TECHNICAL FIELD The present invention relates to grinding mill installations and to methods of tightening fasteners used to retain mill liner components in the mill and to methods of releasing mill liner components from the mill.

BACKGROUND

Grinding mills, such as Semi Autogenous Grinding mills (SAG mills) are used to grind mined ore and are commonly used in first stage processing of gold, copper and platinum bearing ores. The mill takes the form of a rotatable drum. The drum is loaded with ore, along with a charge of grinding balls or rods. Attrition in the grinding balls causes grinding of finer particles. The inside of the mill is lined with lifting plates to lift the material inside up and around the inside of the mill, where it then falls off the plates into the rest of the ore.

The lifting plates are fixed to the inside surface of the drum by way of a series of bolts which project out of the drum to be secured by nuts which are tightened to a specified torque. After a period of mill operation, it becomes necessary to re-tighten the nuts. The mill must be stopped in order to re-tighten the nuts. The nuts are tightened by way of human operators maually applying torquing tools to the nuts in sequence, whilst periodically rotating the drum of the mill. The torquing tools are typically very heavy and the re-torquing procedure is a hazardous operation which brings a risk of injury to the human operators.

Furthermore, after the mill has stopped rotating, it is necessary to wait for an electrical isolation period to allow for static charge that may have accumulated on the drum to dissipate. Regulations can specify a waiting period of about one hour before operators are allowed to work on the mill.

The lifting plates become worn over time. After an extended period of operation of the mill it becomes necessary to replace the lifting plates. It is often the case that, after removing the nuts that secure a lifting plate, the bolts remain stuck in place, or that, even after removing the bolts the plate does not come away from the inside of the drum but has become jammed in place. This can be due to an

accumulation of debris around the bolts or the lifter plate and between adjacent lifter plates, or due to deformation of the lifter plates or fixing bolts. In this circumstance, it has been tried to use a power hammer, such as a Thunderbolt (R) available from rmeglobal.com to free the jammed bolts or lifter plates.

A power hammer is a substitute for a traditional sledgehammer. It is usually hydraulically operated and includes a working bit which can impart a high momentum impact blow of typically between 450 to 1500 joules. A power hammer is usually too heavy for one person to lift and so is mounted on a crane or jib. To free a jammed lifter plate, the power hammer is raised up to align with an aperture in the drum of the grinding mill intended for such a purpose. The aperture is located behind a lifter bar. The bit of the power hammer is aligned with the aperture and the power hammer is activated to deliver one or more blows to the rear face of the lifter plate. However, due to the need to manually align the power hammer, it has been found that the bit of the power hammer may be incorrectly aligned with the aperture, or not located at the correct distance away from the rear of the lifter plate so that the bit of the power hammer penetrates too far into the drum when activated. This may result in damage to the drum of the mill, or deformation of the lifter plate, further hindering the operation of removing the lifter plate.

SUMMARY OF THE INVENTION

In a first aspect the present invention provides a grinding mill installation including: a grinding mill drum; an arrangement of fasteners for securing components of a mill liner in the drum, the fasteners being accessible from the outside the drum; and at least one mechanised actuator which is arranged to manipulate the fasteners.

In an embodiment the mechanised actuator includes an actuator head mounted on a moveable mounting which is arranged to position the head with respect to the fasteners.

In an embodiment the actuator head is arranged to exert its rotational moment onto an adjoining nut or exposed bolt end. In an embodiment the location of the fasteners is determined based on the angular position of the drum. In an embodiment the location of the fasteners is determined based on the output of a visual detection means.

In accordance with a second aspect there is provided a method of manipulating an arrangement of fasteners accessible from the outside of the drum of a grinding mill including the steps of: providing at least one mechanised actuator which is arranged to manipulate the fasteners; and manipulating the fasteners by way of the at least one mechanised actuator.

In an embodiment the step of manipulating the fasteners is carried out whilst progressively rotating the drum of the mill.

In accordance with a third aspect there is provided a grinding mill installation including: a grinding mill drum which is arranged to receive an arrangement of mill liner components; at least one mechanised actuator which is arranged to be positioned in a pre-determined orientation in relation to features on the outside surface of the drum and to impart an impact force to the at least one mill liner component to assist in releasing at least one of the mill liner components.

In an embodiment the mechanised actuator includes an actuator head mounted on a moveable mounting which is arranged to position the head with respect to the at least one feature.

In an embodiment the location of the at least one feature is determined based on the angular position of the drum.

In an embodiment the location of the at least one aperture is determined based on the output of a visual detection means. In accordance with a fourth aspect there is provided a method of removing a mill liner component from a grinding mill, including the steps of: providing a power hammer which is arranged to impart an impact force to the mill liner component; mounting the power hammer on a moveable mounting, the moveable mounting including position detection means to enable detection of the location of the power hammer; and aligning the power hammer with a feature on the drum of the mill by way of the moveable mounting.

In an embodiment the position detection means further enables detection of the orientation of the power hammer.

In accordance with a fifth aspect there is provided a computer program comprising at least one instruction which, when implemented by a computer, is arranged to perform a method as described in accordance with either the second or fourth aspects.

In accordance with a sixth aspect there is provided a computer readable medium comprising a computer program as described in accordance with the fifth aspect. BRIEF DESCRIPTION OF THE DRAWINGS

An embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 is a plan view of a grinding mill installation;

Figure 2 is a perspective view from above of the grinding mill installation of figure 1;

Figure 3 is a close up view of one of the mechanical actuators of the grinding mill installation of figure 1;

Figures 4 to 6 illustrate a sequence of tightening nuts used to retain mill liner components in the drum of the grinding mill installation of Figure 1;

Figure 7 is an alternative view of one of the robotic actuators of figure 1; and Figure 8 shows a robotic actuator controlling a power hammer. DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Referring to Figure 1, a grinding mill installation 10 is shown including a grinding mill 11 which includes a drum 14. Around the drum are positioned a series of six mechanical actuators in the form of robotic arms 20. The robotic arms 20 are fixed in place in relation to mill 11 by being bolted to floor 12. A fence 16 protects human operators from wandering into the working area of the robotic arms 20.

As shown in Figure 2, the drum 14 is fitted with a mill liner by way of a series of nut and bolt fasteners in a known manner. The bolts are inserted from inside the drum to hold mill liner components in place around the internal surface of the drum 14. Nuts 18 are attached to the exposed bolt ends to secure the bolts in position.

Turning now to Figure 3, one of robotic arms 20 is shown in enlarged detail and includes a fixed base portion 21 on which is pivotally mounted a rotatable base portion 22. To this is mounted a first arm portion which is rotatable with respect to base portion 22 about a horizontal axis. A second arm portion 25 of the robotic arm is pivotally and rotatably mounted to first arm portion 23 by way of elbow joint portion 24. A wrist portion 26 is in turn pivotally and rotatably mounted to second arm portion 25. A suitable arrangement for use in this application would be one of the IRB 7600 range of industrial robots available from ABB Robotics ( ).

As can be seen, robotic arm 20 is fitted with an actuator head 30 which is configured with a socket portion for engaging with nuts 18 and uses a source of compressed air to tighten nuts 18 up to a pre-determined torque which may be of the order of, for example, 2000Nm. However, it is to be understood that any suitable level of torque may be applied to obtain the necessary level of tightening of the nuts. The various articulated joints of robotic arm 20 are fitted with positional sensors to allow accurate positioning of actuator head 30 with respect to nuts 18 on the outside surface of drum 14.

As shown in Figure 1, a pair of robotic arms 20 works on each of the front face, rear face, and outer surface of drum 14 simultaneously. In the illustrated embodiment, six robotic arms 20 are programmed to conduct a nut-tightening maintenance routine of grinding mill 11. Referring to figure 4, it can be seen that the nuts 18 are generally provided in rows. Mill 11 is fitted with a 65,000 pulse per revolution rotary encoder that can detect the rotational position of the sag mill to an accuracy of 0.0055 Degrees. For a typical mill with an outside diameter of approximately 10m this provides a positioning accuracy of 0.48mm at the outer surface of drum 14 of the mill. Robotic arms 20 are controlled by a computing system configured with suitable control software. A database storing information in relation to features of the drum including the locations of the nuts 18 around drum 14 is pre-prepared and is utilised by the control software to control the robotic arms to locate the nuts in a maintenance sequence.

As explained above, the information in the database allows the robotic arms to locate the positions of the nuts to within about 0.5mm. This location ability is augmented by additional sensors such as laser and vision sensors as well as mechanical sensors in the actuator 30 to allow more precise location of the nuts and to allow detection of the rotational angle of the nuts to enable a socket to be placed over the nut to allow the nut to be manipulated.

Referring to figure 7, the actuator head is shown in detail and includes a lever arm 32 to allow the tool to exert its rotational moment onto an adjoining nut or exposed bolt end while the robot arm utilises soft servo technology to allow the actuator to twist without damaging the robot in the process.

The actuator 30 can manipulate the fasteners in three modes 1) rattle nut on 2) rattle nut off and 3) torque nut.

Referring to figure 8, the robotic arms 20 may also be used to assist in removing lifter plates from the mill. In this instance, the nut tightening actuator head 30 is removed from a robotic arm and is replaced by a hydraulic power hammer attachment 40, such as an attachment based on, or including a Thunderbolt (R) power hammer.

The weight of the power hammer attachment 40 is borne by crane 42. The power hammer attachment is pivotally mounted to a tie rod 46 which is slidable along the beam 44 of crane 42. Crane 42 is mounted on a rotable base which allows the power hammer to be moved towards or away from the drum. The robotic arm controls the location and orientation of the working bit 41 of the power hammer. The robotic arm can thus be controlled to position the working bit 41 of the power hammer in a predetermined orientation with respect to features on the outside of drum 14. Typically, the robotic arm aligns the power hammer so that the working bit is orthogonal to the local surface of the drum.

The database of features of the drum described previously is also programmed to include data identifying the locations of apertures (not shown) which may be provided in the drum of mill 11 for the purpose of removing mill liner components. Using the output of the rotational encoder fitted to the drum 14, the robot control software is able to control the robotic arm 20 to accurately align the working bit 41 of the power hammer to align with apertures in the drum 14 or with exposed bolt ends projecting out of the drum 14 to deliver blows to assist in removing mill liner components. When in position, the power hammer can be activated by the robot control system to apply blows to assist in removing liner components from the mill.

Accordingly, from the above, it can be seen that embodiments of the invention have at least one of the following advantages:

The risk of injury to human operators handling large and heavy torque tools is eliminated, reducing injury risks.

No need to wait out electrical an isolation period before commencing re- tightening maintenance.

The time taken to complete the process of re-tightening nuts can be reduced, thus reducing mill down time.

In removing wear plates with a power hammer, correct alignment with apertures and correct orientation of the power hammer can be enhanced reducing the likelihood of damage to the drum or to wear plates.

Although the invention has been described with reference to the present embodiments, it will be understood by those skilled in the art that alterations, changes and improvements may be made and equivalents may be substituted for the elements thereof and steps thereof without departing from the scope of the invention. Further, many modifications may be made to adapt the invention to a particular situation without departing from the central scope thereof. Such alterations, changes, modifications and improvements, though not expressly described above, are nevertheless intended and implied to be within the scope and spirit of the invention. The above described embodiments are therefore not to be taken as being limiting in any respects.

Any reference to prior art contained herein is not to be taken as an admission that the information is common general knowledge of the skilled addressee in Australia or elsewhere.

In the claims which follow and in the preceding description of the invention, except where the context requires otherwise due to express language or necessary implication, the word "comprise" or variations such as "comprises" or "comprising" is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention.