Machinery Lubrication magazine published by Noria Corporation
Issue link: https://www.e-digitaleditions.com/i/431954
www.machinerylubrication.com | November - December 2014 | 37 method is typically more effective for lubricants with viscosities above ISO 220. Oils with air-handling concerns usually have demulsibility prob- lems. In other words, the causes of impaired demulsibility are often common to air-handling issues as well. A third alternate test is based on ASTM D892. For this foam tendency/stability test, air is blown into an oil sample to produce foam. The foaming tendency and stability are then measured at 24 degrees C, 93 degrees C and then again at 24 degrees C. The initial foam volume is measured after each blowing (foam tendency) and again five minutes later (foam stability). See the table above for more details on this procedure. Although testing an oil's air content may never be part of a standard test slate for routine sampling, this does not mean that it is unnecessary. Because of the nature of aerated oil, the air concentration that can be tested depends on the time in which it is allowed to sit undisturbed. This makes the typical method of testing oil, like collecting oil in a sample bottle, nearly irrelevant for air concentration testing. Testing for air is all about timing, so if any of these methods are to be applied, be sure to know the unique design requirements. Regardless, a particular machine condition or recognized oper- ating state can be more than enough cause to investigate and quantify air contamination. If foam is a persistent issue or an excess amount of aerated oil is seen through an oil sample inspection or sight glass, a careful investigation should be conducted to deter- mine the source of the issue. There may be an easy solution, such as using a more appropriate lubricant formulation, or it may be more challenging, such as a machine design error. In any case, it's important not to overlook this valuable information, because air contamination can have very destructive effects. About the Author Bennett Fitch is a technical consultant with Noria Corporation. He is a mechanical engineer who holds a Machine Lubricant Analyst (ML A) Level III certification and a Machine Lubrication Technician (MLT) Level II certification through the International Council for Machinery Lubrica- tion (ICML). Contact Bennett at bfitch@noria.com. ML C o n t a m i n a t i o n C o n t r o l Air contamination has the potential to be very destructive, and its effects on oil and machinery deserve more attention. TEST OBJECTIVE/ SUMMARY APPLICATIONS TYPICAL RESULTS LOW HIGH Air Release ASTM D3427 or IP 3B Test determines the tendency of an oil to retain entrained air. Compressed air is blown into sample. Time required (minutes) for air to be reduced to 0.2% by volume determined by density (hygrometer). Most industrial oils and hydraulic fluids 5 200 Minutes (Low result is preferred) Foam Tendency/ Stability ASTM D892 Test determines a lubricant's ability to resist foam formation and dissipate foam quickly. Most industrial oils and hydraulic fluids Low Tendency/ Stability High Tendency/ Stability Sequence I - A 190-ml sample of oil is heated to 50°C and cooled to 24°C. A diffuser (aquarium stone) is immersed in the sample with air flow of 95 ml per minute for 5 minutes. The tube is disconnected and the volume of foam immediately recorded. Then the sample is allowed to stand for 10 minutes, and the current foam volume recorded. 50/0 (Low is preferred) 200/50 50/0 (Low is preferred) 300/100 Sequence II - A 180-ml sample of oil is immersed in a 93°C bath. A diffuser is immersed in the sample with air flow of 95 ml per minute for 5 minutes, recording the foam volume at the end of the blowing and settling period. Sequence III - After the 93°C test has been completed, remove any remaining foam by stirring the sample. Remove the sample from the bath and cool to a temperature below 20°C. Place the cylinder in the 24°C bath and repeat the Sequence I procedure. 50/0 (Low is preferred) 500/250 High Temperature Foaming D6082-11 Sequence IV - A measured quantity of sample is heated to 49°C for 30 minutes and allowed to cool to room temperature. The sample is transferred to a 1,000-mL graduated cylinder, heated to 150°C and aerated at 200 mL per minute with dry air for 5 minutes with a metal diffuser. The amount of foam generated before disconnecting the air, the amount of static foam at optional times after disconnecting the air, and the time for the foam to collapse are measured and the percent increase in total volume calculated. Lubricating oils (specifically transmission fluid and motor oil) at 150°C 50/0 (Low is preferred) 300/100