Internal burner type flame spray method and apparatus having material introduction into an overexpanded gas stream

• US 4,568,019 A
• Filed: 04/20/1984
• Issued: 02/04/1986
• Est. Priority Date: 02/24/1984
• Status: Expired due to Term

• Current Assignee: James A. Browning
• Original Assignee: James A. Browning
• Inventors: Browning, James A.
• Primary Examiner(s): Nase, Jeffrey V.
• Assistant Examiner(s): Jones, Mary Beth O.
• Application Number:
  US06/602,571
• Time in Patent Office: 655 Days
• Field of Search: 239/1, 239/8, 239/13, 239/79-81, 239/83-85, 219/76.13, 219/76.16, 219/121 PL, 219/121 PY
• US Class Current: 239/13
• CPC Class Codes: B05B 7/203 the material to be sprayed having originally the shape of a wire, rod or the like
• CPC Class Codes: B05B 7/205 the material to be sprayed being originally a particulate material
• CPC Class Codes: H05H 1/42 with provisions for introducing materials into the plasma, e.g. powder, liquid arc stabilising or constricting arrangements H05H1/3405; coaxial protecting fluids H05H1/341; electrostatic spraying, spraying apparatus with means for charging the spray electrically B05B5/00 ; cf. B23K9/324, B05B7/22

Abstract

The products of combustion of compressed air and fuel fed to an internal burner issue through one or more orifices into a single large diameter expansion or nozzle bore open to the atmosphere. Solid rod or solid particle material to be sprayed is passed concurrent with the products of combustion through the large diameter chamber with the material being heat softened or melted to form a spray which is impacted against a workpiece after acceleration to high velocity. The pressure within the large diameter chamber is maintained sub-atmospheric. By aspirating atmospheric air flow bearing particulate material or by leaking air about a solid rod to the sub-atmospheric chamber pressure, pre-melting of the wire or particulate material within the material feed passage upstream of the chamber and prevented via hot combustion product gas back flow. Gas flow asymmetrically into an axial particle stream or solid rod within the large diameter chamber may be effected without liquid melt material deposit on the chamber bare wall. Alternatively, material in powder form may be introduced asymmetrically into an axial flow of the products of combustion through the large diameter expansion chamber.

Claims

1. A flame spray method comprising the steps of:

continuously combusting, under pressure, a continuously supplied compressed combustible gas and fuel mixture including oxygen within an internal burner combustion chamber,

discharging the hot combustion product gases from at least one combustion chamber orifice through a single large diameter expansion chamber open at its downstream end to the atmosphere via an exit port while feeding material to be sprayed through said expansion chamber concurrently with said products of combustion by introduction of the material to the products of combustion outside of said combustion chamber, said large diameter chamber being sized in excess to the flow stream diameter of said products of combustion entering said chamber;

whereby, said material is heat softened or melted to form a spray for impact against a workpiece downstream of the exit port of said chamber after acceleration to high velocity by the flame jet comrpising said stream of products of combustion which pass through said chamber and exiting therefrom,

and wherein said method further comprises controlling the operation of said internal burner and sizing the cross-sectional area of said at least one combustion chamber orifice relative to said exit port diameter of said expansion chamber, such that the pressure within said expansion chamber is maintained sub-atmospheric during operation.

2. The method as claimed in claim 1, wherein said combustible gas mixture comprises compressed air and said method further comprises the step of enriching said compressed air provided to said combustion chamber with a flow of pure oxygen.

3. The method as claimed in claim 1, wherein said material to be sprayed is a wire or powder, and said step of causing said material to pass through said large diameter, expansion chamber concurrently with the products of combustion comprises flowing said wire or powder axially relative to the jet comprised of the products of combustion.

4. The method as claimed in claim 1, wherein said expansion chamber comprises a converging chamber, and said step of passing said material concurrently with said products of combustion through said large diameter, expansion chamber comprises feeding multiple flows of material separately into and maintaining said flows seprate through said large diameter, converging chamber.

5. An improved flame spray apparatus for high deposition rate particle deposition on a substrate downstream of said apparatus to form a coating, said apparatus comprising:

an internal burner forming an essential closed combustion chamber,

means for continuously combusting a flow of compressed air and fuel within said internal burner combustion chamber,

a block closing off said combustion chamber having a relatively large diameter converging chamber terminating in an exit port opening outwardly of said block at one end thereof,

products of combustion passage means within said block connecting said combustion chamber to said large diameter chamber and opening to said large diameter chamber, at the end opposite said exit port,

at least one material feed passage means within said block opening to said large diameter chamber at the end of said chamber opposite that of said exit port,

means for feeding a material to be sprayed onto said substrate through said material feed passage means,

and wherein the diameter of said products of combustion passage means connecting said combustion chamber to said large diameter chamber and the minimum diameter of said large diameter chamber at said exit port are such that the pressure within said large diameter chamber is sub-atmospheric and said material to be melted is accelerated by the products of combustion passing through said large diameter chamber to high velocity and is melted to effect particle coating of said substrate at low cost, under extremely high deposition rates with the particles melting downstream of said large diameter chamber well after discharge from said at least one material feed passage means while preventing back flow of the products of combustion from the internal burner into said material feed passage means.

6. The apparatus as claimed in claim 5, wherein said material feed passage means comprises a single passage longitudinally through said block coaxial with said large diameter chamber.

7. The apparatus as claimed in claim 5, wherein said at least one material feed passage means comprises a plurality of inclined passages extending longitudinally through said block and converging towards the large diameter chamber.

8. The apparatus as claimed in claim 5, wherein said large diameter chamber is conical and converges in the direction of flow of the products of combustion therethrough.

9. The apparatus as claimed in claim 8, wherein said combustion products passge means connecting said combustion chamber to said conical large diameter chamber comprises a pair of side by side passages within said block at right angles and to opposite sides of said material feed passage means and opening at one end to said combustion chamber and wherein said combustion product passage means further comprises parallel inclined, converging holes within said block, to opposite sides and above and below said material feed passage means, equally spaced on the diagonal relative to said conical large diameter converging chamber having a common angle of inclination with the conical surface of said chamber and opening at respective ends, to said side by side passages and said large diameter chamber.

10. In a method of flame spraying utilizing an oxidant and fuel, and comprising the steps of burning said oxidant and fuel continuously at high pressure within a restricted combustion volume, conducting the products of combustion to the entrance of an elongate nozzle expansion bore through at least one intermediate passage, the improvement comprising;

introducing the material to be sprayed into the entrance of said elongate nozzle expansion bore and selecting the corss-sectional areas of said elongate nozzle bore and said at least one intermediate passage, while controlling the level of pressure of combustion to produce a zone of sub-atmospheric pressure at the entrance to said elongate nozzle;

whereby, the solid material is melted and sprayed at supersonic velocity as a result of overexpansion of the products of combustion within the elongate nozzle bore without melted particle build up on the bore wall.

11. The method as claimed in claim 10, wherein said solid material is introduced into the entrance of the elongate nozzle bore axially and said products of combustion are introduced into the elongate nozzle bore via said at least one intermediate passage asymmetric to the nozzle expansion bore.

12. The method as claimed in claim 10, wherein said combustion pressure is maintained at a minimum of 100 psig.

13. A flame spray apparatus comprising:

an internal burner having a restricted combustion volume,

means for continuously delivering an oxidant and fuel to the restricted combustion volume of said internal combustion chamber for continuous combustion therein,

an elongate nozzle mounted to said internal burner,

said elongate nozzle including an elongate expansion nozzle bore,

at least one intermediate gas transfer passage communicating said internal burner combustion chamber to the entrance of said elongate nozzle bore,

a material feed passage opening to said elongate nozzle bore entrance,

the cross-ectional areas of said elongate nozzle bore and said intermediate gas transfer passage being such that at predetermined elevated combustion pressure conditions within said combustion chamber, there is thereby produced during discharge of the products of combustion, a zone of sub-atmospheric pressure at the entrance of said elongate nozzle with said products of combustion overexpanded resulting in supersonic flow of the products of combustion as a result of passage through the elongate nozzle bore, and wherein one of said material passage and said at least one intermediate gas transfer passage open axially into the entrance of said elongated nozzle bore and the other of said passages opens asymmetrically to said bore at said entrance.

14. The apparatus as claimed in claim 13, wherein the ratio of the area of the elongate nozzle expansion bore to that of said at least one intermediate gas transfer passage communicating said combustion chamber to said elongate nozzle bore, at its entrance, is at least four to one.