Title of Invention	"A PROCESS OF PRODUCING A WEAR, CORROSION AND WATER DROPLET EROSION RESISTANT COATINGS AND A MULTIPOINT FUEL INJECTOR THEREFOR"
Abstract	This invention relates to a process of producing a wear corrosion and water droplet resistant coating of metallic carbides and metals as herein defined, comprising the steps of: feeding a carbide/metallic powder in a high-velocity, oxy-fuel spraying chamber and accelerating to velocity more than sonic velocity; - detachably attaching a plurality of multipoint fuel injector to said spraying chamber for injection liquid fuel into spraying chamber; gradual stepping up of a flame temperature in said spraying chamber through injecting of liquid fuel; supplying a compressed oxygen to said chamber to produce a high spraying velocity; feeding said carbide/metallic powder into said high temperature flame for melting and acceleration to a high velocity of 700-800 m/sec or more before being deposited into said component. This invention also relates to an injector to carry out the method of producing wear resistant and water droplet resistant coating comprising a HVOF fuel injector provided with a plurality of precise drilled holes for injecting oxygen, corresponding holes for injecting liquid into the stream of oxygen for automization and a separate hole for injecting hydrogen for ignition.

Title of Invention

"A PROCESS OF PRODUCING A WEAR, CORROSION AND WATER DROPLET EROSION RESISTANT COATINGS AND A MULTIPOINT FUEL INJECTOR THEREFOR"

Abstract

This invention relates to a process of producing a wear corrosion and water droplet resistant coating of metallic carbides and metals as herein defined, comprising the steps of: feeding a carbide/metallic powder in a high-velocity, oxy-fuel spraying chamber and accelerating to velocity more than sonic velocity; - detachably attaching a plurality of multipoint fuel injector to said spraying chamber for injection liquid fuel into spraying chamber; gradual stepping up of a flame temperature in said spraying chamber through injecting of liquid fuel; supplying a compressed oxygen to said chamber to produce a high spraying velocity; feeding said carbide/metallic powder into said high temperature flame for melting and acceleration to a high velocity of 700-800 m/sec or more before being deposited into said component. This invention also relates to an injector to carry out the method of producing wear resistant and water droplet resistant coating comprising a HVOF fuel injector provided with a plurality of precise drilled holes for injecting oxygen, corresponding holes for injecting liquid into the stream of oxygen for automization and a separate hole for injecting hydrogen for ignition.

Full Text	FIELD OF THE INVENTION This invention relates to a process of producing wear, corrosion and water droplet erosion resistant coatings and a multipoint fuel injector by making multipoint fuel injection in a high velocity oxy fuel (HVOF) spraying chamber. The invention further relates to a multipoint fuel injector carrying out the method thereof. BACKGROUND OF THE INVENTION In recent years, HVOF spraying has been considered an asset to the family of thermal spray processes especially for materials with melting point below 3000 K. It has proven successful, since it shows advantages in density and bond strength making it attractive for many wear and corrosion resistance applications. Its high coating quality results from the use of a hot combination-driven high-speed gas jet for thermal spraying. These coatings have environmental advantages compares to chemically/electrochemically formed coatings. Tungsten carbide and MCrAlY powders are widely used in the HVOF spraying system. These are used to produce dense, high hardness and excellent wear resistance coatings generally to combat (he erosion and corrosion at high as high as well as room temperature. In applications where abrasive or erosive wear resistance is of primary importance, WC-Co with and without nickel or chrome is used. WC-Co-Cr powders are preferred when high corrosion resistance at room temperature is needed. MCrAlY powder are preferred when high corrosion resistance at elevated temperature is needed. The abrasive and erosive wear resistance depends upon oxides, pores and the phase transformation occurring during spraying. High velocity oxy fuel sprayed coatings are commonly applied by HP /HVOF JP-5000, DS-100, Met jet II, OSU, Diamond jet and Praxair 2000 HVAF systems. These systems are based on liquid as well as gaseous fuel and oxygen/air, The liquid fuel injection system has limited number or injection points maximum two or three. This limitation is due to complexity involved in drilling of the small size fuel injection ports. There are several systems all over the world of providing HVOF coating. The HVOF coatings are generally based on the combustion of liquid fuel such as kerosene and gaseous fuel such as hydrogen, propane or natural gas and oxygen. These system especially liquid based are having limited injection points. The main disadvantage of the present system is that the atomization is not proper and hence the combination leaving carbon in the flame, which in turn leads to formation of unwanted metallic carbide in the sprayed coatings causing spalling of protective coatings. Another disadvantage of the present system is that unwanted carbon and oxygen comes in the coating, which deteriorates the coating properties further. Another disadvantage of the present system is that coatings lacks wear and high temperature corrosion resistance due to unwanted impurities in the surface coatings. The fuel injector are used in HVOF system for injecting liquid fuel and thereby producing thermal energy. This thermal energy is converted into kinetic energy and thereby providing both heat and kinetic energy which is required for proper melting and accelerating the powders for quality coatings. The injection in HVOF system atomizes the fuel. In presence of oxygen, the fuel such as kerosene and gasoline get burnt. At present, these injectors are having two and three injection points which do not atomizes fuel up to the degree required for complete combustion. The Indian aviation fuel is generally used in these injections. Indian fuel being rich in aromatics, do not suffciently burn as it is not atomizing properly, giving rise to excessive carbon. The excessive carbon enhances the changes of heat transfer characteristics as it takes away the combustion heat and put the load on the chilling system. Coating powders generally used in HVOF are WC+Co, Cr3C2+NiCr, WC+Cr3C2+NiCr, WC+Co+Cr, MCrAlY, CoCrAIY, CoNiCrAlY, CoCrNiAl+ ReY and CoCrNiAl+TaY. It is therefore an object of the present invention to propose a method of producing a wear and corrosion and droplet erosion resistant coatings applicable generally to turbines, boilers, textile, steel and paper mills. Another object of the present invention is to propose a method of producing a wear and corrosion resistant coatings which are dense, oxide free and have limited voids. Yet another object of the present invention is to propose a method which improves HVOF spraying system by providing a multipoint fuel injector for injecting liquid fuel and thereby producing a thermal energy which is converted into a kinetic energy resulting in proper melting and accelerating the powders to produce a wear and corrosion resistant coatings. A further object of the invention is to propose a multipoint fuel injector for multipoint fuel injection in a high velocity oxy fuel (HVOF) spraying chamber to produce a wear and corrosion resistant coatings. Yet a further object of the invention is to propose a multipoint fuel injector which achieves improved atomization of liquid fuel to produce a wear and corrosion resistant coatings. SUMMARY OF THE INVENTION In accordance with a first aspect of the present invention, there is provided a method of producing wear and corrosion resistant coatings. The method comprises the steps of detachably attaching a plurality of multipoint fuel injectors to said spraying chamber for injecting liquid fuel into said chamber; gradual stepping up a flame temperature in said chamber through said injecting of liquid fuels; supplying compressed O2 to said chamber to produce a high spraying velocity; feeding continually a carbide/metallic powder into said high temperature flame for melting and acceleration to a high velocity before being deposited. In accordance with a second aspect of the present invention, there is provided a multipoint fuel injector implementing the method comprising a HVOF fuel injector provided with a plurality of precise holes with diameter 0.2 mm and below. BRIFE DESCRIPTION OF THE ACCOMPANYING FIGURES Fig.l - Shows a conventional HVOF fuel injector, Fig 2 - Shows a multipoint fuel injector having precise laser drilled holes for improved Atomization of fuel according to the present invention. DETAILED DESCRIPTION OF THE PRESENT INVENTION HVOF process involves nominal temperature of the order of 3000°C and velocities more than mach 8. The method provides carbide/boride/metallic coatings to combat the wear due to silt laden water in hydro turbine and high temperature corrosion erosive wear of steam and gas turbines components. Fig.l gives the conventional fuel injector in which fuel enters only at limited injection points (not more than three) thereby do not atomise properly. Figure 2 gives the new injector, which atomizes the fuel in a very precise and controlled way. In the present invention the multipoints injection is achieved through a plurality of precise holes less than 0.2mm dia which were drilled by laser drilling. In this improved HVOF thermal spraying method, a medium flame temperature up to 3000°C and a high velocity more than 2500 m/sec are produced. When a carbide/metallic powder is fed in this flame the powder is partially melted and accelerated to high velocity being more than 700 to 800 m/sec and is then deposited on the component. Due to this moderate temperature and very high kinetic energy of the flame, powders do not disintegrates and produces coatings of having higher density and better properties especially abrasion, erosion and metal to metal wear resistance. Drilling of holes in the multipoint injectors is either done by mechanical drilling or by stem drilling. In stem drilling the electrolyte is fed through a small acid resistant tube (usually titanium) which is insulated over its entire length except at the drilling end. The tube or electrode is carefully straightened and guided into the workpiece material. Normally a two or three-tire plastic guide block forms part of the drilling fixture. The voltage, between 6 and 20 volts, applied to the electrode causes anodic dissolution of the positive metal ions to take place in the gap between electrode and workpiece. This voltage is periodically reversed to prevent the building up of undissolved metal ion on the electrode. The electrode returns via a narrow gap between the tube insulation and the hole wall. Electrodes of required size and shape is used. The electrolyte flow through the tubes is closely monitored and controlled to prevent electrode vibration and ensure sufficient flow. The voltage applied to the electrode is accurately regulated. Shaped or round holes including turbulators can be drilled, with depth to diameter ratio 300:1. The electrolyte is chosen on the basis of the workpiece material and is generally either 10 to 20%. Sulphuric Acid (H2S04) or 15 to 30% Nitric Acid (HNO3). However, for drilling smaller dia holes of size 0.2 mm or less, the present invention adapted a NdYAG Laser of capacity 3KW with an adequate focal length, the drilling parameters having been optimized. We Claim: i A process of producing wear, corrosion and water droplet erosion resisting coating of metallic carbides and metals as herein defined, comprising the steps of: - feeding a carbide/metallic powder in a high-velocity, oxy-fuel spraying chamber and accelerating to velocity more than sonic velocity; detachably attaching a plurality of multipoint fuel injector to said spraying chamber for injection liquid fuel into spraying chamber; gradual stepping up of a flame temperature in said spraying chamber through injecting of liquid fuel; supplying a compressed oxygen to said chamber to produce a high spraying velocity; feeding said carbide/metallic powder into said high temperature flame for melting and acceleration to a high velocity of 700-800 m/sec or more before being deposited into said component. 2. The process as claimed in claim 1, wherein said gradual stepping up of flame temperature is carried through atomization of fuel sprayed though a plurality of drilled body of said injectors. 3. The process as claimed in claim 1, wherein in said acceleration of said carbide/metallic power comprises acceleration to a velocity of 700-800 m/sec for deposition on the surface of said component 1o be coated. 4. The process as claimed in claim 1, wherein said flame temperature is increased through fuel injection upto 3000°C. 5. The process as claimed in claim 1, wherein said high spraying velocity generated through Combustion of compressed oxygen and fuel is above 2500 m/sec. b. The process as claimed in claim 3, wherein plurality of multipoint in the fuel injector is carried out by laser drilling, the laser having capacity upto 3KW with an adequate focal length. 7. A multipoint fuel injector implementing the process as claimed in claim 1, 8. The process as claimed in claim 8, wherein diameter of said plurality of holes range from 0.2mm and below.

Full Text

FIELD OF THE INVENTION
This invention relates to a process of producing wear, corrosion and water droplet erosion resistant coatings and a multipoint fuel injector by making multipoint fuel injection in a high velocity oxy fuel (HVOF) spraying chamber. The invention further relates to a multipoint fuel injector carrying out the method thereof.
BACKGROUND OF THE INVENTION
In recent years, HVOF spraying has been considered an asset to the family of thermal spray processes especially for materials with melting point below 3000 K. It has proven successful, since it shows advantages in density and bond strength making it attractive for many wear and corrosion resistance applications. Its high coating quality results from the use of a hot combination-driven high-speed gas jet for thermal spraying. These coatings have environmental advantages compares to chemically/electrochemically formed coatings.
Tungsten carbide and MCrAlY powders are widely used in the HVOF spraying system. These are used to produce dense, high hardness and excellent wear resistance coatings generally to combat (he erosion and corrosion at high as high as well as room temperature. In applications where abrasive or erosive wear resistance is of primary importance, WC-Co with and without nickel or chrome is used. WC-Co-Cr powders are preferred when high corrosion resistance at room temperature is needed. MCrAlY powder are preferred when high corrosion resistance at elevated temperature is needed.
The abrasive and erosive wear resistance depends upon oxides, pores and the phase transformation occurring during spraying. High velocity oxy fuel sprayed coatings are commonly applied by HP /HVOF JP-5000, DS-100,
Met jet II, OSU, Diamond jet and Praxair 2000 HVAF systems. These systems are based on liquid as well as gaseous fuel and oxygen/air, The liquid fuel injection system has limited number or injection points maximum two or three. This limitation is due to complexity involved in drilling of the small size fuel injection ports.
There are several systems all over the world of providing HVOF coating. The HVOF coatings are generally based on the combustion of liquid fuel such as kerosene and gaseous fuel such as hydrogen, propane or natural gas and oxygen. These system especially liquid based are having limited injection points. The main disadvantage of the present system is that the atomization is not proper and hence the combination leaving carbon in the flame, which in turn leads to formation of unwanted metallic carbide in the sprayed coatings causing spalling of protective coatings.
Another disadvantage of the present system is that unwanted carbon and oxygen comes in the coating, which deteriorates the coating properties further. Another disadvantage of the present system is that coatings lacks wear and high temperature corrosion resistance due to unwanted impurities in the surface coatings.
The fuel injector are used in HVOF system for injecting liquid fuel and thereby producing thermal energy. This thermal energy is converted into kinetic energy and thereby providing both heat and kinetic energy which is required for proper melting and accelerating the powders for quality coatings. The injection in HVOF system atomizes the fuel. In presence of oxygen, the fuel such as kerosene and gasoline get burnt. At present, these injectors are having two and three injection points which do not atomizes fuel up to the degree required for complete combustion. The Indian
aviation fuel is generally used in these injections. Indian

fuel being rich in aromatics, do not suffciently burn as it is not atomizing properly, giving rise to excessive carbon. The excessive carbon enhances the changes of heat transfer characteristics as it takes away the combustion heat and put the load on the chilling system.
Coating powders generally used in HVOF are WC+Co, Cr3C2+NiCr, WC+Cr3C2+NiCr, WC+Co+Cr, MCrAlY, CoCrAIY, CoNiCrAlY, CoCrNiAl+ ReY and CoCrNiAl+TaY.
It is therefore an object of the present invention to propose a method of producing a wear and corrosion and droplet erosion resistant coatings applicable generally to turbines, boilers, textile, steel and paper mills.
Another object of the present invention is to propose a method of producing a wear and corrosion resistant coatings which are dense, oxide free and have limited voids.
Yet another object of the present invention is to propose a method which improves HVOF spraying system by providing a multipoint fuel injector for injecting liquid fuel and thereby producing a thermal energy which is converted into a kinetic energy resulting in proper melting and accelerating the powders to produce a wear and corrosion resistant coatings.
A further object of the invention is to propose a multipoint fuel injector for multipoint fuel injection in a high velocity oxy fuel (HVOF) spraying chamber to produce a wear and corrosion resistant coatings.
Yet a further object of the invention is to propose a multipoint fuel injector which achieves improved atomization of liquid fuel to produce a wear and corrosion resistant coatings.
SUMMARY OF THE INVENTION
In accordance with a first aspect of the present invention, there is provided a method of producing wear and corrosion resistant coatings. The method comprises the steps of detachably attaching a plurality of multipoint fuel injectors to said spraying chamber for injecting liquid fuel into said chamber; gradual stepping up a flame temperature in said chamber through said injecting of liquid fuels; supplying compressed O2 to said chamber to produce a high spraying velocity; feeding continually a carbide/metallic powder into said high temperature flame for melting and acceleration to a high velocity before being deposited.
In accordance with a second aspect of the present invention, there is provided a multipoint fuel injector implementing the method comprising a HVOF fuel injector provided with a plurality of precise holes with diameter 0.2 mm and below.
BRIFE DESCRIPTION OF THE ACCOMPANYING FIGURES
Fig.l - Shows a conventional HVOF fuel injector,
Fig 2 - Shows a multipoint fuel injector having precise laser drilled holes for improved Atomization of fuel according to the present invention.
DETAILED DESCRIPTION OF THE PRESENT INVENTION
HVOF process involves nominal temperature of the order of 3000°C and velocities more than mach 8. The method provides carbide/boride/metallic coatings to combat the wear due to silt laden water in hydro turbine and high temperature corrosion erosive wear of steam and gas turbines components. Fig.l gives the conventional fuel injector in which fuel enters only at limited injection points (not more than three) thereby do not atomise properly. Figure 2 gives the new injector, which atomizes the fuel in a very precise and controlled way. In the present invention the multipoints injection is achieved through a plurality of precise holes less than 0.2mm dia which were drilled by laser drilling.
In this improved HVOF thermal spraying method, a medium flame temperature up to 3000°C and a high velocity more than 2500 m/sec are produced. When a carbide/metallic powder is fed in this flame the powder is partially melted and accelerated to high velocity being more than 700 to 800 m/sec and is then deposited on the component.
Due to this moderate temperature and very high kinetic energy of the flame, powders do not disintegrates and produces coatings of having higher density and better properties especially abrasion, erosion and metal to metal wear resistance.
Drilling of holes in the multipoint injectors is either done by mechanical drilling or by stem drilling. In stem drilling the electrolyte is fed through a small acid resistant tube (usually titanium) which is insulated over its entire length except at the drilling end. The tube or electrode is carefully straightened and guided into the workpiece material. Normally a two or three-tire plastic guide block forms part of the drilling fixture. The voltage, between 6 and 20 volts, applied to the electrode causes anodic dissolution of the positive metal ions to take place in the gap between electrode and workpiece. This voltage is periodically reversed to prevent the building up of undissolved metal ion on the electrode. The electrode returns via a narrow gap between the tube insulation and the hole wall. Electrodes of required size and shape is used. The electrolyte flow through the tubes is closely monitored and controlled to prevent electrode vibration and ensure sufficient flow. The voltage applied to the electrode is accurately regulated. Shaped or round holes including turbulators can be drilled, with depth to diameter ratio 300:1. The electrolyte is chosen on the basis of the workpiece material and is generally either 10 to 20%. Sulphuric Acid (H2S04) or 15 to 30% Nitric Acid (HNO3). However, for drilling smaller dia holes of size 0.2 mm or less, the present invention adapted a NdYAG Laser of capacity 3KW with an adequate focal length, the drilling parameters having been optimized.

We Claim:
i A process of producing wear, corrosion and water droplet erosion resisting coating of metallic carbides and metals as herein defined, comprising the steps of:
- feeding a carbide/metallic powder in a high-velocity, oxy-fuel spraying chamber and accelerating to velocity more than sonic velocity;
detachably attaching a plurality of multipoint fuel injector to said spraying chamber for injection liquid fuel into spraying chamber;
gradual stepping up of a flame temperature in said spraying chamber through injecting of liquid fuel;
supplying a compressed oxygen to said chamber to produce a high spraying velocity;
feeding said carbide/metallic powder into said high temperature flame for melting and acceleration to a high velocity of 700-800 m/sec or more before being deposited into said component.
2. The process as claimed in claim 1, wherein said gradual stepping up of flame temperature is carried through atomization of fuel sprayed though a plurality of drilled body of said injectors.
3. The process as claimed in claim 1, wherein in said acceleration of said carbide/metallic power comprises acceleration to a velocity of 700-800 m/sec for deposition on the surface of said component 1o be coated.
4. The process as claimed in claim 1, wherein said flame temperature is increased through fuel injection upto 3000°C.
5. The process as claimed in claim 1, wherein said high spraying velocity generated through Combustion of compressed oxygen and fuel is above 2500 m/sec.
b. The process as claimed in claim 3, wherein plurality of multipoint in the fuel injector is carried out by laser drilling, the laser having capacity upto 3KW with an adequate focal length.
7. A multipoint fuel injector implementing the process as claimed in claim 1,
8. The process as claimed in claim 8, wherein diameter of said plurality of holes range from 0.2mm and below.

Documents:

56-del-2004-abstract.pdf

56-del-2004-claims.pdf

56-del-2004-complete specification (granted).pdf

56-del-2004-correspondence-others.pdf

56-del-2004-correspondence-po.pdf

56-del-2004-description (complete).pdf

56-del-2004-drawings.pdf

56-del-2004-form-1.pdf

56-del-2004-form-19.pdf

56-del-2004-form-2.pdf

56-del-2004-form-3.pdf

56-del-2004-gpa.pdf

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Patent Number

217717

Indian Patent Application Number

56/DEL/2004

PG Journal Number

37/2008

Publication Date

12-Sep-2008

Grant Date

28-Mar-2008

Date of Filing

13-Jan-2004

Name of Patentee

BHARAT HEAVY ELECTRICALS LTD.

Applicant Address

BHEL HOUSE, SIRI FORT, NEW DELHI-110 049, INDIA.

Inventors:

#	Inventor's Name	Inventor's Address
1	JOSHI PANKAJ	C/O. BHARAT HEAVY ELECTRICALS LTD. BHEL HOUSE, SIRI FORT, NEW DELHI-110049, INDIA.
2	MANN BALBIR SINGH	C/O. BHARAT HEAVY ELECTRICALS LTD. BHEL HOUSE, SIRI FORT, NEW DELHI-110049, INDIA.
3	ARYA VIVEK	C/O. BHARAT HEAVY ELECTRICALS LTD. BHEL HOUSE, SIRI FORT, NEW DELHI-110049, INDIA.

PCT International Classification Number

C23C

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA