Classifications

• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H25/00—After-treatment of paper not provided for in groups D21H17/00 - D21H23/00
  • D21H25/08—Rearranging applied substances, e.g. metering, smoothing; Removing excess material
  • D21H25/10—Rearranging applied substances, e.g. metering, smoothing; Removing excess material with blades
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21G—CALENDERS; ACCESSORIES FOR PAPER-MAKING MACHINES
  • D21G3/00—Doctors
  • D21G3/005—Doctor knifes
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
  • F16F—SPRINGS; SHOCK-ABSORBERS; MEANS FOR DAMPING VIBRATION
  • F16F7/00—Vibration-dampers; Shock-absorbers
  • F16F7/10—Vibration-dampers; Shock-absorbers using inertia effect
  • F16F7/104—Vibration-dampers; Shock-absorbers using inertia effect the inertia member being resiliently mounted
  • F16F7/116—Vibration-dampers; Shock-absorbers using inertia effect the inertia member being resiliently mounted on metal springs

Definitions

• the invention relates to a method according to the preamble of claim 1 for controlling vibrations of doctor blade beams used in the coating of paper and paperboard webs.
• Such doctor blade beams support a doctor blade or rod that levels a coating mix applied to the surface of a moving web.
• the invention also relates to an assembly suitable for implementing the method.
• the printability qualities of a paper or paperboard web can be improved by different kinds of coats.
• the coating mix is applied to the web by a suitable application technique, whereupon the applied coating mix is leveled and doctored to the final coat weight by a doctor blade or rod.
• doctoring may also be carried out, e.g., in paperboard manufacture using an air knife, while the limited doctoring effect of an air knife excludes its use in most cases at present running speeds.
• the distance between the doctor blade and the moving web must be kept sufficiently accurately at a predetermined value.
• the position of the doctor blade and the quality of coating mix layer adhering to the web surface are monitored on-line by various kinds of measurement equipment. Based on these measurement results, the doctor blade position can be adjusted to obtain an optimal end result.
• the blade position is today easy to control by a variety of different techniques, continual increase in the web running speed and particularly in the machine width may cause problems in the management of doctor blade beam vibrations. If the doctor blade beam is allowed to vibrate especially at one of its eigen- frequencies, the coat will become uneven.
• the natural frequency of the doctor blade beam could be controlled and attenuated by means of additional weights placed to the center of the beam.
• the weights must be very heavy, however, to attain effective attenuation. Yet this is not possible due to the limited space about the beam.
• a heavy weight placed in the middle of the beam increases the sag of the beam, it becomes necessary to make the beam sturdier or increase the deflection compensation of the doctor blade beam.
• Doctor blade beams used today are supported at their ends by a pivotal joint to the coater station frame and at their middle point to the doctor blade beam cross tube of the coater station.
• This kind of construction has plural eigenfrequencies of which the one having the lowest natural frequency in the direction of the web travel is extremely harmful as to the result of the coating process because of its most drastic effect on the mutual position between the doctor blade and the web.
• the vibrations of the doctor blade beam are evoked by run-time cyclic excitations imposed on the beam during the coating process either via the foundation of the coater machine or generated by the rotational movement of the own rolls of the coater machine.
• the major source of excitation is formed by the rotating rolls when their speed of rotation coincides with the lowest natural frequency of the doctor blade beam in the direction of the web travel.
• the beam begins to oscillate at an increasing amplitude eventually resulting in wide variations in the coat weight on the surface of the paper or paperboard web.
• the natural frequency of the beam decreases and, in combination with the ongoing trend of increasing the machine speed, machines having a width of 8 to 10 m and running at speeds over 1200 m/min invokes operation in a range wherein the exciting frequencies and the natural frequency of the doctor blade beam may coincide.
• the amplitude of natural frequency oscillations evoked in a wide beam may grow more drastic than those of a narrower beam excited by the same source. While the appearance of this kind of excitation could be prevented by way of changing the running speed of the papermaking machine, this is not generally desirable inasmuch as the goal is to run the machine at a maximum possible speed yielding the optimal or an at least acceptable quality of web coating. Hence, it is desirable to attenuate the vibrations of the doctor blade beam in order to eliminate possible resonant vibrations of the doctor blade beam.
• the goal of the invention is attained by virtue of adapting on the doctor blade beam at least one dynamic damper assembly comprising at least one springed element and a mass suspended by the springed element. Furthermore, the damper assembly is advantageously placed at the middle of the doctor blade beam and the springed element is complemented with damper element suitable for limiting the amplitude of the movements of the springed element.
• the invention offers significant benefits.
• the vibrations of the doctor blade beam can be substantially attenuated.
• the mass to be actuated is smaller than that needed if the mass is mounted directly to the doctor blade beam and yet the novel arrangement gives a higher attenuating effect.
• the motion of the damper assembly can be constrained with the help of a hydraulic, pneumatic or frictional damper element so as to prevent an uncontrolled increase of the damper movement amplitude.
• the vibrations of the doctor blade beam are thus kept at a low level, the outcome of the coating application is improved and the quality of the thus manufactured product becomes more uniform.
• vibrations do not prevent increase of web speed even on wider machines. This is an essential benefit inasmuch as increasing the width of machines from present standards is complicated and costly, while on the other hand higher web speeds offer a substantially easier way of achieving a greater production capacity.
• the support to a doctor blade beam 1 implemented is in a conventional fashion by having the ends of the doctor blade beam 1 mounted in bearings that pivotally support the beam to the frame of the coater.
• the doctor blade is mounted between the pivotal support points.
• the pivotal support points in the bearings are implemented using linkage joints such that the support point as well as the end of beam 1 can rotate transversely in regard to the longitudinal axis of the beam.
• beam 1 is equipped with pivotal support joints at its both ends.
• a screw jack serving to support the beam centrally and making it possible to rotate the beam according to the desired blade angle and changes in blade loading.
• the doctor blade beam is denoted by reference numeral 1. Exactly at the middle of beam 1 in the cross-machine direction thereof is adapted a mounting bracket 3 for an angle adjustment j ack 2 of doctor blade beam 1.
• the rod of the angle adjustment jack 2 is connected to the mounting bracket by a pivotal joint 4.
• Mounting arms 5 of the dynamic damper assembly elements extend downwardly from the mounting bracket 3.
• the dynamic damper assembly comprises two damper elements placed symmetrically about the mounting bracket 3.
• Either one of the damper ele- ments includes a bar 6 acting as a leaf spring element connected by its first end to the damper element mounting arm 5, a movable mass 7 and a damper member adapted between the second end of leaf spring bar 6 and doctor blade beam 1.
• the damper element is connected to doctor blade beam 1 by a mounting fixture plate 9.
• the mass is made large, the natural frequency peaks of the damper are separated wide apart from each other, whereby the damper tuning by placing the mass at a correct distance from the support point is easier.
• a large mass added to the own mass of the beam increases the loading of the doctor blade beam and increases the space requirement of the damper.
• use of a small vibrating mass brings the natural frequency peaks closer to each other thus making the tuning of the damper on the natural frequency of the doctor blade beam more difficult. Due to these reasons, the magnitude of the mass has an optimum at about 20 % of the mass of the doctor blade beam. Then, the mass of either damper element is selected to be about 10 % of the doctor blade beam mass.
• an a kinetic-energy-absorbing damper device 8 is mounted to the end of the leaf spring bar 6 that acts as the springed element for the mass 6.
• the function of this absorbing damper device is to convert the kinetic energy of the dynamic damper assembly into heat by way of damping the movement of the end of leaf spring bar 6.
• the absorbing damper device may be any conventional device such as a hydraulic, frictional or gas-filled damper. A variety of suitable absorbing damper devices are available commercially, and also the design of such a device for the purpose is well known to a person versed in the art.
• While the above-described dynamic damper assembly may be dimensioned relatively accurately for the correct natural frequency already during the design stage of the doctor blade beam, the best result will be attained by tuning the damper to the frequency of maximal attenuation during actual operation of the doctor blade beam. Then, the damper natural frequency coincides maximally accurately with the doctor blade beam natural frequency, whereby a damper design causing the damper to oscillate at an inverted phase relative to the doctor blade beam vibrations leads to efficient damping. Tuning can be performed by changing the distance of mass 7 from the support point, that is, the damper element mounting arm 5. In the exemplary embodiment shown in the diagram, mass 7 is divided in two parts that are adapted about leaf spring bar 6.
• the mass can be moved by undoing screws tightened in fixing holes 10, whereby the adjustment of the springedly responsive length of the springed element is possible.
• the final tuning of the damper may be carried out by moving the mass in a running coater and, if necessary, the tuning operation may be repeated if changes are made in the coater or doctor blade beam construction due to servicing or revamping.
• the springed element of the damper assembly is a leaf spring implemented as a rod-like element that is cost-efficient to fabricate and easy to dimension.
• a coiled spring for instance supported to the doctor blade beam may be used as the springed element.
• This kind of construction generally requires more space than the simple damper used in the exemplary embodiment. While the damper could be placed in lieu of the middle of the doctor blade beam also at another point of beam, its damping efficiency may become weaker or require the use of larger masses since the amplitudes of vibrational movements at other points of the beam are smaller thus offering a minor chance of damping by vibrations of inverted phase.
• the natural frequency of the damper must only be tuned to within the resonant frequency band of the doctor blade beam natural frequency, not necessarily exactly at the natural frequency of the doctor blade beam.
• this situation must be understood to cover the resonant frequency band within which the damper natural frequency is so close to the doctor blade beam natural frequency that the efficiency of damping is 50 %. If the damper natural frequency can be tuned very close to the doctor blade beam natural frequency, the amplitude of vibrations can be attenuated as small as one third of the undamped amplitude of vibrations.

Landscapes

• Engineering & Computer Science (AREA)
• General Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Paper (AREA)
• Coating Apparatus (AREA)
• Application Of Or Painting With Fluid Materials (AREA)

Priority Applications (2)

Applications Claiming Priority (2)

Publications (1)

Family

ID=8564300

Family Applications (1)

Country Status (4)

Cited By (8)

Citations (3)

Family Cites Families (4)

• 2002
  • 2002-07-04 FI FI20021318A patent/FI112878B/fi not_active IP Right Cessation
• 2003
  • 2003-07-03 WO PCT/FI2003/000542 patent/WO2004005615A1/en not_active Application Discontinuation
  • 2003-07-03 DE DE10392840T patent/DE10392840B4/de not_active Expired - Fee Related
  • 2003-07-03 AU AU2003238137A patent/AU2003238137A1/en not_active Abandoned

Patent Citations (3)

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