TWI Industrial Member Report Summary 676/1999
'Vortex generator' nozzles, which increase cutting speed by rotating the oxygen stream to supply the cutting front with fresh oxygen, are claimed to double cutting speeds. Gains in productivity of this order without significant increases in running costs could have practical application for steel fabrication.
Oxy-fuel cutting was first discovered in 1904, and despite being the oldest profile thermal cutting process, it is still in very common use. Its main technical advantage is for cutting thicker steels (>60mm), for which there are no practical alternatives. Although it will cut relatively thin steels (ie <20mm), processes such as laser and plasma make much faster and, in the case of lasers, higher quality cuts. For these thinner steels, the advantages of the oxy-fuel process are its relatively low capital cost and its ease of application.
The process differs from most other cutting techniques in that it relies upon a thermal chemical reaction between the cutting stream of oxygen and the iron in the steel. It is largely the speed at which this reaction takes place, which limits the speed of the cutting process. The rate of reaction can be increased by a number of methods such as increasing the purity of the cutting oxygen, using liquid oxygen, heating the oxygen and adding other agents to the cutting stream. All of these solutions result in an increased operating cost.
A novel solution to this problem has been proposed which, if effective, would only result in a very small increased consumable cost. If a twisted insert is placed into the cutting oxygen stream, controlled turbulence can be achieved. The helically twisted oxygen jet can then supply fresh oxygen to the cutting front and the maximum cutting speed can be increased. For conventional nozzle systems is estimated that only 80% of the oxygen stream is actually used to make the cut.
- To determine the potential of vortex generator nozzles for increased cutting speeds in oxy-fuel cutting.