Handbook-Oxygen Cutting By Machine

51 Why use high-speed designs? For a couple of important reasons: 1. It permits us to design a nozzle whose exit pressure can be tailored closely to atmospheric pressure, thereby creating the least disturbance as the stream penetrates the atmosphere. 2. We can design nozzles to operate at considerably higher pressures without the disadvantages of high exit pressures which result in inefficient broadening of the stream thereby creating unnecessarily wide kerfs. 3. We can take advantage of the higher exit velocity which can be achieved and use it to efficiently blow slag from the kerf and achieve faster cutting speeds. 4. By using higher inlet pressures we can use smaller throat diameters to achieve the same volume of oxygen. However, this oxygen is more concentrated since it is at higher pressure. The expansion chamber then permits us to increase the velocity of the oxygen for greater efficiency. The end result is a narrower kerf, and 10-15% faster speed than can be achieved with an equivalent cylindrical orifice. High-speed nozzles can be designed to operate at any desired inlet pressure with virtually any exit pressure by carefully controlling the throat and exit diameters and the expansion angle between them. Fig. 22-27 High Speed Oxygen Orifice Taper Tool