Thermal spraying

Thermal spraying is a deposition technique where a spray of molten particles is directed to the part to form the coating. It is used for the protection of new parts against wear, corrosion and high temperatures thus improving the properties of engineered surfaces. Thermal spraying processes are also applied for repairing damaged and worn parts. Sometimes the thermal spraying can be applied for the decoration thus improving the esthetic properties of parts. Coating material can be either in wire, powder, rod, cord or molten-bath form. By the thermal spraying process relatively thick metallic, ceramic and composite coatings can be deposited. Operations of the process can be manual, mechanized and fully automated.

The DURMAT® products offer a wide range of high-quality materials for the thermal spraying processes of Arc spraying, Flame spraying (powder), Flame spraying (rod / wire), High velocity oxy-fuel spraying (HVOF / HVAF) and Plasma spraying.

The various Thermal Spray processes are briefly described below. If you have further questions, please do not hesitate contact us.

Thermal Spray processes

Thermal Spray processes

Arc spraying

For arc spraying two similar or different types of spray material in wire form are melted off in an arc and propelled onto the prepared workpiece surface by means of an atomizing gas, e.g. compressed air. Arc spraying is a high-performance wire spraying process in which only electrically conductive coating materials can be used, however. By using Flux-cored wires a big range of materials and alloys can be used. When using nitrogen, argon or nitrogen-oxygen mixtures as the atomizing gas, oxidation of the materials can largely be prevented, respectively, specific coating properties can be achieved.

Applications include large-area coating of vessels, anti-corrosion protection, bond coatings, cylinder liners, etc.

Typical DURUM-products:
, 775, 802, 812, 906

Flame spraying with powder

In powder flame spraying, the spray material in powder form is melted or fused in an oxy-acetylene flame and propelled onto the prepared work-piece surface with the aid of expanding combustion gases. If necessary, an additional gas (e.g. nitrogen) can be used to accelerate the powder particles. The range of spray powders available is enormous, comprising well over 350 different types.Powders are classified as self-fluxing and self-adhering. Self-fluxing powders normally require additional thermal post-treatment. In most cases, this “fusing” step is carried out using oxy-acetylene torches, which are extremely well-suited to this task.

The adhesion of the spray coating to the base material is greatly enhanced by the heat treatment, rendering it impervious to gases and liquids. Applications include shaft sleeves, roll-table rollers, bearing seats, ventilating fans, extruder screw rotors.

Typical DURUM-products:
DURMAT® 356, 451, 456

Flame spraying with rods / wires

In wire or rod flame spraying, the spray material is continuously melted in the center of an oxy-acetylene flame. With the aid of an atomizing gas such as compressed air or nitrogen, the droplet-shaped spray particles are discharged from the melting zone and propelled onto the prepared workpiece surface. Flame spraying with wire is a widely applied method with a very high coating quality standard. In the automotive industry, for example, several hundred tons of molybdenum, per year, are used to coat gear selector forks, synchronizing rings or piston rings.

Typical DURUM-products:
DURMAT® 761, 775, 802, 812, 906

High velocity oxy-fuel spraying (HVOF / HVAF)

High velocity oxy-fuel spraying involves a continuous gas combustion under high pressure in a combustion chamber. The spray material, in powder form, is fed into the central axis of the chamber. The high pressure of the oxyfuel gas mixture produced in the combustion chamber in turn produces the desired high flow velocity in the gas jet. In this way, the spray particles are accelerated to high velocities, leading to exceptionally dense spray coatings with excellent adhesion. Due to the sufficient but moderate heat input, the spray material undergoes only slight metallurgical changes as a result of the spray process, e.g. minimal formation of mixed carbides. With this method, extremely thin coatings with a high dimensional accuracy can be produced.

Applications include sliding surfaces of steam irons, rollers for the photographic industry, machine parts for the petrochemical and chemical industry, e.g. pumps, slides, ball valves, mechanical sealings, Kaplan blades, every kind of anti-wear protection, also in connection with anti-corrosion protection, electrically insulating coatings (oxides).

Typical DURUM-products:
, 131, 135

Plasma spraying

In plasma spraying, the spray material, in powder form, is melted by a plasma jet in or outside the spray gun and propelled onto the workpiece surface. The plasma is produced by an arc which is constricted and burns in argon, helium, nitrogen, hydrogen or their mixtures. This causes the gases to dissociate and ionize; they attain high discharge velocities and, on recombination, transfer their thermal energy to the spray particles. The arc is not transferred, i.e. it burns inside the spray gun between a centered electrode (cathode) and the water-cooled spray nozzle forming the anode. The process is applied in a normal atmosphere, in a shroud gas stream, i.e. inert atmosphere (e.g. argon), in a vacuum and under water. A high-velocity plasma can also be produced by means of a specially shaped nozzle attachment. Applications include the aerospace industry (e.g. turbine blades and abradable surfaces), medical technology (implants) and thermal barrier coatings.

Typical DURUM-products:
, 602, 644