Wear Rate of an Advanced Polymer Coating Experiment

Wear instal up of an Advanced Polymer Coating ExperimentCHAPTER 11.0 INTRODUCTIONThe general purpose of last is to protect the substrate and to be decorative, enhancing the appearance of substrate in terms of gloss, colour, adhesion and wetability. Consequently, in addition, surface properties such as resistance to outwear, indentation, and scratching atomic human action 18 critical to retain the basic functions 1, 2. Polymers argon common literals which be astray utilize in in sprinklery. Polymer polish acts as a protective covering in corrosive environments. The properties of polymers wait largely on the structures of someone polymer molecules, molecule habitus and sizing as well as how molecules argon arranged to ca-ca a polymer structure. Polymer molecules be characterised by their very large size a hold that distinguished them from separate nigh organic chemic compositions.The wear rate for an advanced polymer fabrics varies depending on the utilize norm al load and the slide speed which is affected by size, shape, the matrix composition and the test conditions 3. As the load decreases the contact becomes elastic with consequent changes in mechanism of friction. paste resin ar characterized by the presence of three- member cyclic ether group commonly referred to as an epoxy group, epoxies cross-link when a catalyzing agent (hardener) is added, forming a three-dimensional molecular(a) network. Beca put on of their outstanding bonding intensity level, epoxy resins are apply to nurse practical applications, adhesives, composite laminates and have important acts in the aerospace industry. Epoxy pulveriseise natural covering is still widely routined today, especially as a functional and tough application program where flexibility, adhesion, toughness and corrosion resistance are needed. Epoxy coatings are based on epoxy resin they are manufactured in a way which enables the possibility of coating to a certain thickness w ithout defect in the coating after(prenominal) curing 14, 16. Epoxy power coatings get a good adhesion to aluminium or nerve surfaces, and add a good corrosion protection layer (for indoor use). Most outstanding with pulverise finish is the excellent resistance against otherwise chemics. Epoxy demolish coatings are suitable especially in aggressive environments. However, they are non suitable for external use where they become dis washed-out as the pigments are disoriented down by ultra violet rays when undecided to sunlight. They consequently become chalky and actually reduced in thickness as they are washed away 15.1.1 AIMThe main(prenominal) aim of this roll is to determine the effect of sliding speeds on the wear rate of an advanced Polymer coating.1.2 RESEARCH OBJECTIVESThe objective of this offer is to investigate the wear rate of an advanced powder coating using a reciprocating linear ball-on- vapid sliding machine. collect to the nature of the resources requir ed to run the experiments, this investigation included the careful attention taken for wear testing especially in areas of the ball-on-flat sliding machine, data acquisition and wear rate calculation.The technical advance for the investigation will containd preparing polar test specimens vulcanised at temperatures of 140oC, 160oC, 180oC, and 200oC respectively. These test specimens would then be tested for one hour at sliding speeds of 0.02 m/s, 0.03 m/s and 0.04 m/s on a fixed normal load of 0.76 kg. Data from the wear testing would be acquired at once as galvanizing signals by with the help of electronic data acquisition devices. Also this would involve investigating and analysing the microstructure of the all the tested coated sample to see the level of damage done to it at the above temperatures and sliding speeds.CHAPTER 22.0 LITERATURE REVIEW2.1 POLYMERSModern scientific tools revolutionized the processing of polymers thus functional synthetic polymers like useful plast ics, rubbers and fibre poppycocks says (Satish V. Kailas) 38. As with other engineering materials (metals and ceramics), the properties of polymers are related their dowry geomorphological elements and their arrangement. The suffix in polymer mer is originated from Greek word meros which means part. The word polymer is thus coined to mean material consisting of many parts/mers. Most of the polymers are basically organic compounds, however they squeeze out be inorganic (e.g. silicones based on Si-O network). This chapter introduces classification of polymers, processing and synthesis of polymers, followed by mechanism of deformation and machinelike doings of polymers 10, 11, 38.Polymers are classified in several ways by how the molecules are synthesized, by their molecular structure, or by their chemical family. For example, linear polymers consist of coherent molecular chains, while the branched polymers consist of first ache chains and secondary chains that stem from th eir main chains. However, linear does non mean flat lines. The better way to classify polymers is according to their machinelike and caloric behaviour. Individually, polymers are classified into two main classes plastics and elastomers 10, 11.2.1.1 PLASTICSPlastics are plaster bandageable organic resins. These are either natural or synthetic, and are processed by forming or moulding into shapes. Plastics are important engineering materials for many reasons. They have a wide range of properties, many of which are unattainable from any other materials, and in most cases they are comparatively low in cost. Following is the brief list of properties of plastics light weight, wide range of colours, low thermal and electrical conductivity, little brittle, good toughness, good resistance to acids, bases and moisture, senior high school dielectric strength (use in electrical insulation), etc. Plastics are again classified in two groups depending on their mechanical and thermal behavi our as thermoplasts (thermoplastic polymers) and thermosets (thermosetting polymers) 10, 11.2.1.2 TYPES OF PLASTICS2.1.2.1 THERMOPLASTSThese plastics reveal when heat uped and harden when cooled processes that are totally reversible and may be repeated. These materials are normally sham by the simultaneous application of heat and pressure. They are linear polymers without any cross-linking in structure where long molecular chains are bonded to each other by secondary bonds and/or inter-wined. They have the lieu of increasing plasticity with increasing temperature which breaks the secondary bonds between individual chains. Common thermoplasts are acrylics, Vinyl resins (PVCs), polyethylene, polypropylene, polystyrene, polyimide, ABS (acrylonitrile butadiene and styrene) etc 10, 11.Acrylics (poly-methyl-methacrylate)They are characterised by outstanding light transmission and resistance to weathering only fair mechanical properties. Their applications are in the main in lenses, transparent aircraft enclosures (aeroplane windows), drafting equipment, and outdoor signs 17.PolystyreneThey have low specific gravity (1.07), availability in colours form clear to opaque, resistance to water system and most chemicals, dimensional stability, insulating ability. Polystyrene is an excellent rubber backup for electrical insulation. Styrene resin is moulded into battery boxes, dishes, radio parts, lenses, flotation gears etc 17.PolyethyleneThese materials are compromising at room and low temperatures, waterproof, unaffected by most chemicals, capable of being heat-sealed, and plunder be produced in a configuration of colours. Polyethylene, which floats on water, has a density range from 0.91 to 0.96% and is one of the inexpensive plastics, and its moisture-resistant characteristics ensure its use for packing and squeeze bottles 12, 17.Polyethylene PolymerTable 2.1 Properties of polyethylenePolypropylenePolypropylene has excellent electrical properties, high wallop and tensile strength and is resistant to heat and chemicals. Monofilaments of polypropylene are used in reservation rope, nets, and textiles.PolyimideThese thermoplastics are produced in the form of solids, gets or solutions. They have unusual heat-resisting properties up to 750oF (400oC), low coefficient of friction, high gradation of radiation resistance, and good electrical properties. Products from this include sleeve bearing, valves seats, tubing, and various electrical components. The films, tough and strong, are used for wire insulation, motor insulation, and printed circuit backing 17.ABS (Acrylonitrile, Butadiene, and Styrene)This plastic can be compounded to have a degree of hardness or great flexibility and toughness. The ABS plastics are used in applications that requires abuse resistance, colourability, hardness, electrical and moisture properties, and limited heat (2200oF (105oC). These plastics and processed by thermoforming injection, flow, rotational, and extrus ion moulding. Applications include household piping, cameras, electrical clear tool housings, telephone handsets, and canoes 12.Vinyl ResinsThese thermoplastic materials can be processed by compression or injection moulding, extrusion, or blow moulding. Vinyl resins are suitable especially for surface coating and flexile and rigid sheeting. The vinyl resins commercially available include polyvinyl chlorides (PVCs), butyrates, and polyvinylidene chloride. Polyvinyl chloride has a high degree of resistance, to many solvents and does not support combustion. It is used for rubberlike products including raincoat, packaging and blow-moulded bottles. Polyvinyl butyrate is a clear tough resin, which is used for interlayers in preventive glasses, raincoats, sealing fuel tanks, and flexible moulded products. It has moisture resistance, great adhesiveness, and stability towards light and heat 17.2.1.2.2 THERMOSETSThese plastics require heat and pressure to mould them into shape. They are fo rmed into a permanent shape and of age(p) or set by chemical reactions such as extensive cross-linking. They cannot be re- freeed or reformed into another shape but decompose upon being heated to too high a temperature. Thus thermosets cannot be recycled, whereas thermoplasts can be recycled. The term thermoset implies that heat is required to permanently set the plastic. Most thermosets composed of long chains that are strongly cross-linked (and/or covalently bonded) to one another to form 3-D network structures to form a rigid solid. Thermosets are generally stronger, but more brittle than thermoplasts 10, 11.An advantage of thermosets for engineering function applications includes the following high thermal stability, high dimensional stability, high rigidity, light weight, high electrical and thermal insulating properties and resistance to creep and deformation under load. There are two methods whereby cross-linking reaction can be initiated cross-linking can be accomplished by heating the resin in a suitable mould (e.g. bakelite), or resins such as epoxies (araldite) are cured at low temperature by the addition of a suitable cross-linking agent, an amine. Epoxies, vulcanized rubbers, phenolics, unsaturated polyester resins, and amino resins (ureas and melamines) are examples of thermosets 10, 11.PhenolicsThese resins for popular for thermosetting applications. The synthetic resign, made by the reactions of phenol with formaldehyde, forms a hard, high-strength, durable material that is capable of being moulded under a variety of conditions. It is characterized by excellent thermal stability to over 150oC (that is, has high heat and water resistance) and can be coloured in a variety of way may be compounded with a large number of resins, fillers 12. It is used in manufacturing coating materials, laminated products, grinding wheels, and metals as well as glass bonding agents, and can be cast into moulded cases, bottle caps, knobs, dials, knife handles, e lectrical appliance cabinets and numerous electrical parts 17.Epoxy ResinsEpoxy resins, both monomers and oligomers, can be powders or they can be thick and clear or yellow runninesss with strong and unpleasant odours. They are known for their excellent adhesion, chemical and heat resistance, excellent mechanical and good electrical insulating properties. Moulding a fibre reinforced epoxy composite is much easier compared to other thermoset resins 19. The typical applications of epoxy are in adhesives, electrical parts, coating and lamination process, moulds/dies/tools and in military, biomedical and self-propelled fields.Epoxy being a thermoset polymer, during the process of curing, when mixed with curing agent or harder, polymerises and cross-links. In other words, this curing agent reacts with epoxy resin monomers to form epoxy product. The curing agent plectrum will determine to a large extent the writ of execution of the final epoxy composite. Table 2 below shows the proper ties of epoxy resins.Table 2.2 Properties of Epoxy resinsEpoxy resins are the major part of the class of adhesives called structural adhesives. These high performance adhesives are normally used in the construction of aircraft, automobiles, bicycles, golf clubs, snowboards and other applications where strength bond are required. Also, they are exceptional adhesives for wood, metal, glass, and some plastics. Epoxy resins can be made flexible of rigid, transparent, opaque or coloured and fast setting or extremely slow setting. Furthermore, epoxy adhesives are unmatched in heat and chemical resistance among other adhesives. Usually requires heat curing for maximum performance 22. Therefore epoxy adhesives cured with heat will be more heat and chemical resistant than those cured at room temperature. Also, the peak adhesion strengths achievable for epoxy/metal interfaces depends greatly on the types and sequences of wet chemicals used to treat the surface. For all these reasons, they a re used in high performance and decorative flooring applications too 22.Epoxy coatings are in addition widely used as primers to repair the adhesion of automotive and marine paints especially on metal surfaces where corrosion resistance is important. However, they are not used in the outer layer of a boat as they can deteriorate when exposed to ultra violet light. But they are often used during boat repair and assembly and also over-coated with conventional paints or marine varnishes which can provide ultra violet protection 23. Also, metal cans and containers are often coated with epoxy to prevent rusting especially for foods like tomatoes, which are acidic in nature.In addition, epoxy resin is an excellent electrical insulator too. It helps to protect electrical components from short-circuiting due to dust and moisture. Hence, epoxy resins are important in the electronic industry, finding application in motors, generators, transformers, switchgears, bushings and insulators. Also , in the electronic industry, epoxy resins are the primary resin used in moulding integrated circuits, transistors and hybrid circuits. The cured epoxy is an insulator and a much better conductor of heat than air. Using epoxy in transformers and inductors greatly reduces hot spots which in turn give the component a stable and monthlong life than unprotected products 24. Another interesting property of epoxy is that it does not stick to mould liberation compounds like paraffin wax, polyethylene sheeting, sandwich bags and the non glued side of packaging tape which is of great use during lay-ups and also during the manufacturing of precision parts.Though epoxy resins are more expensive than any other resins such as polyester resins, in brief, the purpose of selecting epoxy as the base resin for this research is because of its un-matching high chemical and thermal resistance, good adhesion to various materials, compatibility with various substrates and other additives, low shrinkage, availability of solvent emancipate formulations, light in colour, easy to control viscosity and low vapour pressure besides place good to excellent mechanical properties and very good electrical insulating properties.The properties of polymers depend largely on the structures of individual polymer molecules, molecule shape and size as well as how molecules are arranged to form a polymer structure. Polymer molecules are characterised by their very large size a feature that distinguished them from other most organic chemical compositions.2.1.2.3 ELASTOMERSPolymers are long-chain molecules that are formed by polymerization (that is by linking and cross-linking of different monomers. A monomer is the basic building block of a polymer. One of the fascinating properties of the elastomeric materials is their rubber-like elasticity. That is, they have the ability to be deformed to quite large deformations, and then elastically spring back to their original form. This results from the c ross-links in the polymer that provides a force to doctor up the chains to their undeformed conformations. Elastomeric behaviour was probably fist observed in natural rubber however, the past fewer years have brought about the synthesis of a large number of elastomers with a wide variety of properties. Typical stress-strain characteristic of elastomeric materials is displayed in figure 2 curve.Upon stretchiness, it is immediately noted that there is a flat region in the stress-strain curve. This essentially means that after an initial elongation, there is a region stretching which occurs without increasing strain.2.2 CRYSTALLIZATION, MELTING AND GLASS TRANSITIONPolymers are known by their high sensitivity of mechanical and/or thermal properties. This section explains their thermal behaviour. During processing of polymers, they are cooled with/ without presence of presence from liquid invoke to form final product. During cooling, an ordered solid phase may be formed having a ext remely random molecular structure. This process is called crystallization. The melting occurs when a polymer is heated. If the polymer during cooling retains amorphous or non-crystalline state i.e. disturb molecular structure, rigid solid may be considered as frozen liquid resulting from glass transition. Thus, sweetener of either mechanical and/or thermal properties needs to consider crystallization, melting, and the glass transition.Crystallization and the mechanism elusive play an important role as it influences the properties of plastics. As in bent of metals, polymer crystallization involves nucleation and growth. Near to solidification temperature at favourable places, nuclei forms, and then nuclei grow by the continued ordering and alignment of additional molecular segments. Extent of crystallization is measured by volume change as there will be a considerable change in volume during solidification of a polymer. Crystallization rate is pendant on crystallization temperatu re and also on the molecular weight of the polymer. Crystallization rate decreases with increasing molecular weight.Melting of polymer involves transformation of solid polymer to viscous liquid upon heating at melting temperature, Tm. Polymer melting is characteristic from that of metals in many respects melting takes place over a temperature range melting behaviour depends on history of the polymer melting behaviour is a function of rate of heating, where increasing rate results in an elevation of melting temperature. During melting there occurs rearrangement of the molecules from ordered state to disordered state. This is influenced by molecular chemistry and structure (degree of branching) along with chain stiffness and molecular weight.2.3 POLYMER COATINGThe task of coating engine room is to provide surface protection, decorative finish and numerous special functions for commodities and merchandise by means of organic coatings. galore(postnominal) everyday products are only made useable and thus saleable because their surface treatment. To achieve this, germane(predicate) coating formulations, their production plant, the coating material and suitable coating processes for product must be available. However, the woodland to be achieved by means of coating process is not the only function of the coating material used. The object to be painted or coated itself with its specific material and design and appropriate application process are further variables which play a significant role. Coating itself is a layer of material which is use to a surface to decorate, preserve, protect, seal, or smooth the substrate usually applied by brushing, spraying, mopping, or dipping 26. There are two principal technologies that are the backbone of the coatings industry Liquid coating technology (wet), which has been applied for more than two centuries Powder coating technology (dry), which has been applied on an industrial case for some 30 years.2.3.1 WHY POWDER COAT INGThe global average annual growth for powder coatings has been approximately 7-9% over the last 10 years. From country to country worldwide these figures have varied considerably. This relatively high performance has been achieved by autonomous growth on the one side and by refilling liquid coatings on the other.Powder coating involves applying a finely grounded resin (powder) to a substrate and subjecting this powder to heat. During the heating process, the powder melts and creates a uniform, continuous coating 26. The use of powder coating as a finishing process has grown significantly in the past several years. It dates back to the 1950s when powders were flamed-sprayed on metallic surfaces to protect them from corrosion and abrasion. As the process evolved, most powder-coating application involved trim backing a heated part (sometimes referred to as a ware or a substrate) into a spang of fluidized powder. However, this process resulted in inconsistent film thickness. Electr ostatic introduced in the early 1960s, enabled powder coatings to be applied to cold substrates, resulting in more uniform, thinner surface application and thus, savings in raw materials 26.Today, powder-coating processes are employed in many production settings involving protective finishes. Powder formulations can be created to deliver cosmetic, protective, and length of service characteristic, and to achieve maximum hardness, chemical resistance, and gloss retention. More and more companies have turned to powder coating as a way to produce a high-quality finish while increasing production rates, peeled costs, and complying with increasing environmental pressures. Also, ongoing technological breakthroughs are continually knocking down the few barriers that hindered powder coatings ability to grow in the market.2.4 POWDER COATING MANUFACTURING PROCESSThe process of producing a powder coating is somewhat more complex, the equipments are numerous and the production time is somewhat long. This process can be simplified into 4 basic stages.2.4.1 PREMIXTUREThis is the first stage in the manufacture of a powder coating and is the most crucial for production. In this stage, the various sizes of resin flake, pigment powder, etc must be transformed into a homogeneous blend of similar sizes before they enter the extrusion stage.This is for the fact that the extruder is a simple melt mixer and not a very efficient disperser the premix equipment consists of a mixing bowl with a locking cover. The equipment is usually fitted with a cooling jacket capable of being filled with running water or cryogenic gases. Inside the mixing bowl are mixing-blades placed at different senior high and orientation to one another depending on the machine configuration 27.2.4.2 EXTRUSIONThis is the second stage of the powder coat manufacture. The extruder is composed of a horizontally placed barrel. Within the barrel is a cylindrical jailer shaft that is slightly smaller than the barrel in diameter. As the shaft turns, the premix moves forward through heated mixing zones. The mixing zones contain attachments called paddles that knead the melted premix and blends the various ingredients.2.4.3 GRINDINGThe ordinal phase (grinding stage) is very important to its performance. This is because the average particle size and dispersion are important in the application properties and final surface appearance. In the grinder, grinds the chilled and pressed extruded mix into fine particles. This is usually done using, impact/hammer mill, air jet mill or the air classifier mill.2.4.4 SIFTING AND CLASSIFYINGThe final structuring of the particle size is accomplished by passing the ground materials through sieves or cyclonic separators. This is to sort out the distribution and average particle size of the powder.2.5 ECONOMIC BENEFITS OF POWDER COATINGAlthough equipment and materials cost are similar in powder-coating and liquid-coating processes, yet powder coating processes provi de a number of advantages over other surface coating methods. These includeFewer rejects.Less floor space required.Less material waste. get down energy costs.Lower training and confinement costs.Lower waste-disposal costs.More efficient cleaning operations.More uniform finishes.Powder coating materials are immediately ready for use. They do not have to be mixed with any other ingredients such as solvents or catalysts and are easy to apply, thus labour costs associated with training, setup, and processing are low when compared with liquid-coating processes 26. Liquid coating usually requires thinning before application, leading to additional material and labour costs. This is not the case with powder coating. Liquid paint requires flash-off time before surface can re recoated which is not applicable to powder, meaning that racks can be spaced closer together and thus more parts per hour can be processed 25. Powder coating processes results in fewer rejects than liquid coating proces ses. Since the former is a dry process, air and water associated problems such as sags, runs, and contaminations are nearly eliminated. Blowing off the surface with an air hose and reapplying the powder can easily repair coating rejects in booth or application area.2.5.1 THERMOSETTING POWDERMost powder coating materials are thermosetting powders. The greatest technological advances in powder coatings are being made in this area. Thermosetting powders are composed of solid resins higher in molecular weight than resigns found in liquid coatings and lower in molecular weight than those found in thermoplastics.The solid resins melt and flow chemically, and cross-link deep down themselves or with other relative components forming a higher molecular weight reaction product. The coating film formed by this reaction is heat stable and will not soften back to a liquid on further exposure to heat (Wick and Veilleux 1985). At these higher temperatures, a coating emerges with different chemi cal properties than before heating.Cured coatings have different chemical structures than basic resins. Newly formed cured materials are heat stable and will not re-melt to liquid after further exposure to heat.These powders are ground from brittle resin systems into fine particles in the range of 0.004 0.0016 in (10 40 um) or less. Due to the rheology of these resin systems, they can produce thin like paint coatings in the range of 0.001 0.003 in (25 75 m) with properties equivalent or superior to coatings produced from liquid-compliance technologies 33.The types of resins commonly used in thermosetting powder include several(prenominal) types of epoxies Hydroxyl and carboxyl types of polyesters Several types of acrylics, and Several types of silicones.They require lower temperatures for curing than thermoplastic resins.Table 2.4 main properties of different types of thermosetting powder coatings27Thermosetting powders chemical reaction begins in oven. Ovens produce and maint ain heat-the sole cause of chemical reaction needed for in powder coating. P