MXPA99005624A

MXPA99005624A - Coating blade

Info

Publication number: MXPA99005624A
Application number: MXPA/A/1999/005624A
Authority: MX
Inventors: Freti Silvano
Original assignee: Btg Eclepens Sa
Priority date: 1996-12-20
Filing date: 1999-06-16
Publication date: 2000-02-02

Abstract

A coating blade (5) for controlled application and smoothing of a coating composition on a travelling paper web (7) supported by a co-rotary roll (9), said blade (5) comprising a steel strip (13) elongated in a first direction between first and second edge sections, said first edge section engaging the paper web (7) and being provided with an abrasive wear resistant deposit (15) to extend the life of the blade, wherein an intermediate layer (17) positioned between said deposit (15) and said steel strip (13), said layer (17) having a higher resistance to abrasive wear than said deposit (15).

Description

COVER BLADE DESCRIPTION OF THE INVENTION The present invention relates to a coating blade for the controlled application and smoothing of a coating composition on a mobile paper web supported by a co-rotating roller. In a conventional manner, said blade comprises a strip of steel, an edge of which is provided with a coating or deposit resistant to abrasive wear, to prolong the life of the blade. In the conventional coating of a mobile paper web usually margin sections of the paper along both edges thereof will remain uncoated. This will result in a situation where the coating material along the boundary lines on both sides of the paper web will dry more rapidly than the coating material within said limits, due to a higher degree of absorption of the coating material. water along the edge lines of the coating. The practical disadvantage for such REF .: 30545 Faster drying of the coating material is faster wear of the coating blade around the coating boundaries, where the intermediate section of the blade will be subject to substantially slower wear. Rapid blade wear in these local areas results in frequent blade changes because less edge wear can be tolerated in the coating process, so as not to deteriorate the quality of the paper or disturb the process. If such local wear becomes too significant, too much dry coating material will pass under the blades in these boundary areas and may cause, by descaling or pickling, damage to the coated paper or to the downstream rollers, by local wear and tear. rollers. Descaling or pickling is constituted by the fact that the dry, thick coating material in the boundary lines can be detached from the paper. The use of the coating blades provided with a ceramic deposit along the edge in the coupling with the paper web usually increases the life of the blade compared to the uncoated steel blades, but since the intensity of the wear abrasive is greater in the edge areas, the blade has to be replaced although the larger part of it is still useful. Attempts have been made to avoid this problem of local wear of the coating blade. In this way, the application of the edge lubrication is described in PCT application W095 / 17264. The solution presented here works well, but requires installation and involves supervision and operational maintenance. The main purpose of the present invention is to provide a new coating knife for the application of a coating composition on a mobile paper web. Another object of the invention is to provide a coating blade comprising a strip of steel and a coating resistant to abrasive wear, provided thereon to prolong the life of the blade. A further object of the invention is to provide a coating blade that lies in a sandwich design, whereby the life of the blade will be substantially prolonged, with a high quality of the coated paper still being maintained. Still another object of the invention is to provide a coating blade provided with a wear resistant material to prolong the life of the blade with good maintained smoothing of the coating on the paper, to achieve a high quality. Yet another object of the invention is to provide a coating blade with a sandwich design containing a highly wear-resistant material, such as an intermediate layer without requiring a smoothing operation that lies in a high quality coating. For these and other objects of the invention which will be clear from the following description, the invention provides a coating blade for the controlled application and smoothing of a coating composition on a mobile paper web supported by a co-rotating roller. The cover blade according to the invention comprises an elongated steel strip in a first direction, between the first and second edge sections, the first edge section engages the paper web and is provided with a wear resistant deposit abrasive to prolong the life of the blade. The coating blade is characterized by an intermediate layer placed between the tank and the steel strip, said intermediate layer having a greater resistance to abrasive wear than the deposit or coating. The intermediate layer is suitably comprised of a material selected from borides, nitrides, metal carbides, and compositions thereof. In a conventional manner said metal carbide can be embedded in a metal matrix. The intermediate layer preferably has a thickness in the range of 50 μm to about 150 μm. The intermediate layer can be constituted by a cermet (metal-ceramic material) of a carbide and a metal, and the layer preferably has an abrasive wear resistance that is 2 to 6 times greater than that of the wear-resistant deposit.

It is particularly preferred that said intermediate layer be constituted by chromium carbide and Cr-Ni. The wear resistant deposit of the blade according to the present invention is preferably constituted by a ceramic, such as a metal oxide. A preferred oxide is alumina, optionally together with an amount of another metal oxide such as zirconium oxide. This amount may vary from about 3% to about 40% by weight based on the total composition. The wear resistant deposit conveniently has a thickness of from about 0.1 to about 1.0 mm, such as from about 0.2 to about. 0.5 mm, and a width in a secondary direction normal to the first direction and in the plane of the steel strip from about 4 to about 12 mm. It is preferred that the intermediate layer have a width in the second direction, which does not exceed that of the wear-resistant deposit. The present invention will now be further described in more detail by the non-limiting examples with reference to the accompanying drawings. In the drawings Figure 1 is a diagrammatic plan view of a detailed section of a coating device; Figures 2a and 2b show cross sections A-A and B-B indicated in Figure 1; Figure 3 is a diagram showing the differential wear rates in sections A (boundary lines or coating limits) and B; Figure 4 shows a cross section of an embodiment according to the invention; Figure 5 shows a similar cross section of an alternative embodiment; Y Figure 6 shows a diagram corresponding to that of Figure 3 on differential wear rates in sections A and B for a coating blade designed in accordance with the present invention.

Figure 1 illustrates the conventional knife coating techniques, which show part of a coating apparatus of a conventional design. A knife holder 3 carries a cover knife 5 which is in engagement with a moving paper net 7, the direction of travel is indicated by an arrow. The paper web 7 is supported by a reinforcing roll 9 which rotates in synchrony with the paper web 7. Upstream of the coating blade 5, the coating material is supplied to the network by an applicator not shown, and when it enters the area of contact with the blade the coating material will be evenly distributed over the paper web 7, the excess it is removed in a manner not shown. The coating material is applied to the paper over a width indicated by the double arrow b. Consequently, the paper is not coated across its full width as indicated by the double arrow a, but the uncoated areas indicated by c remain along the edges of the paper web 7. After the operation of coating the final paper will be trimmed along the edges thereof to eliminate the burr sections indicated by e. In Figures 2A and 2B showing the cross sections A-A and B-B of Figure 1, differences in wear rates between the edge sections and the intermediate section of the blade are illustrated. Due to the fact that the areas of the blade around the edge or boundary lines of the coating material applied to the net will be subject to a much faster rate of wear as illustrated in Figure IA, the blade needs to be replaced. even when the wear of the main section of the blade corresponding to Figure IB is very low, typically from about 5 to about 20% of the total thickness only. This means that the blade has to be replaced by a new blade even if only sections A as shown in figure 1 have been subjected to excessive wear, while section B could still be useful.

Figure 3 shows a diagram on the degree of wear in percent of the thickness of the blade at the tip thereof, plotting against time. The ordered sample, the total thickness of the ceramic and steel, as 100%, and the abscissa shows the wear time. The curve A corresponds to the wear of the sections A in figure 1, while the curve B reflects the wear of the intermediate section B of the blade. It can be seen from the diagrammatic curve A that the time for the wear to extend to the steel strip ts is relatively short and the wear then increases rapidly after reaching the steel strip. Figures 4 and 5 illustrate cross sections through the modes of the blade according to the present invention. The blade of figure 4 comprises the steel strip 13 having a bevel along the edge facing the mobile paper web, along the bevel an intermediate layer 17 such as plasma spray, sprayed with HVOF (high speed oxyfuel), or other suitable deposition techniques, and this intermediate layer is preferably comprised of tungsten-cobalt carbide or chromium chromonickel carbide. This intermediate layer preferably has a carbide content in the range of about 75% to about 96%. On the upper part of the intermediate layer 17 a ceramic deposit 15 has been applied, such as by plasma spraying, spraying by HVOF or the like, said deposit 15 extending beyond the intermediate layer 17 along the surface of the steel strip 13. The ceramic deposit 15 conventionally consists of a metal oxide or mixture of metal oxides, such as alumina, optionally together with zirconium oxide. Figure 5 shows an alternative embodiment of the coating blade according to the invention. In this embodiment, the intermediate layer 17 again extends towards the space between the ceramic tank 15 and the steel strip 13. In the embodiment according to figure 5 the intermediate layer 17 is substantially coextensive with the ceramic tank 15 .

In figure 6 a diagram is shown corresponding to that of figure 3. Again, the ordinate shows the total thickness of the blade section according to figures 4 and 5 as 100%. In this case, thanks to the greater resistance to wear of the intermediate layer 17, the time ts for abrasion, to reach the steel strip is significantly longer and the blade can consequently be operated for a correspondingly longer period of time before the replacement. The present invention makes possible the significant extension of the life of the coating blades, while maintaining a high quality coating. The sandwich design described herein is not restricted to the embodiments described above but only requires that the intermediate layer have a higher resistance to abrasive wear than the wear resistant deposit. Accordingly, the invention is limited only by its definition in the appended claims.

It is noted that in relation to this date, the best method known by the applicant to carry out the aforementioned invention, is the conventional one for the manufacture of the objects to which it relates.

Claims

CLAIMS Having described the invention as above, the content of the following claims is claimed as property:

1. A coating blade for the controlled application and smoothing of a coating composition on a mobile paper web supported by a co-rotating roller, the blade comprises an elongated steel strip in a first direction, between the first and second edge sections , the first edge section is coupled to the paper web and is provided with a coating or deposit resistant to abrasive wear, to prolong the life of the blade, characterized by an intermediate layer placed between the tank and the steel strip, the layer having a greater resistance to abrasive wear than the deposit.

2. A coating blade according to claim 1, characterized in that the intermediate layer comprises a material selected from borides, nitrides, metal carbides and compounds thereof, the metal carbides being optionally embedded in a metal matrix.

3. A coating blade according to claim 1, characterized in that the intermediate layer has a thickness at the tip of the blade in the range of about 50 μm to about 150 μm.

4. A coating blade according to any of the preceding claims, characterized in that the intermediate layer is a metal and a carbide cerametal.

5. A coating blade according to claim 4, characterized in that the intermediate layer is constituted by a material having an abrasive wear resistance that is 2 to 6 times greater than that of the tank.

6. A coating blade according to claim 5, characterized in that the intermediate layer is constituted by chromium carbide and Cr-Ni.

7. A coating blade according to any of the preceding claims, characterized in that the deposit is constituted by a metal oxide.

8. A coating blade according to claim 7, characterized in that the deposit substantially consists of alumina.

9. A coating blade according to claim 8, characterized in that the deposit is constituted by alumina together with an amount of another metal oxide.

10. A coating blade according to claim 9, characterized in that the other metal oxide is zirconium oxide.

11. A coating blade according to any of the preceding claims, characterized in that the reservoir has a thickness of about 0.1 to about 1.0 mm, such as about 0.2 to about 0.5 mm, and a width in a second direction normal to the first direction and in the plane of the steel strip from about 4 to about 12 mm.

12. A coating blade according to claim 11, characterized in that the intermediate layer has a thickness of about 50 to about 150 μm.

13. A coating blade according to claim 11 or 12, characterized in that the steel strip has a thickness of from about 0.3 to about 0.6 mm.

14. A coating blade according to any of the preceding claims, characterized in that the intermediate layer has a width in the second direction that does not exceed that of the tank.