Chucks are a critical part of the seaming process, which hold the lid/end in place as the seaming occurs – first operation and then second operation.
Chucks are composed of extremely hard materials, suited to withstand many millions of can closure operations (10-40 million cans, for example). However, when the tooling material is subpar, or when there is too much pressure on the chuck, it can be slowly eroded. In this case, the chuck surface has to be flat and at a consistent angle. The analysis, done by an inROLL profiler, shows the erosion as it occurs on a chuck composed from material that is not strong enough and eroded by roughly 50 microns (0.05mm or 0.002″) after only 4 million cans!
An eroded chuck is dangerous as it will actually produce a much different seam if you use a wire gauge or a filler gauge to set up the seamer.
An eroded chuck will look quite different from damaged tooling, which is typically caused by incorrect seamer setup and can look like this: