Significance and Use
4.1 The process of recirculating MWFs entrains air bubbles which can accumulate, forming foam.
4.2 Optimally, air bubbles burst open quickly after they are created. However, air bubble persistence is affected by MWF chemistry and the mechanisms by which energy is introduced into recirculating MWFs.
4.2.1 The primary mechanisms imparting energy into recirculating MWFs are:
188.8.131.52 Turbulent Flow—The high velocity (typically >0.75 m3 min–1; >200 gal min–1).
184.108.40.206 Impaction—Energy generated when MWF strikes the tool-workpiece zone.
220.127.116.11 Centrifugal Force—MWF moved by the force of rotating tools or work pieces.
4.3 When air bubbles persist, they tend to accumulate as foam. Persistent foam can:
4.3.1 Inhibit heat transfer;
4.3.2 Cause pump impeller cavitation;
4.3.3 Foul filters;
4.3.4 Overflow from MWF sumps; and
4.3.5 Prevent proper lubrication.
4.4 To prevent the adverse effects of MWF foam accumulation, chemical agents are either formulated into MWF concentrate, added tankside, or both.
4.5 Laboratory tests are used to predict MWF foaming characteristics in end-use applications. However, no individual test is universally appropriate.
4.6 This guide reviews test protocols commonly in use to evaluate end-use diluted MWF foaming tendency and the impact of foam-control agents on MWF foaming tendency.
1.1 This guide provides an overview of foaming tendency evaluation protocols and their appropriate use.
1.2 ASTM Test Methods and were withdrawn in 2018. Although each method had some utility, neither method reliably predicted in-use foaming tendency. Since Test Methods and were first adopted, several more predictive test protocols have been developed. However, it is also common knowledge that no single protocol is universally suitable for predicting water-miscible metalworking fluid (MWF) foaming tendency.
1.3 Moreover, there are no generally recognized reference standard fluids (either MWF or foam-control additive). Instead it is important to include a relevant reference sample in all testing.
1.4 The age of the reference and test fluid concentrates can be an important factor in their foaming behavior. Ideally, freshly prepared concentrates should be held at laboratory room temperature for at least one week before diluting for foam testing. This ensures that any neutralization reactions have reached equilibrium and enables microemulsions to reach particle size equilibrium. During screening tests, it is also advisable to test fluids after the concentrates have been heat aged and subjected to freeze/thaw treatment.
1.5 The dilution water quality can have a major impact on foaming properties. In general, fluid concentrates diluted with hard water will foam less than those diluted with soft, deionized, or reverse osmosis water. Screening tests using the expected range of dilution water quality are highly recommended.
1.6 Units—The values stated in SI units are to be regarded as the standard. No other units of measurement are included in this standard.
1.7 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.
1.8 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.