Metal strapping seals come in a variety of styles and sizes. If you aren’t sure which seal is right for your strapping application, this guide will serve as a comfortable starting point to help you figure it out.

Why You Need the Right Seal

The right metal seal will allow you to secure your load with maximum holding power. Whether you’re using poly strapping or steel strapping, the type of seal you choose will determine the joint strength of your load. The joint strength goes on to define your maximum strapping break strength, which is a value you want to stay as high as possible in order to protect your shipments.

Choosing the wrong type of seal for your application will limit your break strength and cause a weak holding power. The right strapping seal will make sure your load is able to withstand impacts and other movements it encounters, so your products arrive in pristine condition every time.

Types of Metal Strapping Seals

Let's exlpore the different types of metal strapping seals that are available. Each type of metal seal is designed for a specific type of application. 

Thread-On Metal Seals

This type of metal seal must be pre-threaded over the strapping ends before you tension them. Once the tensioning process is complete, then you will finish the joint by closing the thread-on seal. These seals are often used for loads such as bales and bundles. Thread-on seals are commonly used for larger strap sizes.

Snap-On Metal Seals

Snap-on metal seals are made for both poly and steel strapping applications. These seals eliminate the need for pre-threading a seal, which helps speed up the strapping closure process. You simply place this seal over the overlapping ends of your strapping during or after the tensioning process. Snap-on seals can be used with manual sealers or powered strapping tools.

Serrated or Grit Coated Seals

Before we go more in-depth into the types of seals available, we wanted to make sure we highlight the difference between serrated and grit coated seals compared to normal, smooth seals. Serrated seals are manufactured with little teeth that dig into the surface of your strap to create higher friction. Grit coated seals feature an interior surface that’s rough enough to grab waxed strapping to provide maximum holding power. Some of the other types of seals mentioned below can come smooth, serrated, or with a grit coating.

Open-Flange Metal Seals

Open-flange metal seals are a heavy-duty version of the snap-on seal. They are used on steel strapping when the application requires high joint strength. They have one side that is open all the way and another that is partially closed. This design allows them to be sturdier than snap-on seals while still eliminating pre-threading.

Push or Push-Type Metal Seals

Push metal seals are able to withstand higher stress because of the overlapping metal flanges, or edges. These seals are pre-threaded onto overlapping strap ends. As the tensioning process begins, the nose of the tensioner is pushed against the seal. These are used mostly in steel strapping applications for heavier load containment.

Nestack Metal Seals

A Nestack metal seal has interlocking nibs that hold it together in a stack. These Signode seals are designed specifically for applications using powered tools or automatic equipment. The stacks can be conveniently placed into the magazines of seal feed combination tools or power strapping machines. They are also easy to store at workstations and help limit the amount of downtown experienced during strapping applications. Nestack seals are available for both poly and steel strapping.

Types of Metal Seal Joints

Choosing the metal seal design for your application is only half of the battle. The next decision you’ll need to make is what type of joint to form using your seal. There are two main joint styles for metal seals, which are notch style and crimp style. Each of these joint types are designed for specific applications to provide the correct amount of joint strength.

Notch Joints

The first joint type is a notch joint, which involves cutting little tabs into the seal and the strapping. Notch joints can either be formed facing down towards the package or facing upward in what is known as a reverse notch joint. Notch joints provide strength through the mechanical interlocking between the seal and the strapping ends. This type of seal joint is commonly used for waxed strapping. It’s a good option for packaging and unitizing applications.

Crimp Joints

The second type of metal strapping joint is called a crimp joint. Crimp joints are formed when the sealer bends or presses undulations into the metal seal and the strapping ends. This creates crimps along the edges of the seal and strapping. The now deformed seal will provide stronger frictional force, keeping the joint strong during transit or storage. This type of seal is frequently used in railcar or cargo ship strapping applications because of it's high strength.

Both notch and crimp joints can be single, double, triple, or even quadruple. The majority of notch or crimp joints with be doubled. Triple and quadrupled notch and crimp joints are used for the heaviest-duty applications, such as railcar loading or freight ship travel.

Matching Seals with the Right Tools

To wrap up our metal seal guide, we wanted to talk about different sealers. Your metal seal is perfectly matched to a type of sealer, and using the correct sealer is important if you want a durable strapping joint.

The first thing to consider when choosing which sealer to use is whether you want to create notch or crimp joints. Sealers are typically only able to do one or the other, so you’ll want to make sure you know which joint type you’re going to be working with for maximum joint strength. Next, you need to decide if your application requires a front-action sealer or a side-action sealer.  

Front-Action Sealers

Front-action sealers are held perpendicular to the strapping in front of the operator. As the operator goes to complete the seal, he or she will push the handles of the sealer together in close position to their chest. Front-action sealers are used mostly for light-duty strapping applications where the strapping is in a normal position that's easy to grip with the strapping sealer.

Side-Action Sealers

Side-action sealers, on the other hand, are generally not placed in front of the operator, but to their side. The lower handle of the side-action sealer can be rested on the package being strapped. As the operator goes to close the seal, they apply all their weight onto the upper handle to finish the closure. Side-action sealers are used for heavy-duty applications and closing strapping in odd positions.

We hope this metal strapping seal guide helps you understand the different types of seals available and how they are used across the packaging industry. For all your strapping needs, we’re here to help. If you still have questions about which seal is right for your application, contact us today to speak with a packaging professional.