GB2087797A - Improvements in printing presses - Google Patents

Abstract

A press having opposed rollers has its bearings disposed in such a way that the rollers deflect in the same sense under load; thus whilst one roller is supported at its ends by bearings, the other roller has a central internal or external bearing and relatively even pressure is imparted across the width of the press. The arrangement is particularly applicable to pressure where a bed plate is passed between the rollers, the bed plate carrying a sandwich of inked- up etched metal printing plate, paper and felt blankets. A much higher construction results which can be converted into a litho press by turning upside down and replacing the centrally supported roller with a pressure pad or a rubber coated roller. <IMAGE>

Description

SPECIFICATION Improvements in etching and other presses This invention relates to presses, and in particular to etching presses, used by artists to produce prints from etched metal plates, and litho presses used to produce prints from litho stones or plates.

Existing etching and other presses are of a traditional form of construction which derives stiffness and rigidity from being extremely robust and massive. Such presses consist essentially of two very substantial rollers, between which a large bed plate passes. The artist's previously inked-up etched plate is placed etched side upwards on the bed plate, the paper placed on top, and felt blankets placed on top of this and the whole lot wound between the rollers to force the paper into contact with the ink in the etched grooves of the artist's plate. Normally, the top (or occasionally the bottom) roller is driven through gears by hand, and the motion imparted through the base plate to the other roller.

The primary requirements for any such press are high and even pressure across the width of the plate to produce a print of high and even definition. In order to achieve this, the traditional rollers, supported by bearings at their ends, have been of massive construction to minimise bending or distortion of the rollers when the plates, paper and blankets are wound through under high pressure.

Naturally, the tendency is for the rollers to deflect (away from the plate) most at the point furthest from support, in the middle, giving rise to prints which are fainter towards the middle. Traditional presses which are stiff enough to provide even pressure across the print are so heavy that their installation becomes an expert and expensive activity, which cannot normally be done by the artist.

This invention, for which I pray that I may be granted a patent, consists of a press, which may be used for etching, the novel construction of which makes it light and simple enough to be moved at will by the artist, and which, when turned upside down, converts readily into a litho press.

A feature of the invention is the novel disposition of the bearings supporting the rollers. This is illustrated in Figure 1 where it is compared with the traditional arrangement. It can be seen that by supporting one roller at its middle region and the other at its ends, the effect of applying load between the rollers (to the blankets, paper, artist's plate and bed plate, in the case of an etching press) is to bend (elastically) both rollers, together with whatever is between them, in the same sense (hogged, in the diagram); whereas in the case of the traditional arrangement, the effect would be for the rollers to bend in opposite senses.

By incorporating the proposed bearing arrangement, use may be made of relatively light rollers, which will deflect significantly under load, but which will nevertheless maintain a relatively even pressure distribution across their width.

Having established this good basic configuration, the evenness of pressure distribution may be further improved by attention to the detail design of the structures of the rollers and bedplatetaken in conjunction. For example, taken in conjunction with a fairly flexible bedplate, a very stiff bottom roller would increase pressure towards edges, whereas a very flexible bottom roller would concentrate pressure in the middle. A carefully designed combination (taking into account wall thicknesses, possibly varying along their lengths, roller diameters, and disposition and dimensions of stiffening rings, webs and ribs) can given an evenness of pressure distribution approaching perfection.

This means of achieving a very even pressure distribution across a significant roller width by using relatively light rollers in combination with the proposed bearing arrangement has application in any situation where even pressure across the width is required, while very slight (elastic) bending of the article while being rolled is tolerable (in this case, the etched plate, paper and blankets).

There are many ways of constructing apparatus which will fulfill these requirements but a particular embodiment will now be described by reference to the accompanying drawings.

Referring to Figures 2 and 3, the top roller 1, fabricated from steel tube, is suported as usual by two end bearings mounted on the sides 7 of the fabricated steel frame, and is driven, via gearing 13 (consisting of a chain drive) and a flywheel 14 by hand. The top roller's position is thus fixed, relative to the frame. The bottom roller 2, also fabricated from steel tube, is supported by a single central bearing 5, of either the spherical roller type or having a spherical mounting, to accommodate possible small tilting displacements of the bottom roller when passing an uneven plate and blankets. Through the bore of this central bearing passes a very substantial axle 6 spanning the gap between the sides of the frame and supporting the roller 2.This axle is designed to give slightly under pressure in the manner of a substantial centre-load leaf spring - and its ends rest on screw adjusters 8, which when screwed upwards press the bottom roller 2 against the plate 3 and top roller 1. Small rollers or plastic stops 9 are fitted at the sides of the bottom roller to prevent unwanted movement of the bottom roller in the horizontal plane.

The bottom roller is thus free to tilt slightly in the vertical plane, so ensuring even pressure on both sides of a centrally located plate; and free to move vertically, either by the slight giving of the axle to even out irregularities in the plate and blankets, or by adjustment of one (or both) ends of the ax!e, to accommodate varying thicknesses and numbers of blankets and different gauges of plate, and set the desired pressure. The bed plate, which must move up and down with the bottom roller, is supported by adjustable outriggers 15 terminating in rollers.

Two alternative embodiments are illustrated in Figures 4 and 5.

Figure 4 shows an arrangement which while maintaining the advantage of central bearings, does not allow the roller to tilt, and eliminates the need for constraint in the horizontal plane.

Figure 5 shows an embodiment in which the point of application of force to the centre of the roller is not on the axis of the roller, being in this case external to the roller, via a jockey wheel or pressure pad.

The traditional method of driving the plate indirectly via the top or bottom roller can be unsatisfactory in that it is possible to get slip between the top pressure roller and the plate, producing smearing in the print. In this press, the top roller drives the bedplate both directly by friction and also through side stabilisation /drive wires 16. These wires effectively gear the top roller to the bed plate in the manner of a rack and pinion, while allowing small movements of the order of 0.2 inches between the bed plate and rollerto accommodate varying thicknesses of etched plate and blankets (which a rack and pinion could not accommodate). The configuration of wire, roller and bedplate is shown diagrammatically in Figure 6.In addition, the wires ensure thatthe bed plate, once set square to the rollers, continues to remain square as it is wound back and forth, thereby eliminating the need for guides or slideways. The registration between roller and bed plate is thus relatively unconstrained, allowing repeated passes of the print - for example, in the application of different colours - without loss of registration, and therefore definition on the print.

This press lends itself to rapid conversion to a Litho Press. Forthis,the press is first turned upside down (Figure 3). The top roller 1 becomes the bottom support roller driving the bed plate 3 through wires as before; the litho stone or plate rests on what was the underneath of the bed plate. The old bottom roller 2 is removed to be replaced by a pressure pad 10 and leaf spring 11 with identical end details to axle 6 (to mate in identical fashion with side plates 7) but much greater flexibility. The pressure pad 10 is connected to the leaf spring 11 via a lever-operated cam device 12 for rapid raising and lowering of the pressure pad. The press is light enough for the above operations to be carried out by two people with ease in a few minutes.

As an alternative to a pressure pad, a centrally supported rubber coated roller may be used. This may be of smaller diameter to accommodate a thick litho stone. The ability of the roller to tilt slightly in the vertical plane helps it to follow the relatively large irregularities in the litho stone, while the rubber or other resilient material helps to absorb local irregularities.

Claims (12)

1. A press, having opposed rollers supported by bearings the disposition of which allow the rollers to deflect in the same sense or direction under load.

2. A press as claimed in claim 1 whereby deflection in the same sense enables the rollers to impart relatively even pressure across the width of the object rolled.

3. A press, as claimed in claim 1, having a roller supported on bearings at its ends, and another opposed roller supported on one or more bearings only at or near the central portion of the longitudinal axis.

4. A press as claimed in any of claims 1,2 or 3 in which one roller is supported by a bearing at each end and in which an opposed roller has supporting means in a position other than at the end or ends.

5. A press, as claimed in any of claims 1,2,3 or 4, which is lighter than a conventional press of simiiar capacity.

6. A press, as claimed in claims 2,3,4 or 5 in which the requirement of even pressure is achieved by the use of rollers having different wall thicknesses and/or roller diameters; or a roller or rollers having a variation of wall thicknesses along its or their length and/or the use of stiffening rings, webs or ribs.

7. A press, as claimed in claims 1,2,3,4,5 or 6 in which one roller is free to tilt slightly in the vertical plane so ensuring even pressure on both sides of the bed plate, without the need for any form of adjustment at the roller ends.

8. A press, as claimed in any of the preceding claims in which the movement of one roller is "geared" to the bed plate by means of wires wrapped round the ends of one roller and fixed to the corners of the bed plate.

9. A press, as claimed in any of the preceding claims when used as a press for the production of etchings.

10. A press, as claimed in any of claims 1 to 10 when turned upside down and used as a litho press.

11. A press as claimed in claim 10 in which the centrally supported roller (which is the upper roller afterthe press has been inverted) is replaced with a centrally supported roller coated with rubber or other resilient material.

12. A press substantially as described herein by reference to any of the accompanying Figures 2 to 3.