In the production of metal can packaging, the edge rolling sealing mechanism is a key device that ensures a tight bond between the can body and the can lid and achieves a seal. Among them, the double sealing technology is the core process, and the GT4B2 vacuum automatic can sealer is a typical application equipment of this technology.
The working principle of double sealing
Double sealing is the process of firmly hooking the tank body and the periphery of the tank lid to form a five-layer (three layers for the tank lid and two layers for the tank body) rolled edge seam. To enhance the sealing performance, the inner side of the can lid is pre-coated with elastic rubber films such as vulcanized latex or other elastic filling materials.
The formation process of double curled edges
First, the can feeding mechanism sends the covered can to the working table of the can sealer, and the upper and lower pressure heads of the can sealer immediately press down on the can and the can lid. Under the action of the transmission mechanism and the radial feed device for sealing, the sealing roller moves towards the flange to be sealed on the tank body and the tank cover, rotates relatively to the tank body at the same time, and performs radial feed motion towards the center of the tank body.
During the first sealing operation, the first roller pushes the sealing flange of the tank lid under the flange of the tank body, causing the two flanges to overlap and curl into a specific shape. After completion, the first roller immediately leaves and the second winding and sealing operation begins. Under the action of the CAM, two rollers feed radially towards the center of the tank body, further bringing the already curled tank body and the flange of the tank cover closer to the tank body and continuously rolling, eventually forming a tightly hooked rolled edge seal.
Characteristics of the coiling roller
The shape and size of the grooves on the sealing rollers directly affect the sealing quality. Moreover, due to their different functions, the groove curves of the first and second sealing rollers vary. Taking the commonly used GT4B6 type can sealer in China as an example, the grooves of its sealing roller are composed of multiple arcs of different radii.
The groove of the first roll sealing roller is narrow and deep, with a small radius of curvature. The upper and middle parts allow the flange of the can lid to bend smoothly downward, while the lower part guides the edge of the can lid to gradually approach the can body and curl upward. At the same time, it avoids being orthogonal to the can body to prevent an increase in roll sealing resistance or the inability to form a five-layer roll edge. Moreover, the lower edge of the groove does not protrude too high to facilitate a smooth separation from the roll edge.
The grooves of the double-wound sealing roller are shallow and wide, with a gentle lower part and a larger radius of curvature than the upper part. It further rolls the rolled edge on the basis of the first sealing, compacts and seals it, allowing the metal in the sealed area to smoothly "flow" during plastic deformation, forming a firm and smooth, beautiful rolled edge.
The sealing roller is a vulnerable part, and its wear resistance should be taken into consideration during the design. Usually, carbon tool steels such as T12 and T18 are selected for water quenching and tempering treatment, or high-speed tool steels and bearing steels such as C12 and GC15 are selected for oil quenching and tempering treatment, so that the hardness of the groove part reaches HRC60-62. Grooves are also processed at the upper and lower ends of some rollers for easy replacement and use. If boronizing treatment is adopted, the wear resistance effect will be even better.
In addition, to adapt to tanks of different specifications, some models are equipped with different specifications of sealing rollers. For instance, the GT4B2 automatic vacuum can sealer can achieve sealing of tanks of different diameters by replacing the sealing rollers within the range of compatible tank diameters. The irregular-shaped can sealing machine mostly uses large-diameter sealing rollers, whose grooves are 0.15-0.2mm narrower than those of the round can sealing rollers. This is because the circumferential curvature of the irregular-shaped can sealing area is smaller, and there is relatively less excess metal at the edge during sealing. The narrow grooves can make the sealing appearance more aesthetically pleasing.
FAQ
Q: Why can double-roller seals achieve a seal between the can body and the can lid?
A: Form a five-layer edge seam firm hook, and fill the tiny gaps on the inner side of the can lid with elastic material.
Q: What are the differences in the functions of the first and second sealing rollers?
A: The first roller overlaps and rolls the can lid with the flange of the can body to shape it, and the second roller further adheres and compacts it to ensure a firm and aesthetically pleasing seal.
Q: What is the protection mechanism of the GT4B2 vacuum automatic can sealer when it malfunctions?
A: ① The V-belt pulley driven by the friction plate stops when it encounters abnormal resistance; ② The safety clutch between the worm gear and the vertical distribution shaft stops the rotation of the distribution shaft in case of faults such as tank jamming.
Q: How to adjust the edge sealing roller of the GT4B2 can sealer to adapt to cans of different specifications?
A: ① The height of the handwheel + lead screw adjustment mechanism is adapted to the height of the tank. ② The worm drives the worm wheel to fine-tune the distance between the edge banding roller and the center of the tank, or replace the corresponding specification of the sealing roller to match the tank diameter.
Q: How does the six-slot turntable of GT4B2 complete can collection, can sealing and can discharge?
A: The distribution shaft drives the volute CAM, which intermittently rotates the process disc to successively complete the process of connecting the empty tank, conveying to the sealed position, and unloading from the tank.