焊接专业英语 教学课件 作者 刘松淼 编著 焊接专业英语（刘松淼）02656课件.pptVIP

尚辅网 尚辅网 尚辅网 An arc is an electric discharge between two electrodes which takes place through ionized gas known as ‘plasma ’. The space between the electrodes can be divided into three regions : a central region in which there is a uniform potential gradient and two regions adjacent to the electrodes in which the cooling effect of the electrodes results in a rapid drop in potential . These two regions are the anode and cathode fall according to the direction of current flow . The length of the central region or arc column is influenced by the arc simultaneously to supply heat and remove surface films – an important advantage where welding is done in the absence of fluxes . Within the envelope of the arc and the weld pool a whole range of complex gas-slag-metal reactions and other metallurgical changes take place . 尚辅网 然而不只一种热源。如果需要它能使熔滴从电极过渡到工件。使用电弧同时提供热能和清除氧化膜也是可能 的，一个重要优点是焊接过程中无需焊剂。在电弧和熔池整个范围内由气-渣联合保护，并且发生其它的冶金反应。 length but , where an arc is shortened to the extreme , the influence of the electrodes may dominate the entire arc gap . With a high-current arc at atmospheric pressure , extremely high temperatures , from 5000 to 50000K , can exist in the axis of the arc column . From this central core the temperatures drop rapidly to the outer layers of the arc plasma and in a given atmosphere both the temperature and diameter of the central core depend on the current passed by the arc . Because most of the current is carried in this central 尚辅网 channel and is influenced by its temperature and diameter , the relationship between arc current and potential is not according to Ohm’s law but takes the non-linear from shown in fig.4.1 . When the current is increased from a low value , the channel is enlarged and its temperature raised so that the potential drops to the minimum . In this part of the curve the arc is said to have a negative characteristic . The curve then remains flat or slightly rising until high currents are reached . 电弧就是在两电极之间发生的一种放电现象，电离的气体称做“等离子体”。电