CALENDERING

CALENDERINGCALENDERINGCalendering is a process of pressing or ironing a fabric at high speed and under high pressure.There are various types of calendering machinery, each producing different types of pressed surface.All calender finishes are classified as mechanical finishing.CALENDERINGA calender machine is fundamentally a mechanical device consisting of two or more, stacked on top of each other.They are generally about 70 inches (178 cm) wide and usually heated.They are in contact with each other under great pressure.

CALENDERING

CALENDERING

CALENDERING

CALENDERINGFabric being calendered passes around and between these cylinders and is pressed under great pressure.The specific type of calender-finished fabric varies with the nature of the cylinder surface, the speed of the cylinders and the nature of the fabric being finished.The object of calendering is to smooth the fabric and to create interesting surface effects.

CALENDERINGCalendering and related treatments are of limited durability when applied to cellulosic materials, but durability can be increased when calendering is carried out in conjunction with a chemical resin.The use of heated rollers makes calendering durable on fabrics of thermoplastic fibers.Calendering treatments are not usually applied to woolen or worsted fabrics.CALENDERING-OBJECTIVESSmoothing the surface of the fabric.Increasing the fabric luster.Closing the threads of woven fabrics.Decreasing the air permeability.Increasing the fabric opacity.Improving the fabric handle.Flattening slubs.Obtaining silk like/ high gloss finish.Surface patterning by embossing.SIMPLE CALENDERINGAlso called swissing or normal glossing.The simplest form of calendering is comparable to ironing a fabric.The calender rolls are heated and the dampened cloth is passed between the cylinders to smooth and flatten the fabric and give it a slightly glossy surface.SIMPLE CALENDERINGIt is a temporary finish and the yarns in the fabric usually return to their natural round configuration on the first laundering or steaming.The speed usually is 100 yards/min.The high pressure tends to flatten the yarns and makes the fabric softer and smoother and enhances the fabrics luster.

GLAZED CALENDERINGIt is also called chintz or friction calendering.This is used to produce the high sheen of polished cotton or chintz.The machine used is called a friction calender or a chasing calender.One of the highly polished steel cylinders, rotates at speeds much higher than the fabric passing through it, thus polishing the fabric.

GLAZED CALENDERINGBefore the fabric is passed through the calender, the cloth is saturated with either starch or resin.The fabric is dried slightly and fed into the machine.It starch is used to produce the glaze, the finish is temporary.If resins are used, the glaze is durable.CIRE CALENDERINGIt is a type of glazed calendering, where the friction roller rotates at speeds much greater than ordinary friction calendering.The resultant fabric becomes highly lustrous and takes on a wet look.Fabrics of cotton, rayon, polyester, nylon and blends of these may be given a cire finish.

CIRE CALENDERINGThe fabrics are treated with waxes or resins prior to calendering, to achieve the highly polished effect.When thermoplastic fabrics are cire finished, the fabric becomes moderately water-repellent due to the flattening and partial fusing of fibers.Cire is not the name of a fabric, but fabrics with this finish are popularly called cire fabric or cire cloth.

EMBOSSED CALENDERINGIt produces a three-dimensional design on the fabric.This is done on a special embossing calender in which the roller cylinder is engraved with the embossing design.The pattern is thus pushed or shaped into the cloth when the fabric passes between the rollers.

EMBOSSED CALENDERINGSome embossed fabrics are made to imitate more costly woven jacquard or dobby designs.Embossed fabrics reveal a regular, consistent weave (plain or twill) whereas jacquard or dobby fabrics have yarns floats in the design area.Embossed patterns of fabrics pre-treated with resins and cured after embossing are durable.EMBOSSED CALENDERINGEmbossing of thermoplastic fabrics is permanent because the heated metal roll heat-sets the design.Embossed designs provide surface texture at a lower cost than do woven designs.Embossed fabrics should not be ironed or pressed as the design may be diminished by the pressure.

MOIRE CALENDERINGA moire finish produces a watered or clouded surface appearance that is sometimes called wood grain pattern, on the face side of the fabric.There are two methods for producing moire.In the first method, an engraved cylinder roller on the calender, flattens one part of the fabric more than another, causing the difference in light reflectance.

MOIRE CALENDERINGThe second method utilizes smooth calender rollers.In this method, two fabrics, each face to face, are fed through the calender.Ribbed fabrics, like taffeta or faille, are necessary for this process.Moire finishes may be temporary, durable or permanent.MOIRE CALENDERINGThe high pressure on the calender rolls causes the ribs to squeeze into each other in certain areas, thus flattening parts of the fabric and creating light reflectance pattern.In the first method, definite repeat pattern moire is produced.The second method produces a completely random, non-repetitive moire.

MOIRE CALENDERING

MOIRE CALENDERING

SCHREINER/SILK CALENDERINGIt produces a low, soft luster on the fabric surface.It is distinct from the high glaze (glassy) of the glazing calender or the luster shine of the simple calender.It is widely used on nylon tricot, cotton and cotton-polyester sateen and damask table linens.

SCHREINER CALENDERINGTo produce this effect, one of the steel cylinders of the calender is embossed with very fine diagonal lines, about 250 lines per inch.These embossings are rarely visible to the naked eye.In addition to soft luster, a softer hand and improved fabric cover is obtained.NAPPINGNapping is a mechanical finish in which woven or knitted fabrics are passed against rotating, bristled, wire-covered brushes.This action results in fibers being raised from the fabric surface, creating a fuzzy and soft finish.Napped fabrics have a softer hand and provide better insulation than the same materials unnapped because they can entrap more air.NAPPINGWidely used in blankets, sleepwear and winter clothing.One difficulty with napped fabrics is that the napped-fiber ends are subject to pilling and rapid wear (abrasion).Napped fabrics have a deeper pile or nap on the surface of the fabric than sueded fabrics.

NAPPINGFabrics are produced deliberately to be napped and may be knitted with loose loops on the surface for producing fleece-type materials.Single napping signifies that both sides of a cloth have been napped in one direction.Double napping signifies that both surfaces have been napped in opposite directions, which produces greater surface density, increased firmness and greater warmth.NAPPING

NAPPING

NAPPING

NAPPING

NAPPINGNapping is also called brushing, raising, gigging.SUEDING/EMERIZINGAlso called sanding, emerizing and peach finish.It develops a low pile on the surface of the fabric, which looks and feels like suede leather.The fabric is passed over a series of rollers covered with a sandpaper-like abrasive material.SUEDINGFabric moves at a speed of 15 to 20 m/min.Too much abrasion or too coarse an abrasive rips or tears the fabric.Too little abrasion may generate sufficient heat to produce a harsh hand with thermoplastic fibers.The process damages the fabric and can decrease its tensile strength (up to 60%).SUEDING

SUEDING

SUEDING

SUEDING

DECATISINGAlso called Decating.Produces a smooth, wrinkle-free finish and lofty hand on woolen and worsted fabrics and their blends.Comparable to steam ironing.The dry cloth is wound under tension on a perforated cylinder.Steam is forced through the fabric.

DECATISINGMoisture and heat relax tensions and remove wrinkles.The yarns are set and fixed in this position by cooling in cold air.For a more permanent set, dry decatising is done in a pressure boiler.Enhances and sets the natural luster of fabrics.Helps to overcome uneven or blotchy dyeing.

DECATING/DECATIZINGThe process is full decating if carried out under pressure and semi decating otherwise.