2-11. EXTERNAL DEFECTS--SEAM DEFECTS
During the manufacturing process of a can, seam defects may occur and result in
a false seam or an improper seam. Such seams are hazardous in that a good hermetic
seal may not have been formed or the seal may rupture under stress.
a. Lipper. A lipper or droop of the end seam is the most common seam defect.
It is a major defect. This end seam defect is caused by an incomplete tucking of the
cover curl or body flange and the untucked portion will project downward in one of two
types, either as a smooth U-shaped droop or a sharp V-shaped projection.
b. Skipper. Skippers are caused by the end seam not being completely
flattened during the second operational roll. This defect may appear as several droops
around the end seam or a slight increase in thickness of the double seam for a short
distance. It is a major defect.
c. Spur. Similar to a lipper, a spur is an incomplete tuckup of the cover curl in
the vicinity of the side seam or at corners of square or rectangular cans. It may be
obvious, or it may be indicated only by a slight increase in the width of the double seam
for a short distance. It is a major defect.
d. Spinner. A spinner (or semiseam) is caused by the can rotating with the
rollers during the second operational roll, thereby failing to compress the double end
seam and allowing the lid to spin on the can body. A spinner has little or no double
seam. It is a critical defect.
e. Cable Cut. This end seam defect is the result of cans, usually large cans,
remaining stationary on the conveyor line and the abrasive force of the moving line
wearing away the metal until the laminations of the double seam are exposed. See
Figure 2-8. It is not a defect unless laminations of metal show. It is a major defect.
f. Open Lap. This is a defect of the side or body seam. Defects of the side
seam are not as prevalent as defects of the end seams, and they all are the result of the
can manufacturing process. It is noted by an unsoldered area at the ends of the side
seam, immediately adjacent to one of the double end seams. It is a critical defect.
g. Wormhole. This is an unsoldered area anywhere along the side seam
except in the lap area (double seam area). It is a critical defect.
h. Cocky Can. A cocky can is a can that does not have the side seam
perpendicular to the end seam. It has an incomplete seam. The side seam is not
hooked uniformly for its entire length. It is a critical defect if it is a leaking can. It is a
major defect if the can is not leaking.