AIR-COOLED ROLLER

The present invention relates to an air-cooled roller. More especially, it relates to an air-cooled roller suitable for use in the printing industry to aid the drying and curing of ink.

An essential part of the printing process involves the drying and curing of ink. A web of substrate carrying ink to be dried and/or cured is passed under high intensity UV lamps using a system of rollers. Use of rollers allows the web to be generally unsupported as it passes under the lamps to prevent the web from being distorted, particularly if the web comprises a heat sensitive film used, for example, in the food packaging industry.

Air-cooled rollers are known, where air is blown down the sides of the roller. However, such cooling methods have proven to be inefficient, most notably due to fact that a temperature differential occurs across the length of the roller which results in the web being distorted in places where the roller is hotter or "less-cooled".

Water-cooled rollers are known which provide a more uniform temperature gradient across the roller. However the use of water as a coolant greatly increases the process costs, often to the extent that such a cooling method is not an option.

The present invention seeks to alleviate the aforementioned problems by providing an air-cooled roller designed to provide a uniform temperature gradient across the entire length of the roller, for use inter alia in printing equipment.

Accordingly, in one aspect the invention provides an air-cooled roller for inter alia a printing machine, the roller comprising an elongate cylindrical housing having a central bore through which cool air can pass, and a

longitudinal channel between the bore and a surface of the housing, the bore having at least one section of reduced diameter, the section having at least one aperture to allow cool air from the bore to enter the channel via the aperture.

Preferably the bore comprises more than one section of reduced diameter. More preferably the bore comprises three sections of reduced diameter, all of which have an aperture to provide a path of cool air from the bore to the channel at that point.

Preferably the or each section comprises a plurality of apertures.

Preferably the channel surrounds the central bore.

Preferably the internal walls of the channel is uneven. Preferably still the walls are provided with a series of ridges or ribs.

In a second aspect there is a provided, a method of cooling a roller using air, the method comprising the steps of : passing cool air through a central bore of the roller; providing means to allow the air to pass from the central bore into a longitudinal channel between the bore and a surface of the roller.

An embodiment of the invention will now be described by way of example with reference to the following Figures in which:

Figure 1 is a side sectional view of a roller constructed in accordance with the present invention;

Figure 2 is cross-section view of the roller of Figure 1 taken through A- A; and

Figure 3 is a simplifies schematic drawing of a system comprising two

rollers of Figures 1 and 2.

Referring to Figures 1 and 2, a roller 10 comprises an elongate cylindrical housing 12 with a central bore 14. The central bore 14, in use, defines a channel within the roller 10 through which cool air can flow.

The central bore 14 has three equi-spaced sections 16 of reduced diameter. The sections of reduced diameter 16 have a plurality of apertures or slots 18 formed within the respective walls of the sections 16.

As can be seen in Figure 2, four channelled apertures 20 extend longitudinally along the housing 12 between the central bore 14 and the outer surface 22 of the housing 12. Each channel 20 has an internal wall that is formed with a series of ribs or ridges 24.

In use, cool air travelling along the roller 10 through the central bore 14 reaches the first section of reduced diameter 16a whereupon the a portion of air passes through the slots 18a formed within the walls of the section 16a and into the channels 20 due to the pressure differential caused by the reduction in diameter of the bore 14 at that section 16a.

The air then travels along the channels 20 thereby cooling the surface wall of the roller 10. The ridges 24 of the internal wall of the channels 20 increases the heat transfer thereby providing efficient cooling of the roller surface 20.

The remainder of the cool air which does not pass through the slots 18a of the first section 16a continues along the central bore 14 to the second section 16b of reduced diameter. Once again, a portion of the, still cool, air passes through the slots 18b of the section 16b and into the channels 20 at that point. This ensures that cool air is directed towards the surface of the roller 10 near its centre to maintain a uniform temperature distribution across the roller 10.

The remainder of the cool air which does not pass through the slots 18b of the second section 16b continues along the central bore 14 to the third section 16c of reduced diameter. Once again, a portion of the, still cool, air passes through the slots 18c of the section 16c and into the channels 20 at that point. This ensures that cool air is directed towards the surface of the roller 10 near to its end to maintain a uniform temperature distribution across the roller 10.

The final remaining portion of cool air passes through the central bore outlet to be re-cycled.

As can be seen in Figure 1, the roller housing 12 is located within an outer housing 26 for assembly within, for example, a print curing machine. The outer housing 26 includes an inlet section 28 to which a pipe or tube (not shown) can be attached to provide cool air into the roller housing 12.

Figure 3 provides a simplified schematic illustration of how air-cooled two rollers 10 can be provided in a printing assembly to provide efficient cooling of both sides a web 30. Here the two air-cooled rollers 10 are provided one above the other and the web 30 travels in an "S" formation over the first roller 10a, between the two rollers 10a, 10b and under the second roller 10b. In this way, both sides of the web 30 come into contact with the cooled surface of the rollers 10.

Although the description refers to there being four channelled apertures 20 extending through the roller housing 12, it is clearly envisaged that these could be replaced by a single circumferential channel between the central bore 14 and the surface 22 of the roller 10.

The above described embodiments have been given by way of example only, and the skilled reader will naturally appreciate that many variations could be made thereto without departing from the scope of the present invention.