An open-die forging company produces forged components for:
Typical products include turbine shafts for power plants and crankshafts for marine drives. These workpieces are hot-formed on a hydraulic open-die forging press with a force of 120 MN. Its hydraulic circuit contains 120,000 litres of HLP 46 AF oil. Repeated hydraulic-system problems had made maintenance on the forging press increasingly frequent.
Because any press failure during forging causes substantial costs, the company looked for a way to improve hydraulic-system reliability.
The first oil analysis made it clear that contamination in the oil was the root cause. Despite a highly sophisticated hydraulic-oil filtration system, ultrafine particles and oxidation products repeatedly caused serious interruptions in the hydraulic system. Operational failures were frequent because of severe material erosion on valves and valve seats, together with deposits in valves and pumps.
To reduce disruptions and secure continuous operation, the maintenance team examined and evaluated three possible measures.
Replacing the oil would involve very high costs for the new charge, tank cleaning and lost production. Because the new oil would quickly become contaminated again, the same failures could return after only a short operating period.
A well-known manufacturer of hydraulic components and filters proposed a different filtration process. Tests showed improved cleanliness, but the expected consumables costs were so high that the process was uneconomical.
The maintenance team therefore contacted FRIESS GmbH to determine whether electrostatic oil cleaning was suitable for this application.
During the initial on-site assessment, a sample of the contaminated oil was taken and analysed with a membrane having a pore size of 0.8 μm. Oxidation residues and numerous metallic particles were clearly visible.
Because of the extremely high contamination load, the membrane blocked very quickly. Only 9 mL of oil could be filtered instead of the usual 30 mL. The analysis showed that, despite the existing filtration system, the circulating hydraulic oil remained heavily contaminated with oxidation products and fine particles.
Given the severe contamination, electrostatic hydraulic oil cleaning was recommended. Four FRIESS EFR D16 electrostatic oil cleaning units were required to treat the complete 120,000-litre oil volume.
Because the purchase and operating costs of the required electrostatic oil cleaning system were significantly lower than those of the alternative processes, a full-scale test under real operating conditions was agreed. Around 200 litres of used hydraulic oil were placed in a test container. The container was additionally heated to simulate the operating temperature of approximately 40–50 °C. A FRIESS EFR D4 electrostatic oil cleaning unit was used to clean the test volume.
Oil samples were taken and analysed every day to monitor cleaning performance. The test ran for six days, or 144 hours. The evaluations clearly showed continuous improvement in the condition of the oil.
Before cleaning began, the oil contained extremely high levels of oxidation products and resinous deposits. Under normal conditions, the membrane used for the analysis can filter at least 30 mL of oil. With the untreated oil, however, the membrane blocked after only 9 mL because of the high resin content. After 24 hours of cleaning, 30 mL could again be filtered without difficulty. This showed that approximately 70% of the oxidation products and resinous contamination had been removed within a short time. Samples taken during the remainder of the test showed a further reduction in oxidation products and varnish-forming residues.
The cleaned hydraulic oil was also analysed by an independent oil-testing laboratory. The laboratory measured the MPC value (Membrane Patch Colorimetry), which indicates an oil’s tendency to form deposits: the higher the value, the greater the risk of varnish and oxidation products. Before electrostatic cleaning, the MPC value was 60. After cleaning, it had fallen to only 8. New hydraulic oil typically has an MPC value between 2 and 3.
Despite the intensive electrostatic cleaning, the oil’s additive balance remained unchanged. Its viscosity also showed no change.
Because the cleaning result was excellent and both investment and operating costs were significantly lower than with the alternatives, the maintenance team decided to use FRIESS EFR electrostatic oil cleaning for the entire oil volume. Four FRIESS EFR D16 units were purchased to clean and maintain the 120 m³ hydraulic-oil system.
For hydraulic-system operators:
FRIESS also provides on-site hydraulic-oil cleaning services. Repair work and spare parts are not included.
