Fabrics are usually pretreated to improve their mechanical and dimensional stability. They can
be treated with silicone to give them better cake release properties. Natural fabrics (wool and
cotton) are usually preshrunk to eliminate bag shrinkage during operation. Both synthetic and
natural fabrics usually undergo processes such as calendering, napping, singeing, glazing, or
coating.
These processes increase fabric life, improve dimensional stability (so that the bags retain
their shape or fit after long use), and facilitate bag cleaning.
Calendering is the high pressure pressing of the fabric by rollers to flatten or smooth the
material. Calendering pushes the surface fibers down onto the body of the filter medium. This
is done to increase surface life and dimensional stability and to give a more uniform surface to
bag fabric.
Napping is the scraping of the filter surface across metal points or burrs on a revolving
cylinder. Napping raises the surface fibers, creating a "fuzz", that provides a large number of sites for particle collection by interception and diffusion. Fabrics used for collecting sticky or
oily dusts are occasionally napped to provide good collection and bag cleaning ease.
Singeing is done by passing the filter material over an open flame, removing any straggly surface
fibers. This provides a more uniform surface.
Glazing is the high pressure pressing of the fiber at elevated temperatures. The fibers are fused
to the body of the filter medium. Glazing improves the mechanical stability of the filter and
helps reduce bag shrinkage that occurs from prolonged use.
Coating, or resin treating, involves immersing the filter material in natural or synthetic resin
such as polyvinyl chloride, cellulose acetate, or urea-phenol. This is done to lubricate the
woven fibers, or to provide high temperature durability or chemical resistance for various
fabric material. For example, glass bags are occasionally coated with Teflon or silicon graphite
to prevent abrasion during bag cleaning and aid in acid resistance. The Teflon coating is generally
applied at 10% of finished weight level.
Summary of pretreatment processes
be treated with silicone to give them better cake release properties. Natural fabrics (wool and
cotton) are usually preshrunk to eliminate bag shrinkage during operation. Both synthetic and
natural fabrics usually undergo processes such as calendering, napping, singeing, glazing, or
coating.
These processes increase fabric life, improve dimensional stability (so that the bags retain
their shape or fit after long use), and facilitate bag cleaning.
Calendering is the high pressure pressing of the fabric by rollers to flatten or smooth the
material. Calendering pushes the surface fibers down onto the body of the filter medium. This
is done to increase surface life and dimensional stability and to give a more uniform surface to
bag fabric.
Napping is the scraping of the filter surface across metal points or burrs on a revolving
cylinder. Napping raises the surface fibers, creating a "fuzz", that provides a large number of sites for particle collection by interception and diffusion. Fabrics used for collecting sticky or
oily dusts are occasionally napped to provide good collection and bag cleaning ease.
Singeing is done by passing the filter material over an open flame, removing any straggly surface
fibers. This provides a more uniform surface.
Glazing is the high pressure pressing of the fiber at elevated temperatures. The fibers are fused
to the body of the filter medium. Glazing improves the mechanical stability of the filter and
helps reduce bag shrinkage that occurs from prolonged use.
Coating, or resin treating, involves immersing the filter material in natural or synthetic resin
such as polyvinyl chloride, cellulose acetate, or urea-phenol. This is done to lubricate the
woven fibers, or to provide high temperature durability or chemical resistance for various
fabric material. For example, glass bags are occasionally coated with Teflon or silicon graphite
to prevent abrasion during bag cleaning and aid in acid resistance. The Teflon coating is generally
applied at 10% of finished weight level.
Summary of pretreatment processes
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