Overall Equipment Effectiveness (OEE) is being used increasingly in industry because it takes the most common sources of manufacturing productivity losses to improve manufacturing and maintenance operations. OEE metric is always the first to be determined and after which is the need to develop a loss map for OEE main factors (uptime, speed and quality).
OEE is a hierarchy of metrics that can be used at the equipment, department, line and facility levels. Improving manufacturing and maintenance operations, OEE helps to uncover inefficiencies in production processes by showing how well a production line is functioning overall in terms of uptime, speed and quality. At this point, it is important to say that, technological inheritance model provides a single metric to integrate all the factors of OEE. Most companies have fairly good systems for capturing and tracking uptime and quality data, but determining design rate can be somewhat contentious. Even at best robust designs that meet desired requirements, still produce sub-optimal reliability results, hence the need to consider technological inheritance model. In order to develop a loss reliability map by taking the inverse of uptime, speed and quality percentage, reliability coefficient map can be developed real-time in terms uptime, speed and quality with technological inheritance coefficient ranging from "0 to 1", where 0 is the minimum reliability level and 1 is maximum reliability level. The next step will be to categorize the reliability growth and degradation distribution into distinct levels (minimum, medium and maximum). The reliability coefficient growth/degradation map is categorized into idle downtime, changeover downtime, early life, useful life and wear-out life.
Although, most companies do a fairly good job of capturing uptime and quality losses, but on the other hand, speed losses are seldom captured, which can vary often to produce major loss of productivity through gradual slow down whcih sometimes goes un notice. When a plant goes down, people notice it, but when it slows down, there isn,t that sense of urgency. However, the extent of lost production due to speed loss came as a surprise to management. More also reliability based on MTBF is not feasible for certain zero tolerance critical equipment, hence the need for automated control system that can capture/track speed, uptime and quality with a single metric during real-time operation in a systematic manner.
Technological Inheritance Model - based Software can now be used to capture and monitor reliability growth, degradation, OEE and other economic data, in order to uncover the hidden nuggets in repetitive small delays, production slow downs, component quality and other essential performance indexes. At the same time, it is used to build a better foundation for improving the business process of equipment maintenance, process control, data acquisition, monitoring, integration and selection of components.
Tuesday, May 29, 2012
Thursday, May 17, 2012
QUALITY DATA IN RELIABILITY AND MAINTENANCE OF EQUIPMENT
Quality and readily available data is needed in order to cost-effectively carryout maintenance activities. This data helps us to take informed decisions that offer optimal results, which in turns affects the maintenance and manufacturing organizations in varying degrees. These organizations are being challenged by factors such as increasing competition, demands of share holders for greater returns on investment, societal expectations for efficient resource utilization with little or no environmental impacts and safety of employees. The evolution of the maintenance function can also be seen in various tools/systems like computerized maintenance management system (CMMS) used to make it more effective. Even at this, the maintenance industry is still plagued with the following problems:
- Human data repository and employee turnover,
- Poor utilization of the CMMS tools in review of previous maintenance activities as a way of understanding equipment failures and thereby in a position to fine-tune maintenance strategies that lead to increased equipment availability and reliability,
- Poor basis of determining maintenance budgets in budgetary allocation,
- Continuous appropriation of using CMMS Tool to demonstrate prudent maintenance practices with the opportunities to negotiate reductions in engineering biased and or fine insurance premiums.
The role of quality data in reliability and maintenance of equipment is great. Various equipment that are under the care of the maintenance function are themselves produced through the compilation of necessary data that were eventually used in equipment design and manufacturing. It has been ascertained by researchers and industrialists that such data collection in equipment design is less than optimal, which results in low inherent equipment reliability, poor availability and maintainability. While it is now standard practice to involve the maintenance function in the design of new plants and equipment in a bid to further assure maintainability.
Some of the main significant areas of quality data in the maintenance and reliability function are as follows:
1. Effectiveness of Maintenance Strategies/Repairs – Maintenance strategies are normally put in place to ensure installed equipment is ever ready to render the services for which they are acquired for. Also to assure installed equipment in its operations will comply with all relevant regulatory and environmental requirements. It is inevitable that equipment in the course of usage will break down and necessary repairs need to be carried out to bring them back to service as quickly as possible. For effective coordination of maintenance activities, it is essential that all works and repairs that are carried out on installed equipment be captured appropriately.
Using the CMMS, the effectiveness can be reviewed and analyzed with a view of identifying areas in need of further optimization or improvement of maintenance practices. Frequent repairs can easily be spotted and subject to further improvement efforts.
It is therefore necessary to select the relevant maintenance data that define the work process, capture the data, and enter the data in the CMMS at the right time and in the right format, with the help of Technological Inheritance Technique.
2. Budgetary Allocation – Activity Based Costing: Business organization exist for the sole reason of maximizing the returns of those who have put their earn income in the business. It is important for maintenance activities and the associated costs be accurately captured by maintenance department. At this point, it is necessary to mention that, maintenance data and its associate costs can be captured accurately, entered into CMMS and used for maintenance function with the help of Technological Inheritance Technique.
3. Equipment Replacement Program – Maintenance and Engineering Organizations are constantly seeking equipment that delivers best service and value for their outfits. Therefore, it is relevant to tract or monitor data such as:
- Spare consumption with associate costs,
- Repairs and associate costs,
- Down Time,
- Mean To Between Failures (MTBF),
- Mean Time To Repairs (MTTR),
- Training Costs
The main reason for this program is to determine the equipment total cost of ownership. Such data should be handy in the economic analysis of replacing old equipment and a new replacement at a future data. The determination of the equipment total cost of ownership and its economic analysis is possible with Technological Inheritance Technique.
4. Insurance Premiums – Evidence of good maintenance practices supported by good maintenance records/reports based on factual data or real-time data with technological inheritance technique can be used to demonstrate insurance risks managers how low the risk is and hence its attractiveness to rather conservative premium payout.
5. Regulatory Compliance – Industrial organizations are increasingly being placed under the radar with respect to the environmental impact of their activities. Legislation in most countries require that certain installed equipment be subject to periodic inspection, recalibration and monitoring to assure their technical integrity, while in operation, hence the need for technological inheritance technique.
In conclusion, all the above significant areas of quality data in the maintenance and reliability function can be integrated with a single – “Technological Inheritance Coefficient”, which can be used to evaluate the overall equipment effectiveness
Wednesday, May 9, 2012
REAL-TIME RELIABILITY MONITORING WITH SURFACE QUALITY CYCLING TECHNIQUE
Tools that can help identify real-time reliability risks earlier and throughout development as well as during the service life of components are becoming increasingly important. One such tool is a real-time wear and its competing failure cycle reliability/surface quality test in which the module is monitored with a technological inheritance coefficient-chain methodology during surface quality cycling. This test provides immediate real-time failure feedback, enhanced failure signature information, failure resistant mechanism and maximum achievable surface quality/reliability. Actually, today’s electronic module packages can integrate several active and passive components within one device, providing simpler board design, reduced component inventory, maintenance and reduced repair costs. Choices in the module material set, coating deposition conditions, component surface quality variables and substrate considerations all play substantial roles in determining the overall package reliability, its real-time monitoring and they ultimately determine which test methodology would be best to verify component reliability.
Over the past decade, the industry has moved from relying on pass/fail test methods toward using design-for-reliability tests that focus on uncovering and analyzing potential problems at an early stage. A facet of this is the increased emphasis on the test-to-failure approach for certain related tests, such as temperature, pressure, speed, surface hardness, surface roughness, surface wavelength, surface stress cycling and others.
Component Surface Quality and Process Factor Cycling
From the perspective of reliability test, component surface and process stress testing has traditionally been a “pass or fail” test where the stress is induced and functional units are subsequently removed from such stress for verification of post electrical-test functionality. In general, a component surface and process stress profile involves the following parameters:
- High extreme component surface quality condition, (Ymax) and Process condition (Xmax);
- Low extreme component surface quality condition, (Ymin) and Process condition (Xmin);
- Component surface quality condition change (Y), where
- Ramp rates;
- Dwell times at extreme component and process conditions,
- Technological Inheritance Coefficients “a – for component surface quality control” and “b – for process condition control”
The lifetime and reliability of a component module can be significantly affected by these parameters tests can be used to characterize product capability and accelerate failure modes (eg die crack, via crack) during initial technology development, product design verification and product qualification.
The Monitoring of Component Surface Quality and Process Factor Cycling
As an enhancement to existing component and process stress methodologies, implementing monitored daisy-chain parameters in real time during component and process condition stresses can help determine if any intermittent failures are beginning to occur. As a result, designers can be alerted to a failure immediately without the need for post electrical test. A monitoring test includes:
- Event Detection: In order to capture a significant component quality and process condition change in real-time, the event-detection capability called for in monitoring failure testing. The failure mechanism associated with condition stresses tend to be very slow to develop and will not change quickly from passing to failing and back to passing. A switch matrix that can be used for all of the modules under test on the scale of one to maximum (success/pass) and 0 to minimum (failure/fail).
- TC Profile: Any type of component/process condition cycle profile can be used in conjunction with monitored condition testing.
- Reliability Growth/Degradation: The component surface quality and reliability grows to maximum as measured with technological inheritance coefficient form point to point (from 0 to 1), degradation moves from 1 to 0.
Monitored Component Surface Quality and Process Factor Data Analyzed
Once reliability growth and degradation is captured, raw data (channel, resistance, count, time and so forth) can be exported, analyzed and graphed within a software package such as LABVIEW, SAS and others. By capturing failure resistance or reliability data throughout the component life cycle, it is possible to detect failures that first develop at extreme conditions of component/process. In contrast, reliability growth/degradation cycles may need to be measured to detect failures and eliminate it with the help of technological inheritance technique and cost effective maintenance procedures. Reliability monitoring and maintenance with technological inheritance technique is useful during development phases when designers must establish confidence in new packaging technologies and throughout its life-time cycle. The ability to detect a failure at the precise cycle count at which it begins to occur is an advantage for earlier detection as well as for accurate statistical analysis. Detailed data regarding the signature of failure and progression of the failure can be valuable in assisting failure-mode determination and reducing failure-analysis time as well as for the attainment of maximum reliability. Technological Inheritance Coefficients can be used to determine failure, time to failure, life-cycle cost, reliability growth and degradation as well as for the selection of cost effective components and processes.
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Monday, May 7, 2012
WEAR AND ITS COMPETING FAILURE MODE FACTORS OF COMPONENTS
The analysis of all the desired contributing factors is necessary to predict the result of a single wear and its competing failure mechanism, but several sources of deterioration may combine to complicate what might otherwise be a straightforward solution. The main multiple factors that influence wear and its competing failure modes are as follows:
- Metallurgical variable (Hardness, toughness, constitution and microstructure, chemical composition)
- Service Variables (Contacting materials, pressure, speed, temperature, surface finish)
- Other factors (Lubrication, corrosion, vibration)
It is actually impossible to generalize about a material’s suitability, such as to say a certain composition is the most wear and its competing failure resistant, without considering factors such as service conditions. For example, two materials, one of which is clearly superior to the other for a specific application, may undergo a complete reversal in wear resistance from only slight changes in service conditions. Although strength, hardness and ductility or toughness are important, wear resistance cannot always be associated with any one property. Wear resistance generally does not increase directly with tensile strength or hardness; however, if other factors are relatively constant, hardness values provide an approximate guide to relative wear behavior among different metal. This is especially true for metal – to – metal sliding and abrasive applications.
In the cases, where other factors may vary, it will be necessary to consider other factors such as service, environmental and manufacturing conditions that combines to produce maximum achievable wear and competing failure resistance (like corrosion, temperature, fatigue, vibration and temperature resistance). As long as these conditions continue to vary, wear resistance and its competing failure resistance is also bound to vary. It will therefore be necessary to optimize all the operating conditions of the technological system in order to make the wear and its competing failure resistant values constant for a specific period of time. The technological system condition of this case includes the followings:
- Metallurgical Conditions
- Surface Coating Deposition Conditions
- Surface Finish Conditions
- Service Conditions
- Monitoring Conditions
- Maintenance Conditions
Multiple regression models is used to relate the technological operating conditions with component surface quality conditions, which helps to select the significant surface quality parameters, manufacturing processes and to determine maximum achievable reliability and life-time. The highest surface quality factor value by any of the technological process is selected for the optimization of the system.
The selected optimization process will ultimately serve as the optimum baseline for all the operating conditions of the technological system. The optimization of a component surface finish condition provides the optimum surface quality, optimum process condition, selects the desired number of parameters and factors as well as determines their optimum values. The multiple surface quality parameters of hard-alloy coating are selected as surface hardness, surface roughness, surface wavelength, surface stress and kinematic coefficient for maximum achievable reliability. The optimum multiple quality values can be integrated together to form a single quality and reliability factor, which can be used to construct wear failure/wear resistant mechanism and other competing failure mechanism or its failure resistance mechanism. Technological inheritance technique is used to plot the mechanism diagram, predict the time of failure, diagnose failures, and determine maximum achievable reliability, reliability growth/degradation, life-time and life cycle cost.
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Wednesday, May 2, 2012
SELF-FLUXING ALLOY POWDERS FOR EXTREME CONDITIONS AND APPLICATIONS
Self-fluxing powders based on nickel are hard alloy materials having a wide application for hardening and reconditioning surfaces of rapid-wearing parts working in aggressive media and wear conditions. This hard alloy powder is similar in chemical composition to those of the granulated spheroidized alloy powders. The self-fluxing powder is slightly different with a lower content of oxygen and other impurities, although classified according to composition. These coatings have complex structures, which consist of minutely dispersed super hard phases of carbides, borides and carboborides with micro-hardness up to 40.103 MPa, uniformly distributed in a hard metallic matrix based on solid solutions and complex nickel-based eutectic.
These hard coatings are chemically resistant to different active media. On the basis of research works, it was ascertained that, within the range of specific pressure 1.5 x 106 – 7 x 106 Pa and sliding velocity up to 8m/s, it is possible to recommend nickel-based self-fluxing powder materials for friction pairs in water and in solutions of NaOH and CH3COOH of 10 – 50% concentration. The wear resistance of this type of hard coating in frictional contact with steel (friction of boundary lubrication) is 4 – 9 times higher than the wear resistance of steel in steel – steel pairs and steel p iron pairs under specific loads of 1.5 x 106 – 10 x 106 Pa and sliding velocities of 8 – 54 m/min; within this range, the amount of wear of steels working in pairs with hard coatings is reduced by a factor of 1.5 – 2.5 times. The friction coefficient in pairs of hard coating – steel with initial surface roughness of Ra = 0.16 – 0.3
These hard coatings are high wear and corrosion resistant, capable of withstanding impact and hard conditions under abrasive wear at temperatures up to 600oC. They are cost effectively used for reconditioning and hardening valves, camshafts, blades, fans, rotors, shafts and sleeves of hydraulic pumps, parts of agricultural machines etc. At this juncture, it is worth knowing that, there are several contributing factors that have combined to determine the results of high wear, corrosion and temperature resistance of these hard alloy coatings. The knowledge of these multiple factors will definitely help to predict the determinant result of a single failure resistance mechanism (wear and its competing failure resistance mechanism) with the help of technological inheritance model that integrates the factors. This single failure resistance mechanism of a particular component can be used to determine maximum achievable wear, corrosion and temperature resistance for extreme industrial conditions.
NICKEL-BASE ALLOYS CHARACTERISTICS AND APPLICATIONS IN THE INDUSTRIES
The term “Nickel-Base Alloys” is used for those alloys wherein, with very few exceptions, nickel is the principal element. These nickel alloys are used where corrosion resistance is of the greatest importance, and metal is exposed to cyclical heating conditions and electrolytic attack. Most commercially available nickel-base hard facing alloys can be divided into three groups: boride containing alloys, carbide containing alloys and laves phase containing alloys. The largest numbers of nickel alloys are those containing boron. These alloys were first commercially produced as sprayed and fused powders. Currently they are marketed by most manufacturers as other hard facing products as well. This group of alloys is primarily composed of Ni-Cr-B-Si-C, the boron content typically ranging from 1.5% to 3.5% depending on chromium content which varies from 0 to 15%. High chromium containing alloys generally contain a large amount of boron which forms very hard chromium borides with a hardness of 1800kg/mm2. Usually other borides high in nickel with a low melting point are also present to facilitate the fusing operation subsequent to spraying. The abrasion resistance of those alloys is a function of the amount of hard borides present. Alloys containing Ni – 14 Cr – 3.4 B – 4.0 Si are extremely abrasion resistant but very poor in resisting impact. Since most of these alloys do not contain high amounts of solid solution strengtheners, considerable loss of hardness occur at elevated temperatures.
The laves phase alloys contain an inter-metallic compound of nickel – molybdenum – silicon in a nickel chromium – molybdenum matrix. The cobalt laves phase alloys are similar in that the cobalt replaces the nickel in the system. Due to the fact that laves are inter-metallic compounds, they are believed to be less abrasive to mating materials than carbide or boride containing alloys. These alloys like Nickel 200. Monel alloy 400, Inconel alloy 800 etc are most likely to found in Agriculture, the Chemical, Petroleum, Space and Aircraft industries. Specifically for Agriculture, certain powder materials of nickel-base alloy composition have been produced by Castoline Company in Switzerland, for hardening new parts and reconditioning worn parts of machine by gas-thermal spraying. The company produces granulated powders (GP), which have been classified into three groups, base on their deposition techniques and service applications.
At this point it will be worth while to consider some of the characteristics of these powder alloy materials.
GP – 10 Ni – 01 is a spheroidized powder alloy based on the system Ni – Cr – B – Si – C – Fe. It is usually deposited on mild stainless steels and irons. This alloy has a low melting point and high yield point, which provides smooth surfaces after deposition. The coated layer is characterized by a very low friction coefficient and high resistance to wear, corrosion and oxidation at normal and high temperatures. Hardness of the coated layer is HRC 55 – 62 and it offers a wear resistance performance, even at a high temperature of about 700oC. It’s available in coating thickness up to 2mm, and can usually be finished by grinding. This alloy material is commonly used for hardening and reconditioning of tools, crank pins, eccentrics, ratchet and pawl gear, transporting chains, mixers, pushers and various spots.
PM – 12 NiWC – 01 is a composite powder material (PM) consisting of a mechanical mixture of the spheroidized powder GP – 10Ni – 01 of the system Ni – Cr – B Si – C – Fe and the very small particles of tungsten carbide WC (35%). It is deposited on mild and stainless steel and irons. It has a high resistance to wear at normal and high temperatures. Coating hardness is HRC 57 – 64, capable of operating under a high temperature up to 700oC. The coating thickness is usually up to 2mm while the surface finish is done by grinding. It is used for hardening and reconditioning of transporting chains, mixer blades and scrapers, fan blades, cutting tools, cutting auger conveyors etc.
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SELECTION OF HARD COATINGS FOR METAL-TO-METAL SLIDING AND ABRASIVE APPLICATIONS
The selection of the proper metal to be used for a job is the most important step in doing a job successfully. Each metal has different characteristics of strength, shrinkage, hardness etc so that there is a metal for almost every purpose. When a metallic wire is sprayed, it forms an alloy different from the original one, which is why when choosing a metal it is necessary to always consider the properties of metal deposition and not just the properties of the original metallic wires. All sprayed metal is porous and brittle as compared with the wire from which it was sprayed as a result of “spraying”. When metal is sprayed it tends to shrink slightly and hence set up internal stresses. The real strength of any sprayed coating is the difference between its original inherent strength and these internal stresses. Since the stresses are produced by shrinkage, those metals which shrink least will have the least internal stresses. Sprayed metals which have high tensile strengths and low shrinkage factors will obviously give the strongest coatings which are least likely to crack or lift. These points are very important, and explain why wires for spraying should be chosen on the basis of the properties of the metallic coatings and not on the basis of imitation and consideration of the parent material.
In general, the maintenance welder will be required to weld according to absolute specification, in which case the filler metal and welding procedures are spelled for him. In the absence of a specification, if the welder can identify the parent metal, he may match the filler metal to the parent metal as closely as possible. If he cannot identify the metal, other than that it is a high nickel alloy (for example), the best practice is to stay with the higher nickel content and choose the other alloying elements according to his knowledge of what those elements might contribute to the weld deposit under the welding in-service environment. When depositing comparatively thin coating on known parent metal, any metal can successfully be sprayed, since the metal is chosen with respect to its hardness and wear resistance characteristics or machinability or its corrosion resistance properties. This type of coating is usually carried out on the majority of parts for thin coatings (up to 1.5mm).
Surface roughening is generally necessary for coatings over 1.5mm thickness wherever there is an edge, such as at a key way. In this case, high shrinkage metals, such as SPRASTEEL 10 or METCOLOY 1 should be used. They should also be used for coatings over 3.0mm thickness wherever there are edges and for coatings that do not have edges (such as continuous coatings on cylindrical surfaces, where the conditions of the service are extremely severe, where there is the danger of layer separations in the coating or where the coatings are heavy and high shrink metals so that danger of cracking exists). In the cases where coating metals are chosen for wear resistance and hardness, steels are not machinable on lathes, and where grinding equipment is available, it is recommended to use METCOLOY 2, SPRASTEEL 80, Nickel-Base Alloys and Self-Fluxing Alloys for heavy coatings with the highest shrinkage.
At this juncture, it is worthy to note that, grinding heavy coatings of hard alloy materials do produce tensile stresses, which will definitely reduce the hardness and wear resistance of components. In order to obtain maximum hardness and wear resistance of components at minimum cost, there is therefore the need to apply technological inheritance technique.
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