Title of Invention	A THERMAL BARRIER COATING SYSTEM FOR APPLICATION ON COPPER /WORKING SURFACES EXPOSED TO HIGH TERMPERATURE ZONES.
Abstract	A THERMAL BARRIER COATING SYSTEM FOR APPLICATION COPPER/WORKING SURFACES EXPOSED TO HIGH TEMPERATURE ZONES COMPRISING : A BOND COAT AS A FIRST LAYER OF COAT ON THE SUBSTRATE OBTAINED OF Ni-Cr-Al ALLOY COMPRISING 17-22% BY WT. Cr, 2-6% BY WT. Al, AND BLANCE Ni, AND A SECOND LAYER OF TOP COAT OF TITANIA TiO2 OVER SAID BOND COAT AND A PROCESS FOR PROVIDING SUCH COATING SYSTEM ON SUBSTRATES. THE COAT SYSTEM AS ABOVE IS DENSE, ADHERENT AND MECHANICALLY STABLE AND HAS A STRONG BONDING WITH THE BASIC SUBSTRATE. THE PROCESS OF APPLYING SUCH COAT IS ALSO SIMPLE AND COST-EFFECTIVE. THE COATING SYSTEM IS ESPECIALLY SUITABLE FOR COATING OF BLAST FURNACE TUYERES EXPOSED TO HIGH TEMPERATURE AS EFFECTIVE THERMAL BARRIERS.

Title of Invention

A THERMAL BARRIER COATING SYSTEM FOR APPLICATION ON COPPER /WORKING SURFACES EXPOSED TO HIGH TERMPERATURE ZONES.

Abstract

A THERMAL BARRIER COATING SYSTEM FOR APPLICATION COPPER/WORKING SURFACES EXPOSED TO HIGH TEMPERATURE ZONES COMPRISING : A BOND COAT AS A FIRST LAYER OF COAT ON THE SUBSTRATE OBTAINED OF Ni-Cr-Al ALLOY COMPRISING 17-22% BY WT. Cr, 2-6% BY WT. Al, AND BLANCE Ni, AND A SECOND LAYER OF TOP COAT OF TITANIA TiO2 OVER SAID BOND COAT AND A PROCESS FOR PROVIDING SUCH COATING SYSTEM ON SUBSTRATES. THE COAT SYSTEM AS ABOVE IS DENSE, ADHERENT AND MECHANICALLY STABLE AND HAS A STRONG BONDING WITH THE BASIC SUBSTRATE. THE PROCESS OF APPLYING SUCH COAT IS ALSO SIMPLE AND COST-EFFECTIVE. THE COATING SYSTEM IS ESPECIALLY SUITABLE FOR COATING OF BLAST FURNACE TUYERES EXPOSED TO HIGH TEMPERATURE AS EFFECTIVE THERMAL BARRIERS.

Full Text	The present invention relates to a thermal barrier coating system for application on copper/working surfaces exposed to high temperature zones and a process for obtained such thermal barrier coatings. In particular the invention specifically relates to thermal barrier coating system for application on blast furnace tuyeres and a process for manufacture of blast furnace tuyeres coated with such thermal barrier coating. A blast furnace is a counter heterogeneous reactive heat transfer system involving dynamic interaction between gaseous, liquid. and solid phases. Preheated air, one of the inputs for iron making, is introduced through cast high purity copper tuyeres. The blast furnace tuyeres are important components of blast furnaces. The tuyeres, 20 in number, are double walled, high purity (-99.5%) cast copper structures, through which preheated air (750-870°C) is introduced into the blast furnace. These tuyeres are located at the intersection of bosch and the hearth of the furnace along the entire periphery. As the tuyeres are exposed to the hottest region in the blast furnace where the raceway adiabatic flame temperature, RAFT, may frequently exceed 2000°C, the tuyeres are cooled internally by circulating water. The tuyere failure may take place due to accidental contact with burning coke particles/lumps, slag or hot metal drops leading to high localised thermal load on relatively small area. The sudden tuyere failure adversely affects the stable operation of blast furnace. Thermal barrier coatings applied to the exposed/working surface of tuyeres lead to drastic reduction in the incidence of tuyere failures The high melting point, low thermal"conductivity, phase stability of ceramic material is found to beiiseful as a good thermal barrier coating material and thermal based ceramic coatings are known to be provided on subjects exposed to high temperature. The ceramic coatings provide a thermal barrier to the heat flux between the hot zone of the furnace and the tuyere members Also, the provision of a bond coat for enhancing the adhesion of ceramic top coat is known as would be evident from the following prior arts : US Patent: 5498484 discloses a thermal barrier coating system for high temperature nickel-based and cobalt-based super alloys including a hardenable metallic coating on the substrate and a ceramic top coat. The metallic coating is preferably a gamma/gamma prime hardenable nickel-based super alloy, and the ceramic top coat is preferably zirconium oxide having* from about 6 to about 20 percent yttrium oxide or from about 15 to about 40 percent cerium oxide. Optionally there may be provided between the hardenable metallic layer and the ceramic topcoat an intermetallic coating such as a nickel aluminide. US Patent 5824423 disclosed an improved bond coat of a thermal barrier coating system useful for enhancing adhesion of a ceramic topcoat to a superalloy substrate. The bond coat includes about 13 to 30 weight percent aluminum between trace and about 3 weight percent of a reactive element selected from the group consisting of yttrium, zirconium, lanthanum, and~ It is the basic object of the present invention to provide for an improved thermal barrier coating .system for application on subjects/working surface exposed to high temperature zones -which would have good and effective bonding to the surface to be coated and wbiild be durable. Another object is to provide an improved thermal barrier coating system based on ceramic titania (TiO2) which would have good thermal barrier properties and would be durable. Yet another object of the present invention is to provide an improved thermal barrier coating system which would provide for dense, adherent, and mechanically stable titania coating as a thermal barrier to the heat flux especially for coating of blast furnace tuyeres which can lead to significant increase in the life of the tuyeres. Yet further object of the present invention is directed to the method of providing improved thermal barrier coating on subjects/working surfaces exposed to high temperature zones which would be simple and cost effective. Yet further object is specifically directed to the method of coating blast furnace tuyeres with an improved thermal barrier coating which would provide for significant improvement in life of the tuyers. Thus according to one aspect the present invention provides a thermal barrier coating system for application on subjects/working surfaces exposed to high temperature zones comprising : a bond coat for coating on the said substrate obtained of Ni-Cr-Al alloy comprising 17 to 22% Cr, 2 to 6% Al, balance Ni; and a top coat-of titaniaTiO2 over said bond coat In order to promote better adhesion of ceramic titania (TiO2) coating with the substrata bond coat of Ni-Gr-Al alloy [17-22% Cr,2-6% Al, Balance Ni] was selected for application on to the virgin copper tuyere surface. The coating materials fpr both the Ni-Cr-Al bond coat and the TiO2 top coat are essentially powders with granulometric particle sizes of -100+325 mesh (150-44 microns) and -230 mesh ( In accordance with another aspect the present invention provides a process for coating substrates exposed to high tempered zones with said thermal barrier coating system comprising : preparing the surface to be coated ; preheating the surface to be coated to a temperature of 120-200°C ; applying the bond coat of Ni-Cr-Al alloy comprising 17-22% Cr, 2-6% Al and balance Ni and allowing the surface to be cooled to a temperature of 50-100°C ; depositing the top a coat of titania (TiO2) on said bond coat of Ni-Cr-Al. The surface to be coated was throughly cleaned by machining 2-4 mm on diameter and hand/spot grinding. An undercut of ~1 mm was made all along the surface. The surface was roughened by grit blasting and knurling to provide mechanical anchorage to further improve the bond between the virgin machined copper surface and the bond coat. The surface is then washed with acetone to degrease and preheated to 120-150°C with an argon plasma arc. A bond coat of Ni-Cr=Al alloy was plasma sprayed on the virgin copper surface. The job surface was then allowed to cool to around 50-100 °C. Following the deposition of the bond coat, the top coat of titania (TiO2) was deposited by argon plasma spray method. The total thickness of coating (bond and titania coating included) was 1.0 to 1.5 mm. The details Of the invention its object and advantages are explained in greater detail in relation to the accompanying figure1 which illustrate in section a blast furnace tuyere with the thermal barrier coating of the invention and the exemplary, embodiment of applying such coat on blast furnace tuyeres as discussed hereunder : EXAMPLE : An exemplary method of provision of the thermal barrier coating system in blast furnace tuyeres is discussed hereunder : a) Surface preparation The surface to be coated was first mechined (around 2 mm) to obtain fresh and uncontaminated surface. The surface was then cleaned by the usual process of alumina-grit blasting. The surface was subsequently cleaned with analar grade acetone to remove greases and oils. b) Preheating the surface The tuyers was placed on a horizontal turnable and heated to around 120°C~200°C with the help of argon plasma torch c) Application of coating Application of coating was done in following two stages : i) Application of bond coat The plasma spray conditions were : Current : 700-750 amp. Voltage : 33-43 VDC Powder Feed : 3.2 rpm Rate Gas pressure : 40 psi Distance of spray gun : 4 to 6 inches. ii) Application of top coat ;- )•• - ^ , com The top coat, the actual working surface exposed to the aggressive atmosphere of the BF is applied on the bond coat. The bond coat facilitates good bonding of the working surface ceramic titaniain the present case. Thus, the coating scheme is cleaned metal surface, bond coat Tand finally the top coat which is the working surface. The following were the plasma spray parameters : Current : 700-900 amp Voltage : 33-40 VDC Powder Feed : 4.5 rpm Rate Gas pressure : 40 psi Distance of Spray gun : 4 to 6 inches. Following the application of the coating, the surface was allowed to cool to the ambient temperature and the surface was inspected for cracks and other defects. The surface roughness of the ceramic coating was measured and found to be around 6.91-8.47 microns Ra. The coatings, as is clear from the above description, should be applied to the flat nose-surface of tuyere which sees the high temperature in the furnace and conico-cylindrical surface of the tuyere which hangs inside the furnace ; this is roughly 5-6 inches from the nose (Fig. 1). All coating powders employed were commercially available plasma grade powders. The .tuyeres were mounted on a, horizontal turn-table and rotated at 3-4 rpm during the coating process. The plasma coating results in dense, adherent and mechanically stable titania coating which acts as a thermal barrier to the heat flux thus leading to significant improvement in the life of the tuyeres. The coated tuyeres have exhibited a service life of more than 500 days in comparison with the average, service life of 72 days for an uncoated tuyere. This translates into an augmentation in the service life by nearly 7 times. WE CLAIM : 1. A thermal barrier coating system for application on copper/working surfaces exposed to high temperature zones comprising : a bond coat for coating on the said substrate obtained of Ni-Cr-Al alloy comprising 17 to 22% Cr, 2 to 6% Al, balance Ni; and a top coat of titania TiO2 over said bond coat. 2. A thermal barrier coating system as claimed in claim 1 wherein said bond coat of Ni-Cr-Al comprise 17 - 22% Cr, 2 - 6% Al and balance Ni. 3. A thermal barrier coating system as claimed in anyone of claims 1 or 2 wherein said Ni-Cr-Al bond coat and the TiC>2 top coat comprise powders with granulometric particle size of -100 + 325 mesh and -230 mesh respectively. 4. A thermal barrier coating system as claimed in anyone of claims 1 to 3 wherein the thickness of said bond coat range from 0.3 to 0.5mm and said top coat range from 0.6 to 1.0mm with said total thickness of the coat system in the range of 1.0 to 1.5 mm. 5. A thermal barrier coating system as claimed in anyone of claims 1 to 4 wherein the surface roughness of the ceramic coating range from 6.91 to 8.47 microns Ra.. 6. A process for coating substrates exposed to high tempered zones with said thermal barrier coating system as claimed in anyone of claims 1 to 5 comprising : preparing the surface to be coated ; preheating the surface to be coated to a temperature of 120-200°C ; applying the bond coat of Ni-Cr-Al alloy comprising 17-22% Cr, 2-6% Al and balance Ni and allowing the surface to1 be cooled to a temperature of 50-100°C ; depositing the top a coat of titania (TiO2) on said bond coat of Ni-Cr-Al. 7. A process as claimed in claim 6 wherein said step of preparation of the surface to be coated comprise : cleaning the surface by machining 2-4 mm on diameter with or without hand/spot grinding ; roughening the surface by grid blasting and knurling to provide mechanical anchorage; and washing the surface to degrease the same. 8. A process" as claimed in claim 7 wherein the surface is washed with acetone for degreasing. 9. A process as claimed in anyone of claims 6 to 8 wherein said Ni-Cr-Al alloy bond coat and said titania top coat are applied by plasma spraying techniques. 10. A process as claimed in anyone"of claims 6 to 9 wherein said bond coat is applied using the following plasma spray conditions : Current - 700 to 750 amp. Voltage - 33 to 43 VDC Distance of spray gun - 4 to 6 inches. 11. A process as claimed in claim 10 wherein for said bond coat the plasma spray power feed rate is preferably 3.2 rpm. and said gas pressure is preferably 40 psi. 12. A process as claimed in anyone of claims 6 to 11 wherein said plasma spray conditions for said top coat of titania comprise : Current - 700 to 900 amp. Voltage - 33 to 40 VDC Distance of spray gun - 4 to 6 inches. 13. A process as claimed in claim 12 wherein for said top coat the plasma spray power feed rate is preferably 4.5 rpm and said gas pressure is preferably 40 psi. 14. A process as claimed in anyone of claims 6 to 13 wherein the coating material for said Ni-Cr-Al bond coat and TiO2 top coat are powders with granulometric particle size of -100 +375 mesh and -230 mesh respectively. 15. A process as claimed in anyone of claims 6 to 14 wherein the said bond coat of Ni-Cr-Al is obtained of 0.3 to 0.5mm thickness preferably 0.4 mm thickness built up in four runs and the total thickness of coating (the bond coat and top coat) is obtained to be 1.0 to 1.5 mm. 16. A process as claimed in anyone of claims 6 to 15 wherein substrate . to be coated is a blast furnace tuyere. 17. A processes claimed in anyone of claims 6 to 15 wherein said substrate to be coated are blast furnace tuyeres and the tuyeres are mounted on a horizontally turn table and rotated at 3-4 rpm during the coating process. 18. A thermal barrier coating system and a process for carrying out such coating on substrate such as blast furnace tuyeres substantially as hereindescribed and illustrated with reference to the accompanying examples and figures. A thermal barrier coating system for application on copper/working surfaces exposed to high temperature zones comprising : a bond coat as a first layer of coat on the substrate obtained of Ni-Cr-A1 alloy comprising 17-22% by wt. Cr, 2-6% by wt A1, and balance Ni, and a second layer of top coat of titania TiO2 over said bond coat and a process for providing such coating system on substrates. The coat system as above is dense, adherent and mechanically stable and has a strong bonding with the basic substrate. The process of applying such coat is also simple and cost-effective. The coating system is especially suitable for coating of blast furnace tuyeres exposed to high temperature as effective thermal barriers.

Full Text

The present invention relates to a thermal barrier coating system for application on copper/working surfaces exposed to high temperature zones and a process for obtained such thermal barrier coatings. In particular the invention specifically relates to thermal barrier coating system for application on blast furnace tuyeres and a process for manufacture of blast furnace tuyeres coated with such thermal barrier coating.
A blast furnace is a counter heterogeneous reactive heat transfer system involving dynamic interaction between gaseous, liquid. and solid phases. Preheated air, one of the inputs for iron making, is introduced through cast high purity copper tuyeres. The blast furnace tuyeres are important components of blast furnaces. The tuyeres, 20 in number, are double walled, high purity (-99.5%) cast copper structures, through which preheated air (750-870°C) is introduced into the blast furnace. These tuyeres are located at the intersection of bosch and the hearth of the furnace along the entire periphery. As the tuyeres are exposed to the hottest region in the blast furnace where the raceway adiabatic flame temperature, RAFT, may frequently exceed 2000°C, the tuyeres are cooled internally by circulating water. The tuyere failure may take place due to accidental contact with burning coke particles/lumps, slag or hot metal drops leading to high localised thermal load on relatively small area. The sudden tuyere failure adversely affects the stable operation of blast furnace.
Thermal barrier coatings applied to the exposed/working surface of tuyeres lead to drastic reduction in the incidence of tuyere failures The high melting point, low thermal"conductivity, phase stability of ceramic material is found to beiiseful as a good thermal barrier coating material and thermal based ceramic coatings are known to be provided on subjects
exposed to high temperature. The ceramic coatings provide a thermal
barrier to the heat flux between the hot zone of the furnace and the tuyere
members
Also, the provision of a bond coat for enhancing the adhesion of ceramic top coat is known as would be evident from the following prior arts :
US Patent: 5498484 discloses a thermal barrier coating system for high temperature nickel-based and cobalt-based super alloys including a hardenable metallic coating on the substrate and a ceramic top coat. The metallic coating is preferably a gamma/gamma prime hardenable nickel-based super alloy, and the ceramic top coat is preferably zirconium oxide having* from about 6 to about 20 percent yttrium oxide or from about 15 to about 40 percent cerium oxide. Optionally there may be provided between the hardenable metallic layer and the ceramic topcoat an intermetallic coating such as a nickel aluminide.
US Patent 5824423 disclosed an improved bond coat of a thermal barrier coating system useful for enhancing adhesion of a ceramic topcoat to a superalloy substrate. The bond coat includes about 13 to 30 weight percent aluminum between trace and about 3 weight percent of a reactive element selected from the group consisting of yttrium, zirconium, lanthanum, and~ It is the basic object of the present invention to provide for an improved thermal barrier coating .system for application on subjects/working surface exposed to high temperature zones -which would have good and effective bonding to the surface to be coated and wbiild be durable.
Another object is to provide an improved thermal barrier coating system based on ceramic titania (TiO2) which would have good thermal barrier properties and would be durable.
Yet another object of the present invention is to provide an improved thermal barrier coating system which would provide for dense, adherent, and mechanically stable titania coating as a thermal barrier to the heat flux especially for coating of blast furnace tuyeres which can lead to significant increase in the life of the tuyeres.
Yet further object of the present invention is directed to the method of providing improved thermal barrier coating on subjects/working surfaces exposed to high temperature zones which would be simple and cost effective.
Yet further object is specifically directed to the method of coating blast furnace tuyeres with an improved thermal barrier coating which would provide for significant improvement in life of the tuyers.
Thus according to one aspect the present invention provides a thermal barrier coating system for application on subjects/working surfaces exposed to high temperature zones comprising :
a bond coat for coating on the said substrate obtained of Ni-Cr-Al alloy comprising 17 to 22% Cr, 2 to 6% Al, balance Ni; and
a top coat-of titaniaTiO2 over said bond coat
In order to promote better adhesion of ceramic titania (TiO2) coating with the substrata bond coat of Ni-Gr-Al alloy [17-22% Cr,2-6% Al, Balance Ni] was selected for application on to the virgin copper tuyere surface. The coating materials fpr both the Ni-Cr-Al bond coat and the TiO2 top coat
are essentially powders with granulometric particle sizes of -100+325
mesh (150-44 microns) and -230 mesh ( In accordance with another aspect the present invention provides a process for coating substrates exposed to high tempered zones with said thermal barrier coating system comprising :
preparing the surface to be coated ;
preheating the surface to be coated to a temperature of 120-200°C ;
applying the bond coat of Ni-Cr-Al alloy comprising 17-22% Cr, 2-6%
Al and balance Ni and allowing the surface to be cooled to a
temperature of 50-100°C ;
depositing the top a coat of titania (TiO2) on said bond coat of Ni-Cr-Al.
The surface to be coated was throughly cleaned by machining 2-4 mm on diameter and hand/spot grinding. An undercut of ~1 mm was made all along the surface. The surface was roughened by grit blasting and knurling to provide mechanical anchorage to further improve the bond between the virgin machined copper surface and the bond coat. The surface is then washed with acetone to degrease and preheated to 120-150°C with an argon plasma arc. A bond coat of Ni-Cr=Al alloy was plasma sprayed on the virgin copper surface. The job surface was then allowed to cool to around 50-100 °C. Following the deposition of the bond coat, the top coat of titania (TiO2) was deposited by argon plasma spray method. The total thickness of coating (bond and titania coating included) was 1.0 to 1.5 mm.
The details Of the invention its object and advantages are explained in greater detail in relation to the accompanying figure1 which illustrate in section a blast furnace tuyere with the thermal barrier coating of the
invention and the exemplary, embodiment of applying such coat on blast
furnace tuyeres as discussed hereunder :
EXAMPLE :
An exemplary method of provision of the thermal barrier coating system
in blast furnace tuyeres is discussed hereunder :
a) Surface preparation
The surface to be coated was first mechined (around 2 mm) to obtain fresh and uncontaminated surface. The surface was then cleaned by the usual process of alumina-grit blasting. The surface was subsequently cleaned with analar grade acetone to remove greases and oils.
b) Preheating the surface
The tuyers was placed on a horizontal turnable and heated to around 120°C~200°C with the help of argon plasma torch
c) Application of coating
Application of coating was done in following two stages :
i) Application of bond coat
The plasma spray conditions were : Current : 700-750 amp.
Voltage : 33-43 VDC
Powder Feed : 3.2 rpm Rate
Gas pressure : 40 psi
Distance of spray
gun : 4 to 6 inches.
ii) Application of top coat ;- )•• - ^ , com
The top coat, the actual working surface exposed to the
aggressive atmosphere of the BF is applied on the bond coat.
The bond coat facilitates good bonding of the working surface
ceramic titaniain the present case. Thus, the coating scheme
is cleaned metal surface, bond coat Tand finally the top coat which is the working surface.
The following were the plasma spray parameters : Current : 700-900 amp
Voltage : 33-40 VDC
Powder Feed : 4.5 rpm Rate
Gas pressure : 40 psi
Distance of
Spray gun : 4 to 6 inches.
Following the application of the coating, the surface was allowed to cool to the ambient temperature and the surface was inspected for cracks and other defects. The surface roughness of the ceramic coating was measured and found to be around 6.91-8.47 microns Ra.
The coatings, as is clear from the above description, should be applied to the flat nose-surface of tuyere which sees the high temperature in the furnace and conico-cylindrical surface of the tuyere which hangs inside the furnace ; this is roughly 5-6 inches from the nose (Fig. 1).
All coating powders employed were commercially available plasma grade powders. The .tuyeres were mounted on a, horizontal turn-table and rotated at 3-4 rpm during the coating process.
The plasma coating results in dense, adherent and mechanically stable titania coating which acts as a thermal barrier to the heat flux thus leading to significant improvement in the life of the tuyeres. The coated tuyeres have exhibited a service life of more than 500 days in comparison with the average, service life of 72 days for an uncoated tuyere. This translates into an augmentation in the service life by nearly 7 times.
WE CLAIM :
1. A thermal barrier coating system for application on copper/working surfaces exposed to high temperature zones comprising :
a bond coat for coating on the said substrate obtained of Ni-Cr-Al alloy comprising 17 to 22% Cr, 2 to 6% Al, balance Ni; and
a top coat of titania TiO2 over said bond coat.
2. A thermal barrier coating system as claimed in claim 1 wherein said bond coat of Ni-Cr-Al comprise 17 - 22% Cr, 2 - 6% Al and balance Ni.
3. A thermal barrier coating system as claimed in anyone of claims 1 or 2 wherein said Ni-Cr-Al bond coat and the TiC>2 top coat comprise powders with granulometric particle size of -100 + 325 mesh and -230 mesh respectively.
4. A thermal barrier coating system as claimed in anyone of claims 1 to 3 wherein the thickness of said bond coat range from 0.3 to 0.5mm and said top coat range from 0.6 to 1.0mm with said total thickness of the coat system in the range of 1.0 to 1.5 mm.
5. A thermal barrier coating system as claimed in anyone of claims 1 to 4 wherein the surface roughness of the ceramic coating range from 6.91 to 8.47 microns Ra..
6. A process for coating substrates exposed to high tempered zones with said thermal barrier coating system as claimed in anyone of claims 1 to 5 comprising :
preparing the surface to be coated ;
preheating the surface to be coated to a temperature of 120-200°C ;
applying the bond coat of Ni-Cr-Al alloy comprising 17-22% Cr, 2-6% Al and balance Ni and allowing the surface to1 be cooled to a temperature of 50-100°C ;
depositing the top a coat of titania (TiO2) on said bond coat of Ni-Cr-Al.
7. A process as claimed in claim 6 wherein said step of preparation of the surface to be coated comprise :
cleaning the surface by machining 2-4 mm on diameter with or without hand/spot grinding ;
roughening the surface by grid blasting and knurling to provide mechanical anchorage; and
washing the surface to degrease the same.
8. A process" as claimed in claim 7 wherein the surface is washed with acetone for degreasing.
9. A process as claimed in anyone of claims 6 to 8 wherein said Ni-Cr-Al alloy bond coat and said titania top coat are applied by plasma spraying techniques.
10. A process as claimed in anyone"of claims 6 to 9 wherein said bond coat is applied using the following plasma spray conditions :
Current - 700 to 750 amp.
Voltage - 33 to 43 VDC
Distance of spray gun - 4 to 6 inches.
11. A process as claimed in claim 10 wherein for said bond coat the plasma spray power feed rate is preferably 3.2 rpm. and said gas pressure is preferably 40 psi.
12. A process as claimed in anyone of claims 6 to 11 wherein said plasma spray conditions for said top coat of titania comprise :
Current - 700 to 900 amp. Voltage - 33 to 40 VDC Distance of spray gun - 4 to 6 inches.
13. A process as claimed in claim 12 wherein for said top coat the plasma spray power feed rate is preferably 4.5 rpm and said gas pressure is preferably 40 psi.
14. A process as claimed in anyone of claims 6 to 13 wherein the coating material for said Ni-Cr-Al bond coat and TiO2 top coat are powders with granulometric particle size of -100 +375 mesh and -230 mesh respectively.
15. A process as claimed in anyone of claims 6 to 14 wherein the said bond coat of Ni-Cr-Al is obtained of 0.3 to 0.5mm thickness preferably 0.4 mm thickness built up in four runs and the total thickness of coating (the bond coat and top coat) is obtained to be 1.0 to 1.5 mm.
16. A process as claimed in anyone of claims 6 to 15 wherein substrate . to be coated is a blast furnace tuyere.
17. A processes claimed in anyone of claims 6 to 15 wherein said substrate to be coated are blast furnace tuyeres and the tuyeres are mounted on a horizontally turn table and rotated at 3-4 rpm during the coating process.
18. A thermal barrier coating system and a process for carrying out such coating on substrate such as blast furnace tuyeres substantially as hereindescribed and illustrated with reference to the accompanying examples and figures.
A thermal barrier coating system for application on copper/working surfaces exposed to high temperature zones comprising :
a bond coat as a first layer of coat on the substrate obtained of Ni-Cr-A1 alloy comprising 17-22% by wt. Cr, 2-6% by wt A1, and balance Ni, and
a second layer of top coat of titania TiO2 over said bond coat and a process for providing such coating system on substrates. The coat system as above is dense, adherent and mechanically stable and has a strong bonding with the basic substrate. The process of applying such coat is also simple and cost-effective. The coating system is especially suitable for coating of blast furnace tuyeres exposed to high temperature as effective thermal barriers.

Documents:

00140-cal-2000-abstract.pdf

00140-cal-2000-claims.pdf

00140-cal-2000-correspondence.pdf

00140-cal-2000-description (complete).pdf

00140-cal-2000-drawings.pdf

00140-cal-2000-form 1.pdf

00140-cal-2000-form 18.pdf

00140-cal-2000-form 2.pdf

00140-cal-2000-form 3.pdf

00140-cal-2000-letter patent.pdf

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Patent Number

211684

Indian Patent Application Number

140/CAL/2000

PG Journal Number

45/2007

Publication Date

09-Nov-2007

Grant Date

07-Nov-2007

Date of Filing

07-Mar-2000

Name of Patentee

STEEL AUTHORITY OF INDIA LIMITED

Applicant Address

DORANDA, RANCHI 834002, BIHAR, INDIA

Inventors:

#	Inventor's Name	Inventor's Address
1	POPLI ANIL MOHAN	STEEL AUTHORITY OF INDIA LTD., DORANDA RANCHI 834002, BIHAR
2	MISHRA PRADIP KUMAR	SAIL, DURGAPUR STEEL PLANT, WEST BENGAL
3	BHATTACHARYYA AMITABH	SAIL, DORANDA, RANCHI 834002, BIHAR
4	SRIKANTI SRIKANTH	SAIL, DORANDA, RANCHI 834002, BIHAR
5	SUBRAMANIAN ALIAS BALAJI	SAIL, DORANDA RANCHI 834002, BIHAR
6	MISHRA KUNJ BIHARI	SAIL DORANDA RANCHI 834002, BIHAR

PCT International Classification Number

C23C 4/02

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA