The present invention relates to a grinding mill and, in particular, to a grinding mill including a direct drive motor.

Grinding mills are used to break large pieces of mined material into smaller, more manageable, pieces of material. There are typically two types of grinding mill, geared mills and gearless mills. Gearless mills are also known as ring motor mills as they are typically driven by a direct drive ring motor which is mounted around the outer shell of the mill body. Gearless mills do not involve components such as gears or pinions and as there are no mechanical parts relied upon to transmit the driving torque, the mechanical losses occurring, for example in the gearbox, are completely eliminated.

An example of such a prior art ring motor mill 10 is shown in Figures 1 and 2. The mill body 12 is supported at opposing sides by bearings 16a, 16b. The rotor poles 18 ofthe ring motor 20 are directly attached to a flange 22 on the outer shell 24 of the mill body 12. The stator 26 of the ring motor 20 is then mounted around the rotor poles 18, leaving an air gap 28 between the rotor 18 and the stator 26. A driving torque is directly transmitted, by way of a magnetic field in the motor 20, to the mill body 12.

Ring motor cost is highly dependent on the cross sectional diameter of the motor. In the case of a grinding mill ring motor, the cross sectional diameter of the motor is currently determined by the cross sectional diameter of the outer shell of the mill body, around which the motor is installed. For a given mill power, as the mill cross sectional diameter increases, the ring motor cost also increases.

Whilst a factor of the power requirement for the mill is related to its cross-sectional diameter, this alone would not preclude standardization ofthe motors manufactured for use with mills. However, each mill is typically custom built for a particular site or use. Therefore, for every mill, the motor must be custom engineered to correspond to the size of the mill body it is to be used with. The constraint of the motor size being determined by the diameter of the mill body means that standardization of motors for this use is not possible. DE 1937895 describes a grinding mill with a mill body forming a grinding cavity and straight circular cylinder shaped engagement portions which are supported by bearings. Two direct drive motors are located on the engagement portions. In this design the size of the ring motor does not depend on the diameter of the mill body but on the diameter of the engagement portions. Therefore, there is a need for a ring motor which is independent of the diameter of the mill cavity and the diameter of the engagement portions and which therefore may be standardized.

It is an object of the present invention to meet or satisfy the aforementioned need.

According to a first aspect of the invention there is provided a grinding mill defining a grinding cavity, the mill body supported at opposing sides by respective bearings, a direct drive motor, such as a ring motor, operable to drive the mill body and arranged adjacent at least one bearing and a torque transmitter that is rigidly connected to the mill body and adapted to transmit to the mill body the torque exerted by the direct drive motor. The diameter of the torque transmitter may be different from the diameter defined by the supporting bearings. If the diameter of the torque transmitter and the diameter of the supporting bearings coincide, the torque transmitter may be considered a part of an engagement portion of the mill body, or trunnion, that extends through the supporting bearings. Locating the direct drive motor adjacent to a supporting bearing of the mill body, rather than mounted on the outer shell of the grinding cavity, avoids the conventional requirement that the dimensions of the motor are determined by the dimensions of the grinding cavity outer shell. In a first embodiment a rotor-end circumference of the torque transmitter along which the torque transmitter is connected to the rotor of the ring motor has a diameter that is larger than the outer diameter of the engagement portion and smaller than the outer diameter of the grinding cavity. The torque transmitter compensates a radial gap between the rotor and the engagement portion, wherein the mill-body-end of the torque transmitter where the torque transmitter is fixed to the mill body may be axially displaced with respect to the rotor, i.e. the torque transmitter is not necessarily exclusively radial. Thus the diameter of the direct drive motor can be chosen independent of the diameter of the grinding cavity and independent of the diameter of the engagement portion which enables the use of standard direct drive motor sizes for various mill sizes.

In another embodiment the mill-body-end of the torque transmitter is fixed to the grinding cavity of the mill body. Thus a more compact design can be achieved. In another embodiment the mill-body-end of the torque transmitter is fixed to the engagement portion of the mill body. Thus an easier handling in the assembly of the direct drive motor can be achieved.

In another embodiment the torque transmitter is a separate element. Thus an easier

transportation of the mill body can be achieved. In another embodiment the torque transmitter is a torque tube with a continuous surface . Thus there is a closed circumferential shear flow which increases the transmittable torque.

In another embodiment the torque transmitter is rotationally symmetrical. Thus the distribution of mass with respect to torque is optimized and a larger torque is transmittable.

In another embodiment the torque transmitter is conical. Thus the flux of forces is straight and increases stiffness with respect to bending and torque can be achieved.

In another embodiment the torque transmitter comprises, instead of a continuous surface, a number of discrete elements distributed along a circumference of the torque transmitter. Thus it is easier to manufacture the torque transmitter.

Embodiments of the present invention will now be provided, by way of example only, and with reference to the following figures, in which:

Figure 1 is a cross-sectional view from the front of a known ring motor grinding mill;

Figure 2 is a cross-sectional view from the side of a known ring motor grinding mill;

Figure 3 is cross-sectional view from the side of a first embodiment of a grinding mill in accordance with the present invention; Figure 4 is a cross-sectional view from the side of a second embodiment of a grinding mill in accordance with the present invention.

Figure 5 is a cross-sectional view from the side of a third embodiment of a grinding mill in accordance with the present invention. Throughout the following description, the same numbering has been used to identify the same component for each of the embodiments.

With reference to Figure 3 there is shown a grinding mill 30 comprising a mill body 31 having a grinding cavity 32 provided at opposing sides 34a, 34b with engagement portions, in this case trunnions 36a, 36b, which are supported by bearings 38a, 38b respectively. Mill side 34a is provided with an input unit 40, in this case including a feed chute 42 into which material (not shown) is fed into the grinding cavity 32 of the mill body 31 to be ground. Mill side 34b is provided with an output unit, in this case an output funnel 44, which extends from mill body side 34b through trunnion 36b beyond bearing 38b. The output funnel 44 transports the material being discharged out of the grinding cavity 32 of the mill body 31 , through trunnion 36b to a trommel (not shown) or screen (not shown). The grinding mill is provided with a motor 50, which in this embodiment is a ring motor. A rotor 52 of a ring motor 50 is located on trunnion 36b with the bearing 38b located between the rotor 50 and the grinding cavity 32. A stator 54 of ring motor 50 is mounted around the rotor 52 with an air gap 56 left between the rotor 52 and stator 54. The ring motor 50 acts on the trunnion 36b which operates as a torque transmitter, or torque tube, to drive the mill body 31.

By arranging the motor 50 on the trunnion 36b, the dimensions of the motor 50 are not constrained by the cross sectional diameter y of the outer shell 33 of the grinding cavity 32 of the mill body 31 and instead are dependent upon the cross sectional diameter x of the trunnion 36b. The mounting of the motor 50 on the trunnion 36b will allow the motor 50 to be smaller and that will typically allow standardization which will lead to a reduction in manufacturing costs.

With reference to Figure 4 there is shown a second embodiment of a grinding mill 30 comprising a mill body 31 having a grinding cavity 32 provided at opposing sides 34a, 34b with engagement portions, in this case trunnions 36a, 36b, which are supported by bearings respectively. Mill side 34a is provided with an input unit 40, in this case including a feed chute 42 into which material (not shown) is fed into the grinding cavity 32 of the mill body 31 to be ground. Mill side 34b is provided with an output unit, in this case an output funnel 44, which extends from mill body side 34b through trunnion 36b beyond bearing 38b. The output funnel 44 transports the material being discharged out of the grinding cavity 32 of the mill body 31 through trunnion 36b to a trommel (not shown) or screen (not shown). The grinding mill is provided with a motor 50, which in this embodiment is a ring motor. A rotor 52 of a ring motor 50 is located on trunnion 36b between bearing 38b and grinding cavity 32 of the mill body 31. A stator 54 of ring motor 50 is mounted around the rotor 52 with an air gap 56 left between the rotor 52 and stator 54. Trunnion is fixed to the end face of the mill body along a circumference with a diameter halfway in-between engagement portion and cavity. The ring motor 50 acts on the trunnion 36b which operates as a torque transmitter, or torque tube to drive the mill body 32.

In the embodiments of Figure 4, the motor size is not constrained by the outer shell diameter y of the grinding cavity 32 of the mill body 31 , but instead, the diameter x of the feed and non- feed end trunnions.

With reference to Figure 5 there is shown a grinding mill 30 comprising a conical torque tube 46 which compensates a radial gap between the rotor and the trunnion 36. It is fixed on one side to the trunnion and on the other side to a rotor 52 of the direct drive motor. In the embodiments of Figure 5, the motor size is not constrained by the outer shell diameter y of the grinding cavity 32 of the mill body 31 nor the diameters of the feed and non-feed end trunnions.

The grinding mill motor arrangement detailed above and accompanied, by way of example only, with the embodiment detailed in Figures 3, 4 and 5 will facilitate use of standardized ring motors and ring motor component in a similar manner as with conventional squirrel cage motors used within industry. Such standardization would increase the ability of grinding mill owners to hold common spares thus significantly reducing the cost of ring motor spare inventories.

Various modifications may be made to the embodiments hereinbefore described without departing from the scope of the invention. For example, it will be appreciated that whilst the engagement portion supported by the bearings and acted on by the motor is described with reference to the Figures as a trunnion, any suitable arrangement of apparatus which acts as a torque transmitter could be used. In addition whilst the above embodiments show arrangements having two bearings there may be more than one bearing provided at either side of the mill body.

List of Reference Numerals

10 ring motor mill

12 mill body

16a, 16b bearings

18 rotor poles

20 ring motor

22 flange

24 outer shell

26 stator

28 air gap

30 grinding mill

31 mill body

32 grinding cavity

33 outer shell

34a, 34b opposing sides

36a, 36b trunnions

38a, 38b bearings

40 input unit

42 feed chute

44 funnel

46 torque tube

50 motor

52 rotor

54 stator

56 air gap