Design and Calculation of Screw Conveyor

Design and Calculation of Screw Conveyor
Shijiazhuang Jingjin Mechanical Equipment Installation Co., Ltd. -- Zhou Yanhui 13833456715
1. Structure and function of screw conveyor
Screw conveyor is mainly composed of screw shaft, cylinder and front and rear gate structures. The rotation of the spiral shaft can transport the soil in the shield machine's soil bin to the belt conveyor for transportation. In case of emergency or maintenance, the spiral shaft can be retracted and the front mud gate can be closed to maintain the pressure of the soil bin. The functions of the screw conveyor mainly include: 1) conveying soil materials in the soil bin; 2) Adjust the rotation speed of the spiral shaft, maintain the pressure on the excavation face of the soil bin, and ensure the safety of the excavation process.
2. Theoretical conveying capacity of screw conveyor
The theoretical slag discharge capacity of the screw conveyor can be calculated by the following formula: Q=π 4 × D2-d2 × P-t × n × sixty
, plot ratio η= 100%。 In the process of excavation, the actual maximum excavated volume can be calculated by the following formula: (assuming that it is at the maximum excavation speed) Q1=π 4 × Ds2 ×ν× 60。 Where: D-inner diameter of screw conveyor; D - Diameter of central shaft of screw conveyor; P-pitch; T - thickness of screw blade of screw conveyor; N - The maximum speed of the screw conveyor, the excavation diameter of the shield machine, and the maximum propulsion speed of the shield machine. The calculation parameters provided by the shield machine this time are: D=0.8m; d=276mm； P=640mm； t=40mm； n=16rpm、6.3m、0.08m/min。
Calculation result: theoretical conveying capacity of screw conveyor Q=280m ^ 3/h（ η= 100%). Shield machine at the maximum tunneling speed
The theoretical slag yield under: Q1 (100%)=150m3/h, Q1 (130%)=195m3/h, and the safety factor is 1.43.
3. Calculation of Driving Torque of Screw Conveyor
When calculating the output torque of the drive unit of the screw conveyor, we consider that the drive device needs to meet the following resistance
Force torque: T1: the torque of the shear force generated when the slag is moved over the surface of the spiral blade; T2: torque required for potential movement of muck; T3: torque required by the radial friction coefficient of the muck between the inner surfaces of the spiral groove; T4: overcome the friction torque between the slag and the surface of the spiral shaft; T5: overcome the friction torque between slag and spiral blade surface; T6: Mechanical resistance torque;
Calculation T1: Figure 1 is a schematic illustration of the spiral blade surface in the form of derivation. Here, Ws: spiral axial force; F: Screw torque; F1: friction force generated on the surface of spiral blade Helix lead angle.
use φ To represent the internal friction angle of soil/sand. Considering the normal balance of the inclined plane, then:
Therefore, equation ① is:. Where, assuming that the shear force Ws generated when moving soil/sand is expressed by Coulomb formula, we can get:. Where: C - cohesion of soil/sand; S1 - Soil/sand produces average axial pressure.
The soil/sand in the screw conveyor slides due to the inclination of the conveyor. Assume that S1 is the stress caused by the soil/sand sliding, and this stress acts on the effective crossing area A of the blade. Then, as shown in Figure 2, we can get:.
Where: Wp - weight of soil/sand per screw pitch Unit weight of soil.
If there is a micro lower part somewhere along the radius of the spiral blade and a push marked as
Force, equation ② can be obtained from equation ① as:. Therefore, twisting
The moment dT1 can be calculated from equation ② and equation ③ is:.
Now, will. Substitute into equation ③, and integrate the result equation with r as the integral variable to get equation ④:. Where:.
Calculation T2: since the screw conveyor inclines at angle A1p, soil/sand will be sent down from below. Wp is the weight of soil/sand for each pitch, and Wp.sin (A1p) is the sliding force. This means that the screw conveyor needs to overcome this force. Use Wp The required force can be obtained by substituting sin (A1p) for Ws in equation ④. Considering the number of blades N, it can be concluded that T2=2 ·π····· N ········· S1 ·· Q.
Calculate T3: Mu1 is used to represent the friction coefficient between soil/sand and spiral groove, then the friction resistance f2 related to the small parts on the inner surface of the spiral can be obtained from the following formula: f2=Mu1. S2. r22. d β. d。 Where: S2 - average axial stress generated by soil/sand. Therefore, the friction torque T3 generated by friction resistance f2 acting on the surface in the spiral groove is equation ⑤:.
Assuming S2 represents the force exerted by the weight of soil/sand in the screw conveyor on the spiral groove, as the average value of this value, it can be obtained that S2=Wp. cos (A1p)/2. π. r2Lp
Calculate T4: Mu2 is used to represent the friction coefficient between the soil/sand and the outer surface of the spiral shaft
The following results can be derived: T4=0L02 π Mu2.S3.r12.d β. dL。 If S3 is approximately equal to S2, we can get:.
Calculate T5: Mu3 is used to represent the friction coefficient between the soil/sand and the outer surface of the spiral shaft, which acts on the friction of a blade
The force f1 can be expressed as:. Therefore, after considering the number of blades, it can be concluded that the torque required for T5 to represent spiral rotation is as follows: T5=N2rMu3. S1.2. π. r2. dr=23. π. N.Mu3. S1.r23-r13.
Calculation of T6: the following items can be considered as the possible causes of torque loss: friction resistance in bearing, tractor
The friction resistance in the conveying mechanism, the mechanical resistance related to accuracy in manufacturing, and other loss sources including energy loss, such as sound or heat.
Based on the above factors, it can be concluded that T6=0.10 kNm. Calculation result: Substitute the specified value into the formula to get
To the following results. These results show that the equipment torque of the screw conveyor used in the discussed project is sufficient to meet these conditions, even considering the pressure tightness of the soil/sand in the screw conveyor or the possibility of the soil/sand remaining in the narrow gap between the invisible.
T1=15.7 kNm、T2=9.0kNm、T3=4.4 kNm、T4=0.4 kNm、T5=1.1 kNm、T6=0.1 kNm。 Total: T=30.7kNm. Torque of equipped screw conveyor: Ts=146kNm, Ts=146kNm. Safety factor: S=4.75.