Завдання №5: Складіть речення з поданих слів

1. The, from, the arc, metal, formed, between, heat, the electrode, and, the melts, the, of the, edges, metal.

2. welding, this, electroslag, is, also, called, process.

3. In, obtained, heat, resistance welding, is, electric, current, metal, from, the re­sistance, of, to, the flow, of, an.

4. creates, this, the metals, causes, heat, which, resistance, melts, and the weld.

5. slower, the rate, of, welding, is, considerably, however, than, processes, in, other.

UNIT 3

Basic principles of welding.

A weld can be defined as a coalescence of metals pro­duced by heating to a suitable temperature with or with­out the application of pressure, and with or without the use of a filler material.

In fusion welding a heat source generates sufficient heat to create and maintain a molten pool of metal of the required size. The heat may be supplied by electricity or by a gas flame. Electric resistance welding can be consid­ered fusion welding because some molten metal is formed.

Solid-phase processes produce welds without melting the base material and without the addition of a filler metal. Pressure is always employed, and generally some heat is provided. Frictional heat is developed in ultra­sonic and friction joining, and furnace heating is usu­ally employed in diffusion bonding.

The electric arc used in welding is a high-current, low-voltage discharge generally in the range 10-2,000 am­peres at 10-50 volts. An arc column is complex but, broadly speaking, consists of a cathode that emits elec­trons, a gas plasma for current conduction, and an anode region that becomes comparatively hotter than the cath­ode due to electron bombardment. Therefore, the elec­trode, if consumable, is made positive and, if non-consum­able, is made negative. A direct current (dc) arc is usually used, but alternating current (ac) arcs can be employed.

Total energy input in all welding processes exceeds that which is required to produce a joint, because not all the heat generated can be effectively utilized. Efficiencies vary from 60 to 90 percent, depending on the process; some special processes deviate widely from this figure. Heat is lost by conduction through the base metal and by radiation to the surroundings.

Most metals, when heated, react with the atmosphere or other nearby metals. These reactions can be extremely detrimental to the properties of a welded joint. Most metals, for example, rapidly oxidize when molten. A layer of oxide can prevent proper bonding of the metal. Molten-metal droplets coated with oxide become en­trapped in the weld and make the joint brittle. Some valu­able materials added for specific properties react so quickly on exposure to the air that the metal deposited does not have the same composition as it had initially.
These problems have led to the use of fluxes and inert atmospheres.

Vocabulary notes:

coalescence – з’єднання

filler – наповнювач

fusion welding- зварювання плавленням

solid - phase processes – твердо-фазний процес

frictional heat – теплота тертя

frictional joining – фрикційне з’єднування

diffusion bonding – дифузійний зв’язок

arc column – дугова колона

detrimental – шкідливий

to entrap – захопити

brittle – крихкий, ламкий

exposure – дія, вплив

Завдання № 1: Дайте відповіді на запитання.

1. What is a weld?

2. Give the definition of fusion welding.

3. Is pressure employed in welding?

4. What parts does an electrode consist of?

5. What is the reaction of metal when heated?

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