GB2252153A

GB2252153A - Removing dust from webs

Info

Publication number: GB2252153A
Application number: GB9201495A
Authority: GB
Inventors: Johann Schlittenbauer; Max Eder; Wilhelm Bezler
Original assignee: MAN Roland Druckmaschinen AG
Current assignee: Manroland AG
Priority date: 1991-01-26
Filing date: 1992-01-24
Publication date: 1992-07-29
Also published as: ITRM920016A1; DE4102276C1; ITRM920016A0; GB9201495D0; IT1254122B; FR2671989A1

Description

1 2252153 Removal of dust from lenqths of material The invention relates

to a device for the removal of the dust from moving lengths of material, preferably from paper, which device has at least one high-voltage electrode for neutralising electrostatic charges on the length of material.

Because of friction and various electrochemical potentials charges flow from one surface to the other at the point of contact of a length of material with the guide rollers guiding it. The length of material is therefore charged electrostatically forming an electric field. Neutral dust particles are polarised in these electric fields, attracted and deposited.

Devices are known which by means of a blast nozzle and a brush rotating against the direction of motion of the web of material remove the dust from the web.

These brushes, however, have an abrasive effect on the material and are themselves subject to wear reducing the cleaning performance.

A device of the type mentioned in the introduction is disclosed in European Patent Specification No. 0 245

526 for removing dust from moving webs of material, in which inside a probe arranged above the web there is provided a high-voltage electrode for neutralising the electric field which emanates from the excess charges on the length of material. In this way the dust sticking to the web is loosened more easily. The dust is whirled up by applying an air jet to the web and carried off into a suction channel. The blast nozzle and the suction channel are also located inside the probe.

With web speeds of the order of 15 metres per second experience has shown that dust particles sticking more firmly to the length of material cannot be removed reliably by means of a device as described in EP 245 526, since the kinetic energy of the air 1 loosening the dust particles from the track cannot be increased to an arbitrary degree, or at least not economically. Moreover moisture is extracted from the length of material by the air-blasting, through which 5 it becomes brittle.

The present invention therefore aims at a high degree of efficiency when removing dust from lengths of material, at the same time avoiding an abrasive or other mechanical or chemical loads on the length of material.

According to the invention there is provided a device for the removal of dust from moving webs of material, comprising: a high-voltage electrode for neutralising electrostatic charges on the web; an auxiliary web guided over at least a part of its length substantially parallel to the web, the auxiliary web being able to be charged electrostatically; a further high-voltage electrode adapted to charge the auxiliary web for generating an electric field between the material web and the auxiliary web; and a means for removing the dust transferred from the material web to the auxiliary web.

In embodiments of the invention the auxiliary web is preferably of plastics. Further,at least one plastics web is provided which is able to be charged electrostatically by means of at least one further high-voltage electrode, which may be guided by means of guide rollers at least partially parallel to and close to one or both surfaces of the length of material. A suction apparatus is preferably provided for loosening the dust particles from the plastics web. By the provision of the generally parallel section of auxiliary web a longer distance is created over which dust can be removed from the length of material. Moreover possible mechanical or chemical material stress due to blasting or suction is transferred to the 1 harder-wearing plastics web.

Further optional features and advantages of the invention can be found in the subclaims. For further explanation of the invention two embodiments will now be described with the aid of the drawings, in which:

Figure 1 shows a section through a first embodiment, and Figure 2 shows a section through a part of a sec ond embodiment.

Figure 1 shows a length of material 1, e.g. a paper web, which is supplied by way of a guide roller 2, and drawn away by way of a further guide roller 3. Directly downstream of the guide roller 2 on the lower and upper surface of the length of material 1 there is in each case a high-voltage electrode 4 of axial configuration, which extends in the vicinity of its surface over the whole width of the length of material 1. Between the guide rollers 2,3 an auxiliary web in the form of a driven continuous plastics web 5 is guided by means of guide rollers 7,8 parallel to the material web, across its lower surface, over its whole width and in the direction of travel; the auxiliary web 5 is then guided back by way of a further guide roller 9. Analogously to the plastics web 5 a further driven continuous plastics web 6 is guided in parallel along the upper side, across the width of the web 1, by means of guide rollers 10, 11 and back by way of further guide roller 12. The path of each plastics web 5, 6 forms a triangle, one side of which extends parallel and one side perpendicular to the direction of travel of the length of material 1.

The guide rollers 7, 8, 9 of the plastics web 5 and the guide rollers 10, 11, 12 of the plastics web 6 are pivoted in a frame 13, 14. The frames 13, 14 are each mounted in a known manner on a linear guide, shown for reasons of clarity only for the frame 13. Each guide has a threaded nut 15 secured to the frame 13, 14, a threaded spindle 16 engaging the nut and a drive motor 17, in a manner allowing the plastics web 5, 6 to be applied to the length of material 1 or retracted for the purpose of maintenance or exchange of a plastics web 5 or 6.

A suction unit 18, 19 extending over the whole width of the plastics web and secured in the frame 13, 14 is allocated to each plastics web 5,6 downstream of the section parallel to the length of material 1. The suction unit 18, 19 for removing an electrostatic charge from the plastics web 5, 6 substantially consists of a high-voltage electrode 36, 37, a blast nozzle 38, 39 and a suction channel 40, 41. Connected to the suction channel 40, 41 there is a suction pump assisting air conveyance of the dust.

Each plastics web 5, 6 has arranged upstream of the guide roller 7, 10 a further high-voltage electrode 20, 21 of axial configuration, which extends over the whole width of the plastics web 5,6 and is also secured in the frame 13, 14. Figure 2 shows a special embodiment of a suction unit associated with a continuous plastics web 22. As with the embodiment of Figure 1 a driven continuous 25 plastics web 22 is led by means of guide rollers 23, 24 parallel to a length of material, and back by way of a guide roller 25. The guide rollers 23, 24, 25 are rotatably mounted in a frame 26 which is able to be applied to or retracted from the length of material. A high-voltage electrode 27 secured in the frame 26 and extending near the surface of the plastics web 22 over its full width of the guide roller 23. Arranged directly after the guide roller 24 there is also a high-voltage electrode 28 secured in the frame 26 and extending over its whole width. Along the following section 33 of the plastics web 22, between the guide 1 rollers 24 and 25, several, in the present case three, metallic field plates 29, 30, 31 extending over the whole width of the plastics web 22 are mounted in the frame 26 and individually connected to a high-voltage generator. In the same section 33 of the plastics web 22 a suction channel 31 is applied to the plastics web 22 after the field plates 29, 30, 31 in such a manner that its funnel 34 partially surrounds the last field plate 31 without contact. The suction channel 32 is connected to a suction pump assisting air removal.

In operation the moving length of material 1, electrically charged by friction, is guided between the high-voltage electrodes 4 arranged above and below it.

The high-voltage electrodes 4 are designed in this embodiment as ionising rods and in each case are connected to a high-voltage generator with variable frequency. A high alternating voltage applied to the ionising rods generates positive and negative ions. An advantage of this high-voltage ionisation consists in that following the sine curve of the alternating voltage dipolar ions and parts are generated at the same time in equal amounts. Therefore irrespective of the polarity sign of the electrostatic charges present the opposing potential is constantly available for balancing, i.e. for the neutralisation of the electrostatically charged length of material 1. The electric forces between the polarised dust particles and the length of material are thus lifted. It is known that with an ionising rod operating speeds of a length of material 1 of up to 1.5 metres per second can be handled. With higher working speeds several ionising rods must be mounted in parallel next to each other.

once the length of material 1 is neutralised and the dust particles are thus able to be loosened easily, it travels between the parallel guided plastics webs 5 1 and 6. The plastics webs 5, 6 are also charged electrostatically, on the one hand by friction on the guide rollers 7, 8, 9, and 10, 11, 12 and on the other by means of the high-voltage electrodes 20, 21. The high- voltage electrodes 20, 21 are also formed as ionising rods, which, however, are connected to a DC voltage. Advantageously the polarity of the voltage applied for charging the plastics auxiliary webs 5, 6 is selected so that it corresponds to the polarising direction of the length of material 1 before neutralisation. This means that the electric field building up between the plastics webs 5, 6 and the length of material 1 is directed so that it opposes the renewed polarising of the length of material by frictional electricity on the guide roller 3. The dust particles on the length of material are attracted in the electric field by the plastics web 5 or 6 and deposited on it. In order not to swirl the air entrained by the length of material 1, which moves parallel to the length of material 1, and not to counteract the attraction and depositing of the dust particles on the plastics webs 5, 6, the plastics webs 5, 6 are preferably driven in the same direction as the length of material 1. With the measures outlined and the comparatively long stretch of the length of material 1 determined by the parallel section of the plastics webs 5,6 a complete loosening of the dust particles from the length of material 1 may be achieved. 30 Each dust-laden plastics web 5, 6 is led past the suction unit 18 or 19 after the guide roller 8 or 12, separating in a known manner the dust from the plastics web 5 or 6. In this way, by means of voltage action, the plastics web 5 or 6 and the dust particles are neutralised, so that a simpler loosening and suction is possible. The high degree of efficiency for the 1 removal of dust required with the length of material 1 is not necessary here.

In the special design of the suction unit 35 according to Figure 2 the plastics web 22, pre-charged by means of the high-voltage electrode 27, designed as an ionising rod, is guided, after removing the dust from a parallel length of material 1, by way of the guide roller 24 past a further high-voltage electrode 28, designed as an ionising rod, and neutralised again.

The field plates 29, 30, 31 following generate an electric field in order to pull off the dust particles from the plastics web 22. Through a determined time sequence of the switching-in of the field plates 29, 30, 31 the loosened dust arrives in the'funnel 34. The loosening of the dust from the plastics web 22 and the further transportation into the funnel 34 can be assisted by blasting the dust by means of a blast nozzle (not shown). From the funnel 34 the dust is removed by way of the suction channel 32. The 20 switching-in of the field plates 29, 30, 31 is carried out in the following sequence. At a point in time Tl the field plate 29 is acted upon by a direct current voltage. At T2 the field plate 30 is connected and at T3 the field plate 29 is disconnected again. At T4 the field plate 31 is connected. In the period between T3 and T4 the dust on field plate 29 can be drawn off to the field plate 30. At T5 the field plate 30 is disconnected and the field plate 29 is connected again so that in the period between T4 and T5 the dust on field plate 30 is drawn off to field plate 31. At the next point in time the field plate 31 is disconnected again, so that the dust on field plate 31 can be sucked up through the funnel 34 and the sequence of the switching-in of the field plates 29, 30, 31 can recommence.

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Claims

1. A device for the removal of dust from moving webs of material, comprising:

a high-voltage electrode for neutralising electrostatic charges on the web of material, an auxiliary web guided over at least a part of its length and parallel to the material web, the auxiliary web being able to be charged electrostatically; a further high-voltage electrode adapted to charge the auxiliary web for generating an electric field between the material web and the auxiliary web, and a means for removing the dust transferred from the material web to the auxiliary web.

2. A device according to claim 1, in which one or more of the high-voltage electrodes are designed as ionising rods.

3. A device according to claim 1 or 2, in which the auxiliary web is made of plastics material.

4. A device according to any preceding claim, in which the auxiliary web is guided by means of rollers.

5. A device according to claim 4, in that the guide rollers for the auxiliary web are mounted in a frame, which is able to be applied to or retracted from the material web.

6. A device according to any preceding claim, in which the frame, seen in the direction transverse to the material web, has the form of a rightangled triangle, the right angle being formed where the auxiliary web leaves the material web.

7. A device according to any preceding claim, in which the dust removal means includes a suction unit.

8. A device according to claim 7, in which the suction unit is constructed as a probe, which contains a further high-voltage electrode, a jet channel and a suction channel, these parts extending over the whole 1 -g- width of the auxiliary web.

9. A device according to claim 7, in which the suction unit has a further high-voltage electrode designed as an ionising rod for neutralising the auxiliary web, several individually switchable field plates along the auxiliary web and a suction channel, the suction channel being arranged downstream of the field plates.

10. A device substantially as described herein 10 with reference to Fig. 1 or Fig. 2.

11. A method for removing dust from a web of material using a device as claimed in any preceding claim, in which the said material is paper.