Bearing maintenance

maintenance

Bearings are robust mechanical components that last for a long time if:

  • They are mounted correctly;
  • Have good maintenance;
  • Have efficient sealing;
  • Are lubricated correctly.

Maximum shelf life

  • Bearings with protection plate (ZZ) ……………………… 2 years.
  • Bearings with sealing plates (2RS) ………………………………….. 3 years

This time limit must be observed in order to keep the grease from hardening.


Storage

Bearings must be maintained clean, bathed in oil or grease and wrapped in paraffin paper.


Bearing check-up

Disclaimer: please note that the following checks must be carefully performed by qualified personnel only.

1) Listen

Hold a wood stick, screwdriver or a similar object against the bearing or as close to its bushing as possible. Get your ear close to the object’s end. A uniform metallic sound indicates the bearing needs lubrication. In case the bearing is already damaged, the sound will be characteristic of wobbling parts hitting each other.

2) Feel

Check the temperature of the bearing by holding a thermometer or heat sensitive chalk to the bushing’s compartment. If the temperature seems higher than usual or varies abruptly, one or more of the following situations could be happening:

  • No lubrication, little lubrication or excessive lubrication;
  • Presence of impurities due to lack of appropriate sealing;
  • Excessive sealing pressure;
  • Damaged bearing;
  • Overloaded bearing;
  • Bearing wrongly specified for application;
  • Not enough internal slack on the bearing.

However, please remember there will be an increase in temperature for one or two days after the bearing is lubricated.

3) Observe

Make sure the lubricant is not leaking through inefficient and/or damaged seals or incorrectly fastened stoppers. The lubricant will present a change in its coloration under the presence of impurities or other contaminants. Automatic lubrication systems must also be checked regularly.

4) Lubricate
4.1 With grease: oils that contain thickening agents in soap form.

Three factors must be taken into consideration when selecting the type of grease to be used:

  • Consistency (classified according to the NLGI scale – National Lubricating Grease Institute)
  • The range of operation temperature
  • Anti-corrosion properties
  • Generally, soap-based greases used in bearings have consistency 1, 2 or 3
4.1.1) Calcium-based greases

Maximum temperature of 60 Celsius
Contain lead soap additives and are recommended for humid applications, including salt water.

4.1.2) Sodium-based greases

Temperature ranging from –30 to +80 Celsius
Offer protection against corrosion because they absorb humidity. If humidity is excessive, the grease might leak out of the bearing.

4.1.3) Lithium-based greases

Temperature ranging from –30 a 110 Celsius
Contain lead soap additives and are recommended for humid applications, including salt water.

4.1.4) Molybdenum-bisulfate-based greases

recommended for extremely high loads and pressures.

4.1.5) Greases for temperatures above 110 Celsius

Generally, they do not contain thickening agents in soap form, like silicone greases, for instance.


Required amount of lubricant in bearings

1) Grease

Taking rotation into consideration, the bearings’ available space must be filled as follows:

  • High rotation: must fill less than 1/3 of available space.
  • Medium rotation: must fill 1/3 of available space.
  • Low rotation: must fill ALL available space.
Note: When requirements are not specified, the ideal amount of grease in the bearing can be calculated applying the formula below:

G = 0,005 DB

G is the quantity (in grams)
D is the bearing’s outer diameter (in millimetres)
B is the width of the bearing (in millimetres).

2) Oil
2.1) Mineral oils

refined and with solvents can be use to lubricate bearings. Normally, mineral oils of medium to high viscosity are used, allowing the formation of an oil film thick enough to lubricate bearings operating in medium and high rotations.

2.2) Synthetic oils

Temperatures above 125 Celsius (polyglicol type). Please refer to the manufacturer’s instructions for other types of synthetic oils.

In high rotations, it is recommended to use low viscosity oils in order to keep the bearing’s temperature low.