| Summary: | 碩士 === 國立彰化師範大學 === 電機工程學系 === 99 === Abstract
Powder coating processing technology applied more and more on metal cutting machinery due to its excellent finishing performance. However, the various coating technologies are facing difficulty on getting quality improvement as applicable limitation on materials or restriction on the operation equipment. Apart from these considerations, the environmental issue has become an important factor which effects development of coating processing technology.The pollution problem is considered seriously because of organic products used on coating processing, and it accompanies with the greenhouse effect concerned by human being. Therefore, coating processing technology challenges to achieve energy conservation, either reducing or even zero the emission of organic compounds. At present, electrostatic powder coating meets mostly current environmental requirements.
Electrostatic powder coating has been considered as a environmentally friendly conditions, but its finished film still has some technical obstacles, causing defects in coating quality. Among that, sheet metal coating for metal cutting machinery is even worse because of sheet metal bending, cavities and holes. In the cavity, the lower effect of electromagnetic induction makes uneven coating, resulting in defect of incomplete adhesion. It thereby affects the coating quality, re-working is required to repair and also results in the consumption of labor hours and proceeding cost. This paper studies the effect of corona discharge, and with the principle, a corona ring is designed to install in front of electrostatic powder spray gun. The corona ring enhances corona discharge intensity and increases the amount of charge on powder. The powder is fully charged as much as possible to penetrate the recesses of the Faraday shielding effect to improve the problem of incomplete adhesion.
An experiment of coating with corona ring on sheet metal of metal cutting machinery is conducted. Base on analysis of measurement result, the defect rate of incomplete adhesion on adverse cavity is decreased of 9% and the overall yield is raised by 9%, a substantial saving in production cost. Moreover, the film thickness measurement result shows the average difference value from the standardized value is narrowed to 3.22%-16.72% from 6.83%-32.50%, in line with the range specification 20% accordingly to standardization SSPC-PA2. It verifies that installation of the corona ring improves the stability of the coating film thickness effectively. Furthermore, the gloss meter testing result shows the coating film gloss is improved 2.22%-3.75% with corona ring, which makes better quality products.
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