How cans are sealed: our guide to the double seaming process

Can seaming to achieve robust, hermetically sealed metal packaging is a preferred practice to protect a wide range of types of products across many industries. 

An effective double seam is crucial to the integrity of a can. The process of can seaming has been around for decades and has undergone some massive transformations over the years. 

There are a raft of checks and counterchecks that can be performed to determine the quality of the can and can makers and fillers must prioritize a healthy double seaming operation. 

When a double seam defect arises, it can lead to health and safety problems, costly product recalls and reputational risk. In this blog we look at how the double seam revolutionized can manufacture and introduce some double seamer machines developed to ensure the quality of every can on your production line. 

How are cans sealed?

Can seaming is an old packaging technique that goes a long way back to the industrialization era. After the double seam was invented, it removed the need to use solder when sealing cans. But what is a double seam closure and why is it so popular?  A double seam is a canning process that creates a seal between the can body and lid (also known as can end). It does this by mechanically interlocking five layers of material together – three layers of the can lid and two layers of the can body. This process creates a hermetic seal to keep the contents protected from contamination or degradation.    

The combination of materials used to make a can has expanded massively since the double seam was first introduced. From traditional tin or steel to aluminum or plastic, there’s now a wide variety of ways to double seam your canned products.  

The benefits of the double seam

The double seam has a number of advantages and benefits when compared to other forms of seaming, here’s just a few: 

• Robust protection: double seaming assures you a tight lid that won’t come off on its own. A well constructed can will continue to protect its contents if knocked or dropped. It’s a useful method for packaging food or even toxic chemicals. When you have fought hard to build your reputation and one leaking can is all it takes to spoil it, double seaming makes sense. 

• Good value: it’s true, double seamer machines can be expensive and sometimes need specialized operators. But companies typically suck up the cost implications as the leak-protecting reliability of the double seam is second-to-none. 

• Versatility: you can use the double seam to protect all kinds of products from industries as diverse as the food and beverage industries through to inks and coatings and automotive manufacture. When companies want to diversify into other products – from beer bottles, to sardine cans, or even huge tanks of paint – they must command control of their double seaming process.  
• Rapid: the double seaming process is fast, automated and can be used to produce a large volume of cans in a matter of minutes. Some can seaming machines are advanced enough to handle tens of thousands of cans in a single day! 

The double seaming process

Not all double seams are the same, but they’re all created using a double seamer machine capable of curling the flange (or edge) of the can body down over the lid to create an interlocked seam. 

Using a double seamer machine, there’s a variety of seaming approaches. While the machines themselves are different, there are three main stages to the double seaming process:   

1. Compression – the body of the can is tightly held in place while the lid is lowered into the correct position, ready for interlocking to take place  
2. First roller operation – the lid is hooked over the edge of the can and a roller pushes against the lid’s flange until it folds neatly around the body’s edge 
3. Second roller operation – a second roller applies pressurized force to the can’s hook, creating a double seam that’s completely interlocked and hermetically sealed. 

Find everything you need to know about double seaming and testing in one handy place by downloading our seam inspection guidebook.   

Typical double seam defects

Can manufacturers and fillers encounter a number of common seam defects, all of which our devices can solve. From buckling and creasing  to false seams and spinners, you can read some double seam terminology and learn about common problems through our glossary of seam defects blog.  

The history of the double seam

The invention of the double seam in 1888, by Max Ams, eliminated the need for solder in the canning process. The German born New Yorker operated a highly successful fruit and vegetable canning and exporting business, and we have him to thank for the double seaming operation.  

With roots in the era of industrialization, the double seam is almost as old as the canning process itself. New processes and techniques have ensured it remains the method of choice for sealing cans right up to the modern day.   

Double seams today

Double seaming remains a simple, proven and reliable way to create a hermetic seal. These days, to set up a successful double seaming operation, companies need a testing and measurement process that conforms to exact seam measurements, industry specifications, and various quality assurances.   

Industrial Physics double seamer machines

Across the Industrial Physics portfolio we make a wide range of double seam inspection tools and accessories.  

Our SEAMetal double seam inspection devices combine highly accurate optical technology with easy-to-learn, intelligent software. They offer the most flexible solution for double seam testing available in today’s marketplace.  

The SEAMetal range includes everything from handheld devices like the SEAMetal Portable through to the SEAMetal HD: double seam inspection for food cans and our SEAMetal machines developed for craft breweries. 

Across the full catalog of double seam inspection options, you’ll also find SEAM Doctor powered devices like the SEAMetal HD for aerosol cans. 

Masters of metal packaging

At Industrial Physics, we love making innovative double seamer machines that protect our customers’ canning lines against costly product defects. 

We share our knowledge with customers and the wider industry. As well as publishing blogs like this one – a glossary of double seam defects or this article on how to measure a double seam, we created an online platform for sharing advice on solving all manner of double seam defects. 

We think the Industrial Physics Seam School platform is the most comprehensive double seam education freely available on the web. You can browse through the articles using the categories and get solutions to improve your double seam operation. 

Whatever the double seam defect you’re dealing with, we can help, and we’re bursting at the seams to hear from you! 

Contact us – Industrial Physics