Transportation System and Devices in Manufacturing: The Zimbabwe Case Study

Authors: Lawrence JONGI, Janusz SZPYTKO

Introduction

This paper looks into manufacturing transportation technology system and devices applicable at Mazowe Mine. This involves the transportation infrastructure, network architecture, sensor technologies, supporting or enabling technologies. Modern sensor solutions play a central role in the optimization of automated production processes. Ore blasted by the miner at the far end of a shaft underground is transported from the near blast area using a crapper which will feed into a bin carefully blasted, which will in turn feed into an inclined shaft backet (sometimes after a series of bin) to a lower level which will ferry the ore to the surface using a single or double drum hoist which is controlled by a hoist driver on the surface a bell ringer underground. This ore will be ferried by conveyors to the jaw crusher to a specified size and then to the Symmons conical crusher to a size less than 2mm. This ore will be ferried to the ore bin which is a reservoir for productions in cases of critical breakdowns. From the ore bin to the ball mill which will ground the ore to less than a micrometer, from the Ballmill the ore goes to vibrator screen that removes not conforming particles back to the process, the conforming will be taken to the Superbowl where visible gold can be harnessed on the principle that gold is the heaviest mineral, and that in solution can then be harnessed using electrolysis in the Acasia plant. Gold in solution is also harnessed using a Carbon In Leach process which is a different plant (1.5km from the main plant), the ore is transported to the CIL plant in slurry form in rubberized pipes by two pumps, one for standby, if these two pumps fail, it means the main plant will shut down because you cannot take in without taking out. In the CIL gold is processed in CIL tanks where gold is absorbed by carbon in solution, the carbon solution is taken into electrolysis boilers, where gold can only be separated from the carbon at very high pressures and temperatures and harnessed using wire gauzes using electrolysis.  Some transportation processes and production processes can be avoided by simply redesigning the plant, by simply having one crusher that crushes to the specified size until the ore has a satisfactory size, using automated settings that continually iterates, thereby eliminating many machineries and a group of conveyors. Or by making the pipeline through which the ore travels the Superbowl and the Acasia plant.

The network of transportation underground, is done using scrappers that scraps ore at the tip end of ore extraction into buckets which are ferried by buttery powered trains which will transport to the vertical hoist to ferry to the surface or it will take to an underground ore bin which has been careful blasted which will inturn feed into the inclined hoist and then ferried to the underground. Mazowe gold mine has three working hoist which are MaryAnne, Orgilv, Stories Hoist, two of them are vertical and only one is inclined. It means kilometers of ore extraction underground and workers should be transportation and supported by these three Hoist.

Transportation of maintenance utilities from machine shop workshop, wood workshop and fabrication workshop to the main plant is done by mere wheel barrows or by human effort when the wheel barrow is not available, things like chainblock, ticktock, gas bottles. Manufactured components from all the workshops are transported to the main plant or any department needing service from the engineering department, by trucks or a heavy vehicle fitted with a hydraulic crane to lift it from the vehicle to the site. Within the plant there is a 50 80 tonnes crane that is lifting equipment during maintenance for example, ball mills, 200HP warman pumps, electric motors, gear boxes.

Since the mine is self sustaining, that is it has a community of its own that is it provides residence, water, electricity, entertainment for all the workers at the mine which are 1500, therefore the resident engineer is responsible for civil engineering works, water reticulation, road maintenance, solid waste reticulation, surface (plant) and underground all engineering problems that is electronic, electrical and mechanical in nature. Therefore, when a breakdown happens during the night, all personnel responsible for restoring the machine to functionality are collected from their homes by a standby truck to the plant, and the process takes 45minutes to 1 hour 30 minutes. Which is a downtime that can be avoided in terms of ounces that are losts due to this down time since the plant is not supposed to stop by any means since the plant works 24/7 365 days.

Planned Maintenance Office do planned plant shutdowns every 3 months, and when a machinery is behaving in an orde manner the plant operator writes a job-card to the PMO indicating the level of priority of the job, and every machine has a checklist both for mechanical and electrical components which will be checked out by the artisan or technician.

Research problem and research methodology

This paper is an investigative and applied research which looks into the transportation technologies at Mazowe Gold Mine. It is clear that conveyor belts for all the industry understudy is the common machinery, and it is a critical machinery in the plant, and the chronicle faults in conveyors include, belt worn out, screw worn out, rollers seizures, bearing faults, gearbox faults and electric motor failure. Slurry pumps (e.g Warman ) and centrifugal water pumps (WKLN 65 stage pumps) are also common in all the industries and their chronicle faults include impellers and involute casing worn out, packing replacement, rubber linning, V-belts wornout, electrical motor failures, bearings faults, that is pump and electric motors. In all the industries since they involve movement of water and slurry from point A to point B, 6m long pipelines are the bloodline of the plant, hence the pipeline is rubberized to prolong its lifeline due to abrasion but however due to the high abrasive nature of the ore the rubber line does not last long and the outside part of the pipe is prone to corrosion even when its painted due to the cyanide exposure.

The main transportation system in these industry  is pumps and conveyor. To increase reliability every pump station is equipped with two pumps, one as a standby pump in case of a breakdown to reduce downtime. The main way of identifying faults is either through routine checks or through a catastrophic breakdown without warning shots, this can be improved by plant redesigning by including embedded instrumentation control in all machineries in the plant for data mining and data communication using wireless intelligent sensors. Designing a plant with a smart transportation technology systems and device is not good enough but every stride should be also in intelligent maintenance management and consequently intelligent manufacturing system. Although the target is manufacturing transport engineering maintenance engineering will benefit in the process. The plant has to be automatic, to reduce labour cost, and increase reliability.

Improving the ore or material handling within the plant by ensuring efficiency and effective plant operation, by reducing break downs, accidents and increasing reliability through making the plant more intelligent through embedded instrumentation and control systems for data mining and data communication amongst wireless intelligent sensors and supervisory levels using Direct Digital Control using Virtual Private Network is the main objective of this paper. There are dozens of different types of pumps and a seemingly endless list of applications but industrial accelerometers can often help the maintenance professional to diagnose sometimes tricky issues with pump operation. Using vibration monitoring in predictive maintenance program can help identify pump problems such as cavitation, recirculation and resonance.

A good rule of thumb is to select an accelerometer that has a linear high frequency response capability to three times the pump's vane pass frequency (vane pass frequency = number of vanes x RPM). Most general purpose accelerometers will have more than adequate high frequency response and thus the next key is selecting a transducer that will survive the application, that is, corrosive environments.

Automation of the plant improves plant efficiency and flexibility. Modern sensor solutions play a central role in the optimization of automated production processes. With high-precision measurement and a reliable signal, human-machine interaction is simplified and made safer, and precise monitoring of the facilities is guaranteed. Wireless intelligent sensors can self-calibration, that is, can adapt to changing conditions while the machines are in full operation. Plant operators do not need to remove them from the machines and have them re-calibrated under altered conditions, reducing downtime and guaranteeing maximum capacity utilization of the equipment. Because of this, maintenance costs are also reduced. The sensors’ suitability for predictive maintenance further contributes to an increase in the plant efficiency, and an increase in intelligent networked systems.

Wireless communication is experiencing explosive growth in many areas of electronics, and it is clear that there are some fundamental advantages in shedding both the cables and the plugs associated with conventional communications. The cost of devices for consumer electronics, such as mobile telephones, toys and computer peripherals, has plummeted. Distributed wireless monitoring is now a reality and it is developing fast.

Connectivity is critical, as part of the wider e-maintenance network. Commercial off-the-shelf (COTS) radio platforms offer high functionality, integration, and low cost, exploiting radio standards such as Bluetooth (IEEE 802.15.1) and Zigbee, an extension to IEEE 802.15.4, which is specially intended for sensors. Size, processing and power supplies are developing rapidly. The sensor’s internal processing capacity is capable of accommodating basic diagnostic functions, trending, prognosis and decision making, and communicating health status indications.

The software for performing remote, automated, distributed monitoring, in a robust fashion without recourse to human intervention, remains a challenge for the success of such a system. The embedding of knowledge and procedure will be important for the penetration of the new devices into the unmanned monitoring of future applications.

Figure 1. below shows an IEEE 1451 smart transducer, which consists of a Network Capable Application Processor (NCAP), a network interface between the user network and NCAP, a Transducer Interface Module (TIM), and a transducer physical interface between the NCAP and TIM. An NCAP consists of hardware and software and provides a gateway function between the TIMs and the user network or host processor. The NCAP is an application processor capable of network communications. A TIM is a module that contains the interface, signal conditioning, analog-to-digital and/or digital-to-analog conversion, Transducer Electronic Data Sheets (TEDS), and the transducer(s). The TIM may range in complexity from a single sensor or actuator to units containing many transducers (sensors and actuators). The NCAP communicates with a TIM via a physical interface, either wired or wireless. The IEEE 1451 family of standards defines a set of common communication interfaces for connecting smart transducers to microprocessor-based systems, instruments, or networks in a network-independent environment.

As shown in Figure 1. below, three user network interfaces are used to access IEEE 1451 smart transducers: the IEEE 1451.1 communication protocols, IEEE 1451.0 Hypertext Transfer Protocol (HTTP), and the proposed Smart Transducer Web Services (STWS) developed at the National Institute of Standards and Technology (NIST) based on the IEEE 1451.0 standard.

Figure 1: Wireless Smart sensor Architecture

The gathering of information was through observation from the researcher and reports from Production Engineers from these companies, and literature review. Chronic and catastrophic breakdowns on plant transportation machineries are affecting gold production and there is need to find a way to monitor condition of material handling machines so as to anticipate breakdowns and increase plant availability and reliability. The paper proposes recommendations to make transportation machineries more efficient and effective by increasing data mining techniques by embedding wireless intelligent sensors into all plant machineries in gold mining, and make the information accessible by the user through Wireless Local Area Network  and Internet of Things. This paper mainly focuses on wireless sensor networks based on the Institute of Electrical and Electronics Engineers (IEEE) 1451.5 standard, including the architecture, network interfaces, wireless transducer physical interfaces, and sensor position for all the plant machineries.

Results

Instrumentation and embedded control units should be built in pumps, gear boxes, hydraulic motors, rollers, gate valves, vibrators, Symmons Crusher, jaw crusher, electric motors, Superbowls, boilers, hoists, ball mill plummer blocks, to performance of the plant whilst he/she is anywhere in the world.

The delimitation of this paper is to focus on the preliminary designs, that is, machine design, plant design or redesign to make the machines compatible with wireless intelligent sensors, before focusing on the integrated production system. The researcher redesigned the Warman pump, WKLN65 multi-stage pump, hoist hydraulic motors sump, Radicon gearbox sump, ballmill plummer blocks, pipeline and boilers by indicating the right position of the transducer for data acquisition.

The STWS allows Internet access of IEEE 1451 transducers via Web Services. The STWS source code is available at the Open1451 project in SourceForge. The IEEE 1451.0 standard defines a common set of functions, commands, TEDS formats, and communication protocols for the IEEE 1451 family of standards. The connectivity between the NCAP and TIM is defined by the IEEE 1451.X physical interfaces, which include the point-to-point interface specified in IEEE Std. 1451.2-1997, the distributed multi-drop interface specified in IEEE Std. 1451.3-2003, and the wireless interface specified in IEEE Std. 1451.5-2007. Normally analog and digital transducers are connected to a TIM directly. However, IEEE 1451.4 transducers can be connected to a TIM through the IEEE 1451.4 Mix-Mode Interface. Likewise, IEEE 1451.7 transducers can be connected to a TIM through radio frequency (RF) interfaces.

Existing wireless sensor communication protocols shown in Table 2 include IEEE 802.11 (WiFi), IEEE 802.15.1 (Bluetooth), IEEE 802.15.4 (ZigBee, 6LoWPAN, WirelessHART, ISA-100.11a), and IEEE 802.16 (WiMAX).

·         IEEE 802.15.1 (Bluetooth)

Bluetooth is a short-range wireless communication technology intended to replace the cables connecting portable and/or fixed devices. The key features of Bluetooth technology are robustness, low power, and low cost. The basic framework of Bluetooth conceives a 1-meter to 100-meter communication area with a transfer rate of 1 Mbps to 3 Mbps at 2.4 GHz. Bluetooth is mainly used for personal area sensor network and short-range portable personal devices. The IEEE 802.15.1-2002 standard is based on the Bluetooth specifications. Most suitable in the Acacia plant because it works with many subordinates one supervisor and because it is very sensitive.

·         ZigBee

The ZigBee Alliance is an association of companies working together to enable reliable, cost-effective, low-power, wirelessly networked, monitoring and control products based on the IEEE 802.15.4 standard for Wireless Personal Area Networks (WPANs). ZigBee is intended for use in embedded applications requiring low data rates and low power consumption, such as smart homes, building automation, mainly applicable in the main plant full of Wkln65 water pumps and Warman slurry pumps.

·         6LoWPAN

The Internet Protocol version 6 (IPv6) over Low power Wireless Personal Area Networks (6LoWPAN) allows IPv6 packets to be sent and received over IEEE 802.15.4 based networks through encapsulation and header compression mechanisms. 6LoWPAN brings IP to the smallest of devices, such as sensors and controllers. The 6LoWPAN protocol is targeted at wireless IP networking applications in the main plant also environments.

·         IEEE 802.11 (WiFi)

IEEE 802.11 is a set of standards for Wireless Local Area Network (WLAN) communications in the 2.4 GHz, 3.6 GHz, and 5 GHz frequency bands. The Wi-Fi name is a trademark of the Wi-Fi Alliance for certified products based on the IEEE 802.11 standards. There are a variety of protocols currently in use for wireless networking. The most prevalent is 802.11b (2.4 GHz at 11 Mbps). The newer 802.11g (2.4 GHz at 54 Mbps) standard improves on 802.11b. The 802.11a is also capable of transmission speeds up to 54 Mbps, like the 802.11g standard, but in a different frequency (5 GHz) range. IEEE 802.11n uses multiple input, multiple output antennas for higher throughput improvements (2.4 GHz or 5 GHz at 50 Mbps to 600 Mbps). IEEE 802.11 is widely used for residential, Storis plant, Carbon In Leach plant, and the main plant applications for general LAN access in work areas.

Table 1 below shows all the applicable wireless intelligent sensors for Mazowe gold mine.

The researcher designed the communication architecture of the entire sensory network system for both underground and surface machinery with reference to IEEE standards. With this system it is possible to supply information ranging fromtemperature monitoring, process parameters, vibration monitoring, acoustic emissions, infrared analysis, lubrication analysis, leak detection, corrosion monitoring, crack detection for condition monitoring and to make any corrective action to the plant in real time through hydraulic actuators. This paper will look at the costs of implementing this project at Mazowe Gold Mine. Underground water pumps section is very critical for dewatering the mine because if the mine floods production will stop.

Architecture of IEEE 1451.5 Standard-Based Wireless Sensor Networks Figure below depicts an architecture of IEEE 1451.5 standard-based wireless sensor networks. Each oval shows one of the IEEE 1451.5 standard-based wireless sensor networks. Figure 4(a) shows a view of an IEEE 1451.5-802.11 wireless sensor network, whereas Figures 4(b), 4(c), and 4(d) show the IEEE 1451.5-Bluetooth, -ZigBee, and -6LoWPAN wireless sensor network, respectively. Each wireless sensor network shown in Figure below consists of an NCAP and a number of Wireless Transducer Interface Modules (WTIMs). The NCAP is a gateway between the WTIMs and the user network. The NCAP supports the required functional specifications, the message structures, the required commands of the IEEE 1451.0 standard, and one of the wireless communication protocols and physical media defined by the IEEE 1451.5 standard. The NCAP can be connected or associated with a number of WTIMs using the same wireless medium.

The WTIM is a module that contains a wireless interface, signal conditioning, analog-to-digital and/or digital-to-analog conversion capability, TEDS, and transducers (sensors and actuators). It also supports the required functional specifications, message structures, commands, TEDS format of the IEEE 1451.0 standard, and one of the communication protocols and physical media defined by the IEEE 1451.5 standard. Thus the NCAP can communicate with each WTIM via one of the four wireless protocols using IEEE 1451.0 messages and it may also communicate with a host via an external network through one of the IEEE 1451 network interfaces. The IEEE 1451.0 standard defines a set of common functions and commands for the entire family of IEEE 1451.X smart transducer standards. It operates under either a client-server or request-response protocol, which is independent of the physical communication media. Basic functions

Figure 2. Architecture of IEEE 1551.5 Standard Based Wireless Sensor Networks

include reading from and writing to transducer channels, reading and writing TEDS, and sending configuration, control, and operation commands. The IEEE 1451.0 was designed to facilitate interoperability and compatibility among the family of IEEE 1451 standards when multiple wired and wireless sensor networks are connected to form a system of networks.

The communications between the NCAP and WTIM are based on IEEE 1451.0 messages through one of the IEEE 1451.5 media. In this architecture, two kinds of interfaces exist for the IEEE 1451.5 wireless sensor networks, 1) network interface and 2) wireless physical interface. The network interface is an interface between the NCAP and user network. The wireless physical interface is an interface between the NCAP and WTIMs.

IEEE 1451.0 HTTP protocol, and the proposed Smart Transducer Web Service. Choosing a network interface for an IEEE 1451.5 wireless sensor network highly depends on the sensor applications.

IEEE 1451.1

IEEE 1451.1 is a standard for a Smart Transducer Interface for Sensors and Actuators -Network Capable Application Processor Information Model. It defines a common object model and interface specification for the components of a networked smart transducer. The IEEE 1451.1 standard specifies a software architecture, which includes three models: data model, object model, and communication model.

The researcher located point/s on all plant machineries to place the wireless sensors and produced working drawings. For pumps barrels it was imperative to measure vibration rather than temperature and for vibrational measurement (for Warman pump, WkLN65/95 pump, Plummer blocks for hoist drums, and hoist sheeve wheels,  and  Ball Mill, , and electric motors) the researcher opt for eddy currents sensor or accelerometer. However, temperature sensors could be embedded in boilers, and electric motors windings for all electric motors in the mine using a thermocouple as a practical instrument for this case. Acoustic sensors should be embedded in big machineries which are very critical to safety and production, and sound is a variable that clearly shows that the machinery is operating healthily, these machineries include; Ball Mills, Symmons Conical Crusher, Jaw Crusher, Compressors, and Hoist. Flow rate sensors preferably a tachometer to measure massflow rate (slurry pumps) or discharge (water pumps and compressors). Tear and wear sensors (Inductive Proximity Sensors)

Figure 3: Accelerometer and temperature sensor

should be placed preferably in the sumps of all hydraulic machines, e.g gear boxes, Symmons Crusher, Hoist Staffa Motors, Hoist break shoes and Compressors. Air receivers for compressors are very critical for safety and metal thickness should constantly be monitored, inductive proximity sensors, are very practical in this situation. Machinery components which are metal should be constantly monitored for crack assessment using RFID wireless sensors. Intelligent thin film corrosion sensors should be used to assess corrosion effect on machineries prone to corrosive environments e.g. pipeline, boilers, hoist infrastructure, and conveyor belts. Digital air pressure sensors should be used to measure pressure in boilers. Broken wire strand sensor for the hoist transportation of ore and workers underground is critical to safety. Figure 3 shows temperature and vibration sensor positions

Figure 4: Flowrate sensor for pumps

Figure 4 show a flange connected to a velocity meter that will measure the discharge either of water or slurry, any deviation will be caused by either a worn out impeller or diffuser which needs replacement.

Corrosion Monitoring

Although the pipeline and some other structures will be painted to protect them from corrosion, it is not enough, iron is witnessed being eaten away by the environmental conditions of production, therefore it is imperative to design an Impressed Current Cathodic Protection system that is automatic based on signals from the wireless intelligent corrosion sensor. It is important to monitor corrosion especially on critical structures like hoist structures and water and ore pipelines as shown in figure 4.

For steel in soil, lowering the steel-to-soil voltage everywhere to at least -0.850 V, with respect to a CU/CUS04 reference electrode, provides complete protection. Since this is not always possible, a shift of 300 mV in the negative direction when cathodic protection is applied is usually sufficient. Other more-disputed voltage criteria are sometimes used if neither of these two potential changes can be made.

Figure 5: Corrosion Monitoring in pipelines and structures

Tear and Wear and Metal Thickness Monitoring

Inductive proximity sensors are non-contact proximity devices that set up a radio frequency field with an oscillators ( Oscillators are devices that are used to generate repetitive signals. They produce output signals without an input signal) and a coil. The presence of an object can alters this field and the sensor is able to detect this alteration.

Vibration Monitoring

Placing accelerometers on plummer blocks, barbican bearings, and pump burrels will give the system knowledge about the condition of bearings and alignment of the machinery to the prime mover. Vibrational analysis is critical on machineries such as  pumps,  hoist Ballmills.

Crack Monitoring

An ultra-low-cost RFID solution has been investigated for monitoring stress concentration and crack formation in structures. In an RFID (radiofrequency identification) system, the reader beams electromagnetic energy to the RFID tag/sensor, which receives the energy and reflects electromagnetic signal back to the reader. Therefore, the sensor is wireless and doesn't require battery power. When the RFID tag is under strain/deformation, the tag antenna shape changes and causes its electromagnetic resonance frequency to shift. This resonance frequency shift can be detected by the reader, and then used to derive the strain experienced by the RFID tag.

Broken Wire Strand Sensor

For total safety of the system it is imperative for the researcher to design a broken wire strand sensor for such sensor do not exist on the market. The main objective of this sensor is to look sense if the wire rope has not broken, if it senses any wire strand broken then the Planned Maintenance Officer has to condemn the whole wire rope and replace with a new one.

Pressure Sensor

Pressure sensors are very important for compressor and boilers at CIL plant for continuity of production and safety. The operational pressure for sensors is about 200kPa for gold absorption into carbon to be efficient, any less will cause the plant to be less efficient therefore there is need to regulate boiler pressure. Also for compressor to supply compressed air to the jack hummer underground and appropriate pressure and also the air receiver should hold air pressure to a certain level without endangering human lives it is imperative to monitor the pressure from the compressor.

Acoustic Sensor

Each and every machinery in the plant has a sound signature which is distinct, placing a sound sensor near machinery like ball mill, Symmons Crusher, Hoist and Jaw Crushers the researcher can remove all the sound signature that do not matter to the machinery understand by filtering all irrelevant sounds leaving out only one which can be analysed for condition monitoring.

Conclusions

It is possible to automate gold production, however, the wireless intelligent sensors should be able to work under harsh environments, that is, corrosive, vibrational, noisy, and humid. From the research it is clear that broken strand sensors are not yet on the market and some designs are at patent stage, the researcher have to design this sensor for total safety of the whole plant. Zimbabwe is the largest gold producer in the world and Metallon Gold Pvt Ltd is the largest gold producer in the country, that makes it the largest gold mining company in the world and if latest technologies are released it is imperative that this is the first company that will embrace the technology. Metallon Gold employees Mechanical, Electrical, Electronic, Industrial, Production Engineers with first degrees, artisans, technicians and semi-skilled workers that makes it competitive enough on the human resource aspect to embrace this technology. The superbowl in the Acacia plant is a machinery that is automatic making engineering department experienced to handle this kind of technology.  Since all the sensors operate with small voltage and current, but differently, they would need a variable voltage transformer with a rectifier for most of the sensors works with a DC.

IEEE 1451.0 is a standard for smart Transducer Interface for Sensors and Actuators and its common function is communication protocols and Transducer Electronic Data Sheet (TEDS) which will be shared with the actuator, the actuator can be hydraulic or mechanical or a hybrid depending with applicability and operational conditions.

Looking into the costs of this project, maintenance cost and the period of return of investment is very important for this project to be implemented.

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