1. Home
  2. Knowhow

What is a waterproof motor and what are the requirements for motor waterproofing?

Date:2022-08-03   Author:XINDA MOTOR
The vast majority of motors are not waterproof, in large part because their operating environment does not require waterproofing, and waterproofing materials limit overall performance while increasing costs that are often only valuable for specific applications 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, and waterproof motors are a key component in solving the problem of water-induced motor failures. The motor industry has a standardized liquid protection measure, called IP rating, that power engineers and motor manufacturers need to comply with application specifications.

The most common and effective method of waterproofing motors

Today's waterproof motors work up to 30 feet below the sea, which is a common industry standard, named after "waterproof", not standard motors that have been modified, but true waterproof motors, and they work well in deep water environments - in various industrial and marine environments. Motors are equipped with redundant shaft seals, O-rings, sealed cable feedthroughs, pressure equalization, and other waterproofing features that allow the motor to meet the design engineer's needs for a motor, even with prolonged exposure to most liquids or immersion Among them, the motor will not fail.

When exploring waterproofing solutions, each strategy offers varying degrees of liquid protection. For example, some special cases just prevent splashing water, while others completely submerge the motor, and to a certain 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 Housing: Covering a motor with a special housing is one of the most common ways to prevent water damage, and specialized housings can be expensive.

  • Waterproof Shaft Seal: Protects the moving parts of the motor, especially the shaft and bearings, and the waterproof shaft seal creates an enclosed area for the inner workings of the motor.

Why can't ordinary motors meet this waterproof requirement?

Although standard motors are the backbone of motion control systems in industry and laboratories, and at the same time, provide reliable and accurate positioning at the lowest cost, their designs have some weaknesses in terms of humidity. First, the coils of a standard motor are wound with magnet wire, which is a solid copper wire coated with enamel or insulation. While the coating process is good, it's 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".

Often, 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 can quickly damage the motor windings. High-quality insulation and dipping processes can prevent this problem, but greatly increase the cost of the product.

In a humid environment, the materials of the stator and rotor are easily corroded and rusted

The rotor and stator of the motor are mostly made of magnetic iron (silicon steel), which is easily corroded in a humid environment. At the same time, in order to optimize the torque, the gap between the rotating and non-rotating teeth of the motor is kept at about 0.05mm. When the motor is running, these rotor cogs get hot, often hot 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 start to rub, which removes the motor's effective torque and loosens the magnets.

If the rust is dry, it will form a sanding powder, if it is wet, it will form a sanding grout. Once the oxide slurry enters the motor bearings, as abrasive, bearing wear accelerates, and as the bearings wear, the centering of the rotor becomes less accurate, causing the rotor to wobble as it turns, eventually hitting the stator. Oxide build-up on the magnetic iron teeth and 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, the metal will be more expensive, more expensive to machine, and the motor performance will be significantly reduced.

The correct way to design a motor is to try to prevent moisture from entering the motor

Standard motors are not designed for easy sealing, and they are designed for low cost. Proper sealing of a watertight motor requires a complete redesign of motor parts, increasing manufacturing costs. The redesign includes shaft seals, O-rings, cable feedthroughs and the aforementioned pressure equalization, among other features combined. 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 to the motor coils requires a sealed feedthrough to prevent water from penetrating the motor through the cable conductors.

Other seal designs, such as: threaded pipe plug design at the rear of the motor to seal the housing after the motor connection is complete, the plug also needs to be equipped with an O-ring seal, and the motor shaft itself has a redundant shaft seal for longer life Additional features include double insulation, coating lamination and pressurized fittings.

Conclusion Some of the above characteristics can be found on standard motors, but it is the combination of these characteristics that results in a waterproof motor with excellent performance and long service life. The existence of new watertight motors, and the design innovations they represent, allow motors to extend motor life in water-filled applications, in many cases applications would not be possible without this type of motor.