FI80087B - MALBLOCK VID EN RAFFINOER. - Google Patents

Description

80087

MILLING BLADE BLADE - MALBLOCK VID EN RAFFINÖR

The present invention relates to a refiner blade block consisting of a steel sector or part thereof made of corrosion-resistant steel.

The most important process in pulp production is the grinding of pulp, which takes place in specially designed refiners. Of these, a disc grinder, in which two opposed discs grind wood chips fed into the gap between them, is the most commonly used device, but also the so-called the cone grinder forms a significant group of equipment. Because wood is ground in a refiner under high pressure using water as a flux and lubricant, and because the decomposing wood pulp is rich in organic acids, great attention must be paid to the material of the refiner blades. On the one hand, the blades must be hard and wear-resistant, on the other hand, corrosion-resistant, and in addition, the blade material must be sufficiently tough so that various pressure shocks and other disturbances do not damage the blades.

The most common blade material is martensitic stainless steel, which contains 14-18% chromium, depending on the carbon content. This steel grade is relatively inexpensive and hard and can still be heat treated and hardened. In addition, it is highly resistant to the chemical conditions prevailing in refiners. However, the greatest weakness of the hardest grades in particular (carbon content 1.2-1.5%) is fragility, which results in poor impact resistance and resistance to tensile stresses. However, these steel grades have been the best compromise to meet conflicting requirements, but if, for example, in a disc mill, in the event of a malfunction, the opposite blades go so-called blades, i.e. their blade patterns suddenly hit each other, a sharp blow will surely break the tens of thousands of marks. Also, the mere centrifugal force caused by a heavy grinding blade rotating at high speed can become too much of a tensile load for itself if it consists entirely of very brittle steel.

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Traditionally, the entire blade was formed from the same corrosion-resistant, hard, and wear-resistant material required for wood pulp milling. Today, blades are assembled from several so-called grinding steel segments, which are actually sectors or parts of a circle or cone. Furthermore, for example, U.S. Pat. No. 4,423,845 discloses a steel sector having a locally hardened grinding surface, thus allowing better controllability of the grinding process. It is also known from the same patent and from English patent publication 1,228,046 and from the Soviet inventor's certificate 502,993 to incorporate various substances, such as ceramics and parts thereof, in the desired places in the grinding blade so as to achieve an even better grinding result.

Although the use of substances of different hardness in the same milling blade must be considered known on the basis of the above, nowhere is a solution proposed to take advantage of this feature so that the milling blade has a significantly longer service life or minimizes production downtime if the mill is broken.

The object of the present invention is to eliminate the above-mentioned drawbacks and to provide a new type of disc or cone refiner blade block in which the above-mentioned aspects are taken into account. To achieve this, the blade block according to the invention is characterized in that at least part of the grinding surface of the block is formed of one or more removable parts of a substantially harder and more wear-resistant material than other parts of the blade block, and members are provided for attaching this removable part.

The advantages of the blade block according to the invention are the prevention of brittle fracture almost completely, the possibility of partial replacement and renewal of the blades, and the high hardness and wear resistance of the removable parts. Of course, it is most advantageous to install the detachable parts in the vicinity of the outer circumference of the blade block, where the highest circumferential speed prevails and thus also the highest stresses.

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Other preferred embodiments of the invention are characterized by what is set out in the claims below.

The invention will now be described in more detail by way of examples with reference to the following drawing, in which

Fig. 1 shows a front view of a blade block according to the invention in a disc mill with two detachable blade parts,

Fig. 2 shows a side view of a blade block according to an embodiment of the invention,

Fig. 3 shows a perspective view of a blade block according to another embodiment of the invention.

In the blade block 1 according to the invention shown in Fig. 1, two removable parts, i.e. blade pieces 2, are formed on the grinding surface of the sector, which are substantially harder and more wear-resistant material than the other parts of the blade block 1. For example, using martensitic stainless steel grades, the blade block 1 can be of medium carbon grade (CrSteel 25 or 50, hardness Hg = approx. η.600. Hardening can be performed, for example, on a forged blank either before or after it is fitted to the blade block.

Other possible materials or combinations of materials for forming said detachable blades are non-metallic materials (ceramics) and metals coated with a wear-resistant coating (ceramics). The conceivable ceramics are various oxides, carbides and nitrides, which are commercially available in several different grades, of which the latter nitrides in particular are well suited for coating., 4,80087

Figure 2 shows members 3 for attaching detachable blade pieces according to an embodiment. In it, protrusions 3 / are formed in the blade block 1, which form a so-called a "lo-tail connection" which, in a form-locked manner, holds the blade bars 2 in place. When the blade blocks are placed side by side to form a grinding wheel, the blade pieces also lock in place laterally in the block, so that no other fastening members are needed.

Figure 3 shows a perspective view of an embodiment in which the attachment of the blade pieces 2 to the blade block 1 is secured with screws 4. Due to the high centrifugal force in use, it is always advantageous to provide the outer edge of the block 1 with the protrusion 3 so that the compressive strength of the piece can be effectively utilized and secured. stability in the blade block 1.

In addition, the detachable blade pieces can be arranged to be attached to the blade block in whole or in part by means of a rigid connection, such as a solder joint. When the blade is damaged, these types of seams usually come off as well, so they do not significantly change the blade pieces. The attachment of the blade pieces to the blade block can also be ensured by means of a binder such as glue.

Using e.g. the fastening method shown in Fig. 2, the blade pieces 2 can also be made of wear-resistant cast iron, such as martensitic white cast iron, and which are cast in place in the blade block 1. In this case, of course, a casting mold is required, which is placed on the blade block 1 during casting. Such a mold is not shown in the figures. To facilitate the removal of the cast pieces 2, the blade block can be treated with a suitable release agent before casting.

It will be apparent to those skilled in the art that the invention is not limited to the above examples, but that its various embodiments may vary within the scope of the claims below. «

Claims (12)

1. A grinding block (1) at a refiner consisting of a corrosion-resistant frame made of a bed sector or a part thereof, characterized in that at least part of the block surface consists of one or more removable parts (2) which are made of substantially harder and more abrasion resistant material than the other parts of the bite block (1), and that means (3,4) have been formed at the bite block for attaching the removable part. Molding block according to claim 1, characterized in that said detachable part (2) is made of a wear-resistant rack, such as a martensitic stainless steel. Molding block according to claim 1, characterized in that said detachable part (2) is made of a wear-resistant non-metallic material, such as of a ceramic material. Molding block according to claim 1, characterized in that said detachable part (2) is made of a metal which is coated with a wear-resistant coating, such as a ceramic material. Molding block according to any of claims 1-4, characterized in that said removable part (2) is arranged to be attached to the milling block (1) substantially by means of mold reading. 6. Grinding blocks according to any of claims 1-4, characterized in that said removable part (2) is arranged to be attached to the grinding block (1) substantially by means of fastening means, such as screws (4). β 80087 7. A grinding block as claimed in any of claims 1-3, characterized in that said detachable part (2) is arranged to be attached to the slab block (1) substantially by means of a rigid joint, such as a solder joint. 8. The grinding block according to any of claims 5-7, wherein the attachment of said detachable part (2) to the grinding block is secured by means of a binder, such as an adhesive. Molding block according to claim 1, characterized in that said detachable part (2) is made of a wear-resistant cast iron, such as martensitic white cast iron, and which part is cast in place in the mold block (1). Molding block according to any one of claims 1 or 2 or 5-8, characterized in that said detachable part (2) is forged in its proper shape and then cured. 11. A grinding block according to any of the preceding claims, characterized in that it forms part of the grinding surface of a disc refiner. 12. A milling block according to any of the preceding claims, characterized in that it forms part of the milling surface of a tapered refiner. Il