ASTM_C_338_-_93_2013.pdf

Designation:C33893(Reapproved 2013)Standard Test Method forSoftening Point of Glass1This standard is issued under the fixed designation C338;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.This standard has been approved for use by agencies of the Department of Defense.1.Scope1.1 This test method covers the determination of the soft-ening point of a glass by determining the temperature at whicha round fiber of the glass,nominally 0.65 mm in diameter and235 mm long with specified tolerances,elongates under its ownweight at a rate of 1 mm/min when the upper 100 mm of itslength is heated in a specified furnace at the rate of 5 61C/min.1.2 The values stated in SI units are to be regarded asstandard.No other units of measurement are included in thisstandard.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.Significance and Use2.1 This test method is useful to determine approximatelythe temperature below which the glass behaves as a rigid solidin glass-forming operations and for a control test to indicatechanges in composition.It has been found useful for specifi-cation acceptance and for providing information in researchand development work with glass.3.Apparatus3.1 The apparatus for determining the softening point ofglass shall consist essentially of an electrically heated resis-tance furnace,a furnace stand,a device for controlling theheating rate of the furnace,equipment for measuring thetemperature of the furnace,and equipment for measuring theelongation rate of a fiber of glass suspended in the furnace.3.1.1 FurnaceThe furnace shall conform in all essentialrespects to the requirements shown in Fig.1.3.1.2 Furnace StandA means shall be provided for sup-porting the furnace so that the fiber hangs below it.This standmust be provided with a leveling device such as three screws.The stand shown in Fig.1 is convenient when used with eithera cathetometer or a telescope and scale.3.1.3 Heating Rate ControllerSuitable controls shall beprovided for maintaining the furnace heating rate at 5 61C/min.NOTE1A continually adjustable transformer has proved effective forcontrolling the heating rate.3.1.4 Temperature-Measuring Equipment The furnacetemperature shall be measured with a calibrated Type R or Sthermocouple and a calibrated potentiometer capable of mea-suring the true temperature of the furnace within 60.2C.Thecold junction shall be maintained at 0C by means of an icebath.An alternative acceptable means of temperature measure-ment is the use of a potentiometer to oppose the thermocoupleelectromotive force.This potentiometer shall be set at astandard setting for the type of glass being measured,andgalvanometer deflection shall serve as a means of obtainingrelative temperatures,the deflection of the galvanometer hav-ing been calibrated.Also acceptable for temperature measure-ment is a solid-state digital thermometer that is capable of theaccuracy specified.3.1.5 Fiber-Elongation Measurement EquipmentThe fiberelongation shall be measured by a device capable of measuringthe position of the end of the fiber within 0.02 mm throughoutthe entire elongation period.NOTE2Suitable devices that have proved effective for measuring theelongation are cathetometers,projection magnifiers,and telescope andscale combinations.3.1.6 TimerA timing device with a least count and accu-racy of 1 s shall be used.4.Preparation of Test Specimens4.1 The fiber specimen used for the test shall meet thefollowing requirements:4.1.1 It shall be round.4.1.2 It shall be smooth and shall contain no void spots orforeign matter.1This test method is under the jurisdiction of ASTM Committee C14 on Glassand Glass Products and is the direct responsibility of Subcommittee C14.04 onPhysical and Mechanical Properties.Current edition approved Oct.1,2013.Published October 2013.Originallyapproved in 1954.Last previous edition approved in 2008 as C338 93(2008).DOI:10.1520/C0338-93R13.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 FIG.1 Details of Softening Point FurnaceC338 93(2013)2 4.1.3 Its average diameter shall be 0.65 6 0.10 mm and themaximum diameter shall not exceed the minimum diameter bymore than 0.02 mm over the entire length of the fiber.4.1.4 It shall be 235 6 1 mm in length,not including the topbead.Test fibers conforming to these requirements may bedrawn by attaching a clean sample of the glass under testbetween two infusible rods(such as platinum-group alloys,porcelain,or fused silica)and flame-working the sample untilt