Welding is the process of joining together pieces of metal or metallic parts by bringing them into intimate proximity and heating the places of contact to a state of fusion or plasticity. This leads to the formation of bond between atoms of the metals in the weld zone, and a strong inseparable joint is formed after the metals have cooled.
Welding is applicable to metals and non-metals such as glass, plastics, graphite, and some rocks.
Welding finds widespread application in almost all branches of industry and construction. Welding is extensively employed in the fabrication and erection of steel structures in industrial construction and civil engineering (frames of industrial buildings, bridge, etc.), vessels of welded-plate construction (steel reservoirs, pipelines, etc.) and concrete reinforcement.
Welding processes may be classified according to the source of energy employed for heating the metals and the state of the metal at the place being welded.
All existing welding processes used in engineering industries may be divided into two broad systems: pressure welding and fusion welding (non-pressure welding).
In fusion welding, the two pieces to be joined are heated to a melting point at the joint, a filler metal is added, the weld pool is stirred, and a weld is allowed to form on cooling. In some fusion welding processes, no filler metal is used.
In accordance with the method applied for feeding the filler metal to the weld, welding procedures are classified as manual, semi-automatic or automatic welding.
In pressure welding, the workpiece is raised at the joint to a temperature below the melting point of the material, and a weld is formed by applying pressure.
Pressure welding processes involve the heating of the metallic parts only to a plastic or slightly fused state and forcing them together with external pressure. Pressure welding processes are applied to metals which are capable of being brought to a plastic state by heating or due to the action of external forces. It has been established that in this process the most weldable metals prove to be those metals which have higher thermal conductivity. Such metals more rapidly dissipate heat from the weld zone and do not allow an excessively high temperature to be concentrated in a small area (the latter may lead to considerable internal stress).
The quality of the joint obtained in pressure welding depends to a great extent upon the magnitude of the applied pressure and the temperature to which the metal is heated at the moment of welding. The higher this temperature, the less unit pressure will be required to produce the weld.
Proper cleaning of the surface to be joined is one of the main conditions for obtaining high-quality welds in pressure-welding procedures.
Fusion welding.
The field of fusion welding can be broken into several processes, the most important of which are arc welding, electroslag welding, gas-shielded arc welding, gas welding, electron beam welding, and plasma-jet welding.
In all arc processes, the source of heat is an electric arc whose temperature may be as high as 6000K (5727 C).
Manual Metal-arc Welding (the Slavianoff process) (Fig.5). In this process an arc 1 is established between the work to be welded 2 and a metallic wire, or electrode 4, clamped in an electrode-holder 5. The intense heat of the arc melts some of the parent metal and tip of the electrode. The molten metal fills the groove between the edges of the work and, on cooling, forms a weld 3.
Exercise 1. Match the words:
| Melting temperature | край, кромка |
| Parent metal | обрабатываемое изделие |
| Filler metal | проволока |
| Flux | температура плавления |
| Edge | присадочный металл |
| Weld pool | основной металл |
| The work | ручная дуговая сварка мет. эл. |
| Wire | флюс |
| Gas shielded arc w. | газоэлектрическая сварка |
| Manual metal arc w. | сварочная ванна |
Exercise 2. Translate the following groups of words:
fusion
pressure
arc
gas
gas shielded arc
manual metal arc welding
electron beam
plasma-jet
low
high temperature
melting
welding
filler
weld metal
parent
высокая
низкая
температура плавления
сварки
высокого качества
шов
низкого качества
Exercise 3. Translate the following nouns with preposition:
example: to melt – плавить; melting –плавление
| 1. to weld - welding 2. to join – joining 3. to heat – heating 4. to coat - coating | 5. to cool – cooling 6. to melt – melting 7. to bond – bonding 8. to cover - covering |
Exercise 4. Fill gaps with prepositions: owing to, between, by, to, on, below, around
1. Joining takes place … the formation of bonds … atoms.
2. Two pieces of metal are joined … heating … a melting temperature.
3. A weld is formed … cooling.
4. In pressure welding the works are heated … a temperature … melting-point.
5. A weld is formed … applying pressure.
6. There is a covering … the weld pool.
7. An arc is established … the work and a metallic were.
Дата: 2019-07-24, просмотров: 247.
