Standards for Fluids Take Time
Developed by General Motors Corp, GM LS2 is an attempt to bring order out of chaos in standards development for metal removal fluids
By Donald J. Smolenski
General Motors Worldwide Facilities Group
When I became involved in industrial lubricants after a dozen years spent working with engine oil, my initial instinct was to see what standards were available for industrial lubricants. In the engine oil arena, there were many good, comprehensive, consensus standards available. In industrial lubricants, there were some standards available, although many were company standards, and not true consensus standards.
General Motors was no different from other firms. There was a GM LS2 Lubricant Standard that was actually a Fisher Body Materials specification. It was more than ten years old, seldom used, and appeared to be inadequate. But there was some good news. First, many good test methods were available from the American Society for Testing and Materials (ASTM), International Standards Organization (ISO), and others. Also, because on the industrial side we are actually the direct customer, we could write our own standards.
We chose to borrow (plagiarize is such an ugly word) from the best existing standards. A significantly revamped GM LS2 was published in 1994. Revisions in 1997, 2000, and 2004 resulted in a pretty good standard (based on industry input), with respect to defining physical, chemical, and performance properties for maintenance lubricants, hydraulic fluids, gear lubricants, way oils, spindle oils, greases, and so on.
Around 1999, the LS2 committee turned toward metal-removal fluids (MRFs). We did not find any suitable industry standards or any useful internal documents. To complicate matters, there were only a handful of consensus test methods available, and many fluid-specification parameters were more or less completely undefined. On a corporate basis, we had far too many different MRFs (over 800 are approved against GM's base-oil specifications). We tended to purchase MRFs as specialized products rather than commodities. Our expectations were based on company reputation, price, or gut feel--not hard data.
GM LS2 establishes base oil specifications that mineral-oil components of metal removal fluids must meet if the fluid is to be used by GM facilities.
To make matters worse, salespeople sometimes intentionally mystified MRFs. "Use this product or your tool life will be short, your part-quality marginal, and your machining workers will all develop mysterious rashes." We did not have systematic checks of key quality-control parameters (e.g., sulfur, chlorine, base number, fat content). When tool life suddenly dropped in a given system, there was no easy way to begin to eliminate a change in MRF formulation as a possible cause. GM plants sometimes experienced periodic health and safety issues, such as dermatitis and respiratory complaints.
We were pretty far into the woods, and our compass wasn't working well. To complicate matters even further, by the very nature of the aqueous MRFs, we would also have to define standards for managing such fluids. A given plant might do a pretty good job managing MRFs, but there was no systematic collection of this knowledge and propagation of best practices across all plants. As a result, plants sometimes experienced Monday-morning stench, ammonia blooms, excessive foaming, emulsion splitting, and so on.
We set out to develop MRF standards--the "we" being the GM LS2 committee. Now numbering more than 150, this group is composed of anyone involved in plant lubrication or fluid management issues--plant and central-staff people, oilers, maintenance managers, capacity assurance coordinators, machine operators, environmental engineers, etc. Some are salaried, most are hourly. All share a desire to do a better job on lubricant and fluid issues within GM. While no single LS2 member knows all there is to know about MRFs, collectively they are a tremendous resource, and they are the reason we have made considerable progress. It's worth noting that our chemical managers and suppliers also participate in LS2 meetings, and add considerable value.
To write specifications, you must define key parameters, seek relevant test methods, select the most promising methods, insert placeholders for parameters for which no standard tests appear to exist, and establish pass/fail limits--where possible. Requesting "report" on those parameters without a specified limit will generate a database with which to establish future limits.
We then must seek plant experience and attempt to semi-quantitatively--or at least qualitatively--correlate this database with the specifications. We must then continuously iterate on all steps, from rechecking the parameters (are there new demands or constraints?) to tweaking test methods, developing new test methods, and setting and revising limits.
The first priority in setting specifications is protecting the health of our workers. For MRFs that contain any oil components, we want to ensure that only highly refined oils are used. Rather than specifying refinery processing conditions, as the International Agency for Research on Cancer (IARC) has done, it's more important and more reasonable to specify the quality of the finished base oils. GM developed and released the base oils specification shown in the table in 1994. Since 1997, GM has required that any mineral-oil components of MRFs must meet these base-oil specifications. We have verified, and continue to verify, that virtually all MRFs in GM plants meet them.
Next, we faced the daunting task of developing MRF performance specifications. Standard LS2 clearly recognized that MRFs are just too complex to allow us to write complete, hard specifications in any reasonable time period. The philosophy for metal-removal fluids had to be different than that adopted for maintenance lubricants. For maintenance lubricants (a hydraulic fluid, for instance), the specification's intent is to exclude all unsatisfactory fluids and address virtually all known performance requirements.
A hydraulic fluid meeting the LS2 performance requirements, if maintained correctly, should provide satisfactory performance in 99% of its intended applications. For a MRF, however, we must accept less than perfection. The intent of the specification is to improve our odds of finding an acceptable fluid. We may inadvertently exclude some good fluids, but with continuous iteration we should reduce the number of inappropriate or poorer-performing fluids.
With this caveat, we identified several key properties that we wanted to include in the specifications for straight and aqueous fluids, respectively. Once draft specifications are developed, it's necessary to solicit data on current fluids in use and to try to develop a correlation with plant performance. Selected performance data are shown in the table.
The results summarized in the table were interesting. For copper corrosion, most fluids provided reasonably good results, with the exception of heavy-duty fluids, which tended to be very aggressive toward copper, probably due to active extreme-pressure (EP) additives. Most passed aluminum corrosion requirements easily, although one did not. Even though this fluid is not intended for machining aluminum, we must consider the machining system components as well as the workpiece. Aluminum housings or other components may be corroded. The test shown is actually for aerospace alloys. It's being modified for use with more commonly encountered automotive alloys.
The four-ball EP test is used only to define whether or not a fluid is an extreme-pressure fluid, with no particular inference regarding its machining performance. It's interesting to note that one of the heavy-duty fluids did not have good EP performance, so probably should not have been designated as a heavy-duty fluid.
For the foam test results, several of the fluids showed fairly high levels of foam generation, with the foam--more problematically--being very stable. One of the worst-performing fluids had a long history of foaming problems in the plant. This test is being tweaked to check a fluid's foaming tendency with both deionized water and standard hard water.
The cast-iron-chip corrosion test is an old industry standard. Its results showed a large variance among fluids with respect to breakpoint (the minimum concentration required to prevent rusting). With respect to biostability, good results in this test are no guarantee of performance in real-world plant conditions, but poor results almost certainly are not encouraging. If you are going to use Fluid J from the table, for instance, better keep the biocide handy.
For seal compatibility, the test is run on undiluted concentrate, which is probably a severe, worst-case scenario. The overall intent here is not to reject fluids, so much as it is to evaluate each fluid with several common elastomers, and give the plants key information on potential seal issues.
The desired future goal is to incorporate an aging procedure to simulate contamination of the fluid with tramp oil, metal fines, bacteria, etc., as well as the fluid's stress with use. A given fluid would be run in key performance tests in new, pristine condition and after the aging procedure. This test should give some indication of the robustness of the fluid, something that cannot be adequately measured with most current tests.
So we are well on the way to defining what we believe will be better fluids. But how do we know what is being delivered to our plants is the fluid that is shown to pass all of our requirements? We sometimes experience abrupt excursions in tool life in a given process. Did the tools change, did the operator do something different, did the coolant change, or was it something else? It would be nice to be able to eliminate at least one possible cause.
We set out to establish key physical and chemical parameters (actually blending targets) that we expect to remain reasonably consistent from MRF batch to batch. But even this was not trivial, as the methods themselves took some sorting out, so that everyone measuring the same property of the same fluid would get the same result within some reasonable reproducibility. We were able to accomplish this by turning to a task group of plant people and suppliers. Good analytical methods benefit both the user and suppliers.
So far, so good, but there is a fluid management issue. GM's Powertrain Division established a template for the elements required for properly managing MRFs. Each plant needs to develop a plan that includes the following components:
Design of MRF management responsibilities, including identifying the person or team with responsibility for the program.
Written testing protocols, where each system will have a specific protocol developed to identify sampling frequency, sampling collection, handling, and results tracking.
Data collection and tracking that encourage the use of an access database system.
MRF system monitoring, maintenance, contamination control, and cleaning.
MRF exposure reduction plan.
We incorporated this template into the LS2 standard, and are currently reviewing our plant plans, from which to develop a set of best practice targets. Training is also important, particularly for our on-site chemical managers. Certification as a Society of Tribologists and Lubrication Engineers (STLE) Metalworking Fluid Specialist may be a requirement in the future.
It's critical for an end user to define the properties of the MRF that are required for a given operation, to routinely check that the proper fluid is being delivered, and to carefully and consistently maintain the fluid. These factors are all interrelated, and are critical to protecting worker health and safety, providing quality parts, optimizing tool life, and minimizing undesirable environmental effects.
This article was first published in the March 2005 edition of Manufacturing Engineering