Metal container crimping process defect analysis and solution
â˜… 1 Overview â˜…
Metal packaging containers have many advantages, such as excellent barrier properties, mechanical properties, good convenience, good surface decoration, and convenient waste disposal. However, metal packaging containers are less chemically stable and economical.
Leaky cans are a common phenomenon in the beverage industry. The poor sealing of the seal is one of the reasons for this phenomenon. Therefore, mastering the principle of sealing method of metal packaging containers, strict production according to the process rules, and improving the business level of operators are of great significance to reduce the occurrence of such phenomena.
The sealing of metal packaging containers is generally achieved by crimping. The crimping can be further divided into double crimping, triple crimping and micro crimping.
â˜… 2 double crimping technology â˜…
2.1 The form of double curling
The double-rolled edge is divided into two types: flat roll and round roll. The application is more flat-edge structure. In addition to the double flat crimping and double round crimping, there is a special double crimping form, namely the welded double seam shown in Fig. 2 .
2.2 Double curl forming principle
The double crimping is performed by the head roller and the two roller. The head roller is radially moved relative to the can body, and the friction between the groove of the pressure roller and the rounded edge of the can lid causes the round edge to curl toward the normal curve of the groove, and the initial setting of the bead is completed, as shown in FIG. After the head roller press is completed, the seam sealing position is exited. The two-way pressure roller starts to contact the crimping position and the preliminary shaped crimping edge, and starts to move radially to the can body, and pushes the crimping to complete the sealing operation, as shown in FIG.
There are two kinds of cases according to the different sealing mechanism when winding; : First, the tank rotates with the bottom plate and the indenter, and the crimping roller rotates and moves radially to the shaft of the tank to complete the double crimping operation; Second, the tank body is fixed, the coil sealing roller rotates around the tank body and rotates, and at the same time, the tank shaft is radially moved to complete the crimping operation.
When the shaped can is wound, the second method is adopted, the can body is not moved, and the pressing roller is rotated around the can to complete the crimping operation.
â˜… 3 triple crimping technology â˜…
3.1 Triple hemming structure
The triple crimping, also known as the seven-layer crimping, is the main form of crimping of the closed steel drum body and the bottom of the bucket (top). Compared with the double crimping edge, two layers of crimping are added, which increases the overlap between the bucket body and the top of the bucket (bottom), thereby improving the sealing performance of the steel drum and making the steel drum have strong impact resistance.
In addition, compared with the double crimping edge, the triple crimping has higher process requirements for the crimping process, and generally requires three press rolls to be formed, so the equipment and technical requirements are high.
3.2 Triple crimping process
Except that a few barrel mills are equipped with three pressure rollers on the sealing machine, most manufacturers carry out the two machines on the pre-roller and the sealing machine, that is, the first pressure roller is pre-rolled on the pre-roller. The roller completes the pre-roll deformation of the bottom (top) semi-finished product, and the second and third pressure rollers are installed on the sealing machine to complete the seven-layer crimping process.
â˜… 4 micro crimp technology â˜…
Miniature crimping is a new molding process technology that optimizes the weight and processing cost of metal cans. Compared with the traditional crimping, the micro-hems are only about half the size of the traditional standard crimp, as shown in Table 1.
The metal can of the micro-bead structure is reduced in size, can it meet the protection of the goods in the circulation and transportation process and the integrity of the packaging container? To this end, the Packaging Technology Center of the Brazilian Institute of Science and Technology made a series of comparative tests. The test results show that the performance of the micro-crimp metal packaging container meets the requirements in circulation.
Micro-crimping technology offers outstanding advantages in all types of metal containers. Not only does it reduce the size of the structure, but it also reduces the amount of sealant. And productivity has increased significantly, which in turn has reduced packaging and shipping costs.
â˜… 5 crimp quality defect detection and solution â˜…
The quality of the crimping directly affects the protection function of the metal packaging container for the built-in products. Curling defects  can cause the seal is not tight enough, can lead to the loss or deterioration of the packaged products, but it also can lead to botulism bacteria (sausage poisoning) may provide potential breeding. Each metal can must be tested for seal quality before use. Once the crimp quality defects are discovered, the sealing process must be re-rolled in accordance with the relevant procedures and requirements.
5.1 Influence of the groove curve of the coiled roller
Coiled rollers, upper indenters, and trays are often referred to as the three elements of the closure of the closure device. As a basic component, it is also a basic factor affecting the curling.
Experience has shown that the quality of the seal depends on the profile of the crimping wheel groove. In the double beading, the main function of the curling is the groove curve of the head roll sealing roller. The main part of the curve is the Archimedes spiral, whose curvature is determined by the winding rate, and the width and depth are The tank type is related to the nature and thickness of the material. The groove curve is widened and deepened as the diameter of the finished can is increased, and the material is thickened and widened as the material is thickened. As shown in Figure 5. In order to facilitate production, the design is replaced by 2 to 4 arcs. The arc segment depends on the width of the groove curve, and the curve is wider instead of the arc segment.
5.2 Curtain sealing technology requirements
The corresponding explanation of the terminology used in the crimping sealing technical requirements is shown in Figure 6 . In order to ensure the production of metal cans, the sealing and sealing must meet the following requirements during the production process.
1) Tightness â‰¥ 50%. Tightness refers to the tightness of the crimp seal and is generally measured by the degree of wrinkle of the cover hook. The degree of wrinkle refers to the degree of unevenness of the unevenness of the inner side of the cover hook after the cuff is disassembled, that is, the percentage (%) of the wrinkle portion of the entire cover hook length. Tightness = 100% - wrinkle. A qualified can requires a tightness of more than 50%, that is, a can with a wrinkle of more than 50% is a non-conforming product.
2) The seam cap hook integrity rate is â‰¥50%. The hook hook integrity rate refers to the extent to which the lid hook sag. The seaming hook of the seam is sagged downward, causing insufficient width of the lid hook, thereby affecting the sealing of the seam.
3) The splicing rate (K) â‰¥ 50%. The splicing rate indicates the degree to which the inner lid hook and the body hook of the curling edge are overlapped with each other, and the size thereof is equal to the ratio of the splicing length to the splicing length and the length of the gap at both ends. The higher the splicing ratio, the better the curling property. The smaller the gap between the cover hook and the body hook, the better, to improve the stacking ratio of the curl.
5.3 Curling seal defects and solutions
1) Drop the lips. A curled lip is a smooth overhang that appears below the normal curl. As shown in Figure 7-(a). This type of defect usually occurs in the edge seal of a three-piece can because the thickness here is larger than elsewhere.
The factors that may cause such defects are: the pressure on the rotating table of the can tray is too large, the pressure is loose during the head winding operation, the contents are left at the curling edge, and the defects of the metal can itself (such as bending or dents) ), the first road winding roller wear and so on.
Different solutions are available for different factors: reducing the pressure of the rotating table of the can tray; tightening the operating pressure of the head winding; carefully removing the can lid and the edge of the can before sealing the can to ensure that there are no contents or other impurities. Residue; check if the metal can is damaged before use; replace the new head roller and so on.
2) Sharp edges. A sharp edge is a sharp edge on the inside of the inside of the seal. As shown in Figure 7-(b). Possible reasons for sharp edges: the head and/or the two rolls of roller are too tight; the contents are left at the bead; the platen table is too hot; the roll and/or the chuck are worn .
Solution: Appropriately loosen the operating pressure of the head track and/or the two rollers; carefully remove the can lid and the edge of the can body before sealing the can lid to ensure that no contents or other impurities remain; Pressure of the table; replacement of the roll-up roller and/or chuck.
3) Breaking. Crimping is a phenomenon in which the crimping is too tight and the outer crimping portion is broken. As shown in Figure 7-(c). Generally, it is caused by the over-tightening of the head roller and the two rollers. The solution is to loosen the pressure of the two rollers.
4) False rolls. The false roll is a serious defect in the crimping process, which can cause leakage of the metal container contents. The metal can can be inspected in detail from the appearance. If the can lid and the can body are not hooked together and only flattened together, then this is a false roll. As shown in Figure 7-(d).
Factors that may cause false rolls: the can lid and the can body are not flat or damaged before the crimping; the contents of the crimping are left or the product in the metal container is filled (filled); the head roller is over pressure Loose; the pressure of the two winding rollers is too tight.
Reference solution: Check the can lid and the can body for damage before sealing; carefully remove the can lid and the edge of the can body before sealing the can lid to ensure that no contents or other impurities remain, and check whether the contents are filled ( Filling) is too full; increase the head roller sealing roller pressure; reduce the pressure of the two winding rollers.
5) Not completely curled. Incomplete crimping refers to the curling defect caused by the unfinished crimping process or the excessive pressure in some parts of the crimping process. As shown in Figure 7-(e).
The possible reasons are: the pressure of the tray rotating table is too tight or too loose; the sealing chuck is worn; the winding roller cannot rotate freely; there is grease on the winding chuck and/or the rotating table.
Corresponding solution: reduce the pressure of the rotating table of the can tray; replace the sealing chuck; clean, oil, repair and other operations of the sealing roller to make it run unimpeded; clean the sealing chuck and/or support Tank rotating table.
For the sealing of the metal sealed cans, in addition to avoiding the above defects, it is also necessary to detect whether there are defects such as fast mouth, large collapsed edge, rolled teeth, iron tongue, jump seal, and crimping at the seal . Whether there is a leak in the pressurization test or the decompression test according to the standard. Other industrial metal cans require uniform curling, no wrinkles, burrs, iron tongues, airtight test, hydraulic test and drop test shall comply with the relevant provisions of the standard.
â˜… 6 Conclusion â˜…
The closure of the metal packaging container is generally based on the crimping, modified as needed, and then associated with the associated metal seal. For the sealing defects that may appear in the crimping seal, the causes of these defects are analyzed and the corresponding solutions are given.
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