Coupling - Wringing

Coupling - Wringing  ( Wringing and coupling are interchangable as a defininition )

Wringability is an important property of gage blocks and refers also to the coupling method of very thin parts to a larger piece of the same material. When coupled /wrung together the parts act as one larger homogeneous piece. Thus meeting the minimum conditions for weight/size and part thickness of a non coupled piece.

Wringability is a test on the integrity of the surface condition of the gage block.   Parts that don’t wring may give erratic and unreliable results.

Wringability itself may be defined as the ability of two surfaces to adhere tightly to each other in the absence of external means.  (They are not magnetized or clamped together.)

Wringing requires two smooth, flat surfaces with surface finishes of 1 microinch AA or better.

The sources of the forces holding gage blocks together are thought to come from:
      1. Air pressure from the surrounding environment as the air is squeezed out when the blocks are slid together.
      2. Surface tension from oil that remains on the gage blocks or water vapor from the air acts as a glue to hold them together.
      3. When two very flat surfaces are brought into such close contact with each other, this allows an interchange of electrons between the atoms of the separate blocks, which creates an attractive molecular force.  (This force will remain even in a vacuum or if no oil or water is present on the blocks.)

The last two sources are thought to be the most significant.

Preparation of Gage Blocks Prior to Wringing

Make sure that the blocks to be wrung are free from nicks and burrs.  It is important that all nicks and burrs be removed BEFORE attempting to wring blocks together because a burr on one block may damage the surface of the other block.

Blocks may be checked for burrs with a gage block stone before wringing.  A gage block stone with serrated grooves is recommended because it gives a better "feel" for nicks and burrs that catch the edges of the serrations.  Badly nicked surfaces will click as a nick passes along the serrations.

Wringing Gage Blocks

1. Make sure that blocks are clean.
2. Wipe the surfaces of the blocks to be wrung gently across the oiled Wring Pad or use a coupling grease.
3. Wipe these surfaces on the dry pad, removing as much oil as possible.
4. Slide the surfaces of the blocks together as shown.  Apply pressure while sliding the blocks.
   The blocks should slide together without any feel of bumps or scratching, and should adhere to each other strongly after being rotated into place.