The vast majority of motors are not waterproof, largely because their operating environments do not require waterproofing. Waterproofing materials increase costs while limiting overall performance. These costs are usually only valuable in specific application areas, such as pumps and fluid handling, off-road vehicles and other applications where the motor may come into contact with liquids. Motion control components are often at risk of corrosion and failure due to water and solvents. Waterproof motors are a key component to solving the problem of water-powered motor failure. The motor industry has a standardized liquid protection measure called IP protection rating, which power engineering and motor manufacturers need to meet application specifications.
1 The most common and effective motor waterproofing methods
Today's waterproof motors can operate 30 feet below the seabed. This is a common industry standard. The name "waterproof" is not a modified standard motor, but a truly waterproof motor that works well in deep water environments - in a variety of industrial and marine environments. The motors are equipped with redundant shaft seals, O-rings, sealed cable feedthroughs, pressure equalization and other waterproof features. These design features enable the motors to meet the needs of design engineers for motors that will not fail even after long-term exposure to or immersion in most liquids.
When exploring waterproofing solutions, each strategy provides a different degree of liquid protection. For example, some special cases only protect against splashing water, while others completely submerge the motor to a specific depth. Many waterproofing methods will restrict air flow to the motor, which will negatively affect the motor's maximum power output. The most common and effective methods of waterproofing motors are as follows:
Special enclosures: Covering the motor with a special enclosure is one of the most common ways to prevent water damage, and specialized enclosures can be expensive.
Waterproof shaft seals: Protecting the motor's moving parts, especially the shaft and bearings, a waterproof shaft seal creates an enclosed area for the motor's inner workings.
2 Why don't ordinary motors meet this waterproofing need?
Although standard motors are the mainstay of motion control systems in industry and laboratories, and can provide reliable and accurate positioning at the lowest cost, their designs have some weaknesses when it comes to humidity. First, the coils of standard motors are wound with magnet wire, which is a solid copper wire 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 this magnet wire is wound into a coil, it is unlikely that any two pinholes will line up and "short out."
Usually, the wire spacing provided by the insulation prevents conduction from one pinhole to the next. If there is water between the windings, it will also promote pinhole-to-pinhole conduction. In this case, the current from the power supply will quickly destroy the motor windings. High-quality insulation and varnishing processes can prevent this problem, but greatly increase the cost of the product.
3 In a humid environment, the materials of the stator and rotor are very susceptible to corrosion and rust
The rotor and stator of the motor are mostly made of magnetic iron (silicon steel), which is very susceptible to corrosion in a humid environment. At the same time, in order to optimize the torque, the gap between the rotating teeth and the non-rotating teeth of the motor is kept at about 0.05mm. When the motor is running, these rotor tooth slots will heat up, and the temperature is usually high enough to turn any water in the motor into steam. Steam is corrosive, so the magnetic iron in the rotor teeth rusts faster than usual. Once the rust fills the 0.05mm air gap, the rotor and stator teeth begin to rub, which eliminates the effective torque of the motor and loosens the magnetic iron.
If the rust is dry, it will form a grinding powder, and if it is wet, it will form a grinding slurry. Once the oxide slurry enters the motor bearings, it acts as an abrasive, accelerating bearing wear. As the bearings wear, the centering of the rotor becomes less accurate, causing the rotor to wobble as it turns and eventually hit the stator. The buildup of oxide layers on the magnetic iron teeth and the loss of bearing accuracy can cause the motor to fail in as little as two weeks. While it is possible to replace the magnetic iron with a non-corrosive metal, this metal will be more expensive, more expensive to machine, and the motor performance will be significantly reduced.
4 The correct design approach for the motor is to try to prevent moisture from entering the motor
Standard motors are not designed to be easily sealed, they are designed to be cheap. Proper sealing of waterproof motors requires a complete redesign of the motor parts, which increases the manufacturing cost. The redesign includes shaft seals, O-rings, cable feedthroughs, and the pressure equalization mentioned earlier, as well as other features that are combined together. For example, standard motor housings are made of painted cold-rolled steel and/or aluminum, and the exterior of waterproof motors is usually made of stainless steel to prevent corrosion. The wiring leading to the motor coils requires a sealed feedthrough to prevent water from penetrating the motor through the cable conductors.
Other seal designs, such as: a threaded pipe plug design at the rear of the motor is used to seal the housing after the motor connection is completed. The plug also needs to be equipped with an O-ring seal. The motor shaft itself is equipped with a redundant shaft seal. Additional features that extend life include double insulation, coating lamination and boost fittings.
Conclusion Some of the above features can be found on standard motors, but it is the combination of these features that produces waterproof motors with excellent performance and long service life. The existence of new waterproof motors and the design innovations they represent allow motors to extend the service life of motors in water-filled applications. In many cases, applications would not be possible without this type of motor.