Inorganic based solid film lubricant composition for coating and method of preparation thereof

Abstract

The present invention relates to an inorganic-based solid film lubricant composition comprising 25 to 35 % w / w of a silicates of metal solution; 1 to 5 % w / w of a graphite; 20 to 30 % w / w of a transition metal sulphides; 5 to 15 % w / w of a metal oxide; and rest being a polar solvent. The present disclosure also relates to a method of preparation of an inorganic-based solid film lubricant composition. The present disclosure also relates to a method for processing inorganic-based solid film lubricant composition coating on a component that reduces the friction in moving parts or sliding surfaces. The present invention in particular is useful in applications related to lander / rover / spacecraft deployment mechanisms which undergo multiple cyclic operations in vacuum and atmospheric conditions (interplanetary) etc. The present invention provides nut factor in the range of 0.13 - 0.15 for the bolt-nut-washer combination with very narrow dispersion (<10%) which is essential for launch vehicle applications where extensive vibration loads are involved.

Description

INORGANIC BASED SOLID FILM LUBRICANT COMPOSITION FOR COATING AND METHOD OF PREPARATION THEREOFFIELD OF INVENTION

[0001] The present disclosure is in the field of production and application of durable inorganic based solid film lubricant coating for reduction of friction in moving parts or sliding surfaces. More particularly, the present disclosure relates to an inorganic based solid film lubricant composition and its method of preparation. The present disclosure also provides a method for processing and extensive testing of solid lubricant. This lubricant composition can find applications in aerospace, automobile sectors and in particular, this is useful in applications related to lander / rover / spacecraft deployment mechanisms, which undergo multiple cyclic operations in vacuum and atmospheric conditions like in interplanetary missions.BACKGROUND OF THE INVENTION

[0002] Background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.

[0003] Solid lubricant currently used cannot meet the demanding stringent end-use requirements of launch vehicles and spacecrafts. Also, current lubricants cannot meet the space endurance & high-cycle requirement of space craft deployment mechanisms which are operated under outer space environmental conditions viz., wide operating temperature 153 to + 393 K, ultra-high vacuum (10‘12torr), resistance to outer space radiation, AO / UV etc.

[0004] For interplanetary missions, lubrication requirements are very stringent to meet the hostile environmental conditions prevailing and any of the existing lubricants cannot meet these requirements. Also, the currently used lubricants provide broad range of dispersion in nut factor value which creates uncertainty in finalizing the torque requirements for launch vehicle integration.

[0005] JP59159898A describes the method for inexpensive solid lubricant having superior antifriction effect for a slider of a pantograph collector for an electric car. It is effective for reducing the wear of a slider and trolley wire. Lubricant should not get scattered or damaged while driving the car. Lubricant is prepared by dispersing graphite and M0S2homogeneously in a mixture of a wax and ethylene vinyl acetate (EVA). The prior art uses organic based binder which is not suitable for application in spacecrafts, which are operated under extreme temperature, ultra-high vacuum & radiation environment and the process does not provide any information related to precise control of lubricant coating thickness.

[0006] JP6551718B2 describes the method which provides the details about metal sulphide coating composition comprises of silicon and fluorine and also discloses the process for depositing a low friction metal sulphide coating over a substrate by vacuum ion or plasma technique. The coating finds application in ball bearings, ball screw, gears, cam shafts, valves, fuel injectors, oil and combustion pumps, cylinders and piston rings, in the automobile and other motor industries. This is highly energy intensive process and require ultrahigh vacuum conditions to deposits the metal sulphide coating.

[0007] US8753417 discloses the method for a composite coating, such as a solid lubricant coating which can be used as a lubricant in a high temperature environment. This is used as a durable, self-lubricating, long life, low friction, oxidation and wear resistant material over a broad range of temperatures, from cryogenic temperatures (e,g., about 88 K) up to at least 1173 K. This composite coating consists of metal fluoride comprising a eutectic mixture of barium and calcium fluorides, silver and further wherein an amount of the metal fluoride in the composite coating ranges from about 1-20% by weight. Invention is energy intensive process and cost of coating is very high. Thin film coating cannot be achieved by this process, which is essential for its application in space craft.

[0008] KA2016034625 includes the method of a coating agent for solid lubrication comprising of a binder and solid lubricant, where in the binder and solid lubricant is coated over the surface of the mechanical material in the form of paint. Solid lubricant used includes molybdenum disulphide, and solvent is graphene. This lubricant can be applied over all kinds of the machined components / surfaces that undergo mechanical touch motion, in the form of the coating and provides lubrication on rubbing. The lubricant coating is not suitable for high temperature application and the patent does not provide the details of lubricant processing and coating.

[0009] JP3109491 A describes the method of production of glass-based lubricant showing softening and fluidity at forging temperature, which is blended with a solid lubricant. The lubricant prevents interruption of lubrication during forging which involves large deformation and thereby reducing the number of processes required. Lubricant compositionincludes graphite, molybdenum disulphide or boron nitride. The application comprises of heating the materials and immersing them in the mixed lubricant. The lubricant is especially effective for the constant-temperature forging of Ti and Ni alloys and it is useful in case of heating of a material such as Ti or Ni alloy which have poor moulding properties to a temperature approximately equal to that of mould and forging.

[0010] US8017668 discloses the composition for dry fdm lubricant and a plain bearing with a sliding layer using the same. This coating is capable of forming a resin fdm having high adhesion to the surfaces of various types of substrates and provides a lubricant fdm that is capable of long-term maintenance with good sliding characteristics. This lubricant has improved flexibility, high conformance ability, reduced cracking in the fdm, and can easily be coated over the substrate. The composition of dry fdm lubricant includes a polymer- alloyed resin binder and the lubricant also includes 1 to 75 % by weight of solid lubricant (M0S2, WS2, PTFE, Graphite, Boron nitride) dispersed in the above resin mixtures. The coating composition is useful for forming a lubrication fdm over the substrate surface, wherein the lubrication fdm is useful as sliding and flexible member.

[0011] US 10836974 describes the method for the solid - state lubricant processed using graphite, grapherie, molybdenum disulphide, tungsten disulphide, hexagonal boron nitride, polytetrafluoroethylene) or other fluoropolymers. The solid - state lubricant particles may be coated over a metallic substrate such as cadmium, lead, tin, zinc, copper, nickel, or alloys containing one or more of these metals. The solid-state lubricant is preferably distributed throughout the coating, solid lubricant processing, coating procedure and rheological properties of lubricant for any specific application.

[0012] U53117932 relates to lubricants that have specific reference to lubricants intended for mechanisms with prevailing temperature and pressure conditions. The materials such as mineral oil, methyl pentachloro butyrate, methyl stearate, stearic acid are used for lubricant processing. This invention also highlights the feature of a lubricant to adhere to the metal without corrosion, under moderate pressures. This lubricant is primarily useful in the case where temperature values are considerably higher than those which could not safely be overstepped with available known products. These lubricants provide the desired seizure resisting characteristic under very high pressures at which the oiliness is not available. This patent doesn't have any information related to rheology of developed lubricant over various substrates including metals, composites.

[0013] CA2885593 includes the invention relates to hard, wear resistant coating vapor deposited over a metallic or non-metallic surface. The invention provides a stable cutting edge consisting of multilayer coating with different architectures on both sides of the blade of rotary tool. The lubricant of this invention comprises of a top wear-resistant, low friction, abrasion and corrosion resistance coating. This coating primarily focusses on reduction of stickiness and friction of the rotating instruments to reduce the torsion fatigue when they come in contact with their counterpart.

[0014] JP2003073609A discloses the method for the production of lubricant fdm having low coefficient of friction, excellent sliding durability and anti-wear quality. Lubricant film formed on the sliding face, maintains friction property over a long period of time. The resin composition contains microcapsule and a solid lubricant with respect to binder resin. The fluid lubricant agent is silicone oil. The resin film contains mixture of amino group resin such as urea, melamine and benzoguanamine. The solid lubricant is a fluorine compound. Preferred properties are achieved for the weight ratio of resin film and fluid lubrication agent in microcapsule between 1.5 : 1 to 0.3 : 1. The microcapsule has a mean particle diameter of 50 pm. The viscosity of silicone oil is adjusted to 20-1000000 cst. The weight ratio of urea and melamine resin in resin mixture is 3:7 to 7:3.

[0015] JP57110979A includes the method for precision parts with solid-lubricated sliding faces provided with a surface layer consisting of a solid lubricant, M0S2, WS2, etc., serving as a sliding face. In this process a ceramic material composed of AI2O3 and Mo (20 wt.%) is ground and then molded into a desired shape by using a press. The molding is then sintered and subjected to a sulphur impregnating treatment using a H2S-N2 mixed gas at 773 K for 2 hours to form a MoS2-lubricating phase. The precision parts have excellent wear resistance because a high performance solid-lubricated sliding face is provided on its surface layer. The parts have higher power transmissive capability and are effectively applicable in the fields of precise machinery.

[0016] US3375729 includes the method for lubrication in bearing or gear boxes in which a still bearing or meshing surface is in contact with cooperating surface of steel or bronze, and aims to provide efficient lubrication under condition of extreme load or high temperature which causes rapid and severe break down of conventional lubricating oils. Suitable lubricating silicate films may be obtained from aqueous solutions of sodium silicate in which the molar ratio of SiC>2 to Na2O is from 1.6: 1 to 4: 1 and from aqueous solutions of potassium silicate in which the molar ratio of SiC>2 to K2O is from 1.4: to 4: 1 mixture ofsuch solution may also be used. The silicate content of the solution may be as high as 60 % by weight, provided the molar ratio of silica to alkali metal oxide or oxides is not too high.

[0017] US3567504 describe the method for processing of polyimide bonded lubricant bearing surfaces. Solid lubricant fdm coating composition is produced by admixing a finely divided solid lubricant material comprising a mixture of molybdenum disulfide (M0S2) and antimony trioxide (Sb20s) into a solution of a poly-pyromellitamic acid and a solvent thereof. In particular, the acid is derived from the reaction between pyromellitic dianhydride (PDA) and either 4,4’ -diaminodiphenyl ether (DADPE) or 4,4"-methylene dianiline (MDA). This invention relates to a lubricant and in particularly to organic bonded solid lubricants. Mixing of ingredients are carried out in a modified vacuum flask. The lubricant is applied through spray method and coating thickness is achieved in the range of 2.54 to 15 pm. The baking of lubricant is carried out for 1 hour at 366 K and further 1 hour at 575 K.

[0018] To overcome the above drawbacks a novel solid film lubricant was developed which can provide consistent nut factor within a narrow dispersion of < 10 %.OBJECTS OF THE INVENTION

[0019] The primary object of the present disclosure is to produce a novel inorganic based solid film lubricant composition which is used for application as a lubricant for fasteners used in launch vehicles, spacecraft (Lander leg, release deployment mechanism, rover hold down release mechanism, solar array deployment mechanism), aerospace industry, automobile and other societal applications.

[0020] Another object of the present disclosure is to provide a method of preparation of an inorganic based solid film lubricant composition.

[0021] Another object of the present disclosure is to develop an economical route for processing a durable inorganic-based solid thin film lubricant and its coating methodology that has good adhesion and imparts lubrication when applied over various substrates (MS, SS alloys, Ti alloys, Aluminium alloys, BeCu, TeCu, Ni alloys, Cd coated fasteners).

[0022] Another object of the present disclosure is to develop a process methodology for the production and coating of inorganic-based solid film lubricant, which provides a consistent nut factor between 0.13 to 0.15 which is suitable for the launch vehicles, friction factor (vacuum COF < 0.1 and Air COF < 0.15) suitable for spacecraft applications.

[0023] Yet another object of the present disclosure is to demonstrate the compatibility of the lubricant when exposed to extreme environmental conditions. The durable coating is also successfully tested and qualified after exposure to conditions such as humidity (RH: 95±5 %; Temperature; 50±2°C; Time: 45 hours). Thermal shock conditions pertaining to spacecraft environment, LOX / LN2 / Methane, Propellant grade Kerosene (ISROSENE), High temperature upto 853 K and water through cold flow test.

[0024] Further object of the present disclosure is to provide a method for processing the said lubricant along with details of equipment used. Detailed process conditions to produce a lubricant grade silicate solution of sodium / potassium / aluminium / calcium / magnesium as individual ingredients or as a mixture is also elaborated.

[0025] Still another object of the present disclosure is to provide details of the graphite / MOS2 with optimized weight ratio which can meet the lubrication requirement under both under atmospheric and vacuum conditions.

[0026] Further object of the present disclosure is to provide details of ratio of oxides to silicates which can meet all the wear requirements in the cyclic operation when applied over various components of spacecraft, launch vehicle and aerospace industry.

[0027] Another object of the present disclosure is to provide a method for mixing sequence to achieve the molecular mixing of graphite, transition metal sulphides, metal oxides and silicates of sodium and potassium solution for wet mixing to achieve an uniform sprayable slurry.

[0028] Still another object of the present disclosure is to provide a method for storing and handling of inorganic solid film lubricant composition for enhanced shelf life.

[0029] Still another object of the present disclosure is to provide a method for surface preparation of components, surface protection of uncoated parts, and handling of components before coating.

[0030] Further the invention is to provide a method of optimized process conditions to achieve a coating thickness between 2 to 25 pm over metallic substrates of various size and shape providing consistent nut factor. The process is also useful to achieve coating thickness beyond 25 pm.

[0031] Further object of the present disclosure is to provide a less energy extensive cure cycle for curing the lubricant coated components made of different alloys (Aluminium, MS, SS, Titanium, BeCu, TeCu, Ni), 15CDV6 with Cd plating and silver coated fasteners.

[0032] Still another object of the present disclosure is to provide a method for air drying and heat curing of the coated components.

[0033] Still a further object of the present disclosure is to highlight the method for storage and handling of coated components to ensure the coating durability for a minimum period of 12 years.

[0034] Yet another object of the present disclosure is that lubricant coated component can be reused multiple times without any functional performance degradation.

[0035] Another object of the present disclosure is that the coating meets the typical requirements of spacecraft deployment mechanisms including thermal cycling (208 to 398 K) for 100 cycles, radiation resistance, AO / UV resistance, outgassing, and ultra-high vacuum.

[0036] Yet another objective of the present disclosure is to demonstrate the coating as protective layer against heat, corrosion, between the mating parts of coated components.SUMMARY OF THE INVENTION

[0037] This summary is provided to introduce a selection of concepts in a simplified form that are further described below in Detailed Description section. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.

[0038] Accordingly, in one aspect, the present disclosure relates to an inorganic based solid film lubricant composition comprising: 25 to 35 % w / w of a silicates of metal solution; 1 to 5 % w / w of a graphite; 20 to 30 % w / w of a transition metal sulphides; 5 to 15 % w / w of a metal oxide; and rest being a polar solvent.

[0039] Another aspect of the present disclosure relates to a method of preparation of an inorganic based solid film lubricant composition comprising: a) processing by purification of silica followed by drying to obtain a purified dried silica; b) dissolving metal hydroxide pellets in the water to obtain a metal hydroxide solution; c) adding purified dried silica in the metal hydroxide solution to obtain a metal silicate solution; d) mixing of 20 to 30 % w / w of a transition metal sulphide, 5 to 15 % w / w of a metal oxide and 1 to 5 % w / w of a graphiteto obtain a mixture; and e) adding 25 to 35 % w / w of a metal silicate solution of step c) and a polar solvent in the mixture of step d) in a ball mill to obtain an inorganic based solid fdm lubricant composition.

[0040] Still another aspect of the present disclosure relates to a method for processing inorganic-based solid fdm lubricant composition coating on a component comprising: taking a spray gun that is connected to a pneumatic source through a suitable hose; mounting a component to be coated in a fixture; applying the inorganic based solid film lubricant composition as defined above by the spray gun on the component in a lubricant coating booth to obtain a coated component; and curing the coated component under condition to obtain a cured inorganic-based solid film lubricant composition coated component.

[0041] Various objects, features, aspects and advantages of the present disclosure will become more apparent from the following detailed description of preferred embodiments, along with the accompanying drawing figures in which like numerals represent like features.BRIEF DESCRIPTION OF THE DRAWINGS

[0042] The accompanying drawing(s) are included to provide a further understanding of the present disclosure and are incorporated in and constitute a part of this specification. The drawings illustrate exemplary embodiments of the present disclosure and, together with the description, serve to explain the principles of the present disclosure. The diagrams are for illustration only, which thus is not a limitation of the present disclosure.

[0043] Figure 1 illustrates the flow chart for the production and coating of inorganic based solid film lubricant according to an embodiment of the invention.

[0044] Figure 2 illustrates the silicate based solid film lubricant.

[0045] Figure 3 illustrates the inorganic based solid film lubricant coated fasteners a) bolt, b) washers, c) nuts, d) guide rod, e) spring guide, f) studs, g) U pin, h) spherical bearing and i) MFP shaft.DETAILED DESCRIPTION OF THE INVENTION

[0046] The following is a detailed description of embodiments of the disclosure. The embodiments are in such detail as to clearly communicate the disclosure. However, the amount of detail offered is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternativesfalling within the spirit and scope of the present disclosure as defined by the appended claims.

[0047] All publications herein are incorporated by reference to the same extent as if each individual publication or patent application were specifically and individually indicated to be incorporated by reference. Where a definition or use of a term in an incorporated reference is inconsistent or contrary to the definition of that term provided herein, the definition of that term provided herein applies and the definition of that term in the reference does not apply.

[0048] Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

[0049] In some embodiments, numbers have been used for quantifying weights, percentages, ratios, and so forth, to describe and claim certain embodiments of the invention and are to be understood as being modified in some instances by the term “about.” Accordingly, in some embodiments, the numerical parameters set forth in the written description and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by a particular embodiment. In some embodiments, the numerical parameters should be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of some embodiments of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as practicable.

[0050] The numerical values presented in some embodiments of the invention may contain certain errors necessarily resulting from the standard deviation found in their respective testing measurements.

[0051] Unless the context requires otherwise, throughout the specification which follows, the word “comprise” and variations thereof, such as “comprises” and “comprising” are to be construed in an open, inclusive sense that is as “including, but not limited to.”

[0052] As used in the description herein and throughout the claims that follow, the meaning of “a,” “an,” and “the” includes plural reference unless the context clearly dictates otherwise. Also, as used in the description herein, the meaning of “in” includes “in” and “on” unless the context clearly dictates otherwise.

[0053] The recitation of ranges of values herein is merely intended to serve as a shorthand method of referring individually to each value falling within the range. Unless otherwise indicated herein, each individual value is incorporated into the specification as if it were individually recited herein. Furthermore, the ranges defined throughout the specification include the end values as well, i.e., a range of 1 to 10 implies that both 1 and 10 are included in the range. For the avoidance of doubt, the applicant shall be entitled to any equivalents according to applicable law.

[0054] All methods described herein can be performed in a suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples or exemplary language (e.g., “such as”) provided with respect to certain embodiments herein is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention otherwise claimed. No language in the specification should be construed as indicating any non-claimed element essential to the practice of the invention.

[0055] Groupings of alternative elements or embodiments of the invention disclosed herein are not to be construed as limitations. Each group member can be referred to and claimed individually or in any combination with other members of the group or other elements found herein. One or more members of a group can be included in, or deleted from, a group for reasons of convenience and / or patentability. When any such inclusion or deletion occurs, the specification is herein deemed to contain the group as modified.

[0056] The description that follows, and the embodiments described therein, are provided by way of illustration of an example, or examples, of particular embodiments of the principles and aspects of the present disclosure. These examples are provided for the purposes of explanation, and not of limitation, of those principles and the disclosure.

[0057] It should also be appreciated that the present disclosure can be implemented in numerous ways, including as a system, a method or a device. In this specification, these implementations, or any other form that the invention may take, may be referred to asprocesses. In general, the order of the steps of the disclosed processes may be altered within the scope of the invention.

[0058] The headings and abstract of the invention provided herein are for convenience only and do not interpret the scope or meaning of the embodiments.

[0059] The following discussion provides many example embodiments of the inventive subject matter. Although each embodiment represents a single combination of inventive elements, the inventive subject matter is considered to include all possible combinations of the disclosed elements. Thus, if one embodiment comprises elements A, B, and C, and a second embodiment comprises elements B and D, then the inventive subject matter is also considered to include other remaining combinations of A, B, C, or D, even if not explicitly disclosed.

[0060] The term “or”, as used herein, is generally employed in its sense including “and / or” unless the content clearly dictates otherwise.

[0061] Various terms are used herein to the extent a term used is not defined below, it should be given the broadest definition persons in the pertinent art have given that term as reflected in printed publications and issued patents at the time of filing.

[0062] The present disclosure describes the method for processing and extensive testing of durable inorganic based solid film lubricant composition, produced for the reduction of friction in moving parts or sliding surface. This lubricant coating acts as a protective layer between the matting surfaces and also shows excellent fire retardant and corrosion resistance characteristics during operation. This lubricant composition can find application in aerospace and automobile sectors and in particular this is useful in applications related to lander / rover / spacecraft deployment mechanisms which undergo multiple cyclic operations in vacuum and atmospheric conditions (Interplanetary) etc.

[0063] An embodiment of the present disclosure provides an inorganic based solid film lubricant composition comprising: 25 to 35 % w / w of a silicates of metal solution; 1 to 5 % w / w of a graphite; 20 to 30 % w / w of a transition metal sulphides; 5 to 15 % w / w of a metal oxide; and rest being a polar solvent.

[0064] In an embodiment, the metal is selected from a group consisting of sodium, potassium, aluminium, calcium, magnesium and combination thereof.

[0065] In an embodiment, the silicates of metal solution are present in the lubricant composition in the range of 25 to 34 % w / w, or 25 to 33 % w / w, or 25 to 32 % w / w, or 25 to 31 % w / w, or 25 to 30 % w / w, or 25 to 29 % w / w, or 25 to 28 % w / w, or 25 to 27 % w / w, or25 to 26 % w / w.

[0066] In an embodiment, the silicates of metal solution are sodium silicate solution with SiC>2 / Na2O ratio in the range of 1:3 to 3:5.

[0067] In an embodiment, the graphite is present in the lubricant composition in the range of 1 to 4 % w / w, or 1 to 3 % w / w, or 1 to 2 % w / w.

[0068] In an embodiment, the transition metal sulphides is selected from a group consisting of molybdenum disulfide (M0S2), tungsten disulfide (WS2), iron sulfide ^6283), copper sulfide (CU2S), nickel sulfide (NiS) and combination thereof.

[0069] In an embodiment, the transition metal sulphides is present in the lubricant composition in the range of 21 to 29 % w / w, or 22 to 28 % w / w, or 23 to 27 % w / w, or 24 to26 % w / w.

[0070] In an embodiment, the metal oxide is selected from a group consisting of antimony(III) oxide (Sb2C>3), zinc oxide (ZnO), lead oxide (PbO) and combination thereof.

[0071] In an embodiment, the metal oxide is present in the lubricant composition in the range of 6 to 14 % w / w, or 7 to 13 % w / w, or 8 to 12 % w / w, or 9 to 11 % w / w.

[0072] In an embodiment, the polar solvent is selected from a group consisting of water, ethanol, methanol and combination thereof.

[0073] In an embodiment, the inorganic based solid film lubricant composition provides coefficient of friction in air < 0.15 and under vacuum < 0.1 (Falex Pin Method as per ASTM D2625, Vacuum Level: 10'12Torr and mating surfaces SS-alloys, Ti Alloys, Al Alloys) for components related to aerospace systems.

[0074] In an embodiment, the inorganic based solid film lubricant composition is resistant to outer space radiation, AO / UV, and also compatible with ultra-high vacuum 10'12Torr, and is used at wide operating temperature 77 K to 853 K in air and upto 1273 K in vacuum.

[0075] In an embodiment, the inorganic based solid film lubricant composition shows comparable tribological performance with various metallic substrates viz,, MS, SS alloys, aluminium alloys, titanium alloys, TeCu, BeCu, Cd coated 15CDV6, Silver coated fasteners.

[0076] In an embodiment, the inorganic based solid film lubricant composition is compatible with propellant grade kerosene like ISROSENE, liquid oxygen, methane, etc. on exposure.

[0077] In an embodiment, the inorganic based solid fdm lubricant composition can meet the requirement of cyclic operation in spacecraft / lander / rover mechanism.

[0078] In an embodiment, the inorganic based solid fdm lubricant composition provides good adhesion (As per ASTM D2510) over various substrates without subjecting them to an energy intensive surface preparation.

[0079] In an embodiment, the inorganic binder solution with a weight ratio of metal oxide / silicate in the range of 1:3 to 3:5, wherein lubricant to binder ratio is maintained relatively high to achieve better structural integrity of coating.

[0080] In an embodiment, the lubricant is processed using various equipment such as Yttria stabilised Zirconia Jar and balls, Ball mill, temperature controlled reaction vessel, lubricant storage tank, lubricant mixing system, spray gun, lubricant booth and air oven.

[0081] In an embodiment, the mixer is made of ceramic material for mixing of individual ingredients in a sequential manner. Yttria stabilized zirconia jar and balls compatible with the lubricant ball milling operation is used, wherein ball milling is carried out after mixing in ceramic mixer at the controlled speed of minimum 100 RPM. The Yttria stabilized zirconia Jar is filled with ceramic balls approximately 2 / 3 of the volume of jar.

[0082] Another embodiment of the present disclosure provides a method of preparation of an inorganic based solid film lubricant composition comprising: a) processing by purification of silica followed by drying to obtain a purified dried silica; b) dissolving metal hydroxide pellets in the water to obtain a metal hydroxide solution; c) adding purified dried silica in the metal hydroxide solution to obtain a metal silicate solution; d) mixing of 20 to 30 % w / w of a transition metal sulphide, 5 to 15 % w / w of a metal oxide and 1 to 5 % w / w of a graphite to obtain a mixture; and e) adding 25 to 35 % w / w of a metal silicate solution of step c) and a polar solvent in the mixture of step d) in a ball mill to obtain an inorganic based solid film lubricant composition.

[0083] In an embodiment, the condition of step c) includes temperature in the range of 423 to 473 K for the preparation of metal silicate solution.

[0084] In an embodiment, the mixing in step d) by ceramic mixture is carried out at a speed in the range of 50 to 150 RPM, preferably at 100 RPM.

[0085] In an embodiment, the inorganic based solid fdm lubricant composition is stored in a container at a temperature in the range of 283 to 288 K. The storage container is preferably made of plastic, wherein the storage conditions are preferably humidity controlled.

[0086] Still another embodiment of the present disclosure provides a method for processing inorganic-based solid film lubricant composition coating over a component comprising: a) taking a spray gun that is connected to a pneumatic source through a suitable hose; b) mounting a component to be coated in a fixture; c) applying the inorganic based solid film lubricant composition as defined above by the spray gun on the component in a lubricant coating booth to obtain a coated component; and d) curing the coated component under condition to obtain a cured inorganic-based solid film lubricant composition coated component.

[0087] In an embodiment, the spray gun has a nozzle diameter in the range of 1.2 mm to 2.0 mm to achieve desired coating thickness over various substrates retaining excellent bondability.

[0088] In an embodiment, the pneumatic source is selected from nitrogen or argon.

[0089] In an embodiment, the pressure of coating is in the range of 2 to 4 Bar (g).

[0090] In an embodiment, the condition includes cured in air at a temperature in the range of 73 K to 473 K for a period in the range of 15-20 min followed by curing in a hot oven at a temperature in the range of 373 K to 473 K for a period in the range of 2 to 4 hrs.

[0091] In an embodiment, the lubricant coating booth is customized coating chamber is capable of providing clean and fresh air during the coating process which is critical to achieve contaminant free thin film coating for components used in outer space environments.

[0092] In an embodiment, the lubricant coating is resistance to corrosion, water and fire.

[0093] In an embodiment, the lubricant coating is carried out in controlled conditions to avoid any contamination, wherein the spray gun is used for coating of the components mounted in a suitable fixture, wherein air pressure, standoff distance and number of passes are optimised to achieve desired coating thickness.

[0094] In an embodiment, the temperature uniformity achieved in air oven is maintained in the range of ± 3 K to ensure good bondability of lubricant over various substrate.

[0095] In an embodiment, the lubricant coating is applied over the components selected from a group consisting of studs, bolts, screws, nuts, shaft with splines, washers, U-pins, latches, spring guides, guide rods in a controlled thickness.

[0096] In an embodiment, the lubricant coating provides consistent value of COF in air and vacuum after exposure to various environmental conditions such as humidity (RH: 95±5 %; Time: 45 hours), thermal shock pertaining to spacecraft environment, LOX / LN2, Kerosene vapour, Gamma radiation dosage (100 Mrad), High temperature up to 853 K in air and 1273 K in vacuum and water through cold flow test.

[0097] In an embodiment, the lubricant coating provides consistent nut factor after subjecting to sinusoidal cyclic frequency of 30 Hz at 11.7 mm DAg level for 30000 cycles as per ISO 5858.

[0098] In an embodiment, the lubricant coating provides a constant coefficient of friction in air and vacuum after exposure to thermal shock between 208 K for 5 minutes, followed by temperature in the range of 293 K at 5 minutes and further at 398 K for 5 minutes for 100 cycles.

[0099] In an embodiment, the lubricant coating meets the spacecraft outgassing requirements (TML < 1 % & CVCM < 0. 1%) as per ASTM E595.

[0100] In an embodiment, the lubricant coating provides excellent adhesion with no peel-off when tested as per the ASTM D2510 over almost all the metal substrates without having any energy intensive surface preparation of components.

[0101] In an embodiment, the inorganic lubricant coating imparts COF< 0.15 in air and COF < 0.1 over all metallic substrates and consistent nut factor in the narrow range of 0.13 to 0.15 with dispersion < 10 %.

[0102] The present disclosure relates to the system and method for the synthesis and coating of inorganic -based solid film lubricant through a simple and cost-effective route. Inorganic-based solid film lubricant is processed with transition metal sulphides, oxides, and silicates of sodium and potassium. Water and sodium silicate solution is added in the dry mix powder in a sequential manner to ensure proper mixing of the ingredients.

[0103] The system further comprises of a spray gun made of stainless steel with nozzle diameter of gun is 1.2 to 2.0 mm for application of coating. Coating of lubricant is carried out in a clean lubricant booth which provides continuous dust free fresh air circulation during the entire coating process. The silicate based solid film lubricant durable coating is used for deployment mechanisms of space craft. It is applied over fasteners used in launch vehicle and also used as a heat-protective coating in the mating components in launch vehicle and other aerospace systems.

[0104] In an embodiment, the method for the synthesis involves the following steps.A. Sodium silicate solution preparation

[0105] Commercially available silica powder is used as raw material after series of purification process. Purified silica powder is dried in air oven at temperature in a sequential manner from ambient to 523 K. Sodium hydroxide pellets is used to prepare the sodium hydroxide solution. Speed of Stirrer is maintained in the range of 200-400 RPM. Lubricant grade sodium silicate solution is prepared with SiO2 / Na2O 1:3 to 3:5. Sodium hydroxide solution, silica powder and distilled water is mixed in a glass reactor at controlled temperature to process lubricant grade sodium silicate solution. Ratio of SiO2 / Na2O is critical for better adhesion and the equipment can handle highly basic medium at high temperature.

[0106] The processing of sodium silicate solution requires use of simple process equipment and instrument such as Glass reactor with temperature controller having stirrer with compatible material of construction, Silica purification unit, Filtration unit drying unit, and air oven for drying of purified silica.

[0107] The merit of the process includes maintaining the ratio of SiO2 / Na2O, which is critical for better adhesion over the coated components / substrates. The selected process equipment is capable of handling highly basic medium at high temperatures.B. Lubricant processing

[0108] Ceramic mixer is used for mixing of dry ingredients such as transition metal sulphides like MoS2, WS2etc., oxides, graphite, and silicates of sodium and potassium along with polar solvent. Ball mill is used for further mixing and grinding of lubricant slurry.

[0109] The processing of lubricant requires use of simple process equipment and instrument such as Ceramic mixer of 3-4 L capacity, which is used for dry and wet mixing of lubricantingredients. Duration of dry mixing of powders and wet nix is optimized to achieve uniform lubricant slurry. Yttria stabilized zirconia Jar and balls are used for ball milling operation of lubricant slurry to ensure no metallic impurities conies in contact with the lubricant. Speed of ball milling process is optimized in the range of 100-200 RPM. Duration of ball milling operation is optimized to ensure no settling of lubricant ingredients.

[0110] The merits include achieving uniform slurry with consistent rheological parameters such as viscosity, ford cup viscosity, etc. Ensuring homogeneous dispersion of additives such as graphite to meet lubricant requirement effectively in air and vacuum. Optimization of metal oxide to Sulphide ratio in such a way to ensure the cyclic requirement of spacecraft and reusability in launch vehicle, Optimization of binder to lubricant ratio is optimized in such a way to meet the adhesion requirement in most of metallic substrates. Lubricant slurry with consistent solid content and constant density is achieved after each batch of processing.C. Lubricant coating and curing

[0111] Specialized spray gun with nozzle opening between 1.2 mm to 2.0 mm is used for coating process. SS-304 spray gun is used for lubricant coating. Spray gun is connected to N2 / Ar source through a suitable hose and the components to be coated are mounted in a fixture. Coating of components is carried out in a lubricant coating booth. Coated components are cured in air for a time duration of 15-20 min Followed by oven curing at a temperature between 373 K to 473 K. Suitable metallic fixtures are used for coating different components.

[0112] The lubricant coating and curing process requires use of simple process equipment and instrument such as Spray gun connected with suitable pneumatic source, Hot air oven used for the curing process, which maintains the temperature uniformity within ± 3 K and lubricant coating booth which maintains dust free fresh air.

[0113] The merits of the process include optimized lubricant coating and curing parameters to achieve the coating thickness within a narrow dispersion range. Uniform coating thickness can be achieved even for lower coating thickness up to 2 microns to meet specific requirements for space systems. Coating and curing of the process are optimized in such a way as to meet the adhesion requirement for almost all metallic substrates. Developed coating process is suitable for coating of components size ranging from millimetre to meter. Developed coating process is also suitable for flat surface, cylindrical surfaces, threaded fasteners, etc.

[0114] While the foregoing describes various embodiments of the disclosure, other and further embodiments of the disclosure may be devised without departing from the basic scope thereof. The invention is not limited to the described embodiments, versions or examples, which are included to enable a person having ordinary skill in the art to make and use the invention when combined with information and knowledge available to the person skilled in the art.EXAMPLES

[0115] The present invention is further explained in the form of the following examples. However, it is to be understood that the following examples are merely illustrative and are not to be taken as limitations upon the scope of the invention.Example 1(A) Inorganic based solid film lubricant composition

[0116] Different inorganic based solid fdm lubricant compositions are given in Table 1.

[0117] Table 1: Different inorganic based solid fdm lubricant compositions of the present invention.(B) Method of preparation of inorganic based solid film lubricant composition

[0118] The inorganic-based solid fdm lubricant compositions were prepared by weighing accurate amounts of the ingredients as given in Table 1. The process steps (a-c) as given above in detail. The transition metal sulphide, a metal oxide and a graphite were mixed in a ceramic mixture at a speed of 100 RPM to obtain a mixture. The metal silicate solution and a polar solvent were added in the mixture in a ball mill to obtain an inorganic-based solid fdm lubricant composition.Example 2 Tribological properties of solid film lubricant

[0119] It has been observed that all the tribological properties of the Example 1 fall within the standard range. The lubricant coating meets the spacecraft outgassing requirements(TML < 1 % & CVCM < 0.1%) as per ASTM E595. Example 1 showed TML in between 0.65 to 0.72 and CVCM in between 0.01 to 0.07 and consistent nut factor in the narrow range 0.13 to 0.15 with dispersion < 10 % which are within the standard range as shown in Table 2. Thus, the present composition falls under the spacecraft outgassing requirements.

[0120] Table 2: Results of tribological properties of Example 1.

[0121] The foregoing examples are merely illustrative and are not to be taken as limitations upon the scope of the invention. Various changes and modifications to the disclosed embodiments will be apparent to those skilled in the art. Such changes and modifications may be made without departing from the scope of the invention.

Claims

We Claim:

1. An inorganic-based solid film lubricant composition comprising:25 to 35 % w / w of a silicates of metal solution;1 to 5 % w / w of a graphite;20 to 30 % w / w of a transition metal sulphides;5 to 15 % w / w of a metal oxide; and rest being a polar solvent.

2. The inorganic based solid film lubricant composition as claimed in claim 1, wherein the metal is selected from a group consisting of sodium, potassium, aluminium, calcium, magnesium and combination thereof.

3. The inorganic based solid film lubricant composition as claimed in claim 1, wherein the silicates of metal solution is sodium silicate solution with SiC>2 / Na2O ratio in the range of 1:3 to 3:5.

4. The inorganic based solid film lubricant composition as claimed in claim 1, wherein the transition metal sulphides is selected from a group consisting of molybdenum disulfide (M0S2), tungsten disulfide (WS2), iron sulfide ^6283), copper sulfide (CU2S), nickel sulfide (NiS) and combination thereof.

5. The inorganic based solid film lubricant composition as claimed in claim 1, wherein the metal oxide is selected from a group consisting of Antimony(III) oxide (Sb2C>3), Zinc oxide (ZnO), Lead Oxide (PbO) and combination thereof.

6. The inorganic based solid film lubricant composition as claimed in claim 1, wherein the polar solvent is selected from a group consisting of water, ethanol, methanol and combination thereof.

7. A method of preparation of an inorganic based solid film lubricant composition comprising: a) processing by purification of silica followed by drying to obtain purified dried silica; b) dissolving metal hydroxide pellets in the water to obtain a metal hydroxide solution; c) adding purified dried silica in the metal hydroxide solution to obtain a metal silicate solution;d) mixing of a 20 to 30 % w / w of a transition metal sulphide, 5 to 15 % w / w of a metal oxide and 1 to 5 % w / w of a graphite to obtain a mixture; and e) adding 25 to 35 % w / w of a metal silicate solution of step c) and a polar solvent in the mixture of step d) in a ball mill to obtain an inorganic based solid film lubricant composition.

8. The method as claimed in claim 7, wherein the mixing in step d) by ceramic mixture is carried out at a speed in the range of 50 to 150 RPM.

9. The method as claimed in claim 7, wherein the inorganic based solid film lubricant composition is stored in a container at a temperature in the range of 283 to 288 K.

10. A method for processing inorganic-based solid film lubricant composition coating over a component comprising: a) taking a spray gun that is connected to a pneumatic source through a suitable hose; b) mounting a component to be coated in a fixture; c) applying the inorganic based solid film lubricant composition as claimed in claim 1 by the spray gun over the component in a lubricant coating booth to obtain a coated component; and d) curing the coated component under condition to obtain a cured inorganic -based solid film lubricant composition coated component.

11. The method as claimed in claim 10, wherein the spray gun has a nozzle diameter in the range of 1.2 mm to 2.0 mm to achieve desired coating thickness over various substrates retaining excellent bondability.

12. The method as claimed in claim 10, wherein the pneumatic source is selected from nitrogen or argon.

13. The method as claimed in claim 10, wherein the condition includes cured in air at a temperature in the range of 73 K to 473 K for a period in the range of 15-20 min followed by curing in a hot oven at a temperature in the range of 373 K to 473 K for a period in the range of 2 to 4 hrs.

14. The method as claimed in claim 10, wherein the lubricant coating booth is customized coating chamber is capable of providing clean and fresh air during the coating process whichis critical to achieve contaminant free thin film coating for components used in outer space environments.

15. The method as claimed in claim 10, wherein the lubricant coating is resistance to corrosion, water and fire.

16. The method as claimed in claim 10, wherein the lubricant coating is carried out in controlled conditions to avoid any contamination, wherein the spray gun is used for coating of the components mounted in a suitable fixture, wherein air pressure, standoff distance and number of passes are optimised to achieve desired coating thickness.

17. The method as claimed in claim 10, wherein the temperature uniformity achieved in air oven is maintained in the range of ± 3 K to ensure good bondability of lubricant over various substrate.

18. The method as claimed in claim 10, wherein the lubricant coating is applied over the components selected from a group consisting of studs, bolts, screws, nuts, shaft with splines, washers, U-pins, latches, spring guides, guide rods in a controlled thickness.

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