The most practical forming method for paper bowl-shaped tableware is secondary forming, which takes into account the unique properties of paper. Unlike paper cups that are typically made from two separate parts, this approach allows for a more seamless and structurally sound design. Although paper is not as malleable as metals, it can be drawn, calendered, and folded, making it suitable for creating complex shapes through controlled deformation.
Based on this understanding, we designed a paperboard die-cut into a disk shape with equal-dividing indentations along the diameter. The goal was to guide the formation of small creases along each indentation line during the molding process, allowing the flat cardboard to transform into a round bowl shape. However, during testing, the results were not as expected. Instead of uniform creases, the cardboard developed irregular large folds in some areas and smaller folds in others, with no consistent crease pattern at all. As a result, the formed bowl-shaped tableware had uneven thickness, was prone to warping, and lacked stability. The indentations alone were insufficient to ensure even folding, especially when the upper mold pressed the cardboard into the lower mold cavity, causing the outer edge to lift unpredictably.
To address these issues, we introduced a thin plate to prevent warping and adjusted the gap to be slightly larger than the cardboard's thickness. This mechanism allowed the cardboard to slide laterally, ensuring only minimal creasing along the pre-determined lines throughout the forming process. Additionally, a spring pressure ring was installed on the upper mold. As the upper mold descended, it applied even pressure to the cardboard placed on the lower mold’s surface, preventing any warping during the entire process. This ensured that the cardboard only bent horizontally, resulting in clean, consistent creases.
1. Lower mold
2. Cardboard feeding flat
3. Cardboard anti-rocking plate
4. Mold 1. Cardboard feeding flat
5. Upper mold
6. Spring pressure ring
7. Cardboard crying board
Using this improved method, the paper bowls produced by the bowl-shaped mold with the spring pressure ring mechanism showed better rigidity and a more attractive appearance. This innovation effectively addressed the challenges of manufacturing large, wide paper bowls.
In other developments, Shanghai Jiaotong University has successfully developed a large-capacity, energy-saving bullet machine. This device uses a capacitor energy storage system and an advanced electric control system. It recently passed safety technical evaluation by experts from the Ministry of Transport and received a product license for use by manufacturers producing road signs. This technology enables the replacement of riveting with welding, offering significant advantages.
The welding machine is capable of handling thick materials, large surface areas, and spot welding. The strength of the spot-welded joints is about three times stronger than nailed joints. It increases work efficiency by approximately ten times, significantly reducing labor. Testing has shown excellent performance, low impact on the power grid, and several innovative features. It is comparable to foreign welding machines and reaches international standards from the early 1990s. This advancement has made a meaningful contribution to the rapid growth of China’s transportation electronics industry and has helped improve traffic safety.
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