1、INTERNATIONAL STANDARD INTERNATIONAL ORGANIZATION FOR STANDARDIZATION ORGANISATION INTERNATIONALE DE NORMALISATION MEXAYHAPOAHAR OPTAHM3Al,! ;y:. 1, 1, ,:?.:li.9.:-:,.:ei; ;-$;y;, Glass - Viscosity and viscometric fixed points - Part 5 : Determination of working point by sinking bar viscometer SO 78
2、84-5 First edition 1987-12-15 Reference number IS0 7884-5 : 1987 (E) 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 technic
3、al 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 Stand
4、ards 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 IS
5、0 7884-5 was prepared by Technical Committee ISO/TC 48, 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 otherwis
6、e stated. 0 International Organization for Standardization, 1997 0 Printed in Switzerland INTERNATIONAL STANDARD IS0 7884-5 : 1987 (El Glass - Viscosity and viscometric fixed points - Part 5 : Determination of working point by sinking bar viscometer 0 Introduction international Standard IS0 7884, Gl
7、ass - Viscosity and viscometric fixed points, consists of the following separate parts : Part 1 : 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
8、 : 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
9、. 1 Scope This part of IS0 7884 specifies a method of determining the working point of glass by means of the sinking bar viscometer. This method has been found useful for characterizing the low- viscosity range of glass working. This viscometric fixed point can be used in determining the viscosity-t
10、emperature relation- ship (see IS0 7884-l 1. 2 Field of application This method is applicable to all glasses of normal bulk- production compositions unless devitrification or evaporation of volatile components takes place during the preparation or testing of the specimen. The working points range be
11、tween 800 and 1 200 OC, depen- ding on the type of glass. 3 Reference IEC Publication 584-1, Thermocouples - Part 7 : Reference tables. 4 Definitions For the purposes of this part of IS0 7884, the following defini- tions apply. 4.1 working point : Temperature at which the melt of usual silicate glas
12、ses possesses an equilibrium viscosity of 104 dPa.s*. 4.2 sinking bar temperature : Working point as deter- mined by means of the sinking bar method. 4.3 sinking bar method : Simple procedure for determining rapidly the viscosity within a range of about 103,7 to IO%5 dPa.s as explained in clause 5.
13、5 Principle A vertically positioned narrow metal rod (the bar) of diameter d is allowed to sink under a force F (its own weight) into the melt. From the rate of sinking of the bar into the melt, the dynamic viscosity q of the melt is calculated. Under the geometrical con- ditions specified in 6.1 an
14、d 6.3, the deviations of this method from equation (1) are small compared with the experimental uncertainties as specified in 9.2. t q = C.rn.12 . . . (I) where C is a constant; 2 is the depth of sinking into the melt; m is the mass of the bar; t is the sinking time corresponding to 1. * 1 dPa.s = 1
15、 s = 1 P (P is the symbol for poise) 1 IS0 7884-5 : 1967 (E) If fixed values of the depth I and the mass m are specified, a constant K for the bar may be defined according to equation (2) : rj =K.t . . . (2) In this part of IS0 7884, the depth of sinking and the mass of the bar are specified as I =
16、20 mm and m = 0,902 g. respec- tively. NOTE - The buoyancy acting upon the immersed part of the bar is taken into account for the density of the reference glass used for calibration (see 6.1). The buoyancy correction for other values of glass density is neglected. 6 Apparatus 6.1 Sinking bar Bar mad
17、e from platinum-rhodium alloy with a mass fraction of rhodium between 0,2 and 0,3, with diameter 0,5 mm and mass 0,902 g (corresponding to a length between 240 and 245 mm depending upon the density of the platinum-rhodium alloy used). The ends of the bar shall be hemispherical. NOTE - With such a ba
18、r, for a viscosity of 104 dPa.s the time for sinking to a depth of 20 mm is 60 s. This corresponds to a bar constant K of about 140 to 170 dPa.s/s. For routine measurements it is convenient to have available several bars made from the same batch of the alloy. Used bars shall be gently cleaned of adh
19、erent glass residues by sudden heating and chilling, or by dissolving the glass in hydrofluoric acid. Afterwards they shall be straightened before re-use. 6.2 Furnace Electrically heated tube furnace capable of achieving temperatures up to 1 200 X. The length of the heated tube shall be about 200 mm
20、, and its inner diameter at least 30 mm. Within a zone of 40 mm in length in which the crucible is placed, the temperature shall be constant within 3 X. 6.3 Crucible The inner diameter of the crucible at the surface of the melt shall be at least 23 mm. Its depth shall be 30 to 40 mm. Crucibles made
21、from platinum or platinum alloys are preferred. For single use, crucibles made from non-porous refractory may also be used. 6.4 Temperature measuring and indicating instruments 6.4.1 The alumina-insulated platinum-10 % rhodium/platinum thermocouples (type S according to IEC 584-l) shall exhibit low
22、thermal inertia (the diameter of the wires should not be greater than 05 mm). 2 The wires shall have a sufficient length within the furnace (with respect to heat conduction along the wires). Platinum-metal- sheathed thermocouples should be preferred. 6.4.2 Control thermocouples should be located as
23、close as possible to the furnace windings for fast response. The measurement thermocouple is placed near the wall of the cruci- ble, dipping about 1 mm into the melt (see figure I). In accor- dance with IS0 7884-l the measurement thermocouple shall be calibrated and the calibration checked regularly
24、. 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 10 pV or better. Precautions shall be taken that the ice-bath for the cold junction is maintained at 0 OC throughout the
25、 test. If the temperature measuring equipment is fitted with automatic cold junction compensation, the ice-bath may be omitted. 6.5 Timer The sinking time shall be measured by means of a stopwatch having scale intervals of 0,l s, or by an equivalent timer. 6.6 Other equipment The following equipment
26、 is necessary. a) Clamp for handling and holding the bar. b) Ammeter for indicating the position when the bar tip touches the surface of the melt. c) Mirror scale for parallax-free reading for measuring the depth of sinking of the bar; a groove should be ground in the mirror scale for gently guiding
27、 the upper end of the bar with minimum friction. In place of the devices listed under b) and c) other suitable devices may be used. Further devices may be useful for the adjustment of the zero position, e.g. cathetometer, adjustable clamping device to achieve central and vertical positioning of the
28、bar (admittable maximum tilt, 5O), etc. 6.7 Assembly of apparatus Figure 1 shows an example of the test assembly. It is conve- nient if the crucible is set on a fixed stand whereas the furnace can be moved downwards; this facilitates the filling of the crucible and removal of the test specimen. The
29、measurement thermocouple (positioned according to 6.4.2) or the platinum alloy crucible serve at the same time as an electrode for the am- meter; the other electrode is the bar whilst it is fastened in the clamp. Draught within the furnace tube should be diminished by closing the orifice in the bott
30、om of the furnace (e.g. by means of ceramic wool). IS0 7884-5 : 1987 (El 7 Preparation of test specimens 1 Mirror scale with groove (see also figure 2) 2 Ammeter with circuit 3 Measurement thermocouple 4 Cover 5 Furnace platen made of ceramics 6 Furnace tube made of ceramics 7 Bar 8 Crucible contain
31、ing glass melt under test 9 Furnace platen made of ceramics 10 Ceramic wool (draught protection) 11 Crucible stand (e.g. made of ceramics) 12 Heater 13 Insulation 14 Control thermocouple Figure 1 - Schematic example of the sinking bar viscometer Figure 2 - Mirror scale with groove The sample of the
32、glass to be tested shall consist of pieces larger than 3 mm. If the pieces do not fit into the crucible, they shall be crushed carefully, avoiding any contamination (see IS0 7994-l : 1987, sub-clause 7.1). If a platinum crucible is used, the test specimen (about 20 to 30 cm? of the homogeneous glass
33、 sample is melted in that crucible. If a refractory crucible is used, it is more convenient, because of possible corrosion, to melt the test specimen in another furnace and to cast it into a mould having a form similar to that of the measurement crucible. Ensure that no air bubbles are included in t
34、he molten sample. However, avoid melting during too long periods, especially in the case of a glass which devitrifies easily. NOTE - If the working point lies above 1 150 C, a simple preparation furnace for temperatures higher than 1 200 OC is convenient. In this furnace the glass can be melted suff
35、iciently fast to produce a bubble- free sample, before it is introduced into the testing furnace. 8 Procedure 8.1 Calibration Calibrate the test assembly by means of a reference glassl), car- rying out the test procedure described in 8.2 at that temperature which corresponds to the viscosity 104 dPa
36、.s of the reference glass. The compositions of the reference glass and of the glass under test should be similar. Calculate the bar constant K from the measured sinking time t, by means of equation (3) : K = lo” . . . t c where K is expressed in decipascal seconds per second; (3) t, is expressed in
37、seconds. Repeat the calibration regularly and after any change in the ap- paratus. The constant K determined as above is used in equation (2) for the determination of the viscosity of other glasses. 8.2 Measurement Heat the specimen in the furnace to that temperature which is expected to correspond to a viscosity of 104 dPa.s. NOTE - In the case of soda-lime glass, this temperature is about 1 000 oc. 1) See for example IS0 7884-l : 1987, annex B, “Examples of certified reference glasses for viscometric calibration”. 3
