Project Status: Complete
Project Participants: University of Queensland
Project Leader: Nenad Djordjevic (University of Queensland)
Within Autogenous Grinding/Semi-Autogenous Grinding tumbling mills, the motion of the charge created from both the rock and steel balls has a critical influence on the mode and intensity of rock breakage, as well as on the wear of the mill liner and steel balls. This project aimed to develop a non-invasive continuous mill charge monitoring system to establish the relationship between the electrical resistivity of sections of the mill shell and the inside of these sections of the shell. This inferred information on position and shape of charge can then be used to optimise the operation of the mill – and improve the overall energy efficiency of rock grinding/comminution.
Minute amounts of electrical current leak from the mill shell into the charge, resulting in differences in the effective electrical resistivity of different parts of the mill shell. Initial measurements in the JKMRC test mill have shown that these leaks can be measured with modern portable voltage instruments connected to electrodes mounted on the outside of the mill shell. It was proposed that this inferred information on position and shape of charge can then be used to optimise the operation of the mill – and improve the overall energy efficiency of rock grinding/comminution.
The “wired” setup used for the experiments earlier in the project was not well suited to rotating
structure so the team developed a wireless voltage measuring system, which sent the resulting
voltages to a computer using a microwave antenna. There are several communication systems that
can transmit information wirelessly. A Wireless Local Area Network (LAN) was used since many of the
components needed in this type of system can be bought off the shelf and have extensive development
support. Wireless LAN can also be operated over a wide range of distances and at higher data rates
than the other methods and is also able to operate over the internet, which allows the measurement
system to be remotely controlled from anywhere in the world with a suitable connection.
Despite the limited performance of the hardware, the team were still able to gain an insight into the behaviour of the system as the mill rotates. Unfortunately, a full rotation of the mill could not be made. Instead, the mill was moved from side to side. Preliminary results showed that the measured first order voltage shifts in accordance with the direction of the mill rotation and can be used to determine the water level in the mill if the positions of the electrodes are known.