alteration of the tempering stress diagram for plate glass

2
The ceramic materials studied are very pure and corrosion resistant and may be used in vessels for making highly near UV transparent lead phosphate flint glass. However, to assess the feasibility of using platinum crucibles for overcuring it is necessary to develop glasses of special composition and carry out preliminary studies on them to establish the optimal time and temperature curing schedule. ALTERATION OF THE TEMPERING STRESS DIAGRAM FOR PLATE GLASS A. I. Shutov, N. V. Lalykin, and A. V. Ovchinnikov UDC 666.155.001.5:666.1.01 The basic properties of the tempering diagram of plate glass (strength, failure char- acteristic) depend on the level of tempering stress. The stress diagram has a character approximating parabolic and is quantitatively estimated according to the parameter ~=I~/'~, (i) where ~p and ~ts are the tempering stresses at the surface of the glass and in a central layer. According to I. A. Boguslavskii [i], the parameter x is determined by the absolute magnitude of the Bio (Bi) number and increases continuously with increase of the latter. Having an improved technique for calculation of the tempering stress [2] and attempt- ing to reproduce the analytical x = f (Bi) dependence, we obtained a function considerably different from the one previously studied (shown in Fig. i by the dash-dot line) which cast doubt on either the computation technique or the data of publication [i]. In this connection, in performing the analysis we used the data of different authors on the relationship between the tempering stress with the cooling rate and glass thickness [3-8]. According to the Bio criteria, Bi= ad/(2X), ( 2 ) where e is the heat transfer coefficient during cooling; d = the glass thickness; and % is the glass thermal conductivity, ~ ~ const. We chose as an alternative de parameter for Bi the de behavior given in [3, 4]. A graph illustrating the effect of the de parameter on Op and Ors is shown in Fig. i. The stress in the central plane was measured with a PKS-56 poiarimeter-polariscope using a set of quartz wedges, and the surface stress was measured with a DSR refractometer from the firm PPG (USA). The thickness range measured was from 3 to 6 mm, and the a values were from 200 to 540 W/(m2.K). The first measurement, which could be verified by comparison of base curve 1 (see Fig. i) with the results of the other independent studies has good comparability: the maximum deviation does not exceed 10% and the mean-square deviation is in the 5% range. Analogous results were obtained with the base curve 2 of R. Gardon. Accordingly, the assumption of the impossibility of comparing the data of dissimilar experiments (for ex- ample, different glass compositions) becomes less valid. The base curves i and 2 can be arranged on the basis of further analysis of phenomena applicable to the alteration of tempering stress. Calculating the parameter < with the relationship (i), we obtained the curve 3 (see Fig. I), the character of which does not correspond to the generally accepted~ In the region of small de values, ~ 500 mm-W/(mm2-K), the parameter ~ increases quite sharply, reaching ~ 2.5, which is specifically predicted by the tempering theory of G. M. Bartenev. BTISM, Tekhstroisteklo Scientific-Production Association. Translated from Steklo i Keramika, Nos. 11-12, pp. 22-23, November-December, 1992. 516 0361-7610/92/1112-0516512.50 @1993 Plenum Publishing Corporation

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Page 1: Alteration of the tempering stress diagram for plate glass

The ceramic materials studied are very pure and corrosion resistant and may be used in vessels for making highly near UV transparent lead phosphate flint glass. However, to assess the feasibility of using platinum crucibles for overcuring it is necessary to develop glasses of special composition and carry out preliminary studies on them to establish the optimal time and temperature curing schedule.

ALTERATION OF THE TEMPERING STRESS DIAGRAM FOR PLATE GLASS

A. I. Shutov, N. V. Lalykin, and A. V. Ovchinnikov

UDC 666.155.001.5:666.1.01

The basic properties of the tempering diagram of plate glass (strength, failure char- acteristic) depend on the level of tempering stress. The stress diagram has a character approximating parabolic and is quantitatively estimated according to the parameter

~ = I ~ / ' ~ , (i)

where ~p and ~ts are the tempering stresses at the surface of the glass and in a central

layer.

According to I. A. Boguslavskii [i], the parameter x is determined by the absolute magnitude of the Bio (Bi) number and increases continuously with increase of the latter.

Having an improved technique for calculation of the tempering stress [2] and attempt- ing to reproduce the analytical x = f (Bi) dependence, we obtained a function considerably different from the one previously studied (shown in Fig. i by the dash-dot line) which cast doubt on either the computation technique or the data of publication [i].

In this connection, in performing the analysis we used the data of different authors on the relationship between the tempering stress with the cooling rate and glass thickness [3-8] .

According to the Bio criteria,

Bi= ad/(2X), ( 2 )

where e is the heat transfer coefficient during cooling; d = the glass thickness; and % is the glass thermal conductivity, ~ ~ const.

We chose as an alternative de parameter for Bi the de behavior given in [3, 4].

A graph illustrating the effect of the de parameter on Op and Ors is shown in Fig. i.

The stress in the central plane was measured with a PKS-56 poiarimeter-polariscope using a set of quartz wedges, and the surface stress was measured with a DSR refractometer from the firm PPG (USA). The thickness range measured was from 3 to 6 mm, and the a values were from 200 to 540 W/(m2.K).

The first measurement, which could be verified by comparison of base curve 1 (see Fig. i) with the results of the other independent studies has good comparability: the maximum deviation does not exceed 10% and the mean-square deviation is in the 5% range. Analogous results were obtained with the base curve 2 of R. Gardon. Accordingly, the assumption of the impossibility of comparing the data of dissimilar experiments (for ex- ample, different glass compositions) becomes less valid. The base curves i and 2 can be arranged on the basis of further analysis of phenomena applicable to the alteration of tempering stress.

Calculating the parameter < with the relationship (i), we obtained the curve 3 (see Fig. I), the character of which does not correspond to the generally accepted~ In the region of small de values, ~ 500 mm-W/(mm2-K), the parameter ~ increases quite sharply, reaching ~ 2.5, which is specifically predicted by the tempering theory of G. M. Bartenev.

BTISM, Tekhstroisteklo Scientific-Production Association. Translated from Steklo i Keramika, Nos. 11-12, pp. 22-23, November-December, 1992.

516 0361-7610/92/1112-0516512.50 @1993 Plenum Publishing Corporation

Page 2: Alteration of the tempering stress diagram for plate glass

161, Mpa 240

12# *#

eo { ~ ~ 2

2 ~ 4 5 2 dc~ -10- s ~'W/(m -K)

Fig. i. Tempering stress as a func- tion of the complex parameter d~: I) Op according to E. Mikhalik and S.

Ohlberg [4]; 2) Ots according to R.

Gardon [3]; 3) calculated values of <; �9 ) according to data of Tekhstroisteklo [6]; o) according to M. Takatsu and D. Watanabe [5].

On further increase of tempering rate (or increase of thickness of the glass), the < = f(d~) curve assumes a faint extremal character in the region d~ = 2000 mm.W/(m2-K). The increase in < with increase of the parameter d~ does not exceed 25%.

Thus, a cardinal change in the tempering stress diagram using the traditional glass- tempering means (heating and continuous cooling) is impossible, and special heat-treatment methods are required.

LITERATURE CITED

i.

2.

3.

4.

.

6.

I. A. Boguslavskii, High-Strength Tempered Glasses [in Russian], Stroizdat, Moscow (1969). A. I. Shutov and N. V. Lalykin, "Algorithm for determination of instantaneous and residual tempering stress," Steklo Keram., No. i, 15-18 (1981). R. Gardon, "Thermal tempering of glass," in: Glass Science and Technology, Vol. 5, New York (1988), pp. 68-74. E. R. Mikhalik, S. M. Ohlberg, and Z. F. Wiss, '~oglichkeiten und Begrenzungen zur Erhohung der mechanischen Festigkeit des Glass," Shiller Univ. Jena, Math.-Natur, DDR, No. 2, 293-292 (1974). M. Takatsu and J. Watanabe, "Residual stresses in tempered glasses," J. Ceram. Soc. Jpn., No. 6, 28-34 (1972). A. G. Shabanov, V. P. Markov, A. F. Shutov, et al., "Intensification of the air tempering process in plate glass," Steklo Keram., No. ii, i0-ii (1980).

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