Choosing the Right Grease to Suite Your Specific Application Has Never Been Easier
Choosing the appropriate grease for your equipment depends 100% on the specific application. Some greases will work in multiple capacities, but understanding the specific use, wear and conditions are essential before any recommendation can be made. Modern steel bearing for both automotive and industrial use generally require a #2 grease - lithium complex Extreme Pressure (EP). Never mix greases. Ever. Before introducing a new grease, it is essential to purge out all of the old product and then clean the bearings and components as much as possible before introducing anything new. When introducing new grease, the color should be fresh - not grimy or mottled. Never over-package grease within a component. This inhibits the expulsion of excess grease from releasing out of the relief plugs or seals. By overloading or over-packing grease within a component, you may wind up causing harm or even destruction to bearings from too much fluid friction and the accumulation of dry paste material.
To understand how to choose the right grease for a particular application, it’s important to assess the specific need and conditions. The newly designed SCL website offers a comprehensive comparison chart that provides you with a grease chart to assess compatibility and to support you as you choose the right grease products that will extend the life of your equipment by protecting against wear.
Unlike lubricant specifications, which are often clearly defined as part of the OEM requirements based on viscosity at operating or ambient temperatures, grease information is often lacking. Specifications for grease based on OEM requirements may suggest choosing a National Lubrication Grease Institute (NLGI) No. 2 lithium grease of optimal quality, which gives the consumer a vague sense of which consistency grease they should choose, but because of the lack of clarity and specification, it’s important to really drill down on the specifics of application. Elements to consider when choosing the appropriate grease include selecting the appropriate:
- Thickener type
- Concentration
- Consistency
- Dropping Point
- Operating Temperature Range
- Worked Stability
- Oxidation Stability
- Wear Resistance
Priority Number One
When attempting to choose the right grease for a particular machine or application, the most important thing to consider is your base minimum and optimum oil viscosity. Knowing the difference between base oil viscosity versus grease consistency is essential, because element bearing applications require the necessary viscosity to adequately protect components. Determining minimum viscosity versus optimum viscosity can be done by using speed factors - the surface speed of the bearing elements represented by DN and NDm values. Different bearings have differing surface speeds based on their pitch and bore diameter, so combining the speed factor (DN or NDm) + the estimated operating temperature allows you to then reference the minimum viscosity requirement from a base oil viscosity index.
The Importance of Additives
After determining viscosity, choosing the appropriate additives is essential. Assess whether you are operating a high-speed, lightly loaded element bearing or a heavily loaded open gear component. It is not essential for a high-speed element to have extreme pressure additives (EP), nor does it require tackifying agents - chemical compounds used in formulating greases and adhesives to increase the  “tack,” or stickiness of a product. Potential grease additives include antioxidants, antifoam agents, anti-wear/extreme pressure components, rust inhibitors, demulsifiers and corrosion inhibitors that are required or not based on whether you are considering a needly bearing, ball bearing, roller bearing, thrust bearing or journal bearing.
According to the online publication, Machinery Lubrication, “Most greases are formulated using API Group I and II mineral oil base stocks, which are appropriate for most applications. However, there are applications that might benefit from the use of a synthetic base oil. Such applications include high or low operating temperatures, a wide ambient temperature range, or any application where extended relubrication intervals are desired.”
The Importance of Thickeners and Maintaining Consistency
Determining a grease’s consistency is determined by the concentration of thickener(s) combined with the base oil’s viscosity. The two are not mutually exclusive, and although consistency is affected by viscosity, it is possible for a grease to have a low base oil viscosity and simultaneous higher consistency, or a high base oil viscosity and lower consistency. Depending on the grade - semifluid to a block grease - the National Lubrication Grease Institute (NLGI) offers an easy to read scale that allows consumers to choose the appropriate grease based on consistency with the most commonly used grease being NLGI grade 2 based on its compatibility with most applications. By assessing speed factors (DN or NDm) + the estimated operating temperature, you can determine the proper NLGI grade and consistency for a specific bearing application, and often a higher speed element bearing will require a higher consistency NLGI grade of grease. Some common thickening agents include polyurea, lithium complex and lithium soaps. Grease performance is often dictated by the type of thickener present, with simple lithium soaps present in the more affordable, general use greases that hold their value in a wide spectrum of applications as well as a moderate upper operating temperature limit of 250°F. Enhanced performance becomes available with the use of lithium complex greases that can accommodate higher temperatures and more extreme operating conditions up to 350°F, while polyureic thickeners provide substantial bleed resistance, oxidation protection and temperature performance. All thickeners should be chosen depending on the specific application of an element bearing, compatibility based on consistency and performance requirements.
The Final Assessment - Performance
Now that you’ve determined the proper viscosity of your base oil, any and all additive requirements and the appropriate consistency based on thickeners, you will want to assess what specific performance requirements you may need for maximum element protection and productivity. Important grease performance properties, all determined by specific application include:
- Bleed Properties and Characteristics
- Pumpability
- Dropping Point
- Mechanical Stability
- Water Washout
It is essential to consider the full spectrum and significance of each of the above performance properties to choose the right grease and determine a proper grease match for a specific application. One size does not always fit all when you are trying to choose the right grease, so being mindful of a product’s composition in reference to an application will provide you with an optimal match. While generic grease choices are possible, be careful to not oversimplify or over-consolidate your grease inventory. To choose the right grease, review your grease specifications regularly to ensure that you are enhancing lubricant and grease specification within your facility or plant. Employing available resources from the National Lubrication Grease Institute (NLGI) and by speaking with an SCL representative you can ensure that you are staying on track with the appropriate grease products to fit your specific automotive and industrial grease applications.
Contact an SCL Consultant Today
In a wide range of industrial sectors, if there’s metal touching metal, oil is involved. At SCL, we’re here to protect and optimize the machines that keep our country moving and we pride ourselves on providing superior logistics and solutions, extensive product and industry knowledge and total performance satisfaction for our customers. For information on how we can assist your fleet in choosing the optimal products at a competitive price, contact an SCL consultant today.