CAN SEAM INSPECTION
Can seam evaluation is the responsibility of company that is filling and closing the can package. Depending on the type of products that are canned, food/beverage, pharmaceuticals, etc., there are specific regulations on how and when can seam evaluations are to be done, as well as documentation and reporting guidelines. Your Quality Assurance program should, at a minimum, include hourly visual seam inspections, and a complete seam tear-down every four hours. A physical report of the complete seam tear-down should be also be completed and kept on file.
Understanding can seaming and proper can seam evaluation takes time and experience. There are many resources available online, see links below. Make sure your can supplier provides you with the Can Manufacturers Seam Specifications for the can(s) and lid(s) they actually ship to you. The specifications are the measurement ranges of each of the individual parameters that make up a can seam. If all measurements are within the range the can manufacture provides, a hermetic seam is achieved. Evaluation of seam measurements will also provide information for adjustment of can seamer, if you are not within the specific ranges, to achieve a hermetic seam.
External examination of can double seams should be made at least every 4 hours of operation (once in the morning and once in the afternoon) to check for proper seam adjustment. Examinations should be more frequent if changes in can size, shut down, or problems with a particular sealing machine have occurred.
In order to make an internal inspection of the seam, the body and end must be separated in a manner which will expose the body hook and cover hook so they can be accurately be measured. This procedure is termed “cut-down”, “stripping”, or “tear-down”.
The seam may be “cut-down” by filing the edge of the can lid with a flat file down to a point where the hooks of the seam are exposed. The seal can then be examined visually for proper hook formation and tightness. The seal can be further evaluated by filing horizontally for about 1 inch along the top of the lid until the edges of the seam can be seen and pulling the outer edge of the seam downward separating it from the can body from the cover hook (Figure 1). Dixie Canner seam production will give you an idea of how the seam is made and how it should look (Figure 2).
Cutover is a situation where the seam is sharp enough to fracture the metal at the top inside portion of the seam. Possible causes are a worn seaming chuck flange or roll grooves, or the first or second seaming operations are set too tightly.
Droop is a situation in which there is a projection of the double seam below the bottom of the normal seam. Possible causes include excessive body hook, or the first operation is too loose.
False Seam is one where a portion of the seam is entirely unhooked and in which the folded cover is compressed against the folded body hook. Possible causes for this situation are a bent can flange, missassembly of can and cover, or the can is not centered on the seaming chuck.
Proper seam formation cannot be judged by purely mechanical means or measurements. The evaluation of good double seams requires experience, skill, and above all good judgement.
Manual Can Seam Tear-Down Video (Sanitary Can): Video is at bottom of page
There are many companies that offer can seam saws and optical scopes with software to evaluate can seams, produce reports, etc. https://doubleseam.com/ is another can seam information resource that provides in-depth information on all types of double seams.
Below are links to important rules and regulations for can seaming. Regardless of product or further processing, you are responsible for making sure all of your products are packaged with an acceptable seam. Your QC program should become more comprehensive as more knowledge and experience are gained.