EP0438410B1 - Drying element - Google Patents

Abstract

In a compact drying element for use in the drying section of a printer, hot blown air is produced in that a heating tube (48) is heated from the outside by an infrared radiator (66) extending parallel to said heating tube. The hot blown air reaches a blower duct (50, 60) extending parallel to the heating tube (48) over a 180° bend (52). A reflector (34, 36) surrounding the heating tube/blower duct unit reflects infrared rays onto the heating tube (48) and delivers the radiation energy it has absorbed to a secondary air current (82, 84), which is mixed into the main hot air current near the outlet of the blower duct (50, 60).

Description

The invention relates to a dryer element for use in a printing press according to the preamble of claim 1, and to a dryer unit constructed from such dryer elements.

A dryer element according to the preamble of claim 1 is known from US-A-2 683 939. For him, the rod-shaped heating element is a conventional heating rod, which is located inside the heating tube and is in direct contact with the blown air to be heated. Such an arrangement is suitable for heating the blown air when no great heat output has to be transferred to the blown air. In the case of very high conveying speed of the printed products, large amounts of very hot blown air are required so that the printed products are reliably dried on a short way before reaching the next printing station.

While warm air dryer elements are preferred for drying water-based paints, such as those used in particular as a clear lacquer over the printing inks, in order to give the surface of the finished product a shine, infrared radiation radiation is preferred for drying conventional offset inks and for drying oil-based paints. Dryer elements use.

It has also already been proposed (see EP-A-0080448) to use a combined radiation / warm air dryer element for drying printed products. In the dryer element described in EP-A-0080448, a plurality of blow strips which follow one another in the conveying direction are predetermined by a zigzag-folded wall, the tips of which face the conveying path and have blown air discharge openings are provided, while infrared heaters are arranged in the spaces between the corrugations. The radiation emitted by the latter partly reaches the surface of the printed products directly, partly it serves to heat the zigzag-shaped corrugated wall on the back with blown air.

Such a combined dryer element is suitable for use with printing inks which respond to both radiation drying and warm air drying. However, if you only want to carry out warm air drying or radiation drying with such a dryer element, as would be advantageous for some applications, this is not possible.

UV radiation dryer elements are also used for special coatings and printing inks that contain prepolymerized plastic materials. UV drying does not require special measures on a larger scale because of the installation of very powerful UV lamps, but also from radiation protection and from the extraction of the ozone generated by the UV rays, so that appropriately equipped printing machines are always combined with UV drying will be busy.

For IR drying and blow air drying, however, a changeover would often make sense if other print jobs are to be processed on a given machine. However, this conversion currently fails because IR dryers and blow air dryers have different space requirements: With IR drying, the printing products can be dried in a very compact space; Conventional blow air dryers, on the other hand, require a lot of space.

The present invention is therefore intended to provide a dryer element which, with a very compact structure, enables the local production of warm blown air in large quantities, so that a blown air dryer unit constructed with it is so compact that a conventional IR dryer can be easily replaced with it .

This object is achieved according to the invention by a dryer element according to claim 1.

In the dryer element according to the invention, a rod-shaped infrared radiator is used to provide a large heat output in a very compact volume. This heat output is first transferred to the blown air by absorption on a heating pipe running parallel to the infrared heater. The blown air to be heated is sent through this. The heating tube is in turn upstream of the blow molding, which emits the heated air.

On the one hand you have an effective intensive heat transfer between the infrared heater and the heating pipe, which you could not achieve by blowing the air directly past the infrared heater. Since the entire heating of the blown air has ended before it enters the blower strip, the same warm blown air also emerges at the various outlet points of the blower strip.

If one were to produce the hot air in a conventional manner by passing the blown air directly past resistance wires, one would have to provide a heating register, which must be installed separately outside the printing press. So you need additional installation space, which is already installed on machines in is usually not available, and you also have additional heat losses on the way from the place of production to the place of use.

Advantageous developments of the invention are specified in the subclaims.

A dryer element, as stated in claim 2, is particularly short overall, since the heating tube and blow bar are kept within the same transverse limits with respect to the direction of conveyance of the printed products.

The development of the invention according to claim 3 is advantageous on the one hand in terms of avoiding eddies in the heating tube. In addition, the convexly curved outer surface of the heating tube ensures that the heat rays striking the heating tube are not reflected back into the infrared radiator, which improves the effective heat flow from the infrared radiator to the heating tube.

It is then possible, according to claim 4, to collect the heat rays running away from the convex outer surface of the heating tube using mechanically simple means and to use them for air heating.

With the development of the invention according to claim 5 it is achieved that those heat rays also reach the surface of the heating tube, which first run past the heating tube starting from the infrared radiator.

According to claim 6, a light funnel leading these rays to the heating tube surface can be accomplished with elements having a circular cross-section that are particularly easy to manufacture.

If you choose the center of the circular reflector and its radius according to claim 7 so that the ends of the two light funnels lying on both sides of the element center plane lie opposite the infrared radiator and taper to a point, a particularly uniform heating of the heating tube is obtained in the circumferential direction.

The development of the invention according to claim 8 is advantageous with regard to the supply of those heat rays to the heating tube which are emitted by the infrared radiator in the half-space remote from the heating tube.

The development of the invention according to claim 9 is advantageous with regard to the supply of large amounts of heat to the heating tube with a compact construction of the dryer element. The electrical installation and maintenance of the dryer element is also simplified by using a twin infrared heater.

To cool the electrical connections and holding devices assigned to the infrared radiator, it is generally necessary to maintain a limited flow of cooling air on the infrared radiator. With the development of the invention according to claim 10, this cooling air flow is obtained very simply and without additional blowers in a mechanically very simple manner in that the reflector is part of a cooling air housing surrounding the infrared radiator, which is coupled in the manner of a water jet pump to the outlet of the blow bar.

As a rule, it is not possible for cost reasons to make the inner surface of the reflector genuinely reflective, for example to polish it and to provide it with a surface layer. A well reflecting surface would be desirable in itself, to bring as much of the heat radiation as possible from the infrared radiator to the outer surface of the heating pipe, where it is then absorbed. However, if a secondary air stream is passed by the reflector and if this secondary air stream, which is warmed up by the reflector, is mixed with the main blown air stream, the amount of heat absorbed by the reflector is also utilized. This side effect is obtained both in the case of a dryer element according to claim 10 and to an increased extent in the case of a dryer element according to claim 11. The secondary air flow is also generated in the dryer element according to claim 11 according to the principle of a water jet pump without an additional fan. The development of the invention according to claim 11 also has the further advantage that the outer housing is already at a low temperature, which is advantageous in terms of accident protection.

The development of the invention according to claim 12 is advantageous in terms of a strong and effective secondary air entrainment effect, since the "water jet pump effect" is better for sharp, fast, small cross-section air jets than for large cross-section, slow air curtains.

A dryer unit as specified in claim 13 can simply be exchanged for an infrared dryer unit provided in the same standard slide-in frame. With short changeover times, this makes it possible to work with one and the same printing press with either infrared drying or blown air drying.

• Figur 1: einen transversalen Querschnitt durch ein Trocknerelement einer Blasluft-Trocknereinheit für eine Offset-Druckmaschine;
• Figur 2: eine Prinzipdarstellung in vergrößertem Maßstabe, anhand welcher die übertragung der Wärme vom Infrarotstrahler zum Heizrohr des Trocknerelementes von Figur 1 erläutert wird;
• Figur 3: eine zu Figur 2 ähnliche Prinzipdarstellung, welche für ein abgewandeltes Trocknerelement gilt; und
• Figur 4: eine Ansicht einer aus Trocknerelementen gemäß Figur 1 aufgebauten Blasluft-Trocknereinheit sowie einer Infrarot-Trocknereinheit, die gleiche Außengeometrie aufweist.

The invention is explained in more detail below on the basis of exemplary embodiments with reference to the drawing. In this show:

• FIG. 1: a transverse cross section through a dryer element of a blown air dryer unit for an offset printing machine;
• Figure 2 is a schematic diagram on an enlarged scale, based on which the transfer of heat from the infrared radiator to the heating tube of the dryer element of Figure 1 is explained;
• FIG. 3: a basic illustration similar to FIG. 2, which applies to a modified dryer element; and
• 4 shows a view of a blown air dryer unit constructed from dryer elements according to FIG. 1 and an infrared dryer unit which has the same external geometry.

FIG. 1 shows a dryer element, generally designated 10, which has an outer housing, generally designated 12. The outer housing 12 is delimited by side walls 14, 16, a bottom wall 18 and a grid 20 which is placed on folded support sections 22 of the side walls 14, 16. The walls 14-18 have a large dimension when viewed perpendicular to the plane of the drawing.

At the bottom left in FIG. 1 of the outer housing 12 there is an elongated discharge duct 24 for warm air, which is delimited by folded wall sections 26, 28 of the side wall 14 and the bottom wall 18.

The side walls 14, 16 carry, via arms 30, 32, reflector walls 34, 36, which together define an inner housing, designated overall by 38. This runs at a distance from Outer housing 12 so that secondary air channels are obtained between the two housings.

As can be seen from FIG. 1, a horizontal bottom section is formed on the reflector wall 36, and the lower ends of the reflector walls 34, 36 essentially end in an extension of the delivery channel 24. Upper wall sections 40, 42 of the reflector walls 34, 36 are arc-shaped. Their free edges delimit a cooling air inlet opening 44 of the inner housing 38, which is at a distance behind the grille 20.

In the inner housing 38, a heating / nozzle unit, designated overall by 46, is provided. This includes a heating pipe 48 running perpendicular to the drawing plane of FIG. 1, a nozzle pipe 50 running parallel and at a distance below the heating pipe 48, and a 180 ° elbow 52 with the same cross section, which smoothes the ends of the heating pipe 48 and nozzle pipe 50 lying behind the drawing plane connects.

The front end of the heating tube 48 in FIG. 1 carries a connecting piece 54 which can be connected to the front of a blower, not shown, e.g. through a flexible hose. The front end of the nozzle tube 50 in FIG. 1 is closed by an end wall 56.

On a surface line, which is aligned with the axis of the discharge channel 24, openings 58 are provided in the peripheral wall of the nozzle tube 50 at intervals, in which nozzle bodies 60 are inserted. These each have a nozzle bore 62 which is aligned with the central plane of the discharge channel 24.

As can be seen from FIG. 1, the nozzle body extends 60 at a distance through the slot 64 delimited by the free edges of the lower ends of the reflector walls 34, 36 up to the start of the discharge channel 24. The nozzle body 60 is thus also at a distance from the left end of the bottom wall 18 and from the lower end of the side wall 14.

In the space lying between the legs of the U-shaped heating / nozzle unit, a twin infrared radiator 66, designated overall by 66, is arranged. This has a transparent housing 68 made of quartz glass, in which two heating coils 70, 72 are accommodated. The infrared radiator 76 extends over the entire length of the heating tube 48 and at a relatively short distance from the lowest point of the heating tube 48.

The half of the outer surface of the housing 68 which is remote from the heating tube 48 is provided with a reflective coating 74, which in practice can be an evaporated gold layer.

The ends of the infrared radiator 66 are held by angle brackets 76, which in turn are screwed to brackets 78 welded to the top of the nozzle tube 50, as shown at 80.

The dryer element described above works as follows:
The air supplied to the nozzle 54 is pressed through the heating tube 48. The heat rays emitted by the infrared radiator 66 are absorbed by the outer surface of the heating tube 48, so that the heating tube 48 as a whole heats up to a high temperature. Heat is emitted from the heating tube 48 to the air pushed through, and the warm air reaches the nozzle tube 50 via the 180 ° elbow 52.

From there, the heated air is discharged through the nozzle body 60 to the discharge channel 24. The heated air is released in the form of sharp jets. Because of the sudden increase in the cross section of the jet at the discharge end of the nozzle body 60, a vacuum is obtained there. As a result, air is drawn through the interior of the inner housing 38, as indicated by arrows 82. In addition, air is drawn in via the secondary air channels, as indicated by the arrows 84.

The reflector walls 34, 36, on which a portion of the radiation emitted by the infrared emitter 66 also falls, are thus surrounded by secondary air on both sides and are thereby cooled. The secondary air preheated in this way, which is drawn in via the grille 20, is mixed in the discharge duct 24 with the very hot air which has flowed through the heating tube 48. A large volume of warm blown air 86 is thus obtained, which emerges from the discharge channel 24 in the form of a curtain and meets, at an angle, a printed printed sheet 88 which moves in the direction of arrow 90. The hot blown air curtain dries layers of paint and varnish on printed sheet 88.

In practice, the infrared radiator 66 can have an output of 3.5 kW and heat an air volume of 60 to 100 m³ of air to about 140 ° C. per hour. Mixing with about half the amount of secondary air then gives blowing air of about 100 ° C., as is desired for drying water-based paints.

The ratio between the radiation power absorbed by the heating tube 48 and the radiation power absorbed by the reflector walls 34, 36 can be specified via the surface properties of these elements:
If the inner surface of the reflector walls 35, 36 is well reflective, the surface of the heating tube 48, on the other hand, absorbs radiation well, so the heat emitted by the infrared radiator 66 largely goes to the air flowing through the heating tube 48. If the reflectivity of the reflector walls 34, 36 deteriorates, an increasing proportion of the radiation power is emitted to the secondary air flow 82, 84 via the reflector walls 34, 36.

FIG. 2 shows, on an enlarged scale, the path of a few selected rays which originate from the heating coil 70. To simplify matters, it is assumed that only a single cylindrical reflector 92 is provided which coaxially surrounds the heating tube 48. With this arrangement it can be seen that rays which emanate from the heating coil 70 at an angle of approximately 45 ° to the vertical are reflected by the surface of the heating tube 48 (assuming incomplete absorption of the rays). Such rays, which after reflection on the inner surface of the reflector 92 then strike the outer surface of the heating tube 48 a second time, bear the reference numerals 94, 96 and 98.

It can be seen that these rays no longer reach the infrared radiator 66 even after reflection on the surface of the heating tube 48.

Rays leaving the heating coil 70 inclined at an angle of more than 45 ° to the vertical, e.g. the beam 100 obviously does not reach the surface of the heating tube 48, but rather is often reflected on the inner surface of the cylindrical reflector 92.

In the case of a cylindrical reflector arrangement surrounding the heating tube 48, part of the power of the infrared radiator 66 is thus already due to the geometry onto the reflector walls 34, 36 transmitted.

In the exemplary embodiment according to FIG. 1, this effect is weakened in that the reflector is cylindrical only above the center line of the heating tube 48 and, on the other hand, is flat below the center line. In this way it is achieved that the rays emitted by the heating coils, which are inclined at more than 45 ° to the vertical, reach the outer surface of the heating tube 48, as is also shown by the ray 100 shown there.

For the same purpose, if a cylindrical reflector is used, the reflector axis can be placed parallel to and at a distance from the heating tube axis, as shown in FIG. 3. There M₁ denote the heating tube axis, M₂ the reflector axis. On both sides of the vertical center line of the dryer element, two crescent-shaped light funnels are obtained, which guide the jet 100 and also a jet 102, which passes straight across the outer surface of the heating tube 48, to the outer surface of the heating tube 48. It can be seen that the rays in between, which represent approximately the same heat output as the rays lying between the vertical and the ray 102, reach approximately the upper half of the heating tube 48 in total. In the arrangement shown in FIG. 3, heating tube 48 is thus heated quite uniformly in the circumferential direction.

FIG. 4 shows a blown air dryer unit, designated overall by 104, with a frame 106 composed of angle profiles, which carries several dryer elements 10.

An infrared dryer unit, designated as a whole by 108, carries a plurality of infrared radiators 66 on an identical frame 106.

It can be seen that the two types of dryer units on a printing press can thus be easily exchanged for one another.

Claims (13)

1. Drying element for use in a printer with a blower duct (50, 60), which distributes hot blown air transversely to the conveying direction of the printed products, with a heating tube (40) located upstream of the blower nozzle (50, 60), with which a rod-shaped heating element for heating the blown air is associated, which extends parallel to the surface of the heating tube (48), characterised in that the heating element is an infra-red radiator (66) and extends outside the heating tube (50, 60) and that the heating tube (48) has a surface absorbing infra-red radiation.
2. Drying element according to Claim 1, characterised in that the blower duct (50, 60) extends parallel to the heating tube (48) and is connected to the latter by way of a 180°-bend (52).
3. Drying element according to Claim 1 or 2, characterised in that the heating tube (48) has a circular cross-section.
4. Drying element according to Claim 3, characterised in that associated with the heating tube (48) is a reflector (34, 36; 92) surrounding it at least partly.
5. Drying element according to Claim 4, characterised in that the distance of the reflector (92) from the heating tube (48) decreases as the distance from the infra-red radiator (66) increases.
6. Drying element according to Claim 5 in conjunction with Claim 3, characterised in that the reflector (92) has a circular cross-section and the reflector axis (M₂ ) extends at a distance from and parallel to the heating tube axis (M₁).
7. Drying element according to Claim 6, characterised in that the inner surface of the reflector (92) is in contact with the heating tune (48) on the surface lying opposite the infra-red radiator (66).
8. Drying element according to one of Claims 1 to 7, characterised in that the infra-red radiator comprises heating coils (70, 72) located in a quartz glass housing (68) and silver-coating (74) is provided on the quartz glass housing in the part remote from the heating tube (48).
9. Drying element according to one of Claims 1 to 8, characterised in that the infra-red radiator (66) is a duplex radiator with two heating coils (70, 72) located at a short distance from each other in comparison with the diameter of the heating tube (48).
10. Drying element according to one of Claims 1 to 9, characterised in that the reflector (34, 36) is part of an internal housing (38), which on a section remote from the infra-red radiator (66) comprises an outlet slot (64), which is connected to a blown air discharge channel (24) and that the internal housing (38) comprises a suction opening (44) for cooling air in a section adjacent the heating tube (48).
11. Drying element according to Claim 9 or 10, characterised by an external housing (12) surrounding the internal housing (38) at a distance, which external housing comprises an inlet (20) for secondary air, which is adjacent to the section of the internal housing (38) on the reflector side, as well as an outlet, adjacent to the blower duct (50, 60), for secondary air heated by the reflector (34, 36).
12. Drying element according to Claim 10 or 11, characterised in that the blower duct (50, 60) comprises separate nozzles (60) following each other at a distance apart.
13. Drying unit for use in a printer, characterised by several drying elements (10) according to one of Claims 1 to 12, which in the same alignment and lying parallel to each other are supported by a standard insertion frame (106), which can be inserted in a guide of a drier frame.

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