Glossary of double seam can defects

Knowing what to look for – and how to describe it – is key when it comes to identifying and preventing double seam can defects. Our glossary of common issues is designed to help your seam testing process run as efficiently as possible. 

Common beverage can seam defects

Can buckling

Can buckling is an obvious twisting or crumpling of the metal that appears after the double seam is completed.  Although it most commonly occurs in the can body just under the seam,  it can appear anywhere, and  

Cover hook wrinkling

A reliable indication of proper seaming pressure is obtained from inspecting the cover hook wrinkling. Wrinkles will naturally occur as the various parts of the seam are pressed together in the inside radius of the cover hook. Measuring the type, depth and quantity of the wrinkles will check that the correct pressure is being applied and ensure your seamer is operating properly. 

Creasing

Also sometimes known as scoring, creasing is the name for tiny dents below the radius of the lid’s hook where  contact has been made with the can wall. This is a can seam defect most commonly found in aluminum beverage cans with a thin neck.  

Cut over

A cut over is a critical defect where the metal is fractured at the top of the seaming chuck wall. 

Dead head

Dead head is a condition where the first and/or second operation seam is not completely formed around the circumference of the can. 

Droop

Noticeable by a scalloped effect along the seam’s bottom, a droop occurs when a small part of the double seam overhangs the bottom.   

False seam

The false seam can be hard to spot – from the outside it looks as though the seam has been completed. However, a false seam occurs when the end and body are not hooked together, instead, they’re folded over against themselves and compressed.  

Knocked down flange

A knocked down flange is a critical can seam defect. It occurs when the cover and body hooks do not interlock in a localized area of the double seam. 

Long body hook

A long body hook is a can seam defect where the body hook length approaches or exceeds the specification. 

Long cover hook

A long cover hook is a can seam defect in which the cover hook length approaches or exceeds the specification.  

Loose first operation seam

A loose first-operation seam may not allow sufficient tuck up of cover curl to form a sufficient amount of cover hook and overlap. 

Low free space

Not always visible to the eye, this can seam defect occurs when the seam is too tightly rolled, during the 2nd operation. The double seam may look mangled, or the defect may be found using testing equipment like a CMC-KUHNKE QbyV End Profile Analyzer. 

Long seam

An overly long double seam can be hard to spot, but it causes weakness in the integrity of the seal. It has a number of causes, including damage with worn tooling or an incorrect roll profile.  

Mismatch

Obvious to the naked eye, this is a can seam defect caused when the flanges of the lid and the can are not properly aligned and amalgamated during the seaming process.   

Seam bump

A seam bump is a short area of the double seam where the seam thickness suddenly increases by .004″ or more. 

Seam impression

As the rollers push the cover and body hook materials together, and against the seaming chuck, an impression is left on the inside of the can body. Too much pressure can cause this impression to damage the can liner. 

Sharp seam

A sharp seam is a can seam defect where the seam has a sharp edge or radius on the upper inside edge of the countersink wall. 

Short body hook

A short body hook is a can seam defect where the body hook does not meet the minimum specification.  

Short cover hook

A short cover hook is a can seam defect where the cover hook does not meet the minimum specification. 

Pleat

A pleat is a fold in the cover hook that extends from the cut edge downward toward the cover hook radius – sometimes below this radius, you’ll see a sharp vee. 

Spinner

When a double seam is not tight enough, the process can be incomplete, creating a spinner effect. It is normally caused by the seaming chuck slipping on the end of the can body.  

Split seam

Also known as a clam shell, a split seam is a serious visual can seam defect that can be seen around the double seam itself. It can be caused by a too high or tight second operation, excessive sealing compound, or too high lifter pressure.   

Sprung Seam

A Sprung Seam is a can seam defect where the seam is pulled away from the body wall. In some extreme cases, the seam is pulled away from the body wall the entire way around the can.  

Tight first operation seam

A tight first operation seam can create flatness on the bottom of the first operation seam throughout its length. The cover hook may also be turned back into the body hook. 

Vee

Similar to a droop, this can seam defect involves a sharp protuberance that can occur anywhere around the seam.  

Wooling

Most common in aluminum cans, wooling (also known as silvering) refers to the shaving of material from the cover or can body flange during seaming. Small flakes of metal can be seen around the seam after the seaming process.   

Get the lowdown on important elements of the canning and testing process with our can guidebook, or find out more about can inspection processes to cut down on potential beverage can seam defects. Whether you’re using visual inspection equipment or traditional seam inspection instruments, we can help protect your production lines.  

Check out our seam inspection solutions here

Diagnose and fix your seam issues

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. 

Expert double seam can testing

We have more than 50 years of experience in beverage packaging testing, with expertise in everything from enamel rating to end buckle testing. We’re here to develop innovative double seam inspection instruments that will protect your canning line against costly can seam defects. 

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

The Industrial Physics Seam School platform is perhaps 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. 

If you’d like help and advice in setting up or adjusting a seam testing solution, you can chat with our knowledgeable team.  

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