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Mining Mobile Equipment | Lubrication chart
The lubrication chart provides an overview of the location of the maintenance points on the machine and of their maintenance intervals. |
Mining Mobile Equipment | The hydrostatic travel drive operates in a closed circuit. The variable displacement pump 20 pumps oil directly to the variable displacement motors 35 and 40. The oil returning from the variable displacement motors is pumped back to the intake side of the variable displacement pump. |
Mining Mobile Equipment | Variable displacement motors
The variable displacement motors drive the transfer gear. A high or low torque is transmitted to the gears depending on the swivel angle and the high pressure. |
Mining Mobile Equipment | The bearing flushing supplies fresh, cooled oil to the tapered roller bearings and into the housing of the variable displacement motors. The hot oil is removed by suction.
The returning flow of oil from the fan motor 1 is supplied to the connection U of the variable displacement motors. The orifice 9 ensures that the oil is evenly distributed over both variable displacement motors. |
Mining Mobile Equipment | Variable displacement pump
The variable displacement pump operates in a closed circuit. It pumps the oil directly to the variable displacement motors. The oil flowing back from the variable displacement motors is fed back to the suction side of the variable displacement pump. |
Mining Mobile Equipment | Pilot control hydro accumulator
The purpose of the hydro accumulator is to store hydraulic energy and supply it when needed.
It has the following applications:
To act as an attenuator for pressure peaks, for example for the ride control system or steering attenuation.
As an energy reserve to supply energy when needed, for example for the brake system. |
Mining Mobile Equipment | Quick-change device (Option)
The quick-change device can be attached to the lift arm of the machine. It is designed to facilitate the fast changing of various attachments on the lift arm. The various working attachments are operated in different ways. For a more detailed description on the operation of the various working attachments, see the operator's manual. |
Mining Cu | SCADA Upgrade Project
TCT was engaged by Tritton Copper Mine to resolve a problem with their existing Wonderware SCADA installation. The issue was evidenced by very slow update times between the Wonderware servers & computers and the Omron PLCs. Other PLCs such as Allen Bradly PLCs and other devices including Modbus TCP were not affected by the slow communication issues. |
Mining Cu | Mine
At the Tritton processing plant combined ore feed is fed to a conventional concentrate processing plant, which was expanded from 900,000 tpa capacity to 1.6 Mtpa in 2007. |
Mining Cu | Mining Operation
The Tritton Decline mine is a conventional mechanised underground operation utilising ?Caterpillar R2900 LHDs ?Tamrock DD420 60 Jumbos ?Atlas Copco M2D Jumbos ?Cat 980H and 972 FELs ?Sandvik DL420 Production Drills ?Normet Charge Up Unit 1610B ?Cat IT28Gs ?Cat AD55 Trucks |
Mining Cu | Processing
?The Tritton processing plant was designed by Ausenco and commissioned in 2005 with a nameplate capacity of 900,000 tpa. Plant has capacity of 1.6 Mtpa rate.
?The crushing circuit comprises an ore bin with a fixed 800 mm aperture grizzly, feeding ore via a vibratory feeder to a Kemco S7N single toggle jaw crusher with a feed opening of 1.22 x 1.02 m
?Crushed ore of P80 100mm is conveyed to a 6,000 tonne stockpile where it is reclaimed via three vibrating feeders.
?Grinding comprises an ANI Ruwolt fixed speed high aspect 6.7m dia X 2.13, 1500 kW SAG Mill, discharging via a trommel screen to the secondary grinding circuit. Lime is added at the SAG to target pH 10.5 for pyrite suppression.
?Secondary grinding comprises a Marcy 3.81 m dia x 5.18 m 1250 kW ball mill operating in closed circuit with 500 mm dia Linatex hydrocyclones. Cyclone overflow discharges to two parallel Metso Vertimills (VTM800STD) installed as part of the TEP and shown in the foreground of the lower photo.
?Each Vertimill is in closed circuit with 250mm dia tertiary hydrocyclones. |
Mining Cu |
?The grinding circuit produces a cyclone overflow product of P80 75 µm at 30 to 35% w/w solids.
?Total grinding circuit power draw is 3,160 kW.
?The tertiary cyclone overflow feeds two 50 m³ Wemco tank cells (installed as part of the TEP) in series for primary rougher flotation.
?Concentrate from the Wemco cells is directed to final concentrate recovering 70% of total copper.
?Primary rougher tails are pumped to conditioning tanks before two parallel banks of ten 8 m³ Dorr Oliver (5) rougher and (5) scavenger cells. Rougher concentrate is then sent directly to rougher cleaner while scavenger concentrate is sent to regrind.
?Regrind is achieved by a 2.0 m dia x 3.4 m 150 kW ball mill in closed circuit with Cavex hydrocyclones. The underflow reports to regrind and overflow to scavenger cleaner, rougher cleaner and final conc.
?The Tritton flotation circuit produces a copper concentrate typically with 25% Cu, <1 g/t gold and 30 g/t Ag from a mill feed of 2.1% Cu, 0.15 g/t Au and 6-7 g/t Ag. |
Mining Cu | ?Power and water are supplied to the Tritton mining areas from infrastructure originally installed for the Girilambone site.
?Power is supplied from the Nyngan-Bourke 66kV transmission line which was extended from Girilambone to the Tritton site.
?The Tritton and Girilambone/North East sites currently use approximately 9MVA of total power, and the grid is able to provide an additional 4.5MVA for future expansions. |
Minning Construction | The Thiess Sedgman Joint Venture (TSJV) has been awarded a $186 million contract to design and construct a Coal Handling and Preparation Plant (CHPP) for Boggabri Coal Pty Ltd.
The CHPP will support the expansion of Boggabri Coals mining operation located in the Gunnedah Basin in New South Wales. Boggabri Coal is expanding the annual production to 6.9Mt.
Thiess Managing Director Bruce Munro said the expansion is a big vote of confidence in the future of the coal sector by Boggabri Coal and its parent company Idemitsu Australia Resources.
This contract recognises the specialised capability of TSJV and is a tribute to the great relationship established between Thiess Sedgman and Boggabri Coal.
The project further cements our position as the leading provider of ore and coal handling and processing facilities, Mr Munro said.
The contract has a direct value to Leighton Holdings Limited of $124 million through its wholly-owned subsidiary Thiess and its 33 per cent stake in Sedgman.
Leighton Holdings' Chief Executive Hamish Tyrwhitt said the contract award illustrates the enormous depth and breadth of the Groups capability in resources.
The Group is a leading provider of construction and contract mining services to the resources market, both in Australia and in the region. Sustained global demand for resources primarily out of Asia will continue to underpin a good range of opportunities for the Group for the foreseeable future.
Detailed design and procurement work is underway with the plant scheduled for completion in the second quarter of 2015.
The Boggabri open cut coal mine is located 17 kilometres north east of Boggabri in north-west NSW. |
Minning Construction | Bulk Materials Handling
Our material handling products and systems include traditional trough-type belt conveyors, fixed/overland conveyors, portable conveyors, at-the-face mining conveyors, stacker/reclaimer systems, mobile conveyors, radial stackers, bulk material and bag loading and unloading systems for barges and ships, shuttle conveyors, chain feeders, belt feeders, apron feeders, spreading technologies, complete crushing and screening plants, fully enclosed pipe conveyors, and ancillary equipment such as high capacity tripper cars.
Considered the worldwide market leader with hundreds of installations and over 60 years of experience from trusted brand names like Möller, KOCH, MVT, RAHCO, Conveyor Engineering and FLSmidth Pneumatic Transport |
Minning Construction | Crushers, Sizers & Feeder Breakers
This expertise is supported by more than 1,700 installed crushers, feeder-breakers and sizers.
The Feeder Breaker is traditionally used between the mobile mining machinery and the fixed conveyor systems. The main function of the Feeder Breaker is to reduce the product down to a manageable size and smooth the flow on to the mines conveyor belts.
Our ABON sizer range utilises a combination of low roll speed / high torque and tooth profiles to arrive at the specified end product sizes with a minimum of fines production. FLSmidth offers and manufactures a range of Buffalo plant flight-bar Feeders and chain Feeder Breakers used in open-pit and underground coal and potash mining applications.
The original Buffalo Feeder Breaker was developed and successfully introduced into coal mines in 1975. FLSmidth offers a complete range of reliable Ludowici vibrating grizzly separators and vibrating feeders to suit almost every application.
Vibrating feeders driven by out-of balance motors have been used for many years to feed and convey all types of bulk materials. The feeders can be installed below hoppers and silos to feed material continuously or intermittently, or can be used to simply transfer material.
All of our crushing and sizing equipment is available for surface or underground installation, for stationary or mobile applications, and for climatic conditions that range from tropical to arctic. |
Minning Construction | Coal Classification & Water-based Cleaning Equipment
From advanced hydro cyclones and classifiers to spiral concentrators, FLSmidth delivers cutting-edge washing, solid-particle recovery and classification technology.
FLSmidth manufactures durable and flexible classifying equipment to dewater, concentrate, size and recover solids. Optimum cyclone performance relies on minimizing turbulence while extending residence time. The Krebs® gMAX® cyclone has the capability to produce finer and sharper particle separations using large high capacity hydrocyclones.
WEMCO® classifiers are designed to settle and dewater relatively coarse particles from high volume, low percent solid streams.
FLSmidth offers a comprehensive range of spiral concentrators* for coal preparation. Krebs® coal spiral concentrators wash the coal while using differences in density to efficiently separate the particles. |
Minning Construction | Heavy Media Separation
Wemco HMS systems are installed and operating on many different minerals ranging from coal, manganese, magnesite, right through to fluorspar, iron ore, and diamonds.
FLSmidth supplies a comprehensive range of modular Dense Media Cyclone Plants utilising Krebs® HM cyclones and Wemco® HM drums.
Particle sizes up to 100 mm can be treated depending upon the size of Wemco and Krebs dense media equipment selected. |
Minning Construction | Thickening
FLSmidth supplies the worlds largest thickeners with the highest torque ratings.
From the well-known brands of EIMCO and Dorr-Oliver, our thickening equipment is utilized around the world and recognized as the leader in minerals-duty thickening applications such as concentrate, tailings, preleach, and CCD.
We offer a wide range of thickening and clarification equipment with enhanced flocculation to accelerate settling, and higher flow and loading rates to help reduce space requirements.
Our engineers will work with you to determine correct heavy-duty thickener and clarifier sizing to determine the most cost-effective mechanism for your application.
Deep Cone & High-Density Thickeners FLSmidth has the most experience when it comes to high solids concentrations and paste thickening. |
Minning Construction | Our EIMCO® Deep Cone® Paste Thickeners produce underflow solids with a paste consistency and the highest solids concentration of any thickener on the market. Paste is a non-segregating liquid/solid mixture with a yield stress and slump. The benefits of producing paste are considerable. |
Minning Construction | Screening
FLSmidth offers a full range of world-class vibrating screens to suit almost every screening application. Through FLSmidth Ludowici we have been producing screens for over 60 years and we are proud to be the market leader in the provision of mechanical screening equipment. Whether your requirements are for wet or dry screening or for polyurethane, wedgewire, wire mesh or rubber, we are able to supply it.
Our range includes:
Exciter driven linear motion screens
High frequency de-watering screens
Unbalanced motor driven horizontal screens
Circular motion horizontal/declined screens
Sieve bends |
Minning Construction | Flotation
FLSmidth is the worlds largest supplier of flotation equipment with over 55,000 units sold.
FLSmidth combines the strength of WEMCO and Dorr- Oliver flotation technology, which accounts for more than two-thirds of all annual flotation sales globally. We attribute this success to our ability to provide either self-aspirated or forced-air flotation technology or a combination of the two.
FLSmidth is at the forefront of the industrys trend to install fewer, but larger units rather than multiple smaller cells, to save space, power, maintenance, and auxiliaries. FLSmidth pioneered the way for large cell technology. From its first Wemco 257m3 cell installed in 2003, to now even bigger 600m3 SuperCells |
Minning Construction | Filtration
Since 1910, FLSmidth has manufactured pressure and vacuum filters and continues to supply filtration technology for minerals and industrial processing flowsheets throughout the world.
Whether using for concurrent or countercurrent cake formation, cake discharge, washing, dewatering, settling, or drying, you can rely on years of experience with industry leading brands (Dorr-Oliver, EIMCO, Pneumapress, and Shriver) to gain the most efficient and cost-effective filtration equipment solutions tailored to your requirements.
A choice of Belt Press for the duty, for example if the product is for sale, as is the case in some coal fines pressing applications, then a type HDP Beltpress would be selected; this gives maximum moisture reduction, giving the lowest possible moisture content. If the product were merely a waste product which just requires stocking out for disposal, then a type MDP Belt Press would be recommended.
FLSmidths AFP IV Automatic Filter Press is another highly efficient solution for coal refuse dewatering when used in conjunction with FLSmidth paste thickening technologies.
Contact our FLSmidth specialists to see which of our filtration technologies will best meet your coal processing requirements. |
Minning Construction |
Step 1- Convey rocks to concentrator
Step 2 34 foot diameter sag mill powered by 2 X 8500 HP motors
Water is added with ore and rolled with 5 inch diameter ball to crush the ore to 2 inch |
Minning Construction | Ore less than ½ inches size will drop down and pumped to two ball mills for grinding |
Minning Construction | Larger than ½ inch travel the conveyed to a pebble crusher |
Minning Construction | Pebble crusher
Crushed into approximately ½ inch size and return back to the sag mill for further processing |
Minning Construction | 225 X 40 Ball mills
Power by 4 X 8500 HP motors, use 3.5 inch balls to grind the ore finer |
Minning Construction | Ball Mill Products pumped into cyclones
Separates coarse material from the finer and revert coarse material to the ball Mills |
Minning Construction | The Water and Fine Ore which is ground above the size of salt is mixterre flows to the rougher flotation circuit |
Minning Construction | The separation of barren rock from the minerals is performed in the rough flotation cells |
Minning Construction | Bubble are created adding air and small amount of alcohol
The mineral concentration from the rougher flotation cells are further processed in regrind mill and cleaner flotation |
Minning Construction | The concentrate with 22% copper will flow to the thickner |
Minning Construction | The thickened concentrator then pumped to the filer press panels |
Minning Maintenance Realibility | SAG Mill Installation and Commissioning
The 40 ft (12.2 m) diameter 20 MW Cadia gearless SAG mill, was commissioned. This was a leap of over 40% above the largest operating SAG mill. A significant saving in capital cost gave the incentive necessary for a single mill line at Cadia, resulting in the selection of the 40 ft (12.2 m) diameter mill. Now, after 18 months of operation,
The grinding ball mills are important in the ore comminution circuits. Depending on numerous factors, such as, for example, inappropriate design, manufacturing, overloads, poor maintenance and inadequate operating procedures, flaws are developed in the structural components of this equipment. The structural components of a mill, basically, shell, heads and trunnions, besides high costs, have lead times that might reach three years. |
Minning Maintenance Realibility | Foundation survey and repair
Foundations of older equipment can be surveyed to assess the condition of the concrete, which can deteriorate over time from movement and/or vibration. New soleplates can be used to modify and repair the foundation, helping to eliminate future problems. |
Minning Maintenance Realibility | Overall inspection and basic assessment
Cracks, missing bolts, wash and wear, excessive vibration, oil or slurry leaks are all examples of what can be discovered during an overall mill inspection. Engineering evaluation complements the inspection in order to troubleshoot the causes.
Recommendations are made to remedy the situation. In some cases, it may be best to do nothing but monitor on a continual basis. |
Minning Maintenance Realibility | Grout injection
Injecting or pumping grout is an effective way of filling-in a cavity or securing a loose trunnion liner within a trunnion. The expertise of grout injection requires designing the inlet and outlet ports strategically to ensure smooth filling of the cavity as well as venting of the trapped air. |
Minning Maintenance Realibility | Trunnion seal upgrade
Older mill trunnion seals and bearing housings can be upgraded to accommodate Metsos current standard of grease purged triple lip seals. |
Minning Maintenance Realibility | Trunnion liner repair
When the fit between the trunnion and the trunnion liner is worn, the trunnion liner becomes loose and the bolts attaching the trunnion liner to the trunnion start breaking.
Rather than machining the trunnions on site, a new machined sleeve is centered and grouted in place.
This becomes the new trunnion bore for a slightly smaller, new trunnion liner. |
Minning Maintenance Realibility | Structural parts remachining
Off-site machining is an effective cost and time means of refurbishing large structural components such as trunnions and heads. Controlled machining in a machine shop environment provides the most accurate clean-up of bearing surfaces, flanges, re-drilling of holes, |
Minning Maintenance Realibility | Site machining
Site machining is an effective cost and time means of refurbishing large structural components. Site machining is generally used after weld repairing large components at site to skim-cut flanges and bolted connections that have distorted or lost their machined surfaces. |
Minning Maintenance Realibility | Finite element analysis (FEA)
Structural evaluation using FEA techniques is a very effective tool to design new and retrofit equipment, to evaluate damage caused by slurry wash, or to verify the effectiveness of mechanical reinforcements such as adding gussets and wrapper plates.
FEA results are continuously verified against strain-gauge stress measurements on actual operating equipment and the in-house developed methods are refined frequently |
Minning Maintenance Realibility | Site shell welding
Worn or cracked shells can be weld repaired at site. Reinforcing gussets can also be welded to minimize distortion due to welding and to add structural strength. Over time, welding procedures have been refined and complemented with weld grinding and shot-peening. |
Minning Maintenance Realibility | First-of-its-kind, complex repairs
First-of-its-kind, complex repairs are usually needed when a crack or severe wash is discovered in the rotating structural components, or when a design improvement is necessary to change operational parameters such as increased mill loading. |
Minning Maintenance Realibility | Pinion temperature monitoring
The pinion temperature monitoring system uses differential temperature checks across the pinion face to ensure proper pinion alignment. Automatic sensing and continuous condition monitoring is accomplished through infrared sensor technology (4 to 20 mA to PLC or DCS). The system uses low-maintenance parts for operational efficiency and is customizable to fit most gear guards. |
Minning Maintenance Realibility | Trunnion bearing RTD installation
Older trunnion bearing housings either do not have RTDs to measure bearing temperatures or the RTDs are embedded in the bearing sleeve making maintenance very difficult. These bearing housings can be retrofitted with RTDs using 100 ohm sensor technology, which rides directly on the bearing surface. They provide automatic, continuous, and accurate differential temperature checks of the trunnion journal surface to ensure alignment. |
Minning Maintenance Realibility | Trunnion bearing lubrication system
Replacing an outdated lubrication system can extend the life of bearings and trunnions. The system automatically maintains constant temperature and even flow as well as improves the efficiency of the oil filtration process. |
Minning Maintenance Realibility | Olympic dam sag mill down
BHP said the huge Svedala mill had experienced an electrical failure and would be out of service for about six months, reducing copper production by 60,000-70,000 tonnes in this financial year |
Minning Maintenance Realibility | Mill Liners
Liners can be metal or rubber
Grate and ware plate are normally made from alloy ware resistant cast steel or rubber. |
Minning Maintenance Realibility | Kanex CG offers the rubber and combined lining for mills, liner bolts, as well as rubber trommels.
Rubber wear-resisting linings, manufactured by the Company, are widely applied in the field of non-ferrous and ferrous metals enrichment, coal mining and electrical power supply.
Such linings are gradually replacing the traditional metal ones because of its superior properties:
-High wear-resistance. Much higher than metal ones.
-Smaller weight lower electricity cost; smaller frame wear efficiency and mills easy starting;
-easy installation and replacement;
-Noise level is less for 8-10 dB;
-High-quality raw materials, the lack of metal impurities;
- Low wear over the service life.
Combined linings, manufactured by the Company, are designed for use in large-sized semi-autogenous grinding mills. Such linings construction is the solution of problem with cracks in the metal linings and slurry leaks through bolt holes. The term of non-stop operation is significantly increased and maintenance costs are reduced. Features:
Shock and wear-resistance. It is suitable for severe conditions.
Long service life. Excellent quality-price ratio.
Reduced noise level compared to the fully metallic analogues.
Smaller weight. It can be easy installedand replaced |
Minning Maintenance Realibility | Bolts by their very nature are designed to undo, from the very moment the load used to tighten a bolt for the very first time is released, a bolt starts to loosen, it can loose anywhere from 10-20% of its load in the first 48 hours and thats without the normal bedding in process.
This is why a re-torque is specified and is usually carried out, (mostly seen on liner bolts), but what about the bolts holding the mill together?, All to often they are just overlooked, and the results can be seen above.
When the mill finally goes into operation the structural bolts on mills are exposed to extreme loads during operation and after a period of time they start to relax and loosen off further, this can lead in a surprisingly short time to joint leakage and eventually failure. |
Minning Maintenance Realibility | Breaking or Leaking Mill Liner Bolts
In many grinding plants mills which have metallic or rubber liners suffer from bolt breakage. |
Minning Maintenance Realibility | Ball Mill Repair
Ball mill preventive maintenance, SAG mill, AG mill planned maintenance
Minor repair cycle for ball mill is about one month, (repair at any time for special conditions) and the repair items include:
1. Check and clean the oil pump, oil filter and lub. Oil pipeline, then renewal the lub. oil;
2. Check all bolts on the equipment, re-fasten them;
3. Examine the large and small driving gear of the ball mill, take notes of the wearing patterns, then repair or change the small worn gear;
4. Check the coupling, replace rubber elastic ring and other spares;
5. Replace the shell liner of ball mill. Wear resistant rubber liners manufactured by Naipu are widely used in mining equipment for replacing traditional cast steel liners. Naipu spare parts for ball mill, SAG mill, AG mill include rubber liners and composite liners (rubber + alloy). Rubber liners include pulp discharger assembly segment, rubber head liner, rubber pan liner, FE head liner, rubber lifter bar etc. Composite liners include composite lifer, head liner, shell liner etc.
6. Check and repair the inlet and outlet pipe;
7. Check the feeding machine, driving system and accessory equipment;
8. Minor repairs for AG mill, SAG mill in mining are the same with that of ball mill.
Ball mill repairRepair cycle of ball mill is 4 to 6 month, the repair items include:
1. All items in minor repair;
2. Examine and replace inlet pipe, outlet pipe and feeding machine;
3. Repair large driving gear;
4. Repairs for AG mill, SAG mill in mining are the same with that of ball mill. |
Minning Maintenance Realibility | Ball mill overhaulIn the repairs of mining ball mill PM, overhaul has the largest workload and the longest cycle. Overhaul means to dismantle most or all the parts of the equipment, then repair or replace the mechanical parts, electric parts, adjust working system, and then do mounting and commissioning, so as to rule out the faults and regain rated performance and precision. Overhaul cycle of ball mill is 2 to 4 years, the repair items include:
1. All items in minor repair and repair;
2. Examine and replace main shaft bearing and large gear;
3. Examine, repair and replace the shell;
4. Repair and replace inlet and outlet end cover. According to the using results of rubber liners and metal liners applied in mines, ball mills equipped with Naipu wear resistant rubber liners or Naipu composite liners have long service life than others.
5. Overhaul for AG mill, SAG mill in mining are the same with that of ball mill. |
Minning Maintenance Realibility | Daily maintenance of ball mill
1. All lubricating points and the oil surface height should be checked at least one time every 4hours.
2. The temperature of the bearing grease should not be higher than 55?, when the ball mill stays in operation.
3. The temperature of transmission bearing and the reducer should be no higher than 60?, when the ball mill is in normal operation.
4. When ball mills works, the large and small gear transmission smoothly, no abnormal noise, and if necessary, adjust the clearance.
5. The ball mill should operate smoothly without strong vibration.
6. Motor current should be no abnormal fluctuations
7. Each connecting fasteners stay no loose, the combined parts have no oil leakage, no leak water and no leak ore phenomenon.
8. The steel ball should be added in time according to the wear situation.
9. If you find the abnormal situation, the ball mill should be stopped immediately to examine and repair. |
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 metalmetal 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. |
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. |
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 |
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. |
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. |
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). |
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. |
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. |
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. |
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.
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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. |
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. |
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. |
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. |
Minning Maintenance Realibility | Copper Mountains 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. |
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. |
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. |
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. |
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. |
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, MCCs (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. |
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 concentrators operation and maintenance supervisor in the US. Furthermore, the mills 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. |
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. |
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. |
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. |
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. |
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 |
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 |
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. |
Minning Maintenance Realibility | REAGENT MIXING AND DOSING
No checking of solution strength and clarity was been carried out which ultimately led to varying strengths of reagent and crystals of PAX and SIPX frequently blocking the reagent dosing lines. The frequency of blockages was at least one reagent line per shift with catastrophic effects
Line blockages occurred more frequently immediately after reagent mixing. The mixing tank feed hopper had no trash screen. Reagent dosing was via manually controlled valves placed on horizontal manifold being fed directly from the holding tank. Due to the lack of attention to reagent strength and particularly reagent crystal dissolution, solids were being introduced into the dosing system with disastrous consequences. The lack of good reagent pumping system compounded the problem.
The mixing tanks were fitted with new hoppers with integral trash screens and the re-circulation stream was re-routed so that it poured onto the trash screen thus enabling lumps of crystalline Xanthate to be washed through the screen, reducing the risk of blockages. |
Minning Maintenance Realibility | HYDROCYCLONE
HYDROCYCLONE MAINTENANCE
As mentioned previously, another source of plant instability was lack of preventative maintenance to hydro cyclones,
The mechanical department according to their scheduled plans was regularly carrying out maintenance; the problem was that this procedure had no metallurgical input as to when and why the internal components should be changed. The only occasion that the operational group became aware of a problem was when the flotation cell dart valves regularly blocked and the false bottoms below the Wemco cells eventually filled up with sand which subsequently scaled to a proud concrete mix and resulted in very poor cell recirculation of pulp requiring air lances to free up tanks etc.
As a consequence, the mechanical department would assume that provided the hydrocyclone had a rubber lining and the vortex finder was not holed,
Therefore, hydrocyclone vortex finders regularly holed (see Figure 17 below), and the rubber internals were being changed as the mechanical department saw fit, but this left significant steps in the joints between the new and old components which caused turbulence, increased wear and generated coarser overflow size distributions than necessary. |
Minning Maintenance Realibility | Another common wear pattern observed on vortex finders in particularly onerous duties is the cutting of the vortex finder around its base which if left unchecked can ultimately result in the vortex finder actually falling off into the hydrocylone vessel itself. This phenomenon is most usually associated with lack of attention to cover plate liner wear.
Once the cover plate liner becomes worn around the vortex finder, is creates a strong swirling action locally in this area and rapidly reduces vortex finder life.
As a consequence of the above, the metallurgical group were made responsible for managing hydrocylone maintenance working with the mechanical department. It soon became clear that vortex finder life was circa 3 months with new cover plate liners. The increased focus in this area resulted in a steady flotation feed size distribution and minimized instability within the flotation plant. |
Minning Maintenance Realibility | Thickeners
The object of a control system on a High Rate Thickener (HRT), as on a conventional thickener, is to obtain the required underflow density and overflow clarity at all feed conditions.
Thickening technology utilizes the principle of sedimentation as a cost effective method of solid-liquid separation.
Sedimentation is used to thicken an incoming feed stream to produce two phases:
Overfl ow - a stream containing minimal solids
Underfl ow - a stream containing minimal liquid
This is accomplished by a number of means inside the thickener:
Settling under the force of gravity
Addition of reagents such as flocculants, which are mixed with the incoming feed to enhance gravity settling such that it occurs faster or at a higher rate
Bed compression due to self-weight of material in the settled bed
Mechanical raking to release water trapped in the settled bed |
Minning Maintenance Realibility | Critical to thickener performance are two parameters:
1. Solids loading based on dry tonnes of solid entering the feedwell
2. Rise rate based on the flow rate (cubic meters per hour) entering the thickener including dilution water
Consequently, improvements in thickener process performance typically include efforts directed at improving the feed system, from upstream of the thickener through to the feedwell.
Thickeners are low-maintenance, designed as critical equipment, and generally have no duty standby installed. As they age, more focus must be placed on them to allow continuous operation.
When the existing tank satisfies the new requirements, modernizing the thickener is an attractive and often economically optimal method to extend the life of equipment or manage changed process scenarios.
Assuming the tank diameter and condition are suitable for increased loads, upgrades are possible to all other elements. Sidewall height can be extended, overflow capacity can be increased with new launders and/or new overflow boxes, floor angle can be increased, and underflow arrangements can be modified.
For old-style conventional thickeners, conversion to a High Rate Thickener (HRT) should be an early priority. HRTs allow for higher solids loading than conventional thickeners by efficiently using flocculation. Computational fluid dynamic (CFD) modeling and other research to improve the understanding of the complex and multiphase fluid flow behavior that occurs in feedwells
Feed pipe size, elevation changes and dilution requirements all need to be considered in upgrading a thickener feedwell.
Often modernization will add weight, either due to larger or additional installed components as in the case of forced dilution. The impact of this weight on the bridge structure must be considered. The modernization may include reinforcing or replacing bridge elements. |
Minning Maintenance Realibility | The drive unit consists of the base supporting structure, hydraulic motor mounts, pinion gears, slew ring gear, cage adapter ring and cage structure. Six motors are used to provide the drive action |
Minning Maintenance Realibility | F-Type Primary Speed Reducer
DBS Manufacturing, Inc. pioneered the concept of using hydraulics as the means of primary speed reduction on clarifier and thickener drive units. DBS incorporated the hydraulic speed reducer on its drive units in the early 1990s and it is now a standard feature on nearly all DBS drives. These primary speed reducers incorporate a hydraulic pump and motor fully enclosed in a reservoir for clean operation.
Speed reduction: Many reduction ratios are available.
Torque limiting: Maximum torque cannot be exceeded. Once maximum torque is reached, the drive will slow down but still maintain torque. This is analogous to a truck shifting into lower gears when pulling a load up a hill.
Low maintenance: Change oil filter every three months.
Long life: Hydraulic components have been proven to last for years in continuous duty industrial clarifier and thickener applications.
Easy repair: All components can be removed with common hand tools. No special skills or training is required to maintain the unit. Most items can be replaced with alternate brands.
Reversibility: An optional directional control valve can provide easy reversing to allow clarifier or thickener rakes to be backed out of an overload condition. Torque overload protection is maintained when operating in reverse.
The main features of the F-type primary speed reducer are its reliability and its ability to operate at high torque in or near a stall mode. In a high-load, over-torque situation, the F-type primary speed reducer will keep the clarifier or thickener operating if at all possible. If the rakes are truly stuck, the F-type primary speed reducer will simply stall at a high, but safe, torque.
The operation of the F-type primary speed reducer is simple. The electric motor drives a hydraulic pump that delivers oil to a hydraulic motor. The hydraulic motor drives the output drive shaft of the F-type primary speed reducer. The displacement of the pump is much smaller than the displacement of the motor. This difference in displacement between hydraulic pump and motor results in speed reduction. A pressure relief valve provides torque-limiting protection.
Since the system pressure is directly proportional to the torque load, the torque gauge and switches operate by monitoring the system pressure. This provides an accurate torque reading and a pressure signal that can be used to drive a 4-20 mA torque transducer. |
Minning Maintenance Realibility | Drive
The drive is a single multi?stage planetary extra heavy duty unit driven via a hydraulic motor. The hydraulic drive minimises any shock loads at start?up (essentially a soft start), thereby minimising the wear on gearboxes and extending the drives service life.
Hydraulic pressure provides a simple and accurate means for monitoring and limiting rake torque. Using a pressure transmitter a 4?20 mA signal is provided for local and remote torque indication and control. |
Minning Maintenance Realibility | Power Pack
The thickener will be installed with a power?pack mounted on the bridge for ease of maintenance. |
Minning Maintenance Realibility | Rake Lift
The unique design of our lifting device has eliminated all operational problems with lifting the rakes out of high torque situations effortlessly.
The lifting mechanism consists of a hydraulic cylinder driven by a hydraulic pump. The lift offered is 300mm for these units. The rake lift raise and lower operation can be actuated manually or automatically. |
Minning Maintenance Realibility | Concentrate thickener feed well upgrade
Issues
Severely corroded
Pipework not plumed into tangential inlet
No dispersion of mixed product into the thickener
Objectives
Reduce loss of concentrate to the overflow
Replace feed wells with improved design
Utilize available process control equipment
Design Criteria
Minimise aeration of slurry
Reduce velocity of slurry entering feed well
Potentially reduce flocculation consumption
Promote mixing in the feed well
Increase throughput capacity
Redirect overflow to process water
Opportunities for improvement
More efficient froth spray design
Flocculation screening
Flocculation optimisation
De-aeration of slurry
Improve the feed box design |
Minning Maintenance Realibility | Thicker operation
Feed slurry becomes very diluted on entering the feed well and leaves the feed well as a dilute suspension from which particulate settling occurs.
A thickener has several basic components: a tank to contain the slurry, feed piping and a feed well to allow the feed stream to enter the tank, a rotating rake mechanism to assist in moving the concentrated solids to the withdrawal points, an underflow solids withdrawal system, and an overflow launder. |
Minning Maintenance Realibility | Conventional Thickeners
The conventional thickener can be used with or without flocculants, depending upon the application. If employed, flocculants are normally added to the feed launder or in the feed well, and flocculation occurs in the resulting turbulence.
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Minning Maintenance Realibility | High Rate Thickeners
High rate thickeners are designed specifically to maximise the flocculation efficiency of flocculants. They differ from conventional thickeners in feed well design, size and control.
Unlike conventional thickeners, high rate thickeners must use flocculants. The basic design of a high rate thickener is below.
High rate thickener feed wells are designed to disperse flocculants thoroughly into the feed end to admit the flocculated slurry into the settling zone of the thickener without destruction of the newly formed floccules. The feed may enter into the sludge bed if the flocculation must be completed by the solids-contact means, or it may enter above the pulp level if it is sufficiently flocculated to produce the desired clarity and the underflow density.
The increase in flocculation efficiency realised in high rate thickeners may increase in a bulk settling rate 2 to 10 times over that obtained in a conventional thickener, thus reducing the unit area requirements by a similar factor.
The control parameters used to maintain stable operation in high rate thickeners are underflow solids density, underflow withdrawal rate, flocculant dosage, solids inventory in the tank, solids feed rate, and mechanical torque limit restriction of rotating rake arm mechanism. |
Minning Maintenance Realibility | Components and Accessories of Thickeners
A thickener consists of a collection of components, which can be supplied in a number of variations. The basic components are the same:
Tank
Drive Support Structure
Drive Unit and Lifting Device
Rake Structure
Feed Well
Overflow Arrangement
Underflow Arrangement
Instrumentation and Flocculation Facilities |
Minning Maintenance Realibility | Rake Lifting Mechanism
These should be provided when abnormal thickener operation is probable. Abnormal thickener operation or excessive torque may result from
insufficient underflow pumping
surges in the solids feed rate
excessive amounts of large particles
sloughing of the solids accumulated between the rakes and the bottom of the tank or on structural members of the rake mechanism
Miscellaneous obstructions falling into the thickener.
The lifting mechanism may be set to raise the rakes automatically when a specific torque level (eg 50% of design) is encountered, continuing to lift until the torque returns to normal or until the maximum lift height is reached. |