Main production process for the body of a three-piece food can

One important method to reduce material consumption is by thinning the tinplate. Manufacturers of tinplate have done significant work in this regard, but simply thinning the tinplate to reduce can cost is limited by the pressure-resistance requirements of the can structure, and its potential is now quite small. However, with advancements in necking, flanging, and can expansion technology, there have been new breakthroughs in reducing material consumption, especially in both the can body and the lid.

The primary motivation for producing necked cans was initially driven by the desire for product upgrades by manufacturers. Later, it was discovered that necking the can body is an effective way to save material. Necking reduces the diameter of the lid, thus reducing the blanking size. At the same time, as the strength of the lid increases with the reduced diameter, thinner materials can achieve the same performance. Additionally, the reduced force on the lid allows for a smaller sealing area, further reducing the blanking size. However, thinning the can body material may cause issues due to changes in material stress, such as reduced resistance along the can axis and the can body cross-section. This increases the risk during high-pressure filling processes and transportation by fillers and retailers. Hence, while necking does not significantly reduce the can body material, it mainly conserves material on the lid.

Given the influence of these factors and market demand, many manufacturers have improved and upgraded necking technology, establishing its unique position in the various stages of can manufacturing.

In the absence of a slitting process, necking is the first process. After coating and curing, the can body is sequentially delivered to the necking station by the can separation worm and infeed star wheel. At the transfer point, the internal mold, controlled by a cam, axially moves into the can body while rotating, and the external mold, also guided by a cam, feeds in until it matches with the internal mold, completing the necking process. The external mold then disengages first, and the can body remains on the internal mold to prevent slipping until it reaches the transfer point, where it disengages from the internal mold and is delivered to the flanging process by the outfeed star wheel. Typically, both symmetric and asymmetric necking methods are used: the former is applied for a 202-diameter can, where both ends undergo symmetric necking to reduce the diameter to 200. The latter can reduce one end of a 202-diameter can to 200 and the other end to 113, while a 211-diameter can can be reduced to 209 and 206, respectively, after three asymmetric necking operations.