Key Processes in Three-Piece Food Can Manufacturing: Expansion, Flanging, and Beading

Key Processes in Three-Piece Food Can Manufacturing: Expansion, Flanging, and Beading

The main production process of three-piece food cans includes shearing, welding, welding seam repair coating and drying, necking, flanging, beading, seaming, leak testing, full-body coating and drying, and packaging. Currently in China, the automatic can production line is generally composed of a can body combination machine, a bi-directional cutting machine, a welding machine, a welding seam protection repair/coating system, an internal full-body coating/curing system (optional), an online leak testing machine, an empty can stacking machine, a strapping machine, and a film wrapping/heat shrinking machine.

The can body combination machine can complete processes such as cutting, necking, expansion, can forming, flanging, beading, first and second seaming, with a speed of up to 1200 cans per minute. In the previous article, we discussed cutting and necking processes. Now, let's analyze the expansion, flanging, and beading processes:

l Expansion:

The expansion process is the opposite of the necking process, where the can diameter is expanded outward. This is commonly used in packaging for canned luncheon meat and pet food to ensure product suitability.

l Flanging:

The flanging process follows the necking and can forming processes. The widely used method is rotary flanging. Each flanging die consists of several small rotary rolling wheels. When the can body enters the station, the lower die rises to push the can body into the upper die. The upper and lower dies, along with the rotary rolling wheels, rotate in opposite directions to form a flange at both ends of the can body. The flanging process is completed when the lower die retracts, and the can body is delivered to the can discharge star wheel. Rotary flanging is a sequentially fed process, and its uniform force distribution during flanging prevents cracking and coating abrasion on the welded seam area of thin iron cans. With the use of DR materials, which are thinner and harder, a swing-type flanging process has been developed, which is more suitable for DR material quality assurance. Currently, there are three different flanging technologies used for necked cans (or non-necked cans), and no single flanging technology is suitable for all necking processes.

The first method is die flanging. This is the simplest and roughest method, where the flange is formed simultaneously with the die. During die flanging, high stress is generated in the axial direction of the material and can neck. This method is suitable for larger can diameters and thicker, softer materials. For cans necked by die following the die flanging or die forming process, pressure marks or flange cracks may occur in the axial direction of the can neck during die flanging.

The second method is round pin flanging. Its technical requirements for equipment and molds are more complex than die flanging. Compared to traditional die flanging technology, round pin flanging works from the contact point between the round pin roller and the can body, and the can body rotates along with the flanging roller. The distribution of the rollers forms a regular polygon, and the forming of the flange is opposite to the curve of the rotating rollers. The can body rotates radially along with the flanging rollers, gradually forming a flange width. The shoulder of the flanging roller controls the flange width. Round pin flanging exerts less axial force on the material and can neck. This process is suitable for flanging various geometric can neck curves.

The third method is rotary flanging. This process has high technical requirements for mechanical equipment, but the mold is relatively simpler compared to pin flanging. The patented technology of rotary flanging combines the advantages of die flanging (such as minimal relative movement between the die and the can body, less wear, and minimal variation in flange width) and pin flanging (continuous process from point to line), while avoiding the drawbacks of the two previous flanging technologies. The main feature of rotary flanging is the rotating die process. The rotational movement of the inner turning shaft drives the rotation of the flanging die head. The can body comes into contact with the rotating flanging die head, and the can body moves radially along with the flanging die head, gradually forming the flange width. The shoulders of the flanging die head control the flange width. During the flanging process, the force acting on the can neck is slightly lower than that of die flanging, but slightly higher than that of pin flanging. The absolute load acting on the can neck is higher than that of pin flanging.

l Beading

The beading process has evolved from the simple circular beading on the can body to today's deep beading, grid beading, and embossed patterns on the can body. This not only enhances the strength of the can body but also improves the appearance and feel of the can lid. Typically, there are two methods for beading: static outer mold and rotating.

Beading, also known as ribbing, is used to increase the compressive strength of the can body made of thin iron sheets after welding. It is generally performed using a mold. Nowadays, most beading machines are not standalone, but are combined with other processes on a single piece of equipment.