ASTM C965-23

Standard Practice for Measuring Viscosity of Glass Above the Softening Point

SIGNIFICANCE AND USE
3.1 This practice is useful in determining the viscosity-temperature relationships for glasses and corresponding useful working ranges. See Terminology C162.
SCOPE
1.1 This practice covers the determination of the viscosity of glass above the softening point through the use of a platinum alloy spindle immersed in a crucible of molten glass. Spindle torque, developed by differential angular velocity between crucible and spindle, is measured and used to calculate viscosity. Generally, data are taken as a function of temperature to describe the viscosity curve for the glass, usually in the range from 1 to 106 Pa·s.  
1.2 Two procedures with comparable precision and accuracy are described and differ in the manner for developing spindle torque. Procedure A employs a stationary crucible and a rotated spindle. Procedure B uses a rotating crucible in combination with a fixed spindle.  
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-Apr-2023
• ICS: 81.040.10 - Raw materials and raw glass
• Technical Committee: C14 - Glass and Glass Products
• Drafting Committee: C14.04 - Physical and Mechanical Properties

Relations

• Refers: ASTM C162-23 - Standard Terminology of Glass and Glass Products
• Effective Date: 01-Oct-2023
• Refers: ASTM C162-05(2015) - Standard Terminology of<brk type="line"/> Glass and Glass Products
• Effective Date: 01-Nov-2015
• Refers: ASTM E220-13 - Standard Test Method for Calibration of Thermocouples By Comparison Techniques
• Effective Date: 01-Nov-2013
• Refers: ASTM E220-07a - Standard Test Method for Calibration of Thermocouples By Comparison Techniques
• Effective Date: 01-Nov-2007
• Refers: ASTM E220-07e1 - Standard Test Method for Calibration of Thermocouples By Comparison Techniques
• Effective Date: 01-May-2007
• Refers: ASTM E220-07 - Standard Test Method for Calibration of Thermocouples By Comparison Techniques
• Effective Date: 01-May-2007
• Refers: ASTM C162-05(2010) - Standard Terminology of Glass and Glass Products
• Effective Date: 01-Oct-2005
• Refers: ASTM C162-05 - Standard Terminology of Glass and Glass Products
• Effective Date: 01-Oct-2005
• Refers: ASTM C162-04 - Standard Terminology of Glass and Glass Products
• Effective Date: 01-Jun-2004
• Refers: ASTM C162-03 - Standard Terminology of Glass and Glass Products
• Effective Date: 10-Jul-2003
• Refers: ASTM E220-02 - Standard Test Method for Calibration of Thermocouples By Comparison Techniques
• Effective Date: 10-May-2002
• Refers: ASTM C162-99 - Standard Terminology of Glass and Glass Products
• Effective Date: 10-May-1999
• Refers: ASTM E220-86(1996)e1 - Standard Test Method for Calibration of Thermocouples By Comparison Techniques
• Effective Date: 10-Nov-1996

Overview

ASTM C965-23: Standard Practice for Measuring Viscosity of Glass Above the Softening Point provides a systematic approach for determining the viscosity of glass when it is in its molten state, specifically above the softening point. Developed by ASTM International, this standard is integral for accurately characterizing the viscosity-temperature relationship of various glass materials. Understanding these properties is essential for optimizing manufacturing processes, quality assurance, and ensuring the performance of glass products.

Key Topics

• Viscosity Measurement:
  The standard outlines methods to measure the viscosity of glass at temperatures where it is above its softening point – typically in the range of 1 to 10⁶ Pa·s. This is achieved using a platinum alloy spindle immersed in molten glass and measuring the spindle torque generated by rotational movement.

• Procedures for Torque Development:

  • Procedure A: Utilizes a stationary crucible with a rotating spindle.
  • Procedure B: Uses a rotating crucible combined with a fixed spindle.

• Equipment Requirements:

  • Electrically heated furnace with precise temperature control.
  • Platinum alloy spindle and crucible or suitable alternative materials.
  • Torque measurement devices and calibrated thermocouples following ASTM E220 for temperature accuracy.

• Data Collection and Analysis:
  Measurements are taken across a range of temperatures. Data is used to develop viscosity-temperature curves, which define the working range of the glass.

• Calibration and Quality Control:
  Calibration with standard reference glasses is emphasized to ensure precision and comparability between experiments.

• Safety and Compliance:
  Users must establish appropriate safety, health, and environmental practices, and obey regulatory requirements before applying the standard.

Applications

Implementing ASTM C965-23 offers practical benefits in glass science and industry, including:

• Manufacturing and Processing:
  Determining the viscosity-temperature characteristics helps optimize glass forming, shaping, and annealing operations, leading to higher efficiency and better product consistency.

• Quality Assurance:
  Routine viscosity testing according to ASTM C965-23 ensures each glass batch meets expected properties, minimizing failure rates and material waste.

• Research and Development:
  Reliable viscosity curves facilitate the development of new glass formulations or the refinement of existing ones.

• Calibration and Standardization:
  Using reference glasses and following standardized testing protocols enables laboratories and manufacturers to compare results and maintain high testing accuracy across locations and over time.

Related Standards

Organizations implementing ASTM C965-23 often reference additional standards to enhance consistency and expand testing scope:

• ASTM C162 - Terminology of Glass and Glass Products
  Provides definitions and clarification of key terms used in glass testing and production.

• ASTM E220 - Test Method for Calibration of Thermocouples by Comparison Techniques
  Ensures precise temperature measurement, which is crucial for viscosity determinations.

• NIST Standard Reference Materials
  Used for calibration and standardization, providing certified glass samples with known properties.

For comprehensive and up-to-date information, practitioners should refer directly to the full text of ASTM C965-23 and related documents, ensuring alignment with the latest industry best practices in glass viscosity measurement.

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: C965 − 23
Standard Practice for
Measuring Viscosity of Glass Above the Softening Point
This standard is issued under the fixed designation C965; 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 3. Significance and Use
3.1 This practice is useful in determining the viscosity-
1.1 This practice covers the determination of the viscosity
temperature relationships for glasses and corresponding useful
of glass above the softening point through the use of a platinum
working ranges. See Terminology C162.
alloy spindle immersed in a crucible of molten glass. Spindle
torque, developed by differential angular velocity between
4. Apparatus
crucible and spindle, is measured and used to calculate
viscosity. Generally, data are taken as a function of temperature 4.1 The apparatus shall consist of an electrically heated
to describe the viscosity curve for the glass, usually in the
furnace equipped with a temperature controller, temperature
range from 1 to 10 Pa·s. measuring equipment, a platinum alloy spindle, a crucible, a
device to rotate spindle or crucible, and equipment to measure
1.2 Two procedures with comparable precision and accu-
torque.
racy are described and differ in the manner for developing
NOTE 1—Spindles and crucibles manufactured from 90 % Pt–10 % Rh
spindle torque. Procedure A employs a stationary crucible and
or 80 % Pt–20 % Rh alloys have been found satisfactory for this purpose.
a rotated spindle. Procedure B uses a rotating crucible in
4.1.1 Procedure A employs an electrically heated tube-type
combination with a fixed spindle.
furnace with a fixed support for the crucible as shown in Fig.
1.3 This standard does not purport to address all of the
1. A platinum alloy resistance-heated crucible also may be
safety concerns, if any, associated with its use. It is the
used.
responsibility of the user of this standard to establish appro-
4.1.2 Procedure B employs a similar furnace but with a
priate safety, health, and environmental practices and deter-
removable, rotatable crucible support as shown in Fig. 2.
mine the applicability of regulatory limitations prior to use.
4.1.3 Furnaces other than resistance-wound muffle types
1.4 This international standard was developed in accor-
may be used provided they give uniform and stable tempera-
dance with internationally recognized principles on standard-
ture conditions. Temperature differences greater than 3 °C
ization established in the Decision on Principles for the
within the crucible (in glass) are excessive for high precision
Development of International Standards, Guides and Recom-
measurements.
mendations issued by the World Trade Organization Technical 4.1.4 A temperature controller shall be provided for main-
Barriers to Trade (TBT) Committee.
taining the glass temperature within 62 °C of a specified
temperature.
2. Referenced Documents 4.1.5 Temperatures shall be measured with a suitable ther-
mocouple calibrated in accordance with Test Method E220 in
2.1 ASTM Standards:
conjunction with a calibrated potentiometer or solid state
C162 Terminology of Glass and Glass Products
instrumentation capable of 0.5 °C accuracy. An immersion
E220 Test Method for Calibration of Thermocouples By
thermocouple is recommended but a thermocouple in air may
Comparison Techniques
be used provided measurements show equivalency.
4.1.6 A crucible to contain the glass similar to those shown
in Fig. 3 preferably shall be fabricated from a platinum alloy,
This practice is under the jurisdiction of ASTM Committee C14 on Glass and
but a refractory material may be used provided it does not
Glass Products and is the direct responsibility of Subcommittee C14.04 on Physical
contaminate the glass.
and Mechanical Properties.
4.1.7 A platinum alloy spindle with the geometry shown in
Current edition approved May 1, 2023. Published May 2023. Originally
Fig. 4 is recommended. An alternative design has a hollow
approved in 1981. Last previous edition approved in 2017 as C965 – 96 (2017).
DOI: 10.1520/C0965-23.
shaft to house the thermocouple (junction at the center of the
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
large diameter portion) which has the advantage of proximity,
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
but the disadvantage of possible electrical disconnection during
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. torque measurement.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
C965 − 23
1—Furnace Winding
2—Crucible
3—Spindle
4—Shaft
5—Viscometer (providing both rotation and torque measurement)
6—Thermocouple
FIG. 1 General Arrangement for Rotating Spindle, Fixed Crucible
Scheme (Procedure A)
NOTE 1—Details are the same as in Fig. 1 except that the viscometer is
replaced by a torque measuring device, and the crucible is mounted on a
removable rotatable stand.
4.1.8 A measurement system is necessary for measurement
FIG. 2 General Apparatus Arrangement for Rotating Crucible
of spindle torque to an accuracy of 1 %.
Scheme (Procedure B)
5. Preparation of Test Glass
5.2 Place the filled crucible in proper position in the furnace
5.1 Select a mass of glass that is free of foreign material.
and heat to a temperature that lowers the viscosity of glass
Break or cut glass into pieces, each weighing about 10 g to 50
sufficiently to allow trapped air bubbles to be released. This
g, and place the correct quantity into the crucible that will
temperature should be below the original melting temperature
make the molten charge reach a level at some fixed distance
(several millimeters) above the point where the spindle nar- to avoid reboil. If reboil occurs, allow additional time for the
glass to clear. Hold at this temperature at least 20 min before
rows down. The weight of glass required can be approximated
starting measuremen
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: C965 − 96 (Reapproved 2017) C965 − 23
Standard Practice for
Measuring Viscosity of Glass Above the Softening Point
This standard is issued under the fixed designation C965; 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
1.1 This practice covers the determination of the viscosity of glass above the softening point through the use of a platinum alloy
spindle immersed in a crucible of molten glass. Spindle torque, developed by differential angular velocity between crucible and
spindle, is measured and used to calculate viscosity. Generally, data are taken as a function of temperature to describe the viscosity
curve for the glass, usually in the range from 1 to 10 Pa·s.
1.2 Two procedures with comparable precision and accuracy are described and differ in the manner for developing spindle torque.
Procedure A employs a stationary crucible and a rotated spindle. Procedure B uses a rotating crucible in combination with a fixed
spindle.
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.
2. Referenced Documents
2.1 ASTM Standards:
C162 Terminology of Glass and Glass Products
E220 Test Method for Calibration of Thermocouples By Comparison Techniques
3. Significance and Use
3.1 This practice is useful in determining the viscosity-temperature relationships for glasses and corresponding useful working
ranges. See Terminology C162.
4. Apparatus
4.1 The apparatus shall consist of an electrically heated furnace equipped with a temperature controller, temperature measuring
equipment, a platinum alloy spindle, a crucible, a device to rotate spindle or crucible, and equipment to measure torque.
This practice is under the jurisdiction of ASTM Committee C14 on Glass and Glass Products and is the direct responsibility of Subcommittee C14.04 on Physical and
Mechanical Properties.
Current edition approved Nov. 1, 2017May 1, 2023. Published November 2017May 2023. Originally approved in 1981. Last previous edition approved in 20122017 as
C965 – 96 (2012).(2017). DOI: 10.1520/C0965-96R17.10.1520/C0965-23.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
C965 − 23
NOTE 1—Spindles and crucibles manufactured from 90 % Pt–10 % Rh or 80 % Pt–20 % Rh alloys have been found satisfactory for this purpose.
4.1.1 Procedure A employs an electrically heated tube-type furnace with a fixed support for the crucible as shown in Fig. 1. A
platinum alloy resistance-heated crucible also may be used.
4.1.2 Procedure B employs a similar furnace but with a removable, rotatable crucible support as shown in Fig. 2.
4.1.3 Furnaces other than resistance-wound muffle types may be used provided they give uniform and stable temperature
conditions. Temperature differences greater than 3°C3 °C within the crucible (in glass) are excessive for high precision
measurements.
4.1.4 A temperature controller shall be provided for maintaining the glass temperature within 62°C62 °C of a specified
temperature.
4.1.5 Temperatures shall be measured with Type R or S thermocouples a suitable thermocouple calibrated in accordance with Test
Method E220 in conjunction with a calibrated potentiometer or solid state instrumentation capable of 0.5°C0.5 °C accuracy. An
immersion thermocouple is recommended but a thermocouple in air may be used provided measurements show equivalency.
4.1.6 A crucible to contain the glass similar to those shown in Fig. 3 preferably shall be fabricated from a platinum alloy, but a
refractory material may be used provided it does not contaminate the glass.
4.1.7 A platinum alloy spindle with the geometry shown in Fig. 4 is recommended. An alternative design has a hollow shaft to
house the thermocouple (junction at the center of the large diameter portion) which has the advantage of proximity, but the
disadvantage of possible electrical disconnection during torque measurement.
4.1.8 A measurement system is necessary for measurement of spindle torque to an accuracy of 1 %.
1—Furnace Winding
2—Crucible
3—Spindle
4—Shaft
5—Viscometer (providing both rotation and torque measurement)
6—Thermocouple
FIG. 1 General Arrangement for Rotating Spindle, Fixed Crucible Scheme (Procedure A)
C965 − 23
NOTE 1—Details are the same as in Fig. 1 except that the viscometer is replaced by a torque measuring device, and the crucible is mounted on a
removable rotatable stand.
FIG. 2 General Apparatus Arrangement for Rotating Crucible Scheme (Procedure B)
5. Preparation of Test Glass
5.1 Select a mass of glass that is free of foreign material. Break or cut glass into pieces, each weighing about 1010 g to 50 g, and
place the correct quantity into the crucible that will make the molten charge reach a level at some fixed distance (several
millimetres)millimeters) above the point where the spindle narrows down. The weight of glass required can be approximated
satisfactorily with the following expression for a cylindrical crucible:
W 5 @πd ~L1h!/42 V #ρ ~12 0.0007α! (1)
T s
where:
h = distance between crucible floor and spindle tip, mm (generally greater than 10 mm to avoid end effects)
W = glass charge weight at room temperature, g,
T
d = inside diameter of crucible, mm,
L = immersed portion of spindle, mm,
V = volume of immersed portion of spindle, mm ,
s
ρ = density of glass at room temperature, g/cm , and
α = 0 to 300°C thermal expansion coefficient, cm/cm·°C (× 10 ).
α = 0 °C to 300 °C thermal expansion coefficient, cm/(cm·°C) (× 10 ).
Avoid very small pieces of glass in the charge as they tend to make the molten glass seedy.
5.2 Place the filled crucible in proper position in the furnace and heat to a temperature that lowers the viscosity of glass sufficiently
to allow trapped air bubbles to be released. This temperature should be below the original melting temperature to avoid reboil. If
reboil occurs, allow additional time for the glass to clear. Hold at this temperature at least 20 min before starting measurements.
C965 − 23
FIG. 3 Two Types of Crucibles
FIG. 4 Typical Platinum Alloy Spindle
6. Calibration and Viscosity Determi
...