pfleiderer

A Pfleiderer is a mechanical shredder equipped with rotating toothed drums or cylinders, used in the pulping stage of viscose rayon manufacture. Its job is to reduce cellulose fiber (usually from wood pulp or cotton linters) into small, uniform fragments that dissolve more readily in the sodium hydroxide and carbon disulfide chemical bath needed to form the viscose solution. Without pre-shredding, the cellulose would remain in large bundles and dissolve unevenly, producing weak or inconsistent yarn.

The machine consists of a hopper feed system and two or more counter-rotating drums lined with hardened steel teeth. The tooth geometry and drum spacing determine fragment size, which typically ranges from 2 to 6 millimeters. The teeth are arranged in helical patterns to push material steadily forward while cutting. Feed rate and drum speed control the residence time and final particle distribution. Most industrial Pfleiderers operate at speeds of 200 to 600 revolutions per minute.

Variants and operation

Drum-type Pfleiderers dominate production settings, but some mills use hammer mills or refiner-type designs with similar shredding action. The cellulose feed must be pre-dried to roughly 8 to 12 percent moisture content; wet pulp clogs the teeth and causes uneven cutting. Shredded material flows directly into storage silos before chemical treatment. Dust collection is essential, as fine cellulose particles present a respiratory hazard and explosion risk in enclosed spaces.

Tooth wear is the primary maintenance concern. After 150 to 300 operating hours, depending on fiber type and hardness, teeth must be replaced or the drum re-sharpened. Dull teeth produce fiber fines and oversized fragments rather than clean breaks, degrading viscose solution quality and downstream yarn strength. Some operators inspect and rotate drums regularly to balance wear.

The name derives from Pfleiderer, a German machinery manufacturer prominent in cellulose and rayon technology from the early 20th century onward. The term is used generically in some regions, though modern equipment from other makers performs the same function. Viscose production without effective shredding leads to high waste rates and quality rejections, making the Pfleiderer step cost-effective despite the capital and maintenance burden.