Classifications

• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21G—CALENDERS; ACCESSORIES FOR PAPER-MAKING MACHINES
  • D21G3/00—Doctors
  • D21G3/005—Doctor knifes
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21G—CALENDERS; ACCESSORIES FOR PAPER-MAKING MACHINES
  • D21G9/00—Other accessories for paper-making machines
  • D21G9/0063—Devices for threading a web tail through a paper-making machine

Definitions

• the present invention relates to paper and board machines. More specifically, the present invention relates to a doctor according to the preamble of claim 1.
• a rotating roll, a drying cylinder or a reeling drum of a paper or board machine can be provided with a doctor.
• the purpose of the doctor is to prevent the web from wrapping around the roll or the cylinder/drum during a web break and to help tail threading.
• a further purpose of the doctor is to keep the roll or cylinder surface clean.
• doctors Regard their operation principle: a contacting doctor in which the doctor blade of the doctor extending across the entire width of the roll or the cylinder is placed against the outer surface of the roll or the cylinder, or a non-contacting doctor in which the doctor blade of the doctor is at a small distance, usually at a distance of a few millimeters, from the outer surface of the roll or the cylinder, so that air is blown into a gap between the tip of the doctor blade of the doctor and the outer surface of the roll from the trailing side of the doctor blade of the doctor to prevent the web from travelling with the roll or the cylinder.
• the present invention relates to a contacting doctor, which is called a doctor in the following.
• the grip of the doctor blade is not sufficient, the grip is uneven, to improve the grip it is necessary to increase pressure excessively, which causes that the moment of the cylinder or the roll need be increased. If the grip of the doctor blade does not suffice or is uneven, it may lead to the fact that the web gets between the blade and the cylinder or the roll. This situation is non- desirable and a malfunction of the device. The blade of the doctor may be broken when the web gets between the blade of the doctor and the cylinder or the roll. Also, the web cannot be passed to the pulping of broke in a desired and controlled manner.
• An object of the invention is to provide a doctor in which the problems and drawbacks of the arrangement known from the prior art are eliminated or at least minimized.
• the doctor for a paper or board machine according to the invention is mainly characterized by what is stated in the characterizing part of claim 1.
• a blow-down device is arranged in connection with the contacting doctor for separating and pulling the web from the doctor using a downwardly directed air jet, and the air jet separates the web from the doctor surface and prevents the web from hitting the doctor blade of the doctor.
• the pull-down blow in accordance with the invention is accomplished as extending substantially across the full width of the web.
• the doctor thus comprises a pull-down blow function of substantially the width of the web, whose aim is to keep the web separated from the doctor and guide the web into a pulper or onto a broke conveyor.
• the pull-down blow of the web By means of the pull-down blow of the web, the web is pulled out of contact with the cylinder or roll surface immediately after it has reached and passed the doctor blade, and the web is tightened between the cylinder surface and the nozzle of the web pull-down blow.
• the pull-down blow is used when the web is run from a cylinder or a roll into a pulper or onto a broke conveyor in order to obtain more reliability for controlled running down of broke, and the web is not able to get around the roll or the cylinder.
• the doctor itself is left with the responsibility for doctoring in the running down process only in the situation when the tail of the web runs past. Later, the doctor has only an assuring role together with pull-down blowing.
• the blow-down device comprises a blow nozzle which is substantially as long as the maximum web width and the feed of air to the blow nozzle advantageously takes place both from the tending and from the driving side of the machine.
• the tail of the web when the tail of the web passes the doctor and starts to run into the pulper or onto the broke conveyor, the tail of the web can be brought under control immediately by means of the pull-down blow, which pulls the tail of the web out of contact with the cylinder or roll surface and tightens it between the cylinder surface and the blow nozzle.
• the web is under control all the time when paper is run into the pulper or onto the broke conveyor.
• a slit nozzle is used as the blow-down nozzle.
• the pull-down blow with compressed air of about 7 bars and the nozzle slit is 1-6 mm, most appropriately 1.5-3 mm.
• a hole row nozzle is used as the blow-down nozzle, the diameter of whose holes is 0.5-8 mm, most appropriately 1-4 mm, and the distance of the holes from one another is 3-30 mm, most appropriately 5-20 mm.
• the blowing force can be profiled in the cross direction, i.e. in the width direction of the web.
• control devices of the doctor and the blow-down devices in accordance with the invention are connected with the break automatics of the paper or board machine, so that in case of a web break the blow function is automatically switched on and the timing of the doctor can be coupled, when desired, to the sequence of threading blows.
• the control device of the doctor and the control device of the blow-down device are coupled together and there is a temporal delay between the control of the doctor and that of the blow-down device.
• the devices can be automatically switched off after a web break has been dealt with.
• the run of the web can be brought under control when the web is passed down into the pulper, because the web running down during the pull-down blow is run directly into the pulper or onto the broke conveyor without any risk of it being allowed to run through the doctor.
• the doctor in accordance with the invention is advantageously used in connection with a reeling drum, but it can also be applied on drying cylinders and at suitable locations of a press and also at other locations where the web is run down from a roll/cylinder.
• the doctor in accordance with the invention can be used up to a speed of at least 1200 m/min and even up to 2500 m/min.
• Figure 1 is a schematic view of a situation in accordance with the prior art, wherein the web is about to hit the doctor blade of a doctor.
• Figure 2 is a schematic view of a situation in accordance with the prior art, wherein the doctor blade of the doctor separates the web from a cylinder.
• Figure 3 is a schematic view of a situation in wliich, in accordance with the invention, the web is separated from the doctor blade of a doctor by pull-down blowing.
• a doctor 20 is arranged in connection with a roll/cylinder/drum 10, and a web W is separated from the surface of the cylinder 10 by means of a doctor blade 21 of the doctor 20.
• the direction of rotation of the cylinder 10 is designated by the reference sign S.
• the web W is just hitting the doctor blade 21 of the doctor 20.
• the web W is separated with the doctor blade 21 of the doctor 20 from the surface of the cylinder 10.
• the web W separates from the surface of the cylinder 10 and begins to fold after the blade 21, dropping into a pulper.
• the web W hits the doctor blade 21 of the doctor 20 with a certain force and at a certain frequency, with the result that, after some time, the doctor blade 21 of the doctor 20 bends, which leads to the fact that the angle of the doctor blade 21 of the doctor 20, i.e.
• Fig. 3 shows an arrangement in accordance with the invention, in which a device 25 is arranged in connection with the doctor 20 for a pull-down blow PA, by which the run of the web W is guided directly down towards a pulper such that the web W does not hit the doctor 20 nor the doctor hlade 21 but stays apart and is guided into the pulper.
• a control device 31 of the doctor 20 and a control device 32 of the blow-down device 25 are most appropriately coupled together and to a break and tail threading control system 30 of the paper or board machine, so that it can be arranged to operate automatically in case of a break and/or taking account of the threading phases, hi the controls 31, 32 of the doctor 20 and the blow-down device 25 there is a temporal delay and both also possibly comprise a temporal duration.
• a nozzle slit 26 of the blow-down device 25 is most appropriately a slit nozzle that extends across the entire width of the web and the blow slit is 1-6 mm.
• the blow-down device 25 produces the pull-down blow PA, in which connection the air current needed by it is pressurized and the pressure is most appropriately 5-7 bars.

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Family

ID=8565120

Family Applications (1)

Country Status (5)

Cited By (1)

Citations (5)

• 2002
  • 2002-12-20 FI FI20022247A patent/FI115310B/sv not_active IP Right Cessation
• 2003
  • 2003-12-18 DE DE10393876T patent/DE10393876T5/de not_active Withdrawn
  • 2003-12-18 WO PCT/FI2003/000971 patent/WO2004057106A1/en not_active Application Discontinuation
  • 2003-12-18 CA CA002507274A patent/CA2507274C/en not_active Expired - Fee Related
  • 2003-12-18 AU AU2003292271A patent/AU2003292271A1/en not_active Abandoned

Patent Citations (5)

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