Apparatus and process for producing high density thermal spray coatings

Apparatus for use with a thermal-spray gun operable to provide an exhaust jet of supersonic velocity exiting from a nozzle having an elongated bore;

• said jet carrying particles to be deposited on a substrate, comprising:
• elongated shroud means having means for detachably securing the same to the outer end of said nozzle for reception of said jet and particles;
• said shroud means comprising manifold means and open ended constraining tube means supported by said manifold means for coaxial passage of said jet and particles therethrough;
• said manifold means comprising plural nozzle means constructed and arranged to distribute pressurized inert gas tangentially over the interior walls of said tube means whereby to effect a helically flowing shroud of inert gas radially outwardly of said jet to insulate the particles carried thereby from ambient atmosphere until the same are deposited on the substrate.

An improved method of producing a uniform, dense and substantially oxide-free metal coating on a substrate in ambient atmosphere by means of a high-velocity, thermal-spray gun apparatus of the type having a high pressure internal combustion chamber in which oxy-fuel gases are continuously supplied, ignited and exhausted therefrom to an outlet as a supersonic, particle-carrying exhaust gas jet, comprising the steps of:

• burning oxygen and hydrogen gases in said combustion chamber at pressure sufficient to obtain a minimum oxygen flow rate of substantially 240 liters per minute and an hydrogen-to-oxygen mass flow ratio in the range of substantially 2.6-3.8 to 1;
• introducing metal particles, having a particle size within the range of 10-45 microns and a low starting oxygen content, coaxially into the exhaust gas jet by means of an inert carrier gas;
• and
• providing a radially confining, helical flowing, pressurized inert gas shroud concentrically about said exhaust jet until the particles carried thereby impact the substrate.

An improved method of depositing a uniform, dense and substantially oxide free metal coating on a substrate carried out by thermal-spray apparatus operating in ambient atmosphere to provide a supersonic-velocity jet stream of hot gases carrying metal particles to be impacted with a substrate to form the coating, comprising the steps of:

• introducing metal particles having a particle size in the order of 10-45 microns and a low initial oxygen content coaxially into said jet stream by means of an inert gas carrier;
• and
• confining the particle-carrying jet stream within a shroud of helically flowing, pressurized inert gas maintained concentrically about said jet stream until the particles carried thereby impact the substrate;
• the gas shroud flowing with a radially outwardly directed component to minimize turbulation with said jet stream.

Apparatus comprising:

• manifold means for receiving and distributing pressurized inert gas;
• means for securing said manifold means to the end of a nozzle that discharges a high temperature, particle-carrying stream at supersonic velocities;
• an open-ended constraining tube means mounted on said manifold means for substantially coaxial passage of said particle-carrying stream therethrough;
• and
• plural nozzle means communicating with said manifold means for distributing pressurized inert gas substantially tangentially over the interior walls of said tube means in a manner to effect a helical flowing shroud of inert gas substantially concentrically about said particle-carrying stream within said tube means and operable upon exit from said tube means to isolate said particle-carrying stream from ambient atmosphere.