The lid is a type of lid that has a nick on the opening and is equipped with a pull tab to facilitate opening. According to the open method, it can be divided into hole open type avulsion type easy cover (RPT), hole open type pressure release type type easy cover (SOT) and full open type easy cover. The opening force is an important part of the quality control of the lid, in order to ensure that the canned food is easy to open, and it is not easy to damage at the time of storage and transportation. The state has strict requirements on the opening force of the open lid: RPT type opening force 9-15N (GB/T17950-1998). There are many reasons for the instability of the opening force of the lid lid. Take the RPT type as an example to analyze some of the unstable factors and discuss:
First, aluminum factors affect the opening force
1) The opening force of different lids produced from different aluminum alloys is different. Easy-to-free cover materials generally use aluminum alloy materials such as 5052 and 5182 with good canning performance. Type 5182, which contains 4%-5% magnesium and 0.35% manganese, is suitable for the production of beer or carbonated beverages Quality material (630kpa). 5052 soft materials are often used for cans (310kpa) with low internal pressure resistance, such as juices and teas. Tests have shown that the opening force of can lids produced from 5182 material to 5052 material is about 1-2N larger.
2) The opening force of the easy-pull lid produced by different manufacturers of aluminum is different. In order to ensure the quality of easy-opening lids, the domestic Yi Laga timber materials currently rely mainly on imports. Commonly Sumitomo Japan and Alcoa America are involved. Some companies also use Zhejiang Huayang aluminum as a substitute. However, there are differences in the production process and alloy distribution of each aluminum manufacturer, which also has a certain influence on the opening force of the lid.
3) The aluminum profile affects the opening force. The aluminum material is formed by secondary cold rolling and observed with a microscope, and its forming profile can be clearly seen. The experiment proves that the easy-pull lid with the same direction as the opening direction of the thread and the pull ring has a larger opening force of 0.3-0.5N than the lateral cover of the grain.
4) The aluminum storage time affects the opening force. Magnesium alloys soften during storage at room temperature. Therefore, the storage period of aluminum and easy lids also has a certain influence on the opening force. In view of the influence of opening force of aluminum materials, it is necessary to strengthen the inspection of incoming materials from suppliers, batch distinction, and inventory management, and make appropriate modifications to the processing technology and enterprise standards according to the requirements of different profiles in accordance with the requirements of the national standard.
Second, the residual volume of the reticle does not meet the specification and affects the opening force
The remnant volume specification is based on the requirements of national standards for opening force, combined with materials, equipment and other factors. It is proportional to the opening force. The residual amount is small, because the material is thinner than the periphery, the strength becomes smaller, and it cracks under the action of the shear force to open. The residual amount is an important basis for adjusting the mold and controlling the opening force, and its accuracy is very high, in micrometers. The oil temperature of the machine in the production and the change of the die temperature will change the change of the residual amount of the dead point under punching, causing the opening force to exceed the standard. Firstly, it is detected if the positive and negative deviations of the residue are large or not parallel, and if necessary, the blade die is adjusted.
Third, the abnormality of the cutting line mold affects the opening force
1) The cutting force caused by the cutting of the scribed line is large. The cutting edge of the die is 50o razor blade, and the front edge of the blade has a 0.038+0.013-0.000mm flat mouth. The stamping cross section is trapezoidal. Under the external force, the trapezoidal notch angle is concentrated and easy to crack. After the knife edge is worn, it is The knife edge of the front end becomes R angle, and the cross section of the stamping line is circular. Under the action of external force, the force is uniform, and it is not easy to crack, and the breaking force increases.
2) The abnormal influence of the dies on the reticle. RPT juice cover knife blade die design has two steps, the residual thickness of the opening is about 0.05-0.06mm smaller than the full opening, in order to ensure that the engraved line conducive to opening, the full open segment meets the requirements of the drop test, when the difference between the two sections of the lower die Before and after the mold point offset, R and R are improperly ground or the plane symmetry is not parallel, and the surface finish is rough, which can cause abnormal opening. To solve the impact of mold on the opening force, mainly to prevent inspection, the general tangent knife die in the punching 3000-50000000 times, after the stamping about 100000000 times, the need to use more than 40 times the microscope surface finish, knife edge wear The situation is checked and combined with the residual thickness and opening force data analysis to determine whether to dress or replace the mold.
Fourth, the pull ring and cover do not closely cooperate to affect the opening force
The riveting of the pull ring and the lid is a key point in the lid manufacturing process. When the pull ring or the basic lid is poorly formed, the pull ring cannot sink to the bottom of the base lid and the lid is tightly riveted, resulting in that the open fulcrum is not fixed and affects the opening force. There are two situations:
1) Pull-ring rivets When the punching pin is worn or punched, there is not enough lubricant for the material, resulting in burr deformation or counter-hole in the rivet hole. When riveting, the bottom of the pull ring sinks to the bottom of the base cover.
2) The third station cover mold rivet wear mold wear, resulting in the base cover blisters R angle is large, the pull ring sinks less than the bottom of the base cover. To prevent the effect of riveting on the opening force, it is necessary to periodically grind the punching pin, regularly check the base cover and the pull ring material of the first three stations, and pay attention to the control of the lubricant amount of the pull ring.
Fifth, the looseness of the cover plate affects the opening force
Easy to pull cover plate surface loose, open, the disk surface deformation, stress is not concentrated, need to increase the opening force, nicks can crack and open, resulting in loose disk surface, affecting the opening force there are three main factors:
1) The size of the ribs on the disk is not adjusted properly. In the manufacturing process, after the tension stamping, the plate surface is deformed and relaxed. Therefore, a disk surface shrinkage reinforcement project is designed at the fourth station of the cover mold. If the size of the project is improperly adjusted, the expected disk surface shrinkage reinforcement effect cannot affect the opening force.
2) The die at the sixth station of the cap mold riveted to the upper and lower molds abnormally affects the opening force. In order to ensure the precise riveting of the pull ring and the cover, a positioning ring punch for positioning the pull ring and a positioning cup (or positioning pin) for positioning the cover are designed at the sixth station. Positioning punch and positioning cup during stamping contact with the center and the opposite shoulder of the cover through the spring lifting, such as the aluminum chips in the two molds, too much or the spring too hard, when the high speed stamping, the ring positioning punch easy to pull the cover surface twice Stretch caused the disk to loosen.
3) The size of the first three stations of the cover mold was improperly adjusted and the disk surface was loosened. The first stop of the cover mold was too high, and the two or three stations were too tight to cause severe deformation and relaxation, which affected the contraction of the fourth station.
Sixth, the detection instrument method does not affect the opening force
1) Detect the cause of the instrument. RPT-type lid open tester simulation artificial open cans designed to cover the surface is 30 degrees tilt pull, domestic manufacturers generally use this type of digital display automatic tension meter, but there are still some small businesses use hand flat pull instrument, Due to the uneven manual force and abnormal opening angle, the illusion of high opening force may be caused.
2) The detection method is abnormal. Easy to pull lids need to be baked in an oven at 200°C for 10 minutes before testing tension. After being naturally cooled, they are tested again. This is a simulation test based on the sterilization process of the lid of the can in the can baking oven and the filling plant. This process is practical. Above is a metal material heat treatment process, such as temperature, time, cooling method is not controlled well, also has a certain influence on the opening force of the easy opening cover.
The above points are based on the theoretical knowledge of the production process of RPT Yi Lagai, as well as some personal analysis of the actual situation of the work, some of the data are produced during the experiment to summarize, other data refer to relevant information. I hope to use this as a reference to exchange ideas with colleagues.
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