Key Processes in Food Three-Piece Can Manufacturing

Key Processes in Food Three-Piece Can Manufacturing

The main process of producing food three-piece cans includes shearing, welding, welding seam filling and drying, necking, flanging, beading, sealing, leak testing, overall spraying and drying, and packaging. In China, it is generally composed of can body combination machine, two-way cutting machine, welding machine, welding seam protection filling/curing system, internal overall spraying/curing system (optional), online leak testing machine, empty can stacking machine, strapping machine, and film wrapping/heat shrinking machine to form an automatic production line for empty cans. Currently, the can body combination machine can complete shearing, necking, expanding, necking, flanging, ribbing, first sealing, second sealing, and other can making processes, with a speed of up to 1200 cans/min.

We have already discussed the shearing process in the previous article, and now let's analyze the necking process:

l Necking

During the development process of food three-piece cans over more than 100 years, it has become one of the cheapest ways of food packaging. There have been countless stages in the development of cans, but some special breakthroughs are still memorable. With the passage of time, the potential space for saving packaging costs is also shrinking. Material accounts for 60% to 70% of the total cost structure of empty cans. In a sense, reducing the consumption of tinplate materials is consistent with the goal of reducing environmental pollution caused by discarded packaging materials. In Germany, reducing the weight of empty cans can reduce the entry fee of canned food into the green channel.

Reducing the thickness of tinplate is an important method to reduce material consumption. Tinplate manufacturers have done a lot of work in this regard. However, relying solely on the one-sided thinning of tinplate thickness to reduce the cost of empty cans, its potential is limited by the bottleneck of the pressure-resistant requirements of the can body structure, which is now relatively small. However, with the development of necking, flanging, and expanding technologies, there have been new breakthroughs in reducing the consumption of materials for empty cans. Both the can body and the can lid have some room for material saving.

The main motivation for starting to produce necking cans is the desire of shippers to update their products; later, people found that necking the can body is actually an effective method to save materials. Because necking the can body requires reducing the diameter of the lid, the geometric dimensions of the lid decrease accordingly. With the decrease in lid diameter, the corresponding lid can achieve the same performance with thinner material. In addition, because the force acting on the lid is reduced, the size of the corresponding sealing line can be appropriately reduced, further reducing the size of the blanking. However, the thinning of the can body material may cause some problems due to the change in material stress. For example, the bearing capacity of the can axis and the cross-section of the can body decreases, which increases the danger during high-pressure filling and transportation by filling and retail companies. The significance of necking to reduce the material consumption of the can body is not significant, mainly reflected in the material saving of the can lid. In view of the impact of these factors and the needs of the market, the necking process technology has been improved and promoted by many manufacturers, and has established a unique position in many can-making process flows.

When there is no shearing process, the necking process is the first process. After the can body filled with coating is conveyed to the necking station by the can feeding screw and entering the transfer point, the inner die is axially moved into the can body by the cam control, while the turning body also rotates. The outer die is guided by the cam to feed until the necking process is completed, then the outer die detaches first, and the can body is still on the inner die at this moment to prevent slipping until it reaches the transfer point, and then it detaches from the inner die and is brought to the flanging process by the discharge star wheel. Usually, symmetrical or non-symmetrical necking methods are used. The former is used for 202 can diameter, and both ends are reduced to 200 can diameter after one necking operation. The latter can be 202 can diameter, one end becomes 200 can diameter after two non-symmetrical necking operations, while the other end becomes 113 can diameter. Similarly, the 211 can diameter becomes 209 can diameter after three non-symmetrical necking operations, and the other end becomes 206 can diameter. Or use 5-necking, one end becomes 202 can diameter, and the other end becomes 300 can diameter. Using 5-necking, one end becomes 206 can diameter, etc. Now we interpret three different types of necking technologies.

The first type is mold necking, where the diameter of the can body can be reduced at one end or both ends simultaneously. The diameter of one end of the necking ring is equal to the outer diameter of the un-necked can body, and the other end is the ideal necking outer diameter. During operation, the necking ring is pushed along the axis of the can body, and the geometric curve of the necking is achieved by the change in diameter of the necking ring. The inner core prevents wrinkles on the can body and ensures precise necking. The reduction amount of necking diameter at each position is limited, depending on the quality of the material, the thickness of the iron sheet, and the diameter of the can body. The reduction amount of each diameter is about 3mm, and the reduction amount of multiple position necking can reach 8mm. Unlike two-piece cans, three-piece cans are not suitable for repeated use of mold necking because the material at the weld is uneven.

The second type is punch follower necking, which is evolved from the necking principle of two-piece cans. According to the material used and the diameter of the can body, the amount of necking per revolution can be adjusted, ultimately achieving a smooth geometric curve. This technology can also be used with iron sheets that have been stretched twice or more, and the amount of necking can reach 13mm. The flexible punch follower necking process is completed between the rotating inner mold and the external forming mold. The number of molding circles depends on the reduction in can diameter and the material. The adjustment amount of necking can be completed from several turns to 25 turns. Specially designed high-precision clamping molds ensure that the can