Doctor blade with rounded-off contact tip

Abstract

The invention relates to a doctor blade the tip of which is rounded off. The doctor blade according to the invention has less tendency for oscillations and a significantly shorter running-in period in comparison with conventional doctor blades so that the properties and functionality of the doctor blade are fully formed immediately when it is put into operation.

Description

[0001] Title: Scraper blade with rounded contact tip

[0002] Description

[0003] The invention relates to a scraper blade according to the preamble of claim 1.

[0004] The doctor blade according to the invention serves to doctor the outer surface of a rotating roller, i.e., to clean it of adhering fibers. Doctor blades are used in particular in machines for producing and / or further processing a material web, in particular a fibrous web. EP 1 754 826 B1 discloses a doctor system in which a doctor blade is brought into tribological contact with the outer surface of the roller with its front side. The tribological contact between the roller and the doctor blade removes material from both the front edge of the doctor blade and the material from the roller cover or the roller.

[0005] To keep wear on the scraper blade and roller as low as possible, this scraper system (scraper blade and roller) is protected by a multi-component coating. Nevertheless, a certain amount of wear cannot be avoided. These scraper systems have proven themselves in practice.

[0006] A disadvantage of these doctor systems is that the doctor blade must first be run in. "Running in" means that the contact tip of a new doctor blade is worn down slightly during running in (due to abrasive wear) and thus takes on the contour of the roller. During the running-in process, the function of the "new" doctor blade is not yet as good as that of a run-in doctor blade. Therefore, the quality of a fiber web produced with this doctor system changes during the service life of the doctor blade. As a rule, the quality of the fiber web improves as the doctor blade runs in. This means that the user must divide the produced fiber web into different batches.

[0007] Another problem with conventional doctor systems is that the doctor blade is prone to vibration due to its flexible structure and large overall length. These vibrations not only impair the quality of the fiber web, but can also lead to the formation of so-called chatter marks on the roller. These chatter marks must be avoided at all costs because they are transferred to the fiber web running over the roller. A roller exhibiting chatter marks must be overhauled or recoated. This leads to production interruptions, which incurs immense costs.

[0008] The invention is based on the object of providing a scraper blade that avoids or at least significantly reduces these disadvantages of the prior art. In particular, the running-in process of a scraper blade should be at least shortened and the vibration excitation of the scraper blade reduced.

[0009] This object is achieved according to the invention in a scraper blade comprising a contact surface and a run-off surface, wherein a tip is formed between the contact surface and the run-off surface, in that the tip of the scraper blade is rounded. The radius at the tip of the scraper blade can be relatively small. Surprisingly, even a small radius has a significant effect on the vibration behavior of the scraper blade. Furthermore, it reduces or prevents the scraper blade from "running in." Volume fluctuations are prevented by the consistent removal of material by the scraper blade.

[0010] A scientific explanation for the advantages of the invention cannot yet be provided. It is assumed that the advantages are achieved through the interaction of the surface of the roller, the contact area of ​​the doctor blade, and a possible film of moisture present on the roller.

[0011] It is also conceivable that instead of the moisture film, the air which is carried along by the rotating roller (keyword: Newton's adhesion condition) contributes to achieving the advantages according to the invention.

[0012] It is assumed that the radius at the leading edge or tip of the inventive doctor blade forms a kind of hydrostatic sliding bearing between the contact surface of the doctor blade and the roll cover, and that the damping of this hydrostatic sliding bearing is promoted or even made possible by the radius at the tip of the doctor blade. Another explanation could be that the rounding of the contact tip partially anticipates the ground or worn-in state.

[0013] In any case, practical tests have shown that, firstly, running-in of the doctor blade is not necessary. Because the running-in phase is eliminated, the fiber web running over the roller has a consistent, consistent quality from the very first minute. As a result, the fiber web does not need to be divided into different batches.

[0014] In addition, the tendency to vibration and, consequently, chatter marks on the roller is significantly reduced. In other words, the operation of the doctor system is simplified and the quality of the fiber web is improved. Tests have shown that the radius of the rounded tip can be within a range of 0.02 mm to 0.1 mm. Radii of 0.045 mm, 0.055 mm, and 0.065 mm have proven particularly advantageous.

[0015] The radius or the rounded tip according to the invention is located between the contact surface and the run-off surface. It has proven advantageous if the angle α between the contact surface and the run-off surface is greater than 69° and less than 125°. Angles of 81° and 96° are particularly preferred.

[0016] The scraper blade according to the invention has a base area and it has proven advantageous if the

[0017] The contact surface and the base surface form an angle ß greater than 3° and less than 15°. An angle of 5° or 6° is particularly preferred.

[0018] Furthermore, it has proven advantageous if the base surface and the drainage surface form an angle greater than 70° and less than 110°. Angles y are particularly preferred. von 90°, 95°, 100° or 105°.

[0019] Regarding these radius dimensions and the claimed angle ranges, it is also true that, based on the current state of research, a scientific explanation for the advantages of these dimensions and angles cannot be provided. However, these values ​​have proven advantageous in empirical tests. The specific angles are process-specific. The angle of the contact surface depends on the system's contact angle. The angle between the discharge surface and the base surface is determined by the desired quality.

[0020] To increase the service life of the scraper blade according to the invention, it is further provided that it has at least one wear-resistant layer at least in the region of the run-off surface. This means that one or more wear-resistant layers can be applied one above the other. The thickness of the wear-resistant layer in the region of the contact surface is preferably greater than 0.1 mm. It is particularly preferably 0.25 mm or 0.30 mm.

[0021] In other words: The wear-resistant layer is generally thicker than the radius at the front tip of the scraper blade, so that the part of the front edge or tip forming the radius is not made of the base material of the scraper blade, but of the material of the wear-resistant layer. This may also contribute to the advantages of the invention.

[0022] Ceramic coatings and / or carbide coatings have proven to be advantageous materials.

[0023] Further advantages and advantageous embodiments of the invention can be found in the following drawings, their description and the patent claims.

[0024] drawing

[0025] It shows :

[0026] Figure 1 shows a first embodiment of a scraper blade; Figure 2 shows a second embodiment of a scraper blade; and

[0027] Figure 3 shows the installation situation of a scraper blade according to the invention or a scraper system comprising a roller and a scraper blade according to the invention.

[0028] Description of the embodiments

[0029] Figure 1 shows a first embodiment of a scraper blade according to the invention in a greatly enlarged (scale approximately 1:100) side view.

[0030] The scraper blade 1 is an elongated prismatic body having a contact surface 3, a run-off surface 5, and a base surface 7. Adjoining the contact surface 3 at the rear is an upper surface 9, which generally runs parallel to the base surface 7.

[0031] Because the upper surface has no contact with a roller or the fibrous web, it is of secondary importance for the function of the doctor blade 1. The same applies to the base surface 7. The base surface 7 is primarily used as a reference surface for various angle specifications and the thickness of the doctor blade.

[0032] Between the contact surface 3 and the run-off surface 5 is a leading edge or tip 11. This tip 11 is rounded according to the invention and has a radius R that can be in a range between 0.035 mm and 0.075 mm. During operation, the contact surface 3 rests against the roller, and the fibrous web runs over the run-off surface. This situation is greatly simplified and not shown to scale in Figure 3. The roller has the reference number 19.

[0033] In the embodiment shown in Figure 1, the angle a between the contact surface 3 and the run-off surface 5 is approximately 94°. However, the angle a can vary. Angles in a range between 81° and 96° have proven suitable.

[0034] In this exemplary embodiment, the angle ß between the base surface 7 and the contact surface 3 is approximately 6°. Here, too, the angle ß can vary within certain limits. Angles in the range between 3° and 15° have proven advantageous.

[0035] In this exemplary embodiment, the angle y between the base surface 7 and the drainage surface 5 is approximately 100°. This angle y can also vary within certain limits. Angles in the range between 88° and 106° have proven advantageous.

[0036] The thickness of the scraper blade 1 is defined as the distance between the base surface 7 and the top surface 9. It can be approximately 1.4 mm, for example.

[0037] A wear protection layer 13 is applied to the upper side of the scraper blade 1. The boundary between the wear protection layer 13 and the base material of the scraper blade is indicated by a line 15. From Figure 1 and Figure 2 it can be seen that the thickness of the wear protection layer 13 does not have to be constant, but in these embodiments increases with increasing

[0038] Distance from the tip 11 decreases. This is indicated by an angle θ in Figure 1. The angle θ can be less than 4°. It can also be zero.

[0039] The thickness of the base material in the area of ​​the run-off surface is designated Li; the thickness of the wear protection layer 13 is designated L2.

[0040] A thickness greater than 0.1 mm has proven advantageous for the wear protection layer 13. In any case, the thickness of the wear protection layer 13 should be greater than the radius R of the rounding at the tip 11. This results in the rounded tip being made of the material of the wear protection layer and not of the base material 17 of the scraper blade 1. As a rule, the base material 17 should account for at least 81% of the total height of the scraper blade.

[0041] Thicknesses of the wear protection layer 13 in the area of ​​the contact surface 3 of 0.2 mm to 0.3 mm have proven to be particularly advantageous.

[0042] The thickness Li of the base material ranges between 0.5 millimeters and 1.5 millimeters. It is preferably 0.9 mm, 1.0 mm, or 1.2 mm.

[0043] The wear-resistant layer 13 can comprise a ceramic coating or a carbide coating. It can also be constructed from multiple layers and comprise either multiple ceramic layers or multiple carbide layers. Combinations of ceramic layers and carbide layers are also possible and can be advantageous.

[0044] Figure 2 shows a further embodiment of a scraper blade 1 according to the invention. The second embodiment differs from the first embodiment with respect to the various angles a1, a2, and a3. The radius R of the tip 11 can also be selected differently.

[0045] The most important dimensions of the two examples are summarized below:

[0046] Example 1 (Figure 1) R : 0.065 mm a: 100° ß: 6° Y : 5° Li : 1.1 mm L2: 0.23 mm

[0047] Example 2 (Figure 2) R: 0.045 mm a: 95° ß: 6° y: 9° Li : 1.05 mm L2: 0.3 mm

[0048] Figure 3 shows a schematic, not to scale, detail of a scraper system comprising a roller with a cylindrical surface 21. The direction of rotation of the roller 19 is indicated by an arrow.

[0049] The scraper blade 1 rests with its contact surface 3 on the cylindrical surface 21 of the roller 19. The normal vector on the contact surface is directed toward the rotational axis (not visible in Figure 3) of the roller 19. This normal vector is indicated in Figure 3 by a line 23. It runs essentially in a radial direction.

[0050] The fibrous web, which is lifted from the roller 19 above the run-off surface 5, is not shown in Figure 3.

[0051] In the scraper blade 1 according to the invention, its front side, or the run-off surface 5, is oriented opposite to the direction of rotation of the roller 19. One could also say: The scraper blade 1 extends in a tangential direction to a surface 21 of the roller.

[0052] In the scraper system known from EP 1 754 826 B1, the scraper blade is aligned radially so that the front side of the scraper blade is in contact with the roller and not, as in the scraper blade according to the invention, via the contact tip.

[0053] Due to the shape, design, and arrangement of the doctor blade 1 according to the invention, running-in of the doctor blade is not necessary, i.e., the doctor blade 1 and its properties are constant from the outset, so that fibrous webs of consistent quality can be produced. The tendency of the doctor blade according to the invention to vibrate is significantly reduced compared to conventional doctor systems.

[0054] A further advantage of the doctor blade according to the invention is that it is subject to significantly less wear. Thus, a hydrostatic sliding bearing is present between the surface 21 and the contact surface 3, which is operated / maintained either by air or a film of moisture on the surface 21 of the roller. This increases the production period and the production quantity of the blades according to the invention, since they can be produced to the desired quality after just a short run-in phase.

[0055] Reference symbol list

[0056] I Scraper blade

[0057] 3 Contact surface

[0058] 5 Drainage area

[0059] 7 Floor space

[0060] 9 Top

[0061] II Point (Rounded) leading edge

[0062] 13 Wear protection layer

[0063] 15 Line

[0064] 17 Basic material of the scraper blade

[0065] 19 Wal ze

[0066] 21 Cylindrical surface

[0067] Li : thickness of the base material 17

[0068] L2 : Thickness of the wear protection layer a : Angle between contact surface and run-off surface ß : Angle between base surface and run-off surface y : Angle between base surface and the boundary line 15 R : Radius of the tip

Claims

Patent claims 1. Scraper blade comprising a contact surface (3) and a run-off surface (5), wherein a tip (11) is formed between the contact surface (3) and the run-off surface (5), characterized in that the tip (11) is rounded.

2. Scraper blade according to claim 1, characterized in that a radius (R) of the tip (11) is greater than 0.035 mm and that the radius (R) of the tip (11) is less than 0.075 mm.

3. Scraper blade according to claim 2, characterized in that the radius (R) of the tip (11) is equal to 0.045 mm, equal to 0.055 mm or equal to 0.065 mm.

4. Scraper blade according to one of the preceding claims, characterized in that the contact surface (3) and the run-off surface (5) enclose an angle (a) greater than 81° and less than 96°.

5. Scraper blade according to one of the preceding claims, characterized in that it has a base surface (7), and that the contact surface (3) and the base surface (7) enclose an angle (ß) greater than 3° and less than 15°.

6. Scraper blade according to one of the preceding claims, characterized in that the base surface (7) and the run-off surface (5) enclose an angle (y) greater than 88° and less than 106°.

7. Scraper blade according to one of the preceding claims, characterized in that a thickness (Li + L2) of the scraper blade (5) in the region of the tip is greater than 1 mm and less than 1.2 mm.

8. Scraper blade according to one of the preceding claims, characterized in that it has at least one wear protection layer (13) at least in the region of the contact surface (3).

9. Scraper blade according to claim 8, characterized in that a thickness (L2) of the wear protection layer (13) in the region of the contact surface (3) is greater than 0.1 mm.

10. Scraper blade according to claim 8 or 9, characterized in that the wear protection layer (13) comprises a ceramic, a carbide or a ceramic-metal coating (cermet).

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