Measures to Control Particles
There are nearly as many techniques to control particles in grease as there are different sources of them. Again we begin at the beginning of the process. Improved raw material quality control is a good place to start. Purchasing raw materials from reputable suppliers who demonstrate a commitment to quality and purity is critical, along with specifying freedom from contaminants and shelf life in certificates of analysis. Another suggestion is for the grease manufacturer to perform incoming inspections on the raw materials to confirm packaging integrity and the absence of visible contamination. Filtration prior to use may be appropriate for base stocks and other high volume liquid raw materials. Stringent raw material inventory control is also necessary to prevent use of materials which are beyond their shelf life.
With raw material contamination controls in place, we next address the manufacturing process itself. Ensuring a clean environment in the grease plant is not always an easy task, but is critical to eliminate many sources of contamination during manufacture. A clean grease plant also helps create a culture of cleanliness and quality for the manufacturing personnel. Careful addition of solid raw materials using screens and other devices to prevent ingress of paper fiber and plastic from packaging materials is a very basic necessity. Thorough flushing of kettles, pumps, lines and other vessels between batches is an effective way to minimize contamination from residual product or hardened thickener. Following a well defined manufacturing procedure is also quite important to ensure addition of raw materials at the correct temperatures for proper dissolution. This procedure should also specify precise control of milling time, pressure, clearance, etc. in order to break up and disperse any large or crystalline particles or thickener agglomerates. And finally, if appropriate for the specific grease, filtration either during or at the end of manufacture can be used to remove any residual particulate over a specified size.
During the packaging process, the most straight forward way to minimize contamination is through proper sequencing of filling operations and effective flushing of the filling lines and pumps between products. Additionally, new containers must be inspected prior to filling to ensure there is no evidence of paper fiber, plastic debris or rust. For some products and/or applications, the use of plastic liners in drums or kegs may be appropriate, which reduces contact with the container itself.
At the end user’s location, we cannot overstate the importance of proper storage & handling practices. All containers of grease should always be stored in doors, or at least under a protective roof, to prevent water and concomitant dust and dirt ingress (Figure 12: proper lubricant storage). Once a container is opened, any attachment to a distribution system, pump or filling of grease guns should be done in a manner to prevent introduction of dirt or debris into the open container. All open containers obviously must be stored in doors with the correct lids properly reattached. And in the process of introducing the grease to the application, a good lubrication program will include guidance to ensure identification of the proper grease, cleaning of zerk or other grease fittings, cleaning of the grease gun nozzle, etcetera. A frequently overlooked best practice is to ensure all purge plugs and pressure relief valves are in proper working condition to prevent over pressurizing during regreasing, which can damage seals, thus allowing easier ingress of contaminants to lubricated equipment.
There are numerous types of deleterious particles which can be found in grease. Some can be harmful to rolling element bearings or clog distribution systems. Some may not be directly harmful, but can cause increased noise levels in bearings, leading to other types of problems.
As with types of particles, there are also many different sources of contaminants in grease. Through good practices, particles can be controlled in every step from the manufacture of the raw materials used in the grease, all the way to the introduction of the finished grease to the end user’s application.
There are several different tests which can be used to quantify and / or characterize grease particulate contamination. Unfortunately, today there is no industry standard or consensus to define grease cleanliness. Continued work is needed within NLGI, ELGI, ASTM, DIN or other standards organizations to develop and promote such test(s).
This is the last installment of this three-part article. Click on the links to read Part I and Part II.
Chuck Coe is the President of Grease Technology Solutions, LLC, President of NLGI, and a member of STLE. You can find his contact information in the STLE member database. He holds both the NLGI CLGS certification and the STLE CLS certification. He is chairman of the STLE/NLGI Grease 101 course, which has been offered at past Annual Meetings, and will be offered again at the 2014 STLE Annual Meeting in Orlando, FL.
Other articles in this issue: