New developments in thermal spray gas supply systems

An important aspect in the successful commercialisation of thermal spray processing is a safe and cost efficient gas supply system. As coating techniques such as High Velocity Oxygen Fuel spraying, (HVOF) High Pressure Plasma spraying (HPPS), High Pressure High Velocity Oxygen Fuel kerosene based systems (HPHVOF) and the recent developments in Cold Gas Dynamic spraying become more prominent, so the requirements on existing standard gas delivery systems designed for less demanding applications such as flame and plasma spraying need to be up-rated and improved. This work highlights recent developments in gas safety supply equipment dedicated to the thermal spray sector, the use of gas detectors in thermal spray workshops, more cost efficient gas delivery systems for fuel gases such as hydrogen, LPG propane, propylene and acetylene, and also covers improvements in gas delivery systems for the process gases such as oxygen, nitrogen and argon. The paper looks at various gas supply options, comparing compressed gas cylinders, liquid gas cylinders and bulk liquid supply vessels outlining the benefits and limitations of each systems in relation to the individual spray techniques. The higher pressures and flow rate associated with the growth of kerosene based fuel guns has resulted in an increased demand on the conventional compressed oxygen supply systems making them less cost effective and unworkable in a production environment. The paper covers new liquid oxygen supply cylinders and novel bulk tank systems that reduce cylinder holdings while reducing gas wastage due to lack of pressure. With the increase in higher thermal energy systems, the necessity to more closely control the temperature of sprayed component has outstretched the demands on conventional compressed air cooling systems. In the past, the use of cryogenic cooling gases such as carbon dioxide has been restricted by increased cost. However it has been shown in a number of cases that often the hidden costs of running air compressors, including the use of moisture traps, and oil filters can be greater than using clean, high purity cryogenic liquid gases such as carbon dioxide and nitrogen. The paper outlines the details of such cooling systems. The commercial success of Cold Gas Dynamic spraying may in future rely on a cost efficient, high pressure and high volume gas delivery systems for either helium or nitrogen. The paper describes a novel high pressure supply system presently used in another application suitable for Cold Gas Dynamic spraying with nitrogen able to generate pressure in-excess of 30 bar and flow rates above 120m3/hr from a liquid vessel.