Bearing noises vary. They can indicate a serious flaw, or simply the normal functioning of a bearing. Do you know how to tell the difference?
Bearing noise generated from inside your electric motor is a natural occurrence in rolling bearings. Each of your bearings clinks or clacks, squeals or whines indicates simply that a certain part of the bearing is moving around. Normally, these noises are barely audible if they’re audible at all. However, if the noise is loud enough for you to hear clearly, that’s generally indicative of a problem.
Below are the common noises that a bearing makes (most of which can be detected by a noise meter) what each one indicates about bearing performance, and how each noise may be eliminated.
- Race noise is the most basic sound in rolling bearings; this occurs when the raceway and rolling elements contact each other. It is smooth and continuous. The faster the running speed, the louder the sound and if the radial clearance is reduced the sound also becomes louder. The higher the viscosity of lubrication, the lower the sound, and if the higher the housing rigidity, the lower the magnitude of the sound. Eliminating this noise entirely is not possible, but it can be minimized by improving the quality of the bearings.
- Click noise occurs more often in large bearings under radial loads. It is generated at low speeds and occurs when the rolling elements and the cage/inner ring collide. Applying a preload is an effective countermeasure to click noise.
- A squeal noise can be loud, and it sounds like metal sliding on metal. Contrary to expectations, this does not indicate a problem. Squeal noise tends to occur with relatively large bearings used under a radial load. The friction between the outer ring and rolling elements is considered to be the cause of squeal noise. Reducing the radial clearance and employing a very shallow groove in the outer ring raceway can be effective countermeasures.
- Cage noises come in two types: a noise suggestive of the cage colliding with the rolling elements (“kacha-kacha”) and a low-frequency noise (“gaga-gaga”) caused by the friction between the cage guide face and the bearing component that guides the cage. The first can be reduced by reducing the mounting error. The second noise, frequently problematic due to its decibel level, can be reduced and often eliminated by selecting a special cage designed to reduce this noise and applying the correct lubricant.
- Rolling element passage vibration occurs in rolling bearings operating under a radial load. “Goro goro” is the best descriptor of this noise. Reduction of radial clearance or application of a preload can be effective countermeasures.
Vibration and sound related to bearing manufacturing cannot be eliminated completely. It is intrinsic to the bearing manufacturer and is usually caused by waviness of the inner or outer ring or the rolling element.
- Flaw noise is caused by a flaw such as rust or when a dent exists on finished raceway surface or rolling bearing. It causes a pulsating, machine-gun like noise. The noise occurs at intervals, generally proportional to the speed of the bearing. It can be reduced with the application of high viscosity grease, but usually this noise means that the bearing must be replaced.
- Contamination noise occurs when a foreign particle makes its way into a bearing. A “chi chi chi” noise, the noise is caused by the foreign particle being caught between the rolling elements and the raceway surfaces. Damage can occur, and is more severe in smaller bearings. The best countermeasure is prevention – always handle a bearing safely and reduce outside contamination.
Conclusively, not all bearing noises are problematic. Some indicate normal bearing performance. Other noises can indicate a real problem. Keep an ear out, and if you hear a noise that causes concern, contact a bearing specialist.