What is the purpose of preheating when welding
Release time:
2023-02-25
【Summary Description】 Heating weldment What is the purpose of preheating when welding 1. Preheating is an effective measure to prevent cold cracks, hot cracks and hardened tissues in the heat affected zone. When welding carbon steel with high carbon content, low alloy steel, heat-resistant steel, and ordinary low carbon steel components with large stiffness, due to the fast cooling rate of the weld, it is easy to produce hardened structures in the weld and heat affected zone, which leads to cracks. Therefore, the welding parts must be preheated. Preheating can achieve the purpose of slowing down the cooling rate, can prevent the weld crack. 2. When welding the welded joint area with large restraint, shrinkage stress will be generated in the joint area due to rapid cooling and rapid heating, thus causing cracks. Preheating the butt area before welding can reduce the shrinkage stress and prevent cracks. 3, in the low temperature area of welding, in order to prevent cracks, even if the thickness of low carbon steel exceeds the preheating treatment must be carried out. 4, preheating can also remove oil, moisture and other factors affecting the quality of the weld, but also to promote the escape of hydrogen in the weld, so as to prevent the occurrence of pores and other defects to play a corresponding role, but also to prevent the occurrence of cracks. The common preheating methods in welding include overall heating in furnace, flame heating, infrared heating and power frequency induction heating. Among them, when the weldment is extremely thick, local heating takes a long time, or the shape is complicated, the weldment can be placed in the heating furnace for heating as a whole, such as the welding of the boiler drum cylinder and the pipe seat, and the welding of the thick-walled water chamber forgings of the high-pressure heater and the water pipe are all by the method of overall heating in the furnace. The use of oxygen-acetylene flame or city gas or liquefied petroleum gas as a fuel to form a flame heating weldment, is a commonly used local preheating method. According to the shape of the welding parts to be preheated, heating torches of various shapes such as ring and straight lines can be made. The principle of infrared heating is to use fuel combustion or electric energy to heat a specially treated surface to generate far infrared rays with a wavelength of 0.7~20 μm, which is a strong heat source and can be used to heat the welding parts. The device that uses fuel combustion to produce far-infrared rays is called the gas far-infrared heater. The device that uses electric energy to generate far infrared rays is called electric far infrared heater. Power frequency induction heating is the use of industrial frequency alternating current to cause alternating magnetic field on the weldment, forming eddy current and generating heat to heat the weldment.
Heating weldment
What is the purpose of preheating when welding
1. Preheating is an effective measure to prevent cold cracks, hot cracks and hardened tissues in the heat affected zone. When welding carbon steel with high carbon content, low alloy steel, heat-resistant steel, and ordinary low carbon steel components with large stiffness, due to the fast cooling rate of the weld, it is easy to produce hardened structures in the weld and heat affected zone, which leads to cracks. Therefore, the welding parts must be preheated. Preheating can achieve the purpose of slowing down the cooling rate, can prevent the weld crack.
2. When welding the welded joint area with large restraint, shrinkage stress will be generated in the joint area due to rapid cooling and rapid heating, thus causing cracks. Preheating the butt area before welding can reduce the shrinkage stress and prevent cracks.
3, in the low temperature area of welding, in order to prevent cracks, even if the thickness of low carbon steel exceeds the preheating treatment must be carried out.
4, preheating can also remove oil, moisture and other factors affecting the quality of the weld, but also to promote the escape of hydrogen in the weld, so as to prevent the occurrence of pores and other defects to play a corresponding role, but also to prevent the occurrence of cracks.
The common preheating methods in welding include overall heating in furnace, flame heating, infrared heating and power frequency induction heating.
Among them, when the weldment is extremely thick, local heating takes a long time, or the shape is complicated, the weldment can be placed in the heating furnace for heating as a whole, such as the welding of the boiler drum cylinder and the pipe seat, and the welding of the thick-walled water chamber forgings of the high-pressure heater and the water pipe are all by the method of overall heating in the furnace.
The use of oxygen-acetylene flame or city gas or liquefied petroleum gas as a fuel to form a flame heating weldment, is a commonly used local preheating method. According to the shape of the welding parts to be preheated, heating torches of various shapes such as ring and straight lines can be made. The principle of infrared heating is to use fuel combustion or electric energy to heat a specially treated surface to generate far infrared rays with a wavelength of 0.7~20 μm, which is a strong heat source and can be used to heat the welding parts.
The device that uses fuel combustion to produce far-infrared rays is called the gas far-infrared heater. The device that uses electric energy to generate far infrared rays is called electric far infrared heater. Power frequency induction heating is the use of industrial frequency alternating current to cause alternating magnetic field on the weldment, forming eddy current and generating heat to heat the weldment.
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