Method and apparatus for pulsed detonation coating of internal surfaces of small diameter tubes and the like

#The present invention is directed to coating technology and, more particularly, to pulsed detonation coating.

#Several techniques have been used to implement thermal spray coating. One approach has been High Velocity Oxygen/Fuel System (HVOF), in which solid particles are injected in high velocity gas produced by reaction of oxidizer and a fuel at high pressure. Such systems typically are used for deposition at atmospheric pressure and primarily are used for coating metal alloys and WC/Co powders with particle sizes larger than about 10μ. Other thermal spray coating techniques include plasma spray, in which particles are heated and accelerated by high temperature plasma produced by an electric discharge in an inert gas atmosphere. Plasma spray systems have been used for both atmospheric- and low-pressure coatings.

#Thermal spray coating also has been implemented by intermittent detonations, e.g., by the use of a detonation gun (D-Gun). D-guns can be used for coating a wide variety of materials, such as metals, cermets, and ceramics. D-guns typically have a relatively long (often about 1 m), fluid-cooled barrel having an inner diameter of about one inch. Typically, a mixture of reactive gases, such as oxidizer and acetylene, is fed into the gun along with a comminuted coating material in two phases. The reactive gas mixture is ignited to produce a detonation wave, which travels down the barrel of the gun. The detonation wave heats and accelerates the coating material particles, which are propelled out of the gun onto a substrate to be coated.

#The present invention will now be described in more detail with reference to preferred embodiments of the invention, given only by way of example, and illustrated in the accompanying drawings in which:

#FIG. 1A is a three-dimensional model of the cross section of a pulsed detonation coating apparatus, shown inside a small-diameter tube, in accordance with a preferred embodiment of the present invention;

#FIG. 1B is a schematic illustration of the cross section of the pulsed detonation coating apparatus shown in FIG. 1A;

#The pulsed detonation coating apparatus of the present invention has utility in applying a wide variety of coating materials to a wide variety of substrates and is particularly useful in coating the inside surfaces of small-diameter tubes and other difficult-to-reach surfaces, such as the inner surfaces of cylinders, the inner surfaces of converging/diverging shapes, the inner surfaces of small rectangular tubes, the inner surfaces of shapes that are partially open, and the inner surfaces of various other non-cylindrical shapes, to improve such properties as corrosion-, erosion-, and wear resistance. Nanoscale ceramic particles can be used, for example, for coating lightweight, low melting point metals used in aircraft structures to impart erosion- and corrosion resistance. Coatings of polytetrafluoroethylene, polymers, and other plastic materials can be applied to the inside surfaces tubes, for example, for corrosion protection and to improve lubricity and other tribological properties of the inner surfaces of the tubes. Metal and metal composite materials, such us Al/SiC, can be coated on the inner surfaces of cylinders of internal combustion engines. As another example, corrosion/erosion protective materials such as alumina/titania, Cr, WC/Co, Ni and Cr based alloys, and other similar materials can be applied to tubes/pipes used in geothermal energy exploration, which often are subjected to high-temperature corrosive environments. Similar coatings may be applied to tubes/pipes that are used to transport corrosive/erosive liquid, gases, and suspensions used in oil exploration, chemicals industry, and energy generation and energy delivery industries. Thermal barrier coatings based on zirconia, alumina, and similar materials can be applied to metal tubes for protection from very high temperature gas or liquid flow and for reduction of thermal losses.

#The term “detonation,” “detonation process,” and similar terms are used herein refer to a physical phenomena characterized by a shock wave propagating in front of a reaction front. The shock wave compresses the initial mixture to high pressures and high temperatures so as to initiate a very high initial rate of reaction behind its front. The detonation front propagates with supersonic speeds, typically on the order of about 1000 to 3000 m/sec.

#The term “deflagration process,” as used herein, refers to a combustion process in which a reaction front propagates slowly through the mixture via diffusion and thermal initiation. Combustion of the unconfined mixture does not yield the high pressures that are characteristic of detonation. The combustion front propagates with subsonic speeds, typically on the order of about 1 to 30 m/sec.