DWI Monobloc Aerosol Can-Making
The DWI starts with making a cup (blank and draw), mostly in multi die presses from coil. The base material can be single reduced ETP or Aluminum. The DWI process was designed for cans with internal pressure only, such as cosmetics or pharmaceuticals. For structural reasons, the wall thickness at the top of the can is thicker than the mid-wall area. Specifications for material thickness varies slightly from one can-maker to another based on their experience or the material used. Shaped cans need a heavier gauge and a lower hardness to stand up to the stresses.
Crucial for their success in maintaining their specifications, is accurate gauging. The results of the process, the actual can, is normally measured after the trimming operation. (See figure 1.)
In order to attain the desired wall thickness, the punch and die (or ring) of the tooling have to be matched accurately. High resolution optical measurement equipment is in use to match the right punch with a ring. Lacking such gauging with sub-micron resolution, forces the can maker to try out the perceived best combination of punch and ring, which takes time, wastes material and reduces run time. (see figure 2.)
A most important test for the completed Monobloc Aerosol can is the Burst testing. Here the can is subjected to a high internal pressure and various events during the pressure increase are measured and reported: buckle and reverse of the bottom dome, bursting of the aerosol can. At each level the pressure has to be held for a specific time. The test procedure mimics possible environmental conditions the cans may be subjected to. Failures in any of the tests may make the containers unsafe to use. (See figure 3.)