Analysis of application of thin cans sealing technology

At present, China has more than 300 production lines for three-piece cans, with an annual production capacity reaching 23 billion cans. The 202 series (Φ52.3) small metal cans are widely used in food, beverage, and chemical industries. Traditionally, tin cans have been made from materials with a thickness ranging between 0.2 and 0.23 mm. However, starting from the late 20th century, foreign countries began using thinner tinplate, reducing the thickness to 0.14–0.16 mm, which improved material utilization by over 30%. This ultra-thin tinplate, referred to as SR tinplate, requires adjustments in steel base composition and heat treatment processes to maintain mechanical strength after thinning. For instance, Corus of Europe produces class A steel plates with a thickness of 0.15 mm by reducing the Mn content in the steel base and lowering the annealing temperature to enhance hardness. Despite the economic benefits of using thin plates, some Chinese enterprises have started adopting them for metal containers. However, due to the significant variation in the mechanical properties of these thin sheets—especially their poor plasticity and high hardness—the current roll-sealing structures and molds need to be redesigned. If the existing roll-sealing design is used for δ=0.21 mm sheets, it may not meet the sealing requirements, leading to issues like wrinkles or improper overlap. In a trial involving 539 cans made from δ=0.16 mm thin plates, two major problems were encountered during the roll-sealing process: excessive wrinkling (over 50%), which affects tightness and causes surface scratches, and unstable splice rates that fail to meet standards. These challenges highlight the complexity of working with such thin materials. According to metal plastic deformation theory, when the deformation exceeds the forming limit, instability and wrinkling occur. Excessive wrinkles can invalidate the curl and compromise long-term food preservation. Therefore, analyzing the causes of wrinkling during the roll-sealing process is crucial for improving quality indicators like wrinkle degree, overlap rate, and tightness. Commercial cans typically accept a wrinkle degree of less than 50%, as shown in Figure 1. Several factors influence the formation of wrinkles, including plate hardness, thickness, and can diameter. Higher hardness reduces formability and increases the risk of wrinkling. Thinner plates are harder to deform and more prone to early elastic instability, which leads to deeper, harder-to-flatten wrinkles. Smaller can diameters also increase the likelihood of wrinkling due to higher compressive deformation. To address these issues, an experimental plan was developed focusing on reducing deformation and optimizing mold dimensions. Key measures included adjusting the external dimensions of the crimping, modifying the can body and lid diameters, redesigning the curling curve, and fine-tuning the indenter and head burying degrees. These adjustments helped improve the seal quality and reduce defects. Machine adjustment is also critical for achieving the desired results. Proper installation of rollers and pressure heads, along with precise adjustments of the wheel position and head burying degree, ensures better performance. Fine-tuning parameters like the overlap rate and wrinkle degree helps achieve the required sealing standards. The research confirmed that the thin double-sealing process for δ=0.16 mm plates in the 202 series cans met all technical requirements. The main technical parameters of this process are summarized in Table 2, offering valuable insights for applying similar techniques to other can types.

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