Wire arc spraying

Wire flame spraying Electric arc flame spraying Powder flame spraying Plasma flame spraying Hypersonic flame spraying... 

In comparison with other wire and powder-formed coatings, arc sprayed coatings are generally more porous. This porosity is unacceptable for components requiring critical surface finishes, for which we use powder... 

Alternative deposited coatings involve thermal spray, such as plasma spray or two-wire arc [60]. Substrate alloy effects are minimal and coating chemistry and morphology can be designed for specific applications. Corrosion protection and good adhesive bond strength can be provided and maintained [61-64],... 

The most important groups of materials for wire flame spraying and arc spraying are... 

During electric arc spraying, an electric arc between the ends of two wires continuously melts the ends while a jet of gas (air, nitrogen, etc.) blows the molten droplets toward the substrate at speeds of 30 to 150 m/s. 

There are three basic categories of thermal spray technologies combustion torch (flame spray, high velocity oxy-fuel, and detonation gun), electric (wire) arc, and plasma arc. Thermal spray processes are maturing, and the technology is readily available. 

Plasma arc spraying melting of solid feedstock (e.g. powder, wire or rod) and propelling the molten material onto a substrate to alter its surface properties, such as wear resistance or oxidation protection. 

A. Edrisy, T. Perry, Y. T. Cheng and A. T. Alpas, The Effect of Humidity on the Sliding Wear of Plasma Transfer Wire Arc Thermal Sprayed (PTWA) Low Carbon Steel Coatings, Surface and Coatings Technology, Vol. 146-147, (2001) 571-577. 

Thermal or Flame Spray Process. The earliest experiments in metal spray used molten metal fed to a spray apparatus, where it was dispersed by a high speed air jet into tiny droplets and simultaneously blown onto the surface of the part to be covered. The metal solidified on contact. Modem processes use a more convenient source than premelted metal. Spray heads using a flame or an electrical arc to melt metal wires or powders directly are much more convenient. These are the only types used on a large scale in the United States. 

Arc wire utilizes two continuously fed 1.6-mm dia intersecting wires with a d-c arc maintained between the wire tips as they meet. Compressed gas (usually air) strips the molten metal from the tips and forms a directional spray stream. This process is widely used to spray most metals. Arc wire is the most economical process because of the wire feedstock. Moreover, it utilizes - 10% of the thermal energy of the other spray processes (0.4 vs 6.6 kWh/kg using stainless steel) because of the direct arc heating of the wire tips. 

Biomedical. Heart-valve parts are fabricated from pyrolytic carbon, which is compatible with living tissue. Such parts are produced by high temperature pyrolysis of gases such as methane. Other potential biomedical apphcations are dental implants and other prostheses where a seal between the implant and the living biological surface is essential. Plasma and arc-wire sprayed coatings are used on prosthetic devices, eg, hip implants, to achieve better bone/tissue attachments (see Prosthetic and BiOLffiDiCALdevices). 

Hard facing of various components in the aircraft gas-turbine engine and in industrial apphcations for textile machinery parts, oil and gas machinery parts, paper-shtting knives, etc, is estimated at 1 x 10 in 1995 with an estimated growth rate of 5% annually. The mix is approximately 45% aerospace apphcations, 55% industrial apphcations. Additionally, repair coatings for gas-turbine blades and vanes is estimated at 500 x 10 . These coatings are primarily deposited by plasma spray, arc-wire, HVOF, and detonation gun techniques. 

Although at the time of his early inventions Dr. Schoop envisaged that an electric arc could be used to produce the molten metal for spraying, forty years passed before the method became commercially important. Then, in Germany, Russia and Japan tools were made based on the arc. Although in Japan alternating current is used, the noise is nearly intolerable and elsewhere direct current from motor generators is employed. The fundamental idea is simple two wires, carefully insulated from each other, are advanced to meet at a point where an arc is formed, immediately in advance of a Jet... 

---