That opportunity can be seized simply by the original equipment manufacturer and the mine working together to break down the processes and equipment design part by part and tailor-designing solutions.
“The process relies on a ground-up review of both installation process and equipment design in order to tailor the results to the stated objectives. No element can be considered a foregone conclusion as it is too easy to adopt the usual in the false expectation that longevity of practice is equivalent to ideal,” Donaldson’s Ross Middleton and Ellton Group’s Mark Elliott said in a paper presented at the 2008 Coal Operators’ Conference in Wollongong this year.
The Tasman bord and pillar operation’s livelihood, with its relatively small 10 million tonne reserve with comparatively low tonnages, relies on cost-effective infrastructure and efficient mining techniques. The mine plan requires repeated relocation of production panel systems in relatively short cycles over the mine life.
In the quest for greater efficiencies mine management identified the non-productive time that occurred during installation of trunk conveyors and the installation and relocation of panel conveyors.
“Aggressive targets were established for the time to be taken from handover of a completed heading by the mining team to engineering team until hand-back with an installed and operational conveyor. These targets, amongst others, necessitated a specific approach to the design of equipment with particular emphasis on simplicity of transport, minimised underground assembly and electrical termination, standardisation of parts and the ability to efficiently add to the installation following initial operation,” Middleton and Elliott said.
To achieve this, the mine and Ellton Group collaborated closely on operational and design experience.
The conveyors at Tasman use 1200mm wide belt and either 75kW or 150kW installed power. The conveyors move at just 2.7m/s to stop any issues arising with the low transfer heights and general wear and tear on the idlers and belts.
During the design process the team had to take into consideration:
- 48 hours target time for installation, powering up and commissioning of a trunk conveyor and 48 hours for the recovery, re-installation and commissioning of a panel conveyor;
- Typical set-up for a new installation to be the starter, mechanical terminal set, structure, boot end and belting for a 100m initial length at handover to the mining team;
- Panel conveyors to be able to load at any point on a trunk conveyor;
- Trunk conveyors to be transom mounted trough idler design, optionally roof hung or floor mounted, panel conveyors to be suspended trough, floor mounted design but to have maximum commonality of components;
- Trunk structure design to provide simple “bolt free” construction to suit the development sequence;
- Minimised types of pulleys in the system;
- Maximum interchangeability and commonality of mechanical hardware in all conveyors; and
- To suit future anticipated roadway limits the panel conveyors had to be installed and able to transfer to a trunk conveyor in no more than 2200mm head height.
The review identified several areas of improvement, resulting in several design innovations.
The entire drive and jib module for the trunk system was pre-assembled prior to underground installation. The chute work and belt cleaner sets were also pre-fitted. The paper presenters said the jib assembly had a pinned and hinged design that allowed the completed unit to fold into a low height, collapsed position for transport.
All electrical field devices were pre-fitted, cabled up and terminated to a common junction box. Prior to delivery or installation underground the entire assembly was wired and tested then broken down for transport. Wiring up underground requires only for the signal cable to be run and terminated to the J box.
If space or time limits require, the trunk conveyor loop take-up can be installed with a reduced number of modules, Middleton and Elliott said. The winch is mounted at the inbye end of the assembly but on a carriage that can be detached and travel along the modules. Once further storage modules are required, they can be fitted to the inbye end of the loop and the winch slid back to the new inbye end. Middleton and Elliott said this feature allowed the loop to be extended at any time without breaking the belt or re-roping the winch.
The panel conveyor system uses completely interchangeable mechanical and electrical components to the trunk system including drive module, pulleys, winch parts and more. The head pulley of the panel is one of the loop pulleys of the trunk system, whereas the head pulley on the trunk is interchangeable with the larger drive pulley. The only two pulley designs used in the entire system are the high tension bend/drive pulley (live shaft) and low tension bend/loop/tail/panel head pulley (dead shaft).
For compactness and portability the shaft mounted drive assembly of the trunk system included standard base plate, coupling and motor is mounted inboard in the panel drive. A low speed chain drive is used to couple the gearbox to the drive pulley.
The drive module incorporates a sliding, retractable jib frame and hinged impact plate/chute. The jib geometry is designed specifically to meet the very low head height.
The entire assembly is divided into separate, self-contained modules that spigot together during installation.
Each section is mounted on wheels with integrated tow eyes at the inbye end of each section. Typically a panel installation will comprise a drive/discharge module and two loop modules. The winch incorporates the relocatable feature of the trunk system so the loop can be extended at any time, Middleton and Elliott said.
The panel load station was designed so a panel conveyor could load to any point on the trunk system, which is based on adding elements to the standard floor mounted conveyor structure to provide sufficient strength, the required impact idler spacing and the skirt and guarding requirements. The parts were all generally less than 25kg so can be managed by hand.
With all the elements and processes designed the team put it into practice at Tasman. The result was that installation times bettered the targets and operating performance since has been excellent.
As of February, three trunk systems have been installed and two panel systems.
“The most recent trunk 3 was installed and running in a total of three shifts including boot end and 120 metres of structure,” Middleton and Elliott said.
“The most recent panel 2 was installed and running in two shifts including boot, structure and belt.
“Idler life has exceeded expectations with zero bearing failures in the rollers since start of operations in September 2006. This result considered partly due to the modest belt speeds that were specified along with good seal design and accurate roller manufacturing tolerances.”
While the design criteria that were used in this project are specific to the Tasman operation, Middleton and Elliott said the results of the process and equipment features have likely applications in other mine operations seeking to improve development efficiencies and minimise conveyor installation times.