The company produced insulating fire brick that are used for industrial applications. They wanted to remove the rejects or oversized regrind brick after the bricks had undergone the crushing process. For consistent material flow into a pub mill hopper, Vibratory Feeders can be applied in the process. However, it is not as standard as the EMF Electromechanical Feeder can provide a multitude of forces and frequencies. Though EMF Models are not typically used in dusty, hazardous environments, they can be fit with explosion proof Rotary Electric Vibrators to handle a larger load capacity.
Step 4: Mixing — To obtain a more chemically and physically homogeneous material prior to forming, the constituents of the ceramic powder is combined using the method of mixing or blunging. Most often, pug mills are the preferred piece of machinery used in this step of the process when dealing with dry mixes. It is also important to add binders or plasticizers as well.
Ceramic Processing | R.A. Terpstra | Springer
For wet slurry mixtures, a filter press would remove the water from the slurry and yield the clay body from the mix. For these wet mixtures, deflocculants and antifoaming agents are added to improve the processing of the materials. In the particular case of dry forming, vibratory compactio n can be used to achieve the desired shape. For molds of a smaller scale with a lighter load, Vibratory Jogger Tables may be desired but in cases that the mold is large, FA Flat Deck Vibratory Tables can be used.
Step 6: Drying — The formed materials hold water and binder in its mix that can in turn cause shrinkage, warping or distortion of the product. Generally convection drying is the most commonly used method in which heated air is circulated around the ceramic piece that alleviates the risk of such imperfections in the final product. Step 7: Glazing — Referring back to traditional ceramics, this step is added to the process prior to firing. Typically, the glaze consists of oxides that give the product the desired finish look.
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Show related SlideShares at end. WordPress Shortcode. Published in: Education , Technology , Business. Full Name Comment goes here. There is an increasing need in the military sector for high-strength, robust materials which have the capability to transmit light around the visible 0. These materials are needed for applications requiring transparent armour. Transparent armour is a material or system of materials designed to be optically transparent, yet protect from fragmentation or ballistic impacts. The primary requirement for a transparent armour system is to not only defeat the designated threat but also provide a multi-hit capability with minimized distortion of surrounding areas.
Transparent armour windows must also be compatible with night vision equipment. New materials that are thinner, lightweight, and offer better ballistic performance are being sought. Such solid-state components have found widespread use for various applications in the electro-optical field including: optical fibres for guided lightwave transmission, optical switches , laser amplifiers and lenses , hosts for solid-state lasers and optical window materials for gas lasers, and infrared IR heat seeking devices for missile guidance systems and IR night vision.
Now a multibillion-dollar a year industry, ceramic engineering and research has established itself as an important field of science. Applications continue to expand as researchers develop new kinds of ceramics to serve different purposes. Glass-ceramic materials share many properties with both glasses and ceramics. Glass-ceramics have an amorphous phase and one or more crystalline phases and are produced by a so-called "controlled crystallization", which is typically avoided in glass manufacturing.
In the processing of glass-ceramics, molten glass is cooled down gradually before reheating and annealing. In this heat treatment the glass partly crystallizes. In many cases, so-called 'nucleation agents' are added in order to regulate and control the crystallization process. Because there is usually no pressing and sintering, glass-ceramics do not contain the volume fraction of porosity typically present in sintered ceramics.
The term mainly refers to a mix of lithium and aluminosilicates which yields an array of materials with interesting thermomechanical properties. The most commercially important of these have the distinction of being impervious to thermal shock. Thus, glass-ceramics have become extremely useful for countertop cooking. The negative thermal expansion coefficient TEC of the crystalline ceramic phase can be balanced with the positive TEC of the glassy phase.
Ceramic forming techniques include throwing, slipcasting , tape casting, freeze-casting , injection moulding, dry pressing, isostatic pressing, hot isostatic pressing HIP , 3D printing and others. Methods for forming ceramic powders into complex shapes are desirable in many areas of technology. Such methods are required for producing advanced, high-temperature structural parts such as heat engine components and turbines.
Materials other than ceramics which are used in these processes may include: wood, metal, water, plaster and epoxy—most of which will be eliminated upon firing. These forming techniques are well known for providing tools and other components with dimensional stability, surface quality, high near theoretical density and microstructural uniformity. The increasing use and diversity of speciality forms of ceramics adds to the diversity of process technologies to be used. Thus, reinforcing fibres and filaments are mainly made by polymer, sol-gel, or CVD processes, but melt processing also has applicability.
The most widely used speciality form is layered structures, with tape casting for electronic substrates and packages being pre-eminent. Photo-lithography is of increasing interest for precise patterning of conductors and other components for such packaging. Tape casting or forming processes are also of increasing interest for other applications, ranging from open structures such as fuel cells to ceramic composites. The other major layer structure is coating, where melt spraying is very important, but chemical and physical vapour deposition and chemical e.
Besides open structures from formed tape, extruded structures, such as honeycomb catalyst supports, and highly porous structures, including various foams, for example, reticulated foam , are of increasing use. Densification of consolidated powder bodies continues to be achieved predominantly by pressureless sintering. However, the use of pressure sintering by hot pressing is increasing, especially for non-oxides and parts of simple shapes where higher quality mainly microstructural homogeneity is needed, and larger size or multiple parts per pressing can be an advantage.
The principles of sintering-based methods are simple "sinter" has roots in the English " cinder ". The firing is done at a temperature below the melting point of the ceramic. Once a roughly-held-together object called a "green body" is made, it is baked in a kiln , where atomic and molecular diffusion processes give rise to significant changes in the primary microstructural features. This includes the gradual elimination of porosity , which is typically accompanied by a net shrinkage and overall densification of the component.
Thus, the pores in the object may close up, resulting in a denser product of significantly greater strength and fracture toughness. Another major change in the body during the firing or sintering process will be the establishment of the polycrystalline nature of the solid. This change will introduce some form of grain size distribution, which will have a significant impact on the ultimate physical properties of the material. The grain sizes will either be associated with the initial particle size , or possibly the sizes of aggregates or particle clusters which arise during the initial stages of processing.
The ultimate microstructure and thus the physical properties of the final product will be limited by and subject to the form of the structural template or precursor which is created in the initial stages of chemical synthesis and physical forming. Hence the importance of chemical powder and polymer processing as it pertains to the synthesis of industrial ceramics, glasses and glass-ceramics.
There are numerous possible refinements of the sintering process. Some of the most common involve pressing the green body to give the densification a head start and reduce the sintering time needed. Sometimes organic lubricants are added during pressing to increase densification.
It is common to combine these, and add binders and lubricants to a powder, then press. The formulation of these organic chemical additives is an art in itself.
Ceramic Processing and Sintering
This is particularly important in the manufacture of high performance ceramics such as those used by the billions for electronics , in capacitors, inductors , sensors , etc. A slurry can be used in place of a powder, and then cast into a desired shape, dried and then sintered.
Indeed, traditional pottery is done with this type of method, using a plastic mixture worked with the hands. If a mixture of different materials is used together in a ceramic, the sintering temperature is sometimes above the melting point of one minor component — a liquid phase sintering. This results in shorter sintering times compared to solid state sintering. A material's strength is dependent on its microstructure. The engineering processes to which a material is subjected can alter its microstructure.
The variety of strengthening mechanisms that alter the strength of a material include the mechanism of grain boundary strengthening.
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Thus, although yield strength is maximized with decreasing grain size, ultimately, very small grain sizes make the material brittle. Considered in tandem with the fact that the yield strength is the parameter that predicts plastic deformation in the material, one can make informed decisions on how to increase the strength of a material depending on its microstructural properties and the desired end effect. The relation between yield stress and grain size is described mathematically by the Hall-Petch equation which is. Theoretically, a material could be made infinitely strong if the grains are made infinitely small.
This is, unfortunately, impossible because the lower limit of grain size is a single unit cell of the material. Even then, if the grains of a material are the size of a single unit cell, then the material is in fact amorphous, not crystalline, since there is no long range order, and dislocations can not be defined in an amorphous material.
It has been observed experimentally that the microstructure with the highest yield strength is a grain size of about 10 nanometres, because grains smaller than this undergo another yielding mechanism, grain boundary sliding. In the processing of fine ceramics, the irregular particle sizes and shapes in a typical powder often lead to non-uniform packing morphologies that result in packing density variations in the powder compact.
Uncontrolled agglomeration of powders due to attractive van der Waals forces can also give rise to in microstructural inhomogeneities. Differential stresses that develop as a result of non-uniform drying shrinkage are directly related to the rate at which the solvent can be removed, and thus highly dependent upon the distribution of porosity. Such stresses have been associated with a plastic-to-brittle transition in consolidated bodies,  and can yield to crack propagation in the unfired body if not relieved.
In addition, any fluctuations in packing density in the compact as it is prepared for the kiln are often amplified during the sintering process, yielding inhomogeneous densification. It would therefore appear desirable to process a material in such a way that it is physically uniform with regard to the distribution of components and porosity, rather than using particle size distributions which will maximize the green density. The containment of a uniformly dispersed assembly of strongly interacting particles in suspension requires total control over particle-particle interactions. Monodisperse colloids provide this potential.