Scheme of the electron-optical system
1 - the product, 2 - electron beam, and h - cathode, 4 - cathode - the control electrode; S - anode, C - crossover, 7 - magnetic lens, 8 - beam deflection system 9 - focal spot; a0 - half-angle divergence of the beam; a1 - half-angle of convergence of the beam on the product, Dcr - the diameter of the crossover; dfp - the diameter of the beam at the focus of electron guns. Electron beam gun is designed to create an electron beam, which is the source of the welding heat. The parameters of the electron beam corresponding to the welding process, determine the basic requirements for the design of the electron gun.
In welding installations electron gun consists of the following elements: cathode electron source; an anode - electrode with a hole in the middle of the beam to pass to the product that is connected to the positive pole of the power rectifier cathode focusing electrode (modulator), which regulates the current in the beam, focusing magnetic lens, deflecting magnet system. guns in the diode cathode electrode has the potential of the cathode in triode - it is applied a negative potential relative to the cathode to control the UM current strength in the gun. Combined, ie, electrostatic and electromagnetic focusing of the beam at the same time, the guns are most common in welding plants (Fig. 85). They are used thermionic cathodes, the emission current is determined by the equation of Richardson Ie = Ae * T ^ 2 * Sk * e ^ (-b / T) where SK - emitting cathode area, and T - absolute temperature of the cathode, Ag, b - constants characterizing the cathode material. in welding facilities cathodes are usually made of refractory metals (tantalum, tungsten) or lanthanum hexaboride. The design of the cathode is given special attention, since the conditions of his work is extremely difficult: high temperatures and intense destruction under the influence of ion bombardment, and the requirements for accuracy and conservation in the size of his work is very high. From the most minor deformities of the cathode depend to a large extent the parameters of the electron beam. Typically, the life of the cathode is less than 20 hours of continuous operation, rarely up to 50 hours power electron beam is determined by the product Pn = Uuskor. | A * and is regulated by variation of the current in it (| A) that any change in the electron guns reached the temperature of heating the cathode. However, this method is very inertial and inconvenient fact that this dependence is nonlinear. The new thermal regime, and hence the new value of current, established only a few seconds. more common method of regulating the current by applying a negative, relative to the cathode, the cathode potential to the control value of 1-3 kV Um. The rate of establishment of the beam current during pulsed electron gun A.852.19 opening is about 2 mA / ms. For the pulsed beam current control in the wiring diagram provided special electronic circuits that produce a signal applied to the modulator. Usually, the scheme also allows you to smoothly control the amount of current in the beam. current density in the beam can be adjusted by changing the diameter on the product without changing the value of the total current through the magnetic lens. Such a lens is a coil with a current whose axis coincides with the axis of the beam. To improve the efficiency of its place in the ferromagnetic screen. In this case, the magnetic field is concentrated in a narrow non-magnetic gap. The focal length lenses (f, cm) - the distance from the middle of this gap to the minimum cross-section passing through the lens of the beam, defined by the design lens, the gun anode voltage and current flowing through the coil lens. Focal length depends linearly on the high voltage installation, but does not depend on current in the beam. The parameters of the weld is directly dependent on the constancy of the energy characteristics of the electron beam, including its diameter, since its value determines the power density of the beam. Therefore, the cathode-ray installations focus on the constancy of the anode voltage. Apply special measures to stabilize it, which eliminates the effect of fluctuations in voltage, ripple power rectifier, etc. deflection system is used to set the beam on the seam, or adjustments to some of its provisions with respect to the joint, move the beam along the axis of the joint when the weld, the periodic deflection when welding with transverse or longitudinal oscillations of the beam and tracking seam during the welding operation. The magnetic field is directed perpendicular to the direction of electron motion, and strength, deflecting the trajectory of an electron, acts perpendicular to the axis of the beam and the direction of the magnetic field. As the electron beam is defocused at a deviation, the deviation of its welding facilities is carried out on small corners, no more than 7-10 degrees. In welding of thick sheet metal and welding in the intermediate vacuum and at atmospheric pressure will inevitably increase the accelerating voltage, as in this way can be especially noticeable to reduce the scattering of the beam. However, increasing the accelerating voltage makes it difficult to combine with the junction of the beam requires special protection of personnel from the X-ray radiation equipment is more complicated.
See also:
Electron Beam Welding Technology
Electron Beam Welding Article
Installations for Electron Beam Welding
Electron Beam Welding Gun
Work Chambers for EBW
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