Plasma transferred wire arc (PTWA) thermal spraying is a

thermal spraying Thermal spraying techniques are coating processes in which melted (or heated) materials are sprayed onto a surface. The "feedstock" (coating precursor) is heated by electrical (plasma or arc) or chemical means (combustion flame). Thermal sprayi ...

process that deposits a coating on the internal surface of a cylindrical surface, or external surface of any geometry. It is predominantly known for its use in coating the cylinder bores of an

internal combustion engine An internal combustion engine (ICE or IC engine) is a heat engine in which the combustion of a fuel occurs with an oxidizer (usually air) in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal comb ...

, enabling the construction of

aluminium Aluminium (or aluminum in North American English) is a chemical element; it has chemical symbol, symbol Al and atomic number 13. It has a density lower than that of other common metals, about one-third that of steel. Aluminium has ...

engine block In an internal combustion engine, the engine block is the structure that contains the cylinders and other components. The engine block in an early automotive engine consisted of just the cylinder block, to which a separate crankcase was attach ...

s without

cast iron Cast iron is a class of iron–carbon alloys with a carbon content of more than 2% and silicon content around 1–3%. Its usefulness derives from its relatively low melting temperature. The alloying elements determine the form in which its car ...

cylinder sleeves. The inventors of PTWA received the 2009 IPO National Inventor of the Year award. This technology was initially

patent A patent is a type of intellectual property that gives its owner the legal right to exclude others from making, using, or selling an invention for a limited period of time in exchange for publishing an sufficiency of disclosure, enabling discl ...

ed and developed by Flame-Spray Industries, and subsequently improved upon by Flame-Spray and Ford.

Process

A single conductive wire is used as

feedstock A raw material, also known as a feedstock, unprocessed material, or primary commodity, is a basic material that is used to produce goods, finished goods, energy, or intermediate materials/Intermediate goods that are feedstock for future finishe ...

for the system. A supersonic plasma jet—formed by a transferred arc between a non-consumable

cathode A cathode is the electrode from which a conventional current leaves a polarized electrical device such as a lead-acid battery. This definition can be recalled by using the mnemonic ''CCD'' for ''Cathode Current Departs''. Conventional curren ...

and the wire—melts and atomizes the wire. A stream of air transports the atomized metal onto the substrate. The particles flatten upon striking the surface of the substrate due to their high

kinetic energy In physics, the kinetic energy of an object is the form of energy that it possesses due to its motion. In classical mechanics, the kinetic energy of a non-rotating object of mass ''m'' traveling at a speed ''v'' is \fracmv^2.Resnick, Rober ...

. The particles rapidly solidify upon contact and can assume both

crystalline A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions. In addition, macrosc ...

and

amorphous In condensed matter physics and materials science, an amorphous solid (or non-crystalline solid) is a solid that lacks the long-range order that is a characteristic of a crystal. The terms "glass" and "glassy solid" are sometimes used synonymousl ...

phases. There is also the possibility of producing multi-layer coatings via stacked layers of particles, increasing

wear Wear is the damaging, gradual removal or deformation of material at solid surfaces. Causes of wear can be mechanical (e.g., erosion) or chemical (e.g., corrosion). The study of wear and related processes is referred to as tribology. Wear in ...

resistance. All conductive wires up to and including can be used as feedstock material, including "cored" wires.

Refractory metals Refractory metals are a class of metals that are extraordinarily resistant to heat and wear. The expression is mostly used in the context of materials science, metallurgy and engineering. The definitions of which elements belong to this group di ...

, as well as low melt materials, are easily deposited.

Applications

PTWA can be used to apply a coating to wear surfaces of engine or transmission components, serving as a

plain bearing file:NYC 100-driving-axle-friction-bearing.jpg, Plain bearing on a 1906 S-Motor locomotive showing the axle, bearing, oil supply and oiling pad file:Linear-table with detail numbered.png, A sliding table with four cylindrical bearings file:GWR Spo ...

. For the cylinder bores of hypoeutectic aluminum-silicon alloy blocks, PTWA's main advantages over cast iron liners are reduced weight and cost. The thinner bore surface also allows for more compact bore spacing, and can potentially provide better

heat transfer Heat transfer is a discipline of thermal engineering that concerns the generation, use, conversion, and exchange of thermal energy (heat) between physical systems. Heat transfer is classified into various mechanisms, such as thermal conduction, ...

. Automotive engines that use PTWA include

Nissan is a Japanese multinational Automotive industry, automobile manufacturer headquartered in Yokohama, Kanagawa, Japan. The company sells its vehicles under the ''Nissan'' and ''Infiniti'' brands, and formerly the ''Datsun'' brand, with in-house ...

VR38DETT, and Ford

Coyote The coyote (''Canis latrans''), also known as the American jackal, prairie wolf, or brush wolf, is a species of canis, canine native to North America. It is smaller than its close relative, the Wolf, gray wolf, and slightly smaller than the c ...

Caterpillar Caterpillars ( ) are the larval stage of members of the order Lepidoptera (the insect order comprising butterflies and moths). As with most common names, the application of the word is arbitrary, since the larvae of sawflies (suborder ...

and Ford also use PTWA to remanufacture engines.

References

{{Reflist

External links

PTWA internal coating system
*http://www.sae.org/mags/aei/manuf/7624 Metallurgical processes Coatings spraying