Filling of liquid materials (1)

The filling of liquid materials is customarily called filling. There are many liquid materials that need to be filled, which can include almost all liquids related to life, in addition to some industrial and agricultural liquids. The chemical physical properties of liquid materials are different, so the filling method is also different. The main influence on the filling of liquid materials is viscosity, followed by whether or not gas is dissolved, and foaming and minute solids content. Therefore, when selecting the filling method and filling equipment, the viscosity of the liquid material must be considered first. According to the needs of filling, liquid materials are generally classified into three types according to their viscosities: fluids, semi-fluids, and viscous fluids.
(1) Fluid: refers to the liquid that can freely flow in the pipeline at a certain speed under the action of gravity, and has a viscosity in the range of 0.001 to 0.1 Pa.s, such as milk, soft drinks, wine, perfume, eye drops, and pure water.
(2) Semi-fluid: In addition to relying on gravity, external force is required to flow in the pipe. Viscosities range from 0.1 to 10 Pa·s, such as condensed milk, ketchup, and hair cream.
(3) Viscous fluid: It must not rely on its own gravity to flow. It must be able to flow with the help of external forces such as squeezing. Viscosities above 10 Pa·s, such as shampoo, toothpaste, paste, peanut butter, jam, etc.
First, the mechanical basis for the filling of liquid materials Liquid material filling is generally taken from the liquid storage tank, so that it flows into the container through the pipe. The condition of the liquid material flowing in the pipe is that there must be a pressure difference between the inflow end and the outflow end, which is also called the pressure head, and the pressure at the inflow end must be higher than the pressure at the outflow end. Assuming that the liquid material flowing through the circular cross-section pipe is laminar, the flow rate can be calculated according to the Poiseuille formula πP r4
V = --
8   L
Where: V - volume of liquid material flowing through each second; P - pressure difference; r - pipe diameter; L - pipe length (refers to the vertical distance);   -- Liquid viscosity coefficient.
It can be seen from the above equation that the flow velocity V is proportional to the pressure difference P and is proportional to the fourth power of the tube diameter r and inversely proportional to the length of the tube. Therefore, the following conclusions can be drawn:
(1) With the same liquid, when the tube length is the same as the tube diameter, if the pressure difference increases exponentially, the flow rate also increases exponentially.
(2) For the same liquid material, when the pipe diameters are the same, if the pipe length and pressure difference are multiplied, the flow rate will not change.
The above two conclusions are the basis for designing the best filling system.
When the filling system is in the state where the tank and the container are at atmospheric pressure, the liquid material flows by gravity. The method of filling using this principle is called gravity filling; if the reservoir is closed, the flow rate will increase when the pressure in the cylinder is higher than atmospheric pressure because the total pressure difference is the gravity pressure difference and the reservoir Sum of pressure inside and outside. The method of filling using this principle is called pressure filling. If the top of the reservoir is open to the atmosphere, the connection between the tube and the vessel is sealed. The pressure in the vessel is below atmospheric pressure and the flow rate will increase. The method of filling using this principle is called vacuum filling.
Second, the specific method of filling liquid materials According to the principle of filling, filling methods can be divided into gravity filling, pressure filling and vacuum filling three categories.
According to the measurement method, the filling method can be divided into fixed level filling method and volume filling method.
There are 10 commonly used filling methods:
1. The pure gravity filling method This method, like the siphoning phenomenon in physics, is one of the oldest filling methods, and it is still the most accurate and simple filling method. Most of the free-flowing liquid materials can be filled in this way. The pure gravity filling method is a fixed level filling, and the volume of the liquid material poured into the container is determined by the volume of the container itself. The wall thickness of round airtight cans or plastics is evener than that of glass bottles, so their volume is more accurate than that of glass bottles.

As shown in Figure 9-1, the reservoir 1 is at the top, and the liquid material flows from the reservoir through the spring-loaded filling valve 4 into the container. The filling into the lifting mechanism lifts up the container (or the filling tube can be lowered). Firstly, the mouth of the container is in contact with the sealing cover 5 of the lower part of the filling valve, and the container is sealed, then the container is raised again. Open the spring and open the filling valve. The liquid material flows down freely by gravity and is poured into the container. At the same time, the air in the container is discharged through the air outlet 2 provided at the end of the filling tube to the exhaust pipe 3 at the upper portion of the liquid reservoir. When the liquid or the upper part of the exhaust port stops flowing, the liquid level reaches a prescribed height and remains unchanged. After the filling is completed, the lifting mechanism lowers the container and the filling valve loses pressure and is automatically closed by the spring.
This method is mainly used for low-viscosity, non-foaming liquid materials, such as milk, liquor, soy sauce, medicine, etc. The equipment used is simple in construction, easy to operate and easy to maintain. It is a filling method that has appeared very early and is still widely used today.
2. Pure vacuum filling method This method is a filling method under the condition of lower than atmospheric pressure. It is a differential pressure vacuum type, that is, the inside of the liquid storage tank is under atmospheric pressure, and only the interior of the packaging container is evacuated. To form a certain degree of vacuum, the liquid material relies on the pressure difference in the two containers to flow into the packaging container and complete the filling. This method is a fixed level filling, is the current domestic vacuum filling method. It is usually limited to filling necked glass bottles. As shown in FIG. 9-2, the reservoir 4 is placed separately from the filling valve 10. The feed tube 1 is controlled by the feed valve 2, and the liquid level is held by the float 3. A vacuum pump 7 and a vacuum chamber 6 are also provided to establish a vacuum. The liquid material overflowing to the vacuum chamber is returned by the liquid supply pump 5 to the liquid reservoir.
When filling with this method, the bottle is lifted or the filling valve is lowered. First, the bottle mouth is sealed, a high vacuum is established in the bottle (860-930 Pa), and then the spring pressure of the filling valve is overcome and the valve is opened. There is a vacuum tube in the valve casing, which is connected with the vacuum chamber. The vacuum chamber is kept in a vacuum chamber. When the valve seals the bottle mouth and opens, the vacuum port is also opened at the same time, and the degree of vacuum in the bottle is the same as that in the vacuum chamber. The liquid material flows into the bottle from the sump by the pressure difference formed between the atmospheric pressure acting on the liquid level of the sump and the high vacuum in the bottle. When the liquid material rises to the vacuum nozzle in the filling valve, it stops flowing and the liquid level remains unchanged. If the bottle does not leave the valve port, the liquid material will continue to flow slowly, as the vacuum will draw liquid material out of the bottle, forming an overflow and backflow. The spilled liquid material flows to the vacuum chamber and is pumped back to the reservoir.

This method is suitable for filling low viscosity liquid materials (such as oils, syrups, etc.), vitamin-containing liquid materials (such as vegetable juice, fruit juice, etc.). This method can not only improve the filling speed, but also can reduce the contact between the liquid material and the remaining air in the container, it is conducive to extend the shelf life of a certain product, in addition to vacuum filling can avoid cracking or nicking jar irrigation The equipment can eliminate the leakage phenomenon of liquid materials, but it consumes more energy. It is not suitable for filling liquors containing aromatic gases, because it will increase the loss of wine.
(To be continued)