Types of materials used in food packaging machinery
Category I of materials in food packaging machinery: bingham plastic fluid. There are many kinds of packing materials in vacuum packing machine. At rest, the fluid has a three-dimensional structure that is strong enough to withstand shear stress of a certain value.
Category ii of materials in food packaging machinery: pseudoplastic fluids. Most non-newtonian fluids belong to quasi-plastic fluids. In arithmetic coordinates, the shear stress and velocity gradient of the quasi-plastic fluids are curved downward, curve 1. However, in logarithmic coordinates, it usually shows a linear relationship within a large range of shear stress. For certain materials, the viscosity decreases with the intensity of stirring, but increases at rest. If sauce, mayonnaise, tomato sauce and some honey are such fluids. The bag feeder will use the stirring function in the feeding device.
Food packaging machinery in the material category three: plastic fluid growth. In contrast to pseudoplastic fluids the apparent viscosity of dilative plastic fluids increases with the increase of velocity gradient. At this time, the exponent a>1 in the formula, that is, when a increases, the expansibility increases. It can be seen that the relationship curve of plastic dilatant fluid is the curve 2 which curves upward through the point, and its slope increases with the increase of shear stress, such as concentrated starch slurry.
Type 4 of materials in food packaging machinery: when materials are stirred, flow is generated due to the action of agitator. This flow has shearing effect, but the shearing force produced by fluid is different for different materials. For Newtonian fluids, the viscosity is the same as at rest, regardless of the degree of agitation, and the viscosity is the same everywhere in the same mixing vessel. Food machinery factories use different packaging equipment for different materials.
The kinds of material in food packaging machinery five: but for non-newtonian fluid, the mixing degree of direct impact on the nature of the fluid, such as mixing pseudoplastic fluid, the fluid apparent viscosity value decrease with the strengthening of the mixing, in the same mix container, fluid shear stress had smaller apparent viscosity with strong, apparently, blender stalling, the apparent viscosity values, for the rose plastic fluid, the influence of the degree of mixing liquid convection on the contrary. That is, the apparent viscosity of the fluid increases with the increase of the shear stress. For viscoelastic fluids (such as dough), the apparent viscosity of more complex materials varies with the degree of shearing and the mixing time.
Types of materials in food packaging machinery: the reasons for the above phenomena are mainly determined by the internal structure of various fluids. In addition, the viscosity of non - Newtonian fluid is significantly affected by temperature. For these complex fluid stirring processes, it is very difficult to express the flow characteristics with correct mathematical formulas, because most cases cannot be calculated analytically, so the apparent viscosity of the stirred material is generally used to replace the Newtonian fluid viscosity for calculation.