1、Glass - Viscosity and viscometric fixed points Part 2: Determination of viscosity by rotation viscometers (IS0 7884-2 : 1987) ICs 81.040.1 O Descriptors: Glass, viscosity, testing, rotation viscometers. Glas - Viskositt und viskosimetrische Festpunkte - Teil 2: Bestimmung der Viskositt mit Rotations
2、viskosimetern (IS0 7884-2 : 1987) DIN IS0 7884-2 - Supersedes DIN 52312-2, February 1975 edition. Previous edition DIN 52312-2: 1975-02. This standard incorporates International Standard IS0 7884-2 Glass - Viscosity and viscometric fixed points - Part 2: Determination of viscosity by rotation viscom
3、eters. A comma is used as the decimal marker. National foreword This standard has been prepared by ISO/TC 48. The responsible German body involved in its preparation was the Normenausschu Materialprfung (Mate- rials Testing Standards Committee), Technical Committee Physikalische Prfverfahren fr Glas
4、. The DIN Standards corresponding to the International Standards and the IEC Publication referred to in clauses O and 2 of the IS0 Standard are as follows: IEC Publication/ DIN Standard IS0 Standard IEC 584-1 DIN IEC 584-1 IS0 7884-1 DIN IS0 7884-1 IS0 7884-3 DIN IS0 7884-3 IS0 7884-4 DIN IS0 7884-4
5、 IS0 7884-5 DIN IS0 7884-5 IS0 7884-6 DIN IS0 7884-6 IS0 7884-7 DIN IS0 7884-7 IS0 7884-8 DIN IS0 7884-8 Amendments DIN 52312-2, February 1975 edition, has been superseded by the specifications of DIN IS0 7884-2 National Annex NA Standards referred to (and not included in Introduction and Reference)
6、 DIN IS0 7884-1 Glass -Viscosity and viscometric fixed points - Part 1 : Principles for determining viscos- ity and viscometric fixed points (IS0 7884-1 : 1987) DIN IS0 7884-3 Glass -Viscosity and viscometric fixed points- Part 3: Determination of viscosity by fibre elongation viscometer (IS0 7884-3
7、 : 1987) I Continued overleaf. IS0 Standard comprises 11 pages. Q No pari of this standard may be reproduced without the prior permission of Ref. No. DIN IS0 7884-2 : 1998-02 Sales No. 0409 02.99 DIN Deutsches Institut fr Normung e. V., Berlin. Beuth Verlag GmbH, D-10772 Berlin, has the exclusive ri
8、ght of sale for German Standards (DIN-Normen). English price group O9 Page 2 DIN IS0 7884-1 : 1998-02 DIN IS0 7884-4 Glass - Viscosity and viscometric fixed points - Part 4: Determination of viscosity by beam bending (IS0 7884-4 : 1987) DIN IS0 7884-5 Glass - Viscosity and viscometric fixed points -
9、 Part 5: Determination of working point by sinking bar viscometer (IS0 7884-5 : 1987) DIN IS0 7884-6 Glass - Viscosity and viscometric fixed points - Part 6: Determination of softening point DIN IS0 7884-7 Glass - Viscosity and viscometric fixed points - Part 7: Determination of annealing point and
10、strain point by beam bending (IS0 7884-7 : 1987) DIN IS0 7884-8 Glass - Viscosity and viscometric fixed points - Part 8: Determination of (dilatometric) trans- formation temperature (IS0 7884-8 : 1987) (IS0 7884-6 : 1987) Page 1 IS0 7884-2 : 1987 Glass - Viscosity and viscometric fixed points Part 2
11、: Determination of viscosity by rotation viscometers 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. E
12、ach 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
13、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 7884-2 was pre
14、pared 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 otherwise stated. Page 2
15、 IS0 7884-2 : 1987 O Introduction International Standard IS0 78 however, at rotational frequen- cies above 1 s- 1 it should be ascertained that inertia forces are negligible. 2 Reference IEC Publication 584-1, Thermocouples - Part I: Reference tables. 3 Definitions For the purposes of this part of I
16、S0 7884, the following defini- tions apply. 3.1 Field of flow, crucible and plunger 3.1.1 field of flow: The whole gap filled by the molten glass sample and the spatial distribution of the flow velocities within it, including its boundaries. 3.1.2 crucible : The outer boundary of the molten glass sa
17、m- ple corresponding to the inner surface of the crucible up to the level of the melt. 3.1.3 plunger: The inner boundary of the molten glass sam- ple corresponding to the outer surface of the plunger up to the level of the melt. 3.2 Flow field coefficient and instrument constant 3.2.1 Rotation visco
18、meters are either of the Searle type or of the Couette type, both of which allow the determination of the viscosity according to basic equation (1) : T rl =f$ where Q is the viscosity; . . . (1) dN.s * 1 dPa.s = 1 = 1 P rn2 IP is the symbol for poise) Page 3 IS0 7884-2 : 1987 .f is the flow field co
19、efficient; T is the torque applied to the plunger; n is the rotational frequency either of the plunger (Searle type) or of the crucible (Couette type). The flow field coefficient f is a function only of the geometrical shape of the field of flow and has the dimension of reciprocal cubic length. The
20、analytical calculation of the flow field coefficient is possible in a restricted number of geometries, e.g. in the following cases see also annex A). a) Crucible and plunger are shaped like infinite concentric cylinders; methods of eliminating experimentally the effect of the plane end surfaces are
21、known from literature, but they are difficult to apply in the case of glass melts. b) Crucible and plunger form two confocal rotation sur- faces of the second order, e.g. two half-ellipsoids, cut perpendicularly to the axis of rotation. If the shapes of the crucible and of the plunger are made up by
22、 several rotational surfaces, the boundaries of the perpendicular median cuts being irregular curves (e.g. cylinders with plane or cone-shaped or hemi-spherical ends), the flow field coefficient can be determined only by means of viscometric standard liquids with Newtonian behaviour. 1) 3.2.2 If, fo
23、r the torque, the length and/or the rotational fre- quency, units are used which do not correspond to the unit for the viscosity, and if the resulting factor is combined with the flow field coefficient, a new constant, the instrument con- stant k, can be defined by equation (2) : . T = k- n where q
24、is the viscosity measured, in decipascal seconds; k is the instrument constant (numerical value), resulting from equation (3); 7 is the torque, in newton millimetres; n is the rotational frequency, in reciprocal seconds. The instrument constant k is related to the flow field coefficient f by equatio
25、n (3), if the flow field coefficient f is expressed in reciprocal cubic millimetres (mm -3) : k = lO7f . . . (3) NOTE - The factor 107 in equation (3) results from the relation 1 Ndmmz = lO7dPa.s 3.2.3 In many cases the rotational frequency n and the torque Tare not read or recorded directly. For th
26、e sake of convenience all the factors needed for their calculation and the flow field coefficient can be combined into a special instrument cons- tant k“. This constant shall be determined by calibration using viscometric standard liquids with Newtonian behaviour. 1) 3.2.4 The flow field coefficient
27、fand the instrument constants k and k“ are, for Newtonian liquids, independent of the rota- tional frequency, of the torque and of the viscosity. They are slightly dependent on temperature because of the thermal ex- pansion of the glass melt, of the crucible and of the plunger see 7.3). 3.3 Torques
28、3.3.1 driving torque : The torque applied by the drive to the boundary surface rotating with the rotational frequency n. 3.3.2 frictional torque: Torque of the opposite sign to the driving torque, arising from the viscous flow between the two boundaries, the one rotating and the other being at rest.
29、 3.3.3 torque of mechanical losses : The frictional resistance caused by influences other than the glass melt (e.g. friction in bearings, air friction; in the case of rotational vibra- tions, also the self-damping of the torsion spring). 3.3.4 In the case of stationary rotation, which is essential f
30、or obtaining correct results, these three torques add up to zero (action = reaction). Torques of mechanical losses, caused by the particular construction of the instrument, shall be eliminated through a correction. 4 Apparatus see annex B) 4.1 Rotation viscometer Two types of rotation viscometer com
31、ply with this part of IS0 7884: al Viscometer of the Couette type with adjustable, revolving crucible. The crucible stands on a turntable which is to be positioned in the furnace through its lower opening; the shaft of the plunger reaches through the upper opening of the furnace up to the torque-mea
32、suring device. b) Viscometer of the Searle type with the crucible at rest and the plunger revolving, the revolving movement be- ing induced through a shaft reaching out of the upper open- ing of the furnace. The torque-measuring device is applied to the shaft of the plunger. Both types can be operat
33、ed a) either at fixed rotational frequencies (e.g. by means of a combination of synchronous motor and gear transmission, the variation range of the rotational frequency n being at 1) See for example IS0 7884-1 : 1987, annex B, “Examples of certified reference glasses for viscometric calibration“. Pa
34、ge 4 IS0 7884-2 : 1987 least 1 :100) with a torque-measuring device (torsion wires, torsion spring or torsion balance) whose possible inaccur- acy shall not exceed 2 % at a torque of about 5 Nmm; b) or at fixed torques (e.g. by means of a weight and pulley system or by means of an electric motor) wi
35、th a measuring device for the rotational frequency (frequency meter, electronic speedmeter with optical or inductive sen- sor, microscope for very low rates). To protect these parts of the apparatus, special screening against heat or, if necessary, water-cooling is recommended. 4.2 Furnace Electrica
36、lly heated tube-shaped furnace, designed for a vertical working position, for temperatures up to 1 400 OC (in special cases up to 1 600 OC), with covers for the upper and the lower ends of the tube which shall be made of heat-resistant ceramic material. The temperature in the flow field area or in t
37、he adjacent space in the furnace shall be constant to I 2 OC with respect to time, and the temperature gradient shall not ex- ceed 1 Wem. NOTE - This requirement is achieved by one or more of the following devices: extra heaters at the two ends of the ceramic tube; baffles made from noble metals e.g
38、. platinum); a suitable cover on the cru- cible; a thick-walled crucible made of noble metal. Good thermal insu- lation of the furnace is required in any case. 4.3 Temperature measuring and indicating instruments 4.3.1 The alumina-insulated platinum-10 O/c rhodium/platinum (type S according to IEC 5
39、84-1). or (for extensive use above 1 Mo OC) platinurn-30% rhodium/platinum-6% rhodium (type B according to IEC 584-1) thermocouples shall exhibit low thermal inertia (the diameter of the wires should not be greater than 0,5 rnm). The wires shall have a sufficient length within the furnace (with resp
40、ect to heat conduction along the wires). 4.3.2 Control thermocouples should be located as near as possible to the furnace winding for fast response. The hot junc- tion of the measurement thermocouple, however, shall be placed in the immediate vicinity of the flow field (the crucible). In accordance
41、with IS0 7884-1, the measurement thermo- couple shall be calibrated and the calibration checked regularly. NOTE - Further improvement in the accuracy of the temperature determination is achieved by dipping the (electrically isolatedi measurement thermocouple into the melt and/or by observation of th
42、e temperature distribution by means of two further thermocouples placed above and below the crucible. If the construction of the viscom- eter permits the positioning of the measurement thermocouple at the centre of the plunger, the best assignment of temperature to the shear area, which is mainly re
43、sponsible for the measured viscosity. is achiev- ed; in that case other special devices (see note to 4.2) may be omitted. 4.3.3 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
44、1 pV. Precautions shall be taken that the ice-bath for the cold junc- tion is maintained at O OC throughout the test. If the temperature measuring equipment is fitted with automatic cold junction compensation, the ice-bath can be omitted. 4.4 Crucible and plunger 4.4.1 Crucibles According to their c
45、hemical resistance to the glass melt under test, the crucibles shall be made of ceramic material (e.g. alumina) or noble metal. If ceramic crucibles are used (normally they can be used only once), it is recommended that such a crucible be placed in a larger crucible made of thin noble sheet- metal,
46、in order to protect the furnace in case the ceramic cru- cible breaks. Noble metal crucibles (preferably platinum or platinum-rhodium alloys) require cleaning, e.g. in a hydro- fluoric acid bath. The volume of the crucibles (sample volume) shall normally be between 20 and 250 cm3. 4.4.2 Plungers The
47、 plungers shall be made of noble metal, preferably of platinum-rhodium alloys. They shall be welded to a long thin shaft, reaching out of the furnace to the torque-measuring in- strument. The shaft may be made entirely of noble metal, or alternatively only that part of it which plunges into the melt
48、 may be of noble metal, the part above the melt being made of ceramic material. The lower end of a cylindrical plunger shall be cone-shaped, not plane, in order to avoid bubbles adhering to it; this would produce scatter in the results. Moreover, the plunger shall have no sharp edges, as sharp edges
49、 would be more easily attacked by the melt. Therefore, the plungers should be spheres, cylinders with hemi-spherical ends, or ellipsoids. NOTE - The contribution to the torque of flow arising from the shaft can be restricted to less than 15 %. If the flow field coefficient is to be determined by calculation, the shape of the plunger shall be chosen accordingly. By means of a set of plungers of different sizes, the ratio of the sizes being for example 1 :2, the possible range of measurement can be extended by about one order of magnitude. 4.5 One of the following methods shall b
