ASTM_C_965_-_96_2012.pdf

Designation:C96596(Reapproved 2012)Standard Practice forMeasuring Viscosity of Glass Above the Softening Point1This standard is issued under the fixed designation C965;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval.Asuperscript epsilon()indicates an editorial change since the last revision or reapproval.1.Scope1.1 This practice covers the determination of the viscosityof glass above the softening point through the use of a platinumalloy spindle immersed in a crucible of molten glass.Spindletorque,developed by differential angular velocity betweencrucible and spindle,is measured and used to calculateviscosity.Generally,data are taken as a function of temperatureto describe the viscosity curve for the glass,usually in therange from 1 to 106Pas.1.2 Two procedures with comparable precision and accu-racy are described and differ in the manner for developingspindle torque.Procedure A employs a stationary crucible anda rotated spindle.Procedure B uses a rotating crucible incombination with a fixed spindle.1.3 This standard does not purport to address all of thesafety concerns,if any,associated with its use.It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2.Referenced Documents2.1 ASTM Standards:2C162 Terminology of Glass and Glass ProductsE220 Test Method for Calibration of Thermocouples ByComparison Techniques3.Significance and Use3.1 This practice is useful in determining the viscosity-temperature relationships for glasses and corresponding usefulworking ranges.See Terminology C162.4.Apparatus4.1 The apparatus shall consist of an electrically heatedfurnace equipped with a temperature controller,temperaturemeasuring equipment,a platinum alloy spindle,a crucible,adevice to rotate spindle or crucible,and equipment to measuretorque.NOTE1Spindles and crucibles manufactured from 90%Pt10%Rhor 80%Pt20%Rh alloys have been found satisfactory for this purpose.4.1.1 Procedure A employs an electrically heated tube-typefurnace with a fixed support for the crucible as shown in Fig.1.A platinum alloy resistance-heated crucible also may beused.4.1.2 Procedure B employs a similar furnace but with aremovable,rotatable crucible support as shown in Fig.2.4.1.3 Furnaces other than resistance-wound muffle typesmay be used provided they give uniform and stable tempera-ture conditions.Temperature differences greater than 3Cwithin the crucible(in glass)are excessive for high precisionmeasurements.4.1.4 A temperature controller shall be provided for main-taining the glass temperature within 62C of a specifiedtemperature.4.1.5 Temperatures shall be measured with Type R or Sthermocouples calibrated in accordance with Test MethodE220 in conjunction with a calibrated potentiometer or solidstate instrumentation capable of 0.5C accuracy.An immersionthermocouple is recommended but a thermocouple in air maybe used provided measurements show equivalency.4.1.6 A crucible to contain the glass similar to those shownin Fig.3 preferably shall be fabricated from a platinum alloy,but a refractory material may be used provided it does notcontaminate the glass.4.1.7 A platinum alloy spindle with the geometry shown inFig.4 is recommended.An alternative design has a hollowshaft to house the thermocouple(junction at the center of thelarge diameter portion)which has the advantage of proximity,but the disadvantage of possible electrical disconnection duringtorque measurement.4.1.8 A measurement system is necessary for measurementof spindle torque to an accuracy of 1%.5.Preparation of Test Glass5.1 Select a mass of glass that is free of foreign material.Break or cut glass into pieces,each weighing about 10 to 50 g,and place the correct quantity into the crucible that will makethe molten charge reach a level at some fixed distance(several1This practice is under the jurisdiction of ASTM Committee C14 on Glass andGlass Products and is the direct responsibility of Subcommittee C14.04 on Physicaland Mechanical Properties.Current edition approved March 1,2012.Published March 2012.Originallyapproved in 1981.Last previous edition approved in 2007 as C965 96(2007).DOI:10.1520/C0965-96R12.2For referenced ASTM standards,visit the ASTM website,www.astm.org,orcontact ASTM Customer Service at serviceastm.org.For Annual Book of ASTMStandards volume information,refer to the standards Document Summary page onthe ASTM website.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 millimetres)above the point where the spindle narrows down.The weight of glass required can be approximated satisfactorilywith the following expression for a cylindrical crucible:WT5d2L1h!/4 2 Vs#1 2 0.0007!(1)where:h=distance between crucible floor and spindle tip,mm(g