FI68268B - SLIPORGAN FOER FRAMSTAELLNING AV MEKANISK TRAEMASSA - Google Patents

Description

68268

This invention relates to an abrasive for use in the mechanical manufacture of wood pulp, comprising abrasive alumina, tungsten carbide, silicon carbide or similar particles and a binder holding them together.

In this application, an abrasive means a homogeneous abrasive stone as defined above, an abrasive layer attached to a separate abrasive stone body, and abrasive segments.

Today, wood grinding stone usually consists of a concrete or metal frame on which a separate grinding layer or segments are attached. The segment structure is generally known and has been discussed e.g. U.S. Patent Nos. 2,887,276 and 2,421,885.

From the point of view of the quality of wood chips, the most crucial part of wood sandstone is the sanding element. It must be able to make the desired type of wood chips and must be able to withstand the mechanical and thermal stresses to which it is subjected during sanding.

The binder for abrasives currently in use is almost exclusively ceramic. In this case, the abrasive particles, which are usually either or SiC, are bonded to each other by a ceramic binder, usually glass. Such a solution is mentioned, for example, in U.S. Patent No. 2,769,286.

The brittleness of ceramic materials contributes to their wear, as a result of which the strength properties of the groundwood are also reduced. Therefore, abrasives made with a ceramic binder often have to be sharpened, which consumes the abrasive very strongly. In sharpening, a dense groove is made on the surface of the ceramic binder with a special tool, which usually forms an angle of 28 ° with the axis of rotation of the grindstone. The distance between the grooves 2 68268 with respect to each other is 2 ... 3 nm and the depth is about 1 nm. The purpose of the sharpening is to create a space for the fibers detached from the wood in which they can leave the grinding zone without having to be re-sanded. In addition, the sharpening brings the grinding surface area of the grinding element into a suitable ratio with the grinding pressure and the quality of the mass to be produced.

Another major drawback, especially with current ceramic abrasive segments, is their cracking, which is also related to their brittleness. With current high-performance wood grinders 11a, this problem is further accentuated. The cracking of a segment occurs when it is subjected to a strong thermal shock. Such a situation arises, for example, when a wood to be sanded rests head-on against the sanding surface. Since the wood at the ends grinds much more slowly than the wood at the end, a very high pressure is generated on such wood. As a result, the temperature also rises very high locally, which can damage the segment.

Such breakage often results in at least one day of production downtime on the grinder. If the stone cannot be repaired and needs to be replaced, then the break will last for several days.

Fragile segments also limit the uptake of the stone from room temperature. In this case, the grindstone must be gently heated for up to 2 days before the actual grinding can begin.

The use of metal in an abrasive element is also already known e.g. SE Publication No. 309,529 · This abrasive has a metal surface on which semi-spherical protrusions are formed to provide a grinding effect.

3 68268 Such a solution is, in practice, superior to implement for a number of reasons. The bumps formed on the metal surface wear quite quickly, so the metal surface must be replaced frequently. Replacement is always a cumbersome and time-consuming operation, which correspondingly reduces the efficiency of production and thus the profitability of the entire grinding process.

The object of the present invention is to provide an abrasive element used in the mechanical production or pulping of wood pulp, such as, for example, a homogeneous abrasive stone or a self-segment, which has better wear resistance and mechanical strength than the solutions used hitherto. According to the invention, this object is achieved in that the binder is a sintered meta11.

From the point of view of the defibering process, it is advantageous that the sintered metal between the abrasive particles, which is softer than the abrasive particles, consumes more during grinding than the abrasive particles.

Due to the conditions prevailing in the defibering process, it is preferred that the metal be a corrosion-resistant or stainless metal, such as, for example, stainless or acid-resistant steel, e.g. A1SI 304 or 316 or 316L. The sintered metal used as a binder can also be copper or a copper alloy, e.g. brass.

In the abrasive element according to the invention, any currently known abrasives e11a can be used as abrasive particles, such as, for example, alumina, various carbides, etc.

The proportion of abrasive particles in the abrasive member is preferably 10 to 70% by volume and most preferably 30 to 50% by volume.

The abrasive member bound to the sintered metal matrix 11a may be porous, e.g. 5-30% by volume.

The size of the abrasive particles is preferably about 150-700.

68268 4

The sintering is performed, for example, as follows:

The mixture of Meta Li powder and abrasive particles is compressed so tightly that the piece already has a hand and can be transferred to the oven without any support or mold. The body is then heated in an oven, e.g. 1000-1500 ° C, i.e. below the melting point of the suitably used metal, if necessary in a suitable shielding gas or vacuum. In this case, the metal particles adhere to each other, forming a matrix around the abrasive particles, in which the abrasive particles are firmly attached.

In this way, it is advantageous to produce, for example, abrasive segments or sectors which are fastened in the usual way, e.g. to the surface of a cylindrical, conical or disc-shaped body made of metal or other suitable material.

Studies have shown that the compressive strength of the heat exchanger according to the invention, which can be up to 1000 N / l, is about ten times and its wear resistance up to five times that of the ceramic segments currently in use. Despite the high compressive strength achieved, the abrasive segment according to the invention is tough and does not break easily, like the current ceramic segment, when subjected to mechanical or thermal shocks.

Better wear resistance makes it possible for the wear layer of the abrasive member to be thinner than at present. Since the strength and toughness of the sintered metal is much better compared to the corresponding properties of the ceramic binder, considerably higher consistencies and temperatures can be used in grinding, whereby, for example, in pressure grinding, the strength properties of the pulp are improved and heat recovery is enhanced.

The structure of the abrasive member according to the invention is illustrated in the accompanying drawing, which shows the structure of the abrasive member according to the invention in the grinding situation, cut in a direction perpendicular to the longitudinal axis of the wood to be sanded.

5 68268

The drawing shows a situation in which the abrasive particles 1 on the surface of the abrasive member contact the surface of the wood 5 to be abraded. The grinding direction of the grinding element is marked with an arrow. The particles are partially pressed into the wood, at the same time squeezing it to size, whereby the fibers / * become detached from the wood as a result of grinding.

The abrasive particles are bonded by sintering a matrix 2 of metal particles around them. During sintering, some (0 ... 20%) pores may remain in the matrix. 3- When the softer binder 2 wears off the grinding surface, the abrasive particles are exposed. As the particles move at a high speed against the surface of the wood, the viscoelastic wood fibers generate a high vibration motion, the heat generated by which softens the lignin that binds the fibers. This removes the fibers from the wood.

The sanding element according to the invention can be used not only in a wood sanding machine but also in various plate, cone and similar refiners, grinders and other devices for mechanical defibering of wood. In this case, of course, the frame structure under the abrasive surface layer must be manufactured in a manner suitable for each purpose. Abrasive particles can be of only one grade or several different grades in a suitable ratio.

Claims (7)

68268 Claims: Abrasive element for the mechanical production or pulping of wood pulp, comprising abrasive alumina, tungsten carbide, silicon carbide or similar particles and a binder holding them together, characterized in that the binder is a sintered metal. Device according to Claim 1, characterized in that the sintered metal as binder is softer than the abrasive components. Device according to Claim 1 or 2, characterized in that the metal is a corrosion-resistant or stainless metal. Device according to Claim 1 or 2, characterized in that the metal is copper or a copper alloy, e.g. brass. Device according to Claim 1, characterized in that the abrasive particles are present in an amount of 10 to 70% by volume. Device according to Claim 1, characterized in that the abrasive particles are present in an amount of from 30 to 50% by volume. Device according to one of the preceding claims, characterized in that the abrasive particles have a size of about 150 to 700 and m.