Basic information about metals used in welding

 

What is the most common method of welding metals?

Steel is an alloy of iron with carbon, the amount of which should not be more than 2%. Classification of steels:

 · According to the production method: converter, open-hearth, electric steel.

 · According to the degree of de oxidation: boiling (kp), semi-calm (ps), calm (SP).

 * By chemical composition: carbon (low -, medium -, high-carbon) and alloyed (low-, medium - and high-)

 · For the intended purpose: ordinary quality, high-quality structural, construction, tool, boiler, shipbuilding.

 · According to special properties: non-rusting, heat-resistant, heat-resistant.

 Classification of carbon and alloy steels:

 * By chemical composition: carbon (low -, medium -, high-carbon) and alloyed (low-, medium - and high-)

 · For the intended purpose: ordinary quality, high-quality structural, construction, tool, boiler, shipbuilding.

 · According to special properties: stainless, heat-resistant, heat-resistant.

 The mode of operation of power sources.

 The parameters of the operating mode of electric welding equipment include:

 - rated welding current,

 - operating and idle voltage,

 - the duration of switching on (PV),

 - duration of the load (MON),

 - duration of work (PR).

 Metal for cutting is divided by thickness into 3 groups: thickness. up to 5 mm, thickness. 5-300mm, thickness. more than 300 mm. The cutting parameters are:

 -gas consumption and type of heating flame,

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 -cutting oxygen pressure,

 - cutting speed.

 The gas consumption increases with increasing thickness of the metal being cut, the color of the heating flame for small and medium thicknesses should be normal, and for large thicknesses it changes to yellow-green (carburizing).

 The pressure of cutting oxygen is 2-3 Atm for thin and thick metals, and for metals of medium thickness increases in proportion to the increase in the thickness of the metal.

 The cutting speed of the metal decreases with increasing thickness of the metal.

 4. Causes of hot cracks and preventive measures.

 When welding alloy steels, the following difficulties appear:

 * Porosity,

 * Overheating of metal and quenching structures due to reduced thermal conductivity,

 * Cold and hot cracks,

 * Tendency to deformities.

 To avoid the appearance of cracks, it is necessary to strictly observe the welding technology: organize preheating of the metal to a temperature of 250-350 degrees, conduct welding at high speeds, after welding, heat treatment in the form of normalization is needed. You can also grind the structure by introducing Mo or Si.

 The effect of electric current on a person.

 Improper operation of electrical equipment can create a danger of electric shock, which affects the heart, nervous system, muscles.

 A current of 0.04 A is very dangerous for human life, and a current of 0.05 A will necessarily lead to serious consequences.

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 Physical and chemical properties of metals.

 The physical properties of steels include:

 -- density is the mass of a substance enclosed in a unit volume;

 -- thermal conductivity is the ability of Me to transfer heat from more heated areas to less heated ones,

 -- electrical conductivity is the ability of Me to pass an electric current

 The chemical properties of steels include:

 -- liability is the ability of a substance to combine with oxygen;

 -- corrosion resistance is the ability of Me not to oxidize and not to enter into chemical reactions with surrounding substances;

 -- heat resistance is the ability of steel not to oxidize at high temperature;

 -- heat resistance is the ability of steel to maintain strength at high temperature.

 Power sources are classified according to the following criteria:

 · According to the type of current, (direct and alternating current)

 · By the number of simultaneously connected posts,

 · As intended, (for manual, p/a, automatic welding)

 · According to the principle of operation,

 · By design,

 * Specialized.

 Arc power sources have a common marking:

 · --the first letter is the name of the IP (T, V, P, G),

 · --the second letter is arc welding,

 · --the third letter is the welding method (K, F,G, Y),

 · --the fourth letter is the number of posts (M),

 · --the first two digits are the rated current in hundreds of amperes,

 · --the third digit is a modification,

 The converter is a combination of an asynchronous three-phase AC motor and a DC welding generator. The converter is used for manual arc welding in carbon dioxide in shop conditions. They have a rigid or falling characteristic.

What is the significance of the polarity during welding

When welding with direct current, you can change its polarity. By connecting the negative to the electrode, it is possible to weld thick Me qualitatively or work with a high welding speed, as well as weld with a W-electrode without overheating it. By connecting the minus on the Iu, you can qualitatively weld: - thin Iu, - alloy steels, - non-ferrous Iu (since they are liquid-flowing), - cast iron, - work with electrodes with a basic coating.

 Quality control of the seam for density.

 The quality control of the seam for density refers to a non-destructive type of control. The seam density is controlled by the following methods:

 -- kerosene,

 - chemical gases,

 - compressed air,

 - by hydraulic method

 - leak detectors

 Types and causes of injuries during welding and cutting.

 The main causes of injuries in welding operations are:

 --high temperature of the welding arc or flame;

 --high arc brightness;

 -- electrotraumatism;

 -- mechanical injuries from mech. processing Me and moving parts.

 -- aerosols released during welding.

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 mechanical properties include: - strength is the ability of Me to withstand an external load without destruction.

 - plasticity is the ability of Me to change shape under the influence of a load and maintain it after removing the load.

 - hardness is the ability of Me to resist the penetration of other harder bodies into it.

 The technological properties include:

 - malleability is the ability of Me to change shape under the influence of external forces.

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 - fluidity is the ability of Me in the molten state to fill narrow gaps and spaces.

 - weldability is the ability of Me to form a high-quality welded joint that does not contain defects.

 - machinability by cutting is the property of Me to be machined by a cutting tool.

 The device of transformers of the TD type.

 For arc welding with piece melting and tungsten electrodes, AC power sources are used – welding transformers.

 They provide ignition and extinguishing of the arc, control of its physical parameters. Welding transformers convert the mains voltage to the reduced voltage required for welding.

 Advantages of tr-rov: - high efficiency (0.9);

 - low specific power consumption; - easier and cheaper to operate and easy to repair.

 Disadvantages: - low stability of arc gorenje; - low stability of the welding mode due to voltage fluctuations in the network.

 Transformers consist of the following parts:

 * Casing,

 · Primary winding,

 * Secondary winding,

 * Magnetic circuit,

 * Throttle.

 The welding current is regulated in two ways: switching to a range of large or small currents - using a switch located inside the housing. Fine adjustment of the current is made by means of a retractable choke, or by lifting the movable winding along the magnetic circuit. All transformers have a falling characteristic.

 List the difficulties that arise when welding cast iron.

 When welding cast iron, the following difficulties arise: porosity, quenching structures, hot and cold cracks, fluidity.

 The "slag inclusion" defect is non-metallic inclusions remaining inside the seam. Reasons: high welding speed, violation of the welding mode, large penetration depth.

 The "undercut" defect is the formation of grooves along the seam. The reasons are: - a large welding current, - a long arc ,- when welding angular seams, the electrode is displaced towards the vertical wall.

 The "influx" defect is the spreading of the molten filler Me without fusing with the main Me. Reasons: --high welding current; --long arc;.- incorrect tilt of the electrode.

 The "crater" defect is a depression obtained after the arc breaks at the end of the seam. Reasons: -- arc breakage, -- incorrect execution of the final section of the seam.

 The defect "pores" are gas cavities formed in the melt due to over saturation with gases.

 Reasons: -- welding on untreated edges, -- non-dried welding materials, --high welding speed.

 A "crack" defect is a break in the metal along or across the seam.

 Reasons: - sudden cooling of the structure, - increased content of sulfur or phosphorus, - improper operation of the welded structure.

Become. Classification and labeling

Steel is an alloy of iron with carbon, the amount of which should not be more than 2%. Classification of steels:

 · According to the production method: converter, open-hearth, electric steel.

 · According to the degree of de oxidation: boiling (kp -, semi-calm (ps), calm (SP).

 * By chemical composition: carbon (low -, medium -, high-carbon) and alloyed (low-, medium-and high -)

 · For the intended purpose: ordinary quality, high-quality structural, construction, tool, boiler, shipbuilding.

 · According to special properties: stainless, heat-resistant, heat-resistant.

 Different groups of steels have their own symbols.

 1. Carbon steels of ordinary quality are marked: St. 0-6 and the letters kp, ps, sp.

 2. High-quality structural carbon steels are marked: according to

 the carbon content in hundredths of a percent, then the letters kp, ps, sp and capital letters, if the Me was subjected to heat treatment (T), or is intended for boiler production (K), for casting (L).

 3. Alloy steels are marked according to the scheme: first, the carbon content in

 hundredths of a percent, then - the capital letter of the alloying element and its percentage, at the end-A-high-quality steel in terms of sulfur and phosphorus content, AA – especially high-quality steel.

 Welding units. Scope of application, device, work.

 Welding units consist of an internal combustion engine and a welding generator. They are used for manual welding in the field, during installation and repair, when there is no electrical power supply network.

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Generators of welding units are collector and valve. Valve generators are a combination of an alternating current generator and a rectifier unit. Collector generators remove direct current from the stator using brushes located on the outside of the stator.

 The welding mode is a set of process parameters that make it possible to produce high-quality welding of Me parts of a given brand and thickness, in the desired spatial position.

 The parameters of the gas welding process are:

 - type of flame,

 - flame power,

 - the diameter of the filler wire.

 - welding speed.

 At the same time, you need to know the brand and thickness of the welded Me.

 Quality control of the seam for impermeability

 The quality control of the seam for density (impermeability) refers to a non-destructive type of control. The seam density is controlled by the following methods:

 --kerosene, chemical gases, compressed air, hydraulic method and leak detectors

 5. Safety precautions for the maintenance of electronic equipment.welding equipment.

 Persons who are at least 18 years old and have a welder's certificate, an entry in the qualification certificate on admission to perform special works and a special fire safety certificate are allowed to perform electric welding works. Electric welders must have an electrical safety group not lower than the second.

 The passages between the welding current power sources must have a width of at least 0.8 m – 1.5 m. The passages between the groups of transformers should be-1m. The distance between the I. P. and the generators is at least 3m.

 The welding current regulator can be placed next to or above the device, and placement under it is prohibited.

 A steel tire of any profile can serve as a return wire, which ensures the safe flow of welding current. The connection of the return wire must be carried out using bolts, clamps, clamps.