Tin cans are widely used in the canning process of various products in the manufacturing industry, most especially in food and beverages. The canning process involves creating double seam tin cans to produce leak-proof and airtight product packages.
In today’s discussion, we are going to talk about the basic components of these double seam tin cans which you should know if you are a packager. But before that, let us take a quick look at how tin cans are manufactured in the next section.
Brief Overview On How Tin Cans Are Manufactured
Tin cans were originally made from sheets of steel dipped in liquefied tin material. However, this “hot dipping” method was slowly replaced by the tin electroplating method.
This new alternative allowed the application of different and more uniform tin weights on the steel sheet’s sides. Moreover, electrolytically coated tin plates are produced in continuous coils instead of individual sheets.
Nowadays, tin-free steel (TFS) sheets that are enamel-coated are extensively used for applications not requiring protection against corrosion or in facilitating the welding process of side seams. They are widely used for manufacturing two-piece tin cans in the food and beverage industry.
Now, onto the basic components of a double seam can.
3 Basic Components of a Double Seam Can
#1 The Can Body
The can body is composed of the flange and body beads and can either be a 2-piece or 3-piece can.
These are concentric ridges or depressions placed on tin cans and are located between the can’s top and bottom parts. They provide the can more physical strength so that it can maintain its integrity and hold out against the pressurization throughout the thermal processing stage.
This is the can body cylinder’s edge that flares outward which results in a ledge or rim. It is an essential component of a double seam and is shaped into a hook in the can body during the double seaming process. Also, it interlocks with the lid’s hook to complete the double seam.
2 Major Classifications of Can Bodies
A 2-piece can is formed using two methods:
- Drawing and ironing (D&I)
- Drawing and redrawing (DRD)
The D&I method is commonly used in processing aluminum cans in which the pressure of the gas during the beverage production retains the can’s shape. This method produces metal can walls that are thinner compared to DRD cans because of the wall ironing process in the can formation completion.
On the other hand, the DRD method produces thicker metal cans. These cans can withstand pressure in the thermal processing stage as well as in the vacuum formation process.
A 3-piece can have a body with two ends and a side seam that is welded. One end of the can is placed by the manufacturer of the can itself while the opposite end is connected after the can is filled.
#2 The Lid or Can End
The lid of the can is composed of an end curl and the sealing compound.
The End Curl
This component is sometimes called the cover curl and provides sufficient metal for the formation of a good lid hook. Some important aspects of an end curl’s design are the following:
- A good curl
- A suitable base for the application of the sealing compound
- Easy feeding into the can seaming machine
The Sealing Compound
A sealing compound or a rubber-based gasket is necessary to help form a reliable double seam. This sealing compound is applied by can manufacturers into the concentric grooves of the can’s ends.
#3 The Double Seam
This component is formed by attaching the lid to the can body using a tin can sealing machine. The flange of the can body and the lid’s curl interlock in the seaming process. Thus, forming a sturdy mechanical structure.
Generally, two operations are needed to form a double seam namely first and second roller operation.
First Roller Operation
During this operation, the lid’s curl is engaged/interlocked with the can body’s flange.
The interlocking process is performed by a can sealing machine’s first roller comprising of contoured grooves.
The initial seam produced in the first roller operation should not be too tight or too loose because you cannot correct the fault in the succeeding seaming stage.
Second Roller Operation
The second roller of the seaming machine that performs this operation has flatter grooves compared to the first one. The grooves in the second roller are meant to compress the initially formed hooks from the first roller operation together.
Moreover, the second roller operation’s purpose is to:
- Iron out wrinkles formed in the lid’s hook
- Distribute the sealing compound throughout the seam
- Develop proper tightness in the double seam
A double seam tin can is composed of components that are all important in creating a secure hermetic seal.
The interlocked can body and lid along with the compound used for sealing the double seam work together to create a hermetically sealed can.
Neither the interlocked lid and can body nor the sealing compound alone is able to create a reliable hermetic seal. Thus, you need to make sure that both are done properly.
Moreover, to help you create hermetic double seams, you need the appropriate tin sealing machine for your application. You should always choose a machine that is customized to your exact needs to avoid unnecessary problems in the double seaming process.