Wringing Gage Blocks: Essential Guidelines and Practices
Wringability is a crucial property of gage blocks, significantly impacting their performance and reliability. Gage block specifications recommend replacing blocks that lose their wringability, as it is indicative of surface integrity. While not everyone uses gage blocks in wrung combinations, wringability serves as a vital test of the block's surface condition. Gage blocks that fail to wring properly can produce erratic and unreliable measurement results.
Definition and Importance of Wringability
The ability of gage blocks to wring is inherently factored into their length measurement. Gage block lengths are defined based on interferometric measurements when the blocks are wrung to a flat platen, incorporating one wringing film in the block’s defined length. This definition simplifies the use of gage blocks in combinations, as no additional correction for the wringing film is needed.
Wringability refers to the ability of two smooth, flat surfaces to adhere tightly without external assistance, such as magnets or clamps. This bond is made possible by several forces that act on the blocks when they are brought together.
Factors Affecting Wringability
For gage blocks, wringing is made possible by the following mechanisms:
Air Pressure: When gage blocks are pressed together, the air is squeezed out from between them, creating a pressure differential that helps hold the blocks together.
Surface Tension: Residual oil or water vapor on the gage blocks creates a surface tension that holds them tightly in place.
Molecular Attraction: The extremely close contact between the two flat surfaces allows electron interchange between atoms, creating a molecular force that attracts the blocks. This force remains even in a vacuum, or in the absence of oils or water vapor.
The latter two forces are thought to be the most significant contributors to wringability.
Surface Requirements for Effective Wringing
For gage blocks to wring effectively, their surfaces must be smooth and flat, typically with a surface finish of 1 microinch AA or better. Wringing becomes challenging if the flatness of the blocks exceeds 5 microinches, which can prevent the blocks from adhering properly.
Preparing Gage Blocks for Wringing
Before attempting to wring gage blocks together, it's essential to ensure that the blocks are free of any nicks or burrs. Any imperfections on the surface may interfere with the wringing process and potentially damage the other block.
To check for burrs, a gage block stone is recommended, especially one with serrated grooves. The serrations provide a tactile feedback that helps detect any burrs or nicks. Blocks with significant damage will produce a clicking sound as they pass along the serrations, signaling the need for further preparation.
The Wringing Process
Clean the Blocks: Ensure that both blocks are clean before starting the wringing process.
Wipe the Blocks on an Oiled Wring Pad: Gently wipe the surfaces of the blocks across an oiled wring pad to add a thin film of oil.
Remove Excess Oil: After oiling, wipe the surfaces on a dry pad to remove any excess oil, leaving just a thin, even layer.
Slide the Blocks Together: Carefully slide the blocks together, applying light pressure. The blocks should slide smoothly without feeling any bumps or scratches. Once in place, they should adhere strongly to one another, allowing for reliable and accurate measurement.
Conclusion
Wringability is a key property that ensures the accurate and reliable functioning of gage blocks. With the right preparation and care, gage blocks can provide consistent and precise measurements over a long service life. Monitoring and maintaining wringability is a simple yet effective way to extend the accuracy and lifespan of these essential tools.