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9.1 Description
"The function of grease is to remain in contact with and lubricate moving surfaces without leaking out under gravity or centrifugal action, or be squeezed out under pressure. Its major practical requirement is that it retain its properties under shear at all temperatures that it is subjected to during use. At the same time, grease must be able to flow into the bearing through grease guns and from spot to spot, but must not add significantly to the power required to operate the machine, particularly at startup." (Boehringer 1992)
Grease has been described as a temperature-regulated feeding device: when the lubricant film between wearing surfaces thins, the resulting heat softens the adjacent grease, which expands and releases oil to restore film thickness.
Bio EP Greases are solid mixtures of a Base Oil, a Thickener and Additives:
Base Oils
The Base Oils performing the actual lubrication are produced from Hybrid grown High Oleic Base Stocks (HOBS), such as Corn, Soy, Sunflower, Canola, and Rapeseed vegetable oils. These Ultimate Biodegradable and Recyclable base oils are renewable and sustainable agricultural commodity crops.
Thickener
A Thickener gives Bio EP Grease its characteristic consistency and is sometimes thought of as a three-dimensional fibrous network or sponge that holds the oil in place. Common thickeners are soaps and organic or inorganic nonsoap thickeners.
Additives
Additives enhance Anti-Wear performance while protecting the biobased grease from oxidation and lubricated surfaces from rust and corrosion.
United Bio Lube's Bio EP Greases are formulated from U.S.D.A. sponsored High Oleic Base Stocks, or HOBS and uniquely processed with patented Stabilized2 chemistry and a Zinc-free additive package for High Performance, Longevity, Anti-Oxidation, Anti-Wear Extreme Pressure, Cold Flow technology, Anti-Rust, Anti-Corrosion, and reduced Hardening.
Bio EP Greases are engineered to OUTPERFORM petroleum based EP greases and function as Drop In Replacements. The natural oily film of these high viscosity products have proven in laboratory and field tests to outperform petroleum (mineral) oil greases in terms of natural Lubricity, Shear Stability, Oxidation Stability, and Load Carrying Capacity.
Note: The majority of greases on the market are composed of mineral oil blended with a soap thickener. These greases lack many of the advanced performance properties and qualities inherent in Bio EP Greases.
9.2 Function of Bio EP Greases
Applications Suitable For Bio EP Greases
Note: Grease and Oil are not interchangeable.
Grease is used when it is not practical or convenient to use Oil. The choice of lubricant for a specific application is determined by matching the machinery design and operating conditions with desired lubricant characteristics.
Bio EP Greases are generally used for:
(1) Machinery that runs intermittently or is in storage for an extended period of time. Because Bio EP Greases remain in place, a lubricating film can instantly form.
(2) Machinery that is not easily accessible for frequent lubrication. High Quality Bio EP Greases can lubricate isolated or relatively inaccessible components for extended periods of time without frequent replenishing.
United Bio Lube's Bio EP Greases are also used in Sealed-For-Life applications such as Electrical Motors and Gear Boxes.
(3) Machinery operating under extreme conditions such as high temperatures and pressures, shock loads, or slow speed under heavy load. Under these circumstances, Bio EP Greases provide thicker film cushions that are required to protect and adequately lubricate, whereas oil films can be too thin and can rupture.
(4) Worn Components. Bio EP Greases maintain thicker films in clearances enlarged by wear and can extend the life of worn parts that were previously oil lubricated.
Thicker grease films also provide noise insulation.
Functional Properties of Grease
(1) Functions as a sealant to minimize leakage and to keep out contaminants. Because of its consistency, grease acts as a sealant to prevent lubricant leakage and also to prevent entrance of corrosive contaminants and foreign materials. It also acts to keep deteriorated seals effective (whereas an oil would simply seep away).
(2) Easier to contain than oil. Oil lubrication can require an expensive system of circulating equipment and complex retention devices. In comparison, grease, by virtue of its rigidity, is easily confined with simplified, less costly retention devices.
(3) Holds solid lubricants in suspension. Finely ground solid lubricants, such as Molybdenum Disulfide (Moly) and Graphite, are mixed with grease in high temperature service (over 315 °C, 599 °F) or in extreme high-pressure applications. Grease holds solids in suspension whereby solids will settle out of oils.
(4) Fluid levels do not have to be controlled and monitored.
Notable Disadvantages of Grease
(1) Poor Cooling
Due to its consistency, grease cannot dissipate heat by convection like a circulating oil.
(2) Resistance To Motion
Grease has more resistance to motion at start-up than oil, so it is not appropriate for low torque, high speed operation.
(3) Difficult To Handle
Grease is more difficult to handle than oil for dispensing, draining, and refilling. Also, exact amounts of lubricant cannot be as easily metered.
9.3 Bio EP Grease Characteristics
Common ASTM tests for Bio EP Grease characteristics are listed on each product's specification page,
i.e. Bio Multi-Purpose High Temp EP Grease - NLGI 2,
i.e. Bio Graphite EP Grease - NLGI 1.
Apparent Viscosity
At start-up, grease has a resistance to motion, implying a high viscosity. However, as grease is sheared between wearing surfaces and moves faster, its resistance to flow reduces. Its viscosity decreases as the rate of Shear increases.
By contrast, an oil at constant temperature would have the same viscosity at start-up as it has when it is moving.
To distinguish between the viscosity of oil and grease, the viscosity of a grease is referred to as Apparent Viscosity. Apparent viscosity is the viscosity of a grease that holds only for the Shear Rate and temperature at which the viscosity is determined.
Pumpability and Feedability
Pumpability is the ability of a grease to be Pumped or Pushed through a system. More practically, pumpability is the ease with which a pressurized grease can flow through lines, nozzles, and fittings of grease dispensing systems.
Feedability is the ability of a grease to be Drawn or Sucked into a pump. Fibrous textured greases tend to have good feedability, but poor pumpability. Buttery textured greases tend to have good pumpability, but poor feedability.
Bleeding, Migration, Syneresis
Bleeding is a condition when the liquid lubricant separates from the thickener. It is induced by high temperatures and also occurs during long storage periods.
Migration is a form of bleeding that occurs when oil in a grease migrates out of the thickener network under certain circumstances. For example, when grease is pumped though a pipe in a centralized lubrication system, it may encounter a resistance to the flow and form a plug. The oil continues to flow, migrating out of the thickener network. As the oil separates from the grease, thickener concentration increases, and plugging gets worse.
If two different greases are in contact, the oils may migrate from one grease to the other and change the structure of the grease. Therefore, it is unwise to mix two greases.
Syneresis is a special form of bleeding caused by shrinking or rearrangement of the structure due to physical or chemical changes in the thickener.
Consistency, Penetration
The most important feature of a grease is its Rigidity, or Consistency. A grease's consistency is its resistance to deformation by an applied force. A grease that is too stiff may not feed into areas requiring lubrication, while a grease that is too fluid may leak out. Bio EP Grease consistency depends on the type and amount of thickener used and the Apparant Viscosity of its HOBS base oil.
The measure of consistency is called Penetration. Penetration depends on whether the consistency has been altered by handling or working. ASTM D 217 and ASTM D 1403 testing methods measure penetration of unworked and worked greases.
To measure penetration, a cone of given weight is allowed to sink into a grease for 5 seconds at a standard temperature of 25 °C (77 °F). The depth, in tenths of a millimeter, to which the cone sinks into the grease is the penetration. A penetration of 100 would represent a Solid Grease while one of 450 would be Semi-Fluid.
National Lubricating Grease Institute (NLGI) Numbers
The NLGI has established consistency numbers or grade numbers, ranging from 000 to 6, corresponding to specified ranges of penetration numbers.
Table 9.1 lists the NLGI Grease Classifications along with a description of the consistency of each classification
Contaminants
Greases tend to hold solid contaminants on their outer surfaces. This action protects lubricated surfaces from wear. If the contamination becomes excessive or eventually works its way down to the lubricated surfaces the reverse occurs; the grease retains abrasive materials at the lubricated surface and wear occurs.
Corrosion and Rust Resistance
This denotes Bio EP Grease's ability to protect metal parts from chemical attack. The natural resistance of Bio EP Greases depends upon the thickener type.
Corrosion resistance is enhanced by patented Bio Corrosion Inhibitors (BCI™).
Dropping Point
Dropping Point is an indicator of the heat resistance of Bio EP Greases. As grease temperature rises, penetration increases until the grease liquefies and the desired consistency is lost. The Dropping Point is the temperature at which a grease becomes fluid enough to drip. The Dropping Point indicates the upper temperature limit at which a grease retains its structure, not the maximum temperature at which a grease may be used.
United Bio Lube's Bio EP Greases regain their original structure after cooling down from the Dropping Point.
Evaporation
United Bio Lube's Bio EP Greases are Low Volatility greases. This means there is very low evaporation rates, or no off-Gassing of harmful vapors and fumes. Low volitility leads to higher Flash Points and higher operating tempertatures.
Note: The mineral oil in traditional greases evaporates at temperatures above 177 °C (350 °F). Excessive oil evaporation causes mineral oil greases to harden due to increased thickener concentration. Therefore, higher evaporation rates require more frequent relubrication.
Fretting Wear and False Brinelling
Fretting is frictional wear of components at contact points caused by minute oscillations. The oscillations are so minute that grease is displaced from between parts but is not allowed to flow back in. Localized oxidation of wear particles results and wear accelerates.
In bearings, this localized wear appears as a depression in the race caused by oscillation of the ball or roller.
The depression resembles that which occurs during Brinell hardness determination, hence the term False Brinelling. An example would be fretting wear of automotive wheel bearings when a car is transported by train. The car is secured, but the vibration of the train over the tracks causes minute oscillation resulting in false brinelling of the bearing race.
Oxidation Stability
Oxidation Stability is the ability of a Bio EP Grease to resist a chemical union with oxygen. Similar to petroleum based EP greases, the reaction of raw, non-stabilized vegetable-oil-based greases with oxygen produces insoluble Gums, Sludge, Carbon, and Lacquer deposits. Prolonged high-temperature exposure accelerates oxidation in these greases.
United Bio Lube's Bio EP Greases are made from High Oleic Base Stocks2 and processed with patented stabilized chemistry to prevent the oxidation, or chemical breakdown of Bio EP Grease formulas.
Stabilized HOBS technology prevents the formation of Insoluble Gums, Sludges, and Lacquer-like deposits that cause sluggish operation, increased wear, and reduction of clearances. Stabilized Bio EP Greases will continue to function under prolonged high-temperature exposure.
Stabilized HOBS technology keeps Bio EP Greases from breaking down and forming acidic residues that harm rubber seals and other elastomers.
Bench tests measuring Oxidation Stability indicate United Bio Lube's Bio EP Greases are superior in comparision with greases made from petroleum in terms of Oxidation breakdown and very low Total Acid Numbers.
Enhanced chemical stability ensures long lasting performance.
Shear Stability
Grease consistency may change as it is mechanically worked or sheared between wearing surfaces. Bio EP Grease's ability to maintain its consistency when worked is its Shear Stability, or Mechanical Stability.
A grease that softens as it is worked is called Thixotropic.
Greases that harden when worked are called Rheopectic.
High Temperature Effects
Note: High temperatures harm greases more than they harm oils.
Grease, by its nature, cannot dissipate heat by convection like a circulating oil. Consequently, without the ability to transfer away heat, excessive temperatures result in accelerated oxidation or even carbonization where grease hardens or forms a crust.
United Bio Lube's Bio EP Greases protect against high temperature breakdown and resultant carbon deposits.
Note: High temperatures induce softening and bleeding, causing mineral oil greases to flow away from needed areas. The mineral oil in traditional greases can flash, burn, or evaporate at temperatures above 177 °C (350 °F). High temperatures, above 73 to 79 °C (165 to 175 °F), can dehydrate certain greases, such as calcium soap grease, and cause structural breakdown. The higher evaporation and dehydration rates at elevated temperatures require more frequent mineral oil grease replacement.
Effective grease lubrication under high temperture operation is a function of Bio EP Grease's consistency.
Low Temperature Effects
If the temperature of a grease is lowered enough, it will become so viscous that it can be classified as a hard grease. Pumpability suffers and machinery operation may become impossible due to torque limitations and power requirements. The temperature at which this occurs depends on the shape of the lubricated part and the power being supplied to it.
United Bio Lube's Bio EP Greases work efficiently in extreme hot and cold applications. The high Viscosity Index of the HOBS base oil naturally lowers heat build up by reducing friction and wear. Bio EP Greases provide exceptional performance over a wide service temperature range of -30 to 280 °C (-22 to 536 °F).
As a guideline, the base oil's Pour Point is considered the low temperature limit of a grease.
Texture
Texture is observed when a small sample of grease is pressed between thumb and index finger and slowly drawn apart.
Texture can be described as:
- Brittle: The grease ruptures or crumbles when compressed.
- Buttery: The grease separates in short peaks with no visible fibers.
- Long Fiber: The grease stretches or strings out into a single bundle of fibers.
- Resilient: The grease can withstand moderate compression without permanent deformation or rupture.
- Short Fiber: The grease shows short break-off with evidence of fibers.
- Stringy: The grease stretches or strings out into long, fine threads, but with no visible evidence of fiber structure.
Water Resistance
This is the ability of Bio EP Grease to withstand the effects of water with no change in its ability to lubricate.
A soap-water lather may suspend the oil in the grease, forming an emulsion that can wash away or, to a lesser extent, reduce lubricity by diluting and changing grease consistency and texture. Rusting becomes a concern if water is allowed to contact iron or steel components.
9.4 Base Oils
The Base Oil selected in formulating a grease should have the same characteristics as if the equipment is to be lubricated by oil. For instance, lower viscosity base oils are used for grease applications at lower temperatures or high speeds and light loads, whereas higher viscosity base oils are used for higher temperatures or low speed and heavy load applications.
Today, with growing environmental concerns and shortages in petroleum, 100% Ultimate Biodegradable and renewable High Oleic Base Stocks (HOBS), i.e. Corn, Soy, Sunflower, Canola, and Rapeseed vegetable oils, are being used in applications requiring safe, nontoxic Bio EP Greases.
Note: Traditionally, petroleum based mineral oils or synthetic base oils are used to formulate greases. For petroleum oils in general, naphthenic oils tend to chemically mix better with soaps and additives and form stronger structures than paraffinic oils. Synthetic oils are higher in first cost but are effective than mineral oils in high temperature and low temperature extremes.
United Bio Lube's Bio EP Greases can outperform synthetics and have the added advantage over synthetics of being lower in cost and manufactured from Renewable High Oleic Base Stocks grown in America.
Renewable agricultural basestocks represent a key sustainable component in Green Chemistry supporting U.S. Oil Independence and eliminating hazardous waste streams while lowering CO2 emissions and other harmful green house gases created directly from the processing, production, usage, and disposal of petroleum based lubricants.
9.5 Soap Thickeners
Dispersed in its base oil, a soap thickener gives grease its physical character. Soap thickeners not only provide consistency to grease, they affect desired properties such as water and heat resistance and pumpability. They can affect the amount of an additive, such as a rust inhibitor, required to obtain a desired quality. The soap influences how a grease will flow, change shape, and age as it is mechanically worked at temperature extremes. Each soap type brings its own characteristic properties to a grease.
The principal ingredients in creating a soap are a Fatty Acid and an Alkali.
Fatty acids can be derived from vegetable fat such as Soybean, Corn, Canola, Sunflower, Olive, Castor, Palm, or Peanut Oils. The most common Alkalies used are the Hydroxides from earth metals such as Aluminum, Calcium, Lithium, and Sodium.
Soap is created when a long-carbon-chain fatty acid reacts with the metal hydroxide. The metal is incorporated into the carbon chain and the resultant compound develops a polarity. The polar molecules form a fibrous network that holds the High Oleic Base Oil (HOBS). Thus, a somewhat rigid gel-like material called Grease is developed. Soap concentration is varied to obtain different grease thicknesses.
Furthermore, the viscosity of the base oil affects thickness as well. Since soap qualities are also determined by the fatty acid from which the soap is prepared, not all greases made from soaps containing the same metals are identical. The name of the soap thickener refers to the metal (Calcium, Lithium, Aluminum, etc.) from which the soap is prepared.
9.6 Complex Soap
The high temperatures generated by modern equipment necessitated an increase in the heat resistance of normal soap-thickened greases. As a result, Complex Soap Greases were developed.
The Dropping Point of a complex grease is at least 38 °C (100 °F) higher than its normal soap-thickened counterpart, and its maximum usable temperature is around 177 °C (350 °F).
Note: In the past, Complex Soap greases were limited to this temperature because the mineral oil can flash, evaporate, or burn above that temperature.
A Complexing Agent made from a salt of the named metal is the additional ingredient in forming a complex grease. A complex soap is formed by the reaction of a fatty acid and alkali to form a soap, and the simultaneous reaction of the alkali with a short-chain organic or inorganic acid to form a metallic salt, the Complexing Agent. Basically, a complex grease is made when a complex soap is formed in the presence of a base oil. Common organic acids are acetic or lactic, and common inorganic acids are carbonates or chlorides.
Lithium Complex Grease
Smooth, buttery textured lithium grease is by far the most popular when compared to all others.
Traditional petroleum based Lithium Soap Grease contains Lithium 12-Hydroxystearate soap. It has a Dropping Point around 204 °C (400 °F) and can be used at temperatures up to about 135 °C (275 °F). It can also be used at temperatures as low as -35 °C (-31 °F) . It has good shear stability and a relatively low coefficient of friction, which permits higher machine operating speeds. It has good water resistance, but not as good as that of Calcium or Aluminum. Pumpability and resistance to oil separation range good to excellent. It does not naturally inhibit rust, but additives can provide rust resistance. Anti-Oxidants and Anti-Wear Extreme Pressure additives are also responsive in lithium greases.
Lithium Complex Grease and Lithium Soap Grease have similar properties except the complex grease has superior thermal stability as indicated by a Dropping Point of 260 °C (500 °F). It is generally considered to be the nearest thing to a true multipurpose grease.
Aluminum Complex Grease
Bio Food Grade EP Greases are premium grade Aluminum Complex biobased Food Grade greases designed to meet the stringent demands of Food, Beverage, Pharmaceutical, and Cosmetic processing plants.
United Bio Lube's Bio Food Grade EP Greases are high performance greases engineered to withstand the moisture, high temperatures (i.e. 536 °F, 280 °C), and high speeds of advanced processing machinery.
Aluminum Complex Grease has a maximum usable temperature of almost 100 °C (212 °F) higher than Aluminum-Soap greases. Aluminum Complex Grease also has a high resistance to water and chemicals.
Note: When made with mineral oils, these greases tend to have shorter life in high temperature, high speed applications.
Calcium Complex Grease
Calcium Complex Grease is prepared by adding the salt, Calcium Acetate. The salt provides the grease with Extreme Pressure characteristics without using an additive. Dropping Points greater than 280 °C (536 °F) can be obtained and the maximum usable temperature increases to approximately 177 °C (350 °F).
Note: Petroleum-based calcium complex greases often have poor Pumpability in high pressure centralized systems, where Caking and Hardening sometimes occur.
United Bio Lube's Bio EP Greases formulated with Calcium Sulfonate have good all-around characteristics making them desirable Multi-purpose bio greases.
Calcium Sulfonate
Calcium Sulfonate-based greases also have a higher Dropping Point, making them attractive for high temperature applications.
These properties, combined with the fact that Calcium Sulfonate can be formulated with Bio EP Greases for use in H-1 Food Grade applications, make it an attractive alternative to other grease additives.
Note: United Bio Lube's Bio EP Greases formulated with Calcium Sulfonate inherently have Extreme Pressure (EP) properties that OUTPERFORM petroleum based greases.
Calcium Sulfonate thickeners have been around over 50 years.
9.7 Additives
Surface Protecting and Performance Enhancing additives that can effectively improve the overall performance of a grease are described in Chapter 5 - Renewable Lubricant Additives.
Solid lubricants such as Molybdenum Disulfide and Graphite are added to grease in certain applications for high temperatures (above 315 °C or 599 °F) and extreme high-pressure applications.
Lamellar Solids
The most common materials are Graphite and Molybdenum Disulfide.
(1) Graphite
Graphite has a low Coefficient of Friction and very high Thermal Stability (2000 °C, 3632 °F) and above). However, practical application is limited to a range of 500 to 600 °C (932 to 1112 °F) due to oxidation.
Furthermore, because graphite relies on adsorbed moisture or vapors to achieve low friction, use may be further limited. At temperatures as low as 100 °C (212 °F), the amount of water vapor adsorbed may be significantly reduced to the point that low friction cannot be maintained. In some instances sufficient vapors may be extracted from contaminants in the surrounding environment or may be deliberately introduced to maintain low friction.
When necessary, additives composed of inorganic compounds may be added to enable use at temperatures to 550 °C (1022 °F).
Note: Another concern is that graphite promotes electrolysis. Graphite has a very significant potential of + 0.25V, which can lead to severe galvanic corrosion of copper alloys and stainless steels in saline waters.
(2) Molybdenum Disulfide (Moly)
Like graphite, Moly has a low friction coefficient, but, unlike graphite, it does not rely on adsorbed vapors or moisture. In fact, adsorbed vapors may actually result in a slight, but insignificant, increase in friction.
Moly also has greater Load Carrying Capacity and its manufacturing quality is better controlled. Thermal stability in non-oxidizing environments is acceptable to 1100 °C (2012 °F), but in air it may be reduced to a range of 350 to 400 °C (662 to 752 °F).
Dispersions of Powdered Solids
Dispersions are mixtures of solid lubricant in grease or fluid lubricants. The most common solids used are Graphite and Molybdenum Disulfide (Moly), discussed above. The grease or fluid provides normal lubrication while the solid lubricant increases lubricity and provides extreme pressure protection.
The addition of Moly to lubricating oils can increase load-carrying capacity, reduce wear, and increase life in roller bearings, and has also been found to reduce wear and friction in automotive applications.
Note: Caution must be exercised when using these solids with petroleum based greases and lubricating fluids:
- Petroleum based grease and oil may prevent good adhesion of the solid to the protected surface.
- Detergent additives in some petroleum based oils can inhibit the wear reducing ability of Moly and Graphite, and some Anti-Wear additives may actually increase wear.
- Solid lubricants can also affect the Oxidation Stability of petroleum based oils and greases. Consequently, the concentration of Oxidation Inhibitors required must be carefully examined and controlled.
9.8 Types of Commom Greases
Although many Environmentally Aware (EA) greases are Biodegradable, EA greases are not made from renewable base oils, rather they are refined from petroleum. Only Bio EP Greases made from Stabilized High Oleic Base Stocks (HOBS) are renewable and economically sustainable.
Note: The following types of greases can be made from either petroleum or renewable vegetable base oils.
Calcium Grease
Calcium or lime grease, the first of the modern production greases, is prepared by reacting mineral oil with fats, fatty acids, a small amount of water, and calcium hydroxide (also known as hydrated lime). The water modifies the soap structure to absorb mineral oil. Because of water evaporation, calcium grease is sensitive to elevated temperatures. It dehydrates at temperatures around 79 °C (175 °F) at which its structure collapses, resulting in softening and, eventually, phase separation. Greases with soft consistencies can dehydrate at lower temperatures while greases with firm consistencies can lubricate satisfactorily to temperatures around 93 °C (200 °F).
In spite of the temperature limitations, lime grease does not emulsify in water and is excellent at resisting Wash Out.
Also, its manufacturing cost is relatively low. If a calcium grease is prepared from 12-hydroxystearic acid, the result is an anhydrous (waterless) grease. Since dehydration is not a concern, anhydrous calcium grease can be used continuously to a maximum temperature of around 110 °C (230 °F).
Sodium Grease
Sodium grease was developed for use at higher operating temperatures than the early hydrated calcium greases. Sodium grease can be used at temperatures up to 121 °C (250 °F), but it is soluble in water and readily washes out. Sodium is sometimes mixed with other metal soaps, especially calcium, to improve water resistance.
Although it has better adhesive properties than calcium grease, the use of sodium grease is declining due to its lack of versatility. It cannot compete with water resistant, more heat resistant multipurpose greases. It is, however, still recommended for certain heavy duty applications and well-sealed electric motors.
Aluminum Grease
Aluminum grease is normally clear and has a somewhat stringy texture, more so when produced from high-viscosity oils. When heated above 79 °C (175 °F), this stringiness increases and produces a rubberlike substance that pulls away from metal surfaces, reducing lubrication and increasing power consumption. Aluminum grease has good water resistance, good adhesive properties, and inhibits rust without additives, but it tends to be short lived. It has excellent inherent oxidation stability but relatively poor shear stability and pumpability.
Other Greases
Thickeners other than soaps are available to make greases. Although most of these are restricted to very special applications, two nonsoap greases are worthy of mention. One is organic, the other inorganic.
Polyurea Grease
Polyurea is the most important organic nonsoap thickener. It is a low molecular weight organic polymer produced by reacting amines (an ammonia derivative) with isocyanates, which results in an oil soluble chemical thickener. Polyurea grease has outstanding resistance to oxidation because it contains no metal soaps (which tend to invite oxidation). It effectively lubricates over a wide temperature range of -20 to 177 °C (-4 to 350 °F) and has long life.
Water resistance is good to excellent, depending on the grade. It works well with many elastomer seal materials. It is used with all types of bearings but has been particularly effective in ball bearings. Its durability makes it well suited for Sealed-For-Life bearing applications.
Polyurea Complex Grease is produced when a complexing agent, most commonly calcium acetate or calcium phosphate, is incorporated into the polymer chain. In addition to the excellent properties of normal polyurea grease, these agents add inherent extreme pressure and wear protection properties that increase the multipurpose capabilities of polyurea greases.
Organo-Clay
Organo-Clay is the most commonly used inorganic thickener. Its thickener is a modified clay, insoluble in oil in its normal form, but through complex chemical processes, converts to platelets that attract and hold oil. Organo-clay thickener structures are amorphous and gel-like rather than the fibrous, crystalline structures of soap thickeners.
This grease has excellent heat-resistance since clay does not melt. Maximum operating temperature is limited by the evaporation temperature of its base oil. However, with frequent grease changes, this multipurpose grease can operate for short periods at temperatures up to its Dropping Point, which is about 260 °C (500 °F).
A disadvantage is that greases made with higher viscosity oils for high thermal stability will have poor low temperature performance.
Organo-Clay grease has excellent water resistance but requires additives for oxidation and rust resistance. Work stability is fair to good. Pumpability and resistance to oil separation are good for this buttery textured grease.
9.9 Compatibility
Greases are considered incompatible when the physical or performance characteristics of the mixed grease falls below original specifications. In general, greases with different chemical compositions should not be mixed. Mixing greases of different thickeners can form a mix that is too firm to provide sufficient lubrication or more commonly, a mix that is too soft to stay in place.
Note: Combining greases of different base oils can produce a fluid component that will not provide a continuous lubrication film. Additives can be diluted when greases with different additives are mixed. Mixed greases may become less resistant to heat or have lower shear stability.
When a new brand of grease is introduced, i.e. United Bio Lube's Bio EP Greases, it is recommended the component part be disassembled and thoroughly cleaned to remove all of the old grease. If this is not practical, the new Bio EP Grease should be injected until all traces of the prior product are flushed out. Also, the first grease changes should be more frequent than normally scheduled.
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