GB2072821A - Infra-red drying oven - Google Patents

Abstract

An infra-red drying oven, in particular for drying of printed circuits 4 and other flat bed printed products is provided with an array of infra-red lamps 8 and cooling means 10 whereby the temperature of the drying environment is maintained constant and uniform. <IMAGE>

Description

SPECIFICATION Infra-red drying oven This invention relates to a drying oven and in particular to an improved infra-red drying oven for drying of printed circuits and other flat-bed printed products in general, the form and arrangement of the oven being particularly advantageous.

Drying plays a most important role in flat-bed printing plants, especially in dealing with plants having large through-put where metallic plates, printed circuits, etc. are mass produced.

In this case it is, in fact, imperative to carry out forced drying of the products, since the inks used have a limited drying speed which is not compatible with the requirements of production times.

For the purposes of drying there have been used hitherto, amongst other systems, drying ovens employing infra-red or ultra-violet rays, the ovens being essentially made up of an array of lamps or independent deflectors, which are suitably spaced from each other and from the surface of the objects which are to be dried. The objects are arranged to move in the plane of incidence of the luminous rays. The infra-red rays constitute a form of radiant energy which, when absorbed by the objects, is transformed into heat.

As a result they have been used with success to dry and polymerise the ink, which becomes fixed on the printed surface. The temperature to which the sheets to be dried are subjected influences to a great extent the quality of the finished product; if in fact the temperature is too low, the sheet emerges still wet, whilst if the temperature is too high the printed matter tends to curl and the ink is noticeably altered with obvious damage to the product.

As a result the arrangement of lamps and reflectors must be suitably chosen above all as a function of the parameter of temperature.

Notwithstanding this, and even if the distribution and the arrangement of the radiating means is the optimum available, temperature variations outside the permitted range may occur.

For example, if the flow of sheets running below the ray of the lamps is constant with respect to time, there exists an equilibrium between the radiant energy supplied by the lamps and the thermal energy absorbed by the material to be dried.

If, however, the flow of sheets decreases, this equilibrium becomes altered and the energy produced is no longer compensated by an equal thermal absorption. There therefore occurs a build up of heat which causes an increase in the temperature of the drying environment, and the sheets which come into contact with this temperature become altered for the abovementioned reasons.

An object of the invention is to obviate or mitigate the above disadvantages of the known state of the art by providing an infra-red drying oven which maintains the temperature within the prefixed optimum levels even when the flow of sheets decreases and, in general, in the case when there occur alterations in the drying plant such as to cause an uncontrolled increase in the temperature of the drying environment outside said optimum limits.

According to the present invention there is provided a drying oven wherein there is provided means adapted to maintain the drying environment temperature constant and uniform.

Said means according to the invention are constituted by a cooling system using water circulation and arranged below the plane in which the sheets run.

An embodiment of the present invention will now be described, by way of example, with reference to the accompanying drawing which shows a preferred form of a drying oven made in accordance with the present invention.

Referring to the drawing, a drying oven is made up of a base 1 having supports 2 between which there is provided a movable belt 3 which constitutes the means for support and movement of a printed sheet 4 in the direction of the arrow F.

Above said belt 3, facing the free surface of the printed sheet 4, there is provided an array of infrared or ultra-violet ray lamps made up of a series of spaced lamps 8 mounted on a support 5. The support 5 is in turn positioned above the sheet 4 by means of telescopic arms 6 controlled by capstans 7.

Below the movable belt 3, underneath the sheet 4, there is provided a heat exchanger 9 having tubes 10 through which a coolant flows (water or other).

The radiant energy supplied by the lamps 8 is absorbed in the form of heat energy by the sheets 4 running below the lamps.

If the flow of said sheets should for some reason decrease, empty spaces of belt would occur between one sheet and the next below the lamps.

In this condition the incident energy is absorbed by the heat exchanger 9 which disperses the heat externally of the drying environment.

Thus heat build up below the lamps 8 is avoided and the temperature of the drying environment is maintained uniform within the desired limits.

The means for effecting movement of the belt 3 and fixing of the heat exchanger 9 to the frame of the machine, are not shown in drawings.

Claims (4)

1. A drying oven, in particular for the drying of printed circuits and other flat-bed printed products in general, of the type having an array of infra-red lamps facing the plane on which printed sheets run, wherein there is provided means for maintaining the temperature of the drying environment constant and uniform.

2. A drying oven as claimed in claim 1 , wherein said means are constituted by a water circulation cooling system arranged below the plane on which the sheets to be dried run.

3. A drying oven as claimed in claim 1 or 2, wherein said water circulation cooling system is made up of a series of tubular elements arranged in a serpentine-like fashion and fixed by means of suitable brackets to the oven framework close to the plane on which the sheets to be dried run, and below said plane.

4. A drying oven substantially as hereinbefore described with reference to the accompanying drawings.