G rease was first used by the Egyptians on their chariot axles more than years ago. Lithium soap greases— the most common worldwide —were introduced in the early s. Lithium complex greases, which are becoming the most popular in North America, were introduced in the early s.
Additives imparting special properties may be included. Some people describe grease as a sponge. This is not entirely a correct analogy, but liquid lubricant is dispersed in a fibrous thickener network resembling the pores in a sponge.
Most people think grease is primarily thickener but, in actuality, it is mostly oil— which is what does the lubricating. This is illustrated in Fig. Composition As previously illustrated, grease consists of three components: thickener, base oil and additives.
Greases are classified into two major families: soap and non-soap thickeners. Soap-based thickeners are produced from an acid base reaction. The acid is a fatty, along with, in some cases, a short-chain organic complexing acid. The consistency of grease is determined by placing a funnel called a penetrometer shown in the accompanying diagram on a smooth cup of grease that has a temperature of 77 F and measuring the penetration in tenths of a millimeter after five seconds.
High penetration greases, such as 00 and 0, are used in centralized lubrication systems in colder temperatures. Thickener classification … Greases are classified according to their thickener composition, as previously discussed, as well as on their consistency, according to the NLGI system shown above in Table I. Base stock and additives… Most of our discussion up until now has focused on the thickener.
The base oil and additives are also key components of grease formulations. For example, a high-temperature thickener grease will not be effective if the base stock does not have good oxidative stability. Key grease properties The basic properties of greases are noted below in Table IV. Product data sheets are available for purchased greases— and they should be consulted to determine the correct grease for the application.
This is an excerpt of the main terms mentioned in SKF grease technical data. A measure of the stiffness of a grease. A proper consistency must make sure that the grease stays in the bearing without generating too much friction. The softer the grease, the lower the number.
Grease for bearings are typically NLGI 1, 2 or 3. The test measures how deep a cone falls into a grease sample in tenths of mm. Comprehends the suitable working range of the grease.
LTL is defined as the lowest temperature at which the grease will allow the bearing to be started up without difficulty. Below this limit, starvation will occur and cause a failure.
Above HTPL, the grease will degrade in an uncontrolled way so that grease life cannot be determined accurately. The traffic light concept illustrates these concepts. It is important to understand that this point is considered to have limited significance for performance of the grease as it is always far above HTPL. For lubricants, a proper viscosity must guarantee an adequate separation between surfaces without causing too much friction.
The consistency of bearing greases should not significantly change during its working life.
Three main tests are normally used to analyse this behaviour:. Corrosive environments demand special properties for rolling bearing greases. During the Emcor test, bearings are lubricated with a mixture of grease and distilled water. At the end of the test, a value between 0 no corrosion and 5 very severe corrosion is given.
Salt water, instead of distilled water or continuous water flow washout testcan be used to make the test more severe. A glass strip is coated with the candidate grease, which is placed into a water-filled test tube. The test tube is immersed in a water bath for three hours at a specified test temperature.
The change in the grease is visually evaluated and reported as a value between 0 no change and 3 major change along with the test temperature.
Glass or metal plate B. Thin layer of grease on plate C.Sure, this giant tub of grease looks cool, but will it work for everything? In short, no. It will do the job for all chassis and wheel bearings though. No, not the stuff left over in the pan after broiling some burgers, real grease, the kind that makes your car do the things it needs to do. There are so many types of automotive grease, it can be a little confusing when looking at the lubricant aisle at the local NAPA store.
Before we get into all that, how about a little background on grease. Lubricating grease is an interesting product, the basic components are mineral or vegetable oil mixed with soap.
Yep, soap. The oil gets mixed with the soap and whipped up into an emulsification, creating the semi-solid we call grease. General purpose grease is designed to work in a variety of applications, but that does not mean it is not specific, either.
Some general purpose greases are made for specific vehicle brands. With so many options, understanding your needs is important when selecting grease.
The most commonly used types of grease in the automotive world is multi-purpose. The main use for this stuff is chassis componentswhere heat is not an issue.
This type of grease is typically made from Calcium sulfonate. These have a high resistance to water, but do not fare well under high heat application, such as wheel bearings. DO NOT use multi-purpose grease for wheel bearings or other high-heat applications. General purpose grease is useful for everything that does not require a specialty grease. This white general purpose grease is commonly used in household applications for door hinges, drawer slides, etc.
It is stable up to degrees and often used for CV joints. Lithium greas e is made from lithium soap, which is the salt from fatty acids, it is a non-detergent soap that yields a stable, non-corrosive grease. White lithium grease is available in an aerosol can or a tube. It works great for hinges and metal-on-metal moving parts.
Mixing greases in a system can cause issues with thickener systems reacting with each other. This can change the physical and chemical structure of the grease, causing an inability to hold or release the base oil. The resulting grease carries unknown performance characteristics load, temperature stability, shear, etc. Proper care must be taken to ensure compatibility when changing from one grease system to another, including cleaning if possible, compatibility verification including base oilmonitoring and assessing, purging and flushing of old grease, and even repurging as necessary.
Do not overgrease a system. Compatibility testing is always the best option, since the base oil and elastomer must also be taken into consideration. Click here to see our Greases. Black cells indicate compatibility testing not performed.
See information about Cookies. The basic grease selection chart provides you with quick suggestions on the most commonly used greases in typical applications. The chart includes the main selection parameters, such as temperature, speed and load, as well as additional performance information.
Location Login. Back to top. Home Products Lubrication management Lubricants Lubricant selection. Lubricant selection. Selecting a grease can be a delicate process. SKF has developed several tools in order to facilitate the selection of the most suitable lubricant.
The wide range of tools available includes those from easy-to-use application driven tables to advanced software allowing for grease selection based upon detailed working conditions. Basic grease selection The basic grease selection chart provides you with quick suggestions on the most commonly used greases in typical applications. LubeSelect for SKF Greases LubeSelect for SKF Greases provides you a user friendly online tool to select the right grease and suggest lubrication frequency and quantity, while taking the particular conditions of your application into account.
Related links. Grease selection chart Grease is a semisolid lubricant. Grease generally consists of a soap emulsified with mineral or vegetable oil. This change in viscosity is called shear thinning. Grease is sometimes used to describe lubricating materials that are simply soft solids or high viscosity liquids, but these materials do not exhibit the shear-thinning properties characteristic of the classical grease.
For example, petroleum jellies such as Vaseline are not generally classified as greases. Greases are applied to mechanisms that can be lubricated only infrequently and where a lubricating oil would not stay in position.
They also act as sealants to prevent ingress of water and incompressible materials. Grease-lubricated bearings have greater frictional characteristics because of their high viscosity. Greases are a type of shear-thinning or pseudo-plastic fluidwhich means that the viscosity of the fluid is reduced under shear. After sufficient force to shear the grease has been applied, the viscosity drops and approaches that of the base lubricant, such as the mineral oil.
This sudden drop in shear force means that grease is considered a plastic fluidand the reduction of shear force with time makes it thixotropic. It is often applied using a grease gunwhich applies the grease to the part being lubricated under pressure, forcing the solid grease into the spaces in the part. Soaps are the most common emulsifying agent used, and the selection of the type of soap is determined by the application.
Soaps include calcium stearatesodium stearatelithium stearateas well as mixtures of these components. Fatty acids derivatives other than stearates are also used, especially lithium hydroxystearate.
The nature of the soaps influences the temperature resistance relating to the viscositywater resistance, and chemical stability of the resulting grease. Powdered solids may also be used as thickeners, especially as clayswhich are used in some inexpensive, low performance greases. Fatty oil-based greases have also been prepared with other thickeners, such as targraphiteor micawhich also increase the durability of the grease.
Lithium-based greases are the most commonly used; sodium and lithium-based greases have higher melting point dropping point than calcium-based greases but are not resistant to the action of water.
The amount of grease in a sample can be determined in a laboratory by extraction with a solvent followed by e. Gear greases consist of rosin oil, condensed with lime and stirred with mineral oil, with some percentage of water. Special-purpose greases contain glycerol and sorbitan esters. They are used, for example, in low-temperature conditions. Some greases are labeled "EP", which indicates "extreme pressure". Under high pressure or shock loading, normal grease can be compressed to the extent that the greased parts come into physical contact, causing friction and wear.
The solid lubricants bond to the surface of the metal, and prevent metal-to-metal contact and the resulting friction and wear when the lubricant film gets too thin. These compounds are working as a release agent. Solid additives cannot be used in bearings because of tight tolerances. Solid additives will cause increased wear in bearings. Grease from the early Egyptian or Roman eras is thought to have been prepared by combining lime with olive oil.
The lime saponifies some of the triglyceride that comprises oil to give a calcium grease. In the middle of the 19th century, soaps were intentionally added as thickeners to oils. For example, black slugs Arion ater were used as axle -grease to lubricate wooden axle-trees or carts in Sweden. A given performance category may include greases of different consistencies.
The measure of the consistency of grease is commonly expressed by its NLGI consistency number. It assigns a single multi-part code to each grease based on its operational properties including temperature range, effects of water, load, etc.Q: I shot a bunch of expensive marine-style grease into the bearing buddies on my bass-boat trailer last fall. It was recommended to me by a marine mechanic as the best product for my trailer, because the wheels get dunked regularly, and this particular type of grease is supposed to be more water-resistant.
I finally got a chance to go fishing last weekend and noticed that the grease cups had all leaked oily snot all over my brakes. So instead, I spent the afternoon cleaning and repacking all six wheel bearings and replacing all of the greasy, oily brake shoes.
Can you suggest a brand of grease that won't do this? A: You mentioned the brand of grease in your letter, which I removed, because it's a perfectly good product, and the correct one for your application.Engine Oil Codes Explained, SAE (Society of Automotive Engineers) numbers explained/Viscosity
Specifically, i t ' s an aluminum-complex grease, and this type of grease has excellent performance when there's a chance of water contamination, like on your trailer. A primer about grease: It's basically nothing more than a heavy oil mixed with enough soap to make it stringy and clingy enough to remain in place as the bearing spins.
This will ensure the bearing's rollers or balls are constantly covered in the oil. The soap is based on a variety of compounds, notably lithium or aluminum complexes for most of the greases used in cars, trucks and boats. Problem: Not all the soaps are compatible with each other. This causes the soap and the oil to separate, letting the latter settle to the bottom of the cavity the bearing is in.
No surprise—a lot of grease caps have a poor metal-to-metal seal and will let the oil leak out after some weeks. Like yours did. Your wheel bearings were probably originally lubed with a lithiumcomplex grease, a perfectly good grease for wheel-bearing use, even on a boat trailer if it's maintained.
Shooting some more grease into the bearing cap with a grease gun isn't a bad idea. Shooting an incompatible grease in is. This counterpoints the need to completely remove the last vestiges of old grease from a bearing whenever it's repacked. Yes, you want to remove the dirt and wear particles, but odds are you won't know what kind of grease the last mechanic used.
I'm not going to print a huge grease compatibility chart here, although that kind of information is available on the Internet. If you always clean the bearings properly before repacking, it will never be a problem. Don't have a nice parts-washing sink with recirculating solvent handy to your driveway? It's still easy to clean the bearings properly. Remove the bearings, inner and outer, and any shims, lockwashers and clamp nuts.
The bearing inner or outer races can stay pressed in place, however.
Grease Compatibility Chart and Reference Guide
Scrub the inside of the bearing cavity with paper towels until you've got as much grease out as possible, and wipe as much off the bearing itself. Dump the used paper towels. My favorite bearing cleaner for the field is a disposable aluminum pie tin, but any suitable vessel will do. One at a time, clean the parts in solvent, whether it's turpentine, paint thinner, kerosene or even hot, soapy water in a pinch.
Keep the bearings separate so they go back into the same wheel-don't mix and match. Use a cheap disposable paintbrush to scrub all the old grease out.
Let dry, then finish with a quick blast of carb or brake cleaner to get the last dust off. If you have compressed air, you can use it to dry the bearings as long as you don't spin them into destruction.
Pack the bearings by hand, and fill the cavity approximately halfway with grease. Type keyword s to search. Today's Top Stories. Advertisement - Continue Reading Below.