Probe for removing dust from moving webs
BACKGROUND OF THE INVENTION 
     The invention concerns a dust-removal probe as recited in the preamble to the major claim. 
     The problem of removing the dust from webs of paper with probes has not as yet been satisfactorily solved. 
     SUMMARY OF THE INVENTION 
     The object of the invention is accordingly to improve the generic dust-removal probe to the extent that dust can be removed more effectively. 
     This object is attained in accordance with the invention in a generic probe as recited in the preamble to the major claim by the characteristics recited in the body thereof. 
     A rapidly moving web, of paper for example, entrains air as it moves more rapidly. The air travels parallel with the web. The result is a laminar flow at approximately the same speed as the web and in the immediate vicinity of hundredths of a millimeter above it that decreases linearly with its distance from the web. The blast of air emerging from the blower acts against the moving web and entrains the almost laminar flow of air traveling parallel with the web. The dust that moves within the flow whirls up along with the dust that does not adhere very tightly and is forced toward the vacuum channel. The vacuum in the vacuum channel is powerful enough to suction up the whirling dust. The high-voltage electrode inside the probe discharges both the web and the particles of dust, allowing the blower to detach them and the vacuum channel to suction them in more easily. 
     The high-voltage electrode and the blower are oriented such that their planes intersect at a line that lies precisely on the web, and the discharging is accordingly optimal along that line. The air also acts like a doctor along the line, detaching the particles of dust. Orienting the vacuum channel down near the web, against the direction that the web travels in, and parallel with the blast emitted by the blower also helps to ensure that the whirling particles of dust can be suctioned up without any problems. The orientation of the flow into the openings into the vacuum channel, which lie within a fourth plane at an acute angle to the web, also contributes to attaining the objective. 
     Furthermore, a metal field plate is preferably mounted on the other side of the web from the probe and connected to a high-voltage generator with variable voltage and frequency. The resulting alternating field eliminates the forces between the particles of dust and the web. The rate of flow of the air employed for blasting and suction can also be adjusted in accordance with the speed of the web. 
     Further practical embodiments and developments of the invention are recited in the subsidiary claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     A sectional view of the probe in accordance with the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Between a probe 5 and a metal field plate 6 is a web 7, preferably of paper, that moves rapidly in the direction indicated by arrow 8. 
     Dust-removal probe 55 has a recess 9 that is trapezoidal as viewed in section parallel with web-travel direction 8. At its smaller base is a high-voltage electrode 10 in the form of a number of pointed subsidiary electrodes 20 arrayed in a line or of a single continuous blade-shaped electrode. Electrode 10 lies in a plane 21 perpendicular to web-travel direction 8. At the downstream end of probe 5 is a blower 11 with round or slotted nozzles 12 that lie in another plane 22. Both planes 21 and 22 intersect at a line 23 that lies in web 7, preferably at a right angle to web-travel direction 8. 
     At the upstream end of the probe is a vacuum channel 13 with round or slotted openings 14. The direction of flow into openings 14 lies in a fourth plane 24, which extends at an acute angle to web-travel direction 8. 
     The nozzles 12 in blower 11 and the openings 14 into vacuum channel 13 are positioned in the vicinity of the sides of trapezoidal recess 9 near its larger base. 
     Both upstream and downstream of trapezoidal recess 9, probe 5 has a ground electrode 15 and 16. Electrodes 15 and 16 are positioned on the bottom of probe 5 facing web 7 and extend over the total width of the probe. The electrodes 15,16 can consist of a number of pointed and/or blade-shaped subsidiary electrodes extending across and preferably at a right angle to web-travel direction 8 over the total width of the probe and hence of the web. 
     Field plate 6, which parallels web 7, is connected to a source of alternating current and can be activated at between 0 and 10 kV and between 0 and 10 kHz. High-voltage electrode 10 is also connected to a positive and negative source of direct or alternating voltage that can also be individually set. 
     The voltages and the rate of flow of the air emerging from blower 11, and the vacuum in channel 13 can all be varied by elements 25,26,27, respectively in accordance with the speed of web 7. 
     The blower can have an additional row of nozzles 29 lying in a plane 28 also intersecting the line 23.