Professional question: What are the responsibilities of the motor base in the motor?
In any organization, different individuals will be assigned different roles and responsibilities, and their division of labor and collaboration will fully demonstrate the functions and strength of a team. In a motor, the base is an important hardware component, what are its responsibilities?
From the analysis of the quantity and type of components, the motor is a mechanical device with a relatively simple structure that can achieve electromagnetic conversion well. Different motors will use different machine bases, but what is the role of the machine base in the entire motor? Ms., I would like to give you a brief introduction today, focusing on the classification of machine bases and their loads.
The role of the machine base on different motors
The role of the machine base in AC and DC motors is different. The base of an AC motor is mainly used as a mechanical support for the stator core and winding, and is used to fix end caps or covers. In some cases, it also forms the air duct or chamber of the ventilation system, and even supports coolers, filters, mufflers, etc., but does not play a magnetic conduction role; On the one hand, the base of a DC motor plays a similar role to the above, and on the other hand, its magnetic yoke also plays a role in magnetic conduction. But whether in AC or DC motors, the base still plays a protective role. In some cases, the surface of the machine base also has to bear the task of heat dissipation.
Another classification method for machine bases
In addition to being divided into casting and welding, vertical and horizontal, with and without feet, the machine base can also be divided according to its structure and shape as follows.
(1) Integral machine base and split machine base
The former is a circular structure with good rigidity and easy processing, generally used in small and medium-sized motors and large motors with transportation conditions. The latter divides the entire machine base into upper and lower halves (also known as split type) or several sections along the circumference for easy transportation, installation, and maintenance. It is generally used for large motors or small and medium-sized motors that require easy installation and maintenance. The frame of the suspended motor structure is a typical split frame.
(2) Integral rack type machine base and combined rack type machine base
The former's frame is welded as a whole, so the processing of the frame and the stacking of magnetic yokes are relatively simple, generally used in large DC motors with less strict requirements for stator external dimensions. The latter's frame is welded after the magnetic yoke is stacked, and the middle plate is installed in the center of the magnetic yoke. The frame has small external dimensions and good rigidity, but the magnetic yoke stacking process requires higher requirements, generally used in large DC motors with limited stator external dimensions. (For DC motors only)
(3) Whole piece magnetic yoke machine base and laminated magnetic yoke machine base
The magnetic yoke of the former is made of cast steel or thick steel plate, and is cast or welded together with the base or frame, mainly used in general small and medium-sized DC motors and large DC motors with stable load and good commutation conditions; The magnetic yoke of the latter is tightly laminated with silicon steel sheets or thin steel plates, and then fixed to the frame. It is usually used in DC motors powered by controllable silicon power sources or with rapidly changing loads, such as main drive motors and their power generators for steel rolling. (For DC motors only)
(4) Circular and polygonal machine bases
The former has a circular shape and is easy to process, used in general AC/DC motors; the latter has a regular or irregular polygonal shape. A regular polygonal base can make better use of the internal space of the motor, thereby reducing the height of the base. However, it requires more processing time and is usually used in lifting, marine, and traction DC motors; Irregular polygonal machine bases have good stiffness but larger external dimensions, and are usually used in large steel rolling DC motors and certain AC motors.
The main load borne by the machine base during operation
(1) Gravity load, usually the self weight of the stator. In motors using end cap bearings, they also need to bear the weight of the rotor, while in suspended hydro generators, they need to bear the weight of the rotating parts of the unit, the upper frame, etc.
(2) Unilateral magnetic pulling force and radial force caused by thermal expansion of the iron core.
(3) In the case of internal pressing and round punching, certain parts of the machine base must withstand the axial rebound force of the iron core; For a suspended hydro generator, it must withstand axial water thrust.
(4) Torque. Including transient electromagnetic torque during sudden load changes and generator short circuits.
Among the above loads, torque is the most important. In addition, the base of a general motor will also be subjected to clamping force, cutting force, lifting force, etc. during processing, transportation, and installation; For motors that require sealing (such as hydrogen cooled steam turbine generators or explosion-proof motors), the machine base must also withstand the test pressure. When using end cap bearings and belt (or gear transmission mechanisms) for transmission, the machine base and its feet will also be subjected to the tension of the belt (or the force of the gear transmission mechanism). Therefore, when designing a machine base, the mechanical calculation of the machine base usually includes the calculation of its stiffness, strength, and natural vibration frequency. For a half machine base, the strength calculation of the joint plate bolts needs to be carried out, and for a welded machine base, the stress calculation of the bottom plate weld needs to be carried out, mainly the stiffness calculation of the machine base.
