Device for cooling a web of material coming out of a drier

Abstract: A cooling device (6) for cooling a web of material (3) coming out of a drier (1), in particular a paper web of an offset printing machine coming out of a drier, which cooling device comprises a substantially closed housing with an inlet slit (5) and an outlet slit (7) for the web of material, said housing being provided at the outlet slit side with a feed aperture (10) for feeding in outside air and at the inlet slit side with a discharge aperture (11, 12) for discharging air from the housing, the air being fed through the housing in counterflow to the direction of movement of the web of material, wherein the housing in the direction of movement of the web of material is provided with two or more cooling units (8, 9) placed in series which bring the infed air successively into contact with the web of material.

Description: The invention relates to a device for cooling a web of material, in particular a paper web of an offset printing machine coming out of a drier, the device comprising: a substantially closed housing with an inlet slit for inlet of the web of material to the housing from the drier through the inlet slit, and with an outlet slit for outlet of the web of material from the housing through the outlet slit; a feed aperture at the outlet slit side of the housing for feeding in outside air into the housing; a discharge aperture at the inlet slit side of the housing for discharging air from the housing; at least one partition in the interior of the housing, the or each partition being placed for dividing the housing into a first compartment toward the outlet slit side of the housing and a second compartment toward the inlet slit side of the housing, each partition having a passage slit for passage of the web of material from the second to the first compartments, and having a passage aperturure for conveying air through the partition from the first to the second compartments in a direction counter to the direction of movement of the web of material; each compartment containing a cooling unit for bringing the air fed into the compartment into contact with the web of material, each cooling unit comprising a fan for circulating air in the corresponding compartment. A similar device, used as a drier, is known from EP-A-0 177 774. In an offset printing machine in particular, the paper web is heated up in the drier, so that the printing ink applied to the paper web evaporates. On leaving the drier, the paper web is conveyed over cooling rollers and is then reeled. When the paper web leaves the drier it is at a temperature of, for example, 130°C, at which temperature some further evaporation still takes place, and the boundary layer of the paper web still contains oil-containing vapours. These vapours surrounding the paper web condense on the cooling rollers, on which a film can form that after some time becomes so thick that the ink soils the paper web and stains thus occur through smearing of the ink. In order to prevent this, the printing machine must always be stopped after some time has elapsed, in order to clean the cooling rollers. In the past, attempts were made to solve this problem by blowing cold air on the web of material at the outlet of the drier, with the object of blowing away the boundary layer before it reaches the cooling roller. Another solution to the problem is cleaning the cooling rollers during operation, for example by means of a cleaning roller. None of these existing solutions has, however, produced the desired result in practice. The object of the invention is then to produce a device for cooling a web of material coming out of a drier, in which the temperature of the web is reduced in such a way that virtually no further evaporation occurs when the web of material arrives at the cooling rollers. This object is achieved by the invention as described in the characterizing portion of claim 1. In this way ambient air at about 20°C is used for cooling the web of material. Due to the fact that the infed cooling air flows counter to the direction of movement of the web of material, the cooling air is heated up and will consequently be able to absorb an increasing quantity of the solvent coming from the web of material. The air thus heated up and discharged from the housing can particularly expediently be fed into the drier. Driers generally require a supply of fresh air which serves as combustion air for the burners present in the drier and to compensate for the flue gases discharged, so that a certain partial vacuum is maintained in the drier. When outside air at ambient temperature is fed into the warm interior of the drier, there is always the risk of condensation forming, in the form of mist which can settle on the fixed parts of the drier and can give rise to pollution. Using air which is already heated prevents the risk of condensation in the drier and also increases the energy efficiency of the drier. According to the invention, each unit for bringing air into contact with the web of material comprises a fan whose outlet side is coupled to a group of spray nozzles situated on either side of the web of material. Alternatively, each unit for bringing air into contact with the web of material comprises two or more fans, whose outlet sides are coupled to a group of spray nozzles situated on one side of the web of material. The construction of the cooling device effects that the outside air enters the cooling device at the side where the web of material leaves the cooling device. The incoming air mixes with the atmosphere present in the cooling device and is drawn in by the fan of the unit which is adjacent to the outlet slit of the cooling device, which unit sprays the mixture through the spray nozzles onto the web. The air leaving this unit is then drawn in by the fan of the adjacent unit, so that the temperature of the air sprayed onto the material web increases in the direction counter to the direction of movement of the web of material. Due to the fact that the outside air is first mixed with the atmosphere present in the cooling device, this outside air is slightly preheated, so that the spray nozzles do not cool down to such an extent that condensation settles on them. In order to make good use of the heat drawn from the web of material, according to the invention the discharge aperture is connected to the interior of the drier. The invention will be explained in greater detail with reference to the drawing which shows an embodiment of the invention in a single figure. The drawing shows a schematically indicated drier 1 which can be of any suitable type, into which a web of material 3 is fed through an inlet slit 2. The web of material moves in the direction of the arrow 4, and leaves the drier 1 at the outlet slit 5. Connected to the drier 1 is a cooling device 6, which in the present case is fixed to the drier, so that the outlet slit 5 of the drier coincides with the inlet slit of the cooling device. The web of material leaves the cooling device through an outlet slit 7. The cooling device contains two units 8 and 9 which are adjacent to each other, viewed in the direction of movement of the web of material, and each of which comprises a group of spray nozzles lying on either side of the web of material and a fan connected thereto. The two units are separated from each other by means of a partition 13, which divides the interior of the cooling device 6 into two compartments 14, 15. The partition 13 has a slit-shaped aperture for the passage of the web of material 3 and an aperture 16 for the passage of air from the compartment 14 to the compartment 15. The suction nozzle of the fan of the unit 8 in the compartment 15 is placed in such a way that air is drawn in both from the compartment 14 and from the compartment 15. This is indicated schematically in the drawing by having the suction nozzle of the fan of the unit 8 open partially into the compartment 14. As is usual in driers, the web of material is conveyed in the cooling device floating between the spray nozzles. At the side of the outlet slit 7 the housing of the cooling device is provided with a feed aperture 10 for feeding in outside air, while at the opposite side of the cooling device discharge apertures 11 and 12 are provided for discharging air form the cooling device. The operation of the cooling device shall now be described. The web of material 3, which can be, for example, a paper web printed by an offset printing machine, is fed into the drier 1, which is not a part of the invention and will not be described in detail here. What is important, however, is that the paper web leaves the drier 1 at a temperature of, for example, 130°C. The paper web then passes through the cooling device 6, and leaves the cooling device at a temperature of, for example, 90°C, following which the web is guided over cooling rollers (not shown) and is then reeled. The object of the cooling device is in the first place to lower the temperature of the paper web from, for example, 130°C to, for example, 90°C, at which temperature the rate of evaporation is so low that little or no further condensation takes place at the cooling rollers. The outside air is admitted to the cooling device through the aperture 10, and this air mixes to some extent with the atmosphere in the compartment 14 before being drawn in by the fan of the unit 9. The outside air thus heated is sprayed through the spray nozzles of the unit 9 on either side onto the paper web 3. The air coming out of the spray nozzles is then partially drawn in by the fan of the unit 8 and mixed with the air present in the compartment 15, and is subsequently sprayed through the spray nozzles of said unit on either side against the paper web 3. The air coming out of the spray nozzles of the unit 8 is then partially discharged through the apertures 11 and 12. It will be clear that the temperature of the air sprayed by the unit 9 onto the paper web is lower than the temperature of the air sprayed by the unit 8 onto the web. In fact, the air admitted through the aperture 10 is heated up in counterflow to the direction of movement of the web. In the example shown the web is cooled in two stages, but it will be clear to the expert that the number of stages can be increased as desired by fitting a larger number of units in different compartments adjacent to each other in the cooling device. The air discharged from the cooling device through the apertures 11 and 12 can advantageously be used as feed air for the drier. This has the advantage for the drier that this air heated up to, for example, 70°C,cannot cause any condensation problems inside the drier. Besides, the energy efficiency of the drier is increased due to the fact that a part of the heat stored in the web material is fed back to the drier. The quantity of outside air admitted to the cooling device through the apertures 10 is regulated by a valve 17 disposed in said aperture, in such a way that a constant partial vacuum is maintained in the cooling device. A further advantage of the cooling device according to the invention is that an after-drying effect also occurs in this cooling device, which means that the actual drier can be made smaller in dimensions.

Claims: Cooling device (6) for a web of material (3), in particular a paper web of an offset printing machine coming out of a drier (1), the device comprising: a substantially closed housing with an inlet slit (5) for inlet of the web of material (3) to the housing from the drier (1) through the inlet slit (5), and with an outlet slit (7) for outlet of the web of material (3) from the housing through the outlet slit (7); a feed aperture (10) at the outlet slit side of the housing for feeding in outside air into the housing; a discharge aperture (11, 12) at the inlet slit side of the housing for discharging air from the housing; at least one partition (13) in the interior of the housing, the or each partition (13) being placed for dividing the housing into a first compartment (14) toward the outlet slit side of the housing and a second compartment (15) toward the inlet slit side of the housing, each partition (13) having a passage slit for passage of the web of material (3) from the second to the first compartments, and having a passage aperture (16) for conveying air through the partition (13) from the first to the second compartments in a direction counter to the direction of movement of the web of material (3); each compartment containing a cooling unit for bringing the air fed into the compartment into contact with the web of material (3), each cooling unit (8, 9) comprising a fan for circulating air in the corresponding compartment (15, 14); characterized in that the fan in the second compartment (15) is positioned such and has an inlet that is positioned such that air is partly drawn in from the first compartment (14) through the passage aperture (16), and that the fan in the first compartment (14) at the outlet slit side of the housing is positioned such and has an inlet that is positioned such that air is partly drawn in through the feed aperture (10) for feeding in outside air into the housing, each cooling unit (8, 9) comprising spray nozzles situated at either side of the web of material (3) for cooling the web of material floating between the spray nozzles. Device according to claim 1, characterized in that each cooling unit (8, 9) comprises a fan whose outlet side is coupled to a group of spray nozzles situated on either side of the web of material (3). Device according to claim 1, characterized in that each cooling unit (8, 9) comprises two or more fans whose outlet sides are coupled to a group of spray nozzles situated on one side of the web of material (3). Device according to claims 1-3, characterized in that the discharge aperture (11, 12) for discharging the air from the housing is connected to the interior of the drier (1). Device according to any of claims 1-4, characterized in that the housing of the cooling device (6) is directly connected to the outlet side of the drier (1). Device according to any of claims 1-5, characterized in that the feed aperture (10) for feeding in outside air into the housing is provided with a controllable valve (17) in order to maintain a constant partial vacuum inside the housing.

Inventors: DE VROOME CLEMENS JOHANNES MAR, JACOBS THOMAS GERARDUS MARIA, DE VROOME, CLEMENS JOHANNES MARIA, JACOBS, THOMAS GERARDUS MARIA
Applicants: HEIDELBERG CONTIWEB BV, HEIDELBERG CONTIWEB B.V.
Application year: 1990
Main classification: B41F23
IPC codes: B41F23, F26B13