Title of Invention

PROCESS FOR CORROSIVE RESISTIVE MULTILAYER COATING TO COMBAT THA CORROSION OF SITVC TANKAGES OF PSLV & GSLV

Abstract

surface preparaton by grit blasting of said SITVC tankage, using 1216 mesh alumina grit with acetone; characterized by applying a bond coat of nickel aluminide on the grit blasted surface of the said tankage by feeding nickel - aluminium powder through oxyacetytene flame in a powder spray gun and spraying onto the said surface placed in front of the spray gun for achieving compatibility between the tankage material and a subsequent main coat to be applied on the said bond coating; appling a main coat of aluminium on said bond coating by wire spray or electric arc spray technique; applying a thin layer of epoxy on the main coat by a spray gun, the bond strength and polarization resistance of the said multiplayer coating being measured to meet the specification of the coating by ekometer adhesion tester method and polarization test method respectively.

Full Text

FIELD OF INVENTION: The invention relates to a process for corrosion resistive multilayer coating to combat the corrosion of SITVC Tankages of Polar Satellite Launch Vehicle (PSLV)and GSLV BACKGROUND OF THE INVENTION: In flying vehicles such as satellite launch vehicles (PSLV & GSLV) and guided missiles, there is a need to correct the flight path of these vehicles if there is deviation from a desired course. This requirement arises due to stringent need for terminal accuracy. One of the methods of flight control is by Thrust vector control in case of PSLV & GSLV. Mechanism of control of thrust vector is by injecting secondary fluid in the primary exhaust portion. Liquid oxidizer such as strontium per chlorate is used for controlling the flight path of PSLV and GSLV rockets. This has certain advantages. Its selection depends upon a number of factors such as mission, cost etc. In PSLV rockets, strontium per chlorate is used as secondary fluid and the tank storing liquid is called as secondary injection thrust vector control (SITVC) tank. Strontium per chlorate being corrosive and explosive in nature is not compatible with the tank material (15CD V6) . So it requires protective layers to overcome this problem. The protective layer consisting of: Nickel aluminium (95:5) bond coat and pure aluminium (99.5 %) as main coat given by thermal spray techniques such as flame and wire spray followed by a thin epoxy sealant layer. The SITVC tankages of PSLV are stored with strontium per chlorate under nitrogen gas pressure. The material of the rocket fuel tank is 15CDV6 steel, which is prone to corrosion in this medium strontium chlorate. After aluminium coating over nickel aluminide bond coat this material (15CD V6 steel) becomes compatible with the above medium. It is therefore an object of the invention to propose a process for corrosion resistive multilayer coating which is compatible with the 15CD V6 steel of SITVC tank. Another object of the invention is to propose a process for corrosion resistance multilayer coating capable of combating a corrosion of SITVC tanks due to storage of fluid called strontium per chlorate. Yet another object of this invention is to propose a process for corrosion resistance multilayer coating having a high polarization resistance. A further object of the invention is to propose a process for corrosion resistance ruuitiplayer coatings, which is applicable to te components of aviation/space vehicles. These and other objects of the invention will be apparent from the ensuing description with reference to the accompanying Figure At the outset of the description, which follows, it is to he understood thai the ensuing description only illustrates a particular form of this invention. However, such a particular form is only an exemplary embodiment and tiie tedinique of the invention is not intended to be taken restrictively. SUMMARY OF THE INVENTION Thus herein provided according to the invention, a process fur currosion resistive multiplayer coating to combat the corrosion of Secondary Injection Thrust Vector Control (SITVC) tankage of Polar Satellite launch (PSIV) vehicle and Geo Synchronous Satellite Launch Vehicle (GSLV) comprising the steps of grit blasting of the tankages by using Al2O3 grit of size 12 16 mesh, the blasted surface is thereafter applied with a bond coat compfising an ailoy uf nickel which achieves a compatibility between the tankage materia! and a subsequent main coat to be applied. The blasted and the bond coated compatible surface is then applied with a main coat comprising aluminium by using a wire spray or an electric arc spray technique, followed by application of a thin layer of epoxy using a paint spraying gun. The bond strength of the multiplayer coating is measured by using an eicometer adhesion tester method BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURE: Fig. 1 shows the major components of a SITVC tank storing strontion per chlorate fluid used for controlling the fligltt patli of PSLV and GSLV locets DETAILED DESCRIPTION OF THE INVENTION: As the first step of the invented ptocess, tiie SITVC tankage of PSLV comprising 15CDV6 steel is cleaned witli acetone and by gat bbstifig witii rotobiasl pressuie blaster type grit blasting equipment", using 12 1G mesh alumina grit The coatings are characterized on the basis of the tnliovving parameters, roating thickness, bond strength, surface roughness result of microstructure and corrosion resistance test COATING PARAMTERS; NICKEL ALUMINIUM COATING ON CYLINDER AND ON END DOMES; (Table Removed) (b) ALUMINIUM COATING ON CYLINDER AND END DOMES (Table Removed) Bond coat of Nickel aluminide is given by powder spray technique in which Ni-Al powder is fed through oxyacetylene flame in a powder spray gun. When the powder meets the flame it melts and then sprayed onto the surface of the 15CDV6 (grit blasted) placed in front of the spray gun. Topcoat of aluminium is given by wire spray technique in which Al wire 3.18 mm in diameter is fed through an oxyacetylene flame and compressed air in a wire spray gun. When the al wire meets the flame it melts and the compressed air atomizes the molten metal which is then sprayed onto the surface of the 15CDV6 (grit blasted and Ni-Al bond coated) placed in front of the spray gun. The com.pressed air also helps in feeding the wire at the required rate. The coating on the cylindrical portion is given by rotation of the shell and by linear movement of the boom. The spray guns are mounted on the boom. The end domes were coated by mounting the spray guns on a micromotor. The tankages were cooled by multiple water spray jets during coating application. Table 1 gives the properties of "Btrontium per chlorate and table 2 gives the composition of 15CDV6 Iffiaterial. Table 3 gives the polarization resistance of coated and tmcoated 15CDV6 samples. TABLE 1. PROPERTIES OF Sr(ClO4)2 (Table Removed) TABLE 2 STANDARD CHEMICAL COMPOSITION-15CDV6 STEEL (Table Removed) After measuring the polarization on the test components strontium per chlorate solution was stored in the tanks for a period of 70 days. The epoxy sealed aluminium coated tank did not show any corrosion. This establishes that the coating is excellent for this application and is compatible with the tank material and the solution. MEASUREMENT OF BOND STRENGTH The bond strength of the Al coating obtained on a 15CDV6 sample with bond coat of Ni-Al was measured by using an Elcometer adhesion tester method. Circular aluminium dollies 20 mm in diameter were cleaned by grit blasting and then degreasing with trichloroethylene. Special grade Araldite was smeared on the base of the dollies, these dollies' 'were then joined to the aluminium coated 15CDV6 samples. The Araldite was cured for 4 8 hrs at room temperature. The aluminium coated sample with the alijm.iniijm dollies was fixed to the tripod assembly of a pulling device. The dollies were then pulled away form the coated sample by using a spring tension system. The load at which the coating became detached from the substrate was recorded. The results are given below: COATING BOND STRENGTH TEST (Table Removed) WE CLAIM : 1. A process for corrosion resistive muliplayer coating in combal the corrosion of SITVC tankage of PSLV and GSIV comprising the step of surface preparation by grit blasting of said SHCVC tankage, using 12-16 mesh alumina gril with acetone ; characterized by applying a bond coat of nickel aluminde on the gril blasted surface of the said tankage by teeding nickel aluminium powder through oxyacetylene flame in a powder spray gun and spraying into ttre said surface placed in front of the spray gun foi achiveving comfjatibility between the tankage materia! and a subsequent main) coat to be applied on the said bond coating; applying a main coat of atutniniurn on said bond colting by when spray or electric arc spray technique, applying a thin layer of epoxy on the main coat by spray gun, the bond strength and polarization resistance of the said multiplayer coating being measured to meet the ^peritiratmn of the c nating hy elrnmeter adhesion lester mthod and polarzation lest method respectively. 2. The process as claimed in claim 1, where in satci step of Grit blasting is done by using rotoblast, presssure type grit bidbtiny equipment using alumina grit of 12-16 mesh 3 the process as riaimerl in riairn 1, where in said step at bond coat application comprises adaptation at a powder spray in a wire spray or an electric arc spray technique 4 The process as claimed in rlairn 1, where in said step of main toat application comprises adaptation of a wire spray or an electric are spray technique. 5. The process as claimed in claim 3, wherein a nickei aluminium alloy powder is used for said bond coat. 6. The process as claimed in claim 4, wherein an aluminium wire is lused for said mam coat 7. The process as claimed in claim 1, wherein coating is given using boom with linear movement and rotation of the tankage 8. The process as claimed in claim 1, wherein the said coating is given on end domes using micromotor 9. The process as claimed in claim 1, wherein the cooling of the tanks during coating is carried out by multiple water spray jets. 10. The process as claimed in claim 1, wherein said epoxy layer is applied to seal the pores arising due to inherent characteristics of said thermally sprayed aluminium coating[[[p 11.

Documents:

1013-del-2004-abstract.pdf

1013-del-2004-claims(cancelled).pdf

1013-del-2004-claims.pdf

1013-del-2004-complete specification (granted).pdf

1013-del-2004-correspondence-others.pdf

1013-del-2004-correspondence-po.pdf

1013-del-2004-description (complete).pdf

1013-del-2004-drawings.pdf

1013-del-2004-form-1.pdf

1013-del-2004-form-19.pdf

1013-del-2004-form-2.pdf

1013-del-2004-form-3.pdf

1013-del-2004-gpa.pdf

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