Innovations in materials teaching: design of demonstrations for lectures
1. Problem Background
The process of teaching of material science involves memorising a more significant amount of data than any other subject in engineering. Dealing with the torrent of data can become tidieous for alot of students and result in lovered concentrarion and lover levels of data retention.
That is also due to the fact that most lectures are designed for people with visual senses as the main developed sense omminitng kinestetisc and providing a lesser quality of data retention for audio centered individuals that often learn and remember data when accompanied by music. In the course of preparation of this project I embarked on a mission to discover alternative ways of presenting of information to appeal to more wide wariety of people, to raise engagement and concentration levels in and off lectures.
1.1 Introduction to Experiments and Reasoning Bechind the Choices
a) Powder Metallurgy and Synthering
For the experiment showing the procedures and technologies used in manufacturing of sinthered products I decided to use a novelty PMC techology that allowes a low level of temperature ant preasure to manufacture metal sinthered products. Those qualities were the main reason for this choice of the experiment as it offered a possibility to convey the proces in lecture theater.
As the importance of coatings and their omnipreence is a obvious fact for many engineers in already in the industry, it many times is overlooked by students or its importance diminished by “fancy” or egsotic materials, I decided to recreate an experiment that I have seen previously conducted. The fluidisation method is a simple way of introducing students to problems and chalenges as well as fascinating technologies and possibilities bechind coating technologies.
d) Ultrasonic Testing
Non destructive testing is a huge part of the industry, especialy in the heavy area such as ship building or heavy mashinery priduction in which often after initial testing and process preparation procedure the quality testing can be at times imposible till after a massive amout of work was already made and prototyping is not an opcion. Non destructive testing can verify quicly if the choice of techology or procedure was correct whiteout the need of producing and destroing a large amount of prototypes. The main use is testing either a finished product pre assembly or, and its indisposible in those areas, to chect existing equipmet or instalations for developing faults or to investigate reasons for failures. I have chosen to present a proposal for an excercise using a Ultrasonic wave emmiting probe to test for flaws in the homogenity of materials.
e) Hardness Testing
Hardness testing is another pivotal cog in the industry machne, it resposible for consistency of the quality of most produced materials and processes used. In my experimental excercise I chose to use the Vickers scale as it alloves to test all types of material, it has one of the widest scales out of all hardeness tests and all calculation are independent of the size of the indenting probe.
2. Powder Metallurgy and the Precious Metal Clay (PMC) Method
“Powder mettalurgy principle of shaping metallic objects, without melting from powdered mateials can be traced back… ancient Egiptian iron implants which date from at least 3000BC” (Indian Journal of History of Science, 18(1) 109-114(1983)) It was the technology of metal powders especially tungsten carbide machining tools that allowed Nazi Germany to mass produce tanks shielded in high strenght steel alloys and unprecedented bores of their guns that were of such an adwantage on WW2 battlefields.Generaly the domain of Powdered Metallurgy ecompases the production of powdered materials, being it trough chemical or mechanical processes and creating a usefull geometries from those materials by applying preassure and introducing heat. The method is applied with success to ceramics, composite materials with nonmetalic and metali phases and polimers both natural and of petrochemical origin. Powder Metallurgy and Synthering are a groving and a dynamic disciplines of Material Science, new methods like Selective Laser Micro Synthering (Journal of Physics Conference Series, volume 276 ISSN: 1742-6588) Spark Plasma Sinthering and Hot Isostatic Pressing ( JOURNAL OF ALLOYS AND COMPOUNDS Volume: 504 Pages: S323-S327 ISSN: 0925-8388) are being constantly developed and the influnce of that type of production is growing. Many dont appricieate the significance of Powder Technologies as the “workhorse” of hightech industry especially in tearms of manufacturing processes that involve high hardness materials mashining, mainly metals, that would not be possible whiteout the ultrahard mashining tools made from powders. Powder technologies allowe for a more uniform or homogenous structure of the material and significantly higher level of influence on the composition of the produced material or detail. Also due to the specifisc of the process that frequently reseamble plastic moulding in tearms of the actual technology and even simulations of the process (Powder Injection Molding (INTERNATIONAL JOURNAL OF POWDER METALLURGY Volume: 46 ISSN: 0888-7462) , a multitude of geometries can be crated from materials that previously would require mashining and by such would be limited in the scope of shapes that could be created, thus Powder Technologies solve a multitude of technological problems. The most recent development in Powder Technoligies has been seen in the sector of 3D printing where a multitude of materials are used in powdered form starting from various plastics to metals or compounds of metals like aluminium. Also nanotechnology of the new century is considered a part of Powder Metallurgy (http://www.mpif.org/newsroom/facts.pdf). Technology is indispensable in the production of porous materials used, but not exclusively, in oil and chemical industries as filters and oter parts of their production processes. The fact of ease of use and high degree of controll of porosity and ad-mayorem significant controll over the grain size/growth that alowes for pores of microscopic size to even 100mm(http://www.afssociety.org/education/0907oneminute.htm) to be uniformly distributed and created makes the technology indispensable in the creation of self lubricating porous bearings that can be seen as omnipresent and taken for granted, also used in sophisticated machines of nuclear or aeronautical industries.
2.2 Description of different metal clay products
Metal Clay is a powder metallurgy derivative that incorporates all standard Powder procedures but with a much reduced technical requirements. As with normal Syntering process heat and preasure is applied but to a significantly lower intensity, which allowes the technology to be used by craft jewelers, artists and enhusiasts. The clay consists of finely powdered metal and an organic non toxic binder, it is sold ready to use in sealed packaging that keeps the material in required humidity and consistency, alloving for it to be imediatly worked on. In the method varoius mterials are used, platinium, gold, silver, bronze, copper or even steel. There are two main types of Metal Clay on the market:
a) Precoius Metal Clay (PMC)
The first to be developed in Japan in 1990 by Masaki Morikawa ( U.S. Patent 5,328,775) working for the Mitsubishi Materials Corporation. Initially the technology was developed using solid-phase sintered gold and later devoped to use silver. The initial formula called PMC standard had a significant drawback caused by the necessity of firing of details in kilns and required a temperature of 900C for binding to occure, also a huge 30% shrinkage made it difficult to create fitting jewelery pieces. The limitations resulted in the development of PMC+ that could be fired at 810C with a shrinkage in the region of 15% and also allowed for detail to be fired using a hand held torch. The last developed version was PMC3 that had the same shrinkage as PMC+ and also could be fired using a handheld torch but it lovered the required sinthering temperature to 599C(http://www.pmcguild.com). Mitsubishi manufactures also platinium and gold varieties of PMC but those are not obtaineable outside Japan.
b) Art Clay Silver (ACS)
Developed in japan by AIDA Chemical Industries. In comparison to PMC the technology developed by AIDA has a significantly lower shrinkage in the region of 8-10% and is readily availeable as gold clay, silver clay, bronze clay, copper clay. The standard range requires a synthering temperature of 800C. The company developed a range of slow dry clays that allowe for a prolonged working time whiteout the loos of plasticity or cracking. The lower synthering temperature Art Clay 650 is availeable in slowdry and standard versions and can be fired in 650C for 30 minutes or at 780C in just 5minutes (http://www.artclayguild.co.uk). The company developed supplementary products that come in the forms of syringe clay, paste, overlay paste, oil paste, paper clay and gold foil. The company just recently developed Art Copper Clay that can be fired using a Kiln or a torch whiteout the neccesity of using baths of activated carbon to protect the material from oxidation.
2.3 Detailed description of the PMC method based on the first patent (us patent 5.328.775)
After an extensive research focused on obtaining a product that would after completion contain no byproducts or residues of the binder, the development came to a fruition when by addin water to a cellulose powder reaserchers created a “jellylike cellulose”. As both components are removed from the final product by evaporation in case of water and during the high temperature synthering cellulose burns out leaving a silver detail of .999 (pmcguild.com) purity. To prevent the mixture from adhearing to surfaces or modellers hands an additive of di-n-butyl phthalate is mixed into the compound, this additive is also removed during the synthering phase of the process.
Ammounts of components, specific properties of the mixture and the justification of their those qualities:
Cellulose is a polisacharide consisting of a varied lenght chains of glucose. The main justificatoin of the use of cellulose as a binder is its non-toxisity and the assurance of total dispertion during the synthering process ad cellulose while burning reduces to CO2 and water. In the solution ethyl and methyl cellulose is used. The cellulose is to be mixed with water to create the jelly substance in proportions from 5/95 to 30/70 parts of cellulose/water. The solution should be mixed with the sinthered metal in the region of 0.8-8% of total mass. As the main property of the cellulose used is the quality of gelling while heated it was discovered that quantity of less than 0.8% negates that quality while a mixture containing more than 8% of the gelly cellulose would have a much lower viscosity to the extent that would not allow the mold to hold shape.
Non stick and surface-active additives
Surface-active additive is a substance that brakesdown solid waste of the reaction of the cellulose with water thus, it should be added in a region of 0.03-3% of the celulose mixture mass in case of the surface-active agent. The boudaries are justified by the facts that a solutions containing less than 0.03% of a surface active additive would not benefit from the qualities that the additive would grant and solutions with 3% and more would develop a high viscosity that would not allow easy molding. The patent lists “alkyl benzene sodium sulfonate” and “polysoap” as preffered substances. For adherence prevention an agent like oil ot fat should be added. The regions required are 0.1% to 3% of tottal mass respectivelly as quantities below the required treashold would not yeald the desired qualities and if the content would be higher than the required the mixture would become oily and handling would be gratly impared. The Patent lists hihger organic acids and esters like “phthalic acid” and di-n-butyl phthalate. Also higher alcohols can be used as adherence prevention agents.
Precious Metal Powders (PMP)
PMP is produced using “gas atomising” or “water atomising” processes explained in detail further, due to passive chemical qualities of preciuos metals the process of submerged reduction cannot be used except the production of gold powders. PMP can be used as pure single metal like in the case of silver used in the presentation or by alloying, mainly used in the production of 18k gold clay. The alloys are used to obtain specific colors, mechanical and synthering qualities. Addition of copper for instance results in a red tint of golden product. PMP were found to be usefull when mixed with the binder in the region of 50-90% of tottal mass. The justificaton behind that derrived from the experiments by the Mitsubishi team is that if the content would be below 50% the synthering process would not occure, while contents of 90% and above would decline the plasticity and strenght of the mixture to the extent that would not allow modeling. Another important factor is the grain size. It was discovered that an average grain size must be smaller than 200um as the result of higher grain size would result in simmilar unvanted qualities as when using more than 90% of PMP.
2.4 Manufacture technologies of Metal Powders
Atomisation – a process of producing metal powders on a comercial mass scale widely regarded as the most effective for producing large amounts of powdered materials. The process starts by melting of the metal in a induction furnace (other types of furnaces can be used but induction furnace has proven to be the most effective) . Depending on the different setups and wether a constant flow can be acheaved or a “batch” production is required the liquid metal is fed trough a tundish that controls the steady flow of metal to the atomising vessel as a steady stream or as a dispersion trough a nozzle. Then the stream of liquid metal is bombarded by the atomising gas or liquid and the stream or dispersion is further dissipated into a fine powder.
As the process is constantly developed the actual definition can be argued as not fit but general consensus in literature is that sintering is, a process used to create density controled products using powders and application of thermal energy and preasure, where adheresion occures below the melting point of the processed material. It can be separated into two main categories Solid-state Sintering and Liquid state Sintering there. Other types of syntering can be distinguished like “transient liquid phase sintering”, “viscous flow sintering”. The relation between different subgoups of the process is visualised in FigDHFJHFH
FigASGAR. Sintering grouping in alloys Souce(Sintering : densification, grain growth, and microstructure – Kang, S.-J. L. (Suk-Joong L.))
2.6 The Experiment
4. Coating Technology and Fluidic Coating of Steel
In the technology of antycorosive protection, plastics find a multitude of uses mainly for economical reasons. For metal corrosive protection we use plastics in multiple forms, such as. Sheets, laminates (applied directly on the protected surface), pastes (coating by the use of gas flame diffusion or melting of coatings in high temperatures), powders, foiles. The most popular methods of powder coating are: fluidisation and electrostatic, in a much smaller degree flame or flameless spraying. IN all those methods the powder is melted on the surface of the coated object to create the coating. The process is taking placein atmospheric preasure and heat is delivered to heat the object before the coating proces in the fluidisation method or after the powder was applied as in the electrostatic method.
4.2 Coating meterials
Coating materials ca by used in the form of pasts dyspertions, liquids, plastic and other material mixtures not containing a solvent. Thus the materials applied create a surface with a specific thickness, bonded thightly and displaying a specific set of phisicial, mechanical and chemical properties. For the creation of coatings the substance used must therefore fulfill those needs:
a) From the lquid state its possible to create using simple phisical or chemical process a solid state.
b) In liquid state they must display the ability to moisturise the surface, should have a specific process and time of solidification (gelling, hardenning, drying) consistency and viscosity and the abitily to adhere.
c) In solid state thye must be able to adhere to the surface, kohesion, elasticity, hardness, resistance for ageing and environmental resiatance.
The main componenet of coating materials are themnoplastics and plastics that solidify in higher temperatures. In such materials stabilisators might occure as well as pigments or plastifiers.
4.3 Methods of preparation of the coated surface.
Adeqate surface preparation is pivotal to the performance of any coating. Surface of objects, on which the coating can be applied, should be preemtively prepared. Preparation consists of cleaning off all contaminants and reducing smoothness as adhesion accures much better on rough surfaces. The surface must be cleaned of all contaminants like millscale, rust, all salts, preproduction compounds by the use of hand or power tools, greases and oils in the proces compoundly called degreasing. The process involves wiping, which must be done immacualtly as the later solvent bath would spread the contaminant in a fine fil rather than remove minimal amounts. Baths can be made in varoius forms, ranging from steaming to emulsions and solid compound baths, in the case of the samples provided ammonia was used. Blast cleaning processes like “sand blasting” or various forms of “hydroblasting” are due to theyr affectiveness and economy videly used in the industry, also the fact of the bility of preparation of a detail fully for production using one process is a great bennefit to. Respectively, the profile of the surface is to be “cleand”, to reduce the possibility of corrosion starting in a“seeded” maner, in a part of unsatisfactory geometry that would empede the adheerence of the coating.
The preparation of the surface must be conducted accordingly to ISO 8504:1992(E)
4.4 Applying the coating using the fluidisation method.
The flow of the process was shown on the table XXY. The powder is contained in a wessel with a porous botom. If a steady flow of compressed air is introduced at a certain moment an expantion of the load occures. It reaches the point of loosening and the particles would start to move and flow between each other. The fluidisation process is dependent on the ability to create a solution of solid bodies in a stream of gas.
4.5 The interferances of fluidisation
The basic interferances are:
Where the fase of diffrent viscosities can be easily distinguished
A fault in process where baubles of air are visible
Where the susspension is separated into layers
Where the air creates streaks in the suspension
4.6 Mechanism of the creation of the coating
The creation of the coat on metal surface by using the fluidising method is the result of the contact of the plastics with the heated surface of the metal object. In a steady stream of particles the proces would occur till a substantial decrease in temperature. Untill the heat of the object will not be sufficient to melt and adhere any more particles.
In the process of the creation of a coat in a fluidal medium we can distinguish 3 stages:
a)A creation of a surface of single particles that are being melted due to the direct contact with the heated surface
b) Growth of the thickness of the coating due to the melting process of melting occuring on the point of contact of the particles with already melted coat. The factor of growth in that fase is the ability to convect the heat trough the melted coating.
c) Halt in the growth of the thickness of the surface due to the loss of heat of the object and a high thermal resistance of the plastic.
The flow of the temperature change in the coat is displayed on the FigX where t1 represents the temperature of the coatant, t2 the temperature of the heated surface and t3 the melting piont of the compound. While the temperature is t2>t>t3 the growth of the coating occures. The growth is sharpelly halted when t falls below t3.
4.7 Aparatus and equipment used to apply coatings
The aparatus used in the excerscise is a double botom vessle with a solid and porous bottoms, trough which the compressed air is being pumped trough. It is posible to use a passive gas like nitrogen or CO2 to negate the harmfull influenco of the contact between the heated surface and oxigen, as corrosion occures much faster in heightened temperature. Due to practical and economica reasons the most frequently used fluidising gas is compressed air from various sources.
4.8 Flaws and defects of coatings
-change of collor – occures as a result of overheating
5. Ultrasonic Testing
5.1 Hardness Testing