As we all know, two-piece aluminum cans have many advantages, such as: light weight, easy to carry; not easy to break, good safety; excellent sealing, long shelf life of contents; beautiful printing on the can body, eye-catching; good thermal conductivity, canned drinks cool quickly; filling faster and more efficient than other packaging materials; easy to stack and transport; cost-effective; 100% infinitely recyclable, with the highest recycling rate among all packaging containers, protecting resources and minimizing waste generation, which is conducive to sustainable development...
These advantages have won the positioning of two-piece aluminum cans as the best beverage packaging container in the minds of consumers in the United States and Europe, and the demand has remained high for a long time. According to incomplete statistics, the market demand for aluminum cans (lids) in the United States alone in 2016 was about 100 billion sets. In contrast, the market demand for aluminum cans (lids) in China is about 38 to 40 billion sets, and the market growth space is very large.
However, whether from the perspective of the product itself or the production process, the production difficulty coefficient of aluminum cans (lids) is relatively high. On the one hand, from the perspective of the product itself, aluminum cans (lids) are thin and "delicate", and the deformation during the manufacturing process is large, and the "growth" process seems difficult. On the other hand, from the perspective of production technology, the production of domestic aluminum cans (lids) is high-speed automated mass production, and the can (lid) technology is purely imported. It is still in the process of reference and application, and it is necessary to continuously accumulate experience and seek progress.
Due to the above two reasons, many problems are prone to occur in the production process of aluminum cans (lids). Among the common problems in can body production, the four most typical problems are wrinkles at the neck shrinkage position, black bottom of the can, stripes on the inner wall of the can, and printing on the can body. In the production of can lids, the five common typical problems include easy-open lid opening failure, easy-open lid cover slag, pull ring cover feathers, easy-open lid sealing glue bubbles and local glue breakage, sheet cover aluminum chips crushing (cracks) the cover surface.
This article will introduce the aforementioned problems and treatment measures in detail, and basically you can follow the following "180-word formula".
The shrinking neck and wrinkled cloak are ugly and unsightly, and can makers must be cautious and work hard to improve them;
The black bottom of the can is not scary, there is a magic method, just add citric acid to safely remove it;
The inner wall of the can has a vertical stripe oblique network, and the coating cover is safe and sound;
The printing of the can is quite complex and the most difficult to control, so the next best thing is to strictly control the key content;
Drinking drinks and removing the pull ring is upset, and the legal lid is opened and checked separately by the manufacturer;
The lid slag is wrapped and solidified by the coating, and there is no impact and it can be used directly without fear;
After the pull ring lid is opened, the coating remains, and it can be investigated or not according to the level;
The bubble and leakage of the sealing glue of the easy-open lid, don't be nervous and use it with confidence, it doesn't matter;
Small aluminum chips of the sheet lid crush the lid surface, and the number is small and concentrated online!
Can neck wrinkles refer to wrinkles of varying degrees (usually mild) at the neck after the empty can is necked. Can neck wrinkles only affect the appearance of the product and have nothing to do with the double-sealing safety.
Cause analysis： There are three causes of can neck wrinkles. First, the thickness of the metal on the neck of the can is not completely uniform. Second, during the production process, the necking mold expands due to temperature rise, which causes a slight change in the gap between the inner and outer molds. Therefore, the matching of the raw material and the matching mold space is not fixed. When the fluctuation during matching exceeds a certain degree, the neck metal may wrinkle during the extrusion process. Third, there may occasionally be foreign matter such as slag and varnish particles on the outer wall of the can neck, resulting in neck wrinkles.
Treatment suggestions： Although it is difficult to completely eliminate the problem of neck shrinkage and wrinkles, the degree is generally not too serious, and the number is often very small. There has never been a precedent for consumers to complain and return the product for this reason, so customers can use it directly. Of course, if this problem occurs in large quantities, it is abnormal and needs to be analyzed and solved.
The black bottom of the can means that the bottom of the can fails to show the normal metallic luster, there are patches/pitting or the whole shows different degrees of gray or black. The black bottom of the can only affects the appearance of the product and has nothing to do with the food safety and flavor of the beverage content.
Cause analysis： The black bottom of the can often appears after the sterilizer of the beer can filling line, and is occasionally seen in soda cans that are wetted by rain in hot and humid weather. The reason is that the metal ions in the aluminum alloy that are not effectively covered at the bottom of the can combine with the hydroxide ions in the alkaline liquid outside to form gray-black hydroxides, such as aluminum hydroxide, under certain temperature conditions.
Treatment suggestions： Adding food-grade citric acid in an appropriate amount to the external alkaline liquid (such as the sterilizing water in the pasteurizer of the beer production line) to neutralize the hydroxide ions in the liquid can prevent the formation of hydroxides, thereby effectively eliminating the blackening of the bottom of the can.
Stripes in the can refer to the phenomenon of stripes in different directions on the inner wall of the empty can, which only affects the appearance of the empty can and has almost no adverse consequences in use.
Cause analysis： Stripes in the can are divided into two types: grid stripes and axial straight stripes, and there are two causes. On the one hand, in order to facilitate the can body to fall off the mold, that is, the punch, smoothly during the stretching process, the punch surface is specially punched with a mesh pattern to overcome the adsorption effect of the vacuum between the inner wall of the can and the punch surface, and the grid stripes on the inner wall of the can are derived from this. It should be noted that the inner wall of the can can also help the inner coating to be more firmly applied on the inner wall of the can.
On the other hand, the axial straight line stripes come from the abnormal friction between the punch and the can body, and similar reasons may also cause longitudinal stripes to appear on the outer wall of the can body.
Treatment suggestions： Since the inner coating process in the subsequent process can effectively cover and block the inner wall of the can, properly separate the metal of the can body and the filling contents, the existence of such slight traces has no effect on the storage of the contents, and since the appearance problems are not easy to see after filling and sealing, the cans with such problems can be used with confidence.
Can printing problems refer to the poor printing effect on the can body and other various printing problems, which will cause the can body appearance to be inconsistent with the standard sample can.
Cause analysis： The printing of the aluminum two-piece can body is high-speed curved surface mobile printing, which has certain special features. The characteristics of its printing process determine that the factors affecting the printing effect are more numerous and more complex than those of ordinary flat printing, which are specifically manifested in the following five aspects.
The particle size and viscosity of the white can and ink used for printing show dynamic instability due to the influence of other factors during use. In addition, as raw materials in a semi-fluid state, white can and ink will be sensitive to the effects of the relevant settings in their flow routes during operation.
The white can forms a metallic luster fluctuation due to the influence of aluminum or can washing effects.
There will be some instantaneous changes in the equipment and mechanical devices during operation, and there will be slight differences in the relevant dimensions of different stations of the printing machine mandrel within the allowable range.
The thickness of the printing substrate (empty can wall, printing rubber) fluctuates within the permitted range.
The ambient temperature of raw materials such as ink and even the printing equipment changes.
Treatment suggestions: These factors may affect the final actual printing effect to varying degrees, and it is not easy to effectively control all possible influencing factors. So far, it is still an industry-wide technical problem to keep the printing effect of the same batch of two-piece cans highly consistent, and practical improvement measures need to be explored.
In terms of the actual situation, the strategy of "grasping the big and letting go of the small" should be implemented, that is, the key elements of can printing, such as logos, barcodes, etc., must ensure the printing effect of sample cans, and other matters should be handled as appropriate.
