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Welding is a manufacturing process and technique for joining metals or other thermoplastic materials such as plastics by means of heat, high temperature, or high pressure. There are many energy sources for modern welding, including gas flame, arc, laser, electron beam, friction and ultrasonic.
Manual arc welding and CO2 gas shielded welding consumables and
equipment
1. The electrode should be dried in a high-temperature drying box,
and the number of times the electrode should be dried should not
exceed two times.
2. The packaging of the welding wire should be in good condition.
If it is damaged, the welding wire should be partially discarded if
it is contaminated, bent or disordered.
3. The purity of CO2 gas should not be lower than 99.9% (volume
ratio), the water content should be lower than 0.05% (weight
ratio), and the bottle should be stopped when the high pressure in
the bottle is lower than 1MPa.
4. The voltage of the welding machine should be normal, the ground
wire should be pressed firmly, the contact should be reliable, the
cable and welding tongs should not be damaged, the wire feeder
should be able to feed the wire evenly, and the gas pipe should be
free of air leakage or blockage.
Installation welding procedures and general requirements
The general sequence of welding is: pre-welding inspection →
preheating and rust removal → installation of welding pad and arc
strike plate → welding → inspection
1. Before welding, check the groove angle, blunt edge, gap and
offset amount, and remove rust spots, oil stains, iron oxide
scales, etc. in the groove and on both sides.
2. Preheat. Before welding, use gas welding or a special baking gun
to uniformly heat the groove and the base metal within 100mm on
both sides, and measure the temperature with a surface thermometer
to prevent the temperature from not meeting the requirements or
local oxidation of the surface, and preheat the temperature.
3. Re-check the preheating temperature, if the temperature is not
enough, it should be reheated to make it meet the requirements.
4. When installing the welding backing plate and the arc striking
plate, the surface cleanliness requirements are the same as the
groove surface. The backing plate and the base metal should be
closely attached, and the arc striking plate and the base metal
should be welded firmly.
5. Welding: The welding bead of the first layer should seal the
connection between the base metal and the backing plate in the
groove, and then accumulate the welding layer by layer until the
groove is filled. After each welding seam is completed, the welding
slag and spatter must be removed. If there are welding defects,
they should be removed and repaired in time.
6. A joint must be welded continuously. If the welding is stopped
halfway as a last resort, it should be treated with heat
preservation and slow cooling. Before re-welding, it should be
reheated according to the regulations.
7. Welding should be stopped in case of rain or snow, and there
should be wind shields and canopies around and above the welding
joints of components. Welding should be stopped when the wind speed
is greater than 5m/s. When the ambient temperature is lower than
zero, preheating and post-heating measures should be taken
according to regulations.
8. The carbon structural steel should be cooled to the ambient
temperature in the weld, and the low-alloy structural steel should
be tested for weld flaw detection 24 hours after completion.
9. Welders and inspectors should fill in the work record form
carefully.
Welding sequence and process parameters for typical joints
1. When the upper and lower columns without lugs are welded
symmetrically to 1/3 of the plate thickness by two welders on both
sides, cut off the lugs.
2. Then two welders symmetrically weld to 1/3 of the plate
thickness on both sides on the side of the cut ear plate.
3. Two welders will be responsible for the welding of the two
adjacent sides respectively.
4. The joints of the weld bead between each two layers should be
staggered from each other. The weld bead joints welded by two
welders should also pay attention to the staggeredness of each
layer. During the welding process, attention should be paid to
detecting the temperature between layers.
5. Welding process parameters:
CO2 gas shielded welding: wire diameter Φ1.2mm, current 280~320A,
welding speed 350~450mm/min
Wire extension length: about 20mm, gas flow 25~80L/min,
Voltage 29~34V, interlayer temperature 120~150℃
Type of welding
1. Electrode arc welding:
Principle - Arc welding method for welding with a hand-operated
electrode. Using the stable burning arc established between the
electrode and the weldment, the electrode and the weldment are
melted to obtain a firm welded joint. It belongs to gas-slag joint
protection.
Main features - flexible operation; low assembly requirements for
the joint to be welded; wide range of weldable metal materials; low
welding productivity; strong dependence on weld quality (depending
on the welder's operating skills and on-site performance).
Application - widely used in shipbuilding, boilers and pressure
vessels, machinery manufacturing, building structures, chemical
equipment and other manufacturing and maintenance industries. It is
suitable for welding of various metal materials, various
thicknesses and various structural shapes (in the above
industries).
2. Submerged arc welding (automatic welding):
Principle - The arc burns under the flux layer. Welds are formed by
melting the wire, flux and base metal (weld) using the heat
generated by the arc burning between the wire and the weldment.
Slag protection.
Main features - high welding productivity; good weld quality; low
welding cost; good labor conditions; difficult to weld in space;
high requirements for welding assembly quality; bad) and short
welds.
Application - widely used in shipbuilding, boilers, bridges,
lifting machinery and metallurgical machinery manufacturing.
Submerged arc welding can be used for any weldment where the weld
can be kept in a horizontal position or with a small inclination
angle. The thickness of the plate should be greater than 5 mm
(anti-burn through). Welding carbon structural steel, low alloy
structural steel, stainless steel, heat-resistant steel, composite
steel, etc.
3. Carbon dioxide gas shielded welding (automatic or semi-automatic
welding):
Principle: A molten electrode arc welding method using carbon
dioxide as a shielding gas. Gas protection.
Main features - high welding productivity; low welding cost; small
welding deformation (concentrated arc heating); high welding
quality; simple operation; high spatter rate; difficult to weld
with AC power; poor wind resistance; Metal.
Application - mainly welding low carbon steel and low alloy steel.
Available in various thicknesses. Widely used in automobile
manufacturing, locomotive and vehicle manufacturing, chemical
machinery, agricultural machinery, mining machinery and other
departments.
4. MIG/MAG welding (melting extremely inert gas/active gas shielded
welding):
MIG welding principle - an arc welding method using inert gas as
shielding gas and welding wire as melting electrode.
The shielding gas is usually argon or helium or a mixture thereof.
MIG uses inert gas, and MAG adds a small amount of active gas, such
as oxygen, carbon dioxide, etc., to the inert gas.
Main features - good welding quality; high welding productivity; no
deoxidation and dehydrogenation reaction (easy to form welding
defects, especially strict requirements for surface cleaning of
welding materials); poor wind resistance; complex welding
equipment.
Application - can weld almost all metal materials, mainly used for
welding of non-ferrous metals and their alloys, stainless steel and
some alloy steels (too expensive). The thinnest thickness is about
1 mm, and the maximum thickness is basically unlimited.
5. TIG welding (tungsten inert gas shielded welding)
Principle - Under the protection of inert gas, the arc generated
between the tungsten electrode and the weldment is used to melt the
base metal and the filler wire (or without filler wire) to form the
welding method of the weld. The electrodes do not melt during
welding.
Main features - strong adaptability (stable arc, no spatter); low
welding productivity (tungsten electrode has poor current-carrying
capacity (anti-tungsten electrode melting and evaporation,
anti-tungsten welding seam)); high production cost.
Application - almost all metal materials can be welded, commonly
used for welding stainless steel, high temperature alloys,
aluminum, magnesium, titanium and their alloys, refractory active
metals (zirconium, tantalum, molybdenum, niobium, etc.) and isobell
metals. The welding thickness is generally less than 6 mm, or the
bottom welding of thick parts. Using a small-angle groove (narrow
groove technology) can realize automatic TIG welding of narrow gaps
with a thickness of more than 90mm.