FI121998B - Bending compensated joist beam - Google Patents

Description

Does the bent blade bend

The invention relates to a deflection compensated blade beam for supporting and loading paper scrapers and scrapers in the paper industry according to the preamble of claim 1.

Paper and board are coated by passing a coating composition onto a moving web of material which is applied in a uniform layer on the surface of the web. The coating can be leveled and the amount of coating remaining on the surface of the material web can be adjusted, for example, with a scraper-10 blade or a scraper bar. The web to be coated passes between the doctor blade and a suitable support, usually a rotating roll, in the coating machine. The blade scrapes off excess coating from the web and smoothes it into a smooth layer on the web surface. In order for the coating layer to be as smooth as possible, the gap between the web and the doctor blade should be as close as possible over the entire width of the web. The force of the hub against the scraper blade should be high and constant over the entire width of the blade so that the coating can be uniformly applied to the web, even at high web speeds. The straightness of the cutter bar should remain constant to approximately 0.1 mm. However, uneven thermal loads due to the environment and changes in the beam angle tend to cause significantly greater deflections. In wide machines, the deflection can be up to 1.0 mm with a web width of 8 to 10 m.

The gap between the material web and the doctor blade does not remain exactly the same for several reasons. When machining, the scraper blade and frame are fastened to the machine tool with sturdy clips in the operating position. Despite precise attachment to the machine tool, machining of the blade and ° 25 frame will result in defects that cause the surface of the web and the blade to be out of alignment. Since the body of the scraper blade is supported by bearings at both ends, the deformation caused by the line load is greater at the center of the blade than at the supported ends, which causes the blade to be closer to the web at the edges of the blade. Because the blade faces the web or roll surface

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The force exerted by g 30 is less in the center of the web than at its ends, any protrusions in the web and variations in coating density and viscosity may lift the blade off the web.

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In order to reduce the above drawbacks, various doctor blade attachment solutions have been developed. In the prior art, the aim is to provide a uniform blade load over the entire length of the web by means of a flexible blade and an adjustable fastening member. In these solutions, the blade is attached to the blade holder such that the blade can be pressed against the web by a resilient member extending across the length of the blade 5, for example by an air or liquid filled rubber hose. Because the pressure inside the hose is constant over the entire length of the blade, the hose presses the blade against the web with the same force across the width of the web. The blade pressure against the web can be adjusted by changing the pressure inside the hose. Sometimes such solutions use a blade that is divided into narrow sections in width. This provides a more flexible blade which better follows the web and roll shape.

The solutions have several disadvantages. Because of the limited deformability of the resilient support member, this solution cannot compensate for large changes in blade-to-web distance and blade load. The blade load adjustment range remains narrow, and if the plating speed is to be increased, the blade must be pressed against the web with an actuator mounted on the scraper blade body. As the blade load increases, the rigidity of the blade attachment member increases, so that the blade can no longer follow the web surface in the desired manner. The body of the doctor blade must be constructed to be very rigid in order to press the flexible blade against the web. Flexible and adjustable blade holder solutions are complex, blade replacement difficult, and elastic members may break when changing blade. The blade holder must be made large and heavy.

U.S. Patent No. 4,907,528 describes a deflection compensated blade beam, -r- based on such a solution. In it, four pressure members are disposed symmetrically around a cu 25 circular frame beam and are surrounded by a tube, which in turn is supported by a square-shaped scraper body. By adjusting the pressure of the pressure members, a deformation of the blade beam is caused which compensates for the deflection of the blade beam. For many, the structure of the beam is intricate, making it also very heavy. In this case, the beam's own weight increases its bending ground and requires stronger compensation. The shape of the bar is not freely selectable for 30 ounces, since the body of the scraper must be square and the number of pressure members ....... ....

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GB 2 251 562 describes a deflection compensated blade beam in which the temperature of the beam is kept constant at the blade holder and the deflection of the beam is compensated by adjusting the temperature of the beam at appropriate points by means of heating or cooling means. The deformation of the beam is thus compensated for by causing displacements in opposite directions by means of temperature changes. The blade bar has a triangular cross-section and the heating elements are located on the sides of the triangle. In the solution, two separate heat transfer circuits can be used and the heating or cooling is done by the fluid flowing in the ducts. Two heat transfer circuits can be used to change the temperature in different parts of the beam. The problem with such a solution is the slowness of the adjustment, since the masses to be heated are the mouthpieces. The set value may also change as the ambient temperature changes.

The heat transfer can also be used merely to maintain the temperature of the beam at the setpoint, whereby the temperature of the beam does not affect the linearity of the beam. The heating or cooling system is poorly responsive to rapid changes in temperature. Slow response to temperature changes is a weakness of all temperature control compensation methods.

U.S. Patent No. 5,269,846 discloses a deflection compensated blade beam having a separate inner tube within the blade beam which rests on the inner walls of the blade beam through air cushions. The deflection of the blade beam is altered by changing the pressure in the air cushions across the inner tube, causing the blade edge to move as desired. It is possible to use fluid instead of air in the pillows. Such deflection control is fast, making it well suited for modern high speed coating machines. However, the deflection-compensated blade bar at atmospheric pressure cannot solve all the problems associated with deflection of the blade bar. The blade beams today are made of steel and the steel has a high thermal expansion coefficient, which is why uneven heat load in the blade beam causes large deflections in the blade beam. This can be compensated for by the above mentioned method g using a heat distribution equalizing fluid circulation or compressed air compensation. However, the problem with pressure-compensated maceration is that the stiffness of the inner tube is necessarily considerably smaller than that of the larger blade bar of surrounding cross-section. In this case, the inner tube bends significantly more when loaded with the cutter bar, and only small displacements can be caused to the cutter bar, even if the inner tube bends to the inside surface of the cutter bar. Since the stiffness of the beam and the inner tube is strongly determined by the diameter of their cross-section, the stiffness of the inner tube cannot be substantially increased as it must fit inside the stern. Thus, the cutter bar is always considerably stiffer than the inner tube if they are made of the same material.

It is an object of the invention to provide a new type of blade bar whose deflections due to its own mass and temperature changes are initially small and whose deflection can be effectively controlled, for example, by means of compressed air compensation.

The invention is based on the fact that the cutter bar is made of a material having a higher specific stiffness than an inner tube material and a lower absolute rigidity than the inner tube material.

According to a preferred embodiment of the invention, the cutter bar is made of fiber reinforced material, most preferably carbon fiber, and the inner tube is made of steel.

More specifically, the cutter bar according to the invention is characterized in what is stated in the characterizing part of claim 1.

The invention provides considerable advantages.

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Because of the very low thermal expansion coefficient of the carbon fiber blade bar, it does not react to external thermal fluctuations and there is no significant deformation due to thermal expansion. For other fiber-reinforced materials, the thermal expansion t - is also very low. Carbon fiber composites and other fiber reinforced materials have a high specific stiffness, i.e. very stiff with respect to their mass, so that the beams made of these materials are of low weight deflection and can thus be easily compensated for or taken into account in the manufacture of the beam. However, the rigidity of fiber reinforced mail materials is typically lower than that of steel, so that now the relative rigidity difference between the blade bar and the inner tube is reduced and compensated, resulting in larger displacements in the blade bar and thus at the blade edge. Thus, compensation is more effective and requires less force. Since the cutter bar is basically just a tube of a certain cross-section, it is relatively easy to make it from fiber reinforced material.

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The invention will now be described, by way of example and with reference to the accompanying drawing, which schematically illustrates one of the cutting blades of the invention.

5 The cutter bar 1 in the pattern is in the form of a truncated triangle and has an inside tube 2 of similar shape supported on the inside walls of the cutter bar 1 by air cushions 3. The holder 4 of the doctor blade 5 is fixed to one corner of the beam 1 and at the same angle is fitted a blade bar straightness measuring device 6, which may be for example a laser measuring device. In such a blade beam, the deflection is compensated by varying the pressure in the air-pads 3, whereby the distance between the blade beam 1 and the inner tube on the higher pressure side increases and on the lower pressure side the distance decreases. Three triangular adjusting members 3 can provide displacement in the desired direction. The method of compensation is similar to that of United States Patent 5,269,846, which describes the operation of the compensation apparatus in more detail.

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The invention is based on the fact that the cutter bar 1 is made of a material having a higher specific stiffness than the material of the inner tube 2 and an absolute stiffness less than the material of the inner tube. In the most preferred embodiment, the blade beam 1 is carbon fiber and the inner tube 2 is steel. Carbon fiber can be used to make a composite structure in which the thermal expansion coefficient of the composite can be adjusted to almost zero, with the orientation of 20 fibers, to the order of -1x10.6 1 / ° K, i.e. its deformations as temperature changes are negligible. 10-6 1 / ° K. Because carbon fiber is extremely stiff in relation to its weight, t—— has a high specific stiffness. On the other hand, the absolute stiffness of the carbon fiber compared to cv 25 steel is low, so that the stiffness of the inner tube made of steel can be even higher than that of the carbon fiber bar. In this case, the air cushions 3 supported on the inner tube 2 provide greater displacements in the blade bar 1 because the inner tube 2 has less flexibility. The need for compensation is less, because the blade bar deflects under its own weight and its deformation is small.

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LO 30 o o Materials other than the above may be used for the inner tube and cutter bar, subject to the above limitations. Because the inner tube must be sufficiently rigid with respect to the cutter bar, it must be made of metal or metal alloys. Along with steel, this is mainly about aluminum alloys, as other metals and alloys, such as titanium alloys, are significantly more expensive. Here, aluminum alloys refer to various light metals and alloyed aluminum. Several fiber reinforced materials can be used to make the cutter bar.

It should be noted here that fiber reinforced material refers to a composite of fibers and binder, and the name of the material used herein is the name of the reinforcement. There are several binders and reinforcements and, for example, carbon fiber can be used to make products that bind carbon between the fibers, whereby the whole body is made up of carbon molecules. The most typical fiber reinforcements are glass fibers, carbon fibers and aramid-10 fibers. It should be noted that the properties of the composite structure differ from those of the reinforcement.

The blade holder can be attached to the blade beam by gluing, bolting or forming a suitable form of attachment to the blade beam, for example a salmon tail groove, which allows thermal expansion. For ease of cleaning, the blade bar should be coated with a coating that is easy to clean, such as stainless steel.

Solutions other than those described above may also be contemplated within the scope of the invention.

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There may be more than three compensating members, for example, four compensating members must be used in a square blade beam. In these bodies, any fluid, i.e. gas or liquid, may be used as the active medium. Often, however, it is preferable to use compressed air because it is readily available at the factory. Often, fluid pressure is also available for cm 25. The shape of the cutter bar and the inner tube may vary, e.g. Instead of the scraper blade, the scraper bar can be used to carry the scraper bar.

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Claims (6)

1. Bending-compensated joist beam for supporting and loading joist bait (5) and joist bars in the paper industry, comprising: ) or the rod, - an error (2) arranged into the actual cabinet beam (1), and - at least three compensation means (3) containing a liquid liquid to support the inner tube (2) against the inner surface of the actual cabinet beam (1), characterized because the absolute stiffness of the actual beam (1) is less than the absolute stiffness of the inner tube (2). 2. A beam according to claim 1, characterized in that the actual beam (1) is made of a material whose specific stiffness is greater than the material of the inner tube (2) and the absolute stiffness is less than the material of the inner tube (2). . 3. Schaber beam in accordance with Claim 1 Clause 2, characterized in that the actual joist beam (1) is made of a fiber reinforced material. in- 4. Schaber beam according to claim 3, characterized in that the actual joist beam (1) is made of carbon fiber composite and the inner tube of (2) frame. cp 4- 20 5. Schaber beam according to claim 3, characterized in that the actual x x joist beam (1) is made of carbon fiber composite and the inner tube of (2) an aluminum minium mixture. oo o 6. A beam according to claim 3, characterized in that the actual beam and beam (1) are made of fiberglass or aramid fiber composite.