Leak Detection in Metal Can Production: Methods and Machinery

Leak Detection in Metal Can Production: Methods and Machinery

Over the past 200 years, with the rapid advancement of science and technology, the shape, material, and appearance of metal cans have been evolving constantly. However, the sealing performance of metal cans remains a crucial aspect. Therefore, leak detection is an indispensable procedure. Leak detection involves testing the sealing performance of completed sealed empty cans through pressurization or depressurization, targeting the welding and seaming quality.

The leak detection process must be carried out under rated test pressure conditions that do not cause deformation of the can body. The leak detection pressure can be set based on the actual thickness of the tinplate and the structure of the can body. Considering that excessive pressure can cause changes in the seam structure, leak detection is typically performed within a pre-pressure range of negative pressure 25~35kPa and positive pressure not exceeding 152kPa (1.5 atm). In high-speed continuous production processes, specialized empty cans with a laser-pre-drilled hole diameter of 0.06mm are used for leak detection of micropores (<0.05mm) in triple empty cans.

The working principle of the leak detection machine is as follows: Firstly, since the leak detection process requires a certain amount of time for pressurization or depressurization and pressure holding, multiple leak detection stations are pre-set in a leak detection device to ensure continuous high-speed production. Secondly, each inflation (vacuuming) port of each station is equipped with an elastic sealing ring pad (which should be replaced promptly when worn) to ensure no pressure loss during operation.

Negative-pressure leak detection machines apply negative pressure to the input empty cans. If there are defects in the welding or seaming of the empty cans, resulting in poor sealing, the vacuum pressure inside the can will be lower than the predetermined value during the pressure reduction process. At this time, the pressure monitoring sensor will transmit a signal to the PLC controller, which will then issue instructions through the electromagnetic gas valve to identify and reject the leaking can. The working structure of the negative-pressure leak detection machine is as follows: After seaming, the empty can is sent by the in-can non-magnetic star wheel through the star wheel groove at the same line speed to the groove position of the machine body non-magnetic star wheel. It is then supported by the bottom guide plate to the leak detection position with the sealing ring pad. Under the action of the given negative pressure, the empty can is sucked and rotates in the air. There is a guardrail below the rotating trajectory. Even if the sealing is not tight, the empty can will not fall randomly but will be outputted by the star wheel within the guardrail and then rejected. For the production switching of empty cans with different heights, it can be solved by adjusting the lifting of the top seat of the leak detection machine.

Positive-pressure leak detection machines apply pressure to the input empty cans. If there are defects in the welding or seaming of the empty cans, resulting in poor sealing, the pressure inside the can will experience pressure loss during pressurization, failing to reach the predetermined pressure requirement. At this time, the pressure monitoring sensor will transmit a signal to the PLC controller, which will then issue instructions through the electromagnetic gas valve to identify and reject the leaking can. The working structure of the positive-pressure leak detection machine is as follows: After seaming, the empty can is sent by the in-can non-magnetic star wheel through the star wheel groove at the same line speed to the bottom support tray, and the tray rotates with the guidance of the bottom guide rail to control the up and down stroke of the cylinder, making the can mouth dock with the pressurization head for sealing. For the production switching of empty cans with different heights, it can be solved by adjusting the lifting of the top seat of the leak detection machine.