Improved design and analysis of differential mechanism of decanter centrifuge
Xin Zhou 1,2 Shang Hongyi 2 Abstract: In order to solve the separation phenomenon of the separation effect of the spiral blade and the rotating drum during the sedimentation and separation of the horizontal screw centrifuge, an improved method of the differential transmission mechanism is proposed. The commonly used two-stage 2K-H differential is combined with the overrunning clutch to achieve differential operation when sediment deposits, avoiding the adverse effects of relative motion. The parameters of mechanism transmission ratio, transmission efficiency and power loss were calculated and analyzed.
(1 Key Laboratory of Digital Manufacturing Technology and Application, Ministry of Education, Lanzhou University of Technology, Lanzhou 730050, China) (2 College of Mechanical and Electrical Engineering, Lanzhou University of Technology, Lanzhou 730050, China)
Key words: decanter centrifuge differential overrunning clutch
introduction
The differential mechanism between the drum and the screw feeder is a key component of the material separation of the decanter centrifuge [1]. In order to allow rapid sedimentation of solid particles of very small particle size, the centrifuge must generate sufficient centrifugal force field to force the microparticles to settle. Therefore, the high rotational speed of the drum only indicates the effectiveness of the suspension separation. The important performance requirement of the centrifuge is to effectively collect the settled solid phase material, so that the ultrafine particles can not be carried away by the clear liquid during the separation process, and the moisture content of the collected solid phase material is as low as possible. It is required that the rotation speed of the unloading device (spiral feeder) be properly configured with the drum. These technical problems depend on the rational design of their differential mechanism devices. In a decanter centrifuge, the movement of the filter cake on the inner surface of the drum is achieved by the relative movement of the differential driven auger to the drum. Because the slip of the decanter centrifuge and the screw feeder have a small slip and the transmission torque is large, the general differential adopts a revolving train structure, a cycloidal pin differential or an involute planetary differential. . At present, the most typical and the most widely used structure is the two-stage 2K-H type differential.
1 The problem existing in the differential process of the horizontal screw centrifuge is continuous feeding, separating, discharging and discharging the slag in the differential process of the traditional horizontal screw centrifuge and the screw feeder. Since the relative movement between the screw feeder and the rotating drum is always carried out, the spiral blade generates a stirring effect on the separated material, and the fine particles which have settled on the drum wall are again stirred up by the liquid, so that the suspension is turbid again. Thereby reducing the separation and clarification effect of the decanter centrifuge. In particular, smaller particle size solid particles create turbulence under the agitation of the helical blades, which makes it easier to re-float the settled particles. Therefore, the separation effect of the spiral discharge centrifuge is not ideal for the difficult-to-separate materials with finer solid phase particles and small difference in solid-liquid phase specific gravity, especially for suspensions with high clarity requirements.
2 differential and overrunning clutch combination mechanism
In view of the agitation caused by the rotation of the screw feeder blade relative to the rotating drum, the subject has improved the differential mechanism of the horizontal screw centrifuge, adding a one-way roller type between the main motor and the differential. The clutch, which is always in contact with the outer yoke and the star wheel under the action of the spring force. When the outer yoke rotates counterclockwise or the inner star rotates clockwise, the clutch enters the wedge state and the working state; otherwise, the clutch is disengaged. Thereby avoiding the adverse effects caused by relative motion. This kind of clutch has a wide working range, the transmission torque can reach 2×105N·m, and the rotation speed can reach 4.5×104r/min or higher [2]. The motion diagram of the differential mechanism is shown in Figure 1.
The improved transmission device integrates the 2K-H type differential with the overrunning clutch, and the outer yoke ring 5 of the clutch is fixedly connected with the gear case 6 of the differential, and is driven by the main motor I through the pulley; the star wheel of the clutch 2 The input shaft 4 of the differential can be connected by a key and driven by the secondary motor II through a pulley. When the horizontal screw centrifuge starts to feed, it can only start the main motor, that is, when the outer yoke of the overrunning clutch is active, since the clutch enters the wedge state, the clutch star wheel is driven to run at the same speed, that is, the differential input shaft. Same speed as the differential case, achieving zero differential operation. At this time, the differential operates as a whole, no differential action, so there is no relative movement between the drum and the screw feeder. The suspension in the decanter centrifuge has no agitation effect and only settles under the action of centrifugal force. During the zero differential separation process, part of the clarified liquid can be separated. When the mud cake in the drum accumulates to a certain thickness and the slagging work is required, the secondary motor is started and the feeding is stopped at the same time. When the differential input shaft speed is higher than the differential gear speed of the differential, that is, the clutch star speed is higher than the outer yoke of the clutch, the clutch enters the disengaged state, and the input shaft and the tooth housing of the differential are respectively The speed is operated, the differential acts as a differential speed, and the drum of the horizontal screw centrifuge and the screw feeder are relatively rotated, and the mud cake deposited in the drum can be pushed out from the slag discharge port.
3 Analysis and calculation of differential mechanism
As shown in Fig. 1, it is known that n4=n2=na1, n5=n6=n7=nb1=nb2, nH1=na2, nH2=n8
When continuously feeding, only the main motor I is started, and the differential case 7 is rotated by the belt drive, that is, n6=(D1/d1)n1
In the 2K-H transmission consisting of a2, b2 and H2 components, there is
Firstly, according to the separation requirement and the separation property of the suspension, the separation coefficient Fr is determined, and the drum rotation speed n6 can be calculated. Then, according to the selected main motor model, the main motor belt transmission ratio i1 is calculated; finally, according to the requirements of the different difference rotation speed Δn Secondary motor gear ratio i2.
4 transmission efficiency calculation
6 Conclusion
The improved centrifuge transmission mechanism can select different working states in the separation and slagging process according to the solid phase concentration of the feed. When the solid concentration of the suspension is very low and clarification is required, the differential operation can be employed, that is, the clutch acts to reduce the agitation caused by the relative movement between the spiral blade and the drum, and the material is prolonged in the drum. The separation time improves the separation effect. When slag is discharged, it can be converted into a conventional differential working state, which has less impact on production capacity. When the solid phase of the suspension is high and needs to be concentrated, the continuous feeding, separation and slagging are carried out in the same manner as the ordinary centrifuge, so that the improved centrifuge is more adaptable.
references
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