Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B31—MAKING ARTICLES OF PAPER, CARDBOARD OR MATERIAL WORKED IN A MANNER ANALOGOUS TO PAPER; WORKING PAPER, CARDBOARD OR MATERIAL WORKED IN A MANNER ANALOGOUS TO PAPER
  • B31F—MECHANICAL WORKING OR DEFORMATION OF PAPER, CARDBOARD OR MATERIAL WORKED IN A MANNER ANALOGOUS TO PAPER
  • B31F1/00—Mechanical deformation without removing material, e.g. in combination with laminating
  • B31F1/12—Crêping
  • B31F1/14—Crêping by doctor blades arranged crosswise to the web
  • B31F1/145—Blade constructions
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B31—MAKING ARTICLES OF PAPER, CARDBOARD OR MATERIAL WORKED IN A MANNER ANALOGOUS TO PAPER; WORKING PAPER, CARDBOARD OR MATERIAL WORKED IN A MANNER ANALOGOUS TO PAPER
  • B31F—MECHANICAL WORKING OR DEFORMATION OF PAPER, CARDBOARD OR MATERIAL WORKED IN A MANNER ANALOGOUS TO PAPER
  • B31F1/00—Mechanical deformation without removing material, e.g. in combination with laminating
  • B31F1/12—Crêping
  • B31F1/14—Crêping by doctor blades arranged crosswise to the web
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B31—MAKING ARTICLES OF PAPER, CARDBOARD OR MATERIAL WORKED IN A MANNER ANALOGOUS TO PAPER; WORKING PAPER, CARDBOARD OR MATERIAL WORKED IN A MANNER ANALOGOUS TO PAPER
  • B31F—MECHANICAL WORKING OR DEFORMATION OF PAPER, CARDBOARD OR MATERIAL WORKED IN A MANNER ANALOGOUS TO PAPER
  • B31F1/00—Mechanical deformation without removing material, e.g. in combination with laminating
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B31—MAKING ARTICLES OF PAPER, CARDBOARD OR MATERIAL WORKED IN A MANNER ANALOGOUS TO PAPER; WORKING PAPER, CARDBOARD OR MATERIAL WORKED IN A MANNER ANALOGOUS TO PAPER
  • B31F—MECHANICAL WORKING OR DEFORMATION OF PAPER, CARDBOARD OR MATERIAL WORKED IN A MANNER ANALOGOUS TO PAPER
  • B31F1/00—Mechanical deformation without removing material, e.g. in combination with laminating
  • B31F1/20—Corrugating; Corrugating combined with laminating to other layers
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B31—MAKING ARTICLES OF PAPER, CARDBOARD OR MATERIAL WORKED IN A MANNER ANALOGOUS TO PAPER; WORKING PAPER, CARDBOARD OR MATERIAL WORKED IN A MANNER ANALOGOUS TO PAPER
  • B31F—MECHANICAL WORKING OR DEFORMATION OF PAPER, CARDBOARD OR MATERIAL WORKED IN A MANNER ANALOGOUS TO PAPER
  • B31F1/00—Mechanical deformation without removing material, e.g. in combination with laminating
  • B31F1/20—Corrugating; Corrugating combined with laminating to other layers
  • B31F1/24—Making webs in which the channel of each corrugation is transverse to the web feed
  • B31F1/26—Making webs in which the channel of each corrugation is transverse to the web feed by interengaging toothed cylinders cylinder constructions
  • B31F1/28—Making webs in which the channel of each corrugation is transverse to the web feed by interengaging toothed cylinders cylinder constructions combined with uniting the corrugated webs to flat webs ; Making double-faced corrugated cardboard

Definitions

• the present invention relates to blades for creping. More particularly, the present invention relates to creping blades provided with a ceramic coating and a method of manufacturing such blades.
• Creping doctor blades are commonly used in the production of tissue.
• the blades have the function of detaching a paper web from a rigid, hot dryer cylinder
• the creping blade must fulfill many requirements: - The blade must overcome the adhesive forces which stick the paper web on the dryer surface, the adhesion being promoted (for purposes of drying the web) by a chemical coating applied to the dryer by means of a spray-boom. - The blade should create the desired crepe structure in the web and thereby provide -the right bulk, softness and mechanical strength to the tissue. For this aspect, the geometry of the blade tip is important. A square edge blade (90 degrees) in a given creping situation will create a different tissue than a blade with a sharp edge of say 75 degrees in the same creping situation.
• the former situation gives a higher bulk and coarser crepe structure than do the latter.
• the blade should keep the tissue parameters as constant as possible for the longest possible period of time. In other words, the wear of the blade tip and its interaction with the layer of coating chemicals on the web are important factors.
• the blade should be as friendly as possible against the dryer surface. This means that any wear should predominantly or exclusively occur on the blade, rather than on the dryer surface .
• the surface of the dryer can be either cast iron (same material as the bulk of the cylinder, i.e. a cylinder without any surface deposit) or a metallisation obtained by, for example, thermal spraying.
• WO 97/22729 describes a method- for coating Yankee dryers .
• Creping blades are subjected to wear for different reasons. First there is sliding wear against the dryer, and second there is impact wear .due to the web hitting the blade during creping. It has been found that the progressive wear of the creping blade is directly related to unwanted evolution of the tissue properties, such as changes in bulk and softness. Practical experience, after having reviewed many tissue mills, has shown that the best properties of the tissue are obtained only with a new blade. For steel blades, this period of good properties could be as short as one reel only. In order to accommodate for such behavior (i.e. blade wear) , tissue makers are specifying ranges of properties which are said to be acceptable. Nevertheless, there would be a high industrial demand for the tissue quality reached in the very first part of the first reel after a blade change.
• US patent proposes the solution to use a groove at the blade tip and a break-in space between the wear resistant material in the groove and the leading edge of the blade.
• GB 2,128,551 discloses a multipurpose scraper which may be used as a creping blade, having an edge coated by thermal spraying in many passes with a wear resistant material from the ceramic or metal carbide families. More specifically, alumina-titania is presented. Focus is further made on flexibility and again is the need for minimum brittleness emphasized. ;
• Other documents, such as US-6,207,021 and US-6, 074, 526 teach the possibility to create a recess on the blade tip in order to obtain an essentially constant contact surface against the dryer, and by this feature a constant scraping efficiency.
• creping blades tipped with thermally sprayed metal carbides such as for example WC-Co or WC- Co-Cr is known.
• thermally sprayed metal carbides such as for example WC-Co or WC- Co-Cr.
• Such materials are less brittle than sprayed ceramic and therefore less sensitive to edge chipping. Nevertheless, the use of such materials should be avoided due to other drawbacks, namely: - There is a potentially higher wear rate of the dryer surface, and potentially high damage due to chattermarks if vibrations develop within the tissue machine and are transferred to the creping blade .
• - Metal carbides are constituted by a metal matrix with embedded carbides. Such situation may promote the micro-welding events between the blade and the dryer surface at the high temperatures present in the sliding contact.
• One object of the present invention is therefore to provide a creping blade having a thermally sprayed ceramic tip, which blade does not present the macrochips limitations explained above, thereby avoiding the large fluctuations in blade lifetime.
• a second object of the invention is to provide a blade that is more resistant to microchips when used on high quality tissue, such as facial tissue, allowing for the tissue properties to be maintained within the desired range for a longer period of time, i.e. an extension of the blade lifetime.
• Another object of the invention is to provide a blade which is compatible with various types of Yankee dryer surfaces, e.g. both cast iron and metallisations, without premature wear of the dryer surface or material transfer from the dryer surface to the sliding contact of the blade due to microwelding .
• Yet another object is to provide a very low sliding wear rate of the creping blade in order to maintain the scraping efficiency of the blade as constant as possible for a prolonged period of time.
• the surprising observation on which the present invention is founded is that the use of one sprayed ceramic compound which is more brittle than alumina-based products will enable the solution of the chipping problem in creping blade applications, and at the same time fulfill the other objects mentioned above. It has been found, to the surprise of the skilled person, that creping blades tipped with a ceramic of chromia-titania (Cr 2 0 3 /Ti0 2 ) , applied by thermal spraying, exhibit no chipping at the leading edge of the blade, neither small edge microchips nor any macrochips .
• the ceramic material covers the blade substrate at least over the section thereof adapted for contact with the dryer cylinder (the working edge or leading edge) , as well as the section thereof upon which the web impacts during creping.
• the ceramic top layer forms both a working edge adapted for contact with the surface of a dryer cylinder, and a web impact area upon which the web impacts during creping.
• Blades tipped with thermally sprayed chromia-titania with a titania-content of up to 25% by weight have been found to be suited for all creping requirements described above, as will be elucidated in the summary and various examples that follow.
• the ceramic coating on the blade tip is chromia-titania (Cr 2 0 3 /Ti0 2 ) with 5% to 25% by weight titania (Ti0 2 ) , more preferably 5% to 15% by weight titania (Ti0 2 ) , and most preferably with 10% to 15% titania.
• the addition of titania to the ceramic composition also provides improved toughness, thereby facilitating coiling of the blades during, or subsequent to, manufacture.
• the chromia-titania ceramic deposit according to the present invention is preferably a single phase coating without any lamella of titania in the coating microstructure . It is believed that this fact adds to the wear resistance of the coating. In a multiphase material, each phase generally behaves differently to wear, leading to roughening of the creping surface and an increased risk of web breakage. This becomes particularly important for low grammage tissue.
• the use of a single phase ceramic top layer according to the present invention provides uniform wear, leading to a -smooth surface over the entire lifetime of the creping blade.
• the coating is applied by thermal spraying from a spraying powder comprised of substantially single phase particles.
• the raw material for the thermal spraying process is not a simple mix of chromia particles and titania particles, but rather a powder in which each particle already has the desired content of chromia and titania.
• the use of a simple mechanical blend of chromia particles and titania particles would lead to a coating having typical double phase properties, thereby not achieving the advantageous, smooth wear behavior described above.
• the properties of the single phase coating composition will be shown in more detail in the description below.
• Figure 1 illustrates the region of engagement between the surface of a dryer cylinder and the working edge of a newly installed creping blade according to the prior art (steel blade);
• Figure 2 illustrates the region of engagement between the surface of the dryer and the working edge of a worn creping blade according to the prior art (steel blade) after a certain working time;
• Figure 3 illustrates the region of engagement between the surface of the dryer and the working edge of a newly installed creping blade according to the present invention;
• Figure 4 illustrates the region of engagement between the surface of the dryer and the working edge of a creping blade according to the present invention after a similar working time as that of figure 2 for the prior art blade;
• Figures 5 to 7 represent EDX spectra for blade sliding bevels and are referred to in Example 1 below;
• Figure 8 is a SEM view of a macrochip event and is referred to in
• An embodiment of the creping blade according to the present invention can comprise the following: - a steel substrate having a thickness in the range from 0.635 to 1.250 mm; and a width in the range from 50 to 150 mm, preferably in the range from 75 to 120 mm; - a prebevel on the steel substrate, with an angle in the range from 0 (no prebevel) to 10 degrees, preferably from 4 to 8 degrees; - a bond coat, suitably applied by thermal spraying of Ni-Cr (80/20) for example by atmospheric plasma spraying (APS) to a thickness in the range from 10 to 50 microns; - a ceramic top layer at the working edge of the blade, the ceramic being a thermally sprayed composition of chromia-titania, suitably applied by for example APS, having a thickness at the front of the blade in the range from 150 to 300 microns, preferably from 200 to 300 microns; - a final grinding of the blade to the desired front bevel, from about
• FIG. 1 illustrates the use of a prior art creping blade and shows the situation for a newly installed steel blade.
• the creping blade 2 is shown in engagement with the surface of a dryer cylinder 1.
• the dryer moves according to the arrow a, transporting paper web 3 and a coating chemical layer 4 up to the working edge 5 of the blade 2.
• FIG. 1 illustrates the working edge 5 as shown in figure 1 and a sliding surface 5' .
• the impact wear located in the area 6 has created a groove on the surface 11 of the blade. Due to the usual constant linear load applied to the blade tip, the development of the sliding surface 5' will , directly decrease the scraping efficiency of the blade 2, whereby the amount of residual chemical layer 8 will increase over time.
• Figure 3 illustrates the use of a creping blade 2 according to the present invention and shows the situation for a newly installed blade. The blade is in contact with the dryer surface at the edge 5.
• the wear- resistant chromia-titania layer is represented by the darker area 9 in the figure.
• the prebevel given to the steel substrate causes the ceramic coating to have a wedge shape as indicated by the darker area 9 in the figure.
• FIG 4 again illustrates the use of a creping blade 2 according to the present invention, but now after a working time of tl (similar working time as shown in figure 2 for the prior art steel blade) .
• figure 4 shows the situation fox a worn creping blade according to the present invention.
• the sliding wear rate is much lower compared to the situation for the prior art blade shown in figure 2, and the sliding bevel 5' is so small that it is practically similar to an edge.
• the scraping efficiency of the inventive blade is only slightly lower compared to a newly installed blade, and the residual amount 8 of the coating chemical layer 4 has only increased by a small amount.
• Example 1 In a tissue mill, trials were performed with three different types of creping blades.
• the first type, labeled A was a blade according to the present , invention, having a ceramic top coating of chromia- titania with 15% titania content.
• the second type, labeled B was a prior art ceramic tipped blade with an alumina-based material for the ceramic coating.
• the third type, labeled C was a prior art metal carbide blade.
• the running conditions for the creping process were the following: - paper web made from 100% recycled fibers; - industrial towel type tissue; - grammages of 19,.
• Blade A (the blade according to the present invention) was run for 19 hrs and was not at the end of its lifetime.
• Blade B was run for 11 hrs and was removed due to 2 chips occurring.
• Blade C was run for 20 hrs and was at the end of its lifetime.
• Figure 5 represents an EDX (Energy Dispersive X-ray) spectrum made on the sliding bevel of blade A after 19 , hrs running time. No peaks are found related to the material of the Curemate-78 surface (W-Co-Cr) . The peaks from Cr, Ti and 0 are related to the ceramic composition of the creping blade coating, and the peak from Au is due to gold sputtering of the sample.
• Figure 6 represents an EDX spectrum made on the sliding bevel of blade B after 11 hrs running time.
• FIG. 7 represents an EDX spectrum made on the sliding bevel of blade C after 20 hrs running time.
• the blade material is WC-Co without any Cr content.
• a small but clearly visible Cr peak in this spectrum is related to the material of the Curemate-78 surface of the Yankee (W-Co-Cr) .
• W-Co-Cr the material of the Curemate-78 surface of the Yankee
• the failure of the ceramic created a line defect on the tissue web, which is unacceptable and therefore lead to a blade change.
• the state of the ' art ceramic tipped blade (blade B) is sensitive to macrochips.
• the state of the • art metal carbide tipped blade (blade C) is not particularly sensitive to macrochips but show signs of unwanted interaction with the dryer Curemate-78 surface.
• the blade according to the present invention (blade A) combines the benefits of the two state of the art blades .
• Example 2 On another tissue machine, currently employing alumina-based creping blades, a trial of ten blades according to the invention was performed.
• the running conditions for the creping process were the following: - paper web made from 100% deinked fibers (recycled) ; - toilet paper tissue type; - grammage of 16 g/m 2 ; - Yankee speed of 770 m/min; - Yankee surface comprised of cast iron; - Reel speed of 560 m/min (crepe ratio 27%) ; - web moisture of 3%; - creping blade dimensions of 1.2 x 120 x 3420 mm (thickness x width x length) ; - a blade bevel of 85 degrees (-5 degrees from square edge) ; - a blade load of 2.5 kN/m; - a stick-out of 60 mm.
• the ceramic blades currently used on this machine exhibits a very large variation in blade lifetime, ranging from 1 hour up to over 100 hours.
• the lifetime of the currently used alumina-based ceramic tipped blades is limited mainly by chipping problems, and the average lifetime is about 50 hours.
• the lifetime of the ten blades according to the present invention tested on this machine were (in hours) 77-116-60-142-76-50-65-109-44-124, with an average of 86 hours and a minimum lifetime of 44 hours. Change of blade was in this case dictated by a change in paper grade, and not by chipping problems .
• An alumina-based ceramic tipped blade was run on the machine for 131 hours and then inspected in a scanning electron microscope (SEM) .
• Figure 9 represents an SEM view of the edge of that blade.
• the sliding wear path, indicated by the arrow in the figure was found to have a width of 550 ⁇ m.
• Figure 10 represents a similar SEM view, but of the creping blade according to the present invention after a running time of 142 hours on this machine.
• the sliding , wear path, indicated by the arrow in the figure was found to have a width of 150 ⁇ m. This should be compared to the result evidenced by figure 9 for the state of the art blade for a similar running time on the same machine.
• the resistance to chips on cast iron for a tissue grammage this low is greatly improved by the use of blades according to the invention.
• the running conditions for the creping process were the following: - paper web made from 100% virgin fibers; - soft toilet paper tissue type - grammage of 21 g/m 2 ; - Yankee speed of 1100 m/min; - Yankee surface comprised of cast iron; - creping blade dimensions of 1.2 x 120 x 2790 mm (thickness x width x length) ; - blade bevel of 75 degrees (-15 degrees from square edge) .
• the blade according to the invention had a 90% chromia - 10% titania composition.
• the softness attributed value is an important criteria for this tissue mill.
• the three blade types were run for about 8 hours during 3 consecutive days of production of the same grade.
• the desired softness value is 3.0, with a minimum acceptable value of 2.6.
• Figure 11 shows a graph representing the results obtained by the three types of blades. Clearly, this trial shows that for high quality tissue grade, the state of the art ceramic blade is not able to reach the same results as the metal carbide blade, i.e. to keep the softness as constant and high as possible.
• the blade according to the invention gives a softness comparable to that of the metal carbide tipped blade, but lacks the potential drawbacks with respect to friction compatibility.
• Example 4 In the tissue machine of Example 2 above, tests were performed (under the same running conditions as outlined in Example 2 above) in order to inspect the wear pattern of the worn blades . A comparison was made between alumina-zirconia ceramic tipped blades of the prior art and chromia-titania ceramic tipped blades according to the present invention. Inspection of the worn blades was made by scanning electron microscopy (SEM) .
• SEM scanning electron microscopy
• Figure 12 shows a SEM view of the wear pattern created by running web on a state of the art alumina- zirconia ceramic tipped blade after a running time of 28 hrs .
• Figure 13 shows a view similar to that shown in figure 12, but now after a running time of 131 hrs.
• Figure 14 shows again a view similar to figures 12 and 13, but now for a blade according to the present invention.
• the blade shown in figure 14 has a ceramic coating of chromia with 15% by weight titania.
• the wear pattern shown in figure 14 was created after a running , time of 116 hrs.
• Figures 12 to 14 which all have the same magnification, clearly show that the wear of a multiphase material such as alumina with 40% by.
• the blade according to the invention has a ceramic top layer covering the working edge of the blade, as well as the surface upon which the web impacts during creping.
• the ceramic top layer is a ceramic composition comprising chromia-titania.
• the ceramic composition of the top layer comprises chromia-titania, with a titania content of 5% to 25% by weight, and most preferably from 10% to 15% titania.
• the ceramic top layer of the blade according to the present invention is comprised of a single phase composition, leading to a comparatively uniform impact wear at- the areas where the web impacts the creping blade.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Paper (AREA)
• Coating By Spraying Or Casting (AREA)
• Polishing Bodies And Polishing Tools (AREA)

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Publications (2)

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• 2004
  • 2004-09-07 WO PCT/EP2004/009954 patent/WO2005023533A1/en active Application Filing
  • 2004-09-07 KR KR1020067004670A patent/KR20060073615A/ko not_active Application Discontinuation
  • 2004-09-07 EP EP04764897A patent/EP1663635B1/de not_active Expired - Lifetime

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