Thermal Processes

By thermal processes in welding taken to imply an increase in temperature of welded products (and the filler material) under the influence of welding heat sources, distribution of heat on the product and its removal in environment. Welding heat sources have a thermal effect on the main and filler metal, resulting in altered structure and properties of the weld metal and heat affected zone. In the process of welding metal is melted, forming a molten pool, and then hardens to form the weld. In the welding area liquid metal interacts with the environment (the slag and gas). The temperature and duration of heating during welding is determined, in addition to the phenomena melting and solidification of metal, the passage of a number of related processes in the materials to be welded: structural transformation, the volume change of the elastoplastic deformation, etc. These processes are significant impact on the quality of the weld and the whole structure as a whole.

Heat supplied to the work piece, electrode and filler metal, is characterized by heat capacity and its distribution law in space and time. These characteristics largely depend on the method and welding conditions, forms of connection and other factors. Consider these questions in relation to the most common way for fusion welding. Delivered to the arc welding electrical energy consumed in part by the processes occurring in the arc, partially transferred the environment by convection and radiation heat transfer and light emission. As the share of non-thermal types of energy in the energy balance of the arc is relatively small, the arc is rightly considered a converter of electrical energy into heat.

Thermal capacity of the arc can be considered proportional to the thermal equivalent electrical energy: Q = , where U and I – respectively, the average value of the voltage drop on the arc and the current in the circuit; I – the power factor. The most probable values of I are in the range of 0,8 0,95. Most of the heat the arc goes to heating and melting of the filler and base metal, electrode coating or flux and the chemical reactions in the weld area, is often lost in the environment. Thermal arc power lost by useless depends on many factors taken into account is difficult. In this regard, the values of the main components of the heat balance of the arc made to determine, using the concept of effective efficiency, such as efficient heating efficiency products arc heating of the electrode arc heat flux and arc, etc.

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