Introduction
Easy-opening lids are widely used in the food canning industry as a convenient way to open metal cans. Despite the various steps involved, the general process includes: sheet metal preparation → basic lid forming → pull ring assembly → post-processing → visual inspection → lid packaging. There are two main types of easy-open lids: circular and non-circular. Non-circular easy-open lids include shapes such as oval, square, and horseshoe.
The primary function of an easy-opening lid is to allow users to easily open the can when consuming its contents. To achieve this, the lid surface is pre-scored with specific depth notches, and a pull ring is riveted onto it. The lid can then be fully pulled along the scored line. Due to the importance of food safety, these lids must remain rust-free and corrosion-resistant from the time they are packaged until the food is consumed. Therefore, tinplate materials used for these lids are typically coated with a corrosion-resistant layer before the scoring process. However, the scoring operation inevitably damages the coating, so the coating must be applied after the scoring is completed. To maximize the opening size, the score line usually follows a path similar to the shape of the lid, making the circular easy-open lid’s score line round. For non-circular lids, the score line follows the same shape as the lid itself.
This article introduces traditional methods of applying coatings to score lines and analyzes their limitations. It also presents improvements in the coating process and equipment optimization, focusing on the application of new numerical control (NC) technology for special-shaped easy-opening lids. This technology offers excellent performance and flexibility.
1. Traditional Coating Technology for Score Lines
The coatings used for this process typically include phenolic resin, epoxy-phenolic resin, acrylic resin, and aluminum paste. These coatings provide good corrosion resistance, adhesion, flexibility, and are non-toxic and tasteless, meeting food safety standards. Additionally, the storage and transportation of paint containers and pipelines require high corrosion resistance and ease of cleaning.
Due to the directional nature of the coating spray, which forms a fan-like pattern rather than a cylindrical one, the coating is more uniform when applied to circular lids. In traditional processes, the cap rotates, resulting in a more even circular coating. However, for irregularly shaped lids, the process becomes more complex. Conventional methods for coating special-shaped easy-open lids include manual brushing, pure mechanical methods, and hybrid approaches.
Manual brushing involves workers directly applying paint to the lid surface. While simple, this method is labor-intensive, inefficient, and results in uneven coating. It is suitable only for small batch production or rare lid types.
Pure mechanical methods require precise coordination of multiple steps, including capping, positioning, and spraying. The mechanism is complex, involving eccentric wheels, cams, and other components. Although this approach is effective for large-scale production, it is difficult to adapt to different lid shapes, requiring frequent replacement of parts, which increases maintenance costs and reduces efficiency.
Combining mechanical systems with numerical control technology allows for more flexible and efficient coating. This method uses servo drives and CNC systems to replace traditional mechanical components, enabling precise movement and synchronization across X, Y, and Z axes. This leads to better coating quality, faster production, and easier changeovers between lid types.
Currently, CNC technology is rarely used in domestic easy-open lid manufacturing. This article explores its application in detail, highlighting its advantages and potential for future development.
2. Application of Numerical Control Techniques in Irregular Easy-Open Lid Coating
2.1 Project Design
By integrating mechanical and numerical control technologies, the coating process for special-shaped easy-open lids becomes more efficient. Mechanical systems handle basic actions like capping and positioning, while the CNC system controls complex movements, such as trajectory synthesis and spray gun motion.
Take the T501 oval lid as an example. The X-axis moves left and right via a ball screw driven by a servo motor, covering 100mm. The Y-axis moves forward and backward over 300mm, while the Z-axis lifts and lowers the spray gun. The spray gun follows a predefined path (A-B-C-D-A-E), ensuring accurate and uniform coating.
2.2 Selection of CNC System
The Delta PUTNC-H6C CNC system offers high-speed response, open architecture, and support for G-code programming, making it ideal for industrial automation. The Delta-A series AC servo drive (ASD-AB) ensures smooth motion with P-CURVE and S-CURVE functions, improving acceleration and deceleration performance.
The X and Y axes use 5mm pitch screws with high-resolution encoders. The system supports two-axis interpolation, essential for fast, short-stroke movements. With advanced control features, the system provides high precision, stability, and flexibility, allowing for quick changes between lid types.
2.3 Advantages of Numerical Control Technology
Compared to traditional methods, the CNC system offers shorter processing times, faster production speeds, and higher coating pass rates. It also reduces noise, maintenance costs, and energy consumption. Additionally, it supports multi-axis control, making it adaptable for different lid shapes.
3. Conclusion
The adoption of numerical control technology has revolutionized the manufacturing of easy-open lids. By replacing traditional mechanical systems with high-precision servos, the process becomes more efficient, accurate, and flexible. This technology enhances product quality, reduces downtime, and improves overall productivity. As the industry evolves, the integration of CNC systems into automated manufacturing will become increasingly important.
Excerpt from: Packaging and Food Machinery, 2011-04
Wuxi Winsun Automation Instrument Co., Ltd , https://www.winsunwx.com