ASTM C326-09(2018)

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

SIGNIFICANCE AND USE
2.1 The purpose of this test is to obtain values of shrinkage after drying and firing of clays or bodies or both, under various processing conditions to enable designers to determine the proper size of mold or die so as to produce a predetermined size of fired ware.
SCOPE
1.1 This test method covers the determination of linear shrinkage of ceramic whiteware clays, both unfired and fired.  
1.2 The values stated in inch-pound units are to be regarded as standard. The values given in parentheses are mathematical conversions to SI units that are provided for information only and are not considered standard.  
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.  
1.4 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

General Information

• Status: Published
• Publication Date: 30-Sep-2018
• ICS: 81.060.10 - Raw materials
• Technical Committee: C21 - Ceramic Whitewares and Related Products
• Drafting Committee: C21.04 - Raw Materials

Relations

• Replaces: ASTM C326-09(2014) - Standard Test Method for Drying and Firing Shrinkages of Ceramic Whiteware Clays
• Effective Date: 01-Oct-2018

Overview

ASTM C326-09(2018): Standard Test Method for Drying and Firing Shrinkages of Ceramic Whiteware Clays is an internationally recognized standard developed by ASTM International. This method provides a reliable procedure for determining the linear shrinkage of ceramic whiteware clays during both drying and firing processes. Understanding shrinkage values is crucial for ceramic manufacturers, designers, and processors, as it informs the proper sizing of molds or dies to achieve the desired final dimensions of fired ceramic ware.

Key Topics

• Shrinkage Measurement: The standard explains the methodology to measure the linear shrinkage of ceramic whiteware clays from the plastic state through drying to the fired state. Consistent specimen preparation and the use of accurate measuring tools are emphasized for precise results.
• Test Specimen Preparation: Specimens can be prepared through casting, extrusion, or pressing in metal molds. Proper handling and identification of each specimen type are necessary to ensure accurate shrinkage data.
• Calculation Methods: The standard provides formulas for calculating:
  • Linear drying shrinkage (percentage reduction after drying)
  • Total linear shrinkage (percentage reduction after both drying and firing)
  • Volume shrinkage (when required, based on linear values)
• Process Variability: Recognizing that forming methods and specimen orientation can affect shrinkage outcomes, the standard advises careful recording of specimen preparation and measurement processes.
• Safety and Unit Standards: ASTM C326 uses inch-pound units as the primary measurement standard, with SI conversions for informational purposes. Users must observe standard safety, health, and environmental practices.

Applications

Implementing ASTM C326-09(2018) offers significant benefits in various ceramic industry processes:

• Mold and Die Design: By quantifying drying and firing shrinkages, designers can accurately determine the necessary oversizing of molds or dies for forming products like tiles, sanitary ware, tableware, and other ceramic components.
• Quality Assurance: Consistent application of this test method enables manufacturers to monitor batch-to-batch consistency of raw materials and finished products, ensuring dimensional accuracy and high product quality.
• Process Optimization: Data from shrinkage testing assists in adjusting clay body formulations, firing schedules, and forming techniques to minimize dimensional defects and improve the reliability of ceramic parts.
• Research and Development: Material scientists and engineers use the test method to evaluate new clay blends, glazes, or manufacturing technologies, supporting innovation while maintaining product standards.

Related Standards

Several other standards complement or relate to ASTM C326 within the ceramics industry and broader materials testing context:

• ASTM C20: Standard Test Methods for Apparent Porosity, Water Absorption, Apparent Specific Gravity, and Bulk Density of Burned Refractory Brick and Shapes
• ASTM C373: Standard Test Method for Water Absorption, Bulk Density, Apparent Porosity, and Apparent Specific Gravity of Fired Whiteware Products
• ISO 10545-2: Ceramic Tiles - Determination of Dimensions and Surface Quality

These standards, among others, enhance the effectiveness of quality control and product development in ceramic manufacturing when used in conjunction with ASTM C326-09(2018).

Keywords: ceramic shrinkage, drying shrinkage, firing shrinkage, whiteware clays, ASTM C326, ceramic testing, mold design, ceramic processing, dimensional accuracy.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: C326 − 09 (Reapproved 2018)
Standard Test Method for
Drying and Firing Shrinkages of Ceramic Whiteware Clays
This standard is issued under the fixed designation C326; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope* of specimens rigid enough to allow careful handling without
distortion immediately after the test specimen is made. Plastic-
1.1 This test method covers the determination of linear
formed test specimens shall be made either by extrusion or by
shrinkage of ceramic whiteware clays, both unfired and fired.
pressing in a suitable metal mold. Where a vacuum pugmill is
1.2 The values stated in inch-pound units are to be regarded
used, a vacuum of not less than 25 in. (635 mm) Hg shall be
as standard. The values given in parentheses are mathematical
maintained during the forming operation. Where no vacuum
conversions to SI units that are provided for information only
attachment is used, the plastic clay shall be thoroughly hand-
and are not considered standard.
wedged to eliminate entrapped air as a preliminary to forming
1.3 This standard does not purport to address all of the
test pieces.
safety concerns, if any, associated with its use. It is the
3.3 The test specimens, cast or plastic-formed, shall be
responsibility of the user of this standard to establish appro-
suitably identified and marked with shrinkage reference lines
priate safety, health, and environmental practices and deter-
4 in. (102 mm) apart on the long axis of the specimen. The
mine the applicability of regulatory limitations prior to use.
shrinkage reference lines may conveniently be made with a
1.4 This international standard was developed in accor-
gage with knife edges at zero and 4 in. (102 mm) and marking
dance with internationally recognized principles on standard-
must be done as soon as the bars can be handled without
ization established in the Decision on Principles for the
distortion.
Development of International Standards, Guides and Recom-
3.4 The marked specimens shall then be placed on a lightly
mendations issued by the World Trade Organization Technical
oiled pallet with semi-circular grooves 0.40 in. (10.2 mm) in
Barriers to Trade (TBT) Committee.
diameter and allowed to dry at 68 to 100°F (20 to 40°C) for
2. Significance and Use
24 h. The purpose of the semi-circular (half round) grooves is
to maintain straightness of the bars during drying. During this
2.1 The purpose of this test is to obtain values of shrinkage
preliminary drying period, the bars shall be turned 90° several
after drying and firing of clays or bodies or both, under various
times at 2-h intervals to eliminate possible warping in the
processing conditions to enable designers to determine the
vertical direction.After the initial drying period, the specimens
proper size of mold or die so as to produce a predetermined
shall be placed in a drying oven at 200 to 230°F (100 to 110°C)
size of fired ware.
and further dried for 24 h.
3. Test Specimens
3.5 The drying shrinkage of the test specimens should be
3.1 Test specimens shall be round bars approximately
determined in accordance with Sections 4 and 5. The speci-
0.75 in. (19 mm) in diameter by 5 in. (127 mm) in length.
mens can now be fired according to a suitable firing schedule
to the desired temperature and the procedures of Sections 4 and
3.2 Test specimens may be prepared either by casting or
5 applied to determine the total shrinkage.
plastic forming, as circumstances require. At least ten speci-
mens shall be prepared. For cast specimens the molds may be
3.6 The test bars must be clearly identified as to whether
either one-piece, or two- or more-part molds; in either instance
they were cast or extruded, and shrinkage data likewise
sufficient space shall be provided to allow solid casting without
identified because of slight differences in shrinkage between
piping. Where plastic-forming is employed, the clay-water
cast and extruded bars.
m
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