Thermal spraying technology
Thermal spray coating involves heating a material in powder or wire form to a molten or semi-molten state. The material is propelled using a stream of gas or compressed air to deposit it, creating a surface structure on a given substrate. The coating material may consist of a single element, but is often an alloy or composite with unique physical properties that are only achievable through the thermal spray process.
The company RADMET uses the following methods of thermal spraying
Flame thermal spraying with wire
We continually feed the spray material in wire form into a fuel gas-oxygen flame where it is melted by the heat of that combustion. Compressed air surrounds the flame and atomizes the molten tip of the wire. This accelerates the spray of molten particles towards the prepared workpiece surface. Combustion wire spray is a common choice for machine element repair and corrosion coatings. You have the option of either hard (higher melt temperature) or soft (lower melt temperature) wires.
Applications of the flame wire method of thermal spraying:
Our combustion wire spray services include anti-corrosion coatings and dimensional surface restoration. Metal-based wires are used in-shop or on-site for coating large steel structures, chemical and petroleum tanks, and marine applications.
Flame thermal spraying with powder
We continually feed the spray material in powder form into a fuel gas-oxygen flame where it is typically melted by the heat of combustion. A powder feed carrier gas transports the powder particles into the combustion flame. The mixed gasses entrain the melted particles onto the prepared workpiece surface where it rapidly solidifies to form the coating.
Applications of the flame powder method of thermal spraying:
Combustion powder spray is suitable for maintenance, repair, restoration and abradable/clearance control applications of machine parts. It uses oxygen and fuel to melt pure metals, alloys, carbides, polymers and ceramic powders.
Arc thermal spraying
For the electric arc wire spray process, we use two metallic wires, usually of the same composition, as the coating feedstock. The two wires are electrically charged with opposing polarity and are fed into the arc gun at matched, controlled speeds. When we bring the wires together at the contact point, the opposing charges on the wires create enough heat to continuously melt the tips of the wires. We use compressed air to atomize the now molten material and accelerate it onto the workpiece surface to form the coating.
Applications of the arc wire method of thermal spraying:
Electric arc wire spraying offers you excellent portability for on-site coatings. It covers applications for welded tube seams, piston rings, capacitors, varistors, boiler walls, and large infrastructures. It uses only electricity and atomized air to melt metallic alloy and pure metal wires.
HVAF (High Velocity Air Fuel) thermal spraying
Depending upon your requirements, propylene, propane, hydrogen, or natural gas may be used as the fuel in our High Velocity Air Fuel (HVAF) thermal spray systems. As a result of the high kinetic energy transferred to the particles through both HVAF processes, the coating material generally does not need to be fully melted. Instead, the powder particles are in a molten state and flatten plastically as they impact the workpiece surface. The resulting coating has a very predictable chemistry that is homogeneous and has a fine granular structure.
HVAF coatings are similar to and generally comparable to coatings produced by HVOF. HVAF is a “warm spray” process that is cooler than HVOF. HVAF guns utilize axial powder injection into an air-fuel jet with a temperature of about 1900-1950°C. Therefore, the process is capable of effectively applying carbide-based materials, but since the air-fuel jet produces considerably less oxides than high temperature oxy-fuel jets, the HVAF process can also apply metals with almost zero oxidation, similar to Cold Spray. All common thermal spray powder materials may be applied with HVAF, except for ceramics.
Applications of the HVAF method of thermal spraying:
For machine parts requiring high hardness in addition to corrosion and wear resistance, our gas-fueled HVOF process is the ideal solution. It produces coatings that are hard, thick, dense, and have fine, homogeneous structures.
Properties of thermally sprayed coatings
Typical properties of heat-treated coatings depending on the materials used and their working conditions are, among others:
- Corrosion resistance – e.g. zinc, aluminum, acid-proof steel,
- Heat resistance – e.g. aluminum oxides and titanium oxides,
- Tribological properties – e.g. bearing alloy (babbit), bronze,
- Resistance to abrasion – e.g. tungsten carbides, chromium carbides, chromium oxide,
- Thermal and electrical conductivity – e.g. copper,
- Thermal insulation and electrical insulation – e.g. polyamide, polyester
- Good workability – eg low-carbon steels, low-alloy steels
- Decorative properties – eg: zinc, bronze, brass