A calender is a series of hard pressure rollers used to finish or smooth a sheet of material such as paper, textiles, rubber, or plastics. Calender rolls are also used to form some types of plastic films and to apply coatings. [1] Some calender rolls are heated or cooled as needed. [2] Calenders are sometimes misspelled calendars.
The word "calender" itself is a derivation of the word κύλινδρος kylindros, the Greek word that is also the source of the word "cylinder". [3]
In eighteenth century China, workers called "calenderers" in the silk- and cotton-cloth trades used heavy rollers to press and finish cloth.
In 1836, Edwin M. Chaffee, of the Roxbury India Rubber Company, patented a four-roll calender to make rubber sheet. [4] Chaffee worked with Charles Goodyear with the intention to "produce a sheet of rubber laminated to a fabric base". [5] Calenders were also used for paper and fabrics long before later applications for thermoplastics. With the expansion of the rubber industry the design of calenders grew as well, so when PVC was introduced the machinery was already capable of processing it into film. [5] As recorded in an overview on the history of the development of calenders, "There was development in both Germany and the United States and probably the first successful calendering of PVC was in 1935 in Germany, where in the previous year the Hermann Berstorff Company of Hannover designed the first calender specifically to process this plastic". [5]
In the past, for paper, sheets were worked on with a polished hammer or pressed between polished metal sheets in a press. With the continuously operating paper machine it became part of the process of rolling the paper (in this case also called web paper). [6] The pressure between the rollers, the "nip pressure", can be reduced by heating the rolls or moistening the paper surface. This helps to keep the bulk and the stiffness of the web paper which is beneficial for its later use.
Modern calenders have hard heated rollers made from chilled cast iron or steel, and soft rollers coated with polymeric composites. The soft roller is slightly non-cylindrical, tapered in diameter toward both ends, to widen the working nip and distribute the specific pressure on the paper more evenly.
In a principal paper application, the calender is located at the end of a papermaking process (on-line). Those that are used separately from the process (off-line) are also called supercalenders. The purpose of a calender is to make the paper smooth and glossy for printing and writing, as well as of a consistent thickness for capacitors that use paper as their dielectric membrane.
The calender section of a paper machine consists of a calender and other equipment. The paper web is run between in order to further smooth it out, which also gives it a more uniform thickness. The pressure applied to the web by the rollers determines the finish of the paper, and there are three types of finish that the paper can have.
The first is machine finish, or MF Paper and it can range from a rough, matte (non glossy) look, to a smooth, high-quality finish.
The second is called a supercalendered finish, or MG Paper (Machine Glazed) which is glossy/glazed and suitable for high-degree, fine-screened halftone printing.
The third type of finish is called a plater finish, and whereas the first two types of finish are accomplished by the calender stack itself, a plater finish is obtained by placing cut sheets of paper between zinc or copper plates that are stacked together, then put under pressure and heating. A special finish such as a linen finish would be achieved by placing a piece of linen between the plate and the sheet of paper, or else an embossed steel roll might be used.
After calendering, the web has a moisture content of about 6% (depending on the finish). It is wound onto a roll called a tambour, and stored for final cutting and shipping.
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. The rolls used to supercalender uncoated paper usually consist of cast iron and highly compressed paper, while the rolls used for coated paper are usually cast iron and highly compressed cotton. The finish produced varies according to the raw material used to make the paper and the pressure exerted on it, and ranges from the highest English finish to a highly glazed surface. Supercalendered papers are sometimes used for books containing fine line blocks or halftones because they print well from type and halftones, although for the latter they are not as good as coated paper.
Calendering is a finishing process used on cloth and fabrics. A calender is employed, usually to smooth, coat, or thin a material.
With textiles, fabric is passed under rollers at high temperatures and pressures. Calendering is used on fabrics such as moire to produce its watered effect and also on cambric and some types of sateens.
Calenders can also be applied to materials other than paper when a smooth, flat surface is desirable, such as cotton, linens, silks, and various man-made fabrics and polymers such as vinyl and ABS polymer sheets, and to a lesser extent HDPE, polypropylene and polystyrene.
The calender is also an important processing machine in the rubber industries, especially in the manufacture of tires, where it is used for the inner layer and fabric layer.
Calendering can also be used for polishing, or making uniform, coatings applied to substrates- an older use was in polishing magnetic tapes, for which the contact roller rotates much faster than the web speed. More recently, it is used in the production of certain types of secondary battery cells (such as spirally-wound or prismatic lithium-ion cells) to achieve uniform thickness of electrode material coatings on current collector foils.
Flexography is a form of printing process which utilizes a flexible relief plate. It is essentially a modern version of letterpress, evolved with high speed rotary functionality, which can be used for printing on almost any type of substrate, including plastic, metallic films, cellophane, and paper. It is widely used for printing on the non-porous substrates required for various types of food packaging.
A paper machine is an industrial machine which is used in the pulp and paper industry to create paper in large quantities at high speed. Modern paper-making machines are based on the principles of the Fourdrinier Machine, which uses a moving woven mesh to create a continuous paper web by filtering out the fibres held in a paper stock and producing a continuously moving wet mat of fibre. This is dried in the machine to produce a strong paper web.
Offset printing is a common printing technique in which the inked image is transferred from a plate to a rubber blanket and then to the printing surface. When used in combination with the lithographic process, which is based on the repulsion of oil and water, the offset technique employs a flat (planographic) image carrier. Ink rollers transfer ink to the image areas of the image carrier, while a water roller applies a water-based film to the non-image areas.
Lamination is the technique/process of manufacturing a material in multiple layers, so that the composite material achieves improved strength, stability, sound insulation, appearance, or other properties from the use of the differing materials, such as plastic. A laminate is a permanently assembled object created using heat, pressure, welding, or adhesives. Various coating machines, machine presses and calendering equipment are used.
Calendering of textiles is a finishing process used to smooth, coat, or thin a material. With textiles, fabric is passed between calender rollers at high temperatures and pressures. Calendering is used on fabrics such as moire to produce its watered effect and also on cambric and some types of sateens.
Photoengraving is a process that uses a light-sensitive photoresist applied to the surface to be engraved to create a mask that protects some areas during a subsequent operation which etches, dissolves, or otherwise removes some or all of the material from the unshielded areas of a substrate. Normally applied to metal, it can also be used on glass, plastic and other materials.
A folding machine is a machine used primarily for the folding of paper. Folding is the sharp-edged bending of paper webs or sheets under pressure at a prepared or unprepared bending point along a straight line according to specified dimensions and folding layouts. Paper can be folded with either a buckle or a knife; thus, there are generally three types of folding machines: buckle folders, knife folders or a combination of these two types. Whilst buckle folding is the more popular of the two methods, knife folding is sometimes preferable. Folding machine models vary in sophistication, with high-end machines capable of processing more complex folding jobs and unusual paper forms. Organizations required to undertake mass mail-out campaigns often employ folding machines to improve efficiency. However it is very commonly used finishing process across the printing industry.
Pneumatic tires are manufactured according to relatively standardized processes and machinery, in around 455 tire factories in the world. With over 1 billion tires manufactured worldwide annually, the tire industry is a major consumer of natural rubber. Tire factories start with bulk raw materials such as synthetic rubber, carbon black, and chemicals and produce numerous specialized components that are assembled and cured.
Nonwoven fabric is a fabric-like material made from staple fibre (short) and long fibres, bonded together by chemical, mechanical, heat or solvent treatment. The term is used in the textile manufacturing industry to denote fabrics, such as felt, which are neither woven nor knitted. Some non-woven materials lack sufficient strength unless densified or reinforced by a backing. In recent years, non-wovens have become an alternative to polyurethane foam.
Coated paper is paper that has been coated by a mixture of materials or a polymer to impart certain qualities to the paper, including weight, surface gloss, smoothness, or reduced ink absorbency. Various materials, including kaolinite, calcium carbonate, bentonite, and talc, can be used to coat paper for high-quality printing used in the packaging industry and in magazines.
Plastics extrusion is a high-volume manufacturing process in which raw plastic is melted and formed into a continuous profile. Extrusion produces items such as pipe/tubing, weatherstripping, fencing, deck railings, window frames, plastic films and sheeting, thermoplastic coatings, and wire insulation.
The Sartell Paper Mill, officially the Verso Paper Sartell Mill, was a paper mill located in the city of Sartell in the U.S. state of Minnesota, operating from 1905 until a disastrous explosion in 2012.
Inkjet paper is a special fine paper designed for inkjet printers, typically classified by its weight, brightness and smoothness, and sometimes by its opacity.
Extrusion coating is the coating of a molten web of synthetic resin onto a substrate material. It is a versatile coating technique used for the economic application of various plastics, notably polyethylene, onto paperboard, corrugated fiberboard, paper, aluminium foils, cellulose, Non-wovens, or plastic films.
A release liner or release paper is a paper or plastic-based film sheet used to prevent a sticky surface from prematurely adhering. It is coated on one or both sides with a release agent, which provides a release effect against any type of a sticky material such as an adhesive or a mastic. Release liners are available in different colors, with or without printing under the low surface energy coating or on the backside of the liner. Release is separation of the liner from a sticky material; liner is the carrier for the release agent.
In textile manufacturing, finishing refers to the processes that convert the woven or knitted cloth into a usable material and more specifically to any process performed after dyeing the yarn or fabric to improve the look, performance, or "hand" (feel) of the finish textile or clothing. The precise meaning depends on context.
Plastic film is a thin continuous polymeric material. Thicker plastic material is often called a "sheet". These thin plastic membranes are used to separate areas or volumes, to hold items, to act as barriers, or as printable surfaces.
Wet Processing Engineering is one of the major streams in Textile Engineering or Textile manufacturing which refers to the engineering of textile chemical processes and associated applied science. The other three streams in textile engineering are yarn engineering, fabric engineering, and apparel engineering. The processes of this stream are involved or carried out in an aqueous stage. Hence, it is called a wet process which usually covers pre-treatment, dyeing, printing, and finishing.
A die in polymer processing is a metal restrictor or channel capable of providing a constant cross sectional profile to a stream of liquid polymer. This allows for continuous processing of shapes such as sheets, films, pipes, rods, and other more complex profiles. This is a continuous process, allowing for constant production, as opposed to a sequential (non-constant) process such as injection molding.
Slot-die coating is a coating technique for the application of solution, slurry, or extruded thin films onto typically flat substrates such as glass, metal, paper, fabric or plastic foils. The process was first developed for the industrial production of photographic papers in the 1950's. It has since become relevant in numerous commercial processes and nanomaterials related research fields.
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