated to remove sulfur that could cause spontaneous combustion.

Welding hose is available in single –hose and double hose lengths. Size is determined by the inside diameter, and the proper size to use depends on the type of work for which it is intended. Hose used for light work has a 3\16 or 1\4 inch inside diameter and one or two plies of fabric. For heavy-duty welding and cutting operations, use a hose with an inside diameter of 5\16 inch and three to five plies of fabric. Single hose is available in standard sizes as well as1\2-inch, 3\4 inch, and 1-inch sizes. These larger sizes are for heavy-duty heating and for use on large cutting machines. The most common type of cutting and welding hose is the twin or double hose which is the fuel hose and the oxygen hose joined together side by side either by a special rib or by clamps. Because they are joined, the hoses are less likely to become tangled and are easier to move from place to place.

The length of the hose is important. The delivery pressure at the torch varies with the length of the hose. A 20-foot 3\16 inch hose may be adequate for a job, but if the same hose was 50 feet long, the pressure drop would result in too little gas flow to the torch. Longer hoses must be wider inside to ensure the correct flow of gas to the torch.

The hoses for fuel gas and oxygen are typically identical in construction, but they differ in colour. The oxygen hose cover is black (in the USA it is green), and the fuel gas cover is red. This colour coding aids to prevent mishaps that could lead to dangerous accidents. The fuel gas connections have left-hand threads and the oxygen connectors have right-hand threads so that the two cannot be interchanged, to help to prevent accidents. The basic hose connection is a nut and gland. The nut has threads on the inside that match up with the inlet and outlet on the torch and re-gulator. The gland slides inside the hose and is held in place by a crumpled ferrule. The nut is loose and can be turned by hand or a wrench to tighten the threaded nut onto the equipment.

Hoses may be made of different materials and may or may not be suitable for all fuel gases. In the USA fuel gas hoses graded R and RM are only suitable for acetylene, as other gases may break down the rubber in the hose. Grade T hoses are suitable for all fuel gases.

Between the regulator and the hose, and ideally between hose and torch on both oxygen and fuel lines, a flash-back arrestor and \ or a non-return valve should be installed to prevent flame or oxygen-fuel mixture being pushed back into either cylinder and damaging the equipment or making a cylinder explode.

The flashback arrestor (not to be confused with a check valve) prevents shockwaves from downstream coming back up the hoses and entering the cylinder, as there are quantities of fuel\oxygen mixtures inside parts of the equipment that may explode if the equipment is incorrectly shut down, acetylene decomposes at excessive pressures or temperatures. The flashback arrestor will remain switched off until someone resets it, in case the pressure wave created a leak downstream of the arrestor.

A check valve lets gas flow in one direction only. Do not confuse it with a flashback arrestor, as check valves are not designed to block a shock wave. A check valve is usually a chamber containing a ball that is pressed against one end by a spring: gas flow one way pushes the ball out of the way, and no flow or flow the other way lets the spring push the ball into the inlet, blocking it. A pressure wave could occur while the ball is so far from the inlet that the pressure wave gets past before the ball reaches its off position.

VOCABULARY

Heavy-duty work –работа, требующая больших усилий

Psi – pounds per square inch

Ply of fabric – слой оплетки

Rib – ребро жесткости

Delivery pressure – подаваемое давление

Left-\right-handed thread – левая \правая резьба

Nut - гайка

Gland - сальник

Inlet – вход, впуск

Outlet – выход, выпуск

Crumped - гофрированный

Ferrule – ободок, манжета

Loose nut – незатянутая гайка

Wrench – гаечный ключ

Flashback arrester – предохранительный затвор, арретир

Non-return valve – обратный клапан

Check valve – стопорный \ контрольный клапан

Shock wave – ударная волна

Unit 21. FUELS IN OXY-FUEL WELDING

There is not a single gas called oxy-acetylene. The most commonly used fuel is acetylene, other gases used are propylene, liquefied petroleum gas (LPG), propane, natural gas, hydrogen and MAPP gas. Acetylene and gases that liquefy under cylinder pressure should only be used where it can be relied on that the gas cylinder containing it will always be vertical with its valve on top.

Acetylene is the fuel first used for oxy-fuel welding and remains the fuel of choice for repair work and general cutting and welding. Acetylene gas is shipped in special cylinders designed to keep the gas dissolved. The cylinders are packed with various porous materials, e.g. asbestos, then filled about half way with acetone. The acetylene dissolves in acetone. This method is necessary because above 207 kPa acetylene is unstable and may explode. Acetylene when burned with oxygen gives a temperature of 3200ºC to 3500ºc which is the highest temperature of any of the commonly used gaseous fuels. Its main disadvantage is its comparatively high cost.

Oxy-gasoline (oxy-petrol) torches have been found to perform very well, especially where bottled gas fuel is not available or difficult to transport to the worksite. Test showed that an oxy-gasoline torch cut steel plate up to 0.5 inch thick as well as oxy-acetylene. The gasoline is fed from a pressure tank whose pressure can be hand-pumped or fed from a gas cylinder.

Hydrogen has a clean flame and is good for use on aluminum. It can be used at a higher pressure that acetylene and is therefore useful for underwater welding and cutting. It is a good type of flame to use when heating much material. The flame temperature is high, about 2,000º C at atmospheric pressure. For some oxy-hydro-gen torches the oxygen and hydrogen are produced by electrolysis of water in an apparatus which is connected directly to the torch.

MAPP gas is a registered product of the Dow Chemical Company. It is liquefied petroleum gas mixed with some chemicals. It has the storage and shipping characteristics of LPG and has a heat value a little less than acetylene. Because it can be shipped in small containers for sale at retail stores, it is used by hobbyists, and large industrial companies and shipyards because it is much less dangerous than acetylene. MAPP gas can be used at much higher pressures than acetylene and the torch can cut up to 12 inch thick steel. Other welding gases that develop comparable temperatures need special procedures for safe shipping and handling. A MAPP gas leak is easy to identify because of its particularly terrible odor.

Propane does not burn as hot as acetylene and so cannot be used for welding. Propane, however, with the right torch can make a faster and cleaner cut than acetylene, and is much more useful for heating and bending than acetylene. It is also cheaper than acetylene and easier to transport.. Like propylene, most propane tips are of a two-piece design. Propane often gets unfair criticism because it really needs changing your torch (from an equal pressure torch to an injector torch) and not just changing your tip to get the best performance. Most torches are equal pressure and designed for gases such as which are lighter than oxygen. Propane is a great deal heavier and runs much better through a low-pressure injector torch.

Propylene is used in production welding and cutting. It cuts faster and cleaner than propane. When propylene is used, the torch rarely needs tip cleaning.

Oxygen is not a fuel. It is chemically combined with the fuel to produce the heat for welding. This is called oxidation, but the more general and more commonly used term is combustion. In the case of hydrogen, the product of combustion is simply water. For the other hydrocarbon fuels, water and carbon dioxide are produced. The heat is released because the molecules of the products of combustion have a lower energy state than the molecules of the fuel and oxygen. Oxygen is shortened to oxy-, as in the term oxy-acetylene torch.

Oxygen is usually produced elsewhere by distillation of liquefied air and shipped to the welding site in high pressure vessels, commonly called tanks or cylinders at a pressure of about 200 atmospheres.

VOCABULARY

Propylene - пропилен

Liquefied petroleum gas (LPG) – сжиженный нефтяной газ

Propane - пропан

MAPP gas (methylacetylene propadiene) – МАПП газ

To liquefy - сжижать

Oxygasolene torch - бензорез

Gasoline - бензин

Hobbyist – любитель, непрофессионал

Oxidation - окисление

Combustion - горение

Distillate – дистиллировать, перегонять