Welding method and auxiliary equipment:
Welding: The process of applying heat or pressure, or both, to combine atoms to form permanent connections. Metal welding is roughly divided into three categories: fusion welding, pressure welding, brazing.
Pressure welding: Welding by applying pressure. Explosive composite plate manufacturing process (both heating and applying pressure).
Brazing: The base material does not melt, but only melts the welding material. Generally used for two kinds of base materials that can not be directly welded are mainly used for sealing, and their bearing capacity is poor.
Fusion welding: welding where the welding site is heated to a melting state.
Electrode arc welding (manual arc welding) (SMAW) : the equipment is simple, easy to operate, suitable for indoor and outdoor welding in various positions, can weld a variety of materials, and is widely used; Low production efficiency and high labor intensity; The technical level and operation requirements of welders are higher.
Submerged arc automatic welding (SAW) : productivity is 5 ~ 10 times higher than manual arc welding, saving welding materials, automatic operation parameters are stable, weld composition is uniform, appearance is smooth and beautiful, so the welding quality is stable; The equipment is more complex and expensive; Because the arc is not visible, the joint processing and assembly are strictly required. The welding position is limited to a certain extent, and it is generally welded in the flat welding position.
Argon arc welding (TIG, GTAW) : manual, semi-automatic, automatic;
Suitable for welding all kinds of steel, non-ferrous metals and alloys, excellent welding quality; Easy to realize all position automatic welding; Heat concentration, smaller weld pool, faster welding speed, less heat affected zone, less welding deformation of the workpiece; Stable arc, small splash, beautiful shape, suitable for double-sided forming.
Argon gas cost is more expensive, argon arc welding equipment and control system is more complicated; The production efficiency of argon tungsten arc welding is low.
CO2 gas shielded welding (GMAW, FCAW) :CO2 gas, mixed gas (argon-rich) low cost, high efficiency, good quality, good operation performance; When control or operation is not appropriate, it is easy to produce pores. Welding equipment is more complex. Carbon dioxide gas shielded welding can be used to weld low carbon steel and low alloy steel in the manufacture of pressure vessels.
Common welding defects:
Porosity (H, N, CO) : A hole in the weld metal (inside or on the surface) where the gas in the molten pool metal has not been able to escape before the metal has cooled during welding. Shape: spherical, striped, dense, insect-shaped.
Slag inclusion: The phenomenon of residual welding slag in the weld metal. Shape: point, strip.
Inclusions: Non-metallic impurities (such as oxides, sulfides, etc.) that are produced by welding metallurgical reactions and remain in the weld metal after welding.
Tungsten clamping: Tungsten particles mixed into the weld metal during tungsten inert gas welding.
Underpenetration: The phenomenon that the root of the joint is not completely penetrated during fusion welding.
Non-fusion: In fusion welding, the joint between the bead and the base material or between the bead and the bead is not completely melted.
Edge: A dip or groove formed by sintering in the base material along the weld toe due to incorrect welding parameter selection or incorrect operation process.
Welding nodules: Metal nodules formed when molten metal flows onto unmelted base metal outside the weld during welding.
Concave: The locally low concave part formed on the surface or back of the weld after welding below the surface of the base material.
Cold crack: the crack caused by the welding joint cooling to a lower temperature after welding; Hydrogen induced crack, delayed crack. Low alloy steel, low alloy high strength steel is easy to produce. Q345R, Q345E.
Hot crack: welding cracks that occur when the weld metal cools to a high temperature zone near the solid phase line during welding; S can form low melting point eutectic with Ni, melting point 650℃. Solidification crack, crystallization crack. It is mainly found in austenitic stainless steel and nickel-based alloys.
Welding quality control measures:
Confirm the correctness of the material: including the base material, welding material grade is selected correctly.
Welding groove quality inspection, assembly accuracy: check the groove size (depth, Angle, blunt edge, etc.). Check the surface roughness and surface defects of the groove. Check the quality of groove surface cleaning. Each side of the groove surface should be cleaned within at least 20mm, polishing out the original metal luster, no debris. Non-destructive testing of bevel surface. If the plate thickness is > 30mm or σs > 400MPa or Cr-Mo class steel, magnetic particle or penetration detection is carried out. Defects (delamination, cracks) should be removed in advance.
For non-ferrous metals (such as titanium, nickel, etc.), the groove must be processed with carbide cutter head, shall not be polished with sand tools, and the finished groove must be wiped with acetone. The amount of wrong side of a group pair.
Personnel qualification verification: According to TSG Z6002-2010 “Special Equipment Welding Operators Assessment Rules” check whether the validity period and the number of certificates match.
Verify whether post-welding heat treatment is required: Conditions for heat treatment: hot pressed carbon steel, low alloy steel heads need to be heat treated to improve material properties; Post-welding heat treatment of containers and their pressure elements according to material, welded joint thickness and design requirements.
Final quality inspection after welding: Final quality inspection includes surface quality inspection, weld non-destructive testing, pressure test and density test. Where the permitted defects exceed the standards, they must be repaired in time to ensure safety and reliability.
Inspection and testing methods:
Destructive testing (damage testing) : generally used to verify whether the welding scheme is reasonable before welding; Welding process evaluation; Welding specimen; After failure, the corrosion mechanism was studied afterwards.
Non-destructive testing (NDT) : Generally used during the production of equipment, or after the equipment and materials have been put into use.
Balingteel can weld according to customer drawings, and at the same time, hot dip galvanizing and experimental physical and chemical analysis of welding products.
