FR2837115A1 - A method for preventing the build-up of charged powder in the injector of a powder injection unit has an electrically insulated housing and metallic sleeve holding the delivery hose - Google Patents

Abstract

The housing (2) has a connection (8) for the conductive hose (20) moulded in electrically insulating material but the powder is electrically charged through an electrically conductive sleeve (16) clamped by a metal nut (17) by which the powder is frictionally charged.

Description

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  PODDER COATING DEVICE INJECTOR

  The present invention relates to a powder coating device injector comprising a frame having a nozzle to which can be connected a transport pipe for transporting the mixture of powder and gas obtained in the injector. The flexible transport pipes used to convey the mixture of air and powder obtained in such a wind injector usually made of electrically conductive material, in order to derive the electrical charges due to the friction of the powder particles. The electrical conductivity of the transport pipes is for example ensured by means of an external conductive jacket or by the fact that the transport pipes are entirely formed of a material.

flexible conductor.

  The electrostatic charge of the transport pipes is currently separated in separate ways, for example by means of flanges fixed on the outside of the pipe and connected to the potential.

of the earth.

  To transmit the load from the transport hose to the injector frame, and thus be able to derive it via the injector frame, it would be desirable for the end piece provided on the injector frame to be also in

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  electrically conductive material. A drawback to this is that there is in this case a strong tendency to stick powder on the internal wall of the nozzle because the powder particles transported in the air flow adhere, due to their charge, on the conductive inner wall of the nozzle. For this reason, we prefer to make the tips in non-conductive artificial material, little conducive to the bonding of powders, such as PTFE (polytetrafluorethyldne). This is the reason that the flexible transport hoses, which wind electrically conductive to derive the charges which arise therein.

  friction, must be grounded separately.

  The object of the invention is to provide an injector as described above, in which one can dispense with separately deriving the charges born by friction, while avoiding the

  tendency to stick powder on the inner wall of the nozzle.

  This object is solved by the characteristics of a

  injector according to the present invention.

  As the nozzle is surrounded by a layer or external envelope of electrically conductive material, the electric charges born by friction can flow directly from the transport pipe on the frame of the injector, and to be derived towards the potential of the ground . This eliminates the need for a separate shunt of electrical charges from the transport hose. As on the other hand the tip is formed, inside, of an electrically non-conductive material, in particular PTFE, the tendency to sticking of powder is avoided in a way

  efficient and gene-free transport of powders follows.

  The invention will be described below in more detail.

  and with other peculiarities related to the figure.

  The figure represents a longitudinal section of an injector according to the present invention comprising a nozzle and a transport pipe for the mixture of air and powder obtained

in the injector.

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  The injector represents a injector frame 2, in which a propulsion nozzle 4 and a collection nozzle 6 are arranged coaxially. The collection nozzle 6 forms a single piece with a nozzle 8 in the form of an electrically non-conductive artificial material, preferably PTFE (polytetrafluorethylene), to avoid sticking of powder on

the inner wall 7 of the tip.

  Conventionally, the frame comprises a connection for powder 10, in relation to a powder storage tank not shown. In addition, a connection 12 is provided for the air from the propulsion nozzle and a connection 14 for the air from the collection nozzle. On the end piece 8 is mounted a casing 16 of metal or another electrically conductive material, such as an artificial conductive material. The casing 16 has conventional ribs 18 for arranging and maintaining the end situated on the injector side of an electrically conductive transport pipe 20 which, for example, is formed from a conductive material. The casing 16 has an annular flange 17 at its end located on the injector side, kept pressed against a radial shoulder 9 of the collection nozzle 6 by means of a coupling nut 22 screwed onto an external thread 24 of a fitting 26 provided for connecting the hose. The coupling nut is also produced using a conductive material

  electrically, for example metal.

  Due to the conductive connection between the conductive components, pipe 20, casing 16 and nut 22, and the frame of the injector 2, which for its part is brought to the earth potential, the charge born by friction in the pipe transport can be derived from the frame of injector 2, without the need for separate earthing of the pipe.

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RENENDICATIONS

  1. Powder coating device injector, comprising an injector frame (2) having a nozzle (8) to which a transport pipe (20) can be connected to transport the mixture of powder and gas obtained in the injector , characterized in that the end piece (8) is made of an electrically non-conductive material and is surrounded externally by a layer or envelope (16) of material

electrically conductive.

  2. Injector according to claim 1, characterized in

  that the envelope (16) is metallic.

  3. Injector according to claim 1, characterized in that the envelope (16) is formed from an artificial material

electrically conductive.

  4. Injector according to any one of the claims

  1 to 3, characterized in that the casing (16) is fixed in a conductive manner to the frame of the injector (2), earthed, by means of a coupling nut (22) of electrically conductive material . 5. Injector according to claim 4, characterized in that the coupling nut (22) is metallic or shaped like a

  electrically conductive artificial material.

  6. Injector according to claim 4 or 5, characterized in that the casing (16) has an annular flange (17), which is held pressed by the coupling nut (22)