|INSTITUTE OF TECHNOLOGY OF METALS|
DEVEOPMENT OF THE INSTITUTE :: Activated arc spray - Hypersonic metallization
New concept of arc spray coating technology and equipment was developed by Belarus in the world for the first time.
As compared to the standard scheme TAS (Traditional arc spray), the spray of liquid metal in AAS (Activated arc spray) of new technology, arising as a result of thermal effect of electric arc on the ends of the two wire electrodes, is performed by a jet of combustion products of propane-air mixture. The speed of the jet, coming from the nozzle reaches1500 m/sec at the temperature of 2200K.
The scheme of traditional arc spray process TAS (Traditional arc spray).
Scheme of the process of źHypersonic metallization╗ by AAS
Developed AAS equipment by Belarus
The coating is formed by spraying wires with diameter of 1.5-2.2 mm. The speed of the spraying jet is ~ 3M (1000 m/sec). Maximal working current ~380 A; air consumption ~60 m3/h; propane-butane consumption ~0.011 kg/hr. Productivity (wire; diameter-2 mm) at performing steel coatings ~18 kg/hr.
Steel coatings, obtained by AAS method have porosity 2~4%, the density of aluminum alloys = 100%. This is especially important at corrosion-proof plating because it allows gaining serious savings of the plated material due to decreasing the thickness of the coating, necessary for protection from through porosity and increases the work life of the coatings. Bond resistance of the coatings 35~60 MPa.
Microstructure of steel coatings: а, b ľ steel 40Х13; c, d ľ steel Свľ08;
a) Traditional arc spray coating b) Activated arc spray coating (Metallographic analysis)
Compact equipment for realization of the process of źHypersonic metallization╗
AAS combine the advantages of arc spraying and high-velocity metal spraying. The main distinctive feature of AAS is the presence of compact high efficiency propane-air mix combustion chamber. Supersonic jet of the mix has at the output the speed of 1500 m/sec and the temperature of 2200 K.
That causes the particles are speeded up to 500 m/s. As a result, coating adhesion strength is twice improved in comparison with traditional metal spraying (MS). This is enough to work in the most extreme conditions and in cases of shock-abrasive wear. The oxide reduction and the alloying elements burning lowering are allowed by that feature also.
For example, EAM coating carbon content was 2~3 times less then initial U10A and 40X13 wires one. In comparison, the AAS coating carbon content was not varied at reduction parameters of propane-air mixture.
The conditions of particles formation and transportation and forming of coating are different from other thermal gas metal spraying methods and cause formation of other structures in the coating material. The use of AAS results in small quantity of fragile oxides, large quantity of intermetaloids, formation of tempering structures and high enough plasticity of the sprayed layer. This allows to use AAS in new fields and to significantly widen the range of parts that can be treated using this method.
Second, as thickness of the coating necessary to cover through-out porosity can be decreased considerable material economy is achieved.
High productivity is a traditional
advantage of arc spraying. The productivity of a manual AAS-10 unit on steel is
18 kg/hour. Ionization of inter-electrode space reduces the arc current by 10-15
% and the productivity is the same as with traditional arc spraying.
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