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THERMAL / METAL SPRAY SPECIALIST (Arc-Spray, Flame-Spray, HVOF, Plasma ) with materials such as : Ceramic, Tungsten, Titanoum, Babbit, Aluminium, Chrome, Nickel, Cobalt, Molybdenum, Stainless Steel, Copper, Tin, Bronze etc, all kind of solid materials can be sprayed.
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Brush Plating in-situ job for rolls, cylinder etc.
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Hard-Chrome Coating Job for cylinders, rolls, rods & rotating parts etc.
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Machining & Grinding Job, making new-critical & complicated parts.
INDUSTRIAL APPLICATIONS :
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OTHER APPLICATIONS:
In Aircraft component repair :-
Most major aircraft engine manufacturers specify the arc spray process for repairs of many aircraft engine components. Coatings are applied to various components for dimensional restoration, hot temperature erosion resistance, and as bond coats.
In Electrical conductivity and resistivity
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Arc sprayed aluminum, tin, zinc and other materials are used in applications requiring good electrical conductivity. Aluminum coating on metal oxide varistors.
In wear resistance
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Cored wire technology has broadened the spectrum of arc spray application with cored wires, it is possible to produce coatings with excellent sliding wear resistance as well as abrasion resistance
What Is Thermal / Metal Spray?
| Examples of Materials That Can be Deposited with Thermal Spray |
| Metals |
| Alloys |
| Ceramics |
| Cermets |
| Polymers |
| Graded Structures |
| Composites |
| Layered Coatings |
| High-density or Engineered Porosity |
The basic process variations of thermal spraying are the spray feed materials, the method of heating, and the method of propelling the materials to the substrate. The feed materials used are in the form of powder, wire, rod, or cord.
Why Use Thermal Spray?
Thermal spray processes are easy to use, cost little to operate, and have attributes that are beneficial to applications in almost all industries. The benefits are typically lower cost, improved engineering performance, and/or increased component life.
A substantial cross section, if not all, of the world industries have coating applications for a wide range of needs including restoration and repair; corrosion protection; wear protection of many types, such as abrasion, adhesive, fretting and erosion; thermal barriers or conductors; electrical circuits or insulators; near-net-shape manufacturing; seals; engineered emmisivity, abradable coatings; decorative purposes; and more.
Surface Preparation
| Surface Preparation Techniques | |
| Cleaning/Degreasing | Surface Roughening |
| Vapor Degreasing | Abrasive Grit Blasting |
| Vapor Blasting | Wet Abrasive Blasting |
| Acid Pickling | Machining/Threading |
| Oven Baking | Water Jet Blasting |
| Wire Brushing | |
| Exothermic Self-Bonding Primer Coatings | |
Proper substrate surface preparation prior to coating or bond coat application is a critical step that influences the bond strength and the adhesion of the coating to the substrate. Typically a good surface preparation process cleans the surface to eliminate contamination that will inhibit the coating to substrate bonding and roughens the surface to provide minute asperities or irregularities to enhance coating adhesion and greater effective surface area. Abrasive grit blasting is the most commonly used surface preparation method. The process involves the impingement of abrasive particles to roughen, breakup oxides, and remove other contaminants from the surface.
| Types of Thermal Spray Processes | |
| Heat Source: Flame Combustion | Heat Source: Electrical |
| Low Velocity Flame Spraying | Plasma Spraying |
| High Velocity Flame Spraying (HVOF) | Wire Arc Spraying |
| Detonation (D-Gun) | Induction Plasma Spraying |
| Cold Spray | |
Thermal Spray Process
According to the method of heat generation, thermal spray processes may be categorized into two basic groups; combustion and electrical.
Flame Combustion
Low velocity flame spray , the simplest thermal spray process, can be used to deposit material supplied as wire, rod, or powder. A low velocity flame spray gun is operated by feeding a fine powder or wire into a combustion flame. This flame is typically acetylene-oxygen, because of the higher temperatures it permits; but other fuel gases such as propane, natural gas, hydrogen, or methyl-acetylene can be used as well. The combustion flame melts the powder or wire tip and propels the molten particles to the substrate to form the coating.
The stream of burning gas carries the particles, molten and atomized, to the work piece or substrate. Flame spray guns are inexpensive, light, and compact. Compared to other coating methods, however, particle velocities and temperatures are low, producing more porous, lower density coatings of lower bond strength. In the simplest form of flame spraying, oxygen aspirates powder from a canister attached to the flame gun and injects it into the oxyfuel flame. In some flame spray guns, pressurized inert gas from remote powder feeders carry the powders into the flame. In this type gun, pressurized air or inert gas increases the particle velocity for higher bond strength and coating density while cooling the substrate. The inert gas also helps in another way; it reduces the oxidation of the particles and the substrate. When wire or rod is the spray feed material, motor-driven gears draw, push, or pull the material through the gun into the combustion flame for melting. Compressed gas, usually air, flows around the flame, atomizing the material as it melts at the tip of the wire or rod, propelling the molten or semi-molten material onto the substrate or workpiece. Powder flame spray can be used to deposit any material that melts below the flame temperature (4,000° to 5,000° F). Wire flame spray can use any feed material, usually metals that can be drawn into wire. Ceramic formed into rod can be sprayed with guns for wire spray, as can powder-filled plastic cord. Typically, flame spray is used to deposit coatings of low melting metals, low melting metal alloys, self-fluxing alloys, self fluxing/carbide blends and various plastics.
The state-of-the-art High velocity oxy-fuel (HVOF) process uses extremely high kinetic energy and controlled thermal energy output to produce low porosity coatings with high bond strength, fine as-sprayed surface finishes and low residual stress. HVOF combustion spray guns combusts kerosene, propylene, propane, or hydrogen fuel and oxygen under pressure and accelerates the combusted gas streams down a confined, cooled tube. Powders are fed axially into the nozzle with carrier gases where the particles are entrained with the confined, high-pressure combustion gases. The gases undergo rapid expansion through a restricted nozzle when combusted with oxygen to accelerate the molten particles to supersonic velocities (up to 4,500 ft/sec). The high gas acceleration has been shown to increase coating density, increase coating adhesion, and produce finer coating oxide inclusion distributions. The low residual stress allows for greater coating thickness, lower porosity, lower oxide content, and higher coating adhesion.
In detonation flame (D-gun) spraying the energy of explosions of oxygen-fuel gas mixtures, rather than a steadily burning flame, is used to melt and propel powdered materials onto the surface of the substrate. The resulting deposit is hard, dense, and tightly bonded. D-Gun coatings have been used with carbides and metal alloys in order to develop unique coating systems.
Electrical
Plasma spraying processes typically use microwave, electromagnetic RF or induction-coupled fields and AC or DC arcs as energy sources for thermal plasmas. Material in the form of powder is injected into a very high temperature plasma flame, where it is rapidly heated and accelerated to a high velocity. The hot material impacts on the substrate surface and rapidly cools forming a coating.
DC-arc plasma spray uses an inert, high-temperature jet created by heating inert gases in a confined electric arc. The hot gas jet created by the arc/plasma column expands, entrains the coating particles, heats the particles, and accelerates the molten or semi-molten particles to the substrate to form a coating. The high degree of melting and relatively high particle velocities provide good deposit densities and bond strengths. Controlled atmosphere plasma spraying using inert gas chambers or inert gas shrouds have reduced the oxide inclusions and improved coating density. Low-pressure (LPPS) or vacuum (VPS) plasma spraying processes have produced clean coatings with no oxide inclusions, extremely high densities, and significantly improved bond strengths. The plasma spray process carried out correctly is called a "cold process" (relative to the substrate material being coated) as the substrate temperature can be kept low during processing avoiding damage, metallurgical changes and distortion to the substrate material.
The plasma spray gun comprises a copper anode and tungsten cathode, both of which are water-cooled. Plasma gas (argon, nitrogen, hydrogen, helium) flows around the cathode and through the anode which is shaped as a constricting nozzle. The plasma is initiated by a high voltage discharge that causes localized ionization and a conductive path for a DC arc to form between cathode and anode. The resistance heating from the arc causes the gas to reach extreme temperatures, dissociate and ionize to form plasma. The plasma exits the anode nozzle as a free or neutral plasma flame (plasma which does not carry electric current) which is quite different to the plasma transferred arc coating process where the arc extends to the surface to be coated. When the plasma is stabilized ready for spraying the electric arc extends down the nozzle, instead of shorting out to the nearest edge of the anode nozzle. This stretching of the arc is due to a thermal pinch effect. Cold gas around the surface of the water-cooled anode nozzle being electrically non-conductive constricts the plasma arc, raising its temperature and velocity. Powder is fed into the plasma flame most commonly via an external powder port mounted near the anode nozzle exit. The powder is so rapidly heated and accelerated that spray distances can be in the order of 25 to 150 mm.
RF or induction-coupled plasma spray has been used to produce thermal plasma jets that provide dense coatings of most materials using coarser particles. The particles are entrained and heated by the plasma jet flow, which accelerates slowly toward the exit resulting in increased particle dwell times in a larger, more uniform heating volume. This allows an increased powder size to be melted.
Wire arc spraying processes utilize a DC electric arc to directly melt insulated electrode wires. As the consumable wire electrodes are advanced to a point, a potential difference applied across the wire initiates an arc that melts the tips in an atomizing gas. Typically argon gas is used to atomize the molten umable costs
Cold Spray is an emerging new spray technology that can rapidly deposit many metals, and even somecomposite materials, at or near room temperature in an ambient air environment without substantiallyheating the material. In this process, powder particles injected into a supersonic jet of compressed gas impact a substrate surface with sufficient energy to cause plastic deformation and consolidation with the underlying material by a process thought to be analogous to explosive welding, but on a micro-scale. With deposition rates similar to many traditional thermal spray processes, cold spray offers several potential advantages for some applications, including: little or no oxidation or phase changes during deposition, near theoretical bulk densities, unusually high thermal and electrical conductivities, and compressive residual stresses.
Selecting a Coating
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Factors to Consider in Selecting A Coating |
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Cost |
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Life Expectancy |
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Corrosion |
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Counter Surface |
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Effect of Process on Substrate Material |
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Surface Finish or Profile |
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Temperature |
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Lubrication |
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Abrasives |
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Loads and Speeds |
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Impact |
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Shock or Fatigue |
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Ability to Work Harden |
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Severity and Angle of Attack |
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Coefficient of Friction |
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Porosity |
Selection of the best coating for an application is not often straightforward. Selection based on hardness or from standard wear testing would indicate coatings like HVOF tungsten carbide/cobalt, plasma sprayed chromium oxide ceramic or fused coatings as giving the ultimate performance. Indeed, these coatings do provide the best solution to many applications, but they are certainly not universally suited to all applications.
Several factors need to be considered when selecting a coating process. Additionally, consideration of other specific coating properties may be required, depending on the application. Key questions include what is the part geometry and what gun can be used for a particular application. Other questions are Does the part need to be finished? If yes, what is the cost and how thick a coating is needed?
Industries
Applications for thermal spray processes and materials have a broad range across all industrial sectors. Thermal spray processes are easy to use, cost little to operate, and have coating attributes that are beneficial to applications in various industries. Applications include coatings for wear prevention, dimensional restoration, thermal insulation and control, corrosion resistance, oxidation resistance, lubrication films, abrasive actions, seals, biomedical environments, electromagnetic properties, etc., and the manufacturing of free-standing components, spray formed parts, and nanostructured materials.
Thermal spray processes and deposited materials have resulted in attractive coating solutions in the aerospace, industrial gas turbine, petrochemical and gas, and automotive industries. The inherent characteristics of it's microstructure can play an important role in enhancing performance. For instance, porosity helps reduce the thermal conductivity of thermal barrier coatings in jet aircraft engines.
In some cases, design limitations of the manufacturing process may be eliminated or reduced by thermal spray post-treatments such as spray-and-fuse. In this post-treatment process, self-fluxing nickel/cobalt alloys are flame sprayed and subsequently fused by another thermal energy source, such as an oxygen acetylene torch, furnace, induction coil, or infrared heating. Self-fluxing alloys typically have small amounts of boron and silicon that help to depress the melting point, which helps these alloys to fuse and coalesce. As they fuse, the coatings form a metallurgical bond with the substrate. The coating is dense and low in porosity, and provides high inter-particle cohesive strength and substrate-to-coating adhesive strength.
Coatings that are applied by combustion spray processes and then fused are typically suitable for highly wear-resistant applications. This is important for the agricultural and glass industries in products such as agricultural blades and glass mold plungers, which require toughness and wear resistance. Blending carbides into the self-fluxing alloys can increase coating wear resistance further.
HVOF processes are suitable not only for applying tungsten carbide-cobalt and nickel chromium-chrome carbide systems, but also for depositing wear and corrosion resistant alloys such as Inconel (NiCrFe), Triballoy (CoMoCr), and Hastelloy (NiCrMo) materials. HVOF MCrAlY coatings and some low-pressure plasma (LPPS) coatings are used for high temperature oxidation/hot corrosion and TBC bond coat applications for repair and restoration of existing components. Low melting-point ceramics such as alumina and alumina-titania are also applied via some HVOF processes for abrasive wear and dielectric applications.
Wear resistant coatings are used in nearly every industry to extend the surface life of a component. Because thermal spray coatings offer superior properties, competitive costs, and environmentally friendly processing, they are increasingly being used in place of hard chrome plating. Today, HVOF materials are being applied to hydraulic rods, landing gears, and the internal diameter of large bore cylinders as hard chrome replacements. The HVOF spraying of carbide materials on the landing gears of commercial airliners has been approved for use. Although original equipment manufacturers (OEMs) still require LP.