Wringing is a specialized process where two extremely flat and smooth surfaces, most commonly gauge blocks, are slid together to create a powerful bond. This bond allows them to adhere tightly to each other, forming a single, highly stable unit for precise measurement.
The fundamental principle involves sliding two blocks together so that their faces bond. Because of their ultraflat surfaces, when wrung, gauge blocks adhere to each other tightly. Properly wrung blocks may withstand a significant pull, such as 300 N (67 lbf), demonstrating the strength of this unique adhesion.
The Science Behind the Bond
The remarkable adhesion in wringing is not due to a sticky substance, but rather a combination of physical forces and the exceptional precision of the surfaces involved. When two ultraflat surfaces are wrung together, several factors contribute to their strong bond:
- Extreme Flatness and Smoothness: The surfaces of gauge blocks are manufactured to incredibly tight tolerances, often flat to within a few nanometers. This means there are very few microscopic peaks and valleys that would prevent intimate contact.
- Expulsion of Air: The sliding motion during wringing helps to push out nearly all the air trapped between the two surfaces. This brings the two blocks into extremely close proximity, often within a few molecular diameters.
- Intermolecular Forces (Van der Waals Forces): When surfaces are brought sufficiently close (typically less than 10 nanometers), weak attractive forces between molecules, known as van der Waals forces, become significant. Individually these forces are weak, but collectively across the entire surface area, they create a substantial attractive force.
- Adhesion Due to Surface Tension (Minor Contribution): A microscopic film of moisture or oil, even from the air, can be trapped between the surfaces. This thin liquid layer, under high surface tension, can contribute to the adhesion, acting like a very thin, strong adhesive layer.
- Atmospheric Pressure: With most of the air expelled, the external atmospheric pressure pushing down on the outer surfaces of the blocks also contributes to holding them together.
Practical Application: Gauge Blocks
The primary application of wringing is with gauge blocks (also known as jo blocks or Johansson gauges), which are precision ground and lapped steel or ceramic blocks used as reference standards for calibration and measurement.
How to Wring Gauge Blocks:
- Cleanliness is Key: Ensure both gauge blocks are meticulously clean and free of dust, oils, or fingerprints. Use a specialized cleaning solution and a lint-free cloth.
- Preparation: Place one block flat on a clean, stable surface.
- Cross-Hatch Sliding: Place the second block on top of the first at a slight angle (e.g., 90 degrees or a small acute angle).
- Gentle Pressure and Rotation: With light, even pressure, slide the top block across the bottom block while simultaneously rotating it until the faces align perfectly. The goal is to create a smooth, continuous sliding action that expels air.
- Achieving the Bond: As the air is expelled and the surfaces come into intimate contact, you will feel a distinct "drag" or resistance, indicating that the bond has formed. The blocks will then resist separation.
Benefits of Wringing Gauge Blocks:
- Exceptional Accuracy: Wringing allows users to stack multiple gauge blocks to create highly accurate custom lengths without introducing significant errors.
- Stability: The strong bond ensures the stacked blocks remain stable and rigid during use.
- Reference Standard: Wringing enables the creation of precise length standards for calibrating other measuring instruments.
Maintaining Wringing Quality
To ensure effective wringing and prolong the life of gauge blocks, it's crucial to:
- Always handle blocks with clean hands or gloves.
- Store blocks in their protective cases to prevent damage and contamination.
- Avoid dropping or scratching the ultra-precise surfaces.
- Demagnetize steel gauge blocks regularly to prevent them from attracting magnetic particles.
Wringing is a testament to the power of surface science and precision manufacturing, enabling unparalleled accuracy in mechanical measurement.
