ASTM C326 Standard Test Method for Drying and Firing Shrinkages of Ceramic Whiteware Clays

This test is widely used for ceramic body development, quality control, production planning, and evaluation of ceramic whiteware clay formulations. Drying shrinkage and total shrinkage after firing can be measured to predict the behavior of a ceramic body during processing and to adjust formulation and/or manufacturing conditions as needed.

Get Certified ASTM C326 Testing for Reliable Ceramic Product Development

Manufacturers use ASTM C326 testing to assess the shrinkage properties of ceramic whiteware clay bodies before full-scale production. Standardized shrinkage testing helps increase dimensional accuracy, optimize the process, and avoid manufacturing defects that can be detected by excessive or non-uniform shrinkage. Accurate shrinkage data also helps engineers design molds and tooling that produce ceramic products with the desired final dimensions. 

• Measures the linear shrinkage during drying of ceramic whiteware clays.
• Measures the total linear shrinkage after drying and firing.
• Determines shrinkage in volume from measured linear shrinkage, if needed
• Calculates the shrinkage rate for mold/die design.
• Assists in quality control and process optimization in the ceramic production process.
• ASTM C326 is primarily designed for use with ceramic whiteware clays and ceramic bodies used in the manufacture of products where dimensional accuracy after firing is important. 

What are the Uses of ASTM C326 Test Standard?

ASTM C326 is widely used for testing the drying and firing shrinkage properties of ceramic whiteware clays in ceramic manufacturing and testing laboratories. The analysis results are used to optimize production, adjust dimensional tolerance, and verify the design and quality of ceramic products. Common applications include:

• Determination of the drying shrinkage of ceramic whiteware clays.
• Calculating the overall linear contraction due to both drying and firing.
• Assists with quality control during ceramic manufacturing.
• Helping to design fired ceramic product molds and dies.
• Comparing the shrinking properties of clay bodies and clay formulations.
• Assisting manufacturers to make ceramic parts of uniform size and lower in manufacturing defects. 

What is Drying and Firing Shrinkage in ASTM C326?

The dimensional changes in ceramic clay specimens during the manufacturing process are called drying and firing shrinkage. Drying shrinkage occurs when water leaves the clay body, and firing shrinkage occurs during high-temperature firing as the clay is compressed and/or bonded. ASTM C326 describes these dimensional changes to assess the processing behavior of ceramic whiteware clays and determines the fired dimensions of the products. 

Why is Drying and Firing Shrinkage Testing Important?

The amount of shrinkage directly influences the dimensional accuracy, fit, and overall quality of ceramic products. Over-shrinkage or uneven shrinkage can cause warping, distortion, cracking, and dimensional error. Shrinkage may vary with clay composition, forming process, drying process, and firing schedule, so ASTM C326 gives manufacturers useful data to control their operations, select materials, and design their molds. 

How Does ASTM C326 Measure Drying and Firing Shrinkage?

After preparing the test specimens, technicians place reference marks 100 mm apart on each specimen. After drying, technicians measure the specimens using vernier calipers with 0.1 mm resolution, fire the specimens according to the specified schedule, and then measure them again. The measured lengths are used to calculate drying shrinkage, total shrinkage after firing, shrinkage factor, and volume shrinkage when required. At least five specimens are used to improve the reliability of the results, with the average measurements used. 

Common Challenges and Troubleshooting

Improper specimen preparation, entrapped air, uneven drying, non-uniform firing, warping of specimens, and inaccurate dimensional measurement can affect the accuracy of ASTM C326 results. Consistency of specimen dimensions, thorough removal of entrapped air during forming, controlled drying and firing procedures, rotation of square specimens for initial drying to minimize warping, and calibration of measuring instruments improve repeatability and reliability. Accurate and repeatable shrinkage measurements are obtained by standardizing the preparation and handling during testing. 

ASTM C326 Testing Technique, Process, and Data Collection Guide

Specimens of ceramic clay are cast, extruded, or pressed and provided with reference lines that are 100 mm apart. The specimens are initially dried under controlled air-drying and oven-drying conditions, and then the shrinkage measurements are made. After drying, technicians fire the specimens according to the specified firing schedule, allow them to cool, measure the final dimensions, and calculate the total firing shrinkage. The test report normally contains the following information: specimen identification, forming method, drying method, firing schedule, firing temperature, original size, dried and fired size, shrinkage calculations, shrinkage factor, and observations made during testing. 

Expertise: Skilled laboratory personnel provide accurate specimen preparation, dimensional measurements, shrinkage calculations, and accurate interpretation of results. 

Cost: This testing helps to reduce manufacturing waste, maintain dimensional consistency, optimize design of molds, and reduce production defects. 

Link to ASTM C326