FI60255B - FOERFARANDE OCH SKIVKVARN FOER ATT MALA MATERIAL - Google Patents

Description

Ι55ΡΠ ΓβΙ μι \ ^ υlutusjυLKAisu, nocc

JegTi m (11) utläggningsskrift 6 02 5 5 (^ ®) Patent oediielat 'S "“ v ^ (51) Kv.ik.3 / inc.ci.3 D 21 D 1/38 ENGLISH —FINLAND (21) P * Mn «lh * k * im» - Patw »tan * 6kning 750819 (22) H« k «mltpllvt — Anteknlngwlag 19.03.75 '(23) AlkupUvi - Gittl (h« tad «| 19 * 03.75 (41) Tullut iulkiMiul - Bllvlt offentHj 20.09.76 __. '(44) NlhUvtk »lp« noo Ja kuL | ulk * bun date - „QQ, • • tent- och registerstyrelsen AmMcan utkgd och utl. * Krtft * n puMicurad 31.08.81 (32) (33) (31) Privilege claimed — Begird priortm (71) Kvaerner Brug A / S, Kvaernerveien 10, Oslo 1, Norway-Norway (NO) (72) Magne Mortenson, Trondheim, Norway-Norway (NO) (7 * 0 Forssen & Salomaa Oy (5h) Method and disc mill for grinding material - Förfarande och skivkvarn för att Mala material

The invention relates to a method for grinding a material in a disc mill. The invention also relates to a disc mill for carrying out the method according to the invention.

Soon, a hundred years have been spent working on the structures of disc mills. None of the many proposals that have been patented has received technical use. This is due to the fact that mill structures have not been very useful or have not proven to be competitive compared to ball mills. This, in turn, is due to the fact that the designers have not understood the special features of the disc mill. It should be noted that the conclusions drawn from the design and operation of the ball mill lead to a little usable disc mill design.

A number of previously unknown facts have been observed in the experiments. On this basis, a special disc mill has been designed with a high grinding efficiency.

In order to obtain a simple characteristic and comparison of mills with different diameters and different speeds, it is appropriate to indicate the speed of the mill compared to the centrifugal conditions in the mill drum. If D is denoted by the inside diameter of a horizontally bearing cylinder rotating at a speed of n, the particles inside the cylinder are centrifuged according to a known form so that these are taken up by the cylinder when n 1 is greater than 42.2 // d. However, vertically placed, free-standing discs are not centrifuged and taken with the cylinder regardless of its rotational speed. Thus, the use of a disc mill has no critical maximum microspeed speed corresponding to the particular formula that applies to ball mills.

If the disc mill is run at a lower speed than n 1, most of the raw material fed into the cylinder remains on the disc feed side and passes through them without comminution. In that case, the mill becomes low power.

When run at a speed above n ^, the raw material enters between the disc and the drum and grinds. A substantial portion of the material follows the discs and is released at their ends back into the flow toward the cylinder. With increasing speed, the grinding capacity of the mill increases very strongly. Experiments show that it seems appropriate to limit the speed of the mill to a value which is about 3-4 times n ^, mm. due to vibration of unbalanced masses in a rapidly rotating machine.

The method according to the invention is characterized in that the mill is operated at maximum speed, which corresponds to 3-4 times the critical speed, and harmful vibrations due to unbalanced masses are limited by centrifuging the grinding material known per se and forming a layer on the inner surface of the mill cylinder. .

The disc mill according to the invention, in turn, is mainly characterized in that the mill is provided with loose, equal-diameter grinding discs with a diameter of about 2/3 of the diameter of the mill cylinder and the discs are collected in an efficient grinding area of about 2/3 of the cylinder diameter.

3 60255

When the mill is run at a speed greater than n 1, some of the components passed between the discs and the drum are centrifuged against the mill-cylinder and form an inner layer therein, and the mill becomes refilled with material. To avoid this, the mill must be equipped with a suitable member which determines the thickness of the out-centrifuged layer. This can be done with a scraper or some other method, such as, for example, a suitably high-pressure water rinse. By adjusting the thickness of the centrifuged material layer, the mill obtains a self-constructing wear layer in the cylinder.

Experiments with disc mill grinding have shown that it is of great importance for efficient grinding that the volume of raw material to be ground inside the cylinder is relatively small. The maximum raw material fill should not exceed 15% of the cylinder capacity. Thus, high power consumption is achieved centrally in a small volume of raw material, resulting in high grinding power.

In order to operate with a small mill fill, the cylinder must not be significantly reduced at the outlet or be provided with suitable means for removing the goods. When dry grinding, the mill is provided with suitable air outlet equipment in the outlet. A mill with a centrally arranged outlet provides an outlet for the pulp, which in a conventional ball mill provides a less efficient grinding process.

When running a disc mill with wet grinding, the addition of water can be reduced by 50% of the corresponding necessary addition of the ball mill. This gives the disc mill better grinding conditions and power.

The disc size in relation to the cylinder diameter is of great importance for the grinding power. Grinding tests with different types of raw materials show that the disc size can be more than 2/3 of the cylinder diameter. When using discs with such a diameter, the discs fill 50-60% of the cylinder volume.

According to these considerations, the built mill should operate in a closed circuit with a sorting device, which separates the pre-ground material and returns the coarse goods to the mill for re-grinding. The mass circulating through the mill «60255 therefore becomes large compared to the addition of raw materials. Thus, a very convenient grinding process is achieved, which is characterized by a minimum grinding with the grain size determined by the sorting device in the closed circuit.

When the mill is run in an open circuit without recovery, it provides selective grinding so that the resistant minerals in the raw material become slightly ground and can therefore be selectively separated in a suitable subsequent process.

In addition to the grinding of the mineral raw material, the disc mill built according to these aspects has proved to be well suited for the processing of some industrial products. An example is the grinding of the ok-pulp of cellulose soup. The twig gives a fibrous product in disc milling, which gives a stronger paper than the previous twig after the usual Raffi treatment.

When the mill is equipped with a set of discs - all of the same diameter but different thicknesses - with decreasing thickness, i.e. the thickest disc in the material input of the cylinder, it is achieved that the coarse feed is subjected to the greatest grinding load. Thus, an appropriate grinding process is achieved, which is not possible in other mills. Such a process has been a coveted wish for mill designers, but no satisfactory solution has been found.

The invention is explained in more detail by an exemplary embodiment with reference to the accompanying drawing.

Figure 1 shows a longitudinal section of a disc mill.

Figure 2 shows an end view, some parts removed for view.

The disc mill consists mainly of a mill drum 1, the other end side of which has a mill inlet 5. The mill drum is rotatably mounted by means of two guide rollers and one support and drive wheel 4 and 3, which drive wheel 3 has a friction drive interaction with the mill drum 5, more closely 2 5 5 with two outer support rings 2 on the outside of the mill drum 1. The support and drive wheel 3 is mounted on a shaft 11, which is suitably mounted on bearings 12, 13 and communicates with a drive device (not shown).

In Fig. 1, the end side of the mill on the right is open and forms an outlet 6.

In this case, three grinding discs 7 are arranged inside the mill drum. A rod 8 is mounted on the bearing 9, with a rounded end 14, which acts as a guide member of the grinding discs 7. A rod 15 protrudes from the rod 8, which at its end supports a scraper 10. In the end view of Figure 2, the rod 8, the arm 15 and the bearing 9 have been removed to facilitate the view in the figure.

Instead of the support devices 8,9,14, the mill can naturally be provided with other means, for example a partition wall, to prevent the exit of the grinding wheels. The mill can, of course, be mounted and operated in different ways than shown in the drawing.