Three stage can pressing and drawing process - presses, draws and finally presses with wall strain limited to 25 per cent during drawing

摘要

The three-stage pressing and drawing process produces cannisters for food storage and distribution. The stages are applied to a circular blank and comprises a first pressing, a drawing, and a final pressing respectively. The drawing stage may utilise a conical punch obtg. a smooth tapered transition (40) between the walls (34) and the base (35) of the can. The process also extends the application of combined drawing and pressing processes to cans where the ratio of height to dia. is globally less than 1 and between 1 and 1.5. The process limits the reduction in wall thickness during the drawing phase to a max. of 25%. The rate of drawing i.e. radial strain may be limited to between 10 and 20% and may reduce to zero in the case of a simple calibration. A punch with a nominal conicity of 5-30 min. may be used in the drawing operation, without lubrication. The final thickness (22) of the upper walls of not less than 75% of the base thickness (44).