The present invention relates to improvements in or relat¬ ing to a sheet offset press, and more specifically to an arrangement of an infra-red (IR) drier for such presses having a low sheet discharge conveyor provided with an IR battery, ready printed sheets being passed under this battery for drying the ink fields on the sheets, and the battery being situated under, or close to the ink rolls in the last stand of the press.

In previously known machines of the type mentioned above, spray powder has been used in drying the printed sheets before stacking the individual sheets. With this procedure the sheets can be stacked before they are properly dry. A disadvantage is, however, that large space is required in the press hall for these stacks of sheets that are put out to dry off, and the drying time may amount to several hours. In addition, large quantities of spray powder are consumed in preventing the individual sheets sticking to each other in the stacks. Attempts have of course been made to use IR lamps for drying the ink on the sheets inside an offset press of the kind in question, but there has been a problem with the heat generated by an IR drier for provid¬ ing a good drying effect in the process also causing drying off the moisture on the platens in the press. This is due to the ink rolls in the last stand generally being placed above or close to the stack of sheets, where the IR drier must also be placed.

One object of the present invention is to provide an arran¬ gement with an IR drier of the kind mentioned in the intro¬ duction, where the disadvantages mentioned have been elimi¬ nated. This object is achieved with an arrangement describ¬ ed above, and with the characterizinq features disclosed in

the claims .

Thanks to the invention there has now been achieved an arrangement which meets its purpose in an excellent way, while being cheap and simple to manufacture at the same time. Apart from an effective cooling of the IR battery, the connections to the IR lamps, the lamps themselves as well as their electric cables are also cooled. Since the IR battery is cooled using a "closed" air cooling system, any leakage of air is avoided, simultaneously as cooling will be very effective. With the aid of the exhaust station there is obtained a sufficient air stream/change of air round the IR drier inside the press, the air to the exhaust station coming from the press hall via a grid at the ink rolls adjacent the stack of sheets and through other open¬ ings, thus providing the ventilation required for prevent¬ ing the heat occurring in the drying process from migrating up through the press, which would give the above-mentioned problems. The combination of IR battery and exhaust station provides a sufficiently "cold" printing press, so that setoff against the platens is avoided.

The invention will now be described in more detail below, and with reference to the accompanying drawing, which illustrates a schematic cross section of the arrangement of an IR battery for a sheet offset press with a low sheet discharge conveyor in accordance with the present inven¬ tion.

On the drawing there is shown a preferred embodiment of an IR drier 2 in accordance with the present invention in a sheet offset press 1 with a low sheet discharge conveyor 13. the drier 2 including an IR battery 3, known per se, in combination with an air cooling system. The ink rolls 5 of the last stand 6 in a printing unit 14 of the press l are

arranged, as will be seen from the drawing, above or ad¬ jacent a stack 11 of sheets 4, close to where the IR bat¬ tery 3 must be placed. An air cooling system is connected to the battery 3 , a supply air fan 7 blowing air into one end 8 of the battery 3 _F such as to emerge from its other end 9 for removal by an exhaust fan 10. This air also cools the terminals of the IR lamps, the lamps themselves and the electric cables to them. There is an exhaust station 12 disposed directly under the drying position of the sheets 4 under the IR battery 3, this station also being connected to the exhaust fan 10 for extracting hot air from the ink rolls 5 in the unit 14, as well as from a region adjacent the IR battery 3. This exhaust station prevents the heat occurring during the drying process from migrating up through the unit 14 to cause setoff against the printing platens.

The IR drier in accordance with the invention is operated from a panel having the functions ON, OFF, infinitely variable IR effect 0-100 % , temperature indication measured by a transducer at the stack 11 of sheets 4. The drier 2 is interlocked to the "start printing" function of the press 1, and for "start printing" the IR lamps are turned on, the supply air fan 7 sends a cooling air stream to the IR battery 3, and the exhaust fan 10 is in operation. For "terminate printing" the lamps are extinguished, but the fans keep going for approximately a further two minutes. This enables them to vent off the post operation heat in the battery 3 and conveyor 13. This is kept up in the mentioned order for each printing run. The temperature in the stack is taken about 2 or 3 cms from the uppermost sheet 4, and should be about 35-40 'C where there are inked areas on the sheets. This temperature may depend on the use of different colours and inks, paper weight etc.