Frequent issues and their remedies encountered in the manufacturing of easy-open lids.
Frequent issues and their remedies encountered in the manufacturing of easy-open lids.
It is widely recognized that two-piece aluminum cans offer numerous benefits, including their lightweight nature and ease of transport; they are also resistant to breakage, ensuring safety. Their outstanding sealing capabilities and extended shelf life for contents have established these cans as the preferred choice for beverage packaging among consumers in both the United States and Europe, leading to consistently high demand. Additionally, there is a significant market potential for aluminum easy-open ends.
In general, beverage can lids that facilitate easy opening are categorized into pull tab lids (RPT) and environmentally friendly can lids (SOT). The pull tab lids provide excellent barrier properties, effectively preventing gas and light from entering, which helps preserve the beverages for a longer period. When comparing easy open lids of the same thickness, eco-friendly lids typically have a smaller scratch tolerance than pull tab lids, as they are specifically designed to meet the requirements of their opening mechanisms.
The production of easy open aluminum lids presents considerable challenges, both regarding the product and the manufacturing process. From the product standpoint, the thin and fragile nature of the aluminum makes it difficult to produce these lids, as they undergo considerable deformation during fabrication. Additionally, on the production technology front, the creation of these pull ring aluminum lids in China relies on high-speed automated large-scale methods. The technology used for manufacturing can lids is entirely sourced from abroad and remains in a phase of adaptation and implementation, requiring ongoing experience to drive improvements.
Below are some typical challenges and their solutions related to the production of aluminum easy-open lids:
Currently, the manufacturing of these easy-open lids relies on differentiating the scratch tolerance between the two types of lids. This specific tolerance is determined based on the machine's conditions and the thickness of the aluminum. If the scratch tolerance for the environmentally friendly lid increases to match that of the pull tab lid, it could lead to difficulties in opening. Conversely, if the notch tolerance for the pull tab lid is decreased to align with that of the eco-friendly lid, it may result in issues such as soda spray or "tongue flying" during use.
An easy-open lid is a specialized can lid featuring a scratch on the opening section and a pull tab for convenient access. Based on the various methods of opening, these lids are categorized into three types: the hole-opening tear-off easy pull cover (RPT), the hole-opening lift-and-press retention easy open lid (SOT), and the fully open easy pull cover. The force required to open these lids is a critical factor in quality control, ensuring that canned goods are easily accessible and that the lids remain intact during storage and transport. Regulations in the country specify strict standards for the opening force of easy pull lids: the RPT type must have an opening force ranging from 9 to 15N (GB/T17950-1998). The choice of aluminum material used for these lids can influence the necessary opening force.
1. The force required to open easy-to-pull lids made from various aluminum alloys differs. Typically, these lids are crafted from alloys like 5052 and 5182, known for their superior can opening capabilities. The 5182 alloy, which consists of 4% to 5% magnesium and 0.35% manganese, is a robust option with a high compressive strength of 630 kPa, making it ideal for beer or carbonated drinks. On the other hand, the softer 5052 alloy is more commonly used for lids that need to withstand lower internal pressures (310 kPa), such as those found on juice and tea cans. Research indicates that the opening force for lids made from 5182 is approximately 1-2 N higher than that of lids made from 5052.
2. The initial force required to open easy-open ends differs among various aluminum manufacturers. To maintain the quality of these easy-open lids, most domestic aluminum can lid materials are primarily sourced from imports. Additionally, the production techniques and alloy compositions used by each manufacturer vary, which influences the opening force of the pull-tab lids.
3.The design of aluminum influences the force required to open it. Aluminum undergoes secondary cold rolling, and its structure can be distinctly seen through a microscope. Experiments indicate that an aluminum lid aligned with the pull tab's opening direction requires 0.3-0.5N more force to open compared to a lid featuring a horizontal pattern.
The duration for which aluminum is stored influences the force required to open it. When magnesium aluminum alloy is kept at room temperature, it tends to soften. Consequently, both the storage duration of aluminum and the ease of pulling covers can significantly affect the opening force. To address the variations in opening force related to aluminum, it is essential to enhance the inspection processes, differentiate batches, manage inventory effectively for incoming materials from suppliers, and make necessary adjustments to processing techniques and company standards in accordance with national regulations for different profiles.
The duration for which aluminum is stored influences the force required to open it. When magnesium aluminum alloy is kept at room temperature, it tends to soften. Consequently, both the storage duration of aluminum and the ease of pulling covers can significantly affect the opening force. To address the variations in opening force related to aluminum, it is essential to enhance the inspection processes, differentiate batches, manage inventory effectively for incoming materials from suppliers, and make necessary adjustments to processing techniques and company standards in accordance with national regulations for different profiles.
Three key factors that lead to stress corrosion in easy-open ends (EOEs) are their sensitivity, resistance to tensile stress, and exposure to corrosive environments. Made from aluminum alloy, EOEs are particularly sensitive materials. Aluminum cans containing carbonated drinks are subjected to significant internal pressure, and the score margin on the EOE is thinner than the lid itself, making it the most robust area regarding tensile stress. During the filling process, leftover beverage liquid on the can's surface and lubricants from the conveyor belt contain chlorides and sulfates. When combined with any residual moisture on the lid, these substances create a corrosive atmosphere.
The cracking of the easy-open lid score is influenced by three main factors: leftover moisture in the score, elevated storage temperatures, and a humid storage setting. Even a small amount of residual moisture, along with chloride and sulfate, can speed up the corrosion of the score's surface. When storage temperatures are higher, the mechanisms of corrosion develop more rapidly, leading to increased stress. Additionally, a humid environment inhibits moisture evaporation, creating a “greenhouse” effect inside the shrink film packaging.
An increase in residual thickness, coupled with persistent residual moisture, indicates that the stress corrosion environment remains constant. Consequently, the duration before cracking occurs from scratching will only be marginally prolonged.