P R O D U C I N G G L A S S S 8 9 - 2 I N E L E C T R I C F U R N A C E

U S I N G M E C H A N I Z E D D R A W I N G O F G L A S S T U B E S

K . A . K o s t a n y a n , A . F . M e l i k - A k h n a z a r o v , A . R . A k o p y a n , A . Y a . R a p o p o r t , Ao S. E l ' b a k y a n , A . V . Y u r c h e n k o , a n d A . A . K h a l a t y a n

UDC 666 ol.031.5 : 666.1.036.5

In the las t decade an inc reased in t e re s t has been obse rved for e l ec t r i c g lassmaking . The number of indust r ia l e t ec t r i c g l a s smak ing fu rnaces in va r ious technical ly advanced count r ies of the world is in- c r ea s ing rapidly . The p rac t i ce of e l ec t r i c g la s smaking has shown that it enables one to sharp ly r a i s e the quali ty of ce r t a in types of g l a s s e s and to i nc r ea se the output of suitable products .

This a r t i c l e p r e sen t s the r e s u l t s of developing and commerc i a l i z ing the technology of producing g lass $89-2 in an indust r ia l e l ec t r i c furnace of 6-8 tons /day capaci ty , using mechanized drawing of g lass tubes . The composi t ion of g lass $89-2 belongs to the p o t a s s i u m - c a l e i u m - a l u m i n o s i l i c a t e s containing up to 3% bor ic anhydride [1-2].

F igure 1 shows the re la t ionship between t e m p e r a t u r e and e lec t r i c conductivity of g l a s se s $89-2 and $52-1. On the bas i s of s tudies conducted in la rge l abo ra to ry fu rnaces [3] the product ion of g lass $52-1 has a l ready been m a s t e r e d in indust r ia l scale [4]. It is evident that g lass $89-2 is c h a r a c t e r i z e d byh ighe r e lec t r i c conductivity due to the higher amount of a lkal i oxides in it.

The di f ference in composi t ion and e lec t r i c c h a r a c t e r i s t i c s of g l a s se s $89-2 and $52-1 has been the cause for conducting p r e l i m i n a r y t r i a l s of producing g lass $89-2 in an exper imen ta l furnace with a view to es tabl i sh ing the specif ic f ea tu res of this technology.

Glass $89-2 was produced in a s ing le -phase e lec t r i c g l a s s - m a k i n g furnace of 0.5 ton /day capaci ty . The e lec t r i c furnace (Fig. 2) cons is ted of two pa r t s : m e l t i n g - f i n i n g and drawing, connected by a channel. The pouring and drawing opera t ions were mechan ica l . Towards the end of the drawing zone a feeder having a bot tom hole of 24 m m d i am e t e r was cons t ruc ted for pouring the mol ten g lass and maintaining i ts con- stant level . The hear th and walls of the tanks were laid with r e f r a c t o r i e s "Armeniya" and the i r upper pa r t

with dinas. The drawing pa r t and the additionally built feeder were

p, ohm. cm

i i ~ . , I

. . . . . . _ a - . . . . . . . . . . . 4 - . . . .

Y g ~ - - 1

ZO . . . . . . . . . . . . . . . . .

5 1 - . . . .

!?ga 139a 1350 l q -O0 t#50 l;, ~

Fig. 1. Rela t ionshipbetween t e m p e r a t u r e and specif ic e l ec - t r i c r e s i s t a n c e of g l a s s e s $52-1 (1) and $89-2 (2).

heated by sil i t rods . The tank walls of both the zones and the roof of the drawing zone were insula ted with chamotte b r i cks for reducing the heat l o s se s . The molybdenum sheet e lec t rodes were used: two pa i r s of them in the g las smaking pa r t and one pa i r in the drawing par t . The molybdenum conductors were cooled by wa te r coo le r s .

The study of g lassmaking p r o c e s s e s in the expe r imen ta l furnace showed that, in spite of the la rge cur ren t load, a lmos t twice exceeding the load in making boros i l i ca te g lass in a s im i l a r furnace, there is a lmos t no i nc rea se in the amount of molybdenum pass ing into the g lass me l t f r o m the e l ec t rodes . Molybdenum, the re fo re , does not have any effect on fu r the r p rocess ing of the g l a s s .

It was also es tab l i shed that the incorpora t ion of commonly used a c c e l e r a t o r s and fining agents, pa r t i cu la r ly NaC1, AS203, and NaNO3, in the charge cons iderably a c c e l e r a t e s the g lassmaking p roce s s without

T rans l a t ed f r o m Steklo i Keramik i , No. 9, pp. 17-19, September , 1975.

�9 76 Plenum Publishing 6brporation, 22 7 West 1 7th Street, New York-, ,~: Y. 10011. No part o f this publication may be reproduced, stored #7 a retrieval system, or transmitted, #7 ally form or by aio, means, electronic, mechanical, photocopying, microfilming, recording or otherwise, without written permission o f the publisher. A copy o f this article is available from the publisher for $15. 00.

603

• Bakor

~ Chamottr

Lightweight Chamotte

~ Dinas

Fig. 2o Layout of the experimental electric glassmaking furnace of 0.5 ten/day capacity and temperature distribution along the depth of the glassmaking tank~

significantly changing the quality of glass . The use of sodium sulfate leads to the formation of bubbles and black stains. In this context a number of fac tors were discovered that could cause difficulty in making $89-2 glass in an industrial furnace because of its low fusibility. To achieve the optimum tempera ture distribution along the depth of the mel t ing- f in ing tank that would ensu re the given pa rame te r s of the glassmaking process steps were evolved to ra ise the level of molten glass with small constructional mod- ification of the furnace set-up.

The data regarding the tempera ture m e a s u r e - ment at depth in the center of the glassmaking part of the furnace are given in Fig. 2. It is evident that the maximum tempera ture in this par t is 1450~ and it is obtained at a depth of 40-50 cm below the level of molten glass~

Pa rame te r s of the Furnace

Production capacity, ten/day . . . . . . . . . . . . . . . 0.5 Depth, m . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.9 Area of the glassmaking and fining zone, m 2 . . . . . (0.6 • 0.7)= 0.42 Wattage of the glassmaking and fining zone, k W . . . 70 Wattage of the drawing zone . . . . . . . . . . . . . . . . 18 Voltage of the e lect rodes in the glassmaking

and fining zone, V . . . . . . . . . . . . . . . . . . . . . 70 Current at the e lect rodes of the glassmaking

and fining zone, A . . . . . . . . . . . . . . . . . . . . . 1015 Current density at the e lect rodes of the

glassmaking and fining zone, A / m 2 . . . . . . . . . . 0.4

The t r ia l s that have been ca r r i ed out showed that the technology of glassmaking under a charge layer can be taken as the bas is of the technology of producing glass $89-2 industrially, using mechanized drawing of glass tubes.

The industrial e lect r ic furnace consis ted of a me l t ing- f in ing tank and two drawing zones on ei ther side with additionally constructed chambers ATG. The drawing zones were connected with the drawing tank by a deep-seated channel and the zones had pouring holes~ The walls and hearth of the furnace below the level of molten glass were lined with e lec t ro- fused re f rac to r i e s and were insulated with chamotte r e - f rac tor ies for reducing the heat losses . The dinas r e f r ac to r i e s were used for the upper s t ruc tures of the drawing zones. The arch roof of the glassmaking tank of the furnace was detachable and it was installed only during the period of d ischarge and at the t ime of prolonged stoppage of supply of e lec t r ica l energy. In the glassmaking tank two pai rs of molybdenum sheet e lec t rodes were used. The electrodes were en- ergized by a s ingle-phase induction regulator . In each of the channels there were two rod e lec t rodes at the bottom with a high-frequency supply (VPCh 50/8000).

The experience of using this furnace showed that with normal working there was no necess i ty of switching on the bottom elect rodes intended to maintain a given tempera ture in the channe l As a result , the e lec t rodes worked only at the t ime of start ing. Thus, the high-frequency heating of the channel should be considered as superfluous.

To increase the power fac tor at the t ime of switching on the t r an s fo rmer (6 kW) four sections of static condensers were installed. To ensure a r e se rve supply the possibility of supplying the e lec t r ica l energy f rom a r e se rve source through a double-pole switch was also envisaged.

The charge and cullet were loaded in an even layer with the help of an automatic vibrat ing charger blocked with an electrocontaet level indicator URK-2. The drawing zones were preheated by natural gas.

604

0,4-- --~

o,a

LO t

1.2

l,J t

800 lO00 r l*O0 ~7C

Fig. 3. Temperature dis- tribution along the depth of the glassmaking tank of the industrial furnace for producing glass $89-2 with a production capacity of 7 tens/day.

On the basis of the studies on producing glass $89-2 in the experi- mental furnace and during the starting and commissioning works, the required temperature distribution along the depth of the furnace was established so as to ensure the given parameters of the technological process of glassmaking (Fig. 3). In this process it was necessary not only to control the electrical regime but also to vary the level of molten glass above the electrodes as well as to change the amount of accelerators in the charge. In an industrial furnace the incorporation of accelerators in the charge has a particularly strong effect due to the absence of the arch roof, as the accelerators help in quick burning of the charge, denude the surface of the glassmaking part, increase the heat losses from the surface, and disturb the temperature distribution along the depth of the furnace, thus, shnultaneously increasing the heat losses.

In order to have a constant layer of charge above the molten glass in the glassmaldng part of the furnace, which ensures a steady distribution of temperature along the depth, the following steps were taken: the charge/ culler ratio was varied, the melting accelerators and fining agents were totally avoided, the production capacity of the furnace was kept on the higher side within the designed limits, the charging interval was reduced, and the moisture content of the charge was decreased.

Electric Glassmaking Furnace Parameters for Producing $89-2 Glass, Using Mechanized Drawing of Glass Tubes

Production capacity, tens/day ............ 7 Wattage, kW ........................ 320 Surface area of the glassmaking, part, m 2 .... 3.1 Specific extraction per 1 m 2 of glass- making surface, tens/(m 2. day) ........... 2.26

Current density at the electrodes, A/crn 2 .... 0.35

The production of $89-2 glass in the electric furnace using mechanized drawing of glass tubes showed that the output of acceptable products by this process is almost double in comparison with a similar fur- nace with gas heating. The rejection, on average, is 5% and the rejection due to capillarity of glass tubes is sharply reduced.

The successful and steady working of the above-described electric glassmaking furnace provides the base for recommending such furnaces for producing not only the borosilicate glasses but also the common sodium-potassilml-magnesium-aluminosflicate glasses such as sg0-1 that has found wide ap- plication in the electrotechnlcal industry.

1. 2. 3.

4o

LITERATURE CITED

Handbook on Glass [in Russian], Stroiizdat, Moscow (1973), p. 94. Handbook on Glass Production [in Russian], Vol. I, Gosstroiizdat, Moscow (1963), p. 715. M. Go Manvelyan, A. F. Melik-Akhnazarov, K.A.Kostanyan, et al., Electrical Glassmaking [in Rus- sian], Armgosizdat, Erevan (1968). S. L Matyusha et al., Steklo i Keram., No. 8 (1973).

605