In the current business environment, manufacturing equipment is constantly being pushed to its limits, with the expectation of running continuously to keep operations going without interruption. Equipment owners are increasingly aware of the total ownership cost, which has led to a push for machines that are low maintenance and have high reliability, high accuracy, short cycle times and low energy consumption.
In a study performed in conjunction with Schoen + Sandt Machinery, a leading German hydraulic press manufacturer, the energy-efficiency impact of a high viscosity index (VI) hydraulic fluid resulted in gains of up to 10 percent less kilowatt hour (kWh) consumption. These hydraulic machine specialists don’t stop at designing and manufacturing top-of-the-line hydraulic cutters and control systems but also go the extra mile to help realize continuous savings through lower energy consumption, higher output via increased machine accuracy, and machine reliability with prolonged service life.
In today’s marketplace for hydraulic cutting machines, energy efficiency has become almost as important as technical innovation. Hydraulic fluid transmits power, making it one of the key components of a hydraulic system. The use of a monograde hydraulic fluid results in poor heat transfer, power transmission losses, reduced responsiveness to controls and oxidative stress in the hydraulic system.
When hydraulic fluid is cold, it is thick and its viscosity is high. This increased viscosity creates high levels of friction. However, hot hydraulic fluid becomes thin, and its decreased viscosity can lead to flow leakage and wear damage. In either case, performance suffers. This type of hydraulic fluid in which viscosity varies greatly depending on the temperature is called a monograde fluid.
High temperatures are the enemy of stable viscosity. As temperature rises, the fluid thins, creating metal-to-metal contact in some cases. This low-viscosity fluid will cause increased wear, resulting in costly repairs and machine downtime.
Hydraulic fluids that are specially formulated to maintain an optimal level of viscosity over wide temperature ranges are referred to as multigrade. Multigrade fluids protect machines by balancing hydro-mechanical and volumetric efficiency in the equipment.
Without a balance, hydraulic systems can face the dilemma of hydro-mechanical losses with a fluid at high viscosity, and volumetric power losses with a fluid at too low of a viscosity. On one hand, mechanical efficiency of the hydraulic system would benefit from a fluid that is very thin and easily flowing. However, too thin of a fluid delivers poor volumetric efficiency, as internal leakage consumes much of the pump’s energy and the fluid gives poor lubrication.
On the other hand, a thick fluid is good for volumetric efficiency, as the loss from internal pump leakage is minimal. However, this thick fluid would be difficult to flow and results in hydrodynamic friction and churning losses in the system. The ideal fluid choice is a compromise.
Fluid testing was conducted on a 6005BA hydraulic press with a cutting force of 1,250 kilonewtons (kN). Such hydraulic cutters with retractable beams are all-purpose punch presses for small and medium lot sizes for processing sheet and roll materials. For the trial, kW power, pump pressure in bar, oil and ambient temperatures were the parameters measured to determine the influence of viscosity on machine performance.
The original equipment manufacturer (OEM) in this case study compared two multigrade hydraulic fluids to one monograde reference oil. The reference oil was a typical fluid, with a common viscosity grade of ISO 46 and a viscosity that was not formulated to withstand operating temperature changes. The first test oil, fluid A, was the same as the reference fluid except it had been formulated to stabilize viscosity across a temperature range. The second test oil, fluid B, had an ISO viscosity grade of 32 and was a thinner hydraulic fluid that was also capable of stabilizing viscosity across a temperature range.
Multigrade fluid A did not show any significant advantages as compared to the conventional monograde reference fluid. This can be explained by the influence of the mechanical loss on the overall efficiency of the hydraulic system being much higher than the volume efficiency gain. Fluid choice contributes to improved reliability and productivity while reducing equipment downtime and total ownership cost. Therefore, the viscosity of the fluid has a major impact on the efficiency of the system.
Multigrade fluid B showed efficiency gains up to 10 percent compared to the conventional monograde reference fluid. When a hydraulic system is exposed to heat and pressure, a viscosity-optimized fluid such as fluid B transports more pump energy due to higher viscosity and less leakage loss. At normal temperatures, it flows better and creates less resistance to the pump.
Proven in the laboratory and corroborated by the OEM’s own equipment tests and in the field by end users, the performance and savings can be confidently predicted by using an ISO 32 hydraulic fluid formulated to withstand and stabilize viscosity across a broad temperature range. Efficiency gains of 4-11 percent have been consistently measured compared to monograde reference fluids, along with additional benefits such as lower oil temperature, equipment protection and longer drain intervals.
There’s no shortage of benefits. The opportunity now exists to increase reliability, prolong the service life of equipment, reduce total cost of ownership, extend oil drain intervals and become a trendsetter in energy efficiency.
This article was previously published in the Reliable Plant 2019 Conference Proceedings.