In the production or maintenance of industrial large fa […]
In the production or maintenance of industrial large fans, some parts need to be welded. However, the thermal process of cooling and solidification after heating in a local area of the weldment results in uneven expansion and contraction of the weldment due to the uneven temperature field, which causes welding stress inside the weldment and causes welding deformation, which affects the large industrial fan Quality and structural carrying capacity. Therefore, it is necessary to use a reasonable welding method and welding process to control the welding of the fan.
The welding stress of industrial large fans is the internal stress existing in the weldment during and after the welding process. Welding deformation, that is, welding piece deformation caused by welding. In most cases, welding deformation is caused by welding stress. Therefore, to control the deformation problem in the welding process of industrial large fans, it is necessary to control welding stress and welding deformation at the same time.
1. Classification of welding residual stress and welding residual deformation
According to the nature of welding stress: tensile stress; compressive stress. According to the basic causes of welding stress: thermal stress, also called temperature difference stress; tissue stress, also called phase change stress; restraint stress, also called reaction stress or shrinkage stress. Divided by the direction of welding stress: longitudinal stress; transverse stress; thickness direction stress. According to the existence of welding stress in the welding structure, it is divided into: unidirectional stress (linear stress); bidirectional stress (plane stress); triaxial stress (volume stress).
Welding deformation is divided into six basic deformation forms: shrinkage deformation: longitudinal shrinkage deformation; lateral shrinkage deformation; bending deformation; angular deformation; wave deformation; twist deformation;
2.Control measures for welding residual stress
It is an inevitable phenomenon that the components generate instantaneous internal stress during welding, residual stress after welding, and residual deformation at the same time. Correction of welding residual deformation is time-consuming and labor-intensive. The first consideration of fan component manufacturing and installation companies is to control welding deformation, which is often neglected to control welding residual stress. Some fixtures and supports are often used to increase rigidity to control welding deformation. It actually increases the residual stress after welding. For some components that are relatively rigid, such as large blades of large industrial fans, and the moment of inertia of the cross section itself is large, although the welding deformation will be small, it will also generate large internal welding stress, and even produce Welding crack. Therefore, for some structures with thick sections, complicated welding nodes, high restraint, high strength levels of steel, aluminum plates, etc., important control of severe conditions should pay attention to the control of welding stress. The goal of controlling stress is to reduce its peak and make it evenly distributed. The control measures are as follows: reduce the size of the weld, reduce the restraint of welding, adopt a reasonable welding sequence, reduce the stiffness of the weldment, and create conditions for free shrinkage. Hammering method is used to reduce welding residual stress, and a shot blasting machine is used to remove rust.