Easy-Open (EO) End-Making
The convenience of Easy-Open Ends (EO) has spread their use to most cans in use today. A pre-scored break line in the end, along with an affixed tab to break the score line and pull out the partial end, makes up the EO end.
Scoring steel or aluminum to enable a trouble free breaking at the score line requires excellent tooling and constant QA on the depth and the configuration of the score groove. Various gauges have been designed to do this, from X-ray to laser, to optical methods. The ideal design has yet to emerge (2.2013), to measure the depth at the micron level reliably and repeatably.
As the score measurement is not yet so reliable, end makers rely in addition on testers which mimic the break and pull forces a user would have to apply during the opening process. So called Pop & Tear (break and pull) testers establish a force curve during the opening process that the ends have to meet.
Much like the Sanitary ends, EO ends have to be tested for their ability to withstand pressure within the can. A special holding device will accept the EO ends, and pressure from the inside is applied. The deep countersink and the convex shape of the EO ends will buckle (outward extension) of the end. Due to the countersink, the end deforms during the test and cannot return to the original position. The buckled EO end will form a V-shaped deformation, a 'nose'. If it does that below the specified pressure it has failed.
During the same test, an EO end with a bad score (not enough residual score thickness) may blow out the internal removable part of the end.
A particular problem with Steel EO ends is rusting, both on the inside (break of the coating) and the outside. These ends thus need to be 'repair coated'. The means to do this is either with a spray method or an electro coating system.
While the spray lacquer is solvent based and requires thermal curing, the electro coating process uses a water based lacquer, also requiring thermal curing. The e-coating covers all raw or exposed metal edges, also those of the tab and is over all the better solution.