Bearing grease
Glossary of
lubrication terms
Selecting grease for bearing lubrication
Bearing grease
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Bearing grease testing

Why are SKF bearing greases so special?
SKF, as a pioneer in designing and manufacturing bearings, has the best understanding of the lubrication needs of bearings under all operating conditions. SKF has developed internationally accepted bearing-related grease testing parameters, which now form many of the standard methods for testing lubricants and resulting in the manufacture of these testing machines. The development of the most comprehensive quality control monitoring procedures ensures that each batch of grease manufactured on SKF's behalf is to the same consistent quality and specification. SKF, at its Engineering Research Centre, uses the latest equipment available for performance testing, quality control and research. This is the assurance to our customers of the SKF expertise in providing the right grease for the right bearing application.

SKF bearing 
grease testing
Corrosion protection
SKF Emcor method and 
SKF Distilled Water Washout Test

Lubricating greases should protect metal surfaces from corrosive attack in service. The corrosion protection properties of rolling bearing greases are evaluated using the SKF Emcor method, which is standardised under ISO 11007. Under this test method a mixture of lubricating grease and distilled water is present in the bearing. The bearing alternates during a defined test cycle between standstill and rotation at 80 rpm. At the end of the test cycle the degree of corrosion is evaluated according to a scale between 0 (no corrosion) and 5 (very severe corrosion). A more severe test method is to use salt water to replace the distilled water following the standard test procedure. In addition the test can also be carried out by continuously allowing water to flow or wash through the bearing arrangement during the test cycle. This test method is called the SKF Distilled Water Washout Test. The evaluation procedure is exactly the same as that used under the standardised method. However the procedure places greater demands on the corrosion protection properties of the grease.
SKF Emcor test
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Rolling bearing grease life
SKF R0F Test
The SKF R0F grease test machine determines the life and high temperature performance limit of a lubricating grease. Ten deep groove ball bearings are fitted into 5 housings and filled with a given quantity of grease. The test is undertaken at a pre-determined speed and temperature. Both axial and radial loads are applied and the bearings run until failure. The time to failure is recorded in hours and a Weibull life calculation is made at the end of the test period to establish the grease life. This information can then be used to determine the re-lubrication intervals for an application.

Mechanical stability
Prolonged penetration
The grease sample is filled into a cup and using an automatic device (called a grease worker) subjected to 100 000 double strokes. At the end of the test the penetration of the grease is measured. The difference between the measured penetration at 60 strokes and after 100 000 strokes penetration is reported as the change in 10-1 mm.

Roll stability
The consistency of a rolling bearing grease should not alter, or only slightly, during the working life of the rolling bearing. The change in the grease structure (amount of softening or hardening) can be evaluated by filling a cylinder with a pre-specified quantity of grease. A roller is placed inside the cylinder and the complete unit is rotated for 2 hours at room temperature in accordance with ASTM D 1403. SKF modified the standard test procedure to reflect the application conditions under which the grease is used to either 72 or 100 hours at a test temperature of 80 or 100C. At the end of the test period the cylinder is allowed to cool to room temperature and the penetration of the grease is measured. The difference between the original penetration and the value measured is reported as the change in penetration in 10-1 mm.

SKF R0F test
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SKF V2F test
The candidate grease is tested for mechanical stability using the following procedure. The test rig consists of a railway axle box subjected to vibration shocks of 1Hz from a bouncing hammer producing an acceleration level between 12-15 g. The test is run at two different speeds, 500 and 1,000 rpm. If the grease, which leaks from the housing through the labyrinth seal and is collected in a tray after 72 hours at 500 rpm, weighs less than 50 grams, the test is continued for a further 72 hours at 1,000 rpm. If the total amount of grease leakage after both tests (72 hours at both 500 and 1,000 rpm) does not exceed 150 grams, a rating of "M" is given. If the grease only fulfils the first part of the test (72 hours at 500 rpm with a grease leakage of 50 grams or less) but fails the second stage, a rating of "m" is given. If the grease leakage after 72 hours at 500 rpm is greater than 50 grams then it is rated a fail.

Shear strength
Shear strength is the maximum shear stress that is possible to transmit through a grease without the onset of grease flow. Grease being a semi-solid material can transmit a shear stress also with the shear strain rate zero. The shear strain rate zero grease can be kept on different surfaces of bearings and housings. This is an important parameter when pumping greases through pipes in a centralised lubricating system.

Shear stability
The ability of a lubricating grease to resist the changes in consistency during mechanical working. The working may be a result of either laboratory tests or in actual service. This is also called mechanical stability.

4-Ball weld load
The 4-ball weld load test method evaluates the EP (Extreme Pressure) performance of a lubricating grease. This test method is standardised under DIN 51 350/4. Three steel balls are held in a cup and another fourth ball is rotated against the three balls at a given speed. A starting load is applied and increased at pre-determined intervals until the rotating ball seizes and welds to the three stationary balls. The test indicates the point at which the extreme pressure limit of the grease is exceeded.

SKF V2F test
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Lubricating ability
SKF R2F Test
The SKF R2F machine assesses the high temperature performance and lubricating ability of a grease, simulating the conditions under which large size bearings operate in housings. The test method is carried out under two different conditions. Test A is conducted at ambient temperature and Test B is conducted at 120 C. A pass rating in the unheated test (Test A) means that a grease can be used to lubricate larger rolling bearings at normal operating temperatures and also in low vibrating applications. A pass in the heated test (Test B) at 120 C means that the grease is suitable for use in large roller bearings operating at elevated temperatures.
SKF R2F test
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Quiet running
SKF BeQuiet+ Test
The SKF BeQuiet+ test measures the noise generated by a lubricating grease during operation conditions. High accuracy bearings are lubricated with the candidate grease and placed to operate in housings in the BeQuiet+ test machine. The vibration levels are measured during operation in three different frequency bands: high, medium and low. The number of vibration peaks above certain reference levels determines the grease noise classification. The outcome is an internationally standardised Grease Noise Classification "GN", ranging from GN4 for extremely quiet running to GN1 noisy.

For more information on SKF bearing greases, please see our Lubricants FAQs section or Lubricators FAQs section or our online catalogue on this site.

SKF BeQuiet+ test
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