Metal spray apparatus with a U-shaped electric inlet gas heater and a one-piece electric heater surrounding a nozzle

• US 5,459,811 A
• Filed: 02/07/1994
• Issued: 10/17/1995
• Est. Priority Date: 02/07/1994
• Status: Expired due to Term

• Current Assignee: MSE, Inc. (Global Technologies Group, Inc.)
• Original Assignee: MSE, Inc. (Global Technologies Group, Inc.)
• Inventors: Verbael, David J., Johnson, Lawrence L., Tierney, John C., Glovan, Ronald J., McLean, Leroy L.
• Primary Examiner(s): Jeffery, John A.
• Application Number:
  US08/192,697
• Time in Patent Office: 617 Days
• Field of Search: 392/479, 392/480, 392/473-475, 392/482, 392/485, 392/488, 392/396, 392/397, 392/388, 392/389, 392/379, 219/424, 219/475, 219/538, 219/221, 219/535, 219/552, 118/302, 118/726, 239/132-135, 239/128, 239/82-84, 239/80, 239/79, 222/146.5, 266/202, 427/422, 338/294, 338/283, 338/287, 338/51, 338/279
• US Class Current: 392/479
• CPC Class Codes: B05B 7/164 the material to be sprayed and the atomising fluid being heated by independent sources of heat, without transfer of heat between atomising fluid and material to be sprayed
• CPC Class Codes: C23C 4/123 Spraying molten metal
• CPC Class Codes: F24H 3/0405 using electric energy supply, e.g. the heating medium being a resistive element; Heating by direct contact, i.e. with resistive elements, electrodes and fins being bonded together without additional element in-between F24H3/06, F24H3/08, F24H3/10 take precedence
• CPC Class Codes: H05B 3/145 Carbon only, e.g. carbon black, graphite
• CPC Class Codes: H05B 3/42 non-flexible

Abstract

An electrically heated metal spray apparatus is provided with a supersonic nozzle. Molten metal is injected into a gas stream flowing through the nozzle under pressure. By varying the pressure of the injected metal, the droplet can be made in various selected sizes with each selected size having a high degree of size uniformity. A unique one piece graphite heater provides easily controlled uniformity of temperature in the nozzle and an attached tundish which holds the pressurized molten metal. A unique U-shaped gas heater provides extremely hot inlet gas temperatures to the nozzle. A particularly useful application of the spray apparatus is coating of threads of a fastener with a shape memory alloy. This permits a fastener to be easily inserted and removed but provides for a secure locking of the fastener in high temperature environments.

Claims

1. A gas heater for a spraying apparatus comprising:

a hollow substantially cylindrical insulator;

a substantially cylindrical resistive element aligned coaxially with the insulator, said element having a size relative to the insulator so as to form an annular hollow space therebetween;

the resistive element being formed of at least two legs, each leg having a semi-cylindrical shape;

the legs being joined at an output end of the heater;

the legs being otherwise electrically isolated from each other throughout their respective lengths; and

means for attaching an electric current source to each of the legs at an input end of the heater.

2. The heater of claim 1 wherein the element has a textured surface which produces turbulence in gas which flows in an annular space between the element and the insulator.

3. The heater of claim wherein the annular space has a thickness no greater than about 0.065 inches.

4. Apparatus for heating materials in a high temperature spraying apparatus which comprises:

a primary gas heater;

a secondary gas heater;

the primary gas heater being adapted to heat propelling gas prior to entry of the gas into a spraying nozzle;

the secondary heater being adapted to heat the propelling gas within the nozzle and to heat the material which is to be sprayed by the spraying apparatus;

the primary heater comprising a U-shaped resistive element which U-shaped element is heated by passing an electric current therethrough;

the U-shaped element is attached to two metal electrodes at a gas input end thereof;

a surrounding cylindrical housing concentric to the U-shaped element having a size relative to the element such that a hollow annular passageway is formed between the element and the housing;

the gas is constrained to pass through the annular passageway;

the secondary heater comprising a single piece of rigid electrically conductive material;

the material of the secondary heater being configured to substantially surround and engage with substantially all the outer surfaces of the nozzle and a tundish which contains material to be sprayed; and

the material of the secondary heater having a substantially uniform cross-sectional area along its length.

5. The apparatus of claim 4 wherein:

the U-shaped element is graphite; and

the secondary heater is graphite.

6. The apparatus of claim 4 wherein the temperature of the gas exiting the primary heater is about 2000 degrees centigrade or greater.

7. In a metal spraying apparatus comprising a nozzle through which gas flows and a tundish that holds molten material to be sprayed, an apparatus for heating gas which is used as a propellant in high temperature spraying operations comprising:

a first heater formed as a U-shaped resistive element which element is heated by passing an electric current through the element;

the heating element is attached to two metal electrodes at a gas input end of the element;

a surrounding cylindrical housing concentric to the U-shaped element having a size relative to the element such that a hollow annular passageway is formed between the element and the housing;

the gas is constrained to pass through the annular passageway;

a second heater formed of a single piece of rigid electrically conductive material

configured to substantially surround and engage with substantially all the outer surfaces of the nozzle and the tundish; and

the material having a substantially uniform cross-sectional area along its length.

8. The apparatus of claim 7 wherein the heater for the nozzle and tundish comprises:

a first heating portion being shaped substantially like a hollow cylinder;

a second heating portion being shaped substantially like a hollow cylinder;

the first heating portion being orthogonal to the second heating portion; and

the first and second heating portions having slots formed through the walls thereof to produce a single current path with a substantially uniform cross-sectional area which current path passes across the substantially an entire exterior. surface area of the nozzle and the tundish.

9. The apparatus of claim 8 wherein:

the first heating portion has an axially oriented slot formed in a first wall and an opposed wall thereof; and

the second heating portion has an axially oriented slot formed in only one wall thereof whereby an opposed wall of the second heating portions functions as part of the current path.

10. The apparatus of claim 9 wherein at least one of the heating portions has at least one transverse slot formed through a wall thereof whereby the wall is reduced in area to achieve a desired uniformity of cross-sectional area of the current path.

11. The apparatus of claim 10 wherein each of the heating portions is provided with at least one of the transverse slots.

12. In a metal spraying apparatus comprising a nozzle through which heated gas flows and a tundish that holds molten material to be sprayed, a heater comprising;

a single piece of rigid electrically conductive material;

the material being configured to substantially surround and engage with substantially all the outer surfaces of the nozzle and the tundish; and

the material having a substantially uniform cross-sectional area along its length.

13. The heater of claim 12 wherein the material is graphite.

14. In a metal spraying apparatus comprising a nozzle through which heated gas flows and a tundish that holds molten material to be sprayed, a heater comprising;

a single piece of rigid electrically conductive material;

a first heating portion being shaped substantially like a hollow cylinder;

a second heating portion being shaped substantially like a hollow cylinder;

the first heating portion being orthogonal to the second heating portion; and

the first and second heating portions having slots formed through the walls thereof to produce a single current path with a substantially uniform cross-sectional area which current path passes across the substantially an entire exterior surface area of the nozzle and the tundish.

15. The heater of claim 14 wherein the material is graphite.

16. The heater of claim 14 wherein:

the first heating portion has an axially oriented slot formed in a first wall and an opposed wall thereof; and

the second heating portion has an axially oriented slot formed in only one wall thereof whereby an opposed wall of the second heating portions functions as part of the current path.

17. The heater of claim 16 wherein at least one of the heating portions has at least one transverse slot formed through a wall thereof whereby the wall is reduced in area to achieve a desired uniformity of cross-sectional area of the current path.

18. The heater of claim 17 wherein each of the heating portions is provided with at least one of the transverse slots.