Low temperature melting metals spray devices are known, in which the molten metal is contained in an electrically heated open pot provided at its bottom with a spray nozzle comprising an inner nozzle communicating with the interior of the pot, and a concentric outer nozzle connected to a suitable source of compressed air, so as to draw the molten metal out of the pot through the nozzle by venturi action, throwing it in form of small droplets against the surface to be coated.
The main disadvantage of the prior art molten metals spray devices of the kind described resides in the fact that the compressed air jet entraining the molten metal droplets expands at the exit from the spray nozzle, thus cooling the entrained metal droplets. The said cooling effect is very objectionable, particularly in those cases in which it is necessary to maintain the temperature of the molten metal in the heated pot at a temperature slightly above and very close to the melting point temperature of the metal being sprayed, due to the heat perishable nature of the objects to be coated. In fact, under the above conditions, the said cooling may cause the solidification of the metal droplets before they reach the surface to be coated.
A further disadvantage of the said prior art molten metals spray devices resides in the fact that under certain circumstances of temperature of the molten metal in the pot, the venturi action of the air jet is not sufficient to drawn the molten metal from the pot through the spray nozzle.