FI112878B - Method and arrangement for damping vibrations of a coating station blade bar - Google Patents

Description

112873

The present invention relates to a method for controlling vibrations of blade beams used in coating paper or cardboard according to the preamble of claim 1.

These blade beams support a doctor blade or rod for leveling the coating to be applied to the surface of the moving web.

The invention also relates to an arrangement for applying the method.

The printing properties of paper or cardboard can be improved by various coating compositions. Typically, the coating composition is applied to the web by a suitable application method and the applied coating layer is smoothed and scraped to a final coating thickness. with a doctor blade or rod. To some extent for scraping »t ....: used, for example, in the manufacture of paperboard, an airbrush, · 1. ·. but its limited scraping capacity prevents the use of an airbrush at much current production speeds.

Since the coating layer is quite thin and, on the other hand, needs to be very smooth, in order to transfer the printable pattern to the surface of the paper as well as possible, the distance between the doctor blade and the moving web must be exactly the right. Therefore, the position of the blade is monitored by various measuring devices and the quality of the coating on the web is constantly monitored. While these measurements can be used to control the position of the blade 112878 2, although increasing control over the speed of the blade, especially the width of the machine, can cause problems in controlling the vibration of the blade. in principle, it should be possible to control the vibration so that amplifying vibration at the bar's specific frequency does not occur. The large mass placed in the middle of the beam also increases the deflection of the beam, so the beam should be heavier i The blade bar straightness compensation must be increased. These disadvantages affect the design of the cutter bar and contribute to limiting the maximum width of the cutter bar.

The currently used blade beams are supported at their ends by a joint on the coating station frame and in the middle ·. *. to the coating station lead-through. This structure has several characteristic frequencies, the lowest of which is parallel to the web: the specific frequency is very detrimental to the coating because it has the strongest effect on the position of the blade and the web. The vibration of the cutter bar is due to periodic excitations generated while driving, which are transmitted to the coating machine via the foundation or can be caused by the rotation of the machine's own rolls. The most important source of excitation is the rotating rolls, which have the same rotational frequency as the directional specific frequency of the lowest track of the cutter bar. When the speed of rotation falls: on the specific frequency of the blade bar, this results in 112878 3 oscillations of increasing amplitude and ultimately large variations in the coating amount on the surface of the paper or board. As the width of the cutter bar increases, its specific frequency decreases, while increasing the speed of the machines, 8-10 m wide machines at speeds above 1200 m / min have to reach an area where the excitation frequencies and the specific frequency of the cutter bar can overlap. On the other hand, in a wide bar, the amplitude caused by the same excitation is greater than in a narrower bar. The excitation could be avoided by changing the machine's running speed, but this is often not desired as the machine is driven at the highest possible speed that guarantees the best or reasonably good quality. Thus, it should be possible to dampen the blade bar vibrations to prevent possible resonance vibrations.

The object of the present invention is to provide a method by which the specific frequency of the blade bar can be attenuated.

The invention is based on providing at least one dynamic damper comprising at least ··. one spring member and a mass applied to the spring.

Further, the damper is preferably arranged in the center of the blade bar and connected to the spring member. an attenuator to control its amplitude of motion.

More specifically, the method according to the invention is characterized in what is set forth in the characterizing part of claim 1.

The arrangement according to the invention, in turn, is characterized by what is stated in the characterizing part of claim 5.

112878 4

The invention provides considerable advantages.

The dynamic dampener significantly reduces the vibration of the cutter bar. The required movable mass is smaller than the fixed mass attached to the beam and the damping power is better. The movement of the damper can be limited by a hydraulic, pneumatic or friction damper so that the amplitude of its movement cannot be uncontrollably increased. By keeping the blade bar vibrations low, the coating results in a better coating and a smoother product quality. With the invention, vibration does not limit speed increase even on wide machines. This is a very significant advantage, as it is difficult and expensive to increase the width of the machine, whereas increasing the speed increases the output much more easily.

The invention will now be explained in more detail with reference to the accompanying drawing, which shows one embodiment of the invention in schematic form.

The hanging of the blade beam 1 is usually implemented such that the ends of the beam 1 have bearing points through which the beam is pivotally suspended on the frame of the coating machine. The doctor blade has pivot points; between. Since the beam 1 can bend under load and under its own weight, the bearing points are formed as a joint so that the suspension point and thus also the end of the beam 1 can rotate transversely to the longitudinal axis of the beam. The ends of beam 1 thus have, according to static rules, articulated support. In the center of the beam 1 is a screw jack which is used to support the beam from the center and which can be used to rotate the beam according to changes in the blade angle and blade load.

The figure shows the part of the cutter bar from the center of the beam. The blade beam is designated by the number 1. Just in the transverse direction of the beam 1 there is an attachment bracket 3 of the blade beam 1 pivoting pin 2. on both sides. Each element comprises at its first end a spring arm 6 attached to a damper bracket 5, a movable mass 7 and a damper element secured between the second end of the arm 6 and the blade beam 1. The damper is attached to the blade beam 1 by a bracket 9.

Because the end movement of the end-supported blade bar is centered on its Y: position, the dynamic attenuator ·: ·: is also positioned in the center of the bar. When dividing 'Ύ into two parts, it requires less space and is>: Y easier to implement. In this case, of course, a symmetrical structure is most advantageous. The specific frequency of the damper must be the same as the specific frequency of the cutter bar. The variables for calculating the damper are the magnitude of the vibrating mass and the distance of the mass from the support point. As the mass is increased, the characteristic frequency peaks of the attenuator are spaced apart, so tuning the mass to the correct distance from the support point is easier. On the other hand, the high mass increases the load caused by the blade's own mass and the need for damper space increases. With a small oscillating mass again, · * the characteristic frequency peaks are close together and it is more difficult to tune the attenuator 6 112870 to the same frequency as the cutter bar. Thus, for the size of the pulp, an optimum of about 20% of the weight of the cutter bar is obtained. In this case, the weight of each damper element is about 10% of the weight of the blade beam.

If the excitation remains at the same frequency as the characteristic frequency of the blade bar and the damper, the amplitude of the damping motion is constantly increasing. In order to keep the amplitude within reasonable limits, an absorber 8 is attached to the end of the arm 6 acting as a spring element of the mass 6.

The purpose of this absorber is to convert the kinetic energy of the dynamic absorber into heat by slowing the movement of the end of the arm 6. Any absorber based on a known principle such as a liquid absorber, a friction absorber or a gas absorber may be used as the absorber absorber. There are several different devices suitable for the purpose and it is not difficult for one skilled in the art to design one.

·; * The dynamic damper described above can be dimensioned! ' reasonably accurate to the right frequency already on the blade bar ·; · In the design phase, but for best results if the attenuator is tuned to the frequency providing the best attenuation during blade operation. In this case, the specific frequency of the damper is as close as possible to the specific frequency of the blade bar, and when the damper is oscillated in the opposite phase to the beam, effective damping is obtained. The tuning can be done by changing the distance of the mass 7 from the support point, i.e. the damper bracket 5. In the case of the figure, the mass 7 is in two parts; and fitted around arm 6. The mass can be moved. * By loosening the screws fitted to the fastening holes 10, whereby the elastic length of the spring element can be adjusted. In such a damper, the final tuning of the damper can be done by moving the pulp during use and, if necessary, the tuning can be renewed if, for example, the structure of the jacket or blade beam is modified for maintenance or rebuilding. It is also conceivable that the mass is adapted to move, even when moved by a screw thread, whereby the tuning can be performed automatically, even in response to the vibration measurement of the blade bar.

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

As the spring element of the damper, it is most advantageous to use an actual bending rod spring which is inexpensive to manufacture and easy to dimension. Within the scope of the inventive idea, the structure of the spring itself has no effect on the operation of the structure, and the spring can be a helical spring, for example, suspended from a blade beam. Such structures, however, require ':' i generally have more space than the simple damper shown in the example. The dampener may be located outside the center of the bar, but in this case either the damping power may be reduced or larger weights must be used. the effect of vibration is also smaller.

)

The specific frequency of the suppressor must be within the specific frequency range of the blade bar and does not necessarily have to be exactly the same as the specific frequency of the blade bar. Here! denotes the frequency range at which the • t frequency of the attenuator is so close to that of the bar 8

1 Λ o o 7 o I i L U / {J

that the attenuation is 50%. If the specific frequency of the attenuator can be tuned closely to the specific frequency of the blade bar, even one-third of the non-attenuated amplitude can be achieved.

• 1 ί f f

I I

• I> i | ? ·> T

Claims (9)

A method for controlling the vibrations of a joist beam in a coating station, said joist beam (1) having a definite intrinsic frequency, characterized in that at least one dynamic damper comprising a spring element (6) attachable to the joist beam (1) is attached to the joist beam (1). ) and a mass provided at the spring element and which attenuator's own frequency is arranged in the region of the beam's own frequency. Method according to claim 1, characterized in that the dynamic damper (6, 7, 8) is arranged at the midpoint of the beam (1). Method according to claim 1 or 2, characterized in that the dynamic damper (6, 7, 9) is divided into two damper elements arranged symmetrically on each side of the center line of the beam (1). 4. A method according to any of the preceding claims, characterized in that the movement of the dynamic damper is damped by means of an absorbent damper. Device for controlling the vibrations of a joist beam in a coating station, comprising a joist beam (1) having a definite eigenfrequency, characterized by an at least one dynamic damper arranged at the joist beam (1) comprising a spring member (1) at least the joist beam ( 6) and a mass provided at the spring element and the damping frequency of which the damper lies; the range of the self-frequency of the beam. Device according to claim 5, characterized in that the dynamic damper (6, 7, 8) is arranged at the center of the beam 12 12 Ί Ο Γ 7 n I lz.0 / 0 (1). Device according to claim 5 or 6, characterized in that the dynamic damper (6, 7, 9) is divided into two damper elements arranged symmetrically on each side of the center line of the beam (1). Device according to any of claims 5-7, characterized by an absorbent damper arranged at the dynamic damper (6, 7), e.g. a friction damper, a liquid damper or a gas damper. Device according to any of claims 5-8, characterized in that at least one of the masses of the dynamic damper (6, 7, 9) is movably arranged at the spring element (6) to control the elastic length of the spring element. * »»