# An Investigation into the Behavior of Cathode and Anode Spots in a Welding Discharge
## 3 Results
### Arc Discharge Stage  
The welding arc is a source of not only visible but also infrared and ultraviolet rays. It is known that about 70% of the radiation energy is released in the form of ultraviolet,  
Figure 7: Stages of spark discharge with current channels of one spark (**a**); the second spark (**b**); transition to arc discharge (**c**,**d**). 15% in the form of infrared radiation; these are all rays not visible to the human eye and only 15% in the form of visible light [1; 2; 3]. The UV radiation of the welding arc is divided into three types by wavelength: UV-A (320-380 nm), UV-B (290-320 nm), and UV-C (180-290 nm). Open shooting without special filters will not give us the opportunity to obtain high-quality photos of anode spots due to the intense glow of the welding arc column. We use radiation from the molten metal of the welding bath and metal vapors above its surface when building passive video surveillance systems. The radiation from the arc column present in the general spectrum should be considered a source of illumination and, at the same time, an obstacle. The intrinsic radiation spectrum of the arc column and its reflex reflection from the surface of the welding bath, consisting of atoms and molecules of ionized shielding gas, are predominantly of nonmetallic origin. On the spectral spectrum, it occupies the ultraviolet, red, and near-infrared zones [1]. The radiation from the welding bath is metallic in nature (glow lines Fe, Ag, Mo, Mn, etc.) and manifests itself in a wide range of spectral frequencies. Interference filters with a degree of monochromatism of 10-20 A are used to increase the ratio of the radiation intensity of the bath to the arc, which provides contrasting boundaries of the contour of the welding bath. The wavelength of the filter is selected in the areas of the spectrum where there is a significant attenuation of radiation from the arc and where the maximum radiation from the welding bath and metal vapors is located at its surface (Figure 8). By looking at a group of graphs for the type of welding being considered, it is possible to pick the wavelength of an interference light filter that blocks the most radiation from the arc while letting the most radiation from the welding bath pass through. In the case under consideration, we observe the highest signal ratio from the bath to the arc at a filter wavelength of about 830 nm. We see in Figure 7d a bright spot on the surface of the melt. The spectral sensitivity of CCD arrays reflects the matrix's sensitivity in relation to the wavelength of the received radiation. Most cameras typically have a wider spectral sensitivity than the human eye, extending into the infrared range up to wavelengths of 1000 nm, unless they use special filters during matrix production. Thus, unlike the eye, whose spectral sensitivity is limited to the visible range of radiation, the camera, due to its fundamentally different device, is also able to register the near range of IR radiation. Of interest is Figure 11, which shows the surface of the cathode and anode at the moment of switching off the welding current. The cathode spot continues to emit a low-intensity plasma torch towards the anode on the cathode's surface (Figure 11b,d). Figure 8: Welding arc shooting under different shooting conditions: (**a**) shutter speed 1/3, aperture F = 32, focal length 82 mm; (**b**) shutter speed 1, aperture F = 16, focal length 82 mm; (**c**) light filter: the wavelength of the filter is about 830 nm. Figure 9: Visualization of the anode spot in the welding arc depending on the burning time: (**a**) 5 c, (**b**) b–7c, (**c**) 10 s, (**d**) 12 c, (**e**) 15 s, (**f**) 20 s (mode-I = 30 A, U = 14.5V). The effect of inertia on emission processes in a moving welding arc is particularly well visualized in Figure 12. It can be seen that as the welding arc moves towards the edge of the sample, the shape of the anode spot changes (Figure 12a-c).