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1、INTERNATIONAL STANDARD INTERNATIONAL ORGANIZATION FOR STANDARDIZATION ORGANISATION INTERNATIONALE DE NORMALISATION MEXJJYHAPOflHAR OPrAHM3AMR n0 CTAHAPTM3AMM 3 ;gJJ,- ,;! : :. ,_; , .a:,%: “i. .,$l b) circular, of diameter d. 3.2 Supports, span The beam is placed horizontally on two supports; the be
2、am axis and the supports are perpendicular. For rectangular cross-section beams the supports are horizon- tal and have straight edges. For circular cross-section beams the support edges may be semi-circles or notches. The distance is between the supports is called the span. The beam juts out only li
3、ttle beyond the supports, satisfying equa- tion (I) : I,1 0,05 are not permissible. Beams deflected down to this limiting value may be turned over for a further run (see also 6.3.3). NOTES 1 The correcting calculations known from the statics of an elastic beam with moderate support ratios q L- 10 ar
4、e subject to the condition that supports are freely movable against one another in the direction of the span. Using the test set-up this is not possible for the flow; therefore mathematical corrections are not available. 2 The dimensions and loads recommended in IS0 7884-7 are taken into account. In
5、 view of a more uniform temperature distribution, shorter beams are proposed. The essential difference in comparison with IS0 7884-7 is that: a) viscosities can be calculated from the bending rates (therefore only considerably smaller relative midpoint deflections are admit- ted); b) the viscosity o
6、f the delivered sample having its own thermal history is determined, if necessary (therefore the sample is not heated up to 1012 dPas, and furthermore no viscosities are deter- mined for decreasing temperatures). 4 Apparatus The requirements for components of the beam bending testing device are give
7、n in 4.1 to 4.6. Figure 2 shows an example of a testing device. 4.1 Viscometer furnace Electrically heated furnace for temperatures up to about 900 X. The introduction of thermocouples for the determina- tion of temperature and temperature distribution along the beam shall be possible. Temperature d
8、ifferences within the beam shall not exceed 1 OC. The furnace shall be controlled by a device for maintaining a constant temperature within + 1 C or better within the work- ing space of the furnace and for the adjustment of linear temperature-time programmes with heating rates up to 6 OC/min. The fu
9、rnace and its control device for the temperature-time programme shall be such that the furnace, starting from a con- stant temperature level, reaches the required heating rate at the latest 5 min afterwards and maintains it to f 10 %. 4.2 Temperature measuring and indicating instruments 4.2.1 The al
10、umina-insulated platinum-10 % rhodium/plati- num (type S according to IEC 564-l) thermocouples or nickel- chromium/nickel (type K according to IEC 564-l) thermo- couples shall exhibit low thermal inertia (the diameter of the wires should be not greater than 0,5 mm). The wires shall have a sufficient
11、 length within the furnace (with respect to heat con- duction along the wires). 1) See for example IS0 7884-I : 1987, annex B, “Examples of certified reference glasses for viscometric calibration”. 3 Copyright International Organization for Standardization Provided by IHS under license with ISO Lice
12、nsee=NASA Technical Standards 1/9972545001 Not for Resale, 04/21/2007 10:22:45 MDTNo reproduction or networking permitted without license from IHS -,-,- IS0 7884-4 : 1987 (El L I h L 5 6 / 1 Support stand, made from vitreous silica 2 Frame, made from a suitable temperature-resistant low- expansion m
13、etal alloy 3 supports 6 Test specimen (beam) 7 Locking rod, made from vitreous silica 8 Upper part of viscometer furnace: vertically movable cap 9 Loadina rod, made from vitreous silica 4 Locking counterpoise, made from a suitable temperature- resistant low-expansion metal alloy 5 Yoke with bending
14、edge, locking edges and suspension of the loading rod, made from a suitable temperature-resistant low-expansion metal alloy A and B : Hot junctions of thermocouples (see 4.2) Figure 2 - Example of a testing device for the beam bending method 4 Copyright International Organization for Standardization
15、 Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/21/2007 10:22:45 MDTNo reproduction or networking permitted without license from IHS -,-,- IS0 7884-4 : 1987 (El 4.2.2 Control thermocouples should be located as close as possible to the furnace
16、 windings for fast response. The hot junction of the measurement thermocouples, however, shall be placed in the immediate vicinity of the beam (see A in figure 2). The axial temperature distribution along the beam shall be monitored by further thermocouples (see 6 in figure 2). In ac- cordance with
17、IS0 7664-1, the measurement thermocouples shall be calibrated and the calibration checked regularly. 4.2.3 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 (acco
18、rding to IEC 564-11, or 4 pV for type K (accord- ing to IEC 564-l) thermocouples. Precautions shall be taken that the ice-bath for the cold junction is maintained at 0 “C throughout the test. If the temperature measuring equipment is fitted with automatic cold junction compensation, the ice-bath can
19、 be omitted. 4.3 Loading pieces A set of loading pieces with masses from about 10 to 200 g (for arrangements according to 6.2.3, up to 1 000 g) made from brass, nickel-plated or equivalent material. The masses of the loading pieces shall be determined to 0,Ol g. The mass of the loading rod including
20、 the core of the displacement pick-up together with the yoke and the bending edge can be limited to about 10 g. 4.4 Beam support 4.4.1 Frame The frame shall be sufficiently rigid against bending and torsion and be made from a suitable temperature-resistant low- expansion metal alloy or hard porcelai
21、n. The front sides of the frame bear sufficiently broad (IO to 15 mm) supports with a radius of curvature of about 0,5 mm, the surfaces of the sup- ports being ground and polished. The span, i.e. the distance between the two lines of contact to the bottom surface of the beam, shall be determined to
22、0,05 mm. Parallelism deviations of the two lines of contact should not exceed 0,05 mm, after the frame has been annealed. After prolonged use, span and parallelism shall be checked. To prevent sticking of the beam to the support, strips of platinum or nickel foil (about 0,Ol mm thick) may be inter-
23、posed. 4.4.2 Support stand The support stand bears the frame upon its upper front surface. In the example shown in figure 2 it is set up separately from the furnace. The stand shall be equipped with an adjustment device for the horizontal support of the beam. The support stand is made from vitreous
24、silica. If temperatures between 750 and 900 OC are often applied, and/or if alkali con- tamination is suspected, alumina refractory as a material for the support stand is a useful alternative. NOTE - Another example for a possible construction of the beam sup- port is shown in IS0 7664-7. In that ca
25、se the supports are machined directly into the top of the stand tube. 4.5 Loading device 4.5.1 Yoke and loading rod The yoke and bending edge are made from chromium-nickel alloy or hard porcelain. The radius of curvature of the bending edge can vary between 0,5 and 2 mm; the cylindrical surface is g
26、round and polished. To prevent sticking of the beam to the bending edge, strips of platinum or nickel foil (about 0,Ol mm thick) may be inter- posed. NOTE - A greater radius of curvature is advantageous for multiple use of the beam after turning it over. The loading rod connects the yoke within the
27、viscometer fur- nace to the loading pieces underneath. The loading rod shall be made from the same material as the support stand tube (see 4.4.2) with respect to similar thermal expansion characteristics. 4.5.2 Locking the Yoke A device is needed for lowering the bending edge onto the beam and for l
28、ifting it after the test. The device shall ensure that the parallelism between the lowered bending edge and the supports is better than 1 o and that the edge is less than 0,5 mm from the median plane. NOTE - A detailed device which is able to fulfil these requirements is given as an example in figur
29、e 2. 4.6 Equipment for the determination of the midpoint deflection rate 4.6.1 Moving indicator (including transducer core) as point of observation for the determination of the deflection rate, placed beneath the viscometer furnace. 4.6.2 Device for the determination of the midpoint deflection Af du
30、ring the measuring time At according to equation (5). Deflections of 0,l mm shall be determined to 1 % (see also tables 1 and 2). 4.6.3 Device for the determination of the total beam deflection f monitoring the limiting condition for the relative deflection z 0,05 with a sensitivity of 0.1 mm. NOTE
31、- Linearly variable differential transformers (LVDTs) with a removable core are suitable for the deflection determination. A measurable elevation adjustment of the coil is then sufficient for the determination off, whilst the measurement of Affsee 4.6.2) is achiev- ed by means of the electronic mete
32、r of the LVDT having several sen- sitivity ranges. With this testing method, recording of the values measured should be aimed at. Alternatively, a measuring microscope with scale micrometers (for Ajl and mounted upon a cathetometer base (forf) may be used. 4.6.4 Measuring device for time intervals r
33、anging from 10 to 10 000 s for the determination of the measuring time At ac- cording to equation (5). Systematic deviations of the measur- ing device shall be determined to 0,2 % and shall be taken into account. 5 Copyright International Organization for Standardization Provided by IHS under licens
34、e with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/21/2007 10:22:45 MDTNo reproduction or networking permitted without license from IHS -,-,- IS0 4.7 4.7.1 7664-4 : 1987 (El Devices for measuring the beam dimensions 5.4 Special requirements Sliding gauge (vernier division l
35、/10 is sufficient) for Special requirements concerning the treatment of sample and beam shall be agreed upon, especially in the following cases : the determination of the beam length 1. 4.7.2 Micrometer caliper for the determination of beam diameter d or beam thickness h and width b. 5 Preparation o
36、f test specimens 5.1 State of delivery The supplied glass sample shall be uniform, bubble-free, homogeneous and annealed. It shall consist of pieces large enough to permit the preparation of the test specimens. 5.2 Preparation of the beams Rectangular beams shall be made from the sample by cold work
37、ing, e.g. diamond-saw cut and mill ground. Cylindrical beams shall be either flame drawn or centreless ground. The beams shall not have any scratches or defects. The dimen- sions shall be within the ranges specified in 6.2.1, 6.2.2 and 6.2.3 and figures 3 and 4. 5.3 Determination of beam dimensions
38、and glass density 5.3.1 Beam length It is sufficient to determine the length of the beam to 0,5 mm. 5.3.2 Rectangular beam cross-section The beam thickness h shall be measured at nine points altogether: viewed in the longitudinal direction, at the ends and at the middle; viewed in the transverse dir
39、ection, near to both edges and at the centre. From these values the arithmetic mean shall be taken. The interval between the highest and lowest measured values shall not exceed 0,02 mm. The beam width b shall be determined near the ends and at the middle, and the arithmetic mean taken from these val
40、ues. The interval between the highest and lowest measured values shall not exceed 0,05 mm. 5.3.3 Circular beam cross-section The beam diameter shall be measured in three different cir- cumferential directions, near each end and at the centre, respectively. The interval between the highest and lowest
41、 measured value shall not exceed 0,02 mm. - 5.3.4 Beam density The beam shall be weighed to the nearest 0,l g. The density shall be calculated from the dimensions and the result of weighing. a) for samples delivered in the form of grains, the condi- tions for melting and annealing the rod (as-drawn
42、or cast from the melt), from which the test specimen will be prepared; b) for specially annealed samples, the highest tempera- tures to which the beams can be exposed without affecting this annealing treatment. 6 Procedure 6.1 Calibration of the testing device Generally, the beam bending measurement
43、 is an absolute determination of the viscosity, i.e. the viscosity is calculated (see 3.5 and 7.2) from the dimensions of the finished test specimen and from the span Is. An examination is recommen- ded by means of a beam of equal dimensions and made from a reference glass of known viscosity. This i
44、s necessary for sup- port ratios q 13 (see 3.6 and 7.3). The calibration includes the adjustment of the frame for horizontal positioning of the plane defined by both supports, Subsequently the highest temperature is set that might occur in this testing device, and after cooling down it is checked th
45、at the horizontal position has been retained. To evaluate the influence of the thermal expansion of the dif- ferent materials used for, the apparatus (mainly the support stand and the loading rod), the following procedure is recom- mended. In place of a specimen glass beam, place a rod of vitreous s
46、ilica of similar dimensions to the test specimen on the supports, engage the loading rod, attach a moderate loading piece, and prepare the furnace for heating up in the usual manner. Heat the furnace to 400 OC and set the device for the determination of the midpoint deflection (4.6.2) near the middl
47、e of its range. With a defined heating rate, increase the temperature to the highest measuring temperature. As a consequence of expansion differences of the different parts of the apparatus, the moving indicator shows an apparent (positive or negative) midpoint deflection f,; this is determined as a
48、 function of temperature and is used, if necessary, for cor- rections (see 7.1.2). The thermocouples shall be calibrated by comparison with a standard thermocouple. This calibration shall be checked at suitable intervals. 6.2 Preliminary estimation of time interval and midpoint deflection The expect
49、ed deformation as a function of load and time inter- val shall be estimated to ensure that the permissible limiting values of the relative midpoint deflection z = 0,05 are not ex- ceeded during a measurement or a series of measurements. For this purpose tables 1 to 3, in connection with figures 3 and 4, shall be used (but shall not be applied when evaluating the real measurements). 6 Copyright International Organization for Standardizatio