Spray nozzle for electrostatic spraying of a coating product and facility for spraying a coating product including such a spray nozzle
A spray nozzle for electrostatic spraying of a coating product including a needle forming a mobile shutter of a valve for controlling the spraying, which is positioned in a recess of a barrel of the nozzle. The recess defines a surface for guiding the axial translation of the needle along a longitudinal axis of the recess. The needle includes a front shaped for abutting a seat to obstruct a duct for flow of the coating product, a rear portion which interacts with means for controlling the translation of the needle and a central portion comprised between the front end and the rear portion, while a high-voltage unit included in the nozzle is capable of applying a high-voltage to the front end of the needle. A raised portion provided on the central portion of the needle, inside the recess, can increase the electric creepage distance along the central portion.
1. A spray nozzle for electrostatically spraying a coating product comprising:
a needle forming a moving shutter of a valve for controlling the spraying of the coating product and positioned in a recess of a barrel of the spray nozzle, the recess defining a guiding surface for guiding the axial translation of the needle along a longitudinal axis of the recess, the needle comprising a front end having a shape suitable for abutting against a seat in order to obstruct a duct for the flow of the coating product, a rear portion which interacts with means for controlling the translation of the needle, and a central portion comprised between the front end and the rear portion,
a high-voltage unit capable of applying a high voltage to the front end of the needle,
wherein at least one first raised portion is provided on the central portion of the needle, inside the recess, the at least one first raised portion being capable of increasing the electric creepage distance between the front end and the rear portion along the central portion relative to a configuration where no at least one first raised portion were present,
wherein the central portion is electrically insulating, and
wherein at least one second raised portion is arranged in the recess and faces the at last one first raised portion and the at least one second raised portion and the at least one first raised portion both intersect a plane that extends perpendicular to the longitudinal axis of the recess.
2. The spray nozzle according to claim 1 , wherein the at least one first raised portion forms a first hollow spiral relative to the envelope surface of the central of the needle.
3. The spray nozzle according to claim 1 , wherein the central portion comprises a globally cylindrical portion and the at least one first raised portion forms a protruding spiral protruding from the cylindrical portion.
4. The spray nozzle according to claim 1 , wherein several second raised portions are arranged in the recess, and wherein the several second raised portions form hollow portions relative to the guiding surface for guiding the needle.
5. The spray nozzle according to claim 1 , wherein the at least one second raised portion forms a second hollow spiral relative to the guiding surface for guiding the needle.
6. The spray nozzle according to claim 5 , wherein the central portion comprises a globally cylindrical portion and the at least one first raised portion forms a protruding spiral protruding from the cylindrical portion, wherein the protruding spiral and the second hollow spiral are in the same direction, wherein the protruding spiral has a globally constant first width, measured along the longitudinal axis, wherein the second hollow spiral has a globally constant second width, measured along the longitudinal axis, and wherein the first width is comprised between 10% and 50% of the second width.
7. The spray nozzle according to claim 5 , wherein the central portion comprises a globally cylindrical portion and the at least one first raised portion forms a protruding spiral protruding from the cylindrical portion and wherein the protruding spiral and the second hollow spiral are in opposite directions.
8. The spray nozzle according to claim 1 , wherein a volume left free by the at least one first raised portion between the needle and its recess is filled with an electrically insulating product.
9. A facility for spraying a coating product comprising a power source, a reservoir of coating product and at least one spray nozzle for electrostatic spraying of a coating product, wherein the spray nozzle is according to claim 1 .
10. The spray nozzle according to claim 1 , wherein several second raised portions are arranged in the recess, and wherein the several second raised portions form hollow portions relative to the guiding surface for guiding the needle.