Printing Press(redirected from Printing presses)
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printing press[′print·iŋ ‚pres]
a machine used to print books, pamphlets, newspapers, magazines, labels, posters, and other items, as well as packaging materials. In addition to printing presses for paper products, machines also exist for printing on sheet metal, packaging cardboard, glass, plastics, textiles, and other materials, as well as for small-job duplication of data and business documents.
The main subassemblies of a printing press are the printing apparatus, which transfers the ink from the plate to the paper; the inking unit, which applies the ink to the plate; the paper-handling system, which feeds paper to the printing apparatus and delivers printed copies from the machine; auxiliary devices for receipt and treatment of the printed product; and the drive and control systems. According to the design principle of the printing apparatus, a distinction is made among rotary, cylinder, and platen presses.
Rotary printing presses are the most common. In such presses the form and paper are both placed on cylindrical surfaces (the plate cylinder and impression cylinder, respectively). The ink is transferred under pressure from the plate to the paper in the zone of contact between the plate cylinder and the impression cylinder, which is covered with an elastic envelope (the blanket). Printing presses may be sheet-fed or roll-fed, depending on the type of material fed into the machine (sheets or web from a roll).
Sheet-fed rotary presses are designed mainly for high-quality multicolor printing. Presses of this type are manufactured for all the main types of printing (relief, offset, and gravure). The PVL-70 and PVL-84 sheet-fed rotary letterpress machines are used in the USSR for printing sheets up to 70 × 100 cm and 84 × 108 cm, respectively, at a rate of up to 7,500 per hr. The ink is spread and applied to the plate in a uniform layer by a large number of rubber rollers and metal cylinders that move axially. After application of the first color, the sheets pass to the second printing section, in which the second color is applied. The sheets are then delivered to the delivery sheet pile.
Printing presses may be of the one-color, two-color, or four-color type, depending on the number of printing sections. In addition to machines of sectional design, there are also printing presses with planetary printing apparatus, in which several plate cylinders are in contact with a single impression cylinder. Sheet-fed rotary relief presses may use stereotype or electrotype plates, as well as full-size flexible plates 0.8 mm thick, made of photopolymers, rubber, or microcrystalline zinc; such presses are called PGF presses (from poligrafiia gibkikh form, “flexographic printing”).
Sheet-fed offset presses have become the most common type. The POL-70 and POL-84 sheet-fed offset presses are based on the same design as the PVL-type machines. The plate cylinder, which is designed for mounting full-size plates 0.8 mm thick, is equipped not only with an inking unit but also with a moistener, which applies a thin film of a solution to the nonprinting elements of the plate. The offset cylinder, which is covered with an elastic, rubber-impregnated fabric whose surface receives the ink layer transferred from the form, contacts the plate cylinder. In the area of contact with the impression cylinder, the layer of ink is transferred to the surface of the paper sheet. Offset presses frequently use a five-cylinder planetary mechanism in which two offset cylinders contact one impression cylinder. This principle has been used in the design of the printing apparatus of the POL-6 sheet-fed offset press, which prints on sheets up to 920 × 1,200 mm. The four-color POL-7 machine has two five-cylinder two-color sections connected by a chain conveyor to transfer the sheets from the first section to the second. Sheet-fed presses for relief printing have limited application.
Roll-fed rotary presses are manufactured for relief, offset, and gravure printing. Roll-fed presses are used for newspaper, magazine, and book printing.
Three models of relief newspaper presses are produced in the USSR. The GAU unit uses a paper web 1,680 mm wide and has a cylinder circumference of 1,188 mm and a maximum speed of 30,000 revolutions per hr. It is designed for printing the mass-circulation central and republic newspapers. The PVG-84 press has a roll width of 840 and 420 mm, a cylinder circumference of 1,188 mm, and a maximum speed of 25,000 revolutions per hr. It is used for printing medium-circulation oblast and city newspapers. The PVG-60 press has a roll width of 600 mm, a cylinder circumference of 840 mm, and a maximum speed of 18,000 revolutions per hr. It is used for printing raion newspapers. Roll-fed presses for printing books and magazines have blankets 1.5–2.0 mm thick, whereas blankets for newspaper machines are 4.0–4.5 mm thick.
Image-printing presses for the production of books and magazines are equipped with drying units in which the fixation of color is accelerated. The PVK-84 press for printing book and magazine illustrations is designed for two-color printing on an 840 × 1,100 mm format, with a maximum speed of 13,500 revolutions per hr.
Roll-fed offset presses are finding increasing use, mainly for multicolor two-sided production of books and magazines. Such presses usually have a four-cylinder printing apparatus; the paper web passes between two elastic offset cylinders, which apply the image simultaneously to both sides. The POK-84 roll-fed offset press uses two two-roll reel stands, which may be positioned on the same level as the press or on a lower level. The POK-70 roll-fed offset press, produced in the USSR, has a onesided three-cylinder printing apparatus; the impression size is 700 × 920 mm, and the maximum speed is 18,000 revolutions per hr. As of 1975, presses for two-sided printing were being prepared for production. These presses use the POK-84 printing assembly in sizes for impressions measuring 546 × 840 mm and 840 × 1,092 mm, with speeds of 30,000 and 25,000 revolutions per hr, respectively. Roll-fed offset presses are used for printing illustrated newspapers.
Cylinder presses are designed for printing only by the relief method, and their speed is lower than that of sheet-fed machines. However, they make it possible to print from the original flat plates or engravings. Such presses are useful for printing short production runs. In cylinder presses the form is mounted on a flat, reciprocating bed, and the paper is placed on the rotating cylinder. Cylinder presses may be of the two-revolution type, in which the cylinder performs two revolutions per cycle; the single-revolution type; the stop-cylinder type; and the perfecting type. Cylinder presses produced in the USSR include the two-revolution PD-3 (paper size, 840 × 1,080 mm; maximum speed, 3,120 cycles per hr) and 2PD-5 (700 × 1,000 mm; maximum speed, 3,000 cycles per hr), the single-revolution PS-AZ (450 × 600 mm; maximum speed, 4,500 cycles per hr), and the stop-cylinder PS-1M (450 × 600 mm; maximum speed, 2,100 cycles per hr).
Platen presses are used for short-run small-format work; only relief printing plates can be used. The form and paper are positioned on the flat surfaces of the bed and platen. Platen presses may be of the light-duty or heavy-duty types. Light-duty presses are designed for printing simple text material. In such presses the platen performs a simple rocking motion. Among the light-duty platen presses produced in the USSR are the PT-4, with manual feed (paper size, 300 × 450 mm; maximum speed, 1,500 cycles per hr), and the PT-2, with automatic paper feed (300 × 420 mm; maximum speed, 3,600 cycles per hr). In heavy-duty presses, the platen performs a complex motion: as it moves away from the bed, it tilts up for placement of sheets of paper on its surface, and as it approaches the form, it moves in a straight line and presses the paper to the form simultaneously over its entire area. Presses of this type are designed for printing illustrations and embossing.
Foreign printing presses are mainly of the offset type, above all the roll-fed and sheet-fed large-size models. The speeds of foreign printing presses are up to 40,000–42,000 revolutions per hr for newspaper units, up to 30,000 revolutions per hr for book and magazine presses, and up to 10,000–12,000 revolutions per hr for sheet-fed rotary presses.
The development of printing equipment is concerned mainly with roll-fed rotary presses, the design of multicolor presses that are capable of producing the work in a single cycle, an increase in the paper size and the speed of operation, and a reduction in downtime by mechanization and automation of the preparatory and auxiliary operations.
REFERENCESBushunov, V. T. Pechatnye mashiny. Moscow-Leningrad, 1963.
Kulikov, B. V. Tipografskie rotatsionnye pechatnye mashiny. Moscow, 1965.
Tiurin, A. A. Pechatnye mashiny. Moscow, 1966.
Zakharov, A. G., and D. A. Furaevskii. Ofsetnye mashiny i rabota na nikh. Moscow, 1972.
N. I. LIBERMAN