In this article, we list 73 welding basics that beginners must know.
These 73 basic welding knowledge are the summary of experience and tell you the most important knowledge in the shortest language.
Even if you are an old hand in welding, I believe there must be some knowledge you don’t know.
Let’s dive right into it.
The mechanical properties of metals include strength, plasticity, hard seat, toughness, fatigue strength, etc.
Hardness indexes can be divided into Brinell hardness, Rockwell hardness and Vickers hardness.
The ability of metal materials to conduct heat is called thermal conductivity.
The physical properties of metals include density, melting point, thermal expansion, thermal conductivity, conductivity and so on.
Heat resistant steel refers to the steel with certain thermal stability and thermal strength at high temperature.
Stainless steel is a stainless and acid resistant stream scale with corrosion resistance to atmosphere, acid, alkali, salt, etc.
The performance of conducting current of metal materials is called conductivity, and its measurement index is resistivity.
The temperature at which a metal changes from solid to liquid is called the melting point.
Weld symbols are generally composed of basic symbols and leaders. If necessary, auxiliary symbols, supplementary symbols and weld size symbols can also be added.
The symbol indicating that the weld surface is flush is -; The symbol indicating that there is a backing plate at the bottom of the weld is ; The symbol representing the weld around the weldment is ○.
According to different heating and cooling methods, heat treatment can be divided into annealing, quenching, normalizing and tempering.
The current whose direction and size do not change with time is DC, on the contrary, it is AC.
The stepped cracks formed along the rolling layer of the steel plate in the welded components due to welding are called lamellar tearing.
When other conditions remain unchanged, the tendency of porosity increases with the increase of welding speed; When the welding current increases, the tendency of porosity increases; When the arc voltage increases, the pore tendency increases.
Manual arc welding is applicable to the welding of various materials such as carbon steel, low alloy steel, heat resistant steel, low temperature steel and stainless steel.
Manual arc welding can be used in horizontal, vertical, horizontal, vertical and other positions, so it is widely used.
Compared with gas welding and submerged arc welding, manual arc welding has fine microstructure, small heat affected zone and good joint performance.
During manual arc welding, the welder’s operation technology and experience directly affect the product quality.
Welding process parameters refer to various physical quantities selected to ensure welding quality during welding.
The electrode for manual arc welding is mainly selected according to the performance of the base metal, the rigidity of the joint and working conditions. The strength grade of the electrode for welding general carbon steel and low alloy steel is mainly selected according to the equal strength principle.
There are many factors to be considered in the selection of welding current for manual arc welding, but mainly the electrode diameter; welding position; weld bead level
The empirical formula for calculating welding current of manual arc welding is I = 10d2.
The basic form of groove commonly used in manual arc welding is I-shape; V-shaped; Double V-shaped; Double Y-shaped; Double U-groove with Bell edge.
The welding crack has the characteristics of sharp notch and large aspect ratio.
The purpose of preheating is to reduce the cooling rate and improve the stress condition.
The slag of alkaline electrode has strong desulfurization and dephosphorization capacity.
After welding, all (or part) of the weldment shall be heated or insulated immediately. The process measure of slow cooling is called post heating, which can effectively escape the hydrogen in the welded joint, so it is an important measure to prevent delayed cracks.
During welding, the bubbles in the solution pool fail to escape during solidification, and the remaining holes are called pores.
The dissolved slag remaining in the weld after welding is called slag inclusion.
The coating layer pressed on the surface of the welding core is called coating.
The length of welding rod depends on the diameter of welding core, material, coating type, etc.
Steel for welding core can be divided into carbon structural steel; Alloy structural steel; There are three categories of stainless steel.
Welding rods can be divided into carbon steel welding rods according to different purposes: Low alloy steel electrode; Stainless steel electrode; Surfacing electrode; Cast iron electrode; Nickel and nickel alloy electrodes; Copper and copper alloy electrodes; Aluminum and aluminum alloy electrodes; Special purpose welding rod;
Related reading: How to Choose the Right Welding Rod?
The butt joint without groove is used for the weldment of thinner steel plate, and the butt joint with groove is used for the weldment requiring full penetration on the thicker surface of steel plate.
Acetylene generator is a device that uses the interaction of voltage and water to produce acetylene.
The function of the pressure reducing valve is to reduce the high-pressure gas stored in the gas cylinder to the required stable working pressure.
Mixing ratio of oxygen and acetylene β Neutral flame at 1.1-1.2, β> 1.2 is oxidation flame, β< 1.1 is carbonization flame.
Gas welding process parameters include welding wire diameter; Flame properties and energy efficiency; Welding nozzle tendency; Welding speed.
Welding is a processing method that enables the weldment to achieve atomic bonding by heating, pressurization or both, with or without filler materials.
There are 13 basic symbols representing the cross-section shape of the weld.
The included angle between the vertical of the weldment surface and the groove surface is called the groove surface angle.
The junction between the weld surface and the base metal is called the weld toe.
When welding non-ferrous metals, cast iron, stainless steel and other materials, gas welding flux must usually be used.
Related reading: Ferrous vs Non-ferrous Metals
The safety of acetylene cylinder is realized by the fusible plug arranged on the cylinder shoulder.
The ignition method of welding arc includes contact moment ignition method; High frequency and high voltage arc striking method.
The general structure of manual arc welding shall be acid electrode, and the important structure shall be alkaline electrode.
According to the slag dissolving characteristics of the electrode coating after melting, the electrode can be divided into acidic electrode and alkaline electrode.
The safety of the oxygen cylinder is realized by the metal safety film in the cylinder valve.
The metal cutting process includes three stages: preheating, burning heat and slag blowing.
In heat treatment production, the common cooling methods are isothermal cooling; Two types of continuous cooling.
The necessary conditions for the generation and maintenance of arc are cathode electron emission and gas ionization.
The main sources of sulfur in the weld are base metal, welding wire, flux skin or flux, so the key measure to reduce the sulfur content in the weld is to strictly control the sulfur content in the welding raw materials.
During fusion welding, the energy input by welding energy to the weld of unit length is called linear energy.
The primary crystallization of molten pool includes two processes: nucleation and nucleation growth.
In CO2 gas shielded welding, nitrogen pores are caused by poor protection or impure CO2 gas.
The reverse wire mode of CO2 semi-automatic gas shielded welding is push wire type; Wire drawing type; Push pull type; At present, push wire welding gun is mostly used.
The gas supply device for CO2 gas shielded welding is composed of gas cylinders; Dryer; Preheater; Pressure reducer; Flowmeter, etc.
Welding equipment for CO2 gas shielded welding, including welding power supply; welding torch; Wire feeding system; Air supply unit; Control system, etc.
Post weld heat treatment includes post weld heat treatment; High temperature tempering; Normalizing or normalizing plus tempering, etc.
The cracks produced when welding gray cast iron include thermal stress cracks; Hot crack; Two types, especially thermal stress cracks are more common.
Cast 238 electrode shall be used for hot welding of nodular cast iron.
The stress and deformation of the weldment in the direction perpendicular to the weld is called transverse stress and deformation.
For the structure with asymmetric welds, the side with less welds shall be welded first, and then the side with more welds, so as to reduce the overall deformation.
In order to offset the welding deformation, the weldment shall be artificially deformed in the direction opposite to the welding deformation before welding. This method is called reverse deformation method.
The heat dissipation method is not suitable for welding materials with high hardenability.
Flame correction method uses the plastic deformation generated by local heating of flame to compress the longer metal after cooling, so as to achieve the purpose of correcting deformation.
The key to flame heating correction is to master the deformation caused by local flame heating, so as to determine the correct heating position, and control the temperature and the number of repeated heating.
The flame heating mode is spot heating; Linear heating; Triangular heating.
Triangular heating is often used to correct the bending deformation of components with large thickness and strong rigidity.
Preheating before welding can reduce the temperature difference and slow down the cooling speed, so as to reduce the welding stress.
The acetylene cylinder shall be used vertically. When the acetylene cylinder is placed horizontally, it must stand for 20min before use.
The pressure reducer shall not be contaminated with grease during use.
Before using the welding torch, check the injection and absorption performance of the welding torch.
For welding stainless clad steel plate, three different Dacron electrodes shall be used to weld the same weld.
If the welding torch backfires, first quickly turn off acetylene and then oxygen.
According to the provisions of the national standard GB3323-82 “classification method for fair trade such as steel weld radiography and negatives”, the quality standard of steel weld radiography is divided into four levels, of which the defects in grade I weld are the least and the defects in grade IV weld are the most.
Gb3323 stipulates that cracks are not allowed in class I welds; Lack of fusion; Incomplete penetration; Strip slag inclusion; crackle; Lack of fusion; II. There shall be no double-sided welding or incomplete penetration in single-sided welding with backing plate in the weld.
When carbon steel electrode is used to connect cast iron and low carbon steel joint, 4-5mm isolation layer can be deposited on the cast iron groove first, and then assembly spot welding can be carried out after cooling.