Influence of technological factors of microplasma spraying of TiO2 on the degree of spraying material utilization
Avtomatičeskaâ svarka (Kiev)
Влияние технологических факторов микроплазменного напыления TiO2 на степень использования напыляемого материала
The work is a study of the degree of the influence of technological parameters of microplasma spraying on the coefficient of material utilization during formation of a resistive coating from titania. Investigations were conducted with application of a multifactorial experiment with fractional replicas 2 4-1 . As a result of processing of experimental data, a regression equation was derived, which allows assessment of the degree of the influence of microplasma spraying parameters, such as
... , spraying distance, plasma gas flow rate and powder consumption on the value of the material utilization coefficient. It is established that current value has the greatest influence on it. During investigations it was shown that selection of the parameters of microplasma spraying of resistive paths from TiO 2 powder will allow minimizing material losses. 4 Ref., 2 Tables. K e y w o r d s : microplasma spraying, TiO 2 ,material utilization coefficient, resistive heating element Thermal spraying (TS) technologies are becoming ever wider accepted during manufacture of flat low-temperature resistive heating elements (RHE) [1, 2] . Such RHE are multi-layer heat-resistant coatings, consisting of an insulation and current-conducting layer, which may be formed directly on the heated metal surface. RHE of this type offer the advantage of lower temperature in the conducting layer, allowing their electrical safety to be increased, as well as cost-effectiveness and longer service life  . However, manufacture of small-sized RHE by TS methods involves material losses, which consist of losses for spattering, spraying particles rebounding, as well as losses due to the geometrical factor. Losses related to the geometrical factor at traditional plasma-arc spraying are due to spray spot diameter of 20-25 mm that is several times larger than the resistive path width of 3-5 mm. Material losses for spattering and rebounding can be characterized by material utilization coefficient (MUC). This parameter not only shows the cost-effectiveness of the process, but is also used as optimization parameter. Increase of the degree of spraying material utilization under the conditions of deposition of resistive paths, can be achieved by application of the technology of microplasma spraying (MPS) due to small diameter of the spray spot (3-5 mm). Moreover, such a technology has minimum thermal impact on the substrate that enables producing a coating on thin-walled parts without their deformation  . The objective of this work consisted in determination of spraying material losses for spattering and rebounding, as well as studying the degree of the influence on MUC of the main process parameters, such as current I, A, spraying distance H, mm, plasma gas flow rate G pl , l/min and powder consumption P pow , g/min. Studies were performed with application of the method of mathematical planning (multifactorial experiment with fractional replicas 2 4-1 ). Ranges of variation of microplasma coating process parameters and results of an experiment to determine MUC at microplasma spraying of TiO 2 powder on a plate are given in Tables 1, 2.