1、INTERNATIONAL STANDARD INTERNATIONAL ORGANIZATION FOR STANDARDIZATION ORGANISATION INTERNATIONALE DE NORMALISATION MEXJJYHAPOflHAR OPrAHM3AMR n0 CTAHAPTM3AMM 3 ;gJJ,- ,;!: :. ,_; , .a:,%: “i. .,$l the beam axis and the supports are perpendicular. For rectangular cross-section beams the supports are
2、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 little beyond the supports, satisfying equa- tion (I) : I,1 L Q 1.15 . . . S (I) * dN.s 1 dPas = 1
3、7 = 1 P (P is the symbol for poise1 1 IS0 7884-4 : 1987 (El Cross-sections of the beams A supports Be bending edge, unloaded B, bending edge, loaded (elastically deformed beam) B, bending edge, sagged position Af after measuring time At CAf is the interval between B, and BP) I beam length Is span; p
4、osition of bending edge at Is/2 Fc force of the load b beam width h beam thickness 1 (rectangular cross-section) d beam diameter (circular cross-section) Figure 1 - Principle of viscosity determination by beam bending 3.3 Load, loading pieces, bending edge The load consists of all parts of the measu
5、ring device on which gravity acts to produce a force on the beam by means of the bending edge, i.e. the loading pieces (variable) and the loading rod together with yoke and bending edge (given for the in- dividual measuring device). The load exerts a vertically downward directed force Fs upon the ce
6、ntral cross-sectional area of the beam (distance Is/2 from both supports). The bend- ing edge is horizontal and parallel to the supports. 3.4 Dead-weight The dead-weight stems from the beam; it can be taken into ac- count by calculation - see equations (13) to (15). Within the span, the force of the
7、 dead-weight acts in the same sense as that of the load. The dead-weight of the overhanging parts of the beam produces a force component opposed to the force of the load; this part of the dead-weight can be neglected if equa- tion (1) is respected. 3.5 Flow When the force of the load (disregarding t
8、he dead-weight) acts upon a beam free from defects and showing Newtonian or linear-viscoelastic behaviour, and all elastic deformations after applying the load have faded out and thereupon the sag is suffi- ciently small, the flow is described by equation (2) as follows : df -= 13, Fo dt 144 ha . .
9、. where (2) dfldt is the midpoint deflection rate, with which the bend- ing edge moves downward (see figure I); I, is the cross-sectional moment of inertia of the beam; 1s is the span; 2 IS0 7884-4 : 1987 (E) q is the dynamic viscosity of the glass. NOTE - The factor 144 comprises the Trouton ratio
10、3 and some in- tegration factors. The cross-sectional moment of inertia for beams with a rec- tangular cross-section is described by equation (3) : I,= J$ . . . and that for beams with a circular cross-section, by equation (4) : nd, z, = - 64 . . . During the measuring time At the beam sags below th
11、e bend- ing edge for a distance Af. The viscosity is calculated according to equation (5) : (5) r is the viscosity in decipascal seconds; Af is the sag of the beam in millimetres during measuring time At; Z, is the cross-sectional moment of inertia in millimetres to the fourth power; At is the measu
12、ring time in seconds; m is the mass of the load in grams; Is is the span in millimetres. When calculating the viscosity it may be necessary to take cor- rections into account (see 7.1 to 7.3). 3.6 Range of applicability of the simplified calculations Equations (2) and (5) hold only for very thin bea
13、ms and very small deflections. That range is characterized by the support ratio q according to equation (6) or equation (7) : q= $f . . . 1,215 4= - d . . . (7) and also by the relative midpoint deflection z: (8) In equation (8) f is the total midpoint deflection of the beam, i.e. f is the sum of th
14、e deflection Af during the measuring time At according to equation (5) together with the elastic deflection of the beam caused by the load and - if necessary - the deflections during previous flows. Measuring devices with q 0,05 are not permissible. Beams deflected down to this limiting value may be
15、 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 are subject to the condition that supports are freely movable against one another in the direction of the span. Using the test set-up th
16、is 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 view of a more uniform temperature distribution, shorter beams are proposed. The essential difference in comparison with IS0 7884-7 i
17、s that: a) viscosities can be calculated from the bending rates (therefore only considerably smaller relative midpoint deflections are admit- ted); b) the viscosity of the delivered sample having its own thermal history is determined, if necessary (therefore the sample is not heated up to 1012 dPas,
18、 and furthermore no viscosities are deter- mined for decreasing temperatures). 4 Apparatus The requirements for components of the beam bending testing device are given 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
19、 to about 900 X. The introduction of thermocouples for the determina- tion of temperature and temperature distribution along the beam shall be possible. Temperature differences within the beam shall not exceed 1 OC. The furnace shall be controlled by a device for maintaining a constant temperature w
20、ithin + 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 furnace and its control device for the temperature-time programme shall be such that the furnace, starting from a con- stant temperature
21、 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 alumina-insulated platinum-10 % rhodium/plati- num (type S according to IEC 564-l) thermocouples or nickel- chromium/nickel (type K acco
22、rding 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 length within the furnace (with respect to heat con- duction along the wires). 1) See for example IS0 7884-I : 1987, annex B, “Exampl
23、es of certified reference glasses for viscometric calibration”. 3 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 metal alloy 3 supports 6 Test specimen (beam) 7 Locking rod, made from vitreous silica 8
24、 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 edge, locking edges and suspension of the loading rod, made from a suitable temperature
25、-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 IS0 7884-4 : 1987 (El 4.2.2 Control thermocouples should be located as close as possible to the furnace windings for fast response. The hot jun
26、ction 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 IS0 7664-1, the measurement thermocouple
27、s 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 (according to IEC 564-11, or 4 pV for type K
28、(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 be omitted. 4.3 Loading pieces A set of
29、 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 the core of the displacement pick-up to
30、gether 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 porcelain. The front sides of the frame bear suf
31、ficiently 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 twolines of contact to the bottom surface of the beam, shall be determined to 0,05 mm. Parallelism deviations of the tw
32、o 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- posed. 4.4.2 Support stand The support st
33、and 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 silica. If temperatures between 750 and 9
34、00 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 case the supports are machined directly int
35、o 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 ground and polished. To prevent sticking o
36、f 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 viscometer fur- nace to the loading piece
37、s 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 lifting it after the test. The device shal
38、l 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 figure 2. 4.6 Equipment for the determination
39、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 during the measuring time At according to e
40、quation (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 - Linearly variable differential transfor
41、mers (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 meter of the LVDT having several sen- sitivit
42、y 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 ranging from 10 to 10 000 s for the determ
43、ination 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 IS0 4.7 4.7.1 7664-4 : 1987 (El Devices for measuring the beam dimensions 5.4 Special requirements Sliding gauge (vernier divi
44、sion l/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 Prepara
45、tion of 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 col
46、d working, 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 dimen
47、sions 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 transver
48、se direction, 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 the
49、se values. 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 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 an
