Rieter

Description

Index

Of the various high-draft systems that have been proposed, some of which were only in use for a short period, only the 3-over-4 cylinder system and the double-apron arrangement are still to be found in modern machines offered by manufacturers. The 3-over-4 arrangement is found relatively rarely, while the double-apron system is standard. Only the double-apron arrangement permits drafts of 20 while holding the fibers more or less under control during their movements. In general, three-cylinder arrangements are used, but four cylinders may be needed for high drafts. They usually comprise fluted lower rollers and rubbercoated pressure rollers. The hardness of the upper rollers is between 80° and 85° Shore, but the rollers over which the apron runs often have a hardness only slightly above 60° Shore. This permits better enclosure and guidance of the fiber strand during drafting. The draft often has limits not only at the upper end (20 - 22) but also at the lower end, namely to about 5 for cotton and 6 for synthetic fibers. If drafts below these lower limits are attempted, the fiber masses to be moved are too large, drafting resistance becomes too high and the drafting operation is difficult to control.

Break drafts are usually selected around 1.1 (1.05 to 1.15) for cotton, and slightly higher for synthetics and strongly compressed cotton sliver delivered from high-performance drawframes. Values of 1.3 and slightly higher can be achieved. The main effect of the break draft is seen in roving evenness.

Modern double-apron systems exist in 3- or 4-cylinder versions. The 4-cylinder version is usually operated with a low draft in the final drafting zone. This may slightly reduce roving hairiness.

Fig. 6 – Three-cylinder, double-apron drafting arrangement