Electrostatics serve molten metal arc spraying

The molten metal spraying technique has been used for restoring the original dimensions of some worn machine elements in Egypt as well as all over the world. In some cases, the droplets are poorly deposited over the surface causing spalling or failure in the deposited layer. Millions of molten metal droplets of expensive alloys such as nickel, chromium titanium, etc., usually escape the sprayed surface which increases the overall cost. To overcome these problems, the conventional equipment was modified to charge the metallic spray droplets using different induction electrode arrangements. As a result of this modification, an additional electrostatic force of attraction was established between the spray droplets and the earthed work piece. Deposited layers were tested using standard material testing techniques. It was found that all the tested physical properties and wearing behaviour of the deposited layers were improved. The hardness and adhesion strength were increased by about 30%, while the tensile strength was increased by about 175% over the conventional method. Electronic micrographs also showed that the deposited particles were arranged with less porosity and oxide inclusions whereas in the conventional method, the particles were randomly arranged.