Cans enter the filling machine through the inlet star wheel and reach the can table, where they are centered at the predetermined position. The filling valve then descends along the support cam, centering the can and pre-pressing the seal. The sealing pressure comes from the weight of the centering bell itself and from an air cylinder. The air pressure in the cylinder can be adjusted by a pressure reducing valve on the pneumatic control cabinet, with a range of 0–40 kPa (0–0.04 MPa). The actual pressure depends on the can material.
While the vacuum channel is opened, back-pressure gas in the filling bowl rushes into the can and flows into the vacuum channel. Vacuum is used to carry out a CO2 flushing program to remove air from the can. This procedure minimizes oxygen pickup during filling and prevents negative pressure inside the can, so even very thin-walled aluminum cans can undergo CO2 flushing.
For filling without vacuum, CO2 gas from the original vacuum channel can be used directly to flush the can. After the vacuum valve closes, pressure equalizes between the can and the filling bowl. The liquid valve opens under spring force, and filling begins. Through three liquid inlet grooves, material flows down along the can wall, while gas inside the can returns to the filling bowl through the gas valve.
The filling level is changed by adjusting the length of the return gas tube. When the liquid level reaches the return gas tube, gas return is blocked and filling stops. An overpressure forms in the upper gas space of the can, preventing material from continuing to flow down.
A fork closes the gas valve and liquid valve. Through the exhaust valve, pressure in the can is equalized with atmospheric pressure. The exhaust passage is kept away from the liquid surface to prevent liquid from being carried out during exhaust. During exhaust, the gas in the can headspace expands, and material in the return gas tube falls back into the can, emptying the tube.
At the moment of can discharge, the centering bell is lifted by the cam. Under the action of the inner and outer guide plates, the can leaves the can table and enters the can transfer chain of the seamer, then moves to the seaming machine.
If the liquid level in the bowl is unstable, filling may result in underfilling or foaming. Therefore, stable control of the bowl liquid level is important for proper filling.
The entire liquid level control device consists of a reed switch float level sensor, a digital regulator, and an eccentric rotary valve with a valve positioner. The liquid level in the bowl is measured by the reed switch float level sensor 1 and converted into a 4–20 mA current signal. This signal passes through the mercury rotary joint 2 to the digital regulator 3. After PID regulation, the output signal is sent to the electric valve positioner of the main inlet valve 4 to control the opening of the main inlet valve and thereby control the filling bowl level. The desired filling bowl level can be set at any time on the digital regulator, and the entire level control device adjusts the bowl level in real time according to changes in the set value.
For filling valves, centering bells, return gas tubes, and related changeover parts used in such machines, Hansheng Automation can machine custom components from customer drawings in single pieces or small batches.
