Electrostatic internal powder coating

摘要

Here is a new method of coating objects internally and externally too, if required, using electrostatic means. An immersion vessel (4) contains a bed of fluidised powder (6), into which dips a hollow body (13) or tube, i.e. the object. All are connected to earth potential. In this novel process, honeycomb electrodes (7) are used. These are maintained at a high potential, and pass an airflow (10) which emerges from side openings (12). This causes additional fluidisation of the charged powder within the object (13). As a result, the object receives an internal coating. The object, through its external mirror charge, acquired by charge separation, is also coated externally. Preferably in a hollow object, including a tube closed at the base, by inserting honeycomb electrodes, an internal coating is produced. Its side openings pass air, fluidising charged powder. A spray lance terminated by a honeycomb at high potential, dusts charged powder from air nozzles, onto the inner wall of a tube, to form a layer there resulting from the electrical field strength. For safety (possible dust explosion), spacing is required between the lance or honeycomb electrodes and the body. For cylindrical shapes of e.g. lance and tubular body, and given inner and outer diameters, the spacing is approximated using: dRi/mm ?< >dE/mm + 20(/!Ua/kV)/ (EZkv/cm) (I). The electrode is introduced into the body centrally through guides distributed over the periphery. A number of configurations, all based on the foregoing principles, are also described. One spray lance inserted into a tube has wall guides at 120 deg or 90 deg , with axial spacing of at least 15 cm.