# Rieter

### The specification of length

#### Index

Fig. 8 - Staple diagram by weight, specification of lengths

Both a parallelized, ordered bundle of fibers in the classers hand and the real staple length derived from it are referred to as the staple. The accurate fiber length derived from this is referred to as the staple diagram. Looking at the staple diagram in Fig. 8, it is clear that various measures of length can be derived, for example:

• maximum fiber length;
• minimum fiber length;
• average fiber length.

With some expections these values may be of interest to the statistician, but they tell the spinner nothing because they enable a statement to be made neither regarding the product nor regarding the process. The trade and the processor commonly use the following data, such as:

• classifying staple (trade staple, classer’s staple length);
• upper quartile length (with end oriented methods);
• upper half mean length or mean length (according to weight) (x);
• 1%, 2.5%, 5% or 50% span length measurements (as setting staples) (e.g. 2.5% span length).

The trade staple (classer‘s staple, s) is the most important specification of length. It is established to 1/32 inch during classifying of the cotton and corresponds to the fiber length in the weight-based diagram at about 25% (s) and in the numerical diagram at about 15% (s). It corresponds also to the 2.5% span length of  FibrogramFibrogram<//a> and to the upper half mean length of HVI (calculated from Fibrogram).

The 1% and 2.5% span length are lengths that are needed in setting machines, especially roller spacings. The following length groupings are currently used in stating the trade staple (classer‘s staple) for cotton:

• short staple: 1“ or less;
• medium staple: 1 1/32“ - 1 1/8“;
• long staple: 1 5/32“ - 1 3/8“;
• extra-long staple: 1 13/32“ and above.

Specification of the trade staple alone is not enough, because the slope of the curve is not taken into account. With the same trade-staple length, the staple diagram could approach either the rectangular or the triangular form. The proportion of short fibers will then be correspondingly high or low. In order to estimate how good the distribution of length is, the following data can be used:

• a second point on the Fibrogram curve (e.g. 50% span length derived from staple);
• the coefficient of variation; or
• the proportion of short fibers (e.g. percentage diagram shorter tahn 1/2 inch); or
• Uniformity Ratio (UR) from HVI measurements.