BACKGROUND

The invention relates to grinding mills, and more particularly to pulp lifters and outer pulp lifter elements.

One of the problems associated with the pulp lifters is that the ground material already lifted to the pulp lifter tends to fall back to the grinding mill drum. This is inefficient for both the flow rate and power consumption.

BRIEF DESCRIPTION

It is thus an object of the present invention to provide a new grinding mill, a new pulp lifter and a new outer pulp lifter element. The object of the invention is achieved by a grinding mill, a pulp lifter and an outer pulp lifter element, which are characterized by what is stated in the independent claims. Some preferred embodiments of the invention are disclosed in the dependent claims.

The invention is based on the idea of forming a pocket in the pulp lifter by providing a vane of the pulp lifter element at an angle in relation to the wall of the pulp lifter element.

An advantage of the arrangement of the invention is that a more efficient flow of material and lower power consumption per a unit of ground material produced can be achieved with a simple structure. Some further advantages are disclosed in the detailed description in connection with embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following the invention will be described in greater detail by means of preferred embodiments with reference to the accompanying drawings, in which

Figure 1 illustrates a grinding mill;

Figure 2 illustrates an embodiment of an outer pulp lifter element for a pulp lifter in connection with a detail of a pulp lifter assembly;

Figure 3 illustrates an embodiment of an outer pulp lifter element for a pulp lifter in connection with a detail of a pulp lifter assembly;

Figure 4 illustrates an embodiment of an outer pulp lifter element in connection with a detail of a pulp lifter assembly;

Figure 5 illustrates an embodiment of an outer pulp lifter in connection with a detail of a pulp lifter assembly; and

Figure 6 illustrates an angle Θ in an outer pulp lifter element. DETAILED DESCRIPTION OF THE INVENTION

Figure 1 illustrates a grinding mill 3, more specifically a rotating drum grinding mill. Grinding mills are used for processing hard solid material such that large solid material is ground into smaller pieces.

A grinding mill 3 may comprise a cylindrical shell 20 arranged ro- tatably around its longitudinal axis D extending in a horizontal direction. The material to be ground may be received into the cylindrical shell 20, for instance through a feed chute (not numbered). The grinding takes place within the cylindrical shell 20 by lifting and dropping the material to be ground inside the cylindrical shell 20. Lifter bars or lifter plates (not shown, but their places inside the cylindrical shell are indicated by dotted lines in the Figure 1) may be used for lifting the material inside the cylindrical shell. According to an embodiment, loose grinding elements, such as balls comprising for instance stone or metal material, may be provided inside the cylindrical shell to aid in grinding.

The grinding mill 3 may comprise at least one inlet 21 for receiving a continuous feed of material to be ground. The material to be ground may comprise for instance mineral ore. The grinding mill 3 may also comprise at least one outlet 22 for continuous discharge of the ground material. The ground material may comprise for instance ore slurry. The inlet(s) 21 and the outlet(s) 22 may be provided at the opposite ends of the cylindrical shell in the direction of the longitudinal axis D of the cylindrical shell. Thus, a continuous grinding process may be provided by feeding material to be ground into the cylindrical shell 20 through the inlet(s) 21, grinding the material to be ground while it is moved through the cylindrical shell 20 and moved within the cylindrical shell by lifting and dropping the material to be ground on its way through the cylindrical shell 20, and discharging the ground material through the outlet(s) 22 at the opposite end of the cylindrical shell.

The grinding mill 3 may further comprise a grate 23 provided be- tween the interior of the cylindrical shell 20 and the outlet 22. The grate 23 may comprise openings 31 for passing through ground material particles of a predetermined size or smaller. In other words, the openings 31 may be dimensioned in such a manner that particles of a predetermined size or smaller fit through the openings 31 and may thus be moved towards the outlet 22, and particles that are larger than the predetermined size do not fit through the openings but are dropped back to the interior of the cylindrical shell for further grinding. Thereby the grate prevents particles larger than the predetermined size passing through the grate. The grinding mill 3 may also comprise a discharger 24 provided at the outlet 22 end of the grinding mill for discharging the ground material through the outlet 22.

The grinding mill 3 may further comprise a pulp lifter 2. The pulp lifter 2 may comprise at least one outer pulp lifter element 1 and/or a pulp lifter 2 provided between the grate and the discharger for guiding the ground material from the cylindrical shell to the discharger 24. More particularly, the pulp lifter 2 may be arranged to lift the ground material passed through the grate 23 to the outlet 22 for discharging the ground material through the discharger 24, when the pulp lifter 2 is arranged to rotate together with the cylindrical shell about the longitudinal axis D of the cylindrical shell. Depending on the embodiment, the pulp lifter 2 may be arranged to rotate, together with the cylindrical shell, in a clockwise or in a counterclockwise direction. Different embodiments of such an outer pulp lifter element 1 and/or a pulp lifter 2 are described in the description.

The pulp lifter 2 may comprise at least one outer pulp lifter element 1. Typically, a pulp lifter 2 comprises multiple outer pulp lifter elements 1. According to an embodiment, an outer pulp lifter element 1 comprises a form of a sector or a truncated sector and a number of such outer pulp lifter elements 1 may be arranged circumferentially side by side, whereby the outer pulp lifter elements 1 may form a disc-shaped or an annulus-shaped pulp lifter 2. According to an embodiment, a pulp lifter 2 may comprise 15 to 35 outer pulp lifter elements 1. According to another embodiment, a pulp lifter 2 may comprise 18 to 32 outer pulp lifter elements 1.

The disc-shaped or annulus-shaped pulp lifter 2 may comprise a conical shape as can be seen in Figure 1, for example. The pulp lifter 2 may be arranged at the end of the cylindrical shell and to conform to the end of the cylindrical shell in such a manner, that the middle point F of the pulp lifter 2 may be arranged on the longitudinal axis of the cylindrical shell. The pulp lifter 2 may be arranged rotatably in the grinding mill 3, such that the pulp lifter 2 is rotatable together as one entity with the cylindrical shell 20 about the longitudinal axis D of the cylindrical shell. Depending on the embodiment, all the outer pulp lifter elements 1 in a pulp lifter 2 may be similar to one another or a pulp lifter 2 may comprise different types of outer pulp lifter elements 1.

Figures 2, 3, 4 and 5 illustrate embodiments of an outer pulp lifter element 1 for a pulp lifter 2, such as a pulp lifter 2 for a rotating drum grind- ing mill 3. More particularly, Figure 2 illustrates a part of such a pulp lifter 2 for a rotating drum grinding mill 3. The outer pulp lifter element 1 may form a sector or a truncated sector of an outer pulp lifter. In other words, the outer pulp lifter element 1 may comprise a sector-like shape or a shape of a truncated sector and a plurality of such outer pulp lifter elements 1 may be pro- vided circumferentially, side-by-side to form an outer pulp lifter of a pulp lifter 2.

The outer pulp lifter element 1 may comprise a first wall 4 directed towards the discharge end of the grinding mill 3. In other words, the first wall 4 may be arranged on the side of the outer pulp lifter element 1 that is opposite to the side where the grate 23 is provided.

The outer pulp lifter element 1 may also comprise at least one vane 6 protruding from the inner surface 12 of the first wall 4 towards the inside of the drum grinding mill 3. The vanes 6 may be arranged to do the lifting of the material passed through the grate 23 towards the middle of the pulp lifter 2 and, thus, the outlet 22. According to an embodiment, the outer pulp lifter element 1 may comprise exactly one vane 6. According to another embodiment, the outer pulp lifter element 1 may comprise two vanes 6 or a plurality of vanes 6. According to a yet another embodiment, a vane 6 may extend to two or more outer pulp lifter elements 1. In other words, a vane 6 may comprise vane portions that may be provided in different outer pulp lifter elements 1, such that the vane 6 is formed when the outer pulp lifter elements 1 are mounted together.

Each vane 6 may extend from an outer part of the outer pulp lifter element 1 towards the inner end 9 of the outer pulp lifter element 1. In other words, the vane may extend from an area at the perimeter or an area close to the perimeter towards the middle point F of the pulp lifter 2. Thus, the inner end 9 of the outer pulp lifter element 1 refers to the end of the outer pulp lifter element 1 directed towards the middle point F of the pulp lifter 2.

The vane 6 may comprise a guiding surface 10 on the front side of the vane 6. The front side of the vane 6 refers to the side of the vane 6 first in the direction of rotation. In other words, the front side of the vane is the side first receiving the ground material, such as the slurry, for instance ore slurry, when the pulp lifter element 1, and more particularly the vane 6, is in the lifting phase of the cycle. The front side of the vane thus depends on the direc- tion of rotation of the pulp lifter 2. In a pulp lifter 2 rotated in first direction, the front side of the vane, thus, is on a first side of the vane 6, whereas the front side of the vane is the opposite side of the vane compared to the first side when the pulp lifter 2 is rotated in the opposite direction.

According to an embodiment, the vane 6 may extend radially from the outer part of the outer pulp lifter element towards the inner end of the outer pulp lifter element, such as in the embodiments of Figures 4 and 5.

According to another embodiment, the vane 6 may extend from the outer part of the outer pulp lifter element towards the inner end of the outer pulp lifter element in a curved manner, such as in the embodiments of Figures 2 and 3. In other words, the vane 6 may comprise a concave guiding surface 10 forming a spiralling formation together with an inner part of the pulp lifter 2. In an embodiment with an opposite direction of rotation compared to that of Figures 2 and 3, an opposite direction of spiralling would provide a similar effect of optimally guiding the ground material towards the middle of the pulp lifter.

At least a part of an outer edge 11 of the guiding surface 10 may be angled in relation to the inner surface 12 of the first wall 4. Throughout the description this feature is referred to the outer edge 11 of the guiding surface 10 being angled in relation to the inner surface 12 of the first wall 4, for the sake of clarity, although the purpose for the angled relation is to form a pocket-like shape preventing the ground material from dropping from the guiding surface and the effect can be achieved even only a part of the outer edge 11 was angled in relation to the inner surface 12 of the first wall 4.

The outer edge 11 of the guiding surface 10 comprises the edge of the guiding surface closest to the outer perimeter of the pulp lifter 2. Accord- ing to an embodiment, the outer edge 11 of the guiding surface 10 may have a profile or shape of a straight line and this line may be angled in relation to the inner surface 12 of the first wall 4. According to another embodiment, the outer edge 11 of the guiding surface 10 may comprise a concave profile or shape, wherein at least a part of the outer edge 11 is angled in relation to the inner surface 12 of the first wall 4. The angled part of the outer edge may, in such an embodiment, also refer to direction of a tangent along the concave outer edge 11. Similarly, the outer edge of the guiding surface may comprise a convex profile or shape, and the angled part of the outer edge may, thus, also comprise a tangent along the convex outer edge 11. Naturally, the outer edge 11 may comprise a profile or a shape that is a combination of curved and straight portions, whereby at least a part of the outer edge 11 is angled in relation to the inner surface 12 of the first wall 4.

The angle Θ between the inner surface 12 of the first wall 4 and the outer edge 11 of the guiding surface 10 may be smaller than 90 degrees. The inner surface 12 of the first wall 4 may be parallel to the head of the mill. In other words, the inner surface 12 of the first wall 4 may be parallel to the discharge end of the mill. The effect of the angle Θ between the inner surface 12 of the first wall 4 and the outer edge 11 of the guiding surface 10 being smaller than 90 degrees is that it directs the ground material flow, such as slurry flow, towards the back of the pulp lifter in a more efficient manner. An angle Θ in an outer pulp lifter element 1 and a direction of rotation C is shown in detail in Figure 6 for clarification. In a pulp lifter 2 with an opposite direction of rotation, a similar angle Θ but at the opposite side of the outer pulp lifter element would have the same effect.

Some advantages of this kind of an outer pulp lifter element 1 comprise preventing ground material, such as slurry, from being dropped back to the inside of the drum, that is to the interior of cylindrical shell, but without a need for added complexity of the pulp lifter structure for keeping the ground material in the pulp lifter; keeping the ground material flow away from the back face of the grate that typically has a rough texture and tends to slow down the material flow thus decreasing the efficiency of the grinding mill; and reducing wear on the back side of the grate since the ground material, such as slurry, does race along the back of the grate.

According to an embodiment, the angle Θ between the inner sur- face 12 of the first wall 4 and the outer edge 11 of the guiding surface 10 may be smaller than 88 degrees. According to another embodiment, the angle Θ between the inner surface 12 of the first wall 4 and the outer edge 11 of the guiding surface 10 may be in the range of 20 to 70 degrees. This is particular- ly beneficial, as angles Θ of less than 20 degrees between the inner surface 12 of the first wall 4 and the outer edge 11 of the guiding surface 10 are more difficult and expensive to build, whereas angles of 70 degrees or less can provide good guiding properties for the outer pulp lifter element 1 and its guiding surface 10. According to a further embodiment, the angle Θ between the inner surface 12 of the first wall 4 and the outer edge 11 of the guiding surface 10 may be in the range of 30 to 60 degrees. According to yet another embodiment, the angle Θ between the inner surface 12 of the first wall 4 and the outer edge 11 of the guiding surface 10 may be about 45 degrees.

According to an embodiment, for instance an embodiment of the Figure 3, an outer pulp lifter element 1 may comprise a second surface 7 extending in a radial direction B of the pulp lifter 2 and forming a front surface of the pulp lifter element 1 in the direction of rotation C of the pulp lifter 2. The front surface of the pulp lifter element refers to the surface first in the direction of rotation C, which is the surface through which the ground mate- rial, such as slurry, from an adjacent, more particularly preceding, outer pulp lifter element first enters the outer pulp lifter element in question. The second surface 7 may comprise an opening 8 for receiving ground material from an adjacent outer pulp lifter element. According to an embodiment, the second surface 7 may be substantially perpendicular to the first wall 4.

In such an embodiment, the direction of the inner surface 12 of the first wall 4 may be defined by the first wall 4 side edge of the opening 8 extending in the direction A- A' in Figure 6 parallel to the head of the mill and the radial direction B of the pulp lifter 2. The outer edge 11 of the guiding surface 10 may comprise the outer edge of the opening 8. The angle Θ be- tween the inner surface 12 of the first wall 4 and the outer edge 11 of the guiding surface 10 may then comprise the angle between the first wall 4 side edge of the opening 8 and the outer edge of the opening 8, such as can be seen in Figure 6, for example.

According to an embodiment, the vane 6 may have an equal angle between the inner surface 12 of the first wall 4 and the guiding surface 10 along the whole length of the guiding surface 10. In other words the vane 6 may be sloped to a similar amount along the whole length of the guiding surface 10, that is it may have the same angle compared to direction A-A' in Figure 6, for example, along the vane from the outer end of the vane, that is the end closest to the outer end of the pulp lifter, to the inner end of the vane, that is, the end closest to the outlet and discharger of the grinding mill.

According to an embodiment, the angle between the inner surface 12 of the first wall 4 and the guiding surface 10 of the vane 6 may vary along the length of the guiding surface 10. According to an embodiment, the angle between the inner surface 12 of the first wall 4 and the guiding surface 10 of the vane 6 may be reversed at a point of the guiding surface 10. In such embodiments, thus, the angle between the inner surface 12 of the first wall 4 and the guiding surface 10 of the vane 6 at the inner end of the vane and/or at a point along the guiding surface of the vane may be different from the an- gle Θ between the inner surface 12 of the first wall 4 and the outer edge 11 of the guiding surface 10. With such embodiments, an improved movement of the ground material along the guiding surface 10 may be achieved. An embodiment, where the angle is reversed at a point of the guiding surface, may be particularly beneficial for guiding the ground material to the discharger and the outlet.

According to an embodiment, the outer pulp lifter element may comprise solid cast steel material. According to another embodiment, the outer pulp lifter element may comprise rubber material finish with a steel frame provided inside. According to a further embodiment, the outer pulp lifter element may comprise an elastomer material, such as urethane.

According to an embodiment, a pulp lifter 2 for a rotating drum grinding mill 3 may comprise at least one outer pulp lifter element 1 as described in this description.

According to an embodiment, the pulp lifter 2 may further com- prise an inner pulp lifter 16. The vane 6 may then extend to the inner pulp lifter 16.

According to an embodiment, at least a part of the guiding surface 17 of the inner pulp lifter part of the vane 6 may also be angled in relation to the inner surface of the back wall 18 of the inner pulp lifter. According to a further embodiment, the guiding surface 17 of the inner pulp lifter part of the vane 6 may be arranged on an opposite side of the vane 6 on the area of the inner pulp lifter when compared to the area of the outer pulp lifter. The opposite side of the vane 6 refers to the backside of the vane in the rotation direction of the pulp lifter. This is beneficial as the ground material falls to op- posite side due to gravity if the material overtops, that is if it does not exit the pulp lifter through the outlet at the highest point of the rotating cycle of the pulp lifter. According to a further embodiment, the vane 6 may extend to the discharger 24 as well.

According to an embodiment, at least a part of the guiding surface 25 of the discharger part of the vane 6 may also be angled in relation to the inner surface of the discharger wall 26. This inner surface of the discharger wall 26 may form a substantially continuous surface with the inner surface of the back wall 18 of an inner pulp lifter element 16 and the inner surface 12 of the first wall 4 of an outer pulp lifter element 1, when the outer pulp lifter element 1, the inner pulp lifter element 16 and the discharger 24 are assembled together, for instance in a grinding mill 3.

According to an embodiment, the grate 23 may comprise at least one grate lifter 27 arranged on the cylindrical shell interior side of the grate 23 for guiding particles of the ground material into the pulp lifter 2 through the openings in the grate 23. This may take place in a manner similar to that of the vanes in the pulp lifter; that is the grate lifters may lift the ground material as the grate rotates. The outer edge 28 of the grate lifter guiding surface 30 may then be angled in relation to a grate wall 29 facing towards the interior of the cylindrical shell 20 in such a manner, that an angle a between the grate wall 29 and the grate lifter guiding surface 30 is smaller than 90 degrees at least at the outer edge of the grate lifter 27.

According to another embodiment, the angle a may be smaller than 88 degrees. According to another embodiment, angle a may be in the range of 20 to 70 degrees. According to a further embodiment, the angle a may be in the range of 30 to 60 degrees. According to yet another embodiment, the angle a may be about 45 degrees.

According to an embodiment, the angle a may vary along the length of the grate lifter guiding surface 30. According to an embodiment, the angle a may be reversed at a point of the grate lifter guiding surface 30. In such embodiments, thus, the angle at the inner end of the grate lifter and/or at a point along the grate lifter guiding surface may be different from the angle a. With such embodiments, an improved movement of the ground material along the grate lifter guiding surface 30 may be achieved. An embodiment, where the angle is reversed at a point of the grate lifter guiding surface, may be particularly beneficial for guiding the ground material to the pulp lifter.

According to an embodiment, the grate lifter and the pulp lifter may be arranged lying on top of each other, and the angle may extend across both grate lifter and the pulp lifter. Thus, the inside face of both the grate lifter and the pulp lifter may be angled.

Grate lifter may comprise a radial, curved or a spiralling form.

Thus, depending on the intended use, combinations of grate lifter form and pulp lifter vane form may be combined in different ways, such as by combining radial grate lifters and radial pulp lifter vanes, spiralling grate lifters and spiralling pulp lifter vanes, radial grate lifter and spiralling pulp lifter vanes or spiralling grate lifter and radial pulp lifter vanes.

According to an embodiment, the same angle Θ may be extended also to the grate lifter, that is the grate lifter guiding surface and the pulp lifter guiding surface may have a same angle. These guiding surfaces may even form a continuous guiding surface on both sides of the grate.

According to an embodiment, the grinding mill may comprise a wet grinding mill. The grinding mill may then further comprise at least one inlet for receiving a continuous feed of a process liquor. Depending on embodiment, this inlet for process liquor may comprise the inlet 21 or a separate inlet for the process liquor.

According to an embodiment, the grinding mill 3 may comprise at least one of the following: a grate discharge ball mill, a SAG mill, and an AG mill.

According to an embodiment, an outer pulp lifter element, an inner pulp lifter element and/or a pulp lifter may comprise a spare part of a grinding mill. According to an embodiment, such a spare part may be retrofitted to an existing grinding mill. The pulp lifter and its structural parts described in this description, such as the outer pulp lifter element, the inner pulp lifter element and the grate lifter, may be retrofitted to an existing grinding mill, even though it would originally be of a conventional design, such as conventional radial or spiral pulp lifter and/or grate lifters in existing grinding mills. In other words, the structural parts of a grinding mill of a conventional design may be replaced by structural parts described in this description. Thereby, a more smooth and efficient flow of the ground material can be achieved and even a longer life cycle of the spare parts.

It will be obvious to a person skilled in the art that, as the technology advances, the inventive concept can be implemented in various ways. The invention and its embodiments are not limited to the examples described above but may vary within the scope of the claims.