Properties of Covering Materials of Roller Used in Cotton Roller Gin

摘要

Cotton ginning process is the mechanical separation of cotton fibres from the seed-cotton (kapas). The roller ginning process for cotton was invented by Fones McCarthy in 1840. This process mechanically separates cotton fibres from seeds by means of one or more rollers to which fibres adhere while the seeds are impeded and struck off or pulled loose. Most of the ginning operations is performed by using double roller (DR) gins which serve an important role in the ginning industries. The roller is the major component of DR gins and one requiring considerable attention. The peculiar gripping action or adherence of the cotton fibres to roller covering surface is an important element in the success of roller ginning process. In the conventional ginning process, the chrome composite leather-clad (CCLC) rollers emit chromium into environment due to the constant dust-producing grinding action. This contaminates the cotton and its products beyond the safe limit prescribed by International Organisation for Standarization (ISO) 14000 standards. CCLC rollers contain about 18,000 to 36,000 mg/kg (ppm) total chromium in trivalent and hexavalent forms, which are toxic to human health and carcinogenic. Current roller gins manufactured by companies in India and abroad commonly employ CCLC rollers. Since semi-finished chrome leather washers, which contain 3% to 4% chromium, are being used by roller ginning mills in India, Africa, Tanzania, China and Egypt, attention has been drawn to the contamination and pollution aspects of the process. This roller covering wears completely out with usage and repairing the roller consists of re-covering it. Specifically, due to persistent rubbing of the leather-clad roller over the stationary knife during the ginning process, the lint is contaminated with about 140 to 1,990 ppm of chromium, and the spun yarns and cotton byproducts contain about 100 to 200 ppm, far in excess of the ISO standards limit of 0.1 ppm. The use of CCLC rollers in the ginning process also causes air pollution due to chrome-specific dust (CSD) in the mill environment and is responsible for synergistic health complications (chromium based diseases and byssinosis) among gin and mill workers. Chromium in CSD and contaminated cotton products acts on human in three ways such as (1) local action as dermatitis or absorption through skin, (2) direct inhalation and (3) ingestion or absorption into the stomach. Toxic effects are produced by prolonged contact with airborne, solid or liquid chromium contamination and pollution, even in small quantities.