FI70529B - SAETT ATT FRAMSTAELLA MALSEGMENT - Google Patents

Description

1 70529

The way to make grinding segments

The present invention relates to disc grinders used for the mechanical processing of cellulosic material and to the parts which form the machining surfaces, the so-called the refiner segments.

Grinders are used to fiberize and grind the cellulosic material. Grinders are often of the lew type.

These are also used for grinding cellulose and various mechanical pulps when it is desired to develop the paper-forming properties of these materials by mechanical processing. Common to all such defibering and milling is that the desired result is obtained by machining the fibrous material as it passes through the refiner. This machining is effected in such a way that the fibrous material, after being fed to the refiner by various types of equipment, leaves the refiner through a narrow gap between two machining surfaces provided for this purpose by machining means consisting of booms with grooves therebetween. Because one and sometimes both surfaces rotate, the material is machined as desired and is carried out of the grinder by rotational forces.

The intensity and quality of the processing on the fibrous material is determined, among other things, by the appearance of the booms and grooves, as well as the number of surfaces to be machined and, in part, the size of the gap. Some wear on grinding surfaces cannot be avoided. For practical reasons, the disc grinder is therefore equipped with replaceable grinding parts, the so-called A refining segment. In the manufacture, these grinding segments are always given a pattern and profile according to the quality of the work to be performed in the grinder. The energy required for defibering and processing is transferred to the fibrous material through the edges and surfaces of the booms.

It has been shown that the structure of the booms and grooves of the grinding segments is important for energy use when grinding 2,70529 cellulosic materials with a particularly high consistency of more than 20%. Even seemingly small variations in the grinding segment pattern can cause large variations in energy consumption.

It has also proved important that the patterning is performed with high accuracy. According to the invention, this is done using spark machining, i.e. the preform of the grinding segment is fitted as an electrode in a dielectric rubber, the second electrode being a graphite or copper material with a pattern that is negative to the desired pattern of the grinding segment.

The pattern of the grinding segment can in principle be shaped as shown in Figures 1 and 2. Such a grinding segment comprises three radially limited zones 2, 3 and 4, the final machining being carried out in the outermost zone 4. The design of the booms 5 and the grooves 6 is shown in more detail in Figure 2, where the boom width, groove width and groove depth are denoted B, S, respectively.

It is also essential that the grinding segments be made of a material that is very resistant to wear, corrosion and erosion. An example of such a material is a steel material containing the following alloying agents.

Alloying agent Weight% C 0.5-1.7

Si 0.5-1.0

Mn 0.3-0.8

Cr 16-19

Ni 1.0-2.1

Mo 0.7-1.0

In addition, the steel material may contain a certain amount of titanium, suitably 1-5% by weight, in the form of very small titanium carbide granules.

3 70529

In the process according to the invention, a suitable alloy was first prepared by casting a preform of a grinding segment, which was then surface ground. Graphite was used as the electrode, which was formed by milling into a tool with a negative pattern with respect to the grinding plate pattern to be produced. The ground, non-patterned grinding segment, the workpiece, was fixed and placed on the table of the Kipi clamping machine and connected to the positive pole.

The tool was attached to the tool socket of the immersion sparking machine and connected to the negative pole of the machine. The nozzles used to flush out the removed material were oriented so that the liquid jets were directed along the surface of the workpiece. The TV tank of the sparking machine was then filled with dielectric rubber so that the liquid surface was 5 cm above the top surface of the workpiece. The machine parameter combinations were adjusted as follows

Idle voltage Ut = ^ 00 V

Operating voltage Varb = 50 V

Pulse time t ^ = 150 yus Interval t = 60 -us P /

The spark gap is determined by the operating voltage that controls the servo amplifier, which in turn controls the servo valves. The valves and the machine's hydraulic system keep the distance between the electrode and the tool correct during machining.

The invention is not limited to the embodiment shown, but this can be modified within the scope of the inventive idea.

Claims (5)

A method of making grinding segments for defibering a cellulosic material, preferably chips, for grinding, respectively, wherein the segment has booms and grooves arranged in a special pattern for processing the material, characterized in that a planar planar blank is preferably formed by casting and the desired pattern or part thereof is formed by forming a segment grooves by a spark-machining method known per se. Method according to Claim 1, characterized in that the blank is surface-ground before the spark machining operation. A method according to claim 1, characterized in that the spark machining is performed as submersible spark. Process according to Claims 1 to 3, characterized in that a steel material is used as the preform, which contains the following alloying agents C 0.5 to 1.7% by weight Si 0.5 to 1.0 Mn 0.3 to 0.8 Cr 16-19 Ni 1.0-2.1 Mo 0.7-1.0 4,70529 Process according to Claim 4, characterized in that the steel material additionally contains titanium, preferably in an amount of 1 to 5% by weight, for example in the form of small titanium carbide granules.