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Ever heard a strange sound coming from your machinery and wondered if your bearings are trying to tell you something? Bearings, when running perfectly, produce a low, gentle hum or buzz. But if you start hearing sharp hisses, squeals, or other irregular noises, that's often a sign that something isn't right. Understanding these sounds can be incredibly helpful for maintaining your equipment!
Not all bearing sounds are bad, but some definitely indicate a problem. Let's learn to distinguish them.
A healthy, well-functioning bearing will typically emit a low humming or buzzing sound. This is usually a sign that everything is in order. You might also hear a smooth, clear sound that doesn't change much with rotation speed. While this could be caused by slight indentations on the bearing's outer ring raceway, it might not be immediately critical.
When the sounds become sharp, irregular, or change with speed, it's time to investigate.
Sharp Hissing or Squealing: This often points to improper lubrication. Is your bearing getting enough grease or oil?
Metallic Sounds: These can indicate inadequate bearing clearance, meaning the bearing might be too tight or too loose.
Intermittent Noise: If the noise comes and goes, it suggests that rolling elements might be damaged. This sound occurs when the damaged surface is rolled over.
Hissing with Contaminants: If dirt or other contaminants get inside the bearing, you'll often hear a hissing sound.
Loud, Irregular Noise: This is a clear sign of severe bearing damage. Don't ignore this!
Noise from Installation Damage: If the bearing was damaged during installation (e.g., from hammering), you'll hear a noise that varies with the bearing's rotation speed.
Let's break down typical abnormal bearing noise characteristics and their likely causes.
"Za-za" or "Gaga" Sounds: If you hear a consistent rattling or clicking, and the sound quality doesn't change with rotation speed, it's often due to dust or foreign matter. If the sound changes with rotation speed, it might indicate scratches on the raceway, balls, or rollers, or a rough surface on these components.
"Cilala" Noises: These are typically heard in small bearings and suggest roughness on the raceway, balls, or rollers.
"Cilala-cilala" (Intermittent): If this sound occurs intermittently and regularly, it could be due to contact with the sealing ring, the cage, or the seal cover.
"Wuwu," "Dididi," or "Hongming" (Humming/Roaring): These noises change in loudness and pitch with rotation speed, often becoming louder at specific speeds. They can even sound like an alarm or whistle. Possible causes include resonance, improper fit (like a poorly shaped shaft), raceway deformation, or waves/corrugation on the raceway, balls, or rollers. (Note: A slight hum in large bearings might be normal).
"Gazi-gazi" (Grinding/Crunching): If you feel this when rotating the bearing manually, it could be scratches on the raceway (if regular) or scratches on the balls/rollers (if irregular). It might also indicate dust, foreign matter, or raceway deformation causing localized negative clearance.
"Longlong" (Rumbling): This is often a continuous sound at high speeds in large bearings, but can also be heard continuously in small bearings, indicating scratches on the raceway, balls, or rollers.
"Wu-" or "Weng-" (Electric Hum): If the sound stops instantly when power is cut, it's likely motor electromagnetic noise.
"Zhila-zhila" (Irregular Squeaking): This irregular sound that doesn't change with rotation speed is mainly heard in small bearings and usually means dust or foreign matter has gotten inside.
"Dingdang-dingdang" (Clanging/Jingling): In tapered roller bearings, a clear, continuous sound at high speed might be normal if it's just the cage. If lubricant softens at low temperatures, that's good. Otherwise, it points to internal cage wear, insufficient lubrication, or insufficient bearing load during operation.
"Xila-huala" (Rattling): More noticeable at low speeds and becoming continuous at high speeds, this is often the impact sound from inside the cage or insufficient lubrication. Reducing internal clearance or applying preload might make it go away. If all rollers are involved, it indicates impact between the rollers.
"Bangbang" (Thumping): A larger metallic impact sound, typically heard in low-speed thin-walled large bearings (TTB). This suggests a rolling element tearing sound, raceway deformation, or general squeaking.
"Guangguang" (Clanking): Primarily from cylindrical roller bearings, this sound changes with rotation speed and can be quite loud and metallic. It might temporarily stop after adding lubricant. Causes include lubricant being too thick, excessive radial internal clearance, or insufficient lubrication.
"Jiangjiang" (Grinding/Biting): This is a metallic biting or sharp sound, often indicating roller-flange biting in roller bearings, internal clearance that's too small, or insufficient lubrication.
"Cila" (Irregular Squeak): An irregular sound from small bearings, often due to bubbles bursting in the lubricant.
"Pacha-pacha" (Irregular Creaking): This irregular squeaking can be caused by slipping in fit areas, squeaking from the mounting surface, or even keyway squeaking.
Overall Excessive Noise Pressure: If the bearing simply seems too loud, it could be due to roughness on the raceway, rollers, or balls, deformation of these surfaces due to friction, or excessive internal clearance also caused by friction.
Beyond the types of sounds, here's a comprehensive list of common culprits and what you can do.
Abnormal Load: Correct the fit, investigate bearing clearance, adjust load, or modify the housing shoulder position.
Improper Installation: Check shaft and housing machining precision, and improve installation accuracy and method.
Insufficient or Unsuitable Lubricant: Replenish lubricant and select an appropriate type.
Contact with Rotating Parts: Modify the contact area of the labyrinth seal.
Indentations, Rust, or Scratches from Foreign Objects: Replace the bearing, clean related parts, improve the sealing device, and use clean lubricant.
Surface Deformation (after steel carburization): Replace the bearing and pay attention to its usage conditions.
Raceway Spalling: Replace the bearing.
Excessive Clearance: Re-evaluate the fit and bearing clearance, and adjust the preload amount.
Foreign Object Intrusion: Consider replacing the bearing, clean related parts, improve the sealing device, and use clean lubricant.
Spherical Surface Damage or Spalling: Replace the bearing.
Contaminated grease.
Insufficient lubrication (low oil level, or oil/grease leakage through seals due to improper storage).
Bearing clearance too small or too large (a manufacturing issue).
Abrasive impurities like sand or carbon particles mixed in the bearing.
Corrosive contaminants like water, acids, or paint mixed in.
Bearing squeezed by the housing bore (poor bore roundness or a twisted bore).
Uneven shims under the bearing housing (leading to bore deformation or even housing cracks).
Debris in the bearing housing bore (e.g., residual chips, dust).
Eccentric seal ring (touching adjacent parts and causing friction).
Bearing subjected to extra load (e.g., axially constrained, or two fixed-end bearings on one shaft).
Loose fit between bearing and shaft (shaft diameter too small or adapter sleeve not tightened).
Bearing clearance too small, rotating too tightly (adapter sleeve overtightened).
Bearing noise (due to roller end face or ball slipping).
Excessive thermal expansion of the shaft (bearing subjected to statically indeterminate axial additional load).
Shaft shoulder too large (touching and rubbing against bearing seals).
Housing bore shoulder too large (distorting bearing seals).
Labyrinth seal clearance too small (rubbing against the shaft).
Bent locking washer teeth (touching and rubbing against the bearing).
Incorrect oil slinger position (touching and rubbing against the flange cover).
Indentations on balls or rollers (caused by hammering the bearing during installation).
Bearing noise (interference from external vibration sources).
Bearing discolored and deformed by heat (caused by using a blow torch for removal).
Shaft too thick, causing excessive interference fit (leading to high bearing temperature or noise).
Housing bore diameter too small (causing high bearing temperature).
Housing bore diameter too large, actual fit too loose (high bearing temperature – outer ring slippage).
Enlarged bearing housing bore (non-ferrous metal housing bore expands, or expands due to thermal expansion).
Cage fracture.
Bearing raceway rust.
Worn steel balls or raceways (unqualified grinding or product bumps).
Unqualified ring raceways (a manufacturing issue).
How do engineers pinpoint these elusive bearing noises? There are two primary approaches: sound-based noise detection and vibration-based detection.
This is a direct measurement method. It involves using high-quality microphones in a quiet environment (with a base noise level below 20 dB). The bearing's sound pressure signal is captured from a specific distance and direction, then analyzed to find any abnormal sound components.
This is an indirect method for detecting abnormal sounds and can be further divided into:
Qualitative Detection: This involves listening for abnormal sounds (often with a stethoscope or specialized listening tools) or observing vibration waveforms to spot irregularities.
Quantitative Parameter Detection: This uses specific measured parameters from the bearing's vibration signal that are related to abnormal sounds. Examples include the vibration peak value, crest factor (a measure of signal spikes), and pulse count.
Several specialized instruments are available for measuring abnormal bearing sounds and vibrations. These can measure the effective value of bearing vibration and also capture parameters reflecting abnormal sounds, such as peak value, crest factor, and pulse count. They're indispensable tools for accurate diagnosis!
Even before installation, how you store your bearings can significantly impact their longevity and performance.
Maintain Original Packaging: Always keep bearings in their original packaging and do not open it arbitrarily. If you find damaged packaging, you must open, thoroughly clean, re-grease, and re-package the bearing.
Controlled Environment: The storage room's relative humidity should not exceed 60%, and the temperature difference should not be too large. Bearings stored in their original packaging can last for several years under these conditions. Be aware that sealed bearings or those with dust covers might experience a degradation in the lubricating properties of their filled grease after long-term storage.
Vibration and Contamination Protection: The storage room should also be protected from vibration and shaking. Bearings not in their original packaging should be stored carefully, and it's strictly forbidden to store them with corrosive substances to prevent corrosion and contamination.
Flat Storage for Large Bearings: Large rolling bearings should only be stored horizontally (flat). Ideally, the entire side surfaces of both the inner and outer rings should be supported. If stored upright, the heavy inner/outer rings and rolling elements, combined with relatively thin ring walls, could lead to permanent deformation.
By understanding these noises, their causes, and proper maintenance, you can ensure your bearings, and your machinery, run smoothly for longer! What's the most common bearing noise you've encountered in your experience?
Please contact us for any questions about bearings, and if you are choosing a ball bearing distributor, we would be happy to give you a quote.
