WO2008037850A1 - Method of manufacturing a doctor blade, a doctor blade and a blade holder - Google Patents

Abstract

The present invention relates to a doctor blade for paper, board, finishing and tissue machines, and a method for manufacturing the doctor blade. The doctor blade includes a tip placed against the surface of a roll or a cylinder. The doctor blade consists of at least two different layers made of fibre reinforced plastic material. The doctor blade of the present invention and the method for manufacturing the same are characterised in that the doctor blade mostly consists of two layers of plastic material. One of the layers forms at least the main part of the body (48) of the doctor blade (40) and one of the lateral surfaces of the doctor blade (40). The other layer (46) made of a more wear-proof material forms at least partially the other opposite lateral surface of the doctor blade (40).

Description

Method of manufacturing a doctor blade, a doctor blade and a blade holder

(001) The present invention relates to a method of manufacturing a doctor blade, a doctor blade and a blade holder. The blade concerned is meant to be installed in contact with a moving surface and the blade can be used either to clean the moving surface or to apply a medium on said surface. The use of the blade and the blade holder of the invention is particularly advantageous in paper and board machines or corresponding web forming apparatus, in which the purpose is, by means of the blade, to keep either the rolls or the fabrics clean, to apply paste or corresponding medium onto the surface of the web, to detach the web from the surface of a roll or for example a Yankee cylinder or to crep the web. The invention also relates to a new type of a doctor blade construction where one of the leading ideas has been, in addition to improving the usage properties of the doctor blade, also to manufacture the doctor blade using, when possible, less expensive materials than before.

(002) Prior art blade holders are in most cases manufactured of a metal material. In a known blade holder used in a paper machine environment the blade holder includes an arm portion at which the blade holder is secured to a body formed by a bar. The arm portion continues in a jaw portion which includes a gap for a blade. Composite materials have recently taken over space from conventional metal materials in different applications, where particular advantages are to be gained when using materials which are better suited for that application. Presently, blade holders manufactured fully of a composite material have not been used for long. A blade holder having a composite structure is light and durable compared with conventional metal blade holders. For example by orientating the reinforcing fibers, the blade holder adapts better to the surface. In spite of this the blade holder is stiff in the loading direction of the blade, in other words in the machine direction. Further, a composite structure reverts to its original form even from extensive deformations.

(003) There is known in the prior art a blade holder disclosed in US patent publication 6,491 ,754 in which there is a recess supporting the doctor blade in the machine direction, provided with a pivot surface allowing swinging of the doctor blade. The doctor blade in turn has been provided with means allowing the swinging. The apparatus discussed include on one hand a projection, located in one side surface of the doctor blade and co-operating with said pivot surface and on the other hand pivoting devices located in the vicinity of the longitudinal doctor blade edge opposite to the tip of the doctor blade, for example a pneumatic hose; the doctor blade is turned around its longitudinal axis by changing the pressure of the hose.

(004) It is known from the prior art, as disclosed for example in Fl patent application 20035010, a treatment apparatus having a composite design comprising a body provided in the vicinity of a moving surface, a blade holder manufactured of a composite material essentially as one piece and connected to the body, a blade disposed in the blade holder, the edge of the blade being arranged to be placed in contact with the moving surface by moving the blade holder, and a separate pressing blade provided in the blade holder, one side of which is disposed to the blade holder while the other side extends closer to said edge than the blade holder.

(005) The blades presently in use, including the blades used in applying different pastes or corresponding media as well as doctor blades used for keeping rolls and fabrics clean, and creping blades, are more and more manufactured of composite materials so that in the blade there is a sharp edge at one long side. In other words one long side edge of the blade has been chamfered to a desired angle and this sharp edge is used for example to scrape a web or impurities from the surface of a roll or a cylinder. This structure imposes both an ecological and an economic problem as only a small portion of the width of the blade is used and thus most of the blade material goes wasted. This problem is partly solved in an approach described in publication US-B1-6,491,754 in which both the long sides of the blade have been chamfered and used. Only a small part of the problem is eliminated by the approach mentioned as the doctor blades are conventionally manufactured totally of the same composite material and thus, when more specialized composite materials are used, the material costs rise high, sometimes there is even lack of these materials on the market.

(006) Various designs of a doctor blade and applications where they are used are disclosed for example in the following prior art publications.

(007) US 4,549,933 discloses a doctor blade comprising a core layer of a fiber material, a graphite fiber layer disposed outside it and fiber material layers on the outer surfaces. The doctor blade is similar along its whole machine direction width and in the direction of thickness essentially symmetric relative to the core layer. (008) US-B1 -6,416,843 discloses a doctor blade used to keep roll surfaces clean, formed all over of a laminated fiber material layers at least one of which is a carbon fiber layer which contains also grinding particle for treating the roll surface. Like the doctor blade according to the previous publication, also this doctor blade is along its entire width made of the same material and essentially symmetric in the thickness direction.

(009) US-B1 -6,565,712 discussed a doctor blade having a composite design having a core of long fibers other than glass fiber material, an intermediate layer, in which at least one layer is of carbon fiber material, and a surface layer which is described to be composed of one or several layers preferably of a carbon fiber material. Also this doctor blade is both homogenous along its entire width and symmetric in the thickness direction.

(0010) It should be remembered as prior art that a large part of the doctor positions of paper and board machines are such that the wear rate of a thermosetting plastic blade of mere carbon fiber, or glass fiber and carbon fiber, is less than 0,5 mm/h. In these scraping positions blades are used, or in fact have to be used, the reinforcing material of which is a glass fiber - carbon fiber hybrid because solid carbon fiber blades do not start to wear and the scraping properties (heat resistance, stiffness, high friction, sharpness) of purely glass fiber- reinforced blades are not sufficient. Because of the limited wearing the composite blade, however, tends to become dull and the tip of the blade become rounded, and the contact between the blade and the surface of the roll becomes weak. Thermosetting plastic blades having glass fiber - carbon fiber reinforcement designs have been manufactured and designed to be similar on both sides of the center line of the blade structure (for example WO 03/060231), resulting in the symmetry of the blade in the thickness direction.

(0011) Prior art also discloses doctor blades used in paper and board machines for scraping belts, in particular conveyor belts, in wet pressing, drying, calendering and coating to keep the belts clean (FI-U-20010246). These belts are relatively soft and thus liable to be damaged, especially when scraping them with a metal doctor blade. The same risk exists with a roll coated with a soft material. Therefore various plastics are usually used instead of metal in the manufacture of doctor blades. Some plastics, in particular prior art fiber-reinforced plastics, have been found to be too hard for scraping belts and thus, in order to avoid damages and to minimize wearing, softer materials must be used than the known fiber-reinforced plastics. For example the tip of a blade made of this kind of a material is swaged when it hits a potential boss in the belt or a transverse groove and thus does not damage the belt. Generally, the doctor blades used in scraping rolls are too hard and thus they are not applicable in the scraping of soft belts.

(0012) The publication FI-U-20010246 mentioned describes an arrangement in a paper or a board machine for scraping a belt or a soft roll coating with a doctor blade having two or at best three functional components which together form the doctor blade. The doctor blade described in the publication for scraping a belt or a soft roll coating is at least partly manufactured of a material, the hardness of which is essentially the same as or lower than the hardness of the surface to be scraped. Thus, the doctor blade is prevented from cutting into the surface. In the doctor blade of the publication, the material described above, which does not damage the surface, has been provided as a layer extending along the entire width of the doctor blade. Further, the thickness of the layers is uniformly at least one half of the thickness of the doctor blade; thus, an adequate abrasion resistance is obtained. Further, a support structure has been provided in the layer which together with the layer forms the doctor blade. The supporting structure has been disposed in the doctor so that even when scraping with a worn doctor blade the belt always contacts the wearing layer of the doctor first, and the layer rather swages in stead of cutting into the belt. According to the publication the material which does not damage the surface is for example high-density polyethylene (HDPE), polyurethane (PU), polytetrafluoroethylene (PTFE), which are soft and their friction coefficient is low.

(0013) The Fl publication in question discloses also a doctor blade in which the top surface of the layer mentioned is provided with a further thin layer made of a harder material than the layer mentioned which extends to the contact point of the doctor blade and the belt as the first one of the different layers of the doctor. When the additional layer is made of a harder material than the layer under it, the doctor blade stays sharp at all times. The additional layer, although it is hard, is designed to become swaged like a soft layer and thus it does not damage the belt. It is described that the additional layer is either a separate structure or even a coating. It is described to be characteristic of the additional layer that it is adequately thin so that it does not prevent the layer from being swaged.

(0014) Today, the laminate accepted to be used as the doctor material is mainly manufactured of thermosetting plastics, which has the majority of the market. Also thermoplastic materials are available already, which enable obtaining an acceptable quality. Doctor blades are to a large extent manufactured so that carbon fiber is used as the reinforcing material, as it is excellent for the tip of the doctor blade. Carbon reinforcement is a suitably hard material but it does not however, damage the roll surfaces, which is what for example some glass fiber are suspected to do. Doctor blades manufactured of this kind of a carbon fiber-reinforces are, however, still made of the same material all over, or alternatively at least they are in the thickness direction essentially symmetric whereby the composite is formed of alternating layers of different reinforced materials. The reason for this is considered to be the different internal tensions of the various materials which, in order to meet the straightness requirement of the material, require symmetry of the composite material in the manufacture of the laminate.

(0015) Generally, it can be stated that carbon fiber, being an expensive material, forms more than half of the cost structure of the present carbon fiber composite doctor blade, when the doctor blade material is homogenous all over. The most common dimension of a doctor blade in the machine or width direction is 75 mm. However, only about 15 mm of the doctor blade is allowed to be worn after which the blade is replaced by a new one. Today, although carbon fiber is expensive, carbon fiber material is even scarce on the market which clearly predicts a further increasing price for the carbon fiber material on the market. For example for this reason the use of carbon fiber should be minimized by all available means.

(0016) The prior art doctor blades described above thus either have been provided at the surface with a very thin swaging coating, which is harder than the basic material of the doctor blade, or the doctor blades both are of the same structure over their entire width and are in the thickness direction either homogenous all over or at least essentially symmetric relative to their core. (0017) A disadvantage of the prior art structures is that in their manufacture, costly materials such as carbon fiber are used in a less cost-efficient way, in other words also in positions where it is not necessary. It has been noted that by using far more inexpensive materials, glass fiber and corresponding fiber materials, the same strength and elasticity properties are obtained as when using a doctor made to a large extent of carbon fiber.

(0018) Thus the general object of the invention is to provide both a new type of a method for manufacturing a doctor blade, a doctor blade and a new type of a blade holder for use in the securing of the new type of a blade according to a preferred embodiment of the invention to the body.

(0019) Thus, one of the main objects of the invention is to manufacture a composite of thermoplastic material reinforced with glass-fiber or other reinforcing material inexpensive to purchase, to be used as the body portion of a doctor blade and to connect to the body material mentioned the tip portion of a doctor blade (the so-called wearing part) manufactured of a thermoplastic composite of thermoplastic material reinforced with carbon fibers or other fibers producing the corresponding properties, or a combination of carbon fibers and glass fibers.

(0020) Another main object of the invention is to design the doctor blade asymmetric whereby the doctor blade wears out during the first wearing stage a little faster but still retains its form, in other words the tip of the blade remains sharp during the whole wearing stage.

(0021) A third main object of the invention is to develop a more economical method of manufacturing a doctor blade than before, according to which only the parts, in other words the tip portion/portions, where more expensive materials, as far as the properties are concerned, are needed are manufactured of these materials.

(0022) Thus, it is characteristic of a method according to a preferred embodiment of the invention for manufacturing a doctor blade of a fiber-reinforced plastic material that a) a first portion of a doctor blade is manufactured of a fiber-reinforced material, b) a second portion of a doctor blade is manufactured of a second fiber- reinforced material, and c) said first and second portion of the doctor blade are joined together.

(0023) It is characteristic of a method of manufacturing a doctor blade of fiber- reinforced material according to second preferred embodiment of the invention that the doctor blade is manufactured in the thickness direction of at least two asymmetric fiber- reinforced portions joined together.

(0024) It is characteristic of a method according to a third preferred embodiment of the invention for manufacturing a doctor blade of a fiber-reinforced plastic material that a) fiber material having enhanced strength properties is placed in a mould in the area producing the tip of a doctor blade, b) glass fiber is placed in the area producing the body of the doctor blade, c) the fiber materials are impregnated with thermosetting plastic resin, d) pressing at an elevated temperature to a doctor blade blank, and e) the doctor blade blank is removed from the mould.

(0025) It is characteristic of a doctor blade according to a preferred embodiment of the invention for paper, board, finishing or tissue machines, the doctor blade comprising a tip portion disposing against the surface of a roll or a cylinder, and the doctor blade comprising at least two layers of different fiber-reinforced plastic materials, that the doctor blade comprises mainly two plastic material layers so that one of the layers forms at least the main portion of the doctor blade body and one side surface of the doctor blade, an the other layer made of a more wear- resisting material at least partly forms the second opposite side surface of the doctor blade.

(0026) It is characteristic of a doctor blade according to a second preferred embodiment of the invention for paper, board, finishing or tissue machines, the doctor blade including a tip disposing against the surface of a roll or a cylinder, and the doctor blade being formed of at least two layers of different fiber-reinforced plastic material, that the doctor blade comprises in the width direction at least two plastic material layers of different fiber-reinforced materials so that one of the layers forms at least the main portion of the body of the doctor blade and the other layer forms at least partly the tip of the doctor blade. (0027) The doctor blade according to the invention provides for example the following advantages compared with prior art doctor blades: inexpensive manufacturing costs (savings in the use of carbon fiber), optimized material consumption, savings in materials, environmentally friendly,

- double operating life, no essential difference in manufacturing costs, optimized operating and wear properties, better stiffness than before - better heat transmission, and enhanced and better sustaining sharpness of the chamfer tip.

(0028) It is characteristic of a blade holder according to the invention, by means of which holder the blade treating a moving surface is secured to the body and the blade holder being provided with means for securing the holder to the body and with a gap formed by an upper and a lower jaw for receiving the blade, that the tip of the lower jaw of the gap mentioned is provided with means for holding the blade in a non-swinging manner in place in its width direction.

(0029) For example the following advantages are obtained by the blade holder according to the invention: it can be used both with prior art blades and new types of blades it can easily be adjusted according to the requirements of any application where the blades are used either by using specific fitting means or by manufacturing it to fit into the securing means in that particular application.

(0030) The doctor blade, its manufacturing method and the blade holder according to the invention are described in the following more in detail with reference to the accompanying drawings of which

Fig. 1 illustrates a prior art apparatus and its application,

Fig. 2 illustrates another prior art apparatus and its application,

Figs. 3a - 3d illustrate prior art blade - blade holder combinations and apparatus used in securing them to the body, Figs. 4a, 4b and 4c illustrate the wearing of a prior art doctor blade, Fig. 5 illustrates schematically a doctor blade according to a preferred embodiment of the invention,

Fig. 6a illustrates schematically a doctor blade according to another preferred embodiment of the invention, Fig. 6b illustrates schematically a doctor blade according to Fig. 6a in combined according to a further embodiment of the invention,

Fig. 7a illustrates a blade holder according to a preferred embodiment of the invention in combination with a blade according to a preferred embodiment of the invention, Fig. 7b illustrates a blade holder according to another preferred embodiment of the invention in combination with a blade according to a preferred embodiment of the invention,

Fig. 7c illustrates a blade holder according to a third preferred embodiment of the invention and a blade according to a preferred embodiment of the invention, and Fig. 8 illustrates the used of a blade holder according to the invention with a conventional blade.

(0031) Figure 1 illustrates a prior art treatment apparatus, described more in detail in Fl patent application no. 20035010, as fitted to cooperate with a moving surface 10. This moving surface 10 is a paper machine roll or a cylinder 11 , of which only a small portion has been illustrated. Generally the treatment apparatus is meant for treating a moving surface. When the treating means is a doctor and it is designed to remove impurities from the surface in question or for example in some paper machine positions to detach the web itself. In paper, board and other web forming machines also the surfaces of various cylinders and fabrics are moving surfaces. The treatment apparatus is used for example in coating a web, in which case coating paste is applied onto the surface of a moving web. This alternative has been illustrated in Figure 2. The apparatus further comprises a body 12 provided in the vicinity of the surface 10 to be treated. In Figures 1 and 2 the body 12 comprises a bar 13 supported to the structure of the paper machine and turnable on a shaft 14. In practice the bar is locked to the correct position by means of turnbuckle screws (not illustrated). On the other hand the bar can be turned with loading members towards the surface in order to improve the scraping result or to compensate the wearing of the doctor blade. (0032) The treating apparatus further comprises a blade holder 15, which according to the Fl patent application mentioned has been manufactured to essentially form a single uniform piece. Correspondingly, the blade holder 15 has been connected to the body 12 via a securing means 19. The means actually treating the surface is a blade 16 disposed in the blade holder 15; the dimensioning and the material of the blade can vary depending on the application. Figure 1 illustrates a scraping blade and Figure 2 a coating blade. The difference is to seen mainly in the location of the blade in connection with the roll; a scraping blade is directed against the rotating direction of the roll and a coating blade in the rotating direction of the roll. The blade 16 comprises a scraping edge located at the longitudinal edge of it further away from the blade holder, the scraping edge being disposed to contact the moving surface 10 by moving the blade holder 15. Then the moving surface becomes treated. Figures 1 and 2 illustrate a so-called stiff blade holder 15, whereby the movement of the blade holder 15 is accomplished by turning the bar 13. The blade holder 15 illustrated in Figures 1 and 2 further comprises a separate top plate or a pressing blade 18 one side of which is disposed to the blade holder 15. Correspondingly, the other side of the pressing blade 18 extends closer to said edge than the blade holder 15, thus supporting the blade 16. In the figures the blades 16 are illustrated unused. In practice the edge of the blade wears down and in the end it is chamfered to the other direction. In practice it is also possible to grind in the blade a chamfer corresponding to that of a worn blade. In Figures 1 and 2 the movement direction of the surface 10 has been illustrated with an arrow.

(0033) Figures 3a - 3d illustrate a prior art blade holder and also a prior art blade more in detail than the previous figures. In other words, the blade holder according to said Fl patent application 20035010 has been detachably disposed in the body 12 by means of a form locking 20, 21. The form locking has been arranged to be steady in the width direction of the blade 16 (in the machine direction) and essentially free in the longitudinal direction of the blade 16. Then the blade holder 15 can be moved in the longitudinal direction of the blade, in other words in the transverse direction of the machine. In practice for example the blade holder of a paper machine can be simply installed by pushing from the side and correspondingly removed by pulling. In spite of the quick locking the form locking 20, 21 is unfailing in the width direction of the blade whereby the blade holder definitely stays in place in the machine direction. As a precaution the movement in the machine direction can be prevented for the time of the operation for example by means of a lock pin. On the other hand, with appropriate material elections the transverse movement can be utilized in oscillation. Then by moving the blade holder, only, the blade can be moved relative to the surface. Preferably all the parts are of a composite material. Then for example the abrasive impact of for example metal rivets is avoided.

(0034) In the prior art treatment apparatus illustrated in Figures 3a - 3d the first securing means 20 of the securing means pair 19 is a contoured projection. Correspondingly, a second securing means 21 has been disposed to cover the first securing means 20 essentially at opposite sides. Then the second securing means 21 forms a groove for the projection-like first securing means 20. In principle the location of the securing means can vary. However, in the blade holder the securing means is preferably disposed in the back part in the direction of the blade holder. Then the blade is secured at the front part of the blade holder. Here the front part means the portion of the blade holder closest to the surface to be scraped. The securing means structure described allows free positioning of the blade holder and the blade holder can be designed optimal in view of the loading and the securing of the blade. At the same time disadvantageous protruding elements are avoided which would collect impurities and would be liable to be damaged. In existing bodies there are usually spiral holes for the securing of the blade holder. Then the securing of the blade holder 15 is easy by using a fitting member 22 according to the invention. Generally one of the securing means of the securing means pair is disposed in a separate fitting member meant to be secured to the body. Securing screws have been illustrated in Figures 3a and 3b with dotted lines.

(0035) A first alternative embodiment of the fitting member 22 is illustrated in Figure 1. The fitting means forms together with the body 12 a securing means for the contoured projection-like securing means of the blade holder 15. The structure presented is very compact and the fitting means is easy to attach to the body 12. Further, even the arm portions of prior art blade holders having a composite structure can by appropriate machining be formed to projection-like securing means. In practice it is, however, more advantageous to finish the blade holder during the manufacture, whereby the structure of the blade holder is uniform. The next embodiments of the fitting member 22 are illustrated in Figures 3a and 3b in which the same reference numbers are used for the functionally similar parts. In these figures one of the securing means 20 or 21 have been provided entirely in the fitting member 22. Then the fitting member 22 can be permanently secured to the body 12 with the bolts or screws illustrated with the dotted lines.

(0036) In Figure 3a a projection-like securing means 20 has been provided in the fitting member 22 while the groove-like securing means 21 is in the blade holder 15. Then the form locking is well protected from fouling. Further, the blade holder 15 can be designed favorable in view of the manufacture. In the treatment apparatus of Figure 3a, the fitting member 22 further comprises a bend 23 which compensates the change in the location of the blade 15 compared with a conventional blade holder. Due to the fitting member 22 the blade 16 extends closer to the surface 10 and thus in most cases the blade angle of the blade 16 changes in relation to the surface. When the blade holder 15 according to Figure 1 is extended the blade angle is reduced which usually has a negative impact on the scraping result. By moving the blade holder in the height direction the problem described is avoided or at least it is avoidable by adjusting the bar and its location. If necessary, the installation of the fitting member in the body can also be reversed. Also the degree and form of the bend , can vary, in different applications. When manufacturing new treatment apparatus, the fitting member can be omitted. This is possible by arranging one of the securing means 20 or 21 of the securing means pair 19 straight in the body 12. This is illustrated in the embodiments of Figures 3c and 3d. In particular the blade holder 15 of the figures 3d can be manufactured very short which allows installing it in confined positions.

(0037) Also adjustable blade holders are used today, in which the body stays in place while the blade holder turns. In addition to the stiff blade holders described above also the blade holder according to the figures presented above can be adjustable. In general, the securing means of the pair of securing means are designed to form a mutually functional joint. Then a change of angle between the securing means is possible while the locking of the blade in the width direction remains unchanged. One way of providing the blade holder adjustable is to design the securing means of the blade holder more open. Then the form locking is preserved while movement of the blade holder is still possible. In order to determine the movement, for example loading means can be provided between the securing means and the blade holder. (0038) The blade holder illustrated in Figures 1 - 3d has been designed to allow insertion of various kinds of blades. Figure 3 illustrates a thick plastic blade, in addition to which also thin metal or composite blades can be used. Due to the design of the blade holder the securing of thin blades can be carried out in many different ways. Figure 3c shows an ordinary rivet 28 while figure 3d illustrates a composite blade secured with a particular adapter 29. In the corresponding composite blade of Figure 3d there is a larger and as to its form different expansion 30 in the back part whereby a separate adapter is unnecessary. Further, there is a gap 32 in the blade holder for the blade 16, defined by a pressing blade 18 serving as an upper jaw and by a lower jaw 33. In the treatment apparatus also the pressing blade is of an essential importance. According to the figures the pressing blade 18 is similar to the blade 16. In addition to this, in the side of the pressing blade 18 to be fitted to the blade holder 15 there is a form-locking means 34 for securing the pressing blade 18 detachably to the blade holder 15. In this case the pressing blade, like the blade holder, is quick-locking and easily replaceable. Further, when choosing and manufacturing a pressing blade, the know-how and manufacturing methods of blades can be utilized which, simplifies the manufacture of the treatment apparatus and reduces costs.

(0039) Figures 4a, 4b and 4c illustrates wearing of a prior art doctor blade 16. In Figure 4a the longitudinal edge of the doctor blade has been chamfered and the doctor blade has just been introduced into use and the tip 36 on its inner surface 35 (the trailing surface in the clockwise rotating direction of the roll 11) has not worn down at all, yet. The tip 36 is sharp and performs well its function of cleaning the roll 11. In Figure 4b the doctor blade has been used for a period of time and the tip 36 of the doctor blade 16 has worn round for example due to process reasons. At this stage the doctor blade 16 allows fibers and other impurities to pass with the surface of the roll 11 and thus does not perform properly its task. In Figure 4c the doctor blade 16 is so much worn that the chamfered portion 37 to be seen in Figures 4a and 4b has totally worn out and, as a consequence of the wearing, the tip 36 of the doctor blade 16 has moved to the outer surface 38 of the doctor blade 16 (the leading surface in the clockwise rotating direction of the roll 11) where it stays sharp until the doctor blade has worn down so narrow, or short seen in the machine direction, that is must be replaced. (0040) The problem with the structure according to Figures 4a - 4c discussed above is conventionally that the doctor blade 16 is essentially throughout its entire thickness the same material whereby it wears out so that in the intermediate stage, that is while the chamfered portion 37 of the doctor blade is wearing down, the operation of the doctor blade is not satisfactory. The reason for the fact that in the intermediate stage illustrated in Figure 4b the tip of the doctor blade has worn down round is that the doctor blade is made entirely of the same material which means that the wearing is equally fast, or rather equally slow. Naturally the approach is that, as the tip of the doctor blade of the apparatus 'travels' along the thickness of the blade, the doctor blade must be manufactured of a material which wears down at an even pace throughout the material. However, when the blade material which is fairly wear- resistant wears down slowly the surface pressure between the blade and the surface to be scraped reduces as the form of the worn blade follows the form of the surface to be scraped. This creates a slightly stronger wearing stress at the tip of the blade due to the impurities on the surface as a consequence of which the tip becomes rounded and the blade starts to 'leak'.

(0041) For solving for example the problem described above, a new type of a doctor blade has been developed, the characteristic feature of a first embodiment of which is that one of the surfaces of the blade is manufactured of a material having improved wear-resistance properties, or is provided with such material, whereby the blade material having weaker wear-resistance properties wears out more easily and in a way leaves the maintaining of the surface pressure to be taken care of by the surface layer having better wear-resistance properties. The more detailed structure of the invention will be described in the following. In principle a doctor blade according to this alternative embodiment of the invention is formed of a basic composite having weaker wear-resistance properties constituting the main portion of the blade thickness and including one side surface of the blade, and of a surface composite having stronger wear-resistance properties, the surface composite being located only on one planar surface of the doctor blade or in the vicinity of it. In a structure according to a preferred embodiment of the invention the basic reinforcement of the doctor blade is composed of machine direction glass fibers present essentially along the entire thickness of the blade. The glass fibers can exist either as individual fibers of as orientated felt; these may be provided in several layers. One surface (corresponds to the outer surface 38 of the doctor blade in Figs. 4b and 4c) of this basic reinforcement or a partial layer in the vicinity of the surface has been provided with carbon or corresponding reinforcement fibers orientated transverse relative to the blade, i.e. in the wearing direction of the blade, i.e. seen from the paper machine in the machine direction. The carbon fibers mentioned may be sewn, stitched, entangled or secured by some other appropriate method to the glass fiber felt. By impregnating the composite produced in this way with a suitable resin and curing the product, a doctor blade is produced which at first wears down relatively fast so that the tip 36 illustrated in Figures 4 stays sharp all the time. The reason for the fast wearing is that the basic material of the blade has weaker wear resistance, whereby the blade does not have time to become rounded. When the blade wears down and the tip 36 reaches the lever 38 the wearing slows down as the surface layer of the blade 16 contains carbon fiber having better wear resistance. . . .

(0042) In a structure according to another preferred embodiment of the invention the basic reinforcing material in a doctor blade is either non-orientated glass fiber felt or woven glass fiber fabric in one or several layers, carbon fibers orientated in the direction mentioned being provided on one surface of the basic reinforcement mentioned. Said carbon fibers are tied to the glass fiber felt/fabric/reinforcement in the Z direction by stitching, entanglement, sewing or by some other suitable method, followed by impregnation with resin and curing as described above.

(0043) In fact it is also possible that in both the embodiments described above the basic reinforcement and the surface layer are manufactured in separate stages and subsequently the components already partly reinforced are joined together for example by heating the components cured with thermoplastic resin so that the resin used melts to an appropriate degree in the boundary surface of components and by subsequently pressing the components together.

(0044) The doctor blade 40 according to a third preferred embodiment of the invention illustrated in Figure 5 eliminates the problem described above so that the outer surfaces, i.e. the coating 44 (illustrated with dotted lines) of the chamfered portion 42 and the outer surface layer 46 of the doctor blade have been manufactured of a material which wears down more weakly than the rest of the doctor blade, i.e. of a harder material. Preferably the outer surface 46 of the doctor blade is manufactured for example in the way described in the preceding embodiments of a harder carbon fiber material or of a compound of carbon and glass fiber materials than the main portion 48 of the doctor blade. The coating 44 of the chamfered portion 42 in turn is preferably of a hard material such as for example ceramic, glass, metal ceramic, metal or a corresponding material. When this is done the tip 50 remains sharp during the whole time the chamfered portion 42 of the doctor blade 40 wears down, as the coating 44 according to the invention wears down more slowly than the main portion 48 of the doctor blade. In the same way, when the wearing has proceeded to the outer surface layer 46 of the blade, the doctor blade remains sharp as the outer surface layer 46 wears down more slowly than the main portion 48 of the doctor blade. The dotted line 52 indicates the wearing or replacement limit of the doctor blade.

(0045) Figure 6a illustrates another alternative preferred embodiment of the doctor blade 60. Thus the doctor blade is formed of a rectangular elongated plate-like piece having two planar side surfaces, two longitudinal edges and two transverse edges. In this alternative the doctor blade has been manufactured clearly of different materials in the width direction of the doctor blade, i.e. in^' the machine direction. In a preferred embodiment of this alternative the doctor blade 60 comprises a body portion 62 and a tip portion 64 subjected to wear. The body portion 62 of the doctor blade 60 may be manufactured for example of a plastic material reinforced with glass fibers or other corresponding advantageous fibers. In the same way the tip portion 64 of the doctor blade 60 may be produced a plastic material reinforced with carbon fibers, a combination of carbon fibers and glass fibers or other fibers giving corresponding usage properties. The plastic material may be thermosetting plastic or thermoplastic. Examples of thermosetting plastic suitable for this purpose are epoxy, phenolic resin and vinyl esters and vinyl ester hybrids for example with urethane (vinyl ester urethane, VEUH) and polyether amide. Examples of suitable thermoplastics are polyolefins, polyamides, polyetherether ketone (PEEK), polyether sulfone (PES), polyether imide (PEI), polyamide imides (PAI). When using thermoplastic, the components may be manufactured separately and joining the components to each other is possible for example by welding so that the plastic materials, which may be the same in both the components although the reinforcing fibers are different, are remelted at the boundary surfaces of the components 62 and 64 and subsequently the components are pressed together. The plastic materials and the manufacturing method mentioned may be used also in the manufacture of the doctor blades comprising different layers in the thickness direction described above in connection with Figures 4 and 5. Quite in the corresponding way the doctor blade structure described in connection with Figures 4 and 5 may be used in doctor blades having sharp edges on both longitudinal sides of the blade.

(0046) When thermosetting plastic is used as the plastic material the manufacture can take place by pressing or for example by pultrusion so that the fiber material having enhanced strength or other properties, such as carbon fiber or a fiber material essentially containing carbon fiber, is provided only in the area forming the tip of the doctor blade, glass fiber being provided on the rest of the area. In pressing, the fiber material is supplied in this way to a mold, impregnated with thermosetting plastic resin and pressed at an elevated temperature and pressure to form a doctor blade blank. The blank is removed from the mold and machined at the area of the tip to a chambered form. In pultrusion, the carbon fiber material impregnated with resin or a corresponding material is supplied to a mold, in other words to a pultrusion nozzle to the desired area forming the tip and resin-impregnated glass fiber is supplied to the remaining area. The fibers may be supplied via the same resin bath but in theory it is possible to use different resins for different types of fibers, presupposing that the process and usage properties of the resins are compatible. For example when a conventional narrow blade blank is produced (one blade width) the carbon fiber or a corresponding material is supplied to one side of the pultrusion nozzle to a somewhat narrow area, approx. 1/4 - 1/6 of the area, while the rest of the fiber material is glass fiber. If a double-edged blade is to be prepared (Fig. 6b), carbon fiber is supplied correspondingly to both edges of the nozzle and glass fiber to the center. In case of a wide blank (two blade widths) the carbon fiber or a corresponding material is supplied to the center portion of the nozzle, whereby, by splitting the blank in the longitudinal direction at the center in two parts and machining the edges of the splitting point to a chamfered configuration, two blades are produced.

(0047) Figure 6a illustrates a further alternative embodiment, in other words a way in which the embodiment of Figure 5 may be combined with a new type of a doctor blade. The Figure illustrates how it is possible to provide the outer surface of the tip portions 64 of the doctor blade 60 with a layer 66 of a harder material than the material of the main portion of tip. One alternative is to form the layer 66 of carbon fibers orientated in the machine direction in the way described above in chapters 40 - 43. In the same way the chamfered portion of the tip portion may be provided with the hard coating described in connection with Figure 5.

(0048) Figure 6b in turn illustrates a doctor blade manufactured according to Figure 6a but constructed so that both its sides can be used. In other words, both the long edge or side portions 64' and 64" of the doctor blade of Figure 6b have been chamfered and manufactured essentially of carbon fiber-reinforced material or a compound of glass and carbon fiber materials whereas the center portion 62' of the doctor blade has been produced of a glass fiber reinforcement or a corresponding less expensive material. Figure 6b further indicates with dotted lines a protruding element 94 disposed, when desired, on one side surface of the blade essentially at the longitudinal center line, by means of which the doctor blade can be installed into the blade holder so that it can be pulled out from the blade holder in the longitudinal direction, turned and pushed back in order to introduce the other blade tip into use. Naturally, the harder outer surface layer and/or the coating of the chamfered portion illustrated in Figure 5 can be applied also to the structure of this embodiment. Further, the protruding element of one side surface of the doctor blade described above can be used also with the doctor blades described in connection with Figures 4 and 5, in other words with doctor blades where one side surface has been manufactured of a harder material than the other one.

(0049) The blade holders and doctor blades according to the invention are discussed below supposing that the blade holder has been cut from its left edge which in practice means that the invention is in no way connected to any particular method of securing the blade holder but the blade holder can be secured to the body by any method.

(0050) Figure 7a illustrates a blade holder 70 according to a preferred embodiment of the invention and also a blade 90 according to a preferred embodiment of the invention illustrated in Figure 6b. The doctor blade according to the invention comprises sharp edges on both longitudinal sides of the blade. In order to improve the wear resistance the edges may be coated with ceramic, metal or metal ceramic. The upper part of the blade holder according to Figure 7, i.e. the upper jaw 72 is in the figure similar to for example that of the prior art blade holder disclosed above (Figures 1 - 3d). The lower part, i.e. the lower jaw 74 of the blade holder 70 according to a preferred embodiment of the invention, however, differs essentially from the prior art approaches. There are two recesses 76 and 78 in the lower jaw of the blade holder in stead of the one previously used. The longer recess 76 of the blade holder 70 which thus is located closer to the securing point of the blade holder to the bar (on the left, not illustrated in Figures 7 - 8) is in this embodiment as to its form of the same type as for example the prior art recess or gap illustrated in Figures 1 - 3d, in other words it is^' provided to accept the edge 92 of the blade further away from the surface to be scraped. However, according to this invention, the edge 92 of the blade 90 is not meant to rest firmly against the back wall of the recess 76 as the chamfered edge must not be damaged. For this reason the support point of the blade 90 must be closer to the center of the blade than according to prior art. The blade 90 is supported in the machine direction, i.e. in its width direction to another recess 78 located in the tip portion 80 of the lower jaw 74 of the blade holder 70, in other words closer to the outer edge 82 of the blade holder as seen from the body 70. The recess 78 is separated from the inner recess of the blade holder by a planar surface 98 which in this embodiment can be considered to continue as planar surface 96 between the recess 78 and the tip of the lower jaw, the other side surface of the doctor blade being located against both these planar surfaces so that the doctor is supported to the blade holder in a non-swinging manner so that the other edge 92 of the doctor blade located in the recess does not touch the bottom of the recess 76. Co-operating with the recess 78, there is a longitudinal protrusion provided in one side surface of the blade 90 according to the invention, a series of rivets or corresponding means 94 with which the blade 90 may be locked in the machine direction in place in the blade holder 70. In other words, during operation the protrusion or the corresponding member 94 is set against the back wall 78' of the recess 78 of the blade holder 70. When using the blade 90 according to this embodiment of the invention it is essential that the protrusion 94 extending along the entire length of the blade 90, or the series of protrusions arranged in a corresponding way, are essentially located at the center line of the blade 90 whereby both edges of the blade 90 may be used. The expression 'essentially at the center line' also covers the structural alternative where the protrusion or the series of protrusions may be provided also slightly off from the center line of the blade 90. This may de done when the wearing allowance of the blade is taken into account. Then in fact the protrusion or protrusions may be located at the center line of the blade when one of the edges of the blade has worn down and the other one has not been touched. The protrusion 94 mentioned may be a separate rivet, a profile, or a portion provided in the blade during its manufacture, for example when manufacturing the blade by pultrusion. In other words, when the edge 96 of the blade 90 being used has worn out so that according to conventional practice the blade 90 would have to be replaced, a blade 90 according to the invention is turned around and the operation can continue by using the edge of the same blade in the longitudinal side of the blade, referred to in the figure with number 92. The blade may be supported also in the approach of the invention in a known way with a pressing blade 48, which is located with the blade in the gap 84 between the upper jaw 72 and the lower jaw 74 of the blade holder 70 and presses the doctor blade against the planar surfaces 96 and 98. Preferably the pressing blade. is locked with form locking at its side facing the blade holder to the groove at the bottom of the gap.

(0051) The blade may be replaced so that the longitudinal locking of the blade, if such is used, is opened (for example by removing the locking pin inserted in the protrusion 94 through the low jaw 74 of the blade holder), the blade is pulled in the longitudinal direction out from the holder, it is turned around and pushed back to the holder so that the edge 92 of the side is set against the surface to be treated.

(0052) Figure 7b illustrates a blade holder according to another preferred embodiment of the invention, in which the design of the low jaw 74 of the holder has been slightly modified compared with the blade holder illustrated in Figure 7a. As there are no rivets, thicker portions or other space-requiring element in either of the side surfaces in the longitudinal edge sections of the double-sided blade 90, the blade holder 70 may be of the type illustrated in Figure 7b, thus lower jaw 74 of the blade holder is provided with one recess 78, only, located in the tip portion of the lower jaw at a distance of at least one half of the width of the blade from the bottom 86 of the groove provided for the blade 90 in the gap 84 of the blade holder 70.

(0053) Figure 7c in turn illustrates a blade 90' according to another preferred embodiment of the invention, the blade causing and/or facilitating modifications also in the blade holder 70. In the doctor blade 90' of this invention, which blade may, preferably but not necessarily, be of a type described in connection with Figures 4, 5 and 6, there are at one of its side surfaces two protrusion 94' and 94" . or series of projections extending in the longitudinal direction of the blade essentially at equal distances from the longitudinal center line of the blade 90'. Also here the term 'essentially at equal distances' must be understood so that if desired the wearing allowance of the blade may be taken into account the way described in chapter 50. In this embodiment the blade 90' leans in the width direction, i.e. machine direction, at its protrusion 94' on the outer edged 82 of the lower jaw 74 of the blade holder 70. Of course the corresponding machine direction support may also be provided between the protrusion 94" of the blade 90' and the inner recess of the of the blade holder, whereby thus the lower portion of the back wall of the inner recess illustrated in the figure must either be transferred to the right in the figure to the level of the blade protrusion 94" or a projecting portion must be provided at the bottom of the inner recess which together with the blade protrusion serves as a supporting member for the blade 90'. It should also be noted that a recess may not be necessary in the tip portion 80 of the lower jaw 74 of the blade holder 70 as there is no corresponding protrusion in the blade of this embodiment.

(0054) Figure 8 still illustrates how a blade holder according to Figure 7a may be used with a conventional one-sided blade 16, whereby the side of the blade opposite the edge 17 of the blade 16 rests against the back surface 86 of the inner recess. In other words, depending on the situation it is possible to use in the blade holder according to Figure 7a either a conventional blade of a blade of the new type.

(0055) As far as the securing of the blade holder to the body is concerned, that can be accomplished as mentioned above by manufacturing the blade holder to fit directly into the securing means of the body or a body type, or by providing it with securing means suitable for use with a fitting means. Examples of suitable fitting means are described in connection with Figures 1 , 2, 3a and 3b, but also other kinds of fitting elements may be employed including the ones used in connection with adjustable blade holders.

(0056) Yet another embodiment of the invention is manufacturing the tip portion of the doctor blade of a material where friction-reducing particles such as for example Teflon have been mixed into the matrix, the resin. The diameter of these particles is preferably about 20 μm. These particles reduce the friction between the blade and for example a ceramic roll, thus allowing reduced wearing of the blade, lower heat formation and savings in energy consumption.

(0057) As can be seen from the above, a new type of a manufacturing method has been developed and a doctor blade which is in use at least equal to prior art doctor blades but induces significantly lower raw material costs. I should also be noted from the above that only a few most preferred embodiments of the intention have been discussed in the description which, however, in no way intend to limit the scope of protection from what has been defined in the appended patent claims.

Claims

We claim:

1. A doctor blade for paper, board, finishing or tissue machines, the doctor blade including a tip disposed against the surface of a roll or cylinder, and being formed of at least two layers of different fiber-reinforced plastic material, characterized in that the doctor blade (40) mainly constitutes two plastic material layers so that one of the layers forms at least the main portion of the body (48) of the doctor blade (40) and one side surface of the doctor blade (40), and the other layer (46) made of a more wear- resisting material forms at least partly the other, the opposite side surface of the doctor blade (40).

2. A doctor blade according to claim 1 , characterized in that the doctor blade (40) has been divided into said layers (46, 48) in the thickness direction.

3. A doctor blade according to any of the preceding claims, characterized in that said layer (48) forming at least the main portion of the body of the doctor blade (40) is mainly glass fiber-reinforced plastic material.

4. A doctor blade according to claim 3, characterized in that the glass fibers are essentially orientated in the longitudinal direction of the doctor blade.

5. A doctor blade according to any of the preceding claims 1 - 4, characterized in that said layer (46) at least partly forming the other surface of the doctor blade (40) is mainly carbon fiber.

6. A doctor blade according to any of the preceding claims 1 - 4, characterized in that said layer (46) at least partly forming the other surface of the doctor blade (40) is mainly a composite of carbon fiber and glass fiber.

7. A doctor blade according to claim 5 or 6, characterized in that the carbon fibers are essentially orientated in the machine direction, in other words transverse relative to the longitudinal direction of the doctor blade.

8. A doctor blade according to any of the preceding claims, characterized in that the matrix material used in thermoplastic.

9. A doctor blade according to any of the preceding claims, characterized in that the body portion (48) of the doctor blade (40) and the portion (46) forming the other side surface are manufactured separately from each other

10. A doctor blade according to any of the preceding claims, characterized in that the body portion (48) of the doctor blade (40) and the portion (46) forming the other side surface have been manufactured separately from each other by using as the matrix material the same thermoplastic material and joined together for example by welding.

11. A doctor blade according to any of the preceding claims 1 - 8, characterized in that the portion (48) of the doctor blade (40) and the portion (46) forming the other side surface have been manufactured as one piece for example by pultrusion.

12. A doctor blade according to any of the preceding claims, characterized in that the portion (46) of the doctor blade (40) at least partly forming the other side surface is made of a harder material than the body portion (48) of the doctor blade (40).

13. A doctor blade for paper, board, finishing or tissue machines, the doctor blade including a tip disposed against the surface of a roll or cylinder, and the doctor blade being formed of at least two layers of different fiber-reinforced plastic material, characterized in that the doctor blade (60; 60') is formed in the width direction of at least two different layers (62, 64; 62', 64', 64") of fiber-reinforced plastic material so that one of the layers forms at least the main portion of the doctor blade body (62; 62') and that the other layer (64; 64', 64") at least partly forms the tip of the doctor blade (60, 60').

14. A doctor blade according to claim 13, characterized in that the doctor blade (60') is formed of three portions (62', 64', 64") and thus also of three layers so that the portions (64', 64") forming the tip of the doctor blade (60; 60') are located on both sides of said body portion (62').

15. A doctor blade according to any of the preceding claims 13 - 14, characterized in that said layer (62; 62') forming at least the main portion of the body of the doctor blade (60; 60') is mainly fiber-reinforced plastic material.

16. A doctor blade according to any of the preceding claims 13 - 15, characterized in that said layer (64; 64', 64") forming at least partly the tip of the doctor blade (60; 60') is mainly carbon fiber.

17. A doctor blade according to any of the preceding claims 13 - 16, characterized in that said layer (64; 64', 64") forming at least partly the tip of the doctor blade (60; 60') is mainly a composite of carbon fiber and glass fiber.

18. A doctor blade according to any of the preceding claims 13 - 17, characterized in that the matrix material used is thermoplastic.

19. A doctor blade according to any of the preceding claims 13 - 18, characterized in that the body portion (62; 62') of the doctor blade (60; 60') and the portion (64; 64', 64") forming the tip have been manufactured separately from each other.

20. A doctor blade according to any of the preceding claims 13 - 19, characterized in that the body portion (62; 62') of the doctor blade (60; 60') and the portion (64; 64', 64") forming the tip have been manufactured separately from each other by using the same thermoplastic material as the matrix material and by joining them together for example by welding.

21. A doctor blade according to any of the preceding claims 13 - 20, characterized in that in that the body portion (62; 62') of the doctor blade (60; 60') and the portion (64; 64', 64") forming the tip have been manufactured as one piece for example by pultrusion.

22. A doctor blade according to any of the preceding claims 13 - 21 , characterized in that the portion (64; 64', 64") of the doctor blade (60; 60') at least partly forming the tip of the doctor blade (60; 60') is of a harder material than the body portion (62; 62') of the doctor blade (60; 60').

23. A doctor blade according to any of the preceding claims 13 - 22, characterized in that the portion (64; 64', 64") at least partly forming the tip of the doctor blade (60; 60') has been coated with a layer (66) of a more wear-resisting material.

24. A doctor blade according to claim 23, characterized in that said layer (66) contains machine direction carbon fiber.

25. A doctor blade according to any of the preceding claims 1 - 24, characterized in that the chamfered tip portion of the doctor blade (40; 60; 60') has been coated with a hard material such as for example ceramic, glass, metal ceramic or metal.

26. A doctor blade according to any of the preceding claims 1 - 25, characterized in that the wearing tip portion of the doctor blade (40; 60; 60') has been manufactured of a material, in which particles reducing friction such as for example Teflon particles, have been mixed into the matrix, i.e. resin.

27. A doctor blade according to any of the preceding claims 1 - 12 or 14 - 26, characterized in that the blade (40; 60'; 90; 90') has been provided at one of its sides with a protruding portion (94; 94', 94") for placing the blade (40; 60'; 90; 90') to the blade holder (70).

28. A doctor blade according to claim 27, characterized in that the blade (60; 90) has been provided at one of its sides with a protruding portion (94) located essentially at the longitudinal center line of the side for placing the blade (60';90) to the blade holder (70).

29. A doctor blade according to claim 27, characterized in that the blade (90') has been provided at one of its sides with two longitudinal protruding portions (94', 94") located essentially at equal distances from the longitudinal center line of the blade for placing the blade (90') to the blade holder (70).

30. A doctor blade according to claim 27, characterized in that said protruding portion (94; 94', 94") is as long as the entire blade (60, 90, 90').

31. A doctor blade according to claim 27, characterized in that said projecting portion (94; 94', 94") is formed of several individual projecting portions.

32. A doctor blade according to any of the claims 27, 28, 29 or 31 , characterized in that said protruding portion (94; 94', 94") is a rivet, a stud or a corresponding member.

33. A doctor blade according to any of the preceding claims 27 - 32, characterized in that said protruding portion (94; 94', 94") is has been provided in the blade (60, 90', 90") during its manufacture for example by pultrusion.

34. A doctor blade according to any of the preceding claims 27 - 33, characterized in that the blade (40, 60, 60', 90, 90') is used to keep rolls, cylinders or belt-like fabrics clean.

35. A doctor blade according to any of the preceding claims 27 - 33, characterized in that the blade (40, 60, 60', 90, 90') is used to apply coating paste or some other medium onto the surface of a web-like material.

36. A doctor blade according to any of the preceding claims 27 - 33, characterized in that the blade (40, 60, 60', 90, 90') is used to detach the web from the surface of a

Yankee cylinder of a roll.

37. A doctor blade according to any of the preceding claims 27 - 33, characterized in that the blade (40, 60, 60', 90, 90') is used to crep a web.

38. A method of manufacturing a doctor blade of a fiber-reinforced plastic material, characterized in that the a) a first portion (46; 64; 64', 64") of the doctor blade is manufactured of a first fiber-reinforced material, b) a second portion (48; 62; 62') of the doctor blade is manufactured of a second fiber-reinforced material, and c) said first and second portions of the doctor blade (40; 60; 60') are joined together.

39. A method according to claim 38, characterized in that said first portion (64; 64', 64") is as long as the entire doctor blade (60; 60') and one of its longitudinal sides is limited by the tip of the doctor blade (60; 60').

40. A method according to claim 38 or 39, characterized in that said second portion (62; 62') is the body portion of the doctor blade and as long as the entire doctor blade (60; 60').

41. A method according to claim 38, characterized in that said first portion (46) is as wide as the entire doctor blade (40) and one of its longitudinal sides is limited by the tip of the doctor blade (40) and the other side surface forms the other side surface of the doctor blade (40).

42. A method according to claim 38 or 41 , characterized in that said second portion (48) is as wide as the entire doctor blade (40) and the other side surfaces forms the other side surface of the doctor blade (40).

43. A method according to any of the preceding claims 38 - 42, characterized in that said portions (62, 64; 62', 64', 64") are manufactured of fiber-reinforced thermoplastic material.

44. A method according to any of the preceding claims 38 - 43, characterized in that said portions (46, 48; 62, 64; 62', 64', 64") are joined together by remelting them at their boundary surfaces and after that pressing said portions (46, 48; 62, 64; 62', 64', 64") against each other.

45. A method according to any of the preceding claims 38 - 44, characterized in that the reinforcing fiber used in said first portion (46; 64; 64', 64") is mainly carbon fiber.

46. A method according to any of the preceding claims 38 - 45, characterized in that the reinforcing fiber used in said first portion (46; 64; 64', 64") is a compound of carbon fiber and glass fiber.

47. A method according to any of the preceding claims 38 - 46, characterized in that the reinforcing fiber used in said second portion (48; 62; 62') is mainly glass fiber.

48. A method according to claims 38, 39 and 40, characterized in that a third portion substantially similar to the first portion is manufactured for the doctor blade and is joined to the second portion at its opposite edge relative to the first portion.

49. A method of manufacturing a doctor blade, characterized in that the doctor blade (40) is manufactured in the direction of its thickness of at least two fiber- reinforced portions (46, 48) asymmetrically joined to each other.

50. A method according to claims 49, characterized in that said first portion (46) is the surface layer located at the inlet surface of the doctor blade.

51. A method according to claims 49 or 50, characterized in that said first portion (46) is of a harder material than said second portion (48).

52. A method according to claims 49, characterized in that said second portion (48) is the body portion of the doctor blade (40) and as long as the entire doctor blade.

53. A method according to any of the preceding claims 49 - 52, characterized in that the reinforcing fiber used in said first portion (46) is mainly carbon fiber.

54. A method according to any of the preceding claims 49 - 53, characterized in that the reinforcing fiber used in said first portion (46) is a compound of carbon fiber and glass fiber.

55. A method according to claims 53 or 54, characterized in that the carbon fibers are orientated in the machine direction, that is transverse to the longitudinal direction of the doctor blade.

56. A method according to any of the preceding claims 49 - 54, characterized in that the reinforcing fiber used in said second portion (48) is mainly glass fiber.

57. A method according to claim 56, characterized in that the glass fibers are orientated in the longitudinal direction of the doctor blade.

58. A method of manufacturing a doctor blade of a fiber-reinforced plastic material, characterized in that a) fiber material having enhanced strength properties is placed in the mould in the area producing the tip of the doctor blade, b) glass fiber is placed in the area producing the body of the doctor blade, c) the fiber materials are impregnated with thermosetting plastic resin, d) the materials are pressed at an elevated temperature to a doctor blade blank, and e) the doctor blade blank is removed from the mould.

59. A method according to claim 58, characterized in that the fiber material of stage a) is fiber material impregnated with thermosetting plastic resin and the glass fiber of stage b) is glass fiber impregnated with thermosetting plastic resin.

60. A method according to claim 58 or 59, characterized in that mainly carbon fiber is used in the forming of the tip area of the doctor blade.

61. A method according to claim 58 or 59, characterized in that a compound of carbon fiber and glass fiber is used in the forming of the tip area of the doctor blade.

62. A method according to claim 60 or 61 , characterized in that the carbon fibers are orientated in the machine direction.

63. A method according to any of the preceding claims 58 or 62, characterized in that at least one thermosetting plastic resin is used in the impregnation of the fiber material.

64. A method according to any of the preceding claims 58 or 63, characterized in that, after the blank has been removed from the mould, at least one of its long sides is machined to have a chamfered configuration.

65. A method according to claim 58 or 59, characterized in that the portion of the mould producing the tip portion of the doctor blade in stage a) is located at both long sides of the mould.

66. A method according to any of the preceding claims 58 - 65, characterized in that a layer (66) of a harder material than the material of the main portion of the tip area (64; 64', 64") is supplied to the outer surface of the tip portion of the doctor blade (60; 60').

67. A method according to any of the preceding claims 58 - 66, characterized in that the chamfered portion of the doctor blade (69; 60') is coated with a hard material, such a ceramic, glass, metal ceramic or metal.

68. A blade holder, via which the blade treating a moving surface is secured to the body, the blade holder (70) being provided with means for securing the holder to the body and with a gap (84) formed of an upper jaw (72) and a lower jaw (74) for receiving the blade, characterized in that the tip portion (80) of the lower jaw (74) of said gap (84) has been provided with means (78, 82) for holding the blade (90) in its place in the blade holder (70) both, in the width direction and in a non-swinging manner.

69. A blade holder according to claim 68, characterized in that said means for holding the blade in place comprise a recess (78) in the lower jaw (74) of the blade holder and of planar surfaces (96, 98) located at its sides, against which surfaces the blade is pressed in a non-swinging manner.

70. A blade holder according to claim 68 or 69, characterized in that the distance of said recess (78) from the bottom (86) of the gap (84) receiving the blade is at least one half of the width of the blade.

71. A blade holder according to claim 68, characterized in that said means for holding the blade in place are formed of the outer edge (82) of the lower jaw (74) of the blade holder and of a planar surface (96) located at its side, against which the blade is pressed in a non-swinging manner.

72. A blade holder according to any of the preceding claims 68 -71 , characterized in that the gap (54) further includes a groove for a pressing blade (18).