Electrolytic Plasma Polishing of Pipe Inner Surfaces

Abstract

Smooth surfaces are becoming increasingly important in many industries, such as medical, chemical or food. In some industrial areas, the mechanical treatment of surfaces (grinding and polishing) does not fulfil desired specifications. Non-abrasive methods (chemical and electrochemical) have the advantage that even complex geometries and free-form shapes can be polished. In the context of this paper, electrochemical surface treatment is considered in more detail. Both electro polishing, which is state of the art, and the novel electrolytic plasma polishing (EPP) process are presented. This paper focusses on the electrolytic plasma polishing because it has many advantages compared to the process of electro polishing. The theoretical operation of the electrolytic plasma polishing is shown. A prototype system for plasma polishing of internal surfaces of pipes was installed and a polishing head was developed. Several parameters are investigated, such as the width of the adjustable polishing head gap and different velocities v or different applied potential differences U, and first results of the average surface roughness Sa as function of the various parameters were evaluated. It can be seen that a stable polishing process can be achieved at the highest potential difference of 320 V and that the average surface roughness Sa reaches a range from 0.065 to 0.090 µm. At the same time, it has been shown that with increasing potential difference, the average surface roughness becomes independent of the width of the adjustable polishing head gap.

Influence of the Velocity and the Number of Polishing Passages on the Roughness of Electrolytic Plasma Polished Pipe Inner Surfaces

“…The results show that increasing numbers of plasma polishing passages n lead to lower average surface roughnesses Sa v at constant velocities. On the other hand, the results also confirm the findings of the previous study [22], that lower velocities v lead to lower average roughnesses Sa v at constant numbers of plasma polishing passages n. Figure 3 depicts the average roughness Sa v depending on the number n of plasma polishing passages for the different velocities v and finally illustrates the derived basic relations. It can been learned from Table 1 and Figure 3 that the mean average surface roughnesses Sa v reach a range from 0.030 µm to 0.040 µm for the pipe inner surface after a certain number n of plasma polishing passages dependent on the chosen velocity v of the polishing passage.…”

“…It can been learned from Table 1 and Figure 3 that the mean average surface roughnesses Sa v reach a range from 0.030 µm to 0.040 µm for the pipe inner surface after a certain number n of plasma polishing passages dependent on the chosen velocity v of the polishing passage. This means better polishing results can be achieved with optimized polishing parameters compared to the results found in the previous study [22]. It can also be recognized from Table 1 and Figure 3 that comparable average surface roughness Sa v can be achieved either at a high passage velocity combined with a high number of passages or a low passage velocity combined with a low number of passages.…”

“…The used plasma polishing system has already been described in detail [22] and the schematic design of the system can be seen in Figure 1. 2 depicts the schematic design of the used polishing head.…”

“…Therefore, the acceleration ranges of 5 mm have been excluded from the measuring area at each end. Previous studies [22] have shown that the plasma polishing process is more stable at higher applied potential differences U. Therefore, the applied potential difference was set to 320 V. The width of the adjustable polishing head gap h gap was set to 1 mm.…”

“…Previous papers on plasma polishing deal with process development [10][11][12][13][14], polishing of various materials like copper, titanium alloys and different grades of stainless steel [15][16][17][18] as well as application studies [19][20][21]. The plasma polishing process was recently transferred to a medium-carrying pipe inner surface using a newly developed prototype system and first experimental results were previously presented by the authors [22]. When considering the plasma polishing of pipe inner surface, the following fundamental process parameters can be identified: the type and the properties of the electrolyte (electrical conductivity, pH value, temperature), the parameters of the technical setup (dimensions of the polishing head and the workpiece) and the operating parameters (applied voltage, current, velocity and number of polishing passages).…”