The double curling is the part formed by the can lid and the can body being rolled together. During the double-rolling operation, with the help of two rollers with different contour curves, the can body flanging (body hook) and the can lid round edge (cover hook) are hooked to each other to form a firm crimping structure. The double hemming is generally composed of the thickness of the three-layer can lid and the thickness of the two-layer can body, but the double hemming at the seam of the can body varies depending on the can making method. Fill an appropriate amount of sealant between the double crimp layers to ensure tightness. The double curling of cans is usually completed by the combination of the first round of sealing operation and the second round of sealing operation, so it is called double curling.
1. The formation of double curling
The formation of double crimping is to mechanically hook the round edge of the can lid (see Figure 1) and the can body flange (see Figure 2) to each other, lock and flatten them to form a firm mechanical structure. The re-rolling edge is composed of a three-layer can lid and a two-layer can body iron sheet, and an appropriate amount of sealant is filled in the double-rolling edge to ensure sealing.
For each station on the sealing machine, there is a supporting base, a sealing head, at least one first roller and one second roller.
The double crimping of the can is completed in the can sealing machine. When the can sealing machine is in operation, it mainly relies on the cooperation of the working parts such as the pressure head, the supporting base plate, the first roller and the second roller. When the can body and the can lid are sent to the sealing operation position at the same time, the supporting base plate rises so that the can body pushes the can lid and makes the lid fit on the pressure head, and the pressure head and the supporting base plate together clamp the can body and the bottom lid Hold the positioning, and then roll the seal by the head and the second roller in turn.
2. The first roll seal
In the first rolling-sealing operation, the round edge part of the can lid and the flanging part of the can body are hooked with each other (bending, hooking or embedding). This hooking is completed by a roller with a special contour line.
The most important point is that the first roll seal must form the correct roll seal, not too tight or too loose. If the first roll seal is not good, it cannot be remedied or corrected in the subsequent roll seal steps. A good head roll seal should make the body hook and the lid hook almost parallel, the body hook formed by the can body flange is rolled into the corner of the lid hook, and the head roll is close to the can body wall.
If the following conditions are met, a good first pass can usually be completed.
(1) Correct the height of the pin gauge so that the distance between the indenter and the support chassis is correct.
(2) Correct the pressure of the supporting chassis.
(3) Calibrate the position of the head roller and the indenter.
(4) Adjust the position of the head track roller to make it have the correct tightness.
3. Second volume seal
After completing the first step of rolling operation, the first roller will exit and no longer contact the can lid, and then the second roller will move to contact with the can lid, press the body hook and lid hook tightly, and flatten the wrinkles of the lid hook . The contour of the secondary roller is different from that of the first roller. The typical shape is shown in Figures 8 and 9.
The tightness of the double hemming is determined by the shape, degree of use and adjustment of the second roller. If the secondary rollers used are improperly formed or severely worn, they will not meet the required standards.
4. Sealant
The sealant and the body cover are mechanically closed to each other to make the double crimping seal. In the two-pass sealing operation, considerable pressure is applied to the can lid and the can body, and the pressure is also applied to the sealant in the groove of the can lid. The sealant should be completely sealed during double-rolling. In the double curling. Due to the pressure during the rolling and the increase in the metal temperature caused by the rolling, the sealant moves, thereby filling the gaps in the curling, and blocking possible leakage.
Sealing glue or body cover hooks alone cannot make the container completely sealed. They must complement each other. Although the sealant is elastic and can block the gaps, it cannot compensate for the defects formed by the crimping. On the contrary, good crimping alone cannot remedy the defects caused by improper selection of sealant or improper application position, or abnormal amount of glue.
5. The name of each part of the double hemming
The indexes of double curling are related to the quality of the final product of the can. The sealing technology and the sterilization technology are the two major technical processes in the processing of canned food.
