packaging materials 7. metal packaging for foodstuffs - Europa

Pa c k a g i n g ma t e r i a l s: 7. m e t a l pa c k a g i n g f o r f o o d s t u f f sEarlier technology soldered instead of welded the side seams of the can bodies, which resulted in leadcontamination of the contents. This practice started to cease in Europe in the early 1980s and has beenreplaced by welding all over the world today. Soldered cans are not traded internationally anymore. Theuse of a pure tin solder is retained for a few very specific applications.In some types of three-piece cans, the side seam is crimped rather than welded or soldered. Non-weldedseams are either folded or interlocked folded. A gasket could be used for sealing. This does not apply forthe standard food can that is sterilised.It should be noted that some three-piece food can bodies, particularly those with ETP bodies, are notinternally lacquered, but their TFS ends are. However, three-piece cans to be filled with dry food, e.g. milkpowder, instant baby food, sweets or roasted nuts, are usually not coated at all on the internal surface.Dry foodstuffs such as biscuits or tea are available in tin boxes. These are in essence a cylindrical orrectangular three-piece can. The lid is not seamed on but is formed as a “slip on” or “plug” lid. The foodis not processed in such boxes.Can endsThe lids are always attached after filling the can with foodstuffs, thus the packers and fillers purchaseempty cans and lids and seam the lids onto the can.The ends on a can are seamed onto the body to give a hermetic seal. The lid is seamed on when the canis filled. The exceptions are open top cans (for example sweet or biscuit tins). A double seam is shownin Figure 1. Many of the dimensions are critical to ensure that any potential microbiological ingress isminimised (can integrity).Figure 1: Double seamSeamThicknessSeam GapBody HookCountersinkDepthOverlapEnd/CoverhookSeam LengthEndThicknessFlangeThickness10