Spray Nozzle For Plasma Guns

Abstract

A spray nozzle having a series of helical grooves cut in the outside surface of the nozzle in order to shape and confine the flame ejected from the interior of the gun. The force of the flame draws air through the grooves and thereby provides a helical shield which prevents the flame from spreading and makes it more stable.

Description

Plasma jets are formed by passing a gas under pressure through an electric arc. In order to spray powdered material by means of the arc, a stream of fluent powder is added to the plasma after it passes from the arc chamber but before it reaches the end of the nozzle. It has been found that ordinary nozzles cause the ejected flame to spread and, in many cases, to oscillate and exhibit other unstable characteristics. This causes an uneven coating of the sprayed material and also uneven heating.

The above objections can be overcome by the invention herein described. The grooves provide the stabilizing effect necessary to confine the flame and, in addition, to mix the fluent powder with the hot gases so that the powder temperature can be controlled and an even integral coating of the material can be deposited on a substrate.

A feature of the invention is the provision of a plurality of helical grooves, having variable depth, which contain and stabilize the arc flame without the expenditure of any power and without the addition of mechanical motion.

For a better understanding of the present invention, together with other details and features thereof, references is made to the following description taken in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a side view of the nozzle showing the helical grooves.

FIG. 2 is a cross-sectional view taken along an axial plane showing the conduits which add powdered material to the plasma.

FIG. 3 is an end view of the nozzle showing the groove ends and the relative location of the conduits which add the fluent material.

FIG. 4 is a cross section view (enlarged) of a portion of the nozzle showing the entrance means to the fluent material conduits and a method of producing a right angle bend in the conduit lines.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the figures, the nozzle 10 is a generally cylindrical piece of high melting point metal having an axial conduit 11 for conveying and expelling the plasma. At the entrance end of the conduit 11, an enlarged portion 13 houses an arc chamber where an electrical discharge is created between a first electrode 14 and the inside surface of the conduit. The arc discharge heats and ionizes the gas flowing through the arc chamber and thereby creates a plasma. The details of the arc discharge and the electrodes which support it are set forth in a patent application, Ser. No. 835,876, filed June 4, 1969, now U.S. Pat. No. 3,591,759, granted July 6, 1971. These details of construction are not a part of this invention so will not be described here.

The fluent material, which may be Teflon powder, is entered through two flexible tubes 15 and 16 secured to the outside of the nozzle and connected to a reservoir (not shown) under pressure. The powdered material is forced into two conduits 17 and 18 disposed at an angle of about 20.degree. to the nozzle axis. These conduits may be formed by drilling holes in the nozzle block starting from a position 20 on the other side of the rim 19 and then closing a portion of the hole with a plug 21.

The gas or mixture of gases which are forced through the arc chamber are given an initial helical direction which causes the plasma to turn on its axis as it passes through and out of the nozzle. This action tends to mix the powder with the plasma in an even manner but only in the space near the gas surface. The centrifugal force of the gas motion also tends to keep the powder near the surface.

To control the ejected gas flame, a series of helical grooves 22 are cut into the outside cylindrical surface of the nozzle 10 as shown in the figures. Each groove 22 starts near the rim 19 and has a depth about equal to its width. The grooves 22 continue around the surface of the nozzle, with increasing depth, until they terminate at the face of the nozzle (see FIG. 3), having a depth about three times their width. The circular direction of the grooves must be the same as the circular motion of the plasma gas. That is, if the plasma is given a clockwise rotation, as viewed from the arc chamber, then the grooves must also be clockwise.

When the gun is operated, the heated gases expelled from the nozzle conduit 11 move at great speed and because of their velocity, create a reduced pressure near the nozzle face. This reduced pressure draws air through the grooves 22 from the atmosphere and, because they move in a helical direction, the air jets surround the plasma flame and prevent its spreading. The air jets also protect the flame from outside movements of air and make the flame more stable. In the drawings, four spaced helical grooves are shown, all having a variable depth. More grooves may be employed if desired. The grooves function without the attention of the operator of the gun and need no adjustment. They consume no power, instead the indications are that less power is required to operate the gun when the grooves are used.

The foregoing disclosure and drawings are merely illustrative of the principles of this invention and are not to be interpreted in a limiting sense. The only limitations are to be determined from the scope of the appended claims.

Claims

What is claimed is:

1. A spray nozzle for a plasma gun comprising; a cylindrical nozzle having an axial opening through which plasma gases are ejected, said nozzle having a flat end face disposed substantially perpendicular to the nozzle axis; said nozzle formed with a plurality of equally spaced helical grooves cut in the outside surface of the nozzle open to the atmosphere and terminating in the nozzle face for providing jets of air which surround and limit the plasma gases.

2. A spray nozzle as claimed in claim 1 wherein conduit means are provided in the nozzle for adding solid fluent material to the plasma for ejection with the plasma gases.

3. A spray nozzle as claimed in claim 1 wherein directive means are provided for giving the plasma gases a helical flow through the axial opening.

4. A spray nozzle as claimed in claim 1 wherein the helical grooves are formed with a depth which increases as the nozzle face is approached.

5. A spray nozzle as claimed in claim 1 wherein the axial opening is formed with an abrupt step in the opening diameter between two axial portions thereof for creating a turbulent flow and for mixing a quantity of solid fluent material into the plasma gases.