Is my car A/C compressor clutch bearing bad?
Types of bearings
- Ball Bearings
- Deep-Groove Ball Bearings
- Self-Aligning Ball Bearings
- Angular-Contact Ball Bearings
- Thrust Ball Bearings
- Roller Bearings
- Tapered Roller Bearings
- Spherical Roller Bearings
- Cylindrical Roller Bearings
- Needle Roller Bearings
Load characteristics and noise level determine the type of bearings that should be selected for the motor. Two common types are the sleeve bearing and the ball bearing. Large motors use a type of ball bearing called a roller bearing, which has cylindrically shaped rollers instead of balls.
The sleeve bearing is used where the load is light and the noise must be low. Sleeve bearings are quiet and dependable, but they cannot stand great pressures (e.g., if belts are too tight).Motors that use sleeve bearings can have either vertical or horizontal shafts.
Sleeve bearings are made from material that is softer than the motor shaft. The bearing must have lubrication-an oil film between the shaft and the bearing surface. The shaft actually floats on this oil film and should never touch the bearing surface. The oil film is supplied by the lubrication system.
Types of lubrication systems
- The Oil Port lubrication bearing
- The Permanently Lubricated bearing
The Oil Port lubrication bearing:
The oil port lubrication bearing has an oil reservoir that is filled from the outside by means of an access port. This bearing must be lubricated at regular intervals with the correct type of oil. If the oil is too thin it will allow the shaft to run against the bearing surface. If the oil is too thick, it will not run into the clearance between the shaft and the bearing surface.
What is the correct interval for lubricating a sleeve bearing?
The correct interval for lubricating a sleeve bearing depends on the design and use of the motor. The manufacturer’s instructions will indicate the recommended interval.
The Permanently lubricated sleeve bearing:
The permanently lubricated sleeve bearing is constructed with a large reservoir and a wick to gradually feed oil to the bearing. This bearing truly does not need lubrication until the oil deteriorates, which will happen if the motor has been running hot for many hours.
Bearing type and noise
Ball-bearing motors are not as quiet as sleeve-bearing motors and are used in locations where the noise levels will not be a problem.
Bearings needing lubrication have grease fittings so a grease gun can force grease into the bearing. This is often done by hand. Only approved grease should be used. The slotted screw at the bottom of the bearing housing is a relief screw. When grease is pumped in to the bearing, this screw must be removed or the pressure of the grease may push the grease seal out, and grease leak down the motor shaft.
What are the most common causes of bearing failure?
Most bearing failure can be attributed to one or more of the following major causes:
- Foreign Matter: One of the most common sources of trouble in bearings is wear a pitting caused by foreign particles. This could be in the form of dirt, abrasive grit, lint, dust, steel, chips, etc.
- Improper Mounting: Bearings should be mounted with a press fit on the rotating ring. Generally, the shaft rotates and the inner ring is mounted with a press or interference fit.
- Bearing Misalignment: A frequent source of trouble resulting in overheating and separator failure. Common causes are bent shafts, out-of-square shaft shoulder, out-of-square spacers, and out-of-square clamping nuts. Inspection of the raceways will show the ball track veering from one side to the other.
- Vibration Brinell(False Brinell): Caused by the rapid movement of the balls in the raceway while the equipment is idle. Rolling elements quickly remove lubrication and, because there is not enough rotation of the bearing, fresh lubricant is not moved back into the spot. This means the bearing is sitting in one spot, devoid of lubrication, and the movement of the rolling elements wears away the metal. The indentations run axially across the races.
- Electrical Damage (Fluting): When electric currents pass through a bearing, there is arcing and burning at the points between the races and the rolling elements where the current jumps the air gap. Pitting or cratering o a bearing is caused by relatively large charges of electricity. A line of small burns along the line of contact of the rolling elements is caused by a low current constantly passing through the bearing. This fluting or grooving is formed on all parts as the current continues to pass through the bearing, and the contacts points change as the bearing rotates. The steel melts in the affected zone. Electrical damage will cause early spalling and results in a noisy bearing which will have to be replaced.
- Improper Bearing Lubrication: Lack of or improper lubrication generally causes overheating or excessive wear in the bearing. These conditions can result from insufficient lubrication, improper lubricants, complete absence of lubrication, or insufficient lubrication due to loss through leakage. Also to be considered is the breakdown of lubricants either by oxidation or exposure to atmospheric conditions.
- Bearing Fatigue: Fatigue means the fatiguing of the metal in the components of the bearing. It is a result of stress reversals produced when rotating members create flexing of the metal. Fatigue develops due to the magnitude of the load and the number of times it is repeated. Actually, the rolling elements create a wave of metal in front of them as they roll. Thus, the metal in the components is alternately put in tension and then compression. This action eventually results in flaking of the metal.
- Bearing Corrosion: The finely finished surfaces of ball and roller bearings are readily subject to corrosion by water, acids, and other agents. Corrosion is basically abrasive in nature and will account for excessive or abnormal wear in bearings. Common causes of corrosion include moisture, acid action, poor or broken down greases, poor wrappings, and condensation resulting from excessive temperature reversals.
- Defective Sealing: This enables foreign material and contaminants to enter the bearing, causing wear.
- High Temperatures: High temperatures frequently cause premature bearing failure, the nature of the failure being predicated on the temperature to which the bearing is raised and the grease with which it is lubricated. Mild temperature elevations may cause grease to bleed which reduces the efficiency of the lubricant. Under increasingly elevated temperature conditions, oxidation causes loss of lubricant elements and the formation of carbon. The carbon thus formed may lock or jam the bearing. High temperatures may also reduce the hardness of the metal causing early failure. High temperatures can cause loss of internal clearance and preloading results.
Many bearing failures can be traced to dirt. Cleanliness is always a must.