GB2053728A - Roller mill - Google Patents

Abstract

A roller mill comprises a grinding table (3) rotatable about a vertical axis and supported by thrust bearings (11). Rollers (5) are suspended above the grinding table from a pressure yoke (4) which is urged downwards to force the rollers against a grinding path on the grinding table by means of at least one drawbar (10) connected to a central part of the pressure yoke and passing down through a central opening in the grinding table. <IMAGE>

Description

SPECIFICATION Roller mill The invention relates to a roller mill of the kind hereinafter referred to as of the kind described, comprising a grinding table which is rotatable about a vertical axis and is supported by thrust bearings, rollers suspended above the grinding table from a pressure yoke, and driving means for rotating the grinding table.

Roller mills of this kind are known and used, for example for grinding cement clinker. The raw material to be ground in the mill are fed through a filling hopper down onto a grinding path on the rotating grinding table and are ground during the passage of the grinding table beneath the rollers. The ground material is discharged through the upper end of the mill by means of air blown up around the grinding table through a ring of nozzles surrounding the grinding table. The pressure yoke, which in known roller mills is designed as a pressure frame extending fully to the circumference of a housing surrounding the grinding table is prevented from turning about the axis of the mill by means of abutments attached to the mill housing.The pressure frame of the known roller mills is forced down towards the grinding table by means of drawbars positioned around the table adjacent to the periphery of the mill housing. The grinding table rests on thrust bearings, for example in the form of slideshoes resting directly on a foundation of the roller mill or on the lower part of the mill housing, and the grinding table is rotated buy a motor through a gear box and a central shaft on the mill table or by means of a ring motor a rotor of which is attached to the grinding table.

According to the invention, a roller mill of the kind described is characterized in that the pressure yoke is urged downwards to force the rollers against a grinding path on the grinding table by means of at least one drawbar connected to a central part of the pressure yoke and passing down through a central opening in the grinding table.

A roller mill ofthis new construction, with a centrally directed yoke pressure transmission has the advantage, compared with known roller mills that the drawbar acts on the pressure yoke centrally at the point where the upward and downward movement of the yoke owing to varying thickness of the layer of material on the grinding path is less than at peripheral parts of the yoke. As a result there is a reduced variation in the tension in the drawbar and reduced impacts on the roller yoke and the drawbar.

When the rollers, which are often used in a number of three, move up and down owing to variations in the thickness of the layer of material on the grinding path, the central part of the pressure yoke will move less in a vertical direction than the peripheral parts of the yoke.

A single central drawbar will normally suffice, and in that case the roller mill will have fewer components than the known roller mills and consequently fewer parts reducing the flow area of the conveying air through the mill.

The lower end of the drawbar may be connected to the piston of an hydraulic cylinder. In this way it is possible to vary the pressure exerted by the rollers against the grinding table and at the same time to exert a pressure with a certain elasticity.

The hydraulic cylinder may be double-acting, by which it is possible, for exchange of rollers, to lift the pressure yoke by means of the hydraulic cylinder and consequently to raise the rollers from the grinding table.

Normally the rollers are not suspended directly from the pressure yoke, but are only pressed down against the grinding table by the yoke. However, the rollers may alternatively be suspended pendulumfashion from the pressure yoke which may be prevented from turning about the mill axis by the engagement with abutments of extensions of the roller shafts. When the rollers are suspended pendulum-fashion the advantages obtained are that the rollers can be lifted with the pressure yoke by activation of the hydraulic cylinder of the drawbar, and at the same time it is possible in a simple way to adjust individually each roller and to use more rollers than the conventional number of three rollers.

The hydraulic cylinder of the drawbar may be anchored to the foundation of the mill, but alternatively the hydraulic cylinder may also bear against the underside of the grinding table via a thrust bearing. In the latter case a more advantageous reaction is obtained between the pressure yoke and the grinding table, since the forces from the drawbar are transmitted directly to the grinding table rathr than through the mill housing.

In order to accommodate the drawbar, the grinding table may need to be driven off-centre, for example by means of a ring motor with an annular rotor fixed either to the periphery of the grinding table orto a cylindrical sleeve depending from the grinding table.

Two examples of roller mills constructed in accordance with the invention are illustrated in the accompanying drawings in which: Figure lisa diagrammatic axial section through such parts of one roller mill as are necessary for understanding same the invention; and, Figure 2 is a corresponding section through the second example of a roller mill.

The drawings show roller mills comprising a housing la a foundation 2, a rotary grinding table 3, a pressure yoke 4, and grinding rollers 5 which are forced down against a grinding path on the grinding table 3 by the pressure yoke 4. For the sake of clarity only one grinding roller is shown in the drawings.

According to Figure 1 the grinding rollers are supported in known manner beneath the pressure yoke 4 which in this case takes the form of a pressure frame that is prevented from turning about the mill axis by means of abutments 6 attached to the mill housing 1, and allowing a movement in the vertical plane of the yoke.

The grinding table 3 is in known manner surrounded by a ring of nozzles 7 for air which is blown over the grinding table for carrying away ground material. The grinding table is rotated by a ring motor the rotor 8 of which is attached to the lower peripheral part of the grinding table and the stator winding 9 of which is attached to the mill housing.

The pressure yoke 4 is pressed down towards the grinding tables 3 by means of a central drawbar 10 movably suspended by a joint 10a in the pressure yoke 4. The grinding table rests on the foundation via thrust bearings, shown here in the form of slideshoes 11 provided beneath the points where the rollers press against the grinding table.

In the example show in Figure 1 tension is exerted on the drawbar by means of an hydraulic cylinder 12 which via a thrust bearing 13 bears against a portion 14 of the grinding table 3 specially designed for this purpose. The grinding table is guided radially in relation to the foundation by means of a radial bearing 15.

It should be observed that with the support of the hydraulic cylinder 12 shown in Figure 1, a direct reaction with the grinding tableis obtained so that the reactions commonly transmitted through mill casing and/orfoundation are voided.

In the drawings 16 and 17 indicate various sealing means for sealing the grinding chamber proper against the escape of air and material from the mill.

In the examples illustrated in the drawings the hydraulic cylinder of the drawbar is double-acting, and it is possible via a pipe 18to the hydraulic cylinder to vary the force exerted by the drawbar and via a pipe 19 to lift the drawbar and consequently the pressure yoke 4 for relief of the grinding pressure and any desired replacement of the grinding rollers 5.

Figure 2 shows another example of roller mill which differs primarily from the example shown in Figure 1 in that the rollers 5 are suspended pendu lum-fashion from the pressure yoke 4.

As indicated, each roller 5 is suspended on, and forced against the grinding table 3 by, a pivotal arm 20 which may turn about a pivot 21 provided in the pressure yoke 4. The rollers 5, one of which, only, is shown in Figure 2, are furthermore adjustably anchored to a common ring 23 and 22. The shaft 24 of the roller is extended to the circumference of the mill housing where it rests in contact with an abutment 6 so that the roller is prevented from turning about the vertical mill axis, but allowing for movement of the shaft in the vertical plane.

With the special embodiment of the suspension of the roller 5 and the pressure yoke 4 illustrated here it is possible to provide any desired number of grinding rollers along the grinding table 3 and each individual grinding roller may be adjusted individually in relation to the grinding table 3 by means of the adjustment member 22.

The example shown in Figure 2 distinguishes further from the example shown in Figure 1 in that the rotor 8 of the ring motor is mounted on a cylindrical, sleeve 25 attached to the underside of the grinding table. In this manner the diameter of the ring motor may be reduced and, further, the ring motor becomes more readily accessible for repairs than in the example shown in Figure 1. The grinding table according to Figure 2 is guided radially by a radial bearing 15 which rests against the cylindrical jacket 25.

According to Figure 2 the hydraulic cylinder 12 of the drawbar 10 is supported in more conventional manner in the foundation 2 as indicated by means of the rods 26 which are secured to the foundation by casting.

Finally, it should be observed that the various structural features of the two examples may be combined in various manners. Thus, as an example the support of the hydraulic cylinder 12 and the provision of the rotor of the ring motor on a cylindrical jacket beneath the grinding table as illustrated in Figure 2 may be used in the example according to Figure 1 as well, just as the corresponding arrangements according to Figure 1 may be used in the example according to Figure 2.

Claims (8)

1. A roller mill comprising a grinding table which is rotatable about a vertical axis and is supported by thrust bearings, rollers suspended above the grinding table from a pressure yoke, and driving means for rotating the grinding table, characterized in that the pressure yoke is urged downwards to force the rollers against a grinding path on the grinding table by means of at least one drawbar connected to a central part of the pressure yoke and passing down through a central opening in the grinding table.

2. A roller mill according to claim 1, characterized in that the lower end of the drawbar is connected to the piston of an hydraulic cylinder.

3. A roller mill according to claim 2, characterized in that the hydraulic cylinder is double-acting.

4. A roller mill according to claim 2 or claim 3, characterized in that the hydraulic cylinder is anchored to a foundation of the mill.

5. A roller mill according to claim 2 or claim 3, characterized in that the hydraulic cylinder bears againsttheunderside of the grinding table via a thrust bearing.

6. A roller mill according to any one of the preceding claims, characterized in that the rollers are suspended pendulum-fashion from the pressure yoke and the yoke is prevented from turning by the engagement with abutments of extensions of the rollers shafts.

7. A roller mill according to any one of the preceding claims, characterized in that the driving means comprises a ring motor with an annuiar rotor fixed either to the periphery of the grinding table or to a cylindrical sleeve depending from the grinding table.

8. Arollermill according to claim 1, substantially as described with reference to Figure 1 or Figure 2 of the accompanying drawings.