The curves area characterized by an elastic region, which is related to the rigidity of the mass against the deformation. Furthermore, it is possible to distinguish an elastic limit, where the clay begins to enter the plastic region, that is, if a force is imposed on it, it retains its shape after removal of that force. This would be the region from which the work of conformation has significant effects. Figure 5 shows a typical sequence of events related to the so-called barreling effect during compression test.
This effect is attributed to the attrition between the punch and the clay. To avoid errors associated to the measurement, the radius was estimated from the contact surface between the punch and the compact, and at the intermediate height of the sample.
An average value was then calculated from those points. From the results presented in Table 4 , a relationship between the effective stress of compression and the moisture can be observed. In Figure 6 it can be seen that there is a good correlation between these two parameters within the same type of clay. However, there was no correlation between these parameters, when different clays are compared.
This can be explained by differences in chemical and phase composition of the clays, which develop different plasticity despite the similar moisture content. The plasticity measured from compression tests allows that the results obtained by the mathematical modeling may be applied to describe the behavior of a clay during shaping processes such as extrusion 16 or pressing.
In this work, the compression test to characterize the plasticity of clay-water systems was applied. This type of test may serve as a complement to Atterberg's and Pfefferkorn's traditional tests, since it allows more precise information, is less operator-dependent in performing the tests and also some characteristics are obtained for the design of the process to which the clays will be submitted.
It was observed that there is a correlation between the effective stress of compression and moisture present in the mass. This condition was valid only within each group of clay, since equal humidity may produce different results in clays with different compositions.
Although the coefficient of friction is a dynamic variable depending on the test and process parameters, in this work it was considered constant, due to the difficulty of its formulation. New studies may be performed to observe if there is a correlation between the phases present in the clays and the coefficient of friction. A quantification of this influence should be included in a further modeling in order to optimize the processing parameters in accordance with the mass formulation.
Abrir menu Brasil. Materials Research. Abrir menu. Keywords: clays, extrusion, plasticity, modeling 1. Introduction The plasticity in the processing of ceramic materials is a fundamental property since it defines the necessary technical parameters to convert a particulate ceramic body to a component with a given shape by application of pressure.
Mathematical Modeling of Compression Test The mathematical knowledge applied to metallic porous materials was used as a basic tool for plasticity modeling of clays 10 taking into account few experimental parameters. Reed JS. Principles of Ceramic Processing 2 nd ed. New York: Wiley; Plastic behaviour of different ceramic pastes processed by extrusion.
Ceramics International ; 31 4 Workability test method for metals applied to examine a workability measure plastic limit for clays.
Applied Clay Science ; 20 On the mechanics of cold die compaction for powder metallurgy. Any particular clay's plasticity is greatly influenced by the clay's particle size, water content, and aging. The more workable a clay is, the easier it is to mold into whatever shape you desire. There are two types of workable clay, one which has more elasticity, the other which has a wider variety of different minerals in it, for example, grog, which will make the clay a little easier to work with.
There are three primary groups of clay minerals and each one of them is formed with their own distinct properties. They are kaolin, Illite, and Montmorillonite. Looking a little more in-depth into how clay is formed, UCL states that "clay is the common name for a number of fine-grained earthy materials that become plastic when wet.
Clay rocks can contain up to 40 percent of water within them. A pure clay of which there are said to be around 30 types is one that is not made of any other materials; a clay body is made up of many different clay materials like kaolin or grog. There are hundreds of types of clay bodies, as there are so many different types of combinations of clay minerals. The main three types, which you may well work with are porcelain, stoneware, and earthenware.
Individual clay particles are absolutely tiny and measure in at smaller than 0. Flocculation happens when the particles clump together, and deflocculants usually an alkaline material are commonly used by potters to disperse these tiny particles repelling them against each other. It is easy to find out how plastic a clay is. Make a coil of the clay and then wrap it around your finger. This tester can be useful with glazes also, since they employ clay which most do they have plasticities that is what hardens them on drying and suspends them in a slurry.
The degree of plasticity walk a line between enough to deliver needed dry hardness but not too much to produce drying cracks. This thrown vessel has sat on this plaster bat for almost 24 hours and yet still has not released. The bat was dry. It had to be slowly pried off with a flat scraper which deformed it somewhat.
When clay bodies are high in ball clay and bentonite they dry slower. If this is taken to an extreme, it can slow down production.
This item was made in India. Their pottery tradition expects that ware can be sun-dried immediately after it is made. To make that possible their clay bodies have low plasticity and lots of large particle sizes. They have learned to work with these and regard them as normal. However potters in the west would find bodies like this unusable they are accustomed to taking lots of care in drying in exchange for having much more plasticity.
However, if Indian potters let the fine plastic clay portion of the body recipe decline too much then this type of surface-cracking issue can occur. This shows the soluble salts in the material and the characteristic cracking pattern of a DFAC test disk when made from a low plasticity clay. Notice the edges have peeled badly during cutting, this is characteristic of very low plasticity clays.
It takes alot of time to dewater on a plaster bat. But, these are like nothing I could make from any other material. They are incredibly refractory fired to cone 10 they look like bisqued porcelain.
However I have had mixed results for thermal shock resistance. Worthington Clear is a popular low fire transparent glaze recipe. GB is also very plastic, like a clay. I have thrown a pot from this recipe! This explains why high Gerstley Borate glazes often dry so slowly and shrink and crack during drying. When recipes also contain a plastic clay the shirinkage is even worse. GB is also slightly soluble, over time it gels glaze slurries. Countless potters struggle with Gerstley Borate recipes.
How could we fix this one? Second: It is possible to calculate a recipe having the same chemistry but sourcing the magic melting oxide, boron, from a frit instead. Boxes are 20kg Plus there are enough trimmings to make about two more. That is about g of pugged clay per mug. These have been trimmed and engobed using our standard cone 6 engobe and are drying.
Notice I have waxed the outers of some of the handles to slow their drying down to keep it in sync with the mug itself. M is likely the most plastic native Plainsman body. Although it was not overly soft I stiffened up the clay for ten minutes on a plaster bat to make it my ideal throwing stiffness. This is from half a box!
Polar Ice porcelain double the price of others. Why use it? Because it is so plastic that you can make more pieces, many more, enough to more than pay the extra clay cost. And you can charge more for each piece. These have a weight-to-capacity ratio of 1. That means the mug itself is lighter than the weight of water it can hold each 1 gram of fired porcelain can contain 1.
This is much better than most other clay bodies. Pure kaolins are clay. It seems logical that "pure clay" is plastic. However most kaolins are not plastic compared to a typical clay for throwing or modelling.
This is because they have a comparatively large particle size compared to ball clays, bentonites, etc. This small bowl was thrown from 6 Tile kaolin. It is, by far, the most plastic kaolin available in North America. It's throwing properties are so good that one might be misled into thinking it should be possible to make pottery from it. Unfortunately, if it was survive drying without cracks, it would not make it through firing without this happening.
This was fired, unglazed, to cone 6. Pure kaolin particles are flat and the throwing process lines them up concentric to centre. So shrinkage is greater across than along them. A filler is needed to separate the kaolin particles. All pure kaolins are also refractory , so even if this bowl had not cracked, the porosity of this piece is very high, completely impractical for functional ware it needs a flux like feldspar to develop fired maturity. Louise Solecki Weir working on one of her large sculptures.
Sculptors can be passionate about the clay they use. For good reason, they have a lot to lose. While it might seem that Louise would be most concerned about drying shrinkage and drying performance resistance to drying cracks , not so.
To her, the ability to re-wet sections that dry out is paramount. And she has learned to overcome drying challenges posed by the high plasticity to benefit from the smooth texture, workability and rewetability it offers. How plastic is this clay Plainsman F96?
All four of the clays are highly plastic to super plastic. These offer a far higher surface area than coarse grog and provide channels for water to re-enter. If you would like the recipe of this body non-production please contact us.
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