Reducing and closing broad-walled metal spinnings and metal fabrications
Broad or thick walled metal spinnings require special roller paths and roller geometry. The application of heat is essential to the process, leading to the development of specific function machinery.
The ratio of wall thickness to diameter is critical in regard to metal stability and the ability resist buckling. Broad-walled metal tube, as used for high-pressure gas bottles offer particularly agreeable ratios.
In the instance of high-pressure gas bottles, the working strokes and roller geometry set-up can be approached so that the metal spinning is almost entirely under compression with minimal tension, reducing risk of buckling of the spun metal. Hot working techniques for the metal spinner means that the process limits are no longer dictated to by the formability of the metal. Instead it is possible that the metal tube will deflect around the unshaped metal cylindrical area as a result of the high axial load applied during the wall thickening process. In real terms this is of little concern because wall thicknesses can generally be achieved which are far superior to the requirements of high-pressure gas bottles. A three to four-fold increase in wall thickness can be achieved as a rule.
The metal spinning roller is mounted upon a pivotting slide with a simultaneous motion parallel to the axis of rotation. By introducing radial and axial motions via CNC, any required path can be produced. The main benefit of the radial motion is that the metal spinning roller is vertical to the face of the metal spinning at each stage and the flat compression inducing face of the roller is permanently in contrast. The technique also works at high speeds of up to 1200 rpm.
For forming the base, a fixed pad can be introduced instead of a metal spinning roller. The advantage is that the thickening effect is increased, but potential life is reduced due to frictional wear, so in reality rollers are preferred.
Before the final pass in base metal spinning, a specialised attachment, integrating a burner removes the oxide layer produced by the high temperature processes. At the same time, the temperature is raised to welding heat. The metal spinning roller has a sizeable contact area which welds the base by applying high pressure, to form an airtight closure. This final operation integrates an annular gas burner to prevent any further oxidation.
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