Semi-fluid refers to the fluid material with the viscosity range of 1000-10000mPa ·s. When filling this kind of the material, often because of the filling valve diameter selection is not reasonable and the situation of leakage, which not only affects the filling accuracy, but also cause pollution.
In actual filling, the filling problem of viscous materials is often solved by changing the caliber multiple times or using auxiliary mechanisms. This method is not only time-consuming and labor-intensive, but also increases the manufacturing cost. If it can be analyzed theoretically, the surface tension of the material can be used to prevent dripping initially, and the caliber of the filling valve can be selected by the calculation method, and then a good effect will be obtained.
This paper mainly analyzes the influence of the viscosity, temperature and surface tension of semi-fluid materials on the diameter of the filling valve, and finally determines the optimal diameter of the filling valve.
1. The relationship between viscosity and temperature of semi-fluid.
The viscosity of semi-fluid materials is greatly affected by temperature and usually decreases exponentially. Because the relationship between the viscosity and temperature of the semi-fluid measured by the experiment is only some discrete points, in order to facilitate the analysis, this paper constructs a relatively simple mathematical model under the premise of ensuring the accuracy. Based on the experimental data, the relationship between the viscosity and temperature of the semi-fluid is constructed by using the polynomial regression method. The following table:
Temp/℃
20
30
40
50
Viscosity×102/（Pa·s）
7.4022
4.8316
2.8921
1.7973
Temp/℃
60
75
85
95
Viscosity×102/（Pa·s）
1.0338
0.8387
0.7412
0.5719
2. The relationship between viscosity and surface tension.
Both the viscosity and surface tension of semi-fluids vary with temperature. As the temperature of the material increases, the
amplitude of the vibration of the molecules at its equilibrium position increases, the relaxation time increases sharply, and the diffusion rate of the molecules increases; at the same time, as the temperature increases, those molecules with larger thermal kinetic energy It can overcome the gravitational attraction of the molecules of the object and become vaporized molecules, so the density of the object decreases, the attractive force of the molecules also decreases, and the surface potential energy decreases accordingly. Therefore, the viscosity and surface tension decrease accordingly. This is a theoretical analysis of the reason why the viscosity and surface tension of the material decrease with the increase of temperature. In order to obtain a more accurate quantitative relationship between viscosity and surface tension, the corresponding values of viscosity and surface tension were measured at different temperatures, as shown in the following table:
Viscosity×102/（Pa·s）
7.4022
4.8316
2.8921
1.7973
Surface tension×10-2/（N·m-1）
7.275
7.118
6.824
6.609
Viscosity×102/（Pa·s）
1.0338
0.8387
0.7412
0.5719
Surface tension×10-2/（N·m-1）
6.322
6.251
6.186
6.037
3. The relationship between surface tension and caliber.
When determining the relationship between the surface tension and the diameter of the filling valve, the experimental principle of measuring surface tension by the drop volume method can be used as the basis. A dropper for transferring liquid is used to slowly drop the material. When the droplet is about to drop, Consider the surface tension of the liquid multiplied by the length of the perimeter of the tip of the dropper to equal the mass of the drop. After the droplet is dropped, there will still be some liquid left at the front end of the dropper, and the surface of the pendant drop is not perpendicular to the dropper when it is about to drop, so it is usually necessary to introduce a correction factor F. The correction factor is the empirical data established by predecessors through precise experiments and mathematical analysis methods. After a series of improvements and supplements, the correction factor is gradually obtained.
4. Conclusion:
It can be seen from several relational models analyzed above that when the required filling temperature is constant, first determine the viscosity of the liquid material at this temperature, then determine the surface tension at this time, and finally calculate the diameter of the filling valve. When the actual filling valve diameter is less than or equal to the calculated diameter, the material can be prevented from dripping by means of its surface tension. This theoretical study on the diameter of the filling valve achieves the purpose of simplifying the mechanism design of the filling valve, and has certain practical value. Combined with the addition of new mechanisms and components, the occurrence of dripping can be better prevented.
