ISO-7884-6-1987.pdf
INTERNATIONAL STANDARD INTERNATIONAL ORGANIZATION FOR STANDARDIZATION ORGANISATION INTERNATIONALE DE NORMALISATION MEXAYHAPOAHAR OPrAHM3AMR ll0 CTAHFAPTM3Al. f' 1: 'h' e Glass - Viscosity and viscometric fixed points - Part 6 : Determination of softening point SO 7884-6 Grst edition 987-12-15 Reference number IS0 7884-6 : 1987 (E) Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/26/2007 20:56:53 MDTNo reproduction or networking permitted without license from IHS -,-,- Foreword IS0 (the International Organization for Standardization) is a worldwide federation of national standards bodies (IS0 member bodies). The work of preparing International Standards is normally carried out through IS0 technical committees. Each member body interested in a subject for which a technical committee has been established has the right to be represented on that committee. International organizations, govern- mental and non-governmental, in liaison with ISO, also take part in the work. Draft International Standards adopted by the technical committees are circulated to the member bodies for approval before their acceptance as International Standards by the IS0 Council. They are approved in accordance with IS0 procedures requiring at least 75 % approval by the member bodies voting. International Standard IS0 7664-6 was prepared by Technical Committee ISO/TC 46, Laboratory glassware and related apparatus. Users should note that all International Standards undergo revision from time to time and that any reference made herein to any other International Standard implies its latest edition, unless otherwise stated. 0 International Organization for Standardization, 1997 0 Printed in Switzerland Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/26/2007 20:56:53 MDTNo reproduction or networking permitted without license from IHS -,-,- INTERNATIONAL STANDARD IS0 7664-6 : 1987 (E) Glass - Viscosity and viscometric fixed points - Part 6 : Determination of softening point 0 Introduction International Standard IS0 7664, Glass - Viscosity and viscometric fixed points, consists of the following separate parts : Part 7 : Principles for determining viscosity and viscometric fixed points. Part 2 : Determination of viscosity by rotation viscometers. Part 3 : Determination of viscosity by fibre elongation viscometer. Part 4 : Determination of viscosity by beam bending. Part 5 : Determination of working point by sinking bar viscometer. Part 6 : Determination of softening point. Part 7 : Determination of annealing point and strain point by beam bending. Part 8 : Determination of ldilatometricl transformation temperature. 1 Scope This part of IS.0 7884 specifies a method of determining the softening point of a glass. It has been found useful as a control test to indicate changes in composition, for specification ac- ceptance and for providing information in research and development work with glass. 2 Field of application This method is applicable to all glasses of normal bulk- production compositions unless devitrification takes place dur- ing the preparation or testing of the specimen. The softening points range between 370 and 1 000 OC, depen- ding on the type of glass. 3 Reference IEC Publication W-1, Thermocouples - Part 1 : Reference tables. 4 Definition For the purposes of this part of IS0 7884, the following defini- tion applies. softening point, dr2 : Approximately the temperature above which the glass is capable of most forming operations. NOTES 1 A viscosity of about 107,s dPa.s* may be assigned to the softening point for glass of density Q = 2,5 g/cm3 and surface tension G = 300 mN/m. (For glasses with other values of density or surface tension, see IS.0 7884-l .I 2 The softening point is also called the Littleton temperature. 5 Principle Determination of the temperature at which a round fibre of the glass, nominally 0,65 mm in diameter and 235 mm long with specified tolerances, elongates under its own weight at a rate of 1 mm/min when the upper 100 mm of its length is heated in a specified furnace at the rate of (5 + 1) Wmin. NOTE - In principle, the device used in this method corresponds to a fibre elongation viscometer (see IS0 7884-3). Closely defined re- quirements for the test specimen, procedure and apparatus lead to a good repeatability of the specified temperature point. The related viscosity value, however, is of less certainty. 6 Apparatus 6.1 Furnace The furnace shall conform in all essential respects to the re- quirements shown in the annex. Equivalent material may be employed, where available. dN.s * 1 dPa.s = 1 ,2 = 1 P (P is the symbol for poise) 1 Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/26/2007 20:56:53 MDTNo reproduction or networking permitted without license from IHS -,-,- IS0 7664-6 : 1987 (El 6.2 Furnace stand A means shall be provided for supporting the furnace so that the fibre hangs below it. This stand shall be provided with a levelling device such as three screws. The stand shown in the annex is convenient when used with either a cathetometer or a telescope and scale. 6.3 Heating rate controller Suitable controls shall be provided for maintaining the furnace heating rate at (5 k 1) Urnin. NOTE - A continuously adjustable transformer has proved effective for controlling the heating rate. 6.4 Temperature measuring and indicating instruments 6.4.1 The alumina-insulated platinum-10 % rhodium/platinum (type S according to IEC 564-l) thermocouples, or nickel- chromium/nickel (type K according to IEC 564-l) ther- mocouples placed in a double-bore porcelain tube in accor- dance with the diagram in the annex shall exhibit low thermal inertia (the diameter of the wires should not be greater than 0,5 mm). 6.4.2 The measurement thermocouple shall be placed in the furnace core in accordance with the specifications in the annex (No. 4 and 17). In accordance with IS0 7664-1, the measure- ment thermocouples shall be calibrated and the calibration checked regularly. 6.4.3 The electrical output of the thermocouples shall be determined at zero current by means of potentiometers, or high-resistance electronic amplifiers having a sensitivity of 1 pV for type S (according to IEC 564-l), or 4 pV for type K (accor- ding to IEC 564-I) thermocouples. Precautions shall be taken that the ice-bath for the cold junction is maintained at 0 OC throughout the test. If the temperature measuring equipment is fitted with automatic cold junction compensation, the ice-bath can be omitted. 6.5 Fibre elongation measurement equipment The fibre elongation shall be measured using a device capable of measuring the position of the end of the fibre within 0,02 mm throughout the entire elongation period. NOTE - Suitable devices that have proved effective for measuring the elongation are of both optical and electronic types. For some devices it may be convenient if they are fixed with the furnace stand, e.g. by a short optical bench. 6.6 Fibre diameter measurement equipment The fibre diameter shall be measured by a suitable device (e.g. a micrometer) with 0,Ol mm divisions. 6.7 Timer A timing device with a least count and accuracy of 1 s shall be used. 7 Preparation of test specimens 7.1 The fibre specimen used for the test shall meet the following requirements : a) it shall be round; b) it shall be smooth and shall contain no voids or foreign matter; c) its average diameter shall be (0,65 f 0,l) mm and the maximum diameter shall not exceed the minimum diameter by more than 0,02 mm over the entire length of the fibre; d) it shall be (235 f I) mm in length, not including the top bead. 7.2 A test fibre conforming to these requirements may be drawn by attaching a clean sample of the glass under test be- tween two non-fusible rods (such as platinum-group alloys, porcelain or fused silica) and flame-working the sample until the glass is sufficiently fluid to be drawn into a fibre. If the sample is in long stick form, it may be flamed-worked directly without attaching it to a handle. Acceptable fibre sections may then be broken from the fibre and a bead formed on one end of the fibre section by fusing in the flame. The opposite end shall then be broken to the specified length and the tip may be fire polished if desired. Fibres may also be drawn by any suitable device. 8 Procedure 6.1 Calibration with reference glass Calibration of the apparatus shall be carried out by measuring in duplicate the softening point of appropriate reference glassfes) ), the softening points of which are near to that of the test glass. Compute the difference between the average measured softening point and the certified softening point for the reference glassfes) I), and the average of these differences. If the average difference from the certified values is greater than 1 OC, add or subtract this difference as a correction to the measured softening points of the glasses to be tested. 6.2 Measurement 8.2.1 To equalize the heat distribution of the furnace, heat the furnace to about 30 “C above the expected softening point of the glass under test. Then cool the furnace to about 20 “C below the expected softening point, and determine the settings on the heating rate controller that will give a heating rate of (5 f I) Wmin. I) See for example IS0 7884-l : 1987, annex 6, “Examples ot certrtred reference glasses for viscometric calibration”. 2 Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/26/2007 20:56:53 MDTNo reproduction or networking permitted without license from IHS -,-,- IS0 7664-6 : 1987 (E) 8.2.2 Again, cool and hold the furnace about 20 OC below the expected softening point, and insert the fibre in the furnace by placing the bead end in the furnace sample holder. Check the fibre to ensure that it is hanging freely in the centre of the fur- nace, and re-level the furnace if necessary. Prepare the temperature measuring equipment and adjust the elongation measuring equipment. 8.2.3 Set the furnace control for a heating rate of (5 f 1) YYmin. Observe the fibre as the furnace heats, and when it begins to elongate at the rate of approximately 0,l mm/min, start recording the fibre length to within 0,02 mm. Take a length reading at the end of each minute and take the temperature of the furnace at each 1 min interval, displaced with respect to the length readings by 0,5 min. Con- tinue to read and record the length and the temperature until the elongation becomes 1.2 mm or greater in a 1 min interval. When the elongation exceeds 1,2 mm in a 1 min interval, remove the fibre and cool the furnace in readiness for a duplicate run. If the difference between the results for two fibres evaluated is greater than 2 OC, repeat the complete test with two new fibres. 9.2 Precision and accuracy This method in general will yield softening points having a repeatability of 1 OC. The accuracy of results should be checked by determining the softening point of appropriate reference glasses as indicated in the calibration procedure (8.1). 10 Test report The test report shall include : An alternative acceptable method is to read the length at the a) reference to this part of IS0 7864; 0,5 and 1 min points, and the temperature at the 0,25 and 0.75 min points, continuing to read and record length and b) description of the sample; temperature until the elongation becomes 0,6 mm or greater in a 0,5 min period. c) method of sampling; d) number of test specimens; 9 Expression of results e) method of preparation; 9.1 Method of calculation f) type of softening point apparatus used; Determine the temperature at which the elongation is 1 mm/min. This may be done by using any reliable method, one of which is as follows. Plot the data on semi-log paper, with the potentiometer or temperature readings on the linear scale, and the difference between length readings per unit time on the logarithmic scale. The point where a straight line drawn through the data points crosses the 1 mm/min line shall be taken as the indicated softening point. Make the calibration corrections as specified in 8.1, if necessary. g) method of calculation (9.1); h) corrections applied; j) SOftening point in degrees Celsius, i.e. the arithmetic mean of both runs; j) any change in the glass, observed during and/or after the test. 3 Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/26/2007 20:56:53 MDTNo reproduction or networking permitted without license from IHS -,-,- IS0 7664-6 : 1987 (El Annex A Details of softening point furnace (This annex forms an integral part of the standard.) 19 18 17 16 15 - 1 2 3 , 4 5 6 P 7 8 1 Furnace top, 12,7 mm thick by 100 mm outside diameter, having a hole of 12,7 mm diameter at the centre and three holes (for tie rods) 5,6 mm in diameter spaced 120° apart on an 82,5 mm diameter circle; also, two small holes, suitably placed, for thermocouple wires and two binding posts, with small holes nearby, for heater wires. Material to be heat-resistant fibre- reinforced cement. One required. 2 Spacer rings, 12,7 mm thick by 94 mm outside diameter by 70 mm inside diameter, having holes for tie rods (see 1). Material to be heat-resistant fibre-reinforced cement. Two re- quired. 3 Webs, 6,5 mm thick by 94 mm outside diameter, having a hole of 19 mm diameter at the centre and six holes 19 mm in diameter spaced 60° apart on a 51 mm diameter circle; also, holes for tie rods (see 1). Material to be heat-resistant fibre- reinforced cement. Two required. The upper web shall have two small holes, suitably placed, for the heater wires. 4 Furnace core, 95 mm high by 29 mm outside diameter, with a 65 mm length at each end turned to 19 mm outside diameter. Having a bore of 5,6 mm diameter at the centre throughout its entire length and two symmetrical holes 3,2 to 5,6 mm in diameter drilled (one from each end) adjacent, parallel and as near as possible to the central bore to a depth of 47,5 mm (from either end respectively). Material to be nickel. One required. 5 Core wrapping, of double-thickness mica, or fibre ceramics paper. 6 Round resistance wire, wound equidistantly over the whole length of the furnace core. The wire shall exhibit a resistance of I,76 Q at room temperature, corresponding to a power of 1 kW at the maximum voltage of 42 V (e.g. an 80 % Ni- 20 % Cr wire, I,6 mm in
