Lyntas/mining_domain_knowledge_reference_dataset huggingface dataset:
Area: Minning Maintenance Realibility
Fractures in ball mill trunnion
Cracks observed in a ball mill trunnion and compared the theoretical values of growth rate of these defects with actual values obtained through periodic inspections performed in this component. The cracks nucleation was caused by lack of lubrication in the trunnion bearings, generating circumferential thermal stresses, thus the estimated temperature of the trunnion and bushing contact achieved 150 °C. The lack of lubrication was originated by a logic failure which allowed the mill to start and run over the trunnion bearing bushing without the lubrication systemto be turned on, that is, without oil film. The logic failure was caused by an operator fault.
The maximum trunnion temperature during a normal operation is 57 °C. There is a heat exchange device in the lubrication system that always tries to keep the oil to the mill at 40 °C. The metalmetal contact generates heat, therefore temperature raise and since the lubrication unit was shut down, the root problem was not oil temperature, but oil not reaching the bushing.
Thermal stresses were calculated by the use of Strand7 software, version R.2.4.6, according to an estimated temperatures distribution indicated in Fig. 5. This distribution was based on the cracks location at the trunnion shown in Fig. 6 and assuming the most critical cracks were found at the ends of the trunnion shoulder.
There is no clearance between the bushing and the trunnion shoulder from an axial direction. Different thermal expansion between the trunnion and the bushing led to higher contact, and consequently heating as assumed in Fig. 5.
The standards BS7910 and ASME Section XI, Appendix A were used to calculate the theoretical crack growth, since there is no specific standard for grinding mill cracks evaluation.
Area: Minning Maintenance Realibility
SAG Mill Motor Breakdown
one of two 6.5MW motors that drive the SAG  mill at the Phu Kham Copper?Gold Operation failed. The SAG mill draws only 50% of its installed motor power whilst treating the softer transitional ore.
It is anticipated that the process plant will be down for between 11 and 23 days dependent on the speed with which the motors can be repaired or the availability of identical motors.
Since commercial production commenced in June 2008, the mechanical availability of the process plant has steadily improved from 80% to 90% in the three months to May 2009. This represents excellent progress towards a long?term goal of 95% availability
Accordingly, the first annual major plant shutdown, incorporating a 7?day SAG mill re?line, which was scheduled for July has been brought forward to minimise disruption to production.
Area: Minning Maintenance Realibility
Recent development of Milling 
Firstly, the advent of ring motors has removed the constraint applied by the power that a single pinion gear was able to transmit.
The next constraint was the difficulty of casting a mill head at 40-ft (12.2 m). Although it could and has been done, the number of facilities capable of achieving such castings is limited. In response, manufacturers have advanced the design of shell-supported mills that do not rely on accurate head castings. The bearings are located under the shell and mated to a riding ring. This technology has assisted in freeing up the length/diameter ratio constraints normally associated with high aspect mills.
In parallel with increases in mill size has been the development of larger pumps and higher efficiency cyclones. Ball mill suppliers have adopted the same technologies to move beyond the traditional limit of 7500 kW.
Increasingly, liner systems have become the critical components in the mill. Developments reviewed here include
 Use of DEM and CFD for optimising the design of mill liners, grates and pulp lifters
 Innovative pulp lifter systems
 Shell supported mill discharge systems
 Larger liner handlers to handle heavier liner sections
Area: Minning Maintenance Realibility
Shell supported mill
In place of trunnion bearings, mills can be supported on mutli-pad hybrid type bearings mated to journals machined on the ends of the shell of the mill. This design gets away from the problem of casting large diameter heads.
The CCV  ring motor (gearless) drive is used at Cadia (20 MW) and Olympic Dam (18 MW). It has been the industry standard for SAG mills above 13 MW capacity.
Area: Minning Maintenance Realibility
SAG Mill Excessive Vibration during Commissioning and Operation
At Cadia, excessive vibration and deflections in the drive stator were encountered during commissioning of the mill and later during operation (Meimaris, Lei and Cox, 2001).
Vibration measurements indicated that the amplitude of the motion was approximately 7 mm (> 300 mm/s) at the top of the stator. The stator also exhibited excessive static or mean deflections that reduced as a function of speed from a maximum of 7 mm during inching to 3 mm at near full speed. These problems effectively reduced the drive air-gap to less than half the nominal value. The drive would often trip during inching and thus hamper mill relining.
The vibration meant that the mill could not be run above about 9.0 rpm without reliance on temporary chocks installed between the stator and the foundation. A light weight strong back was designed that could be fitted to the stator with minimal shutdown time. The stator now behaves correctly and the motor has excellent availability. There are few inching and no vibration problems, as the strong back has provided the additional stiffness required.
Area: Minning Maintenance Realibility
Change in Lifter Face Angle
The advent of computer simulation techniques has enabled the effect of changes in liner geometry on ball trajectory to be simulated. Various sets of computer code have been used for this, ranging from two dimensional single particle flight path simulations.
The current trend in lifter system design for large mills was initiated at Northparkes and has greatly decreased liner damage, increased mill efficiency and reduced ball damage. Two key aspects of mill design have been improved, lifter face angle and the number of lifters.
The lifter face angle on the original Cadia mill lifters was 12 degrees and led to high ball/shell impacts and contributed to ball breakage. Increasing the face angle to 25 degrees reduced the ball trajectory, decreasing ball breakage and shell damage. The adverse theoretical consequence of this is a drop in the mill power developed.
Cadia was commissioned with 78 rows of lifters but has now been reduced to 52 rows. Decreased packing between the lifters resulted, increasing the power drawn by the mill.
Higher face angles have led to the adoption of Top-hat type lifter bars in place of Rail or L-shaped bars. (Top hats were adopted at Cadia prior to high face angles due to higher strength).
Area: Minning Maintenance Realibility
Larger Liner Pieces
The attraction of a reduced number of larger pieces is a shorter re-line time. Liner handlers capable of lifting up to 3500 kg pieces and lengths exceeding 2 m are now available, and systems have been developed for rapid removal of worn liners.
Area: Minning Maintenance Realibility
Mill Discharge Systems and Pebble Discharge Issues
The efficiency of the mill grate and slurry discharge system decreases with increasing mill diameter and mill length. The efficiency of the mill discharge system for slurry and pebble discharge is compromised by the current standard pulp lifter and trunnion pulp discharge design.
Area: Minning Maintenance Realibility
Use of curved pulp lifters
Incomplete and back-flow of coarse solids down the pulp lifter is a major source of wear in the base and head-side corners of the discharge system. Use of curved pulp lifters is advocated to ensure effective discharge of solids and minimise wear.
Area: Minning Maintenance Realibility
Composite Materials
There are many benefits claimed for the use of rubber lining systems. However, the harsh environment of a large SAG mill has dictated against their use. The advent of composite liners, with steel-capped lifter bars mated to rubber shell plates has done much to counter the problems experienced. Trials are under way in several large mills, and there is a high acceptance of them in smaller mills.
Area: Minning Maintenance Realibility
AG Mills
The attraction of fully autogenous milling (AG mill with/without a pebble mill) is the reduction in operating cost derived by elimination of steel media. Typically, a SAG mill based circuit (P80 of 106 to 150 um) has media costs of around A$1/t.
Area: Minning Maintenance Realibility
Maximising Plant Throughput
The majority of operations aim to maximise plant throughput to match the maximum cost effective mining rate. The SAG mill is usually the rate limiting process stage in plant upgrades. Plants based on single stream primary mills rely on one of the following strategies to significantly increase mill throughput:
 Increased ball load;
 Implementation of pebble crushing;
 Optimisation of blasting practice in the mine and finer primary crushing, or
 Implementation of secondary crushing

The acceptance of crushing technology has, in general, been limited by historical factors of high wear, resultant maintenance costs and dust issues. However, secondary and even tertiary crushing prior to SAG milling offers opportunity to significantly increase (double or even triple) primary milling capacity.
Area: Minning Maintenance Realibility
Improving Wear Life and Plant Availability
There is significant scope for increasing capacity by decreasing downtime. Improving the life of the mill internals and minimising downtime for relining gives higher availability. The use of wear resistant rubber/steel composites, larger and fewer liner pieces, and a reduction in the number of, or even elimination of, fixings presents opportunities for improved productivity.
Recent availability of DEM and CFD modelling has assisted in the acceptance of modified liner and lifter designs, and this trend will continue with ever increasing computational capacity.
Area: Minning Maintenance Realibility
Process Optimisation
Power analysis for SAG and ball mills and cyclone/screen efficiency evaluations allow the circuit to be tuned to current conditions. Similar approaches to the modelling of all unit operations in the plant will lead to improved designs and plant performance.

Instrumentation and systems that are expected to become standard in the future include:
 Visual feed size analysis systems such as Split® and Wipfrag®
These measure size distributions on the feed belt via a camera connected to a computer. Advanced dedicated image analysis systems generate 3D distributions.
Continuous Charge Monitoring sensors
Measuring mill load directly in rubber lined mills is now possible. Charge monitoring provides information which is complementary to bearing pressure or load cells since it may discriminate between liquid and solids, or rocks and fine ore and contains information about charge location and in some cases conditions of lifters.
Sound sensors:
The nature and location of the sound generated by impacts within the mill contains information about what is happening inside the mill. The analysis of frequency and amplitude data using sound sensors is a promising area of development.
On-line estimators
Ball charge and mill load predictions are generated using algorithms derived from historical databases and models of SAG mill operation
Optimising control systems.
When soft sensor and predictor optimisers are in operation, real time information on feed size and mill load comparisons (estimated vs observed) improve the accuracy of ore hardness and grindability inferences, and make it possible to better anticipate overload trends or opportunities for increasing feedrate.
Area: Minning Maintenance Realibility
Copper Mountains concentrator
The plant design was based on a 35,000 tpd comminution circuit followed by a rougher-regrind-cleaner-scavenger flotation plant. Ore grades averaged 0.33% Cu with a copper recovery of approximately 82%.
Mining Copper Mountain mining operations operate in open-pits utilizing three hydraulic shovels and twenty-two haul trucks supported by four production drills and other mine operations equipment.
The Copper Mountain Flowsheet is a traditional configuration with a SABC circuit followed by a rougher flotation circuit, regrind, cleaner and cleaner scavenger flotation. Final copper concentrates are pressure filtered before transport to the port site and tailings cycloned to produce coarser material for wall building, while the water and fines are deposited in the dam impoundment area.
The Copper Mountain comminution circuit originally consisted of a 34' x 20' F/F SAG mill (17,000 hp - 12,677 kW), two (2) 24' x 39'6" ball mills (17,000 hp - 12,677 kW) and a Raptor XL900 pebble crusher (900 hp - 671 kW). 
The comminution circuit product (cyclone overflow) feeds the rougher flotation circuit. The circuit was originally designed for 35,000 tpd capacity (1585 mtph) with a final target grind size P80 of 150 microns. 
The flotation circuit consists of ten 160 m3 rougher flotation cells, two 3 m x 12 m cleaner column flotation cells and five 50 m3 cleaner scavenger cells. There is a regrind mill between the rougher flotation cells and the cleaner cells. In the original design, the regrind was specified as two Vertimills, but the plant was constructed with a single ball mill in this application. The regrind ball mill is a 15.5' x 29' mill with 3,600 hp (2,687 kW) installed power.
Area: Minning Maintenance Realibility
During the early operating months, plant operators were making changes in the milling circuit as required. These included changing the SAG mill discharge grates to a larger opening size, changing the SAG mill operating speed, changing the grinding media ball supplier, increasing the grinding ball size, increasing the SAG mill discharge screen opening slot size and initiating the overall expert system into the control strategy.
 Plant data through the first four months of operation showed that the milling circuit was not making the target tonnage rate (1,585 mtph) and, in fact, was peaking at just over 1,200 mtph by the end of October, 2011. The SAG mill appeared to be the bottleneck in the flowsheet as the power in the SAG was consistently high and approaching the full motor power, while the ball mills were consistently operating at less than 75% of installed power.
Area: Minning Maintenance Realibility
With the enhanced knowledge gained about the ore hardness and competency, the option of a pre-crusher being added to the Copper Mountain flowsheet was proposed. One of the critical factors affecting the SAG mill throughput is F80 to the SAG mill and a pre-crusher will reduce the feed size to the SAG mill. Modelling with the JK SimMet simulator confirmed that the SAG mill throughput could be increased with the finer feed size distribution that would result from adding the pre-crusher into the existing flowsheet.
Area: Minning Maintenance Realibility
These changes would ultimately include; modifying the primary crusher product conveyor and adding three conveyors, one for feeding the pre-crusher surge pile, one for feeding the pre-crusher and one for the transporting the product back to the stockpile conveyor.
Area: Minning Maintenance Realibility
Copper Mountain personnel decided to test the pre-crusher concept with the use of smaller temporary crusher plants that would crush some of the primary crusher product before it was fed to the SAG mill. In the end, there were as many as three crushing plants running at Copper Mountain crushing on up to 40% of the SAG mill feed.
Area: Minning Maintenance Realibility
Gearless Mill Drive
GEARLESS DRIVES FOR GRINDING MILLSGearless Mill Drive (GMD) systems are characterized by having the motor wrapped around the mill like a ring. For this reason, they are often referred to as ring motors. The rotor poles are attached directly to the mill (head) flange, and hence the rotor becomes an integral part of the mill, as shown in figure.
The Gearless Mill Drive system consists of the ring motor with its feeding cycloconverter, pre-installed in an E-house. It also includes the excitation rectifier, the automation system (for mill and motor) including HMI, monitoring and diagnostic system, MCCs (for mill and drive auxiliaries), differential protection, UPS, the cross-redundant converter cooling system and the E-house infrastructural systems. Externally installed converter and excitation transformers complete the supply.
Area: Minning Maintenance Realibility
Variable speed for process optimization
The speed of the GMD can be adapted to the operational requirements at any time across the full operating range. Variable speed allows to compensate for throughput changes as well as for harder ore, and to prevent meta-to- metal contact between the grinding media and the mill liners.
This leads to optimized operation and significantly less wear to the mill liners and ball consumption, as explained by a concentrators operation and maintenance supervisor in the US. Furthermore, the mills direction of rotation can be simply changed with a switch, so that the wear on the liner is distributed equally at both sides. Reduced wear of the liners prolongs the mill maintenance intervals.
Rather than adjustment of the ball charge to suit harder or softer ore entering the mill it is far more practical to adjust the speed  as stated by a senior process engineer of an Australian EPCM.
Area: Minning Maintenance Realibility
Flotation cells
Closed loop control of the milling is achieved by using a classification circuit. This is typically achieved using either hydro-cyclones or a set of screens. Hydro-cyclones are density separation devices that have an underflow of coarse particles and an overflow of fine particles. For a screen, the fine particles pass through the screen, while the coarse particles do not. In both cases, the coarse particles are fed back to the mill for regrinding.
The fine particles are passed on to the flotation section. It is not uncommon to have multiple mills, screens and hydro-cyclones in the grinding circuit.
Before being pumped into the flotation cells, the slurry typically goes through a set of conditioning tanks. Various reagents are added to the slurry at the conditioning tanks, which allow for the time required for the reagents to react with the slurry before the flotation process begins.
The slurry is pumped from the conditioning tanks into the first flotation cell. A Flotation cell is essentially a large tank that contains an impeller to agitate the slurry/air mix, and by so doing, promote contacting between air bubbles and particles in the slurry. In some flotation cells the rate at which air is added is fixed, while in other models it is possible to set the air flow rate to a desired amount.
If the froth depth is shallow, it is likely that these entrained particles (most of which are gangue) will report to the concentrate, lowering the grade. Deeper froth depths have more time for unattached particles to drain back through the pulp due to gravity. The result is fewer gangue particles reporting to the concentrate. A level sensor is used to determine the froth depth, which is controlled in closed loop by varying the flow rate of the pulp through the tailings outlet.
Area: Minning Maintenance Realibility
In addition to the reagents added, the flotation process depends on two main parameters.
	 Retention time needed for the separation process to occur determines the volume and number of flotation cells required.
	 Agitation and aeration needed for optimum flotation conditions, determine the type of flotation mechanism and the power input required.
Area: Minning Maintenance Realibility
Column flotation cells:
Do not use mechanical agitation (impellers). Instead, mixing is achieved by the turbulence provided by rising bubbles. 
Mostly used to produce final grade concentrates because they are capable of great selectivity.
Area: Minning Maintenance Realibility
Flotation circuit
Flotation process is broadly divided into rougher, cleaner and scavenger stages, each using many (bank of) flotation cells : Concentrate from the rougher stage are further concentrated in the cleaner stage. 
Tailings from the rougher or cleaner stage are fed to the scavenger stage. With all the internal recycles, operation of a flotation plant is a somewhat delicate balancing act.
Area: Minning Maintenance Realibility
Heavy Duty Flotation Tank Construction
Robust mild steel construction
Option for stainless steel construction for corrosive slurries
Various tank liner options available
I-Beam support structure on larger models

Removable Flotation Machine Wear Liners
Rubber lined bottom tank liner
Wear resistant tank side liners
All liners easily replaceable

Flotation Machine Superstructure
A-frame superstructure
Mild steel construction
Supports mechanisms
Acts as a header for air delivery to flotation mechanisms
Air connections at both ends provide greater installation flexibility
Flotation Machine Mechanism
Heavy-duty spindle bearing assembly
Low maintenance design
Robust standpipes
Urethane lined mild steel impeller and diffusers
Various options available for lining wetted parts

Flotation Machine V-Belt Drive
V-Belt and sheave sets
Drive guards to OSHA specifications

Flotation Machine Feed Box
Welded to flotation tank for no-leak operation
Wear resistant plate liners

Flotation Machine Transition Box
Provided between different levels of flotation cells in the same bank
Controlled weir bar assembly
Controlled dart valve assembly
Cast urethane dart valves and seats

Flotation Machine Discharge Box
Controlled weir bar assembly
Controlled dart valve assembly
Cast urethane dart valves and seats
Discharge nozzle provided as per customer specifications or pump design
Area: Minning Maintenance Realibility
Flotation Cell Reliability Improvement
Plant stability can be defined when a plant is running with flows and tonnages in equilibrium and steady state. Unstable plants never reach equilibrium and the cause for this is sometimes due to fundamental flow sheet design but mainly due to poor control of key factors that cause oscillations in flow and tonnages.
A poor operating strategy can also provide an unstable circuit due to over operation and/or mis-understandings of causation- effect.
Operational problems associated with 
Cell level control
Reagent mixing/dosing 
Holed vortex finders in the primary hydrocyclones 
Amongst others were creating an unstable process and this was exasperated by dramatic reagent changes (On/Off). Collector dosages were at an all time low whilst metals entering the plant were at an all time high!!. This type of operating strategy created more instability in the plant and complete operator confusion
Area: Minning Maintenance Realibility
Cell Level Control
Possibly one of the biggest challenges in controlling liquid level in applications such as flotation cells has to be the accurate measurement of the liquid level below the froth. Knowing the liquid level to an accurate value provides the opportunity of determining froth depth. This in turn allows the operator to manage the froth depth and finally be able to optimise recoveries of the minerals
As a consequence the ball would stick in the tube and the dart valves would open, promptly dumping the contents of the cells downstream.