Most motors are not waterproof, largely because their working environment does not need waterproof. Waterproof materials not only increase the cost, but also limit the overall performance. These costs are usually only valuable for specific applications, such as pumps and fluid treatment, off-road vehicles and other applications that can come into contact with the motor. Due to water and solvent, motion control components often face the risk of corrosion and failure. Waterproof motor is the key component to solve the problem of motor failure caused by water. The stepper motor industry has a standardized liquid protection measure called IP protection level. Power engineering and motor manufacturers need to meet the requirements of application specifications.
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The most common and effective motor waterproof method
Today's waterproof motors can work 30 feet below the seabed. This is a general industrial standard named "waterproof". They are not modified standard motors, but real waterproof motors. They can work well in deep water - in various industrial and marine environments. The motor is equipped with redundant shaft seal, O-ring, sealed cable feed through line, pressure equalization and other waterproof functions. These design features enable the motor to meet the needs of the design engineer for the motor. Even if it is exposed to most liquids or immersed in them for a long time, the motor will not fail.
When exploring waterproof solutions, each strategy provides different levels of liquid protection. For example, some special cases just prevent splashing water, while others completely submerge the motor and reach a specific depth. Many waterproof methods will limit the flow of air to the motor, which will have a negative impact on the maximum power output of the motor. The most common and effective motor waterproof methods are as follows:
Special case: covering the motor with special case is one of the most common methods to prevent water damage. Special case will be very expensive.
Waterproof shaft seal: protect the moving parts of the motor, especially the shaft and bearing. The waterproof shaft seal creates a closed area for the internal work of the motor. one
Why can't ordinary motors meet this waterproof need?
Although standard motors are the backbone of motion control systems in industry and laboratory, and can provide reliable and accurate positioning at the lowest cost, their design has some weaknesses in humidity. First, the coils of standard motors are wound with magnetic wires, which are solid copper wires coated with enamel or insulation. Although the coating process is good, it is not perfect, and there are always some small pinholes in the varnish.
When the magnetic wire is wound into a coil, any two pinholes are unlikely to line up and "short circuit".
Typically, the wire spacing provided by the insulation prevents conduction from one pinhole to the next. If there is water between windings, it will also promote pinhole to pinhole conduction. In this case, the current from the power supply will quickly destroy the motor winding. High quality insulation and dipping process can prevent this problem, but greatly increase the product cost. one
In humid environment, the materials of stator and rotor are easy to corrode and rust
The rotor and stator of the motor are mostly made of magnetic iron (silicon steel), which is easily corroded in humid environment. At the same time, in order to optimize the torque, the gap between the rotating teeth and non rotating teeth of the motor is maintained at about 0.05mm. When the motor is running, these rotor slots become hot and the temperature is usually high enough to turn any water in the motor into steam. The steam is corrosive, so the magnetic iron in the rotor teeth rusts faster than usual. Once the rust fills the air gap of 0.05mm and the rotor and stator teeth begin to rub, this will eliminate the effective torque of the motor and loosen the magnetic iron.
If rust is dry, it will form frosting powder. If it is wet, it will form frosting slurry. Once the oxide slurry enters the motor bearing as abrasive, the bearing wear accelerates. With the bearing wear, the centering of the rotor becomes inaccurate, resulting in the rotor shaking during rotation and finally hitting the stator. The accumulation of oxide layer on magnetic iron teeth and the loss of bearing accuracy will lead to motor failure in just two weeks. Although non corrosive metal can be used to replace magnetic iron, this metal will be more expensive, the processing cost will be higher, and the motor performance will be significantly reduced.
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The correct design method of the motor is to try to prevent moisture from entering the motor
Standard motors are not designed to facilitate sealing, and their design cost is very low. The correct sealing of waterproof motor requires a thorough redesign of motor parts, which increases the manufacturing cost. The redesign includes shaft seals, O-rings, cable feedthrough lines and the previously mentioned pressure equalization, as well as other combined features. For example, the standard motor housing is made of painted cold rolled steel and / or aluminum, and the outside of the waterproof motor is usually made of stainless steel to prevent corrosion. The wiring to the motor coil requires a sealed feed through device to prevent water from penetrating the motor through the cable conductor.
Other seal designs, such as the threaded pipe plug at the rear of the motor, are used to seal the housing after the motor connection is completed. The plug also needs to be equipped with O-rings. The motor shaft itself is equipped with redundant shaft seals. Additional functions to prolong the service life include double insulation, coating lamination and pressurization accessories. Conclusion some of the above characteristics can be found in the standard motor, but it is the combination of these characteristics that produces a waterproof motor with excellent performance and long service life. The existence of new waterproof motors and the design innovation they represent enable the motor to prolong the service life of the motor in water filled applications. In many cases, the application is impossible without this type of motor.
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