Design and calculation of wall thickness of drum of centrifugal grease disc centrifuge
Lan Xiaofei Wang Kai
(College of Mechanical and Electrical Engineering, Lanzhou University of Technology, Lanzhou 730050, China; Department of Mobile Equipment, Polyolefin Business Unit, PetroChina Lanzhou Petrochemical Company, Lanzhou 730060, China)
Abstract: According to the characteristics of raw milk, according to the characteristics of raw milk, under the condition of centrifuge structure and operating parameters of suitable cream separation, according to the principle of disc centrifuge, the causes of centrifugal stress on the drum wall were analyzed. . And using the third strength theory, the calculation formula of the wall thickness of the centrifuge drum is derived, and the wall thickness of the drum is calculated according to the physical properties of the original milk.
Key words: dish centrifuge, skim milk, fat drum, wall thickness
Chinese map method classification number: TS252. 3; Document code: A
In the process of separating fat by a disc centrifuge, the fat, skim milk and many other impurities in the milk are completed by rotating a drum and a set of discs in the drum. These mixtures enter the separator from the lower part of the separator, enter the disc group through the small holes in the disc fixing bolt, and go up through the small holes in the disc, and separate the fat from the skim milk by the thin layer separation principle between the discs. And precipitated impurities. During the separation process, the skim milk and impurities are directed downward and outward along the surface of the disc and are smashed toward the outside of the disc. The skim milk flows out from the skim outlet along the passage between the upper blade and the lid of the uppermost part of the disc group. Then it flows on the inner wall of the drum. The cream is discharged upwards and inward along the surface of the disc through the small holes in the disc, and is discharged from the center cream outlet [2]. Figure 1 is a schematic view showing the outlet positions of the components after the centrifuge separates the milk.
In the process of separating milk fat, due to the poor quality of the raw milk and the unreasonable operating parameters, the separation efficiency is often low. The disc centrifuge typically has a rotational speed of 5 000 r/min, a drum diameter of 600 mm and a drum cone angle of 40°. Large-scale centrifugal stress is generated in the drum of the high-speed rotating disc centrifuge. When the stress exceeds the yield limit or the strength limit of the drum material, the drum will have large deformation or failure, and cause serious casualties. Therefore, it is necessary to calculate the wall thickness according to the drum drum strength [1].
1 Centrifugal stress analysis
The centrifuge drum drives the material inside to rotate at a high speed. Therefore, the centrifugal stress in the drum wall is generated by the drum wall itself and the materials therein.
1. 1 Centrifugal stress caused by drum wall quality
As shown in Fig. 2, the conical drum under high-speed rotation has a centrifugal force generated by the drum mass perpendicular to the rotary axis, and there is no component in the axial direction, and the stress in the warp direction cannot be generated, that is, (σ'1) Ï = 0 . The component force of the centrifugal force generated by the mass of the drum wall in the normal direction of the wall surface and the circumferential stress caused in the wall of the drum can be calculated as follows.
In the formula, the inner radius of the Ï cone drum at any point, the half cone angle of the α cone drum, the γ0 drum wall metal material gravity, and the ω drum angular velocity. It can be seen from the above formula that the circumferential stress generated by the centrifugal force of the drum wall itself is independent of the thickness of the drum wall, only the density of the material and the peripheral speed. It is related to the inner radius at any point of the cone. Therefore, increasing the thickness of the drum wall does not reduce the circumferential stress, and the maximum circumferential stress is at the large opening of the conical drum.
1. 2 Stress and deformation caused by the centrifugal force of the separated material
1.2.1 warp stress (σ′′1)Ï
As shown in Fig. 3, the warp stress (σ"1) Ï at any radius Ï of the conical drum can be calculated according to the axial force balance condition.
2 Determination of the wall thickness formula of the drum The total meridional stress of the drum is
3 Determination of the wall thickness of the drum
references
1 Sun Qicai, Jin Dingwu. Principle structure and design calculation of centrifuge. Beijing: Mechanical Industry Press, 1987
2 Guo Benheng. Milk powder. Beijing: Chemical Industry Press, 2003
3 Yu Guozhen. Handbook of Chemical Machinery. Beijing: Chemical Industry Press, 2003
4 Guo Benheng. Liquid Milk. Beijing: Chemical Industry Press, 2004
5 Wei Wei. Influencing factors and parameter relationship diagram of centrifuge drum wall thickness. Filtration and separation, 2002; (12): 18-20
6 Feng Yingwei. Discussion on mechanical properties of high-speed centrifuge drum. Large castings and forgings, 1997; (2): 19-23
7 Wang Zuyin. Basic stiffness requirements for centrifuge drums. China Well Mineral Salt, 1996; (5): 33-35
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