Functions of Grease

A satisfactory grease for a given application must:

  • Reduce friction and wear in the machine element being lubricated under various operating conditions.
  • Protect against rust and corrosion.
  • Prevent dirt, water and other contaminants from entering the part being lubricated.
  • Maintain its structure and consistency during long periods of use.
  • Perm it free motion of moving parts at low temperatures and pump freely at those temperatures.
  • Have suitable physical characteristics for the method of application and retain those characteristics during storage.
  • Be compatible with Elastomer seals and other materials associated with the parts being lubricated.
  • Tolerate or resist some degree of moisture contamination without significant loss of performance.

Important characteristics a grease must have

  • High Temperature Capabilities
  • Low Temperature Capabilities
  • Shear and Mechanical Stability
  • Water Resistance
  • Oxidation Resistance
  • Rust and Corrosion Protection
  • Variable Speed Conditions
  • Very Good to Excellent Pump-ability
  • Reversibility

Types of thickeners commonly used in the formulation of greases
Soap base:

  • Lithium
  • Lithium 12-Hydroxysterate
  • Lithium Complex
  • Calcium
  • Calcium 12-Hydroxysterate
  • Calcium Complex
  • Barium
  • Barium Complex
  • Aluminum Complex

Non-soap base:

  • Benton
  • Polyurea

Lithium soap base greases

  • Low to relatively high thickener content 7-12% by weight
  • Smooth to slightly fibrous texture
  • Dropping point of 350°F-400°F (177°C to 204°C)
  • Maximum usable operating temperature of 230°F-275°F (110°C to 135°C)
  • Will emulsify with small quantities of water and soften significantly in the presence of moisture
  • Good work stability
  • Fair to good shear and mechanical stability. Will immediately release its base oils when severe mechanical shear stresses are encountered
  • Good resistance to oil separation
  • Slight to moderate reversibility, 40% to 65%
  • Good oxidation stability
  • Good to excellent pump-ability

Lithium 12-hydroxysterate greases

  • Relatively high thickener content 10-15% by weight
  • Smooth buttery texture
  • Dropping point of 350°F-400°F (177°C to 204°C)
  • Maximum usable operating temperature of 250°F-285°F (121°C to 141°C)
  • Good water resistance. Will slightly emulsify with water. In the presence of large amounts of water the grease will soften and run
  • Fair resistance to rusting in the presence of moisture
  • Good work stability. Softens in consistency when worked severely in a bearing
  • Fair to good shear and mechanical stability. Will rapidly release its base oils when severe mechanical stresses are encountered
  • Fair to good resistance to oil separation
  • Good oxidation stability
  • Slight to moderate reversibility, 45% to 65%
  • Good to very good pump-ability
  • Rapid softening of the grease with increasing temperature

Lithium complex base greases

  • Relatively high thickener content of 10-15% by weight
  • Smooth and buttery texture
  • Dropping point up to 500°F (260°C)
  • Maximum usable operating temperature of 300°F-350°F (149°C to 177°C)
  • Good resistance to water. In the presence of large amounts of water these greases will soften in consistency and run out
  • Good work stability. Some softening in consistency when severely worked in a bear.
  • Good mechanical and shear stability. Will release its base oils fairly rapidly when severely worked.
  • Fair to good resistance to oil separation
  • Moderate to good reversibility, 70% to 85%
  • Good to very good stability
  • Good to very good pump-ability

Calcium soap base

  • Relatively high thickener content of 10-15% by weight
  • Smooth and buttery texture
  • Dropping point up to 500°F (260°C)
  • Maximum usable operating temperature of 300°F-350°F (149°C to 177°C)
  • Good resistance to water. In the presence of large amounts of water these greases will soften in consistency and run out.
  • Good work stability. Some softening in consistency when severely worked in a bear.
  • Good mechanical and shear stability. Will release its base oils fairly rapidly when severely worked.
  • Fair to good resistance to oil separation
  • Moderate to good reversibility, 70% to 85%
  • Good to very good stability
  • Good to very good pump-ability

Calcium 12-hydroxysterate greases

  • Relatively high thickener content 10-15% by weight
  • Smooth and buttery texture
  • Dropping point of 275° to 300°F
  • Maximum usable operating temperature of 230°F
  • Good to very good water resistance
  • Poor to very good protection against rust in the presence of moisture
  • Good work stability. Will soften in consistency when severely worked in a bearing
  • Fair to good shear and mechanical stability
  • Poor to fair reversibility, 10-30%
  • Fair to very good pump-ability
  • Poor to good oxidation stability

Calcium complex greases

  • High thickener content 15% to 25% by weight
  • Buttery to fibrous texture
  • Dropping point of 450°F
  • Maximum usable temperature of 350°F
  • Good to very good resistance to water washout
  • Fair to good protection against rust in the presence of moisture
  • Good work stability
  • Will soften in consistency when severely worked
  • Poor to good mechanical stability
  • Fair to good resistance against oil separation
  • Poor reversibility, 10 to 30%
  • Poor to good oxidation stability
  • Poor to fair pump-ability
  • Can harden in consistency in storage or under pressure in lubrication systems

Barium soap base greases

  • Very high thickener content. Up to 35% by weight
  • Fibrous and stringy in texture
  • Dropping point of 370°F to 400°F
  • Maximum usable temperature of 250° to 285°F
  • Very good resistance to water washout
  • Fair to good protection against rusting
  • Good work stability
  • Fair to good shear and mechanical stability. Will separate into its base oils and thickeners when high to severe mechanical shear stresses are encountered.
  • Fair resistance to oil separation
  • Poor Reversibility. 0% to 30% Reversibility
  • Poor pump-ability, especially at low temperatures
  • * Possibility that compounds containing barium are highly toxic

Aluminum complex base greases

  • Low thickener content of 6.5 to 9.5% by weight
  • Smooth and buttery texture
  • Dropping point of 400°F-500°F (204°C to 260° C)
  • Maximum usable operating temperature of 350°F-spot temperatures of 400°F (177°C to 204°C)
  • Excellent resistance to water washout. Slightly hardens in consistency in the presence of water, especially when subjected to mechanical shear stress, in order to act as a seal against water contamination and to allow the grease to remain in the bearing.
  • Very good to excellent resistance against rusting, especially in the presence of moisture
  • Very good to excellent work stability
  • Very good to excellent mechanical and shear stability. Slightly to moderate hardening in consistency when subjected to high shock loading and severe shear stresses. This hardening in consistency allows the grease to stay put in the bearings.
  • Very good to excellent mechanical and shear stability. Slightly to moderate hardening in consistency when subjected to high shock loading and severe shear stresses. This hardening in consistency allows the grease to stay put in the bearings.
  • 95% to 100% Reversibility
  • Excellent pump-ability
  • Compatible with all types of greases except bentone base greases
  • Excellent versatility. Can be used in a wide range of application

Non-soap base greases – Bentone base

  • Low to relatively high thickener content 6-15% by weight
  • Smooth to buttery texture
  • No dropping point
  • Maximum usable temperature of 350° to 700°F (177°C to 371°C) The maximum usable temperature is dependent upon the quality and type of base oil used in the formulation of the grease and its re-lubrication cycle.
  • Fair to excellent water resistance. The lower the thickener content the better the water resistance.
  • Good to excellent protection against rusting in the presence of moisture
  • Good to very good work stability
  • Good to very good shear and mechanical stability. Depends upon the thickener content
  • Good to very good low oil separation characteristics
  • Moderate to very good Reversibility. 50% to 95%
  • Good to very good oxidation stability
  • Good to very good pump-ability
  • Not compatible with any types of soap base greases and polyurea base greases

Non-soap base greases – Polyurea base

  • Low thickener content 8-10% by weight
  • Smooth and buttery texture
  • Dropping point of 460°F-500°F (238°C to 260°C)
  • Maximum usable operating temperature of 350°F (177°C)
  • Good mechanical stability. Can soften in consistency and run out if subjected to very high to severe mechanical shear stresses.
  • Good to very good low oil separation characteristics
  • Good rust protection, especially in the presence of moisture
  • Good to excellent resistance to oxidation
  • Good high temperature stability
  • Poor to moderate Reversibility. 20% to 60% Reversibility
  • Good pump-ability
  • Frequently used in sealed-for-life bearings which are filled during assembly, permanently sealed and operated without re-lubrication for the normal life of the equipment.

High temperature capabilities
Many applications require the use of a grease which is able to withstand high temperatures and still carry on its function of lubrication. When heated, a grease generally becomes softer and flows more readily. At elevated temperatures, oxidation is more rapid, oil separation (“bleeding”) increases and the grease’s base oil will evaporate significantly.

A grease’s high temperature capabilities are dependent upon on not only the type of base oils used in its formulation, but also upon the type of thickener system used.

Schaeffer Mfg’s Aluminum Complex base and Bentone Base Greases, because of the use of 100% pure paraffin oils and/or severely hydrotreated polyalphaolefin base oils and the use of aluminum complex base or bentone base thickener systems in their formulation, have the ability to withstand high temperatures and still carry on its function of lubrication.

88% to 94% better resistance to leakage at high temperatures
Wheel bearing leakage test (ASTM D-1264)

  • Used to measure a grease’s high temperature capabilities by evaluating the grease’s ability resist leakage from a bearing housing and not from varnish-like deposits, when exposed to high temperatures.
  • The test method utilizes a modified automobile front wheel hub assembly operated at an equivalent speed of 60 mph.
  • The hub is packed with 90 grams of grease using 2 grams for the small bearing and 3 grams for the larger bearing and operated for 6 hours at a test temperature of 235°F.
  • At the end of 6 hours the apparatus is dismantled while hot, and the hub cap and leakage collector are weighed separately to the nearest 0.1 gram to determine the amount of leakage that occurred. Also, at the end of the test the bearings are washed and examined for any varnish, gum and lacquer-like deposits.
  • At the end of the test Schaeffer Mfg’s various greases showed no signs of any varnish or lacquer deposits.

Resistance to evaporation at high temperatures
In some applications greases are exposed for extensive periods to elevated temperatures. These elevated temperatures may cause evaporation of the base oils resulting in hardening and caking of the grease.

Schaeffer Mfg’s Aluminum Complex Base and Bentone Base Greases due to the use of 100% pure paraffin base oils and/or severely hydrotreated polyalphaolefin synthetic base stocks, exhibit lower vapor pressures and significantly higher boiling points than conventional greases. This results in:

  • Reduced grease consumption
  • Significantly reduced deposit formation
  • Longer bearing life
  • Increased oxidation stability
  • Significantly less wear

40% to 83% less evaporation characteristics
Evaporation loss test (ASTM D-2595)

  • Test method is used to determine the evaporation loss of lubrication greases for applications where evaporation loss is a factor.
  • Evaporation loss data can be obtained at any temperature in the range of 210° to 300°F (99° to 145°C)
  • The grease is weighed to the nearest 1 milligram before placing in the evaporation cell
  • The grease is placed in the evaporation cell and the cell is placed in a bath at the desired test temperature. Heated air is flowed through the evaporation cell for 22 hours.
  • At the end of 22 hours the sample is allowed to cool to room temperature and reweighed in order to determine the percent evaporative loss.

Oxidation resistance
Due to high temperatures that can be encountered in many bearing application, the oxidation resistance of a grease plays an important role in its performance.

It has been found that for every 20°F rise in temperature above constant operating temperatures of 200°F to 250°F, the oxidation rate of a grease will be doubled. If the grease being used in these high temperature applications is unable to resist oxidation this can result in premature hardening and caking of the grease, destruction of its base oils and inactivation of its extreme pressure and antiwear properties.

A greases ability to resist oxidation is dependent upon two main factors:

  • The type of base oils and oxidation inhibition additives used
  • The type and amount of thickener system used

If a grease is not properly inhibited and uses a low thickener content oxidation will occur.

Schaeffer Mfg’s Aluminum Complex Base and Bentone Base Greases due to the use of 100% pure paraffin base oils and/or severely hydrotreated polyalphaolefin synthetic base stocks, their low thickener contents, and the use of a highly effective oxidation inhibiting additive system possess exceptional resistance to oxidation especially when high temperatures conditions are encountered.

65% to 82% better oxidation stability than conventional aluminum complex base greases
Grease oxidation stability test (ASTM D-942)

  • Used to evaluate the resistance of greases to oxidation under static conditions for long periods of time
  • The test is run at 210°F/99°C, utilizing an oxidation bomb filled with oxygen to 110 pªl
  • Five dishes are each filled with 4 grams of grease and placed in the oxidation bomb. The bomb is then charged with 100pªl of oxygen and after a 24 hour leak-proof test is adjusted to 100pªl.
  • Test is run for 100 hours. At the end of 100 test hours the pressure drop in pªl is reported

69% to 85% better oxidation stability than conventional lithium and lithium complex base greases

65% to 83% better oxidation stability than conventional polyurea base greases

50% to 65% better oxidation stability than conventional Bentone base greases

Shear and mechanical stability
In many bearing applications a grease can be subjected to high mechanical shear stresses or high loading conditions. These high mechanical shear stresses or high loading conditions can severely work a grease. Unless the grease exhibits good to excellent shear stability, the grease will either run out of the lubrication area or will separate into its base oils and thickener components, thus allowing the oil component to run out of the bearing and leave the thickener behind to lubricate.

Shear stability is the property that best reflects a grease’s ability to retain its integrity or consistency. It is a means of judging the grease’s ability to “stay put” in the bearing. It is important that when a grease is worked in a bearing, any change in the grease’s consistency must be moderate in order for the grease to stay in the bearing and act as a seal to prevent water, dirt or other contaminants from entering the bearing.

Schaeffer Mfg’s Aluminum Complex Base Greases and Bentone Base Greases due to not only their low thickener contents but also due to their processing through a collodial mill after formulation in order to tighten them exhibit very good to excellent shear stability. This very good to excellent shear stability results in the Schaeffer greases’ ability to moderately harden in consistency when subjected to high mechanical shear stress or high loading conditions. By moderately hardening in consistency, this results in the Schaeffer Greases “staying put” in the bearing.

19% to 82% better shear stability
Roll stability test (ASTMD-1831)

  • After the worked penetration is determined and recorded a 60 gram sample of grease that has not been worked is placed in the test cylinder and distributed uniformly on the inside wall of the cylinder.
  • A weighted roll is placed inside the cylinder, the cap tightened and the entire cylinder assembly is mounted onto the test assembly.
  • The test assembly is started and the weighted rolle revolves along the inside of the cylinder at 106 rpm for a period of 2 hours.
  • At the end of a two hour rolling period the cylinder assembly is dismantled and the grease being tested is removed so that its worked penetration according to the ASTM D-1403 can be determined.
  • From the before and after penetration readings the percent change in consistently is calculated.

Resistance to water washout and water spray-off
Many bearing applications in industry, mining, construction, farming, etc. are constantly exposed to copious amounts of water (sometimes water spraying onto the bearing at high pressure). Unless a grease has the ability to resist softening and/or emulsification with water it will wash out of the bearing. Once the grease has been removed from the bearing due to water washout, this results in:

  • Loss of the grease’s ability to act as a seal against contaminants
  • Rusting and corrosion of critical moving parts
  • Enhanced oxidation of the lubricant
  • Increased wear
  • Increased grease consumption
  • Reduced bearing life

Schaeffer Mfg’s Aluminum Complex Base and Bentone Base Greases exhibit very good to excellent resistance to water wash-out and water spray-off. This is due to the ability of the Aluminum Base Greases to moderately harden in consistency when worked in the presence of moisture and the use of an advanced structure modifying additive sytem in the formulation of all the Schaeffer Mfg greases. This very good to excellent resistance to water wash-out and water spray-off results in:

  • Increased protection against rusting and corrosion of critical moving parts
  • Resistance to emulsification and absorption of moisture
  • Increased oxidation inhibition
  • Increased anti-wear protection
  • Reduced grease consumption
  • Increased bearing life

42% to 58% better resistance to water wash-out than conventional lithium and lithium complex base greases
Water wash-out test (ASTMD-1264)

  • The test method is used to evaluate the resistance of a grease to washout by water from a bearing.
  • The test method can be run at a temperature of either 100°F or 175°F.
  • 4 grams of the grease being tested is packed into a tarred ball bearing which is inserted in a housing with specified clearances and rotated at 600 +/- 30rpm.
  • Water at the specified test temperature is impinged on the bearing plate at a rate of 5ml per second for 1 hour. At the end of 1 hour the unit is turned off and the bearing is placed in an oven for 16 hours at 170°F.
  • At the end of the 16 hour drying period the bearing is cooled and weighed to determine the amount of grease lost through water washout.

28% to 47% better resistance to water washout than conventional Polyurea base greases
Water washout test (ASTM D-1264), loss percentage at 176°F

42% to 50% better resistance to water washout than conventional Bentone Base greases
Water washout test

17% to 82% better resistance to water spray off than conventional soap base greases
Water spray off test (ASTMD-4049)

  • The test is used to evaluate the ability of a grease to adhere to a metal surface when subjected to an intense water spray.
  • In this test a stainless steel panel is coated with a 1/32 inch film of grease and weighed.
  • The panel is then sprayed with water at a temperature of 100°F and a pressure of 40 pªl for 5 minutes. The spray apparatus is held 1 foot from the steel panel.
  • At the end of the 5 minute test time the panel is oven dried for 1 hour at 150°F (66°C)
  • After allowing to cool off to room temperature the steel panel is re-weighed to determine the weight and the percentage of the grease washed away.

61% to 67% better resistance to water spray off than conventional Bentone base greases

Rust and corrosion protection
Rust and corrosion protection is another very important property a grease must possess. Many greases are used in applications that may be exposed to large volumes of fresh and salt water in both a liquid and vapor state. The degree of protection a grease provides is dependent upon its composition, how it reacts in the presence of water, its ability to form and maintain a seal against the entrance of corrosive and other undesirable materials and the presence of a rust inhibiting additive system.

Schaeffer Mfg’s Aluminum Complex Base and Bentone Base Greases contain a highly effective rust and corrosion inhibiting additive system, that is not readily depleted during the life of these greases. These greases also offer excellent rust and corrosion protection as a result of their excellent shear stability and their resistance to water washout and water spray-off.

Extreme pressure and anti-wear protection
One of the primary functions of a grease is to reduce friction and wear in the bearing being lubricated under various operating conditions. Many bearing applications are subjected to high shock loading, continuous low speed/high torque conditions and in some cases severe overload conditions. These conditions often result in boundary lubrication conditions that result in metal to metal contact between the moving parts of the bearing. Once metal to metal contact occurs, excessive wear and eventual premature failure of the bearing will occur.

Because of these aspects it is important that a grease possesses good to very good extreme pressure and anti-wear properties.

Schaeffer Mfg’s Aluminum Complex Base and Bentone Base Greases provide significant anti-wear and extreme pressure protection, not only due to the naturally high film strength contributed by the 100% pure paraffin base oils and polyalphaolefin synthetic base fluids, the use of low thickener content that allows morew base oiland fluid to be available to help dampen shock and distribute the solid lubricants and extreme pressure additive system, but also due to the presence of Molybdenium Disulfide, Synthesized Moly and/or other solid lubricants. Once the Molybdenium Disulfide, Synthesized Moly and/or other solid lubricants are plated to the metal surface of the bearing, they form a long-lasting solid lubricant film that is capable of withstanding pressures in excess of 500,000 psig. This long-lasting solid lubricant film prevents metal to metal contact and damaging frictional wear from pressure. This results in not only reduced wear and a reduction in contact area temperatures, but also in increased bearing life, less downtime and extended lubrication cycles.

25% to 60% better extreme pressure and anti-wear protection than conventional extreme pressure greases

43% to 77% better extreme pressure protection under heavily loaded conditions

Reversibility
When a grease encounters abnormally high temperatures for short periods of time and then returns to normal operating temperatures, or encounters high shock loading conditions, bleeding of the grease’s base oils from the grease can occur. Also, during normal operation of a bearing it is the function of a grease to release its base oils in order to lubricate the bearing. However, when the machine is shut off, or when conditions of high temperature or high shock loading occur, the grease must have the ability to recapture its base oils in order to return to its original consistency and continue to function as intended. In other words, it must exhibit Reversibility.

The Reversibility of a grease is defined as the grease’s ability to recapture its base oils in order to return its original consistency and to continue to function as intended. A grease’s Reversibilty characteristics are dictated by the type of and the amount of thickener used. The higher the thickener content the less the grease’s Reversibility.

Schaeffer Mfg’s Aluminum Complex Base Greases contain a thickener content of 7.5% which results in 100% Reversibility characteristics.

Schaeffer Mfg’s Bentone Base Greases contain a thickener content of 6% to 7%, which results in 95% Reversibility characteristics.

Percentage of reversibility for various grease thickeners

Thickener Type Reversibility (%)
Aluminum Complex 95 – 100
Barium 3 – 5
Barium Complex 0 – 30
Bentone 50 – 95
Calcium 12-Hydroxystearate 10 – 30
Calcium Complex 10 – 30
Lithium 40 – 65
Lithium 12-Hydroxystearate 45 – 65
Lithium Complex 70 – 80
Polyurea 20 – 60

( Reversibility percentage for various thickeners )

Schaeffer Mfg’s Aluminum complex base and Bentone base greases are performance driven to meet your lubricating grease needs

  • Excellent pump-ability characteristics for use in centralized lube systems.
  • Very good to excellent resistance to water washout and water spray-off.
  • Excellent shear and mechanical stability.
  • Very good to excellent high temperature capabilities.
  • Excellent anti-wear and extreme pressure load carrying properties.
  • Excellent Reversibility characteristics.
  • Excellent resistance to oxidation.
  • Excellent rust and oxidation inhibiting characteristics.
  • Excellent resistance to bleeding.
  • Excellent adhesive-cohesive properties.
  • Reduced grease consumption
  • Increased bearing life.
  • Reduced downtime.
  • Lower overall operating costs.

Tags: