Background of the invention

This invention relates to a doctor blade which is used in paper machines for guiding the paper web and for the maintenance of the roller or rollers of the paper machines.

There are prior known a variety of solutions of doctor blades, and generally there is a rivet made of metallic material in the doctor blade with which it can be fastened to its intended holder, for example by pushing the doctor blade into a groove in the holder, in which case the rivet prevents the doctor blade from becoming detached from the holder.

The weakness in the doctor blades according to the known solution is that because the rivet which fastens the doctor blade is metallic, this causes severe damage to the paper web of the paper machine, should the metallic rivet become detached from the blade, this can break the wire/felt of the paper machine and cause damage to the surface of the rollers, the rivet may even destroy the paper web and this will require major and costly repairs and furthermore, the production process will be interrupted while the repairs are being completed.

Furthermore, in known solutions, the problem is that because there may be dirt remaining between the doctor blade and the holder, it is awkward to remove the doc- tor blade from the holder, since the doctor blade is removed from the holder by pulling, the dirt causes friction between the doctor blade and the rivet, and the holder.

The aim of the present invention is to provide a doctor blade to avoid problems existing in the prior known solutions and to provide an effective and reliable as well as an economical solution for the doctor blade. Brief description of the invention

The doctor blade according to the invention is characterized by what has been said in the characterizing part of claim 1.

The preferable embodiments of the doctor blade according to the invention are characterized by what has been said in claims 2-10. The doctor blade according to the invention has certain advantages when comparing it with known solutions. The solution according to the invention also functions better and in a more simple way than the known solutions, and it is more reliable in operation than the known solutions. As the rivet of the doctor blade is made of plastic, it cannot become detached from the doctor blade as easily as a metallic rivet, and even should the plastic rivet according to the invention actually become detached from the doctor blade and become trapped in the paper web (wire/felt) of the paper machine, it will still not cause as much damage to the web of the paper machine as would be caused by a metallic rivet when it becomes trapped in the web. Secondly, because within the rivet of the doctor blade according to the invention, there are grooves or recesses or slots having been formed whose function is to clean the holder (to clean the groove of the holder from impurities) when the doctor blade is being removed from the holder, this means that the holder (the groove, slot or the corresponding in the hold- er) remains clean, and the doctor blade is light and easy to change in the holder.

Brief description of the figures

The doctor blade according to the invention has been described in more detail in the following with reference to Figs. 1-4 in which

Fig. 1 shows a front view of a doctor blade and the rivet within it. Figs. 2a and 2b show a sectional view of the doctor blade and its fastening to its intended holder.

Figs. 3a and 3b show the grooves, recesses or slots formed in the rivet of the doctor blade.

Fig. 4 shows the doctor blade in which the rivet is elongated. Detailed description of the invention

Fig. 1 shows a doctor blade 1 used in a paper machine according to the invention; into this doctor blade at least one rivet 2 has been fitted. The doctor blade according to the invention is made of a composite material, for example, a carbon fiber composite; and the rivet or rivets 2 in the doctor blade with which the doctor blade will be fastened to its intended holder (shown in Fig. 2b), are made of a plastic material, being either thermosets or thermoplasts. The rivets 2 can be any desired shape as seen from the top, for example, they can be round, elongated, triangular, etc. Fig. 2a shows a sectional view of the fitting (fastening) of the rivet 2 to the doctor blade 1 , and the rivet 2, according to the figure, has been fastened into a hole 8 in the doctor blade. The rivet 2 can be fitted into the doctor blade by unsoldering (for example, by injection molding) it into the hole 8 in the doctor blade, but also other solutions for fastening the rivet to the doctor blade can be possible.

Fig. 2b shows the fastening of the doctor blade into its intended holder 4, and according to the figure, in the holder 4 there are protruding parts 3 by which the rivet 2 is supported thus preventing the doctor blade 1 from becoming detached (falling and moving sideways) from the holder. The doctor blade has been fitted into the holder by pushing the doctor blade in a perpendicular direction against the plane in Fig. 2b into the holder 4.

Fig. 3a shows the grooves, recesses or slots 6, 7 formed in the rivet 2, and their function is to remove impurities from the holder 4 (or more specifically, from that space of the holder in which the rivet is) when the doctor blade 1 is being pulled away from the holder 4. The grooves, recesses or slots 6, 7 can be on the end surfaces 9 or side surfaces 10 of the rivet, and they can be any desired shape or size and there can also be any desired numbers of them in each rivet. The grooves, recesses or slots can also be any desired depth or width depending on the need.

Fig. 4 shows the doctor blade 1 according to the invention, in which the rivet 2 is elongated in shape. The rivet can also be other shapes, such as triangular, rectangular, etc. depending always on the use of the doctor blade.

It will be clear to a person skilled in the art that the invention is not limited only to the examples shown above, but it can be varied within the scope of the attached claims. In the solution according to the invention, the material from which the rivet for the doctor blade is made can be a plastic material which will have a high heat resistance, for example, the kind of plastic which resists temperatures even higher than 150 degrees Celsius. Also some material other than plastic material can have been added to the rivet of the doctor blade in order to strengthen the rivet, for ex- ample, fiberglass fibers.

In the solution according to the invention, the rivet in the doctor blade is thinner in the middle than at its ends, but the rivet can also be uniform for its entire length.