Method of Controlling a Powder Sprayer and Printing Press Having a Powder Sprayer

Abstract

A method of controlling a powder sprayer having a fan jet nozzle configuration in a printing press, includes controlling the fan jet nozzle configuration as a function of operating parameters of the printing press. A printing press having a powder sprayer is also provided.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a diagrammatic, longitudinal-sectional view of a complete printing press including a sheet delivery and a powder sprayer disposed therein;

FIG. 2 is a diagrammatic and schematic view of the powder sprayer; and

FIG. 3 is a sectional view of the powder sprayer taken along a line III-III of FIG. 2, in the direction of the arrows and representing a nozzle bar and a nozzle head disposed thereon.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the figures of the drawings in detail and first, particularly, to FIG. 1 thereof, there is seen a printing press 1 including printing units 2 to 5 and a sheet delivery 6. The sheet delivery includes a chain conveyor 7, which deposits printed sheets on a delivery pile 8. Moreover, the printing press 1 includes a reversing device 9, which can be switched from a straight-printing mode, in which only one side of the sheets is printed, to a perfecting mode, in which both sides of the sheets are printed. In the straight-printing mode without sheet reversal, both the printing units 2 and 3 located upstream of the reversing device and the printing units 4 and 5 located downstream of the reversing device print on the front side of the printed sheets. In the perfecting mode, the printed sheets are printed on the front side in the upstream printing units 2 and 3 and on the back side in the downstream printing units 4 and 5. The sheet delivery 6 includes a powder sprayer 10, which powders the printed sheets as they are conveyed past by the chain conveyor 7.

FIG. 2 shows that the powder sprayer includes a nozzle bar 11 that has surrounding jet nozzles or fan jet nozzles 12 disposed thereon. The fan jet nozzles 12 are disposed in a row over the width of the printed sheet. Together, they form a fan jet nozzle configuration 13. The nozzle bar 11 is connected to a first blown-air generator 21, and to a second blown-air generator 22 through a metering device 23. The metering device 23 includes an injector 24, which introduces the powder into the blown air generated by the second blown-air generator 22 to form a powder/air mixture. The blown-air generators 21, 22, which belong to the powder sprayer 10, may be disposed outside the printing press 1 and are controlled by an electronic control unit 25.

FIG. 3 shows that each of the fan jet nozzles 12 is constructed in the form of a nozzle head 14 attached to the nozzle bar 11. Each fan jet nozzle 12 includes an outer fan jet nozzle channel 15, which has a substantially annular cross section, and an inner core jet nozzle channel 16, which is surrounded by the fan jet nozzle channel 15.

The outer fan jet nozzle channel 15 is connected to the first blown-air generator 21 through a supportive-air line 17. The core jet nozzle channel 16 is connected to the second blown-air generator 22 through a powdered-air line 18. The supportive-air line 17 and the powdered-air line 18 are formed of air channels formed in the nozzle bar 11 and of hose or tube lines connected to the nozzle bar 11. The outer fan jet nozzle channel 15 emits a supportive-air fan jet 19 from its opening and the core jet nozzle channel 16 emits a powdered-air core jet 20 from its opening.

In a non-illustrated modified embodiment, the fan jet nozzle configuration is formed of a row of core jet nozzle channels that is disposed between an upstream row of fan jet nozzle channels and a downstream row of fan jet nozzle channels, as viewed in the direction of sheet travel. The core jet nozzle channels emit powdered-air core jets, which are locked in between two blown-air curtains emitted by the two rows of fan jet nozzle channels, to form supportive-air fan jets.

The powder sprayer 10 operates as follows:

The second blown-air generator 22 supplies blown air at a pressure of between 0.5 bar and 1.0 bar to the powdered-air line 18. However, the effect of the second blown-air generator 22 is unavoidably reduced by the injector 24. As a result, the total of the forces, which result from the differentiation of the momentum of the powdered-air core jets 20 as a function of time, only range between 0.1 Newton and 2.0 Newton, preferably between 0.5 Newton and 1.0 Newton. The forces may be measured at the openings of the core jet nozzle channels 16, and their number corresponds to the total number of nozzle heads 14 of the nozzle bar 11. The total of the forces can be said to be the resultant force. The first blown-air generator 21 supplies blown air at a pressure of approximately 0.2 bar to the supportive-air line 17. This pressure is comparatively low, so that a central blown-air supply of the printing press 1 may be used as the first blown-air generator 21. The second blown-air generator 22 may be a compressor that is separate from the central blown-air supply. The total of the forces, which results from a differentiation of the momentum of the supportive-air fan jets 19 as a function of time, ranges between 0.5 Newton and 18.0 Newton, preferably between 2.0 Newton and 6.0 Newton. These forces may be measured at the openings of the fan jet nozzle channels 15, and the number of these forces corresponds to the total number of fan jet nozzles 12 of the nozzle bar 11, which is 24 in the given example.

The momentum of the supportive-air fan jets is not only varied in dependence on the machine speed, the format of the printed sheets, the settings of the delivery, and a powder removal by suction, but also in dependence on the grammage of the printed sheets and on whether the printing press 1 is being operated in the straight-printing mode or in the perfecting mode.

Sheets of higher grammage require a higher supportive-air momentum than sheets of lower grammage. Once the grammage of the printed sheets of the upcoming print job have been input into the electronic control unit 25, the latter automatically adjusts the output of the first blown-air generator 21 in such a way that the blown-air generator 21 generates the air pressure required for the necessary supportive-air momentum in the supportive-air line 17.

A higher supportive-air momentum is needed in the straight-printing mode than in the perfecting mode. Once the mode of operation of the printing press 1 for the upcoming print job has been input at the control unit 25, for example the straight-printing mode, the electronic control unit 25 adjusts the reversing device 9 and the first blown-air generator 21 in a corresponding way.

It is an advantage that the powdered air and the supportive air are supplied from separate sources and that it is not the momentum of both air lines that is increased but only the momentum of the supportive-air line 17. This means that the existing central blown-air supply (first blown-air generator 21) of the printing press 1 can be used to increase the momentum. The momentum of the powdered air generated by the second blown-air generator 22 may be maintained at a constant minimum value. The total momentum of the air required to stabilize the powdered-air jet is primarily generated by the outer supportive air rather than by the inner powdered air. This feature reduces cost and saves construction space. Of course, it is possible to adjust the amount of powder introduced into the printing press, which is also referred to as a characteristic powder curve, in a manner corresponding to the respective effectiveness of the powder application.

Claims

1. A method of controlling a powder sprayer having a fan jet nozzle configuration in a printing press, the method comprising the following steps: controlling the fan jet nozzle configuration as a function of operating parameters of the printing press.

2. The method according to claim 1, wherein the operating parameters are different grammages of printed sheets.

3. The method according to claim 1, wherein the operating parameters are settings of the printing press for perfecting or straight printing.

4. The method according to claim 1, which further comprises varying an emission speed of supportive-air fan jets of the fan jet nozzle configuration as a function of the operating parameters.

5. The method according to claim 4, which further comprises maintaining unchanged an emission speed of powdered-air core jets of the fan jet nozzle configuration when the emission speed of the supportive-air fan jets varies.

6. The method according to claim 1, which further comprises: selecting the operating parameters as different printed sheet grammages;varying an emission speed of supportive-air fan jets of the fan jet nozzle configuration as a function of the printed sheet grammages; andincreasing the emission speed of the supportive-air fan jets when the printing press is switched from processing printed sheets of lower grammage to processing printed sheets of higher grammage.

7. The method according to claim 1, which further comprises: selecting the operating parameters as settings of the printing press for perfecting or straight printing;varying an emission speed of supportive-air fan jets of the fan jet nozzle configuration as a function of the settings; andincreasing the emission speed of the supportive-air fan jets when the printing press is switched from a perfecting mode to a straight-printing mode.

8. The method according to claim 6, which further comprises maintaining unchanged an emission speed of powdered-air core jets of the fan jet nozzle configuration when the emission speed of the supportive-air fan jets is increased.

9. The method according to claim 7, which further comprises maintaining unchanged an emission speed of powdered-air core jets of the fan jet nozzle configuration when the emission speed of the supportive-air fan jets is increased.

10. The method according to claim 5, which further comprises generating the supportive-air fan jets with a first blown-air generator and generating the powdered-air core jets with a second blown-air generator.

11. The method according to claim 8, which further comprises generating the supportive-air fan jets with a first blown-air generator and generating the powdered-air core jets with a second blown-air generator.

12. The method according to claim 9, which further comprises generating the supportive-air fan jets with a first blown-air generator and generating the powdered-air core jets with a second blown-air generator.

13. A printing press, comprising: a powder sprayer having a fan jet nozzle configuration; anda control unit for controlling said fan jet nozzle configuration in dependence on operating parameters of the printing press.