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What Is Thermal Spray
The Steps of Thermal Spray Application
Application Examples 
Many well known applications exist such as coatings of zinc or aluminum applied to bridge structures in order to drastically reduce rusting and extend the structure's service life. There are many applications designed to extend the service life of industrial machinery components such as molybdenum coatings on shifter forks to improve lubricity and extend life or the use of zinc or aluminum coatings on gas bottles (such as acetylene or oxygen bottles) to extend their service life by keeping them from rusting. There are highly technical applications like thermal barriers utilizing complex alloys and high tech ceramics and garden-variety applications using steels or stainless steels to build up worn areas. Industry Examples Thermal spray is well recognized as a tool for component performance enhancement in many industries including:
Designing components with thermal spray coatings as one of the features is a method for optimizing performance of machinery by the original equipment manufacturer. For example, pump manufacturers often specify specialized coatings called self-fluxing alloys as a means to increase service life of components - especially pump sleeves. These coatings are applied using the combustion powder process and then the coating is melted onto the part. A diffusion layer is formed with the substrate and the coating becomes a part of the component. The coating is then ground to size and the component exhibits superior wear life as a result of the hard self-fluxing alloy overlay. CTS is expert at the application of these self-fluxing alloy coatings. Land based gas turbine manufacturers design in thermal barrier protection to many of the components that are exposed to hot gasses, particle erosion and severe thermal cycling. Many other industries also use this method to insure maximum service life for their critical components and wear parts. Thermal spray coatings can also be used to rebuild worn parts and can be used to make components better than new by analyzing the wear patterns and operating environment, then prescribing coatings to extend service life. In addition to thermal spray coatings, CTS offers dry film lubricants and release coatings all of which can enhance the surface properties of our coatings or can sometimes improve the performance of components even without using thermal spray coatings. It is important to note that coatings are applied selectively where they are needed and that they protect components from exposure to heat, chemicals, molten metal, abrasion, adhesive wear, galling, fretting, or something as simple as weathering. The limit to the applications that are possible is your imagination. Top Wire and Powder Combustion Combustion thermal spray includes coatings produced using powder or wire as a feedstock.
The combustion powder process uses a powder feed stock that is blown into the combustion flame using inert gas (normally nitrogen), or powder is delivered through a gravity feed. The flame melts and accelerates the particles onto the workpiece. A much broader range of materials may be used to produce coatings with powder than with wire. Combustion powder coatings are typically fairly well bonded and fairly dense. Special techniques can be developed to improve properties. Frequently the combustion powder process is used at CTS to apply coatings containing graphite. The relatively low flame temperature allows maximum graphite retention in the coating. Characteristics The combustion powder process produces coatings that are well bonded, fairly dense and serviceable. Coatings can be applied quite thick because of the relatively low stress involved in the production of these coatings. Materials Coating materials available for the combustion powder process include self-fluxing alloys, most of the pure metals, many alloys, carbides, ceramics and a class of coatings called self-bonding Self-bonding materials exhibit high bond strengths and excellent machinability or grindability. Properly applied, they can be machined to a feather edge Spray and Fuse 
Spray and fuse is terminology used to describe coatings applied with the combustion powder process that are subsequently heated to about 2000 F. and melted to the substrate material. These coating are typically nickel or cobalt based and form hard carbide and boride phases during processing - thus are considered hard facing applications. Spray and fuse as a process has several advantages over conventional weld overlay hard facing techniques. The component being sprayed is heated all at once during the fusing operation instead of being heated in a localized area as happens in welding - therefore distortion of the component is minimized. Since the coating thickness can be controlled to a much better extent than is possible in weld overlay, it is possible to use a minimum of material, and since that material is fairly smooth after fusing, machining/grinding time can be minimized. Coatings applied using the spray and fuse process are 100% dense and show a diffusion layer with the substrate. They are specified and used where there is high potential for corrosion or corrosion combined with severe wear. Therefore they are often used in such machine elements as pump sleeves and valves. They may also be used in impact applications such as hammers.
Electric Arc Electric arc, sometimes also called twin wire arc, is a process that uses two wires, electrically charged and run into a dead short. The heat produced by the electricity in the short is sufficient to melt most materials. Compressed gas — usually air — is then used to project the molten particles onto the work piece. High Velocity Oxygen Fuel Process 
HVOF coatings are the densest among the processes and also the most securely bonded. Bond strength usually exceeds the strength of the glue used in the tensile bond test - normally above 10,000 psi. Coating porosity for many materials is 1% or less. These are the most wear and corrosion resistant coatings of all the processes.Materials 
Coatings of tungsten carbide materials are optimized using HVOF because the HVOF flame is not hot enough to cause the formation of complex phases of carbides. Tungsten carbide coatings produced with the HVOF process are among the most wear resistant coatings possible with thermal spray technology. These coatings routinely outwear chrome plating by factors in excess of five to one.Coatings of high alloys are another popular use for HVOF - oxidation resistant, heat resistant alloys such as hastelloys, inconels, stellites® (registered trademark of Deloro Stellite), tribaloys and some proprietary alloys make up a key area of HVOF coatings. All of these materials protect against temperature, wear, chemical attack or some combination. HVOF is also used frequently as a component rebuilding process utilizing steel and stainless steel as coating materials. Plasma Spray The plasma spray process uses inert gas — usually nitrogen or argon — excited by a pulsed DC arc to ionize the gas and produce a state of matter called plasma. Other gasses — mainly hydrogen and helium — are often introduced in small quantity in order to increase the ionization. The plasma gasses are introduced at high volume and high velocity, and are ionized to produce a plume that ranges in temperature from about 12,000° to 30,000° F. Powder feedstock is then injected into this hot gas stream (called a plume), heated very quickly, and deposited onto the work piece. 
Materials that are very difficult to melt, such as virtually any ceramic or refractory metal can be used to produce serviceable coatings using the plasma spray process. Plasma coatings are very dense, well bonded structures.Plasma spray is the most versatile of the thermal spray processes. Excellent coatings of metals, ceramics, cermets, refractory metals, plastics, all can be produced using the plasma process. Of all the potential coating choices, plasma is best suited to apply ceramic coatings because of their high melting temperature. Plasma spray is especially effective in applying hard to melt materials like refractory metals and ceramics although it is certainly possible to apply the other classes of materials such as metals, alloys, and plastics using plasma. The extremely high temperatures and gas velocities second only to HVOF produce well bonded dense coatings of the broadest range of materials of any of the processes. |
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Thermal spray refers to a set of processes that utilize heat energy to produce coatings using feedstocks that include metals, cermets, ceramics and plastics. The feedstock is deposited in a molten or semi-molten state in layers and adheres to the work piece by mechanical means. The coating material may be in powder or wire form. 
The typical thermal spray application consists of several basic steps:
Wire Combustion Process
Arc coatings are typically well bonded, although bond coats — special coating layers used to improve the strength of subsequent layers — are often used. Coatings can range from relatively porous to quite dense. Arc spraying is very versatile in terms of applying metals and some cermets. Arc is especially useful for thick overlays or coatings on large areas. It's also especially effective as a process for coating projects done on site.
Plasma is the most versatile of the processes with the ability to spray almost any feedstock in powder form. Extensive experience with this process makes it the one most used at CTS. We spray thousands of pounds of a broad range of materials through our plasma systems. Almost all of these applications are sprayed robotically.