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Can seam inspection – frequently asked questions

Canned goods are big business all over the world. Everyone relies upon them these days, from food and beverage manufacturers to major pharmaceutical corporations. They’re relatively inexpensive to make and fill…but when things go wrong and a seam defect occurs, they can go very wrong!

Thankfully, the well defined and practiced process of double seam inspection stops potential problems before they unfold. It’s a comprehensive subject and across the Industrial Physics website you’ll find lots of blogs, articles and expert advice on the technical ins and outs of best practise. And the types of machines you can use to check your seam quality. 

But for now here is a condensed overview of double seam inspection basics. We looked into the main questions that people ask online when investigating the topic. And now we present you with our frequently asked questions (FAQ) guide to double seam evaluation 

What is a double seam?

Simply put, a double seam is an effective way of making sure that your canned goods are sealed properly. So that your product stays on the inside and environmental contaminants remain on the outside. 

It’s a clever, two-stage method of creating a solid hermetic seal. This seaming process mechanically interlocks the edges of the can’s body to the can’s ends. It replaced the crude method of soldering or welding the parts together and was developed as a safer and cheaper alternative.  

The double seam is created when the can maker interlocks layers of can end and can body material together. It’s an effective way of ensuring seam quality. 

During the first stage of the double seaming operation the end curl is pushed up towards the seam, which creates the cover hook. Meanwhile the can’s ‘flange’ is pushed downwards to form the ‘body hook.’ Now the seam of the metal is ready to be compressed during the second part of the process – forming the double seam. 

The initial operation seam is the more important stage of the two: if you get it wrong from the outset and cause a seam defect, it can’t be corrected by the second operation roll.  

 Can a seam be inspected?


To protect against leak-causing seam defects and ensure that your goods are protected, you’ll need to meticulously inspect the double seams of your cans. Plus when you encounter product defects, it’s normally a good idea to double check your can seam measurements! 

 Metal packaging is a great choice for food and beverage makers. Properly made cans with good quality seams keep your products safe and give them a long shelf life.  They’re recyclable and relatively inexpensive…plus they look smart too. 

But if your cans and metal packages aren’t properly finished. If your double seams aren’t hermetically sealed, then you’ll run into problems. For example, if your products leak out of their containers, or if contaminants seep into your cans, then this will lead to product recall. All of which will cost you time and money with the added threat of reputational damage.  


How do you measure a can’s seam?


You’ll need to know a few details to properly undertake can seam measurement. Measure up properly, with highly accurate double seam inspection equipment, for confidence that your seams won’t be too tight, or too loose. Here’s an brief summary of the essential measurements to understand: 


  • Cover/end hook length – the curled end of the lid during the formation of a double seam  
  • Body hook length – the size of the can’s ‘flange’ after the double seaming process  
  • Seam thickness –  width of the entire double seam, once curled and completed   
  • Seam length/width – measured from top to the bottom of the double seam  
  • Overlap – measures the outer side of the double seam, as it interlocks over the body wall 
  • Countersink – total height of the double seam, once curled and completed.   
  • Body wall thickness – last, but not least…the width of the can’s body.

Got an infrequently asked double seam question?

 These were some of the top can seam inspection frequently asked questions at the time of writing this guide. But if you need further advice, get in contact with our seaming process experts today. They’d be happy to talk you through any aspect of double seam inspection. They can also explain which of our industry-leading devices best suits the needs of your business.