GB2024719A - Roller printing unit - Google Patents

Abstract

A roller printing unit (10) for marking articles (18) has magnetic means for biasing the roller into engagement with the article. If the article is magnetisable, then the roller (11) may comprise magnetic tyres (12); alternatively magnets can be positioned adjacent the article. The unit is particularly suited to marking "wet" steel, and can also be used for non-magnetisable sheers. <IMAGE>

Description

SPECIFICATION Printing units This invention relates to printing units employing printing rollers.

Hitherto roller printing units have typically comprised a printing roller which, for example, may be of rubber wetted with ink, and means for ensuring that the roller rolls over the surface to be marked without slippage. Such means have commonly comprised unwetted rubber bands located one on each side of the printing drum for engaging the surface to be marked, but under some circumstances these can exhibit insufficient adhesion to eliminate slippage.

Alternatively, therefore, the means has comprised an arrangement which drives the roller relative to the surface to be marked, such that rolling contact only is possible and slippage eliminated. Normally such an arrangement comprises means for con veyingtheobjectto be marked past the roller and for rotating the roller at the correct speed whilst exerting a suitable force on the roller normal to the surface to be marked. Such arrangements tend to be cumbersome in use however and relatively complex owing to the need to interconnect the conveyor and printing roller drives.

According to the present invention there is provided a printing unit including a printing roller, having magnetic means for producing an attractive force between said roller and an object to be marked.

Where the object to be marked is of a magnetisable material, the roller will preferably be provided with a magnetic tyre for rolling on or adjacent the surface to be marked. The magnetic tyre may comprise an electromagnet but for modestly sized rollers it is preferred to provide a permanent mag net, which may comprise a ring made up of a plurality of permanent magnets. The permanent magnets may be separated by magnetisable mate rial such as steel.

Alternatively the roller could be provided with a magnetisable tyre and the material of the object to be marked would then be magnetised instead. In the case of marking sheet metal, a magnet can be located at or adjacent one surface of the metal and the roller will then engage the other surface of the metal opposite the magnet. The latter arrangement could be used for marking thin non-magnetisable objects also, such as polyurethane sheet, the magnetic flux passing from the magnet through the polythene sheet to the roller to produce in effect an attractive force between the roller and the object to be marked.Clearly under such circumstances the roller could be magnetised itself and the aforesaid magnet could be retained or replaced by magnetisable material since in either case the roller will be attracted to the magnet or magnetisable object, drawing it into engagement with the object to be marked.

Embodiments of the invention will now be described by way of example and with reference to the accompanying drawings in which: Figure 1 is a cross-sectional side view of printing unit in accordance with a first embodiment of the invention; Figure 2 is a plan view of the unit of Figure 1; and Figure 3 is a cross sectional front view of a printing unit in accordance with a second embodiment of the invention.

Figures 1 and 2 show a printing unit 10 for use in printing so-called "wet steel". Conventional units employ rollers having rubber tyres for engaging the steel which are extremely prone to slippage when used for this purpose, and whilst the tendency to slip can be reduced by increasing the contact force of the roller with the wet surface, if the process is stopped then restarted flat spots can be produced in the tyres due to the high loading, and further slippage results.

A printing roller 11 has, in place of rubbertyres, steel tyres 12 which have a multiplicity of cylindrical magnets 13 disposed therein. The spacing of the magnets 13 is such that the steel between the magnets is effectively magnetised itself. The tyres 12 flank a rubber printing surface 14to which letters, numerals etc., (not shown) can be affixed to lie with their faces substantially flush with the radially outer surfaces of the steel tyres. The faces of the printing numerals are inked by a roller 15 whose porous surface 16 is impregnated with ink.

Rollers 11 and 15 are carried by an arm 17 pivotally mounted about an axis A-A, which enables the roller 11 to move bodily vertically in response to variations in height of the wet sheet steel 18 that it marks.

In use the roller 11 is maintained in close contact with the steel 18 by the attractive force between the magnetic roller tyres and the steel. As a result substantially no slippage occurs between the roller and the steel.

It will be clear that according to the invention many variations are possible from the form of printing unit shown in Figures 1 and 2. For example, the printing roller 11 has been shown as having steel tyres since these are readily detachable for interchange with conventional rubber tyres or for replacement purposes, moreover it is envisaged that detachable tyres could be used to modify existing rubbertyred rollers. However, it may be preferred to use a one piece roller unit into which the magnets are set. This could be achieved for example by using strip magnets moulded into a plastics roller.

Figure 3 shows another embodiment of the invention which would be equally suitable for making thin sheet steel or unmagnetisable material such as polythene sheet. As in the previous embodiment an arm 17a carries a printing roller 1 lea and an ink roller 1 spa, but in the present case the printing roller is provided with plain steel tyres. A magnetic attractive force between the printing roller 1 1a and the surface of the sheet steel 18a is provided by magnetic rollers 19 which attract the steel tyres 1 2a of roller 11 a through the steel sheet. Rollers 19 are carried on a shaft 20 comprise a plurality of magnetic strips 21 moulded into plastics rollers.

If the embodiment of Figure 3 were to be used with non-magnetisable material, it would be preferably for both rollers 19 and tyres 1 2a to be magnetic to produce a sufficiently strong attractive force.

Claims (10)

1.. A printing unit including a printing roller, having a magnetic means for producing an attractive force between said roller and an object to be marked.

2. A printing unit as claimed in Claim 1, including a tyre which acts as a magnet in use.

3. A printing unit as claimed in claim 1 or 2, wherein a rolling surface of said unit comprises a magnetisable material and a plurality of circumferentially disposed permanent magnets.

4. A printing unit as claimed in claim 1 or 2, wherein a rolling surface of the roller is magnetised by an electromagnet.

5. A printing unit as claimed in any one of Claims 1 to 4, including a further roller for disposition on the opposite face of sheet or strip material to said printing roller, said roller being magnetic, at least in use.

6. A printing unit as claimed in any one of claims 1 to 4, including a rubber printing surface.

7. A printing unit as claimed in any preceding claim, including an inking roller having a porous surface for dispensing ink.

8. A printing unit as claimed in claim 3, including a pair of steel rolling surfaces disposed one at each side of a printing surface, and including a plurality of permanent magnets disposed in said rolling surfaces.

9. A printing unit as claimed in any preceding claim, wherein said roller is mounted on a pivotally mounted arm, whereby variations in height of an object to be marked can be accommodated.

10. A printing unit substantially as hereinbefore described with reference to Figure 1 or Figure 2 of the accompanying drawings.