FI111398B - Grinder for grinding paper, cardboard or a moving web of a vegetative based fibrous raw material, has rollers or belts having a grinding surface coated with triboelectrically charged particles - Google Patents

Abstract

Grinder has rollers or belts (2,6,10) having a grinding surface in contact with a moving web, and rails (3,7,11) for moving the surface against the web direction and for adjusting the grinding force, the contact length and the web tension. The grinding surface is coated with triboelectrically charged particles having the same charge with the surface of the web. An Independent claim is also included for a process of grinding paper, cardboard or a similar continuous web of a fibrous raw material based on vegetable fibers, comprising conveying the web into a grinding apparatus with at least two grinding means, contacting the web with the grinding means so that the web tension can be adjusted as desired, adjusting the web tension so that a desired grinding force between the grinding means can be obtained, and thermally spraying triboelectrically charged particles on the grinding surface. The particles have the same charge with the surface to be ground.

Description

111398

The present invention relates to a device according to the preamble of claim 1 for grinding a continuous web made of paper, cardboard or against a vegetable fiber based fiber raw material.

The invention also relates to a grinding method according to the preamble of claim 19.

The present invention relates to the treatment of paper and board and similar fiber-based webs, in particular their single or double-sided grinding. In our previous patent applications PCT / FI98 / 00341 and 980044, we have discussed the benefits of paper surface grinding, which can partially or fully replace surface calendering without compromising the strength properties of the paper or board, and without impairing opacity. We have also shown that it is easier to apply different coating layers to the sanded surface and, accordingly, that the coating plastic adheres more easily to the sanded surface than to a normal surface. This is due, among other things, to the removal of the fibrils from the fibers of the web surface resulting in the formation of a very fine lint which increases the adhesion surface of the coating particles. Typical paper and board surface roughness is of the order of 6 microns and can be sanded down to one micron. Because the inner structure of the paper is not compressed, its rigidity and strength properties are retained and in some cases improved by up to 10%.

In principle, grinding can be done in several different ways. Thus, an abrasive belt or an abrasive roll 35 coated with abrasive material or an abrasive stone can be used. These solutions are pure mechanical abrasives. It is also possible to grind 2 111398 different pigments / which are used at the same time or later for coating, for example by wedging the pigments at high speed against the paper web.

5 However, if you want to do a grinding so that the surface of the paper at the same time so-called. calibrating is the tape or roller or grinder the only sensible option. Of these, abrasive roll or abrasive rolls are substantially the most preferred.

A problem with known abrasives is their clogging of wood resins with hemicellulose and possibly lignin combined with fine dust generated during grinding. In general, the abrasive pressure has been difficult to adjust in known devices, whereby excessive surface grinding causes the surface temperature of the web 15 to rise too high, resulting in the aforementioned clogging. Adjusting the grinding pressure is also important to accurately remove only a desired portion of the surface of the web without otherwise damaging the web.

It is an object of the present invention to overcome the drawbacks of the prior art and to provide a novel solution for grinding paper and board webs and the like, fiber-based continuous webs.

The invention is based on the idea that the abrasive pressure can most easily be arranged by tightening the so-called. tensioning rollers, i.e. arranging a different tensioning angle between each sanding roller and the paper, and adjusting the natural tension of the paper in addition. A plurality of rollers or belt sanders 30 in series are still advantageous because calibration of the shape and dimensions of a single grinding member to a perfectly accurate dimension is difficult to achieve, so that subsequent grinding members compensate for the errors of the previous one.

Therefore, the present invention employs a device consisting of a plurality of 3,113,398 deflection members deflected from the straight line of travel of the web, which can be brought into contact with the web. The grinding members are arranged so that they can be moved in the transverse direction of the surface of the web towards the web and away from the web to adjust the tension of the web and thus the strength of its grinding. Preferably, each sanding member removes up to 1.5 microns of material from the web surface on average.

More specifically, the device according to the invention is essentially characterized by what is stated in the characterizing part of claim 1.

The process according to the invention, in turn, is characterized by what is set forth in the characterizing part of claim 24.

The invention provides considerable advantages. This allows the desired amount of material from its surface to be precisely separated from the paper or board web. By adjusting the grinding pressure, the heat build up and clogging of the grinding wheels 20 can be reduced. Controlling the rise of heat can prevent clogging of the sanding surface. The present invention also describes solutions for cleaning abrasive members, which can quickly and efficiently remove material adhering to the abrasive surface, even continuously. The surface of the web is very smooth because the abrasive members naturally remove material at the highest (thicker) points of the web. The smoothing effect is also of a different type than in calendering, where the thicker points of the web are squeezed and the web density at these points increases more than at the thinner points. Fibrillation of the web surface fibers improves the post-sanding coating performance and binds the coating particles to the web by providing a larger bonding surface.

35 The invention will now be more fully understood by reference to the accompanying drawings, with reference to the accompanying drawings.

Figure 1 is a side elevational view of a structure according to a first preferred embodiment of the device according to the invention.

Fig. 2 is also a side elevational view of a structure according to another preferred embodiment of the device according to the invention.

Figure 3 is a side elevational view of the basic structure of a sanding belt solution used as a grinding member.

Figure 4 shows one shape of the surface of the abrasive roll.

Figure 5 shows one embodiment of a device for use as a grinding member.

In the following description, track tension refers to the friction caused by friction formed by a grinding member, for example a roll, and not merely external track tension produced by the track-carrying members.

Figure 1 illustrates a basic embodiment of the invention in which the web 16 is ground in a roll grinder 1-15. The apparatus comprises a track mounted on the frame 1 25, the shafts of the rolls 2, 4, 6, 8, 10 and 12 being mounted on rails 3, 5, 7, 9, 11 and 13, along which the rolls can be moved perpendicularly to and away from the track. The rolls 2, 4, 6, 8, 10 and the longitudinal axes are at least substantially parallel and in a substantially horizontal plane. In the case of Figure 1, the rolls are alternately disposed on opposite sides of the web. By moving the rolls perpendicular to the track, the device and at the same time the track tension can be adjusted. The roller transfer can be accomplished by any known actuator and mechanism such as air or liquid cylinders and electric motors. The direction of movement of the rolls does not have to be perpendicular to the 5111398 track, but the rolls can be displaced e.g.

The path of the track to be processed may deviate from the average straight line described in the example and may be implemented according to the abrasive devices used in the desired manner. The movements of the rollers can also be used to adjust the grinding distance, ie how much the web rotates around the roll shell.

Fig. 2 shows a device solution similar to Fig. 1 if the corresponding parts of the device (track 35, frame 21, track 22 - 33) are provided. Again, the tension of the web can be adjusted by means of rollers.

Instead of the rollers, grinding drums or belt abrasive stations may also be used as grinding members in the apparatus of Figures 1 and 2. According to one embodiment, the grinding members comprise grinding rolls or drums arranged on one side of the web (e.g., 2, 6, 10; 22, 26, 30) and adjusting rollers (4, 8, 12; 24, 28, 32).

Contrary to the solutions shown in the figures, the grinding members of the apparatus may also be implemented by arranging grinding rollers or drums on one side of the web and aligning them with press rolls on the opposite side of the web which are rotatable in the direction of travel of the web. Press rollers can reduce track tension and thus adjust the grinding result.

We have found that the sanding surface of the grinder remains clean under certain conditions and that, under certain conditions, it is blocked by the material being sanded. This is one essential observation of the present device design and the invention. When grinding paper containing wood fibers, this fibrous material always contains resin and resin materials having a softening point or a melting point of between 65 and 75 ° C, depending on the type of wood. When the paper is pulp paper, i.e. containing chemical cellulose, the paper is substantially free of resin and resinous materials, but to some extent lignin, which typically has a glass point of 124 ° C.

5 The above rollers are used to perform grinding without locally exceeding the above temperatures at the grinding site. Thus, one sanding head will remove up to about 1.5 microns of material from the paper or fibrous web per sanding. In other words, when more 10 are to be removed, more grinding heads or grinding rolls respectively have to be used to grind the same side. To further ensure that, for example, the abrasive roller does not overheat, it is preferable to use either internal or external cooling to set the abrasive tool temperature (see below).

15

In the preferred embodiments shown in Figures 1 and 2, two or three rotating rollers are required for grinding one surface of the paper, which can preferably rotate in the opposite direction to the direction of travel of the paper. Their rotational speed 20 can be reversed when the web is driven through a grinder. A direction of rotation parallel to the path of the web may also be used.

For the abrasive apparatus of the invention, it is preferable that the grinding wheel, i.e., the roller, drum or belt, rotates at a high speed relative to the abrasive fiber web, in order to minimize surface pressure and prevent the device from tearing the intact fibers out of the paper. The device should consume and fibrillate the fibers therein into tiny particles. The recovery of these is important and can be used either as a binder or to re-coat the same paper.

The abrasive members have an abrasive powder on their surface, preferably having a particle size of about 10 to 40 microns. As an abrasive, for example, alumina, diamond, tungsten carbide, silicon carbide, silicon nitride, tungsten nitride, boron nitride or boron carbide, chromium oxide, titanium oxide, chromium oxide or silica may be used. . The abrasive powder may be attached to the abrasive surface by electrolytic or thermal spraying, or it may be fixed by gluing into a uniform layer using a resin such as phenolic resin or epoxy resin or mixtures thereof or a suitable rubber mixture. The hollow surface may also be the edge of a roll surface that abracts the curved paper either as a mere suitably shaped sharp 10 edge or by the shape of the edges of the edge. For example, the edges can be made by milling grooves in the roll and then sanding the roll so that the edges of the heels between the grooves remain sharp. Also, densely parallel grooves can be laser-etched on the surface of the roll by the laser, whereby the edges of the burn mark remain jagged. From such a surface, abrasion is obtained by grinding the surface of the roll to calibrate it, leaving a cutting jagged edge.

It is advantageous to cool each roll and blow or suck it away immediately from that part of the abrasive dust which does not get caught in the web being ground. These two alternatives are illustrated in Figures 1 and 2. Fig. 1 illustrates a case in which dust is aspirated under vacuum through vacuum connections 14, 15. Figure 2 illustrates how air can be blown towards the long air roller or drum to cool the surface of the roll and blast away the dust 34. Preferably, the powerful airflow to be blown is guided from the pneumatic tube against the direction of rotation of the roll or drum.

30 The surface of the abrasive roller or drum may be provided with holes which are connected to a vacuum source and through which material to be removed from the abrasive web can be removed. The grinding roller or drum may also advantageously be grooved so that only the ridges between the grooves have the portion roughened by the grinding particles 35 which performs the grinding and the intermediate groove serves as a collection point for the grinding dust. In this way, the abrasive surface does not slip and clog as easily as continuous abrasion. The same groove system also functions as a cooling word. Figure 4 schematically shows one form of a grooved roll. In this solution, the surface of the roll has V-shaped grooves 47, between which there is an abrasive base 48, which may be coated with abrasive material or surface may be machined with an abrasive pattern.

A sanding belt may also be used as a grinding member (see Figure 3).

Preferably, a metal strip 41 coated with abrasive particles is used and rotated on rollers 42-44. To keep the tape clean, it can be adapted to pass at least occasionally in a water bath 46, and an ultrasonic source 45 is connected to the water bath to direct radiation to the tape in the ultrasonic range.

Preferably, the abrasive roll or abrasive tape may be formed by electrolyzing the metallic smooth polished or turned surface using an abrasive member as an anode. With different voltages and electrolyte compositions, a desired pattern can be etched on the surface, the edges of which act as price edges. The electrolysed surface may be tempered or the electrolytic treatment may be applied to the tempered surface.

The electrolytic etching can be done, for example, in the following way. Place the stainless steel in an electrolyte containing 7 g / l of soda and 2.5 g / l of NaOH and apply a distance of 15 mm between the anode and the cathode and a high voltage of 12 V. There was obtained a surface 30 completely covering the original surface, which was filled with holes of 0.1-0.3 mm, which were almost completely hemispherical and completely sharp-edged. In this method, it is essential that the electrolysis voltage is high enough to cause uneven corrosion to occur. The voltage must therefore be higher than that of the uniform 35 electrolytic plating.

9111398

The electrolytically produced abrasive surface is particularly suited to abrasive the paper surface when, due to other abrasive effects or originally due to the properties of the paper, large fibers protrude from its surface, whereby the abrasive surface 5 cuts the fibers like a razor blade and not a sharp edge. Such a surface is particularly advantageous as the last abrasive surface because it effectively smoothes the surface by breaking the fibers protruding from it.

According to the present invention, it can be ensured that the abrasive device cannot become blocked in the following way: As the abrasive surface begins to become obstructed at some point, this place generates more heat than usual and this obstruction site begins to spread and form e.g. obstructing a parallel track; which tends to spread.

This is particularly true for grinding paper or paperboard grades containing wood. Such clogging can be removed by sanding the surface of the roll or tape with a strong light beam in the same way as, for example, US Polycon Indust-20 Ries removes paint from the surface of ships, for example, with powerful Xenon lamp flashes.

The abrasive surface can also be cleaned with a surface containing adhesive, which removes particles from the abrasive surface when the adhesive surface is pressed onto and removed from the abrasive surface. A surprising finding was that the surface formed by the Al 2 O 3 abrasive particles did not per se adhere to the adhesive adhesive (e.g., styrene-butadiene-based adhesive) nor did the adhesive adhere to said abrasive tape.

30

In the case where the abrasive element is a metal abrasive element (e.g. a roller or belt covered with abrasive material), the device may be provided with an inductive heater which enables the abrasive element to be heated. In this case, the device 35 is preferably connected to a pneumatic tube for directing an airflow 10111398 towards the heated abrasive member to remove the loose dust. The metallic surface, or the surface coated with an electrically conductive material such as chromium dioxide or titanium oxide, can be electrolytically cleaned by placing the electrolysis of the abrasive cathode into a cathode, whereby the gas formed by the cathode blows the material accumulated therefrom.

Preferably, a laser beam may be used to monitor the condition of the grinding surface of the grinder. From a normal clean abrasive pin 10, the laser beam is reflected by a typical reflection angle of the abrasive particles to a specific reflection pattern, which depends on the abrasion particle's roughness and quality. As soon as the grinder starts clogging or losing abrasive properties for another reason, the nature and amount of the reflection pattern changes so that it can be immediately detected and corrected, for example, by removing the clogging components from the grinder or by replacing the grinder with another previous one.

20

A fine pigment can be added to the belt or grinding roller during grinding to enhance the grinding and to clean the grinding surface, either continuously or occasionally, which binds the sanding dust to itself and keeps the grinding surfaces clean. A laser or other light source whose reflection is used to monitor the purity of the abrasive surface must be below the wavelength of red light, otherwise a fine surface of 10-30 micron particles will not provide sufficient scattering of control light. Surveillance with a laser beam formed of 30 abrasive particles can only be done when the laser beam has a wavelength less than 20 times the particle size. In this case, the clogged surface and the clean surface give different reflections in the radial direction. In this case, the direction of the beam must be nearly the same as the direction of the grinding surface. The direction of the beam 35 should not deviate from the surface direction by more than 0.5 -3 degrees.

11 111398

In addition to the above, the present invention has other embodiments.

The abrasive material need not necessarily be fixedly bonded to the abrasive surface. Fig. 5 illustrates an arrangement in which a magnetic abrasive is attached to the surface of an endless belt 50 by means of a magnet 49 during a grinding operation. The abrasive may be any sufficiently hard magnetic powder, for example iron, steel, magnetite, cobalt-10, nickel or a mixture of these or other known magnetic materials. The abrasive device comprises said belt, which may be made of metal or polymeric material or other suitable material from which a continuous endless belt can be made. The belt material should not be magnetic in order to completely magnetize it. The passage of the belt 50 is controlled by rollers 51, 52 and a magnet 49 is disposed between the rollers 51, 52 on the inside of the belt loop, a counter roll 53 is disposed opposite the magnet 49 and the treated web 16 is guided through the ground 20 roll 53 by guide rolls 54, 55. The counter roll 53 can be fitted so close to the belt 50 that the web 16 passing through it can be pressed against the belt. The belt 50 can be rotated at a desired speed according to the desired grinding effect, and the belt speed is preferably different from that of the web 25.

The abrasive dust and abrasive are collected in the movement direction of the belt 50 by a magnet-fitted vacuum cleaner 56 connected to a vacuum generating blower 56 which supplies the abrasive and dust to the cyclone separator 58. Instead of the cyclone separator, magnetic separation or other suitable separation may be used. The abrasive is fed back to the belt by a blower 59 along line 60 and dust is removed through line 61. To enhance the abrasive collection, magnet or suitably directed air blowing can be used at the separation point.

12 111398

Grinding force and web tension can be set to a value suitable for grinding, for example, by the following means. First, the grinding force is set by moving the grinding members and the track guiding members (4, 8, 12) in an initial position to form an initial tension in the web, then the final grinding force and track tension are set by conventionally adjusting the track tension. On the other hand, the grinding force can be set by adjusting the track tension by means of the track pulling devices 10, usually by adjusting the track tension to an initial value, after which the final track tension and grinding force are adjusted by adjusting the position of the grinding elements (2, 6, 10). Track tension can be measured with conventional tension measuring devices.

Claims (33)

An apparatus for treating paper, cardboard or a corresponding moving web (16) made of plant-fiber-based raw material, comprising: 5. a frame (1), and - means (2) arranged at the frame (1) , 4, 6, 8, 10, 22. for guiding the movable web (16) along a defined web, characterized by 10 - at least two treatment means (2, 6, 10) comprising a grinding surface which can be arranged against the surface and - means (3, 7, 11) for moving the at least one abrasive surface (2, 6, 10) at least partially in the direction of the surface of the moving web (16) to be moved. is used for adjusting the abrasive strength between the web (16) and the abrasive surface, the contact distance of the abrasive and the web and the web tension. Device according to claim 1, characterized in that it comprises a plurality of abrasive means which deviate from the straight direction of movement of the web and which can be brought into contact with the web and are arranged to move transversely in relation to the surface of the web towards the web and away from the web for government. of the web tension and thereby the abrasive strength directed towards the web. 3. Device according to claim 1, characterized in that the grinding means consist of successively arranged grinding rollers or drums or belt grinding stations. 4. Device according to claim 3, characterized in that the grinding means comprise grinding rolls or drums 5 arranged alternately on both sides of the web. 5. Apparatus according to claim 3, characterized in that the grinding means comprise grinding rolls or drums arranged on one side of the web and control rollers arranged on the opposite side of the web. 6. Apparatus according to claim 3, characterized in that the grinding means comprise grinding rolls or drums arranged on one side of the web and pressing rollers which can be rotated in the direction of movement of the web arranged on the opposite side of the web. Device according to any of claims 3-6, characterized in that at least the abrasive surfaces of the abrasive rolls or drums can be cooled. Apparatus according to any one of the preceding claims, characterized in that the abrasive means can be arranged to be pressed against the web in such a way that the surface temperature of the abrasive means does not exceed a predetermined temperature limit, which, when grinding wood-containing webs, preferably reaches 65 ° C and when grinding cellulose-containing webs preferably at 124 ° C. Device according to any of the preceding claims, characterized by a laser device, whereby a movable laser beam can be directed towards the abrasive surface of the abrasive, and wear and / or obstruction of the abrasive surface can be determined on the basis of changes in the reflection pattern of this beam. Apparatus according to any of the preceding claims, characterized in that the surface of the abrasive means has an abrasive powder which, to its particle size, is up to 10 - 40 microns. 11. Device according to claim 10, characterized in that the abrasive powder is attached to the abrasive surface by electrolytic or thermal spraying, or it is fixed by gluing as a uniform layer of resin, such as phenol resin or epoxy resin or mixtures thereof, as adhesive. -subject. 12. Device according to claim 1, characterized in that the grinding means consists of a roller, the surface of which is formed, for example, by a laser beam (47) in the axial direction of the roller, the edges of the roller forming a grinding edge or a rough cutting edge. Device according to any of the preceding claims, in which a grinding roller or drum is used as grinding means, characterized in that the heels formed on the surface of the grinding roller or drum, which are connected to a source of negative pressure and through which the substance is released from the web being ground can be removed. Device according to any of the preceding claims, in which a grinding roller or drum is used as grinding means, characterized in that the surface of the drum or drum is provided with a groove, the groove is arranged substantially perpendicular to the direction of movement of the web and the shaft of the groove is provided with abrasive particles implanted. in the surface for performing grinding. Apparatus according to any of the preceding claims, in which a grinding roller or drum is used as grinding means, characterized by a compressed air pipe directed to at least one drum or drum and by means of which such a strong stream of air can be blown against the drum or drum. direction of rotation that cools the drum and avio removes the dust that gets stuck to the surface of the drum or drum. Device according to any one of claims 1-11, characterized in that the grinding means is a metal band coated with abrasive articles. Device according to Claim 15, characterized in that the band is at least occasionally arranged to run in a water bath and to the water bath is connected an ultrasonic source, whereby the ultrasonic region can be directed towards the band. Apparatus according to any of the preceding claims, in which the grinding means is made of a grinding device made of metal, characterized by an inductive heater, by means of which the grinding means can be heated, and a compressed air pipe, whereby an air flow can be directed against the heated grinding means for remove the dust that is released during the heating. 19. Apparatus according to any of the preceding claims, characterized by a light source of light, whereby powerful flash light rays can be directed towards the abrasive surface to remove the substance stuck to the abrasive surface. Apparatus according to any one of the preceding claims, characterized in that the abrasive articles are aluminum oxide, diamond, tungsten carbide, silicon carbide, silicon nitride, tungsten nitride, boron nitride, boron carbide, chromium oxide, titanium oxide, a titanium oxide-silica mixed oxide or silica oxide blend oxide. or more of these topics. Device according to any of claims 1-11, characterized in that the abrasive surface is made of metal and treated as an anode in an electrolytic treatment with at least high voltage, that an uneven corrosion of the surface is started. 15 Apparatus according to claim 21, characterized in that at least one abrasive means, in particular the member which performs the last grinding, is constituted by an electrolytically produced abrasive member, the surface of which, like a shaver, cuts off the fibers protruding from the surface being ground. Apparatus according to any of the preceding claims, characterized by at least one abrasive surface comprising conductive material and an electrolysis device, to which the abrasive surface can be arranged as a cathode for cleaning the surface by means of the gas bubbles which are electrically emitted at the cathode. 24. A method of grinding paper, cardboard or a corresponding continuous web made of plant fiber-based raw material, characterized in that the web is guided to a grinding device comprising at least two grinding means, - the grinding means are contacted with the web so that the web tension can be adjusted to 5. the web tension is adjusted so that the abrasive strength between the abrasive means and the web adjusts to the desired level. 25. A method according to claim 24, characterized in that the abrasive means are brought into contact with the surface of the web, which is adjusted to a predetermined tension, and the final web tension is controlled by changing the position of the abrasive means. 26. A method according to claim 24, characterized in that the abrasive means are contacted with the surface of the web, which is adjusted to a predetermined voltage, and the final web tension is controlled by controlling the rotational speed and / or torque of the driving rollers. 27. A method according to claim 24, characterized in that the side of the web to be treated is treated with a plurality of abrasive means and by means of each grinding means 20 the average of 1.5 microns of material is removed from the surface of the web. 28. A method according to claim 27, characterized in that, in order to maintain the abrasive surface, it is fed together with the web to be pigmented, which in itself binds the dust that is released from the web. Process according to claim 28, characterized in that calcium carbonate, talc, kaolin, silica or aluminum or magnesium silicate are fed together with the web. A method according to any of claims 28 or 29, characterized in that the resin and abrasive dust released from the web are bonded by the pigment fed in with the web, and the pigment is fastened e.g. by wetting enyo at the abrasive surface together with abrasive dust or by applying known adhesives in connection with the dust such as water-soluble polymers and / or emulsified polymers. 31. A method according to claim 25, characterized in that the abrasive surface of the abrasive means is cleaned by, on the other hand, directing an air stream, ultrasonic radiation or powerful flash light beams, or by means of a glue band. 15 32. A method according to claim 25, characterized in that the abrasive strength is adjusted by displacement of the abrasive means (2, 6, 10) and the means (4, 8, 12.) which guide the web to the original position, whereby the web receives an initial voltage, after which the The final abrasive strength and web tension are adjusted by means of the devices which drive the web by normally regulating the web tension. 33. A method according to claim 25, characterized in that the abrasive strength is adjusted by regulating the web tension by means of the devices which drive the web by normally regulating the web tension to an initial value, after which the final web tension is controlled by controlling the position of the grinding means (2, 6). , 10) and the means (4, 8, 12) controlling the web.