Thermal spray gun with improved thermal efficiency and nozzle/barrel wear resistance

Abstract

The present invention discloses a thermal spray apparatus with improved thermal efficiency and wear resistance in both the nozzle and barrel combustion chamber. Specifically, disclosed herein is a thermal spray apparatus for spraying substrate coatings, comprising a high velocity oxygen fuel (HVOF) gun wherein said gun includes a combustion chamber generating heated flow therefrom and a nozzle downstream from said chamber. The nozzle and / or chamber contain a first layer of material heated by the flow, and a second layer of material which contacts the first layer when said first layer is heated. The first layer has a thermal conductivity that is lower than said second layer and preferably a lower thermal expansion coefficient. In use, the contact of the first heated layer of material with the second layer operates to remove heat from the first layer therein providing automatic / self-regulating temperature control of the HVOF apparatus.

Description

FIELD OF THE INVENTION[0001]This invention relates to a thermal spray device, and more particularly, to a high velocity thermal spray gun providing improved thermal efficiency (lower heat losses that are self-regulating) in both the nozzle and combustion chamber along with increased durability of the hardware employed therein.BACKGROUND OF THE INVENTION[0002]Thermal spraying was initiated as early as 1910 when a stream of molten metal was poured into the path of a high pressure gas jet causing metal droplets to spray in a conical pattern onto an adjacent substrate to immediately freeze and form a coating of deformed particles in a lamella structure. Today, there are essentially two types of thermal spraying that use wire feedstock: combustion flame spraying and electric are spraying.[0003]In electric-arc (two wire) spray coating, two consumable wires form electrodes of an electric arc or “arc ball”. The two wires are electrically energized and converge at a point in which the electr...

AI Technical Summary

Benefits of technology

The present invention is about a thermal spray apparatus that improves thermal efficiency and wear resistance for spraying substrate coatings. It includes a high velocity oxygen fuel (HVOF) gun for spraying. The gun has a combustion chamber and a nozzle downstream from the chamber. The nozzle has a first layer of material with low thermal conductivity and a second layer of material with high thermal conductivity. The first layer is positioned in the combustion chamber or nozzle and the second layer is positioned in non-contacting relationship with the first layer. The second layer removes heat from the first layer and the first layer returns to its non-contacting position. This continuous heating and cooling cycle helps to regulate the temperature of the HVOF apparatus. The technical effect of this invention is to improve the efficiency and wear resistance of thermal spray coatings.

Problems solved by technology

However, the high thermal conductivity of copper comes at a price.

That is, copper is relatively soft, and wear problems are common, particularly when making use of carbides and other hard powders for the resulting thermal spray.

In addition, the high thermal conductivity of copper results in a relatively low inner surface temperatures in either the gun chamber or nozzle section.

This corresponds to low thermal efficiency of the overall process due to such heat losses, resulting in low deposition rates and deposition efficiency as well as limiting the ability to spray high temperature materials.

First, high temperature alloys still require one to manufacture relatively thick walls (not less than 0.635 cm) to create the proper thermal resistance for heal, transfer of the combustion products to the outer cooling (water) jacket. However, the low thermal conductivity of these materials give rise to problems with the o-rings attached to the outer surfaces thereof. That is, due to the low thermal conductivity, the high temperature alloys can overheat the o-rings and cause o-ring failure.

However, once again, due to the relatively low thermal conductivities of these materials compared to copper, ceramic materials have similar problems associated and reviewed above.

In addition, ceramic materials have their own peculiar problems, such as being relatively brittle.

Furthermore, as the thermal expansion properties of ceramics are different than that of the surrounding metal components, cracks are commonly observed in the heating cycle thereby further complicating HVOF design.

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