Упражнения

1. Найдите в тексте английские эквиваленты следующих слов и словосочетаний:

1. Питающий провод, 2. источник тока постоянной величины, 3. горелка, 4. небольшие колебания, 5. накапливаться на электроде, 6. изменять полярность на противоположную, 7. положительно \ отрицательно заряженный электрод, 8. сердцевина электрода, 9. состав электрода 10. влиять на свойства, 11. фтористый кальций, 12. хрупкость, 13. высокое содержание влаги, 14. добавка, присадка, 15. предпоследняя цифра, 16. низколегированная сталь, 17. полуавтоматический процесс, 18. удвоить результат, 19. угловой шов, 20. стыковой шов.

2. Переведите на РЯ следующие слова и словосочетания:

1. A steady arc distance, 2. constant voltage, 3. dramatic heat variations, 4. to maintain constant current, 5. fluctuations in the current, 6. weld penetration, 7. melting rate, 8. to purify the weld, 9. fast-fill electrodes, 10. fast-freeze electrodes, 11. fill-freeze electrodes, 12. low hydrogen electrodes, 13. calcium fluoride, 14. feasible options, 15. composition of the electrode core, 16. non-ferrous materials, 17. electrode coating, 18. to encourage cracking, 19. hygroscopic, 20. to assign electrodes with a number

3. Вставьте нужное слово или словосочетание:

1.The power supply used in SMAW has constant current … . 2. Most SMAW applications are … . 3. Maintaining a steady … is difficult. 4. The preferred … of the SMAW system depends primarily upon the electrode used and the desired properties of the weld. 5. With … the polarity changes over 100 times per second. 6. The … of the electrode core is sometimes identical to that of the base material. 7. Rutile electrodes create welds with high hydrogen content, … embrittlement and cracking. 8. Electrodes containing CaF2 are … and must be stored in dry conditions. 9. The first two or three digits of the number … the tensile stress of the weld metal. 10. The welding current and type of electrode coating are specified by the last two … together.

4. Охарактеризуйте различие в семантике синонимов:

To decompose – to disintegrate, to influence – to impact – to affect, to purify – to clean, figure – digit, manual – hand-made

5. Соотнесите термин и его определение:

1. Electrodes designed to melt quickly so that the welding speed can be maximized

2. Electrodes designed to supply filler metal that solidifies quickly

3. Electrodes intermediate in the speed of melting and solidifying

4. Welding process employing consumable electrodes coated in flux which, while disintegrating, gives off a shielding gas

5. Current which does not change its amperage or voltage

6. Positive or negative charge of the electrode

7. Negative impact that gases making air get upon the weld

8. Materials easily absorbing moisture from the environment

9. The process or property of being easily broken or cracked

10. One of the elements that combine to form numbers in a numeric system

Unit 8. PLASMA ARC WELDING

Plasma arc welding (PAW) is an arc welding process similar to gas tungsten arc welding (GTAW). The electric arc is formed between an electrode, which is usually but not always made of sintered tungsten and the work-piece. The key difference from GTAW is that in PAW, by positioning the electrode within the body of the torch, the plasma arc can be separated from the shielding gas envelope. The plasma is then forced through a fine-bore copper nozzle which connects the arc and the plasma exits the orifice at high velocities, approaching the speed of sound, and temperature approaching 20 000º C.

Plasma arc welding is an advancement over the GTAW process. It can be used to join all metals that are weldable with GTAW, i.e. most commercial metals and alloys. Several basic PAW variations are possible by varying the current, plasma gas flow rate, and the orifice diameter, including: micro-plasma (<15 Amperes); melt-in mode (15 – 400 Amperes); key-hole mode (100 Amperes). Plasma arc welding has a greater energy concentration as compared to GTAW. A deep narrow penetration is achievable, reducing distortion and allowing square-butt joints in material up to 12 mm thick. Greater arc stability allows a much longer arc length and much greater tolerance to arc length changes. Its limitation is that PAW requires relatively expensive and complex equipment as compared to GTAW.

At least two separate (and possibly three) gas flows are used in PAW: plasma gas which flows through the orifice and becomes ionized; shielding gas, which flows through the outer nozzle and shields the molten weld from the atmosphere; back-purge gas, required for certain materials and applications. These gases can be the same, or of differing composition.

Key process variables are: current type and polarity; usually DCEN from a CC source; AC square wave, common on aluminum and magnesium. Current can vary from 0,5A to 1200 A; current can be constant or pulsed at frequencies up to 20 kHz. Gas flow rate is a critical variable and must be carefully controlled based upon the current, orifice diameter and shape, gas mixture, and the base material and thickness.

Depending upon the design of the torch, e.g. orifice diameter, electrode design, gas type and velocities, and the current levels, several variations of the plasma process are achievable, including plasma arc welding, plasma arc cutting, plasma arc gouging, plasma arc surfacing and plasma arc spraying.

VOCABULARY

GTAW – gas tungsten arc welding – дуговая сварка вольфрамовым электродом

в среде защитного газа

Sintered - зд. металлокерамический

Gas envelope – зд. газовый пузырь

Fine bore – отверстие малого размера

To constrict - сжимать

Orifice - отверстие

Velocity - скорость

Commercial metals – металлы промышленного значения

Plasma gas flow rate – скорость потока плазмы

Arc stability – устойчивость, стабильность горения дуги

Tolerance – зд. допуск, допустимое отклонение от заданных параметров

Arc length – длина дуги

Outer nozzle – наружный мундштук

Back-purge gas – газ, очищающий обратную сторону шва

Square wave – прямоугольный импульс

Constant current – ток постоянной величины

Gourging – строжка, поверхностная резка

Surfacing – нанесение покрытия, обработка поверхности

Arc spraying – электрометаллизация, нанесение металлического покрытия