Modern paper machine clothing is manufactured with a specific set of design and quality specifications for each paper machine’s performance requirements. Such specifications, i.e. surface characteristics, open area, void volume, permeability, smoothness, etc. are engineered to achieve specific goals in the papermaking process. The need to implement an effective PMC cleaning program has become increasingly crucial in recent years. This change is primarily due to increasing levels of recycled furnish, faster machine speeds and accompanying technology, elevated sheet quality requirements, and the desire for longer fabric life. Forming fabrics must be kept free of contaminants in order to maintain surface characteristics, adequate open area, and to prevent sheet marking.
FORMING FABRIC CLEANING
Each forming fabric is designed with a specific set of characteristics to suit a particular paper machine. Regular and efficient cleaning of the fabric will maintain these characteristics and thereby assist in achieving an efficient and economic fabric life. Fabrics can be cleaned by mechanical or chemical means and frequently by a combination of both. The cleaning can be continuous or for short periods at regular intervals. It is also usual to clean the whole fabric with chemical solvents during machine shut downs. Chemical Cleaning Continuous chemical cleaning is possible by using a metering pump feeding into the water supply, but it can be very expensive. It is more usual to program the cleaning into one or two intensive periods during each shift. It is recommended to use a fabric coating if the contamination is proving particularly troublesome. It is common to chemically clean the fabrics at machine shutdowns, and a number of different methods for applying cleaning agents are available including:
• A gravity fed shower
• A felt applicator saturated with solution
• An application roll mounted under the return roll
• A spray from hand held pump tank units
• A foam generator to achieve a thorough exposure to the chemicals
The method chosen should be compatible with the type of chemical used. In all cases, the machine is run at crawl speed and the solution applied until the fabric has been well saturated for 20-30 minutes. It is then given a shower rinse at normal machine speeds. Cleaning Chemicals Cleaning chemicals fall into three main groups: Acid-based; Alkali-based; and Organic-based.