Micronaire test
|
DIN 53941 |
|---|---|
| Area | textiles |
| title | Testing of textiles - Determination of the micronaire value of cotton fibers |
| Brief description: | Testing the fineness of cotton |
| Latest edition | 11/2008 |
| ISO | - |
The Micronaire test , the Micronaire test or the Micronaire value determination is a standard fineness test for cotton (CO). It is carried out in accordance with DIN 53941 "Testing of textiles - determination of the micronaire value of cotton fibers ".
A defined (weighed) amount of cotton is placed in a measuring chamber which is provided with a compressor , a float (in a riser pipe) and an air-permeable sealing piston. Air / gas , which is under a certain pre-pressure, flows through the measuring chamber of the test device , whereby the fibers in the measuring chamber oppose a flow resistance to this flow . In the riser there is a float that is raised to a greater or lesser extent by the flow pressure, depending on the flow velocity.
A gram of coarser fibers have less surface area than a gram of thin fibers, which is why the air has less resistance to flow through the coarser ones . This means that the finer the fibers are on average, the stronger the resistance and the higher the pressure drop that can be read on the measuring cylinder.
An older method uses a U-tube . The (homogeneous) air flow is fed in at one end. The predefined amount of cotton is placed on the same side. On the other side, a small ball , which fits exactly into the cross-section of the pipe, floats along a scale (which is marked on the pipe).
The measuring range can be calibrated in two ways:
- Oak cotton
- a 6.0 g calibration plug
The micronaire scale is graded from 2 to 8, with 2 representing the finest and 8 the coarsest fibers.
The following applies to Micronaire values:
- Below 3.0: very fine
- 3.0 - 3.9: fine
- 4.0 - 4.9 average
- 5.0 - 5.9: slightly coarse
- from 6.0: very coarse
The following relationship applies (approximately) to converting Micronaire values into fiber counts :
Number metric ( Nm ) =
The Micronaire value is also a good measure of the risk of nits. Values below 3.0 indicate fibers that tend to pinch. A nit is a dense tangle of intertwined fibers with a pure fiber core or with remains of seeds or husks firmly enclosed by fibers . Mostly spherical, their diameter is less than 1 mm. An increased occurrence of nits is called semolina .
Some possible sources of error for the DIN test are:
- A small amount of samples was tested and / or no average was taken.
- The normal climate is not maintained.
- The air flow device has not been calibrated.
- The test device is not calibrated.
- The form was not selected correctly for the fiber sample.
- Unsuitable gas is used for the experiment.
- There is moisture residue on the cotton due to incorrect handling (working without gloves).