What Is A Bump on The Edge of The Mouth of An Easy Open Aluminum Can?

Aluminum can is a very common packaging container in our daily life,

widely used in the packaging of various beverages and food. Many people may notice a noticeable bump around the edge of the can mouth when using an aluminum can, but few know the science behind and role of this design. Ask you what's inside that bulging circle around the edge of an aluminum can, and you'll probably blurt out, "I'm sure it's hollow." But it's not!

In 1810, to improve the preservation of food, Peter Durand of England invented the world's first metal can. It was not until more than a century later, however, that a truly easy open aluminum can was invented. In 1959, the Americans through innovation, the use of can cover materials made of rippers, and then set the pull ring and riveting, with accurate scoring, successfully manufactured a complete metal aluminum easy open can lid . This innovation significantly promoted the advancement of metal container technology. By the 1970s and 1980s, the production of aluminum cans gradually spread to Japan, South Korea and other regions.

in China, in the early 1980s, Qingdao Brewery introduced well-printed all-aluminum 2 piece cans from Japan for the first time in order to adapt to the packaging needs of product exports, which marked the beginning of the wide application of cans in China. Cans can be divided into two main categories according to the raw materials: one is made of tinplate, such as Lulu Almond Renlu and JDB packaging; The other is made of aluminum, such as canned Coca Cola and beer, carbonated drinks and so on

The structure of metal cans can be further subdivided into two-piece cans and three-piece cans. The three-piece can is composed of three parts: the can body, the can bottom and the can cover. The can body has joints, and the can body is connected with the can cover and the can bottom through the rolling edge. The two cans are composed of two parts: the can cover and the stamped seamless can body with the bottom. The can body and the can cover are formed into one by rolling.

In brief, when aluminum is used as a material, it is usually made into a two-piece can; When tinplate is used, it is mostly in the form of three-piece cans. The main difference between the two is the manufacturing process of the tank body: the two cans have no welds and form a joinless whole, which helps prevent leakage.

In fact, the body of an aluminum can is formed by stamping aluminum sheets. The thickness of this aluminum sheet is about 0.3 millimeters. During the stamping process, the aluminum sheet is placed on a tool called a stretch die. A cylindrical punch then presses down on the sheet from above, turning it into a short cylinder shaped like an ashtray. This process is called stamping.

However, after only one stamping, the cylinder formed by the aluminum sheet is still relatively wide and thick, which has not yet reached the shape of the final aluminum can, so multiple stamping is needed. Each stamping makes the aluminum sheet thinner and smaller in radius, while increasing in height. After several such presses, the original round aluminum sheet gradually forms the outline of the aluminum can.

At this point, there are only two steps left to make the aluminum can: one is to form the depression at the bottom of the aluminum can, and the other is to seal it. Forming the bottom depression requires only the use of a dome-shaped tool, similar to the stamping process where an aluminum can is pressed against the top of the half-circle to create a depression shape. This recessed design is similar to an arch bridge and is able to withstand greater stress. All of these processes together take only a seventh of a second.

After the top of the aluminum can is trimmed, the outer packaging can be sprayed. At the same time, the inside of the aluminum can also needs to be coated to prevent acidic drinks from reacting with the aluminum and avoid excessive intake of aluminum affecting the health of the nervous system. Next, the neck of the can needs to be pulled thin to prevent wrinkles in the thin-walled aluminum can. Finally, the most critical step is to seal the aluminum can, which is why there is a bump around the edge of the aluminum can mouth.

What is a bump on the edge of an aluminum can?

To keep the soda from leaking, we seal the top of the aluminum can. At this point, it is the turn of our protagonist today - the ring of the drum to play a role. This technique of sealing aluminum cans is also called double sealing, so what is double sealing?

As shown in the picture below, red represents the aluminum sheet on the lid of the aluminum can, and blue represents the aluminum sheet on the body of the aluminum can. The lid of the tank and the rim of the tank will be tightly fitted under the action of mechanical pressure, and this process will form the first layer of the rim. Then, by applying pressure again, a second layer of coilings is formed, which is located inside the first layer of coilings. In this way, two layers of seals are formed between the lid and the body of the tank, which look like spring rolls.

However, the double sealing itself can not completely isolate the inside and outside of the can, in this layer of double sealing inside the gap filled with liquid sealant. It acts as a special glue that holds the two aluminum sheets together tightly and prevents the soda from leaking out. What's more, it prevents dirt from getting inside the aluminum can. The composition of the sealant is generally a mixture of latex, rubber or resin, and dissolved in an oily solvent. So who would have thought that an oily liquid would be wrapped around the rim of an aluminum can?