Longer Lasting Lubricants for The Aluminum Industry
This project, like so many others, had a humble beginning. About five years ago, after returning from a routine sales call to the smelter where a representative was selling synthetic and specialty greases, he challenged the authors to develop a series of lubricants that he could sell to the aluminum industry. In a discussion with a group of maintenance people at the smelter, he was told that if his company could develop lubricants that would last longer and protect equipment better than the current product, they would buy from him.
The challenge was on! With their combined experience in both lubrication formulation and infrared analysis, the research team at Thermal-Lube set out to determine the underlying cause of premature oil degradation at the Alcan Smelter facility in Jonquière, Quebec. This is what they found.
|Figure 1. Antioxidant Decrease in Used Lubricants|
Unique Demands of Aluminum Smelters
The task was simple: develop a diesel engine oil that would last longer than the current oil used, which typically needed changing every 75 hours. However, this was perhaps not the most serious problem. Due to the nature of the harsh environment, engine breakdowns requiring rebuilds were occurring every 1,200 hours. It was believed that this rebuild interval was due, at least in part to the effects of lube degradation, as well as the abrasive effects of airborne contaminants or other environmental stressing factors.
Few environments are more demanding on equipment than those found in aluminum smelters. The high-torque diesel engines that power mobile machines are constantly subjected to wide temperature fluctuations, often operating in conditions of abnormally high ambient temperatures, intense magnetic fields, contamination by extremely abrasive, highly reactive alumina dust particles and short haul runs. This combination of environmental operating factors forced the Alcan maintenance team to accept premature engine failures and reduced lubricant service life as a normal cost of doing business.
To achieve its objectives, the team used its expertise in condition monitoring and specifically infrared analysis to analyze the underlying chemistry behind the problems. The rationale was that if the root cause for premature lubricant degradation could be determined, then an appropriate strategy could be implemented, involving customized formulation and additive blending.
Based on its experience, the team hypothesized that the rapid degradation of the oil was due to depletion of the antioxidant additive, resulting in premature base oil oxidation. To test this theory, infrared spectra of new and used samples were taken. Based on the results, their hypothesis was proven; infrared spectra of new and used oil samples clearly indicated a rapid and sudden depletion of the antioxidant additive in the oil.
Surprised by the rapid rate at which the oil was depleting, the team wanted to know why this was occurring. An experiment simulating the effect of a variety of probable contaminants was set up in the research laboratory in an attempt to reproduce the depletion results. Despite several types of contaminants and stressing conditions used, only one of the samples, contaminated with a particular aluminum dust and heated to 300°F (150°C), showed a similar rapid depletion of antioxidant when compared to a control, noncontaminated sample (Figure 2).
|Figure 2. Rate of Antioxidant Degradation in Lab Experiment After 16 Hours of Heating @ 150°C|
Data produced from this experiment led to a conclusion that the catalytic effect of the contaminant (alumina dust) resulted in a rapid depletion of the antioxidant additives in the oil, therefore allowing the base oil to oxidize prematurely. Because oil oxidation is known to change the ability of the oil to lubricate, particularly by promoting sludge and varnish build-up, the team concluded that this may be in part responsible for the short engine rebuild interval.
At the same time, the abrasive effects of alumina dust contamination were investigated. After all, eliminating the contaminant completely seemed a more logical solution than simply trying to mitigate its impact after the fact. Unfortunately, the conclusion suggested the limited space aboard the mobile equipment in question precluded the installation of a filtration system capable of filtering the contaminants from the fluid. As a result, the team further concluded that because there was no mechanical or physical means to eliminate the contaminant, a chemical method was needed to neutralize the effects of the alumina dust on premature oil oxidation.
Based on the infrared analysis, an antioxidant cocktail, chemically structured to provide higher resistance to oxidation in the presence of alumina dust, was incorporated in the formulation of a semisynthetic Polyon® engine oil. The decision to use a semisynthetic base stock – a carefully selected blend of mineral oil and PAO synthetic – was made because the level of contaminants in the oil would prove to be the limiting factor determining the fluid’s service life. The semisynthetic would provide additional protection against premature oil oxidation, and offer a higher viscosity index for a wider operating temperature window, without the significantly higher cost associated with a fully synthetic base stock.
The newly formulated engine oil was subjected to the same laboratory-based tests used to ascertain the root cause of the problem. Specifically, the oil was doped with aluminum dust and heated to 300°F (150°C), before being analyzed to determine the extent of antioxidant additive depletion. The results of the lab analysis, which are shown in Figure 3, showed that 90 percent of this new additive package remained after 140 hours.
|Figure 3. Comparative Antioxidant Degradation Curves (in the Presence of Aluminum Dust) of Semisynthetic Polyon® vs. the Customer’s Traditional Mineral-Based Engine Oil|
Let Proof Speak
The next step was to field test the new formulation. The Alcan Smelters and Chemicals facility in Jonquière, Qué., operates more than a hundred pieces of mobile equipment. For the field trial, three industrial lift trucks were selected. Two were filled with Polyon® 10W-40, CG-4 motor oil, and the other was filled with a conventional 15W-40, CG-4 mineral oil as a control vehicle. All three machines were returned to normal service and oil samples were taken regularly at short intervals.
The data from this trial are shown in Figure 4.
Although the viscosity and soot loading found with both lubricants were fairly similar, the newly formulated Polyon® fluid with the aluminum-resistant additive package was found to be significantly more robust in preventing not only antioxidant depletion, but also depletion of the antiwear additive.
Based on the successful field trial, Alcan switched its mobile fleet to the new Polyon oil in January 1998. Since this time, the customer performs routine oil changes at 250 to 350 hours (3.3 to 4.6 times the original change intervals) and has not suffered a lubricant-related breakdown or engine rebuild in more than 25,000 hours. Clearly, the ability of the lubricant to retain both antioxidant and antiwear additives has resulted in significant cost savings, not only from extended oil drain intervals, but more importantly extending engine rebuild intervals, a significant cost to any mobile equipment operator.
Based on the engine oil successes, Alcan has converted all the other fluids (TDH, ATF, AW hydraulics, GL-4 gear oils) in its mobile equipment, as well as some stationary equipment operating in the same environment to equivalent Polyon fluid, and has witnessed similar results and similar cost savings.
While this case history illustrates a unique situation involving a unique set of circumstances, it illustrates an important message. Oil analysis, when used appropriately, is an important tool for determining the underlying root causes of many problems, whether they result from lubricant degradation as in this case, or some other factor. By applying knowledge, skills and expertise to the situation, proactive solutions to supposedly intractable problems can be found. Don’t accept poor lubrication as “the cost of doing business,” but investigate the root cause of the problem and start practicing proactive instead of reactive maintenance.