The analysis and identification of contaminants found in industrial hydraulic and lubricating systems often requires the use of intricate investigative methods far beyond the realm of the usual particle counting or spectrometric analysis. Often, the situation is further complicated when dealing with remote sites or when the original equipment manufacturer or the operator are not aware of everything that has taken place in the course of system operation. In many cases, Hydacs Fluid Care Centre is presented with a cup or bottle of something that is obviously interfering with proper system operation and asked to identify it, as well as provide recommendations for how best to remove it from circulation.
Hydac International GmbH produces and distributes components, systems and services related to hydraulics. Its Fluid Care Center, located in Sulzbach, Germany, is a research and development center that conducts filter performance tests and fluid analysis in support of the companys customers.
In contrast to popular belief based on television crime dramas, it is often impossible to draw appropriate conclusions from the results of even highly sophisticated analytical techniques. Additional information, as detailed as possible, is required if the source of the problem is to be identified and solved in a timely manner. When such information is not provided, the laboratory analyst must work blindly and often employ superfluous methodologies before stumbling onto the correct result.
Although this approach may bring its own rewards to the investigator by providing the satisfaction of solving an intricate puzzle, in practice it prolongs the implementation of the appropriate remedial action. This only extends costly downtime and magnifies the extent of the system upset. The case described herein belongs exactly to this category.
The investigation involved a highly unusual contaminant in the hydraulic system of a large press operated in Medellin, Colombia. Quantities of the contaminant were sufficiently large to completely occlude the entire surface of the systems filters, leading to an extremely and unacceptably short service interval. Initially, neither the press OEM nor the operator chose to divulge the nature of the application for which the press was employed, leaving the entire detective work of contaminant identification in the hands of our laboratory.
Rather than working directly with the press operator, the Fluid Care Center dealt with the Germany-based hydraulic press manufacturer, which was eager for deployment of its equipment to go smoothly. This exacerbated the urgency of the situation and placed additional pressure on our investigators. Moreover, the geographic separation of our laboratory in Germany and the operator in Colombia meant a five-hour time zone difference as well as considerable delays in oil sample and filter element shipment, which became serious impediments to the progress of the investigation. All laboratory work had to be carried out with the utmost urgency immediately upon receipt of the samples.
An easy and still highly effective analytical technique involves simply looking at the sample. The size and nature of typical contaminants found in hydraulic systems often require the use of a high-resolution optical microscope, but a simple visual inspection of the returned filter elements revealed them to be extensively covered with an orange substance resembling caviar. Microscopic examination showed the substance to be crystalline in nature and nearly uniform in shape and size.
The contaminant was then analyzed with a scanning electron microscope, which confirmed the crystalline and uniform nature of its constituent particles. In addition, the sample was analyzed by energy-dispersive X-ray spectroscopy, which revealed the contaminant to be organic, in that its main chemical constituents included carbon, nitrogen and oxygen. This rather surprising outcome confirmed that the contaminant did not originate from oil additive degradation, but rather entered the system from an unidentified source.
The organic nature of the contaminant suggested that it would lend itself to an analysis by infrared spectroscopy. Somewhat surprisingly, the contaminant exhibited a well-defined IR spectrum-quite unusual for contaminants isolated from similar systems where mixtures of substances of various origins are often involved, making an unequivocal identification either extremely difficult or outright impossible.
What scant background information was supplied indicated nothing unusual about the oil or the application itself. The oil employed in the system was an ISO 46 viscosity grade hydraulic oil, formulated with a high-quality base stock and a select additive system intended for use in industrial applications where antiwear lubricants are required. The results of a standard laboratory analysis likewise indicated that nothing unusual was going on. Except for the moderately elevated particle count compared to those found in modern hydraulic applications, all other physical and chemical characteristics such as viscosity, total acid number, water and chemical elemental content were perfectly normal and consistent with those typically expected for an oil of this type.
Nevertheless, the external appearance of the filter elements, as well as their exceedingly high load-approaching 60 milligrams per square centimeter, compared to standard values in the neighborhood of 20 mg/cm2-left no doubt that something highly unusual was going on within the system.
The fluid itself exhibited a gravimetric load of nearly 4,000 milligrams per liter, in contrast to typical values of 10-15 mg/L-very high even when compared to systems usually considered moderately to highly contaminated. It was becoming quite clear that the puzzle would not be solved by relying on the results of standard analytical techniques, and that the results of more advanced technologies would have to be taken into consideration.
A scanning electron microscope proved to be a useful extension of observations made with the optical microscope. The size of the contaminant particles were more exactly determined and found to be nearly uniform at 500 micrometers.
Looking at the combined data, investigators discovered that the FT-IR spectrum was nearly perfectly and uniquely matched to a singular product: melamine-formaldehyde resin. Melamine based resins are a class of amino-plastic resins often used as wood adhesives in liquid form, or in powdered state for special applications. Numerous types of resins are used in wood manufacturing for the production of particleboards, medium density fiberboards, oriented strand boards, plywood and blockboards, among others. The melamine based resins show duroplastic hardening behavior that leads to crosslinking, which makes them insoluble and non-meltable.
In the course of a subsequent conversation with the customer, the nature of the process for which the press was employed and the identity of the contaminant were positively confirmed: The hydraulic press was being used to manufacture medium density particle boards, in which melamine-formaldehyde resins are employed. In the course of these conversations, it was discovered that the oil destined for the press was temporarily stored in intermediate bulk containers previously used for transport of the melamine resin and deemed sufficiently clean for this purpose.
Because it was not possible to shut the press down in order to perform proper flushing procedures, the only option was to work through the temporary upset and allow the system to clean itself up while the press was in operation. This recommendation was carried out, and after approximately two months in operation, the particulate contaminant level in the oil was reduced ten-fold and the situation stabilized itself sufficiently to allow for normal press operation.
The investigative work required to solve this intriguing case employed several sophisticated and highly specialized analytical techniques that allowed for successful and decisive identification of the contaminants nature, pinpointed its source and even elucidated the process for which the press was utilized.
This case study illustrates the importance of proper fluid storage and maintenance in order to prevent the ingress of the contaminants into an operating system at each and every possible point of entry.
Valrie Diehl-Klein conducted the laboratory analytical work described in this story.
John K. Duchowski, Ph.D., is corporate director of research and development, filtration, at the Hydac Fluid Care Center in Sulzbach, Germany. He is a fellow of the Society of Tribologists and Lubrication Engineers and an STLE Certified Lubrication Specialist and Oil Monitoring Analyst I and II. Contact him at firstname.lastname@example.org.
Achieving Hydraulic Fluid Cleanliness
Like any other type of lubricant, hydraulic fluids are susceptible to contaminants before and during operation. Making sure the fluid stays clean in every step of the process is crucial to ensuring proper functioning of hydraulic equipment. Below are some recommended best practices from ExxonMobil, MTS Systems and Case Construction:
Inspect the oil. Clean hydraulic fluid usually is amber colored. If it shows a milky consistency or a dark or abnormal color, this could indicate the presence of water or contaminants. A distinct change in the fluids odor could also indicate chemical breakdown.
Store fluid properly. To prevent contamination, use clean, dedicated containers to store the hydraulic fluid and place them in a protected area.
Maintain hydraulic system cleanliness. Contaminants such as dirt, water, metal particles and other fluids should be kept from entering the hydraulic system through the reservoir cover, suction and drain line openings, breather fill openings, piston rod packing and leaks in pump suction lines. The hydraulic system, even a newer one, should be cleaned before use.
Monitor filters. Filters are used to keep the fluid clean while the equipment is in operation. They should be inspected frequently and cleaned or changed before going into bypass mode, which would allow dirty oil to circulate into the hydraulic system.
Sample fluid regularly. Frequent oil analysis can provide accurate detection of contaminants and particles, as well as the chemical composition, to ensure the additive package is still performing as originally intended.
Provide proper training. Operators should make sure their staff is trained to detect any contamination in the hydraulic fluids and systems, conduct maintenance on components and pay close attention to any leaks.