| Résumé : |
The purpose of dry milling is principally to restore the softness and suppleness to leather alter drying or surface finishing operations. This is achieved simply by tumbling the pack of leather for several hours in a drum, normally equipped with plain internai shelves. The repeated tumbling and flexing of the leather frees loose fibres and dust from the flesh side. Early milling drums were normally wooden, sometimes with numerous holes drilled in the circumference to allow the dust to escape, and sometimes of slatted construction, to achieve the same end. The release of the dry dust around the drum made for a very dirty working area, and was a considerable fire risk. Simple dust extraction systems were developed, with an external fan drawing dust-laden air through a hollow axle and into a separation cyclone for collection. Wooden drum drives were normally by ring gear and pinion, and horribly noisy. Re-humidification of the leather was sometimes carried out by injecting low pressure steam via a hollow axle, but this was a hit-or-miss affair, and could often result in irregular wet patches on the leather. So-called "stuffing" drums (Figure 1) were used with some types of leathers, with hot air blown through the hollow axles to aid the re-impregnation of the leather with oils and greases as it was tumbled in the drum. |
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The milling drum - from blunt instrument to sophisticated process vessel in WORLD LEATHER, Vol. 18, N° 6 (10/2005)
