Seam Thickness is one of the key parameters that ensures that the seam is hermetically sealed. A seam with a tight thickness would have very little freespace, which means that the compound material will form a gasket and the seam will be properly sealed.
The ideal Seam Thickness:
Seam Thickness= 3x Cover thickness + 2x Body thickness + sealing compound allowance
- Sealing compound allowance can be around 0.005″ (0.13mm).
What to do if Seam Thickness is out of spec?
In most cases where there is a seam thickness problem, it is recommended to ensure that the second operation is properly set up.
How to measure Seam Thickness?
- Seam micrometer – a seam micrometer is not a very accurate tool, it is highly recommended not to use this type of tool these days.
- A fixed angle Seam Thickness Gauge – this type of gauge is essentially a micrometer (digital or analog) that is set at a particular angle. This is not recommended as the seam thickness measurement has to be exactly measured at the chuck wall angle for a repeatable exact measurement.
- Balanced Seam Thickness Gauge – this is a self balanced seam gauge that has a high repeatability and is balanced to the Exact Chuck wall angle of the double seam. Typically, this measurement is done before emptying and cutting the can in order to maintain the internal pressure.
- Optical Measurement – Using software like SEAMetal, the cut seam is visually inspected with software after it is emptied and cut. In this case, the pressure is lifted from the double seam, however you should use software that can compensate for difference in compression.