EP1279496B1 - Offset press with improved cylinder mounting - Google Patents

Abstract

The offset press comprises a frame, at least one plate cylinder, a press cylinder, and a blanket cylinder interposed between the plate cylinder and the press cylinder, together with bearing assemblies carried by the frame and receiving the longitudinal ends of the cylinders so that each cylinder is rotatable relative to the frame about a respective longitudinal central axis. Each of the longitudinal ends of at least a first cylinder are received in a first bearing assembly and a second bearing assembly, the second bearing assembly being spaced apart from the first bearing assembly along the longitudinal axis of the first cylinder.

Description

The present invention relates to an offset press according to the preamble of claim 1.

In such a press, the plate and blanket cylinders usually have the same diameter and each cylinder end is mounted through a rotational bearing on the frame. Driving means make it possible to rotate the rolls.

In operation, the plate carried by the plate cylinder is moistened and then inked. The plate decals the ink from its printer regions on the blanket carried by the blanket cylinder. The blanket then decodes the ink onto the printing paper that passes between the blanket cylinder and the pressure cylinder.

In order to be able to transfer the ink from one part of the plate to the blanket, and secondly from the blanket to the paper, the plate, blanket and pressure cylinders must, in operation, be plated against each other. The cylinders then exert on each other radial bending forces.

To prevent the cylinders from bending too much under the action of these forces, which could adversely affect the proper functioning of the press, it is ensured that the ratio between the length of each cylinder between its two end bearings and the The diameter of the cylinder remains relatively low and generally less than about 6.

Thus, the diameters of the rolls of a press of the aforementioned type are relatively large which induces a large mass and relatively high realization and installation costs.

This poses an additional problem for the plate cylinder which, because of its large circumference, requires either to use very long plates and whose assembly is complex, or to mount two plates each corresponding to a half-circumference, this which also involves significant costs because of the greater number of plates to be used for a given print run and the difficulties of simultaneously installing two plates on a plate cylinder.

EP-686 502 proposed a mechanism to limit the bending of the blanket cylinder.

An object of the invention is to solve these problems by providing a press according to the preamble of claim 1 which allows to reduce the costs associated with this press.

For this purpose, the subject of the invention is an offset press according to claim 1.

According to particular embodiments, the offset press may comprise one or more of the features of claims 2 and 3.

• la figure 1 est une vue schématique latérale d'une presse selon l'invention,
• la figure 2 est une vue schématique, partielle, agrandie et en coupe prise suivant la ligne II-II de la figure 1, cette figure illustrant les paliers de montage d'une extrémité du cylindre porte-plaque sur le bâti de la presse de la figure 1
• la figure 3 est une vue schématique, latérale et agrandie illustrant les paliers de la figure 2 dans une première position relative,
• la figure 4 est une vue analogue à la figure 3 illustrant une deuxième position relative des paliers.

The invention will be better understood on reading the description which follows, given solely by way of example, and with reference to the appended drawings, in which:

• the figure 1 is a schematic side view of a press according to the invention,
• the figure 2 is a schematic, partial, enlarged sectional view taken on line II-II of the figure 1 , this figure illustrating the mounting bearings of one end of the plate cylinder on the frame of the press of the figure 1
• the figure 3 is a schematic, lateral and enlarged view illustrating the bearings of the figure 2 in a first relative position,
• the figure 4 is a view similar to the figure 3 illustrating a second relative position of the bearings.

Diagrammatically shown on the figure 1 an offset press 1 which essentially comprises a frame 2, a plate cylinder 3, a blanket cylinder 4 and a pressure cylinder 5.

The blanket 4 and pressure cylinder 5 have double identical diameters of that of the plate cylinder 3.

The frame 2 essentially comprises two lateral uprights 6 in the form of vertical panels and only one of which is visible on the figure 1 . These uprights 6 are arranged on either side of the cylinders 3 to 5.

The cylinders 3 to 5 are rotatably mounted by each of their ends on the uprights 6, as will be described later, to rotate each about a respective longitudinal central axis A3, A4 and A5.

More precisely, and as illustrated by the figures 1 or 2 each longitudinal end 31 of the plate cylinder 3 is rotatably mounted on the corresponding upright 6 via a first laterally outer bearing 32 and a second laterally inner bearing 33.

The press 1 being substantially symmetrical with respect to a median vertical plane, only the connection of an end 31 to the frame 2 will be described later.

The bearings 32 and 33 are spaced from each other by a non-zero distance d along the longitudinal axis A3 of the plate cylinder 3.

The bearings 32 and 33 each comprise a bearing 34. The bearing 34 of the bearing 32 bears on a first region 35 of the end 31 considered. The bearing 34 of the bearing 33 bears on a second region 36 of the end 31 considered.

The bearings 34 have central geometric axes which respectively constitute those of the bearings 32 and 33. These axes, which are tangent to the axis A3 in the regions 35 and 36, will be referenced A32 and A33.

Note that the bearings 34 have not been represented on the figure 1 to facilitate representation.

As illustrated by figure 2 the second bearing 33 comprises a sleeve 331 flanged by a laterally outer flange 332 to the corresponding upright 6. The second bearing 33 is therefore fixed relative to the frame 2.

A stepped bore 333 is formed in the sheath 331.

This bore 333 comprises a laterally inner section 334 centered on the axis A3, an intermediate section 335 also centered on the axis A3 but of smaller diameter than the section 334, and a laterally outer section 336 of larger diameter than the section intermediate 335 and eccentric with respect to the axis A3. The section 336 is centered on an axis P3 located in the same vertical plane as the axis A3 above the latter. Typically, the distance separating the axis A3 and the axis P3 is 3 mm.

The bearing 34 of the second bearing 33 is disposed in the inner portion 334 of the bore 333.

The first bearing 32 comprises a movable support 321. The support 321 has a general shape of circular flat plate centered on the axis P3 and extended upwards by a drive arm 322.

A circular bore 323 is formed in the support 321. This bore 323 is eccentric with respect to the axis P3, the center of the bore 323 being located substantially opposite the axis P3 relative to the arm 322.

The support 321 is extended laterally inwards by a sleeve 324 received in the laterally outer section 336 of the bore 333 of the sleeve 331, so that the support 321 can pivot in the sleeve 331 about the axis P3.

The bearing 34 of the first bearing 32 is received in the bore 323 of the support 321. The bearing 32 is therefore pivotable relative to the frame 2.

The offset press 1 further comprises for each end 31 of the plate cylinder 3 an adjustable displacement cylinder 37 connected by a first end to the corresponding upright 6 and the other end to the arm 322 of the support 321 of the first bearing 32. The cylinder 37 is typically a pneumatic cylinder.

This jack 37 makes it possible to move the support 321, and therefore the first bearing 32, between two positions illustrated respectively by the Figures 1 to 3 and by figure 4 .

In the position of Figures 1 to 3 or first position, the axis A32 of the first bearing 32, and the axis A33 of the second bearing 33 are combined.

The first bearing 32 thus has a zero eccentration with respect to the second bearing A33.

The longitudinal axis A3 of the plate cylinder 3 is therefore rectilinear and the plate cylinder 3 is not subjected to any bending stress.

In the position of the figure 4 or second position, the cylinder 37 caused the pivoting of the support 321 relative to the frame 2 about the pivot axis P3 in the clockwise direction.

Thus, the axis A32 of the first bearing 32 has pivoted about the axis P3 and is therefore no longer confused with the axis A33 of the second bearing 33.

The axis A32 is then shifted radially with respect to the axis A33 substantially in the direction and in the direction of the bending force F exerted by the blanket cylinder 4 on the plate cylinder 3 when the press 1 operates.

The longitudinal axis A3 of the plate cylinder 3 is then bent to be tangent to the axes A32 and A33 in the corresponding regions 35 and 36 of the ends 31 of the cylinder 3.

Thus, the plate cylinder 3 is prestressed in flexion opposite the force F. The first and second positions of the bearing 32 are end positions.

It will be noted that Figures 3 and 4 the pivot angle of the support 321 between its two positions and the distances separating the axes P3, A33 and A32 have been exaggerated to facilitate the representation.

It will also be noted that the bearings 34 of the bearings 32 and 33 have not been represented on the Figures 3 and 4 to simplify the representation.

As we see on the figure 1 , each longitudinal end 41 of the blanket cylinder 4 is mounted, as in the state of the art, on the upright 6 corresponding to a single bearing 42 movable relative to the 6. This bearing 42 has a structure similar to that of a bearing 32 and thus comprises a support 421 pivotally mounted on the corresponding upright 6 about an axis P4. The support 421 is extended by a drive arm 422. The support 421 has a bore 423 of axis A42 eccentric with respect to the axis P4 and receiving the end 41 considered of the blanket cylinder 4. An adjustable cylinder of displacement 47 is connected to the upright 6 and the arm 422 to drive the support 421 in rotation about the axis P4 and thus move the axis A4 of the cylinder 4 to bring it closer to or away from the plate cylinder 3.

Each longitudinal end 51 of the pressure cylinder 5 is mounted, as in the state of the art, on the upright 6 corresponding to a single bearing 52 movable relative to the upright 6. This bearing 52 has a structure similar to that of a bearing 32 and thus comprises a support 521 pivotally mounted on the corresponding amount about an axis P5. The support 521 is extended by a drive arm 522. The support 521 has a bore 523 of axis A52 eccentric with respect to the axis P5 and receiving the end 51 considered of the pressure cylinder 5. An adjustable displacement cylinder 57 is connected to the upright 6 and the arm 522 to drive the support 521 in rotation around the axis P5 and thus move the axis A5 of the cylinder 5 to bring it closer to or away from the blanket cylinder 4.

Finally, the press 1 comprises conventional non-represented means for rotating the cylinders 3 to 5 about their axes A3 to A5.

In order to use the press 1, the respective longitudinal axes A4 and A5 of the rollers 4 and 5 are displaced by the movable bearings 42 and 52 in order to position them relative to the axis A3 in a manner allowing a satisfactory transfer of the ink plate carried by the cylinder 3 to the blanket carried by the cylinder 4 and to the printing paper passing between the cylinders 4 and 5.

Such relative positioning is perfectly conventional for those skilled in the art and will therefore not be described in more detail.

Prior to this positioning, the first bearings 32 of the plate cylinder 3 have been moved from their first position to their second position or to an intermediate position under the action of the cylinders 37.

The cylinder 3 is then bent as described above. Thus, when the blanket cylinder 4 is applied against the plate cylinder 3 to ensure a satisfactory transfer of the ink, the bending force F applied by the blanket cylinder 4 on the plate cylinder 3 is compensated by the prestressing of the plate cylinder 3 created by the eccentration of the first bearings 32 with respect to the second bearings 33.

Thus, the overall deformation of the cylinder 3 when the offset press 1 operates, measured for example by the arrow of the deformation of the cylinder 3, is particularly low. However, the diameter of the cylinder 3, and therefore its mass and the associated costs, are reduced.

By using the adjustable jacks 37, the prestress applied to the cylinder 3 can be set to an acceptable value by placing the bearings 32 in intermediate positions between their first and second positions.

In reality, the bending of the plate cylinder 3 is limited on the one hand because of the presence for each end 31 of the plate cylinder 3 of two bearings 32 and 33 spaced longitudinally from one another, and on the other hand the relative eccentricity of these two bearings 32 and 33 when the press 1 operates.

It should be noted that the first of this characteristic can be used alone to limit the bending of the plate cylinder 3.

It has thus been found that, under identical operating conditions, the use of two fixed end bearings spaced longitudinally from one another makes it possible to reduce by two the deflection deflection of the plate cylinder 3.

In more general terms not relating to the present invention, the above principles can be applied separately or separately to each of the cylinders 4 and 5 of the offset press 1 to reduce their respective diameter, although they are of particular interest according to the invention. invention for the plate cylinder 3 since they avoid the problems associated with the assembly of large plates or the simultaneous assembly of two plates.

Thus, although not the subject of the present invention, the diameters of the rolls 4 and 5 can also be reduced independently or independently of that of the roll 3.

Claims (3)

1. Offset press (1) of the type comprising a frame (2), at least one plate cylinder (3), a pressure cylinder (5) and a blanket cylinder (4) placed between the plate and pressure cylinders, and bearings (32, 33, 42, 52) borne by the frame and receiving the longitudinal extremities (31, 41, 51) of the cylinders so that each cylinder can rotate in relation to the frame about a respective central longitudinal axis (A3, A4, A5), characterised in that the plate cylinder (3) has a diameter of half that of the blanket cylinder (4), in that the longitudinal extremities (31) of at least the plate cylinder (3) are each housed in a first bearing (32) and a second bearing (33), the second bearing (33) being spaced from the first bearing along the longitudinal axis (A3) of plate cylinder (3), in that the press comprises, for each extremity (31) of the plate cylinder (3) means (37, 321, 322) for creating eccentricity between the first bearing (32) and the second bearing (33), in that the first bearing (32) can move with respect to the frame (2) between a first position of smaller or zero eccentricity and a second position of greater eccentricity in relation to the second bearing (33), in that the means for bringing about eccentricity comprise means (37) for moving the first bearing (32) between its first and second positions, and in that the first bearing (32) can pivot with respect to the frame between its first position and its second position about an axis (P3) which is substantially parallel to the axis (A33) of the second bearing (33).
2. Press according to claim 1, characterised in that the displacement means comprise a jack (37) extending between the frame and the first bearing.
3. Press according to claim 1 or 2, characterised in that the displacement means (37) for each extremity (31) of the plate cylinder (3) can be adjusted in order to bring the first bearing (32) into an intermediate position between its first position and its second position.

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