Super calendarKumar shantnu (121416)Pankaj nishant (121420)

calender

A Calender is employed, usually to smooth, coat, or thin a material. With textiles, fabric is folded in half and passed under rollers at high temperatures and pressures

Calanders come in various forms including a machine calender, (soft calenders and super calenders).

. Calanders are made up of steel roller sets, between which the paper passes

Super calendar

supercalender gives paper a high-gloss finish A supercalender is a stack of calenders consisting of alternating steel

and fiber-covered rolls through which paper is passed to increase its density, smoothness and gloss.

It is similar to a calender except that alternate chilled cast iron and softer rolls are used.

A supercalender is a vertical alternating stack of hard polished steel and soft cotton (or other resilient material) rolls.

The hard roll is pressed heavily against the soft roll, compressing the material.

calendering

Calendering is a mechanical finishing process used on cloth where fabric is folded in half and passed under rollers at high temperatures and pressures.

Calendering is used on fabrics such as moire to produce its watered. Calendaring is a high speed ironing process that primarily imparts

lustre and is usually the final treatment for the fabrics in the finishing sequence.

The basic principle of calendaring is to expose the cloth to the combined effect of moisture, heat and pressure until the fabric acquires a very smooth and light reflecting surface and gets a good lustre.

Calendering

OBJECTIVS:

To compress the fabric and reduce its thickness. To upgrade the fabric handle and to impart a smooth silky

touch to the fabric To improve the Opacity of the fabric. To reduce the Air Permeability of the fabric by changing its

porosity. To impart different degree of Lustre to the fabric.

Super calendering

A paper finishing operation consisting of an additional degree of calendering performed on a special machine not connected to the main papermaking machine.

The supercalender gives paper a high-gloss finish, the extent of supercalendering determining the extent of the gloss.

Supercalendering, in enhancing some paper properties, diminishes others in the same way the regular calendering does.

History of Calendering

The calendering processes that we know today are the finishing methods developed from the early 1800s mainly to make machine-made papers sufficiently smooth for printing and writing and to give some grades a glossy appearance.

These two properties are quite distinct. the former being related to the ability of a paper surface to receive

ink satisfactorily and uniformly. the latter referring to its light reflecting characteristics. the methods employed since well before 1000 AD to increase

smoothness invariably also increased gloss, they used to be called 'glazing'

The embossing unit is used to imprint special features on the film The winding station includes cutting devices for edge trimming of rolls . The extrusion process converts plastic powder or pellets into a continuous uniform melt

and forces this melt through a die, which upon cooling yields a desired shape. The end products are custom profiles, sheet, pipe, tubing, fibers, film, coatings, and pellets.

To begin the process the polymer must go through blending and fluxing before it goes through the calender. Blending is a process that creates the desired polymer and fluxing heats and works this blended polymer to make it a consistency easier for the calender to handle

The polymer is then ready to go through the calender and will leave it at a thickness dependent mainly on the gap between the last two rollers. The last set of rollers also dictate the surface finish; for example, they can influence the glossiness and texture of the surface.

That is why calenders typically end with a smaller roller at a higher speed to peel the sheet off. It is also why the middle roller is normally kept cooler so that the sheet won't stick to the other rollers nor will it split by sticking to both rollers which can happen.

types of calender

7- bowl calendar Chasing calendar Friction calendar Schreiner calender Felt calender

7 BOWL CALENDER:

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7 BOWL CALENDER: Generally the compressed material bowls are made from either

Cotton or Wool paper, Linen paper or Flax paper.

The hard bowl is made up of either Chilled Iron or Close Grained Cast Iron or Steel.

Iron bowls are made with highly polished surface and are heated from inside by steam or gas.

The fabric is passed through the machine in between the bowls and as the result Gloss is developed in the calendered fabric.

They run at a speed of 8 mts / min.

In this machine, there are 3 iron bowls, and 4 cotton bowls.

In between two metallic bowls, one cotton bowl is arranged.

Care should be taken in such a way that no two iron bowls are arranged together to avoid damage to the fabric.

CHASING CALENDER

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CHASING CALENDER

It is also a 7 bowl calendar. A chasing calendar finish is obtained with all the bowls of the calendaring machine running with the same surface speed, and the cotton fabric is passed through the nips of the calendar fro several times, each layer of the cloth overlapping one another

Chasing gives a Thready – Linen appearance and a special soft handle to the fabric. Here, all rollers are run at the same speed. The fabric is passed through the nips of rollers for several times.

FRICTION CALENDER

FRICTION CALENDER:

For producing this effect, the top four bowls of a 7bowl calendar can be lifted up, disconnecting the contact between the third and the fourth bowls so as to use only three bowls.

The Friction calendar with a 7 bowl calendar after disconnecting the top four bowls.

The three bowl calendar, one of which is cotton and the other two are of chilled iron.

Friction calendaring gives a higher Gloss and greater closing of the yarns, it is produced by bringing the cloth in contact with a heated polished chilled iron bowl which is rotating at a faster speed than the cloth itself.

The polished chilled iron bowl is heated by steam or gas and using gear wheels, the top chilled bowl is rotated at double the speed of the fabric and of the lower two bowls.

FRICTION CALENDER:

As a variation, the top bowl may be run at 1&1/2 times the speed of the lowest bowl, with the middle bowl running at an intermediate speed.

The top bowl with its higher surface speed produces the friction effect by polishing the cloth.

This finish is generally imparted to loose construction cloth such as binding cloth, low quality printed cloth etc.It is generally run at a speed of 32 mts/min.

The speed of the calendar when used in friction calendaring is determined by the amount of finish desired on the fabric and by the number of bowls used.

SCHREINER CALENDER

SCHREINER CALENDER

The usual schreiner calendar consists of two bowls, the upper bowl is made up of specially polished steel bowl and the lower bowl is made of compressed cotton.

The top metallic bowl is engraved with parallel lines normally 200 lines / inch2 at 20 angle. For some special cases it maybe drawn at an angle of 45.

The metallic bowl is heated by gas usually at 150 C. The two bowls are in contact with each other when the machine is running and

are kept separated when not in use. Otherwise the cotton bowl may get destroyed.

The top bowl is fixed and the lower is movable.

Very high pressure of100 tons or more is exerted on the fabric as it passes through the nip by hydraulic means.

SCHREINER CALENDER

The lower bowl, in some cases is set at an angle by Skewing arrangement to give enhanced brilliancy.

Mercerized fabric when treated in this calendar gives Silk finish. Like other calendar finishes, it is also not permanent.

It is destroyed while washing the fabrics. Generally Umbrella cloth and Aniline Black dyed cloth

are finished by this calendar. Speed is 10 to 25 mts/min.

FELT CALENDER

Light weight cotton goods like super fine Dhoti's, Sarees,etc., are finished on this machine.

This is also employed for the finishing of knitted goods. Blanket drying is a special method of cylinder drying. Here the cylinder is used for both drying and finishing.

The main cylinder is 6 to 8 feet in diameter made up of Tinned Sheet Iron or Stainless steel.

The cylinder is heated by steam and rotates freely. An endless wollen felt blanket passes around the major

part of the cylinder. The cylinder is rotated along with the endless blanket.

FELT CALENDER

Before feeding the fabric to the machine, the fabric is passed through a padding mangle for applying the finishing mixture and then passed over an expander or a small stenter.

Then the fabric is fed between the blanket and the cylinder and is kept against the hot surface by the pressure of the blanket during drying.

In this manner, there is no undue tension on warp. In addition to drying, it gives an attractive finish with soft feel and a smooth surface.

In another type of felt finish, the fabric is finished on hot air stenter, damped on a damping machine and then passed through felt calendar to get required feel.

Speed of this machine is30 to 40 mts/min.Fabric width of 1 to 2.5 cm can be reduced by this machine.

Calendering effects on paper properties

Positive effect Smoothness Gloss Absorption and porosity Caliper control Two-sidedness control (printing

papers

Negative Effects Bulk and stiffness Strength properties Opacity and brightness Light scattering Costs

Following attentions should be paid for maintenance Calendar roll should be inspected with utmost care and defect

causing any unusual sound should be found and rectified All bearing of calendar rolls should be lubricated frequently Rolls should be ground to proper finish and crown Calendar rolls should be periodically changed and sent for grinding