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Tests

Every ceramic production facility should have some sort of materials, body and glaze testing program in place. Amazingly, many large factories have little or no testing! Then one day the kiln operator notices a large number of cracked, warped and off-size items and every one in the plant is blaming him. Likely the real causes are in a number of places earlier in the production. This underscores one of the primary reasons for testing and quality control: to establish specifications and to set off procedural alarms when test results fall outside those specifications so problems can be identified before a product goes to the next step of production.

It is not easy to know where to start when it comes to setting up a testing program. The huge array of ASTM test procedures, their complexity, test equipment requirements and their expense intimidates many people (try finding tests for ceramics on their website to see what I mean). These tests are great if you want to generate numbers that can be compared across an industry (for data sheets for example). But if you only need to do testing within your own facility to determine product consistency, a simpler and more accessible approach is better. Of course, either way, there is the problem of dealing with the mountain of data that is generated by a quality control program. The is where good software comes in (e.g. Digitalfire 4Sight Server).

Where do you start? Think of it this way: What physical properties of your bodies and glazes are important to maintain and are signals of changes you need to be aware of. For plastic bodies likely you want to monitor particle size distribution, drying shrinkage, water content, fired shrinkage and fired porosity. Two tests (SIEV and SHAB) can give you all of this information. You might like to add the DFAC test if you are using a plastic forming body. For casting bodies you must also watch rheology properties (use the RHEO test). For productions glazes use the GLAZ test to maintain the slurry (others will of course to need for color, surface, hardness, expansion, etc). Remember, we are talking about where you start here, of course there is no limit to how fancy a quality control program can be.

Tests in this database are defined as Multi-variable or Single-Variable. Single-variable tests are used to define a value for a specific property. For example, the melting point of a material is specified under the MLPT test and simply appears on pages as a label and a value. Multi-Variable tests are where data is being collected and measured over time and the system compiles and computes results and displays them accordingly. Data values for multi-variable tests are recorded with the Sample/Test/Specimen/Variable to uniquely identify them. For example, in the SHAB test you collect the dry length, fired length, fired weight and boiled weight for a number of specimens of a particular clay body run and the system generates a chart showing the data, the calculated dry and fired shrinkages and the porosity.

Related Information

Links

Articles Low Budget Testing of the Raw and Fired Properties of a Glaze
There is more to glazes than their visual character, they have other physical properties like hardness, thermal expansion, leachability, chemistry and they exhibit many defects. Here are some simple tests.
Articles Outdoor Weather Resistant Ceramics
How can you be sure that the porosity of your fired ceramic ware is low enough to prevent freeze-thaw breakdown in the winter?
Articles Are You in Control of Your Production Process?
Potters often run operations that are on the edge of control tolerating production and ware problems that industry would not. However ethics will sooner or later demand a better knowledge of process and materials.
Articles Firing Clay Test Bars
Being able to make good consistent test bars and fire them in a consistent and proper way is a basic requirement of getting valid results for shrinkage and porosity measurement.
Articles Understanding Thermal Expansion in Ceramic Glazes
Understanding thermal expansion is the key to dealing with crazing or shivering. There is a rich mans and poor mans way to fit glazes, the latter might be better.
Articles The Physics of Clay Bodies
Learn to test your clay bodies and recording the results in an organized way and understanding the purpose of each test and how to relate its results to changes that need to be made in process and recipe.
Articles A Low Cost Tester of Glaze Melt Fluidity
This device to measure glaze melt fluidity helps you better understand your glazes and materials and solve all sorts of problems.
Glossary Firing Shrinkage
During drying, clay particles draw together and shrinkage occurs. During firing the matrix densifies and shrinkage continues. More vitreous bodies shrink more.
Glossary Clay Body Porosity
In ceramics, porosity is considered an indication of density, and therefore strength and durability. Porosity is measured by the weight increase when boiled in water.
URLs http://www.astm.org/Standards/glass-and-ceramic-standards.html
ASTM Ceramics and Glass Testing Standards

By Tony Hansen


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