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Shaft design experience

author: Elvin [ 2024-05-23 17:24:48 ]

1. Overview of the shaft Shaft is an important part of the machine, it is commonly used to support the rotating parts in the machine, so that the rotating parts have a certain working position, and transmit motion and torque. Which raises the question, where are shafts commonly used?
 
The shaft is most commonly used in the motor, by combining with the rotor, to drive other components to rotate (gears, belts, bearings, couplings, etc.)
 
2. The classification of the shaft according to the role and the nature of the load it bears, it can be divided into the following three categories, mandrel, rotating shaft and transmission shaft.
 
Mandrel: only bear the bending moment but not the torque.
 
Rotating shaft: bear both bending moment and torque. Transmission shaft: the main bearing torque. According to the structure shape is divided into straight shaft and crankshaft. According to the diameter change, it is divided into optical axis and stepped axis. There are also solid shafts and hollow shafts. This paper mainly introduces the rotating shaft.



3.General requirements of the shaft 3.1 shaft material selection Motor shaft generally choose 45#, special products choose 40Cr, SUS304 or SU316(stainless steel).
 
The reason for choosing 45 high-quality carbon steel is that it has good magnetic permeability. If the working environment is humid, stainless steel will be used instead in order to prevent rust. In the power tool industry, 40Cr material shafts are used more.

3.2 Shaft material heat treatment

3.2 Surface treatment of Shaft 3.2.1 Surface not treated: apply anti-rust oil.
 
3.2.2 Surface treatment: blackening, chrome plating, nickel plating, phosphating, surface high-frequency quenching, surface carburizing, nitriding, rolling, shot peening and other strengthening treatment
 
3.3 Materials shall comply with RoHS management regulations of the company. 3.4 Unmarked dimensional tolerances shall be executed at GB1804-m level; The unmarked position tolerance is executed in GB/TT1184-H class; 4. The structural design of the shaft The structural design of the shaft is to reasonably determine the structural form and size of the shaft according to the requirements of the installation, positioning and manufacturing process of the shaft. When designing the shaft, there are the following requirements: 4.1 The shaft and the parts on the shaft should have an accurate working position. The parts on the motor shaft mainly include rotors, bearings, fans, and centrifuges. Bearings are fixed on both ends of the shaft shoulder, rotor, fan, centrifugal is based on the shaft shoulder or shaft end positioning, 4.1.1 shaft parts on the axial fixed → no axial movement
 
Axial fixation is to ensure that the parts have a certain relative position, prevent it from doing axial movement, and can withstand axial forces. The shoulder and ring are the most common fixation methods and can withstand large axial forces.
 
The axial fixation of the motor is realized by the shaft shoulder and the retaining ring. For small and medium-sized motors, the axial force is small, and the elastic retaining ring is used to fix it.








4.1.2 Circumferential positioning of parts on the shaft → no circumferential swing parts are fixed on the shaft in order to transfer torque and prevent parts from rotating relative to the shaft. Commonly used circumferential fixing methods are: key connection, spline connection, interference fit, pin connection, forming connection.
 
The axis and rotor can also be installed by hot sleeve process, the rotor can be heated, using the principle of thermal expansion and contraction, the oven heated rotor into the shaft, adjusted to the appropriate position after cooling fixed. H7/s6, H7/r6 are often used.
4.2 The parts on the shaft should be easy to assemble and disassemble, adjust the shaft into a ladder, to ensure that the parts can be successfully assembled and disassembled, the diameter of the shaft increases step by step from the end of the shaft to the middle, and different parts can be installed in turn.
 
The shaft end and each shaft end should have chamfer, chamfer size can refer to the manual. Leave the necessary axial clearance between the parts. 4.3 The axle should have a good manufacturing process, and the excessive rounded corners at the shoulder of the axle should be unified as far as possible, in order to reduce the specifications and the number of tool changes used in processing.
 
The keyway shall be located on the same bus for ease of milling. For the shaft segment that needs grinding, in order to facilitate grinding, the grinding wheel crossing groove should be left in the axle journal and the axle shoulder. When cutting thread on the shaft, there should be a thread retreat groove that is convenient for the turning tool to exit. The relevant size can be consulted in the manual.



1) : Dimensional accuracy: The dimensional accuracy of the shaft mainly refers to the diameter and circumference accuracy of the shaft. The axial coaxiality of the supporting journal relative to the supporting journal is a common requirement for the accuracy of its mutual position.
 
Form and position tolerance: Reference: The bearing neck is used as the reference, and the vertical line of the reference symbol is aligned with the diameter and dimension line. The coaxial degree of the two bearings based on A-B, the tolerance value of 7 grades in the diameter of 0.01 A-B as the basis of the output end of the radial runout, the value is consistent with the above, the rotor journal runout with A-B as the basis, the value is consistent with the above
 
2) : surface roughness: according to the precision of the machine, the level of the running speed, the requirements of the shaft surface roughness are not the same, the rougher the surface, the lower the fatigue strength, so the surface roughness must be reduced. Selection of surface roughness: two bearing necks, rotor neck 0.8, center hole 12.5. For the rest, take 3.2 (note at top right).

4.4 Minimize stress concentration and improve the stress state of the shaft Stress concentration occurs at the edge of sudden changes in section or interference fit.
 
The solution is as follows:
 
a) : Excessive use of rounded corners. b) : Try to avoid making transverse holes, notches or grooves on the shaft. c) : The positioning sleeve is used instead of round nuts and elastic retaining rings to fix the parts axially. d) : Improve the surface quality of the shaft. Surface strengthening treatment is used to improve the surface roughness of the shaft.

Note: The drawing is obtained by the network, the blogger and the company shown in the drawing have no relationship. Welcome to add the blogger's wechat, communication and discussion


 

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