Abstract: Disclosed is a method for measuring the metal exposure in a resin covering area of a metal container or a constituent member thereof, which comprises contacting the resin covering area of the metal container or the constituent member thereof with a measuring electrode through an electrolytic solution, relatively moving the resin covering area and the measuring electrode in a certain direction while always holding the electrolytic solution between the measuring electrode and the resin covering area, measuring a leak current between the metal substrate of the metal container or constituent member at predetermined pitches and detecting the metal exposure of the resin covering area as leak currents at respective parts discriminately.According to this measuring method, the degree of the metal exposure can be easily measured as the leak current at respective parts discriminately, and statistical processing of the measured leak current values can be easily performed.

Abstract: A rotary light tester for continuously inspecting empty cans discriminates between good cans and defective ones by judging the amount of transit light entering the interior of the empty cans. The light seal circular plate and the freely-reciprocative slide pusher which rotates with the continuous rotating star wheel face each other sandwiching each can receiving seat therebetween. The nozzle opening of the tip of the slide pusher vacuously holds the bottom end of an uncoated or unprinted bright can received in the can receiving seat one by one when the can enters into the empty can supply station just after the trimming. Then, in the light detection station, the opening end of the can is inserted into a groove of the light seal circular plate having a black non-luster surface to further the reflection attenuation of outer entry light, a trap is disposed in the deepest portion thereof, and a conical introduction arrangement makes it easy to insert the opening end therein by advance pushing of the slide pusher.

Abstract: Method and apparatus for inspecting empty cans entirely automatically includes a flange inspecting process and a drawing condition inspecting process. The flange and the drawing condition inspections are simultaneously carried out in the same inspecting station during the forcible rotation of the can. The flange portion is checked for craks and length, and the outer body surface is checked for the drawing conition respectively in a non-destructive and contactless manner by utilization of static electromagnetic inspection and light reflection inspection methods. A prestored reference value signal, which is compared with a converted electrical signal for the determination of whether cans are good or not, is a signal of a value calculated by a microcomputer on the basis of values which are sampled, equally divided, signal values corresponding to one rotation of a forcibly rotated standard good empty can.