# Rieter

### The drafting operation

#### Index

Fig. 43 – Draft through a roller drafting arrangement

During drafting, the fibers must be moved relative to each other as uniformly as possible by overcoming the cohesive friction. Uniformity implies in this context that all fibers are controllably rearranged with a shift relative to each other equal to the degree of draft.

However, such regularity is utopian as regards both the fiber material and the mechanical means available. Drafting operations always run irregularly, and each draft stage will therefore always lead to an increase in unevenness.

Drafting is effected mostly on roller-drafting arrangements (Fig. 43). The fibers are firmly nipped between the bottom steel rollers and the weighted top pressure rollers. If the rollers are now rotated in such a way that their peripheral speed in the throughflow direction increases from roller pair to roller pair, then the drawing apart of the fibers, i.e. the draft, takes place. This is defined as the ratio of the delivered length (LD) to feed length (LF), or the ratio of the corresponding peripheral speeds:

$V = \frac{L_D}{L_F} = \frac{V_D}{V_F}$

where v = peripheral speed of cylinder, D = delivery and F = feed. The drafting arrangement illustrated has two subdrafting zones, namely:

• a break draft zone (B): VB = v2 / v3, and
• a main draft zone (A): VM = v1 / v2

The total draft is always the product of the individual drafts and not the sum:

$V_{total} = V_1 \times V_2 \times ...V_n$