Canning and Fish Packaging Technology

Unit 3 - Unit operations in canning

3.2.4.2.5.Steps involved in Examination of double seam
External Examination of double seam : Seam is checked all round the can to see whether seen characteristics are different from a good seam. The defects noted down.

Measurement of external dimensions : Seam thickness counter sink and seam length using screw gauge.

Part of the Seam Gauge to measure seam thickness and seam length

Examination of inner parts of a seam : After cutting the seam of 2 mm width, seam is visually examine or by using a magnifying glass. If the gaps are more or if the hooks are too small or if the overlap is less, on a note has to be made.

Measurement of inner dimensions of seam parts : The seam is separated into body hook and cover hook and their dimension are measured. Overlap% is calculated and whether these are within the limits for a particular can has to be checked.
 
In addition, the lid is cut all-round and cover portion of the seam is removed in the form of bangle. The inner portion of this bangle is the cover hook and examined for minute wrinkles. If there is no wrinkle there it is considered that the seam is tight. Downward wrinkles at the spreading downward from the upper edge to the lower edge indicates loose seam. These wrinkles should not cover more than a quarter of its length and if it is more than the seam is not safe. However, the safety of seam cannot be judged only based on wrinkles. In small cans as the curvature is more, there is a possibility of formation of more wrinkles than large sized cans.