Questions about steel aerosol cans
1. Either from the microscope view above or using your own USB microscope and a mm scale work out the pulse frequency of the weld current if the can seam is is 20 cm long and moves through the welder in 0.5 s.
2. Why does the printing on the can stop few millimetres from the seam line?
3. Why is copper used for the electrode wheels and the wire in the welding machines?
1. Each nugget is the result of one pulse of current. The nuggets are 1mm apart. The speed is 40 cms-1 or 400 mms-1. This is 400 nuggets per second, so the pulse frequency is 400 Hz.
2. The printing inks and varnishes are insulators. They would stop the current flowing through the steel sheet.
3. Copper is a very good conductor of electricity. It can take high currents without getting too hot.
Questions about aluminium aerosol cans
1. Why is the extrusion process used for aluminium cans not suitable for steel cans?
2, What is the difference between the printing process between aluminium cans and steel cans?
1. Steel a harder metal. It cannot be extruded from a cold slug. Steel can be stamped and punched, but it will not flow into a long can shape.
2. Steel cans are printed as a flat sheet before cutting. Aluminium cans are printed when they are cylindrical. The shaping of the top of the can is done after printing.