It has been generally accepted that amperage and voltage are the only variables used to determine spray rate with the twin wire arc spray process. This belief has led to the common practice of defining spray rates in terms of kgs (pounds) per amperes. The "pounds to amperes" theory has been disproved with die advent of equipment capable of successfully arc spraying 4.8 mm (3/16 inch) diameter wires of zinc, aluminum, or 85/15 (zinc/aluminum). Changes in equipment design, that allowed the use of the larger diameter wires, resulted in the issue of a U.S. patent for arc spraying wires over 3.2 mm (1/8 inch) diameter. To achieve production capabilities for spraying 4.8 mm (3/16 inch) diameter wire, numerous problems needed to be solved, which led to additional patent claims.

The fluid and particle dynamics of a High-Velocity Oxygen-Fuel Thermal Spray torch are analyzed using computational and experimental techniques. Three-dimensional Computational Fluid Dynamics (CFD) results are presented for a curved aircap used for coating interior surfaces such as engine cylinder bores. The device analyzed is similar to the Metco Diamond Jet Rotating Wire (DJRW) torch. The feed gases are injected through an axisymmetric nozzle into the curved aircap. Premixed propylene and oxygen are introduced from an annulus in the nozzle, while cooling air is injected between the nozzle and the interior wall of the aircap. The combustion process is modeled using a single-step finite- rate chemistry model with a total of 9 gas species which includes dissociation of combustion products. A continually-fed steel wire passes through the center of the nozzle and melting occurs at a conical tip near the exit of the aircap. Wire melting is simulated computationally by injecting liquid steel particles into the flow field near the tip of the wire. Experimental particle velocity measurements during wire feed were also taken using a Laser Two-Focus (L2F) velocimeter system. Flow fields inside and outside the aircap are presented and particle velocity predictions are compared with experimental measurements outside of the aircap.