應用滑移電弧於熱噴塗系統之研究

Abstract

熱噴塗可提供重腐蝕環境保護塗層，且基材不受高溫影響而變形或強度降低、屬於環保型防蝕技術，因此常用於防蝕工程。但其設備費用昂貴、設備複雜繁重，為了降低成本與攜帶方便，本研究自行組裝熱噴塗系統，首度將熱源改用滑移電弧系統，因產生滑移電弧之設備和電源結構簡單，使熱噴塗系統達到簡易輕量化且高可攜性。 本研究將利用不同電極幾何形狀、電極角度、電極間隙觀察流量與電弧滑移距離的關係，以瞭解滑移電弧的加工限制範圍。接著再進行噴塗實驗，以評估滑移電弧噴塗系統的可行性。 滑移電弧觀察結果發現，電極夾角越大會有越短的電弧滑移距離，因電極夾角越大，電弧向下滑移時，電極下方間隙增大，使電場強度下降，導致電源供應器所提供的電壓無法維持電弧，因此電弧滑移距離縮短。增加流量造成電弧滑移距離縮短，因相同噴嘴孔徑時，流量增加，流速就增加，電弧易因受到冷卻，使電弧中電子由激發態降回基態，且電弧密度隨著流量增加而增加，因此高流量下之滑移電弧具有高熱源。電極間隙增大使電弧滑移距離增長，因相同流量下，電極間隙增大，電極間流速降低，因此冷卻效果差，電弧中電子較不易由激發態降回基態。但電極間隙拉大至10mm 時，已接近臨界引弧間隙，因此電極間電場強度極弱，導致電弧滑移距離急遽縮短。 由噴塗實驗結果發現，在電極間隙2mm、氣體流量30L/min 時，不論是SEM表面形貌、表面粗糙度值、塗層體積改變量、噴塗效率，均有最好的表現，因高流量有高電弧密度熔融粉末，小電極間隙使熔融粉末有較高動能撞擊基材，因此塗層表面形貌平坦，噴塗效率高。

Thermal spray can provide the substrate with coating surface for heavy corrosion environment, preventing the substrate from deformation caused by high temperature or strength decrease. As a corrosion prevention technology, thermal spray is environmentally friendly. The thermal spray equipment is expensive and complex. For decreasing cost and being portable, in this study ,a new thermal spray system to be developed with substitutes gliding arc system for heat source. Through the adjustment of the electrode gap, the coating area can also be adjusted. This study uses electrodes of different geometric shapes, angles, and gaps to measure the relation between gas flow and arc gliding distance, and to decide the working limit of the system. In the following spray experiment, the coatings were examined by SEM, roughness measurement, coating efficiency test, and the changed amount of coatings volume in different parameters. The consequences of the above tests help estimate the practicability of thermal spray. The observation of gliding arc indicates that the increase in electrode angle results in the decrease in the arc sliding distance. The main reason is that when the arc slides down, the electrode angle will be greater, which makes the gap below electrode become wider, and consequently, the intensity of the electric field between the electrodes will decrease. This will cause the power unable to maintain the arc; therefore, the greater the electrode angle is, the shorter arc sliding distance will be. When the flow rate increases, the arc sliding distance becomes shorter – with the fixed diameter of the nozzle, whenever gas flow increases, the flow rate increases; thus, the arc is easily cooled, so that the electronics in the arc will transform from the excited state to the ground state. The increase in electrode gap distance will make the arc sliding distance longer, and the main reason is that with the same gas flow, the wider the electrode gap is, the lower the flow rate will be. As a result, the cooling effect is not good enough to make the electronics of the arc transform from the excited state to ground state. However, when the electrode gap is widened to 10mm, this gap is close to the critical gap for arc ignition, which weakens the electric field strength, resulting in drastically shortened arc sliding distance. Spraying result indicates that with 2mm electrode gap and 30L/min gas flow, coatings show smoother surface, lower roughness, higher coating efficiency, and larger change in coating volume. The main reason for the good result is that high gas flow and small electrode gap allow melting powder to have high kinetic energy to hit the substrate. Therefore, the coating surface is smooth and has better attaching ability.