JPH0657452B2 - Assembling method of magnetic cylinder - Google Patents

Description

FIELD OF THE INVENTION The present invention relates to a method of assembling a magnetic cylinder for use in rotary offset printing and others.

(Prior Art) In rotary offset printing, ink is applied to a plate mounted on one cylinder (plate cylinder). The ink is transferred to the elastic blanket on the next cylinder (blanket).
A paper web is printed with the ink on the blanket. Each plate and blanket cylinder must incorporate a mechanism for holding the plate (generally a lithographic plate) or blanket on the surface of the cylinder. Such a mechanism
Typically, it extends in the longitudinal direction of the cylinder and is arranged in a gap having a peripheral dimension on the order of 3/8 inch (about 9.5 millimeters). The web portion passing through the gap of the blanket cylinder is not printed, which means that the portion is scrap. This leads to waste of paper and high costs. Further, in rotary offset printing, the cylinders rotate at high speed with considerable pressure between the cylinders. The gaps described above reduce print quality and cause shocks and vibrations in the press that contribute to maintenance problems. Gaps also compromise the symmetry of the cylinder, creating an undesirable situation at high speeds.

A cylinder has been proposed which holds the plate magnetically. Conventionally available magnetic cylinders do not have sufficient holding capacity to operate reliably in rotary web offset printing.

(Summary of the Invention) According to the present invention, a pole member disposing step of disposing two spiral pole members separated from each other and defining two magnet receiving pores on a cylinder surface in a cylinder, By disposing one of the two flexible magnets in one of the pores and the other of the magnets in an adjacent pore with the same poles facing each other. A step of winding the two magnets around the surface of the cylinder, the step of winding the magnet after the magnet to be wound first has completely entered the pores between the pole members, and A method for assembling a magnetic cylinder is provided, wherein the magnet to be wound is angularly offset so as to enter an adjacent pore.

(Explanation of a preferred embodiment) The printing roll 10 shown in FIG. 1 has a cylindrical cylinder body 11 in which a short shaft 12 extends from each end. The cylinder barrel is preferably of the general construction shown in U.S. Pat. No. 3,810,055. On the surface of the cylinder body, there are two spiral pole members 14 and 15 as shown in FIG.
Are spaced apart and define spiral pores 17, 18 therebetween.
Magnets 20, 21 are placed in the pores to establish a magnetic field through the pole members. The magnetic field holds the plate 23 on the surface of the cylinder. Plate 23 is not shown in FIG.

The magnet has a smaller radial dimension than the pole member. Annular members 25,26 cover the magnets and fill the outer portions of the pores 17,18.

A typical printing cylinder is on the order of 40 inches (about 1 meter) in length and 7.5 inches (about 19 centimeters) in diameter. The magnetic structure on the cylinder surface will be 1/2 inch (about 1.2
Centimeters) or less in the radial dimension.

For comparison, the conventional magnetic structure is shown in FIG. 3, and the magnetic structure of the cylinder and plate of the present invention is shown in FIG. Elements corresponding to those of FIGS. 1, 2 and 4 in the conventional structure of FIG. 3 are designated with the same reference numeral “′”. Differences in material geometry and properties substantially increase the holding force of the printing plate on the cylinder. The dimensions shown in FIGS. 3 and 4 and referenced in the specification only provide an example for purposes of comparing the prior art and the present invention. Although the absolute amounts of the individual dimensions are not critical, the relative dimensions of the elements in Figure 4 provide the increased plate holding force achieved by the present invention.

The cylinder body 11, which may be made of steel, has on its surface a sleeve 28 made of a non-magnetic material for isolating the magnetic structure from the body. The sleeve is typically made of brass and has a radial dimension of 0.050 inch (about 0.3 millimeters).

The magnets 20, 21 are preferably an elastic rubber-like material having magnet particles embedded therein. The Minnesota Mining and Manyufu Actuating Company sells such magnets under the Plastiform trademark. The magnets will be used during assembly of the cylinder as will be described below in the pole members 14, 1
It is wound along the pores 17 and 18 between the five members. The magnetic field of the magnet is oriented so that the same poles face each other as shown. The magnet has a longitudinal dimension of 0.051 inch (approximately 1.3 millimeters) and a radial dimension of 0.25.
It is 0 inch (about 6.4 mm). Pole member 14,
15 is a low reluctance material, preferably stainless steel. AISI No. 430 ferrite type stainless steel is preferred. This material resists corrosion by the inks, solvents and detergents used in printing to maintain the peripheral surface of the pole member in the desired dimensions and tubular shape. The longitudinal dimension of the pole member is 0.032 inches (about 0.8 millimeters) here, which means that when the printing plate is mounted in the cylinder, the surrounding surface of the pole member is substantially saturated. As achieved, it is determined by the coercivity and longitudinal dimensions of the magnets 20, 21 and the magnetic permeability of the pole piece material.

The printing plate 23 is made of a magnetic material and has a wall thickness associated with its magnetic reluctance so that a substantially saturated magnetization is achieved in the annular plate section between adjacent pole members 14, 15. .

In the embodiment illustrated in FIG. 4, the plate thickness is 0.015.
It is an inch (about 0.4 mm). Such wall thickness facilitates cutting, handling, and preforming of the end sections to match the cylinder surface, as described below.

The magnetic field through the plate 23 preferably does not exceed saturation, i.e. no magnetic field exists above its upper surface. In the presence of stray magnetic fields outside the plate, particles of magnetic material are attracted to the plate surface. This reduces print quality and damages the plate or blanket. Worse, such stray fields do not add plate holding forces on the cylinders, but rather reduce them. The force required to lift the plate edge from the cylinder, sometimes referred to as "anti-peel strength", is directly correlated to the plate thickness to the 3 / 4th power. This relationship exists over the range where the graph of attractive force per unit area as a function of the gap between the plate and the pole member is substantially linear. Both the measured and calculated data show that the graph is substantially linear until the peel strength is reduced to about 40-50% of the initial value. The plate must be sufficiently thick to resist peeling and therefore not be peeled from the cylinder in the sticky ink. However, excessive wall thickness increases the difficulty of cutting, handling and forming the plate and its mounting on the cylinder.

As used herein, "substantially saturated" means a state of saturation of the order of 90 to 95%. In designing to achieve a high level of saturation, the coercive force and / or longitudinal dimension of the magnet must be excessively increased to minimize the increase in magnetic flux. Furthermore, at such high levels of saturation, stray magnetic fields will appear outside the plate, reducing the anti-peel strength and attracting force increments. Flux levels as low as 90% saturation indicate that the material is not being effectively used in pole members and plates.

The magnets 20 and 2 are provided between the outer parts of the pole members 14 and 15.
The annular members 25, 26 overlying 1 are made of a high magnetoresistive material to minimize the magnetic flux path shunting from the plate 23. Austenitic stainless steel AISI
It turns out that No. 310 is satisfactory.

The peripheral surface of the pole member and the inner surface of the plate 23 are preferably in intimate contact. This minimizes the occurrence and size of air gear traps in the magnetic circuit. The air gear significantly increases the magnetic reluctance of the circuit and reduces the attractive force acting on the plate.

The advantages of the structure of FIG. 4 will be appreciated by considering the conventional structure of FIG. In the conventional construction of FIG. 3, the magnets 20 ', 21' have a longitudinal dimension of 0.093 inches (about 2.4 millimeters). The coercive force is such that the electrode plate members 14 ', 15' are saturated and the magnetic attractive force that the magnet should originally be able to use is not effectively used. The annular magnet covering members 25 ', 26' have a radial dimension of 0.100 inch and are made of stainless steel AISI No. 304. The reluctance of the stainless steel AISI No. 304 is typically lower than the AISI No. 310 material. The magnet covering member is
It provides a number of magnetic shunts that reduce the magnetic flux in plate 23 ', thus dampening the attractive force.

The attractive force is concentrated on the pole members 14 ', 15'. In the prior art shown in FIG. 3, 1 inch in the longitudinal direction of the cylinder (about 2.
There are four sets of magnets and pole pieces in the conventional magnet width per 54 cm. The area ratio of the pole member to the magnet on the outer surface of the cylinder is 0.34 to 1. In the structure of FIG. 4, there are 6 sets of magnets and pole members per inch in the cylinder longitudinal direction, and the area ratio of pole members to magnets is 0.63: 1.
Is. Such differences in element geometry and magnetic properties result in an increase in anti-peel strength of the order of 50% and in attractive force of the order of 80% compared to that for plate 23 '.

The peeling force required to lift the edge of the plate 23 is proportional to the pulling force when the plate is in contact with the pole member, and between the pulling force and the gear tape between the plate and the pole member. Constant 4
Inversely proportional to the root. This degree of ability to resist the peeling force depends on the relationship between the pulling force and the gearup being linear over the first 46% of the peel strength drop, as well as the plate edge lifting. It is accurate when the bending of the plate when pressed does not exceed the mechanical yield strength of the plate material. Sticky inks exert such a peeling force. If the edge of the plate is lifted too much, the position of the plate will move or dislodge on the cylinder. As mentioned above, it is desirable to minimize the cap between the plate and the pole member, so that the inner surface of the plate adheres to the pole member over the perimeter and the entire length of the plate.

An additional element to enhance the close contact between the plate and the pole members is to pre-bend each of the front and rear edges 30, 31 of the plate as shown in FIG. The bend preferably has a curvature substantially equal to or slightly less than the curvature of the cylinder surface. This helps establish and maintain a close contact between the plate and the pole pieces at the most important edge of the plate.

FIG. 5 also illustrates a preferred structure for disposing the plate 23 on the cylinder. The pins 33 and 34 are extended from the cylinder surface outward in the radial direction and positioned. The semi-circular complementary notches and elongated notches on the plate edge receive the pins and position the plate on the cylinder while meeting manufacturing tolerances. After positioning the plate edge 30 as shown, the remainder of the plate is wrapped around the cylinder surface.

The plate 23 in FIGS. 1, 4 and 5 is a printing plate. A line drawing of the material to be printed is appropriately formed on the outer surface by the ink from the ink fountain in an offset printing operation. As illustrated in FIG. 6, magnetic cylinders can also be used for elastic blankets. The cylinder and magnetic structure of FIG. 6 may be the same as in FIG. An elastic blanket sheet 37 is appropriately fixed to the outer surface of the plate 36. Similar to FIG. 4, plate 36 is made from a magnetic material of magnetic resistance and radial dimension such that it is substantially saturated by the magnetic flux between plates 14 and 15. The inner surface of the plate 36 is in close contact with the outer surface around the pole member.

Magnetically mounted blankets sometimes tend to cleave or deviate circumferentially on the surface of the cylinder. The cause of these movements has not been completely clarified, but it is believed to be a partial detachment of the plate 36 from the cylinder surface. Maximizing the attractive force is one of the factors to eliminate such deviation. Increasing the area ratio of pole members to magnets above the 0.63: 1 ratio of the cylinder construction described above is very attractive with very small gap dimensions, for example 0.0005 inch (about 0.01 mm). It turns out to bring power. However, at such high area ratios the attractive force drops rapidly as the gap increases. High attraction forces in very small gaps with area ratios between about 0.45 to 1 and about 0.65 to 1 were achieved under conditions where damping with increasing gap was acceptable. Therefore, the peel strength required to lift the edge of the plate is maximized.

FIG. 7 illustrates a method of incorporating the flexible magnets 20, 21 in the cylinder. A sleeve 28 and pole members 14 and 15 are attached to the cylinder body 11. The flexible magnet is then wound into the pores 17, 18 between the pole members, such as by rotating the cylinder in the direction of arrow 39. The magnet is oriented adjacent to the pole member. If the magnets were brought into close proximity in this orientation,
The magnetic fields of each magnet tend to demagnetize each other. According to the invention, the magnet is one of the magnets 20 which may be considered as a leading magnet.
Is offset angularly in a state where the trailing magnet 21 completely enters the pore between the adjacent pole members before entering the pore adjacent thereto. Therefore, the pole members are interposed between the magnets before the magnets come too close together to minimize demagnetization of the magnets during assembly.

If the pole member is work hardened, the magnetic resistance increases. Annealing reduces reluctance and maximizes retention.
By combining the annealing with the previously mentioned magnet assembly method, the holding force is increased by a factor of about 1.2 compared to that of the conventional cylinder shown in FIG.

Although the present invention has been described based on the embodiments, it should be noted that many modifications can be made within the present invention.

[Brief description of drawings]

FIG. 1 is a partially cutaway perspective view of a cylinder and a plate according to the present invention. FIG. 2 is an enlarged partial cross-sectional view of the cylinder surface with the pole members shown in the longitudinal direction and the magnets in the transverse direction. FIG. 3 is an enlarged partial sectional view showing a magnetic structure and a plate of a conventional cylinder. FIG. 4 is an enlarged partial sectional view showing the magnetic structure and plate of the cylinder of the present invention, taken along line 4-4 in FIG. FIG. 5 is a perspective view showing winding of the plate on the cylinder. FIG. 6 is an enlarged partial cross-sectional view similar to FIG. 4 with an offset blanket on the surface of the cylinder. FIG. 7 is a partially cutaway side view of a cylinder illustrating the winding of a magnet within a gap between pole members. The names of the main parts in the figure are as follows. 11: Cylinder body 14, 15: Pole member 17, 18: Pore 20, 21: Magnet 23, 36: Plate 25, 26: Annular member 28: Sleeve 37: Blanket sheet

Claims (2)

[Claims] 1. A pole member arranging step of arranging in a cylinder two spaced apart spiral pole members which define two magnet receiving pores on the surface of the cylinder, and the two flexible members. Of the two magnets by disposing one of the magnets in one of the pores and the other of the magnets in the adjacent pores with the same poles facing each other. A step of winding a magnet around the surface of the cylinder, wherein the step of winding the magnet is performed after the magnet to be wound first completely enters the pores between the pole members, and A method for assembling a magnetic cylinder, characterized in that it is performed in a state in which it is angularly offset so as to enter an adjacent pore. 2. The method of assembling a magnetic cylinder according to claim 1, wherein the pole member between the pores shields each magnet from the magnetic field of each other.