THERMAL SPRAY COATINGS

General Description

Thermal spraying is a well-established technology that is used to produce a wide variety of coatings for applications ranging from jet engines and medical implements to pump parts and Valve components. Thermal spraying encompasses a group of processes that are capable of depositing coating materials of metal, ceramics, carbides, and various alloys onto machine parts surfaces.

There are hundreds of materials and alloys that can be deposited as a functional coating.  Most of them can be applied using more than one Thermal spray process; however, certain coatings excel and perform best if applied with a certain specific process.  Thermal spraying may be generally grouped into four major categories, as follows:

• HVOF (High Velocity Oxy-Fuel ), excellent for Carbide coatings and other super alloys.
• Plasma Spray, excellent for all Ceramic coatings and other specialty alloys.
• Twin wire Arc Spray, excellent for high build coatings of many alloy variations.
• Combustion/Flame Spray, mainly used to apply non-ferrous materials and other alloys.

Each process is effective in its own way in terms of capability, application spec, coating performance, cost effectiveness, versatility, and materials selection.

Thermal spray facts

Every time you get into a car, an airplane, or flip a light switch, you should remember that you are relying on technologies that utilize thermally sprayed coatings.

Thermally sprayed coatings are used right across the spectrum of engineering and manufacturing to impart certain properties and enhance the surface of components made from low cost or lightweight materials. This allows the designer to create cost-effective, high-performance parts with a functional surface exactly where it is required.

Additionally, Thermal spray coatings are widely used for repair, refurbishing, or resurfacing of worn components and restoring them to better than new condition using superior materials as compared to the substrate base metallurgy.

Thermally sprayed coatings can be used to impart many surface properties and characteristics such as:

• Wear resistance
• Heat & oxidation resistance
• Corrosion resistance
• Electrical resistance or conductivity
• Traction & Gripping
• Release & Non-stick
• Alteration of surface properties
• Surface restoration

Confidence in thermal spraying

Aerospace, aircraft, power generation and automotive manufactures are the biggest users of Thermal Spray coatings, both at the original equipment manufacturing stage and during subsequent repair and overhaul.

Other applications and industries take advantage of Thermal Spray coatings technologies including, but not limited to:

• Textile
• Pumps
• Valves
• Motors
• Agriculture
• Papermaking and Printing
• Electronics
• Petro Chemicals
• Nuclear Power
• Utilities/Power/Water/Sewage
• Military
• Offshore Oil Platforms
• Refineries
• Railroad
• Automobiles

Advantages of thermal spraying

Since its inception almost a century ago, thermal spraying has evolved from a technology designed to be a cost-effective repair of worn components and mis-machined parts to a process used to provide improved part performance and longer life to OEM components.

As part of its growth process, thermal spray has developed from the original oxy-acetylene flame spray process to electric arc, plasma, and high-velocity HVOF systems.  In addition, the palette of materials available for thermal spraying has expanded from simple metal alloys to ceramics, polymers, and carbides.

One of the many industrial areas in which thermal spray has established itself is as a better hard-facing alternative to weld build-up and chrome plating.  Thermal spraying, like weld cladding or chrome plating, is a coating process.  In thermal spray, wire or powder is melted by a flame or electricity and sprayed onto the surface to be coated.  During the actual process, the spray gun makes successive passes across the parts’ surface to produce a coating.  Thermal spray coatings have more benefits than other alternative processes in terms of the following:

• Cost reduction In lieu of making the entire part out of an expensive material, a high-performance material is sprayed onto a low-cost base material.
• No distortion Because of the low heat input thermal-sprayed coatings do not impact the substrates’ microstructure.  The coatings do not penetrate the base material, i.e., there is no heat-affected zone.
• Versatility Almost any metal, ceramic, or plastic can be sprayed.
• Thickness range Coatings can be sprayed from 0.001 in. to more than 1 in. thick, depending on the material and spray system.   Normally coating thickness generally range from 0.003” to 0.150” in.
• Processing speed Components surfaces can be built up and finished by grinding with relative quickness without the need to stress relief or worry about plating contamination.

In many cases component service life can be increased up to 500%.  By reducing premature component failure, thermal spraying proves to be an effective cost saving service.  With a variety of application methods and coating selections, thermal sprayed surfaces offer solutions for parts renewal, and premature wear prevention.

Thermal spray is recognized by major manufacturing companies with many specifications written to include its use, such is the case with Military Standard Mil Std 1687-A and Mil Std 2138 for thermal spray repairs and new component manufacturing.