EXCHANGE

OF EXPERIENCE

PRODUCTION

LINING

FOR

N.

UTILIZATION

AND

D.

SOAKING

OF

LARGE

BLOCKS

PITS

UDC 666.76:621.783.224

Sergienko

Modern technologies of constructing and overhauling fur, naces are based on industrial methods in which manual work has been mechanized. The mechanization of lining work makes it n e c e s s a r y to use large r e f r a c t o r y Mocks in place of standard size brick. The n e c e s s i t y for increasing the output of roiled steel slabs and blooms has resulted in a sharp inc r e a s e in the demand for ingots which can only be met by constructing m o r e soaking pits or by increasing the productivity of existing plant. A t the Magnitogorsk Metallurgical Combine the decision went in favor of i n c r e a s i n g the productivity of the soaking pits by increasing the charge of ingots, improving the durability of the r e f r a c t o r y lining, lengthening the period between overhauls, and reducing the time required for renewing the lining. The time required for overhauls was reduced and the period between overhauls shortened by using two types of unfired dinas blocks for the lining. Experiments and industrial experience showed that the e r o s i o n of a r e f r a c t o r y lining of dinas brick usually s t a r t s in mechanically weak s e a m s and then spreads over the entire brick lining. Erosion is at maximum in the middle part of the working zone at the contact points with the ingots and in the top part of the pit framing as a result of the frequent t e m p e r a t u r e changes and the m e c h a n i c a l action of ingots being charged into the pit and subsequently removed. The durability of a dinas b r i c k lining v a r i e s from 2.5 to 3 months. The f i r s t stage of the work of i n c r e a s i n g the period between the overhauls of the soaking pits was started in 1967. In a joint project with the Eastern Institute of R e f r a c t o r i e s engineers and technicians at the Magnitogorsk Metallurgical Combine developed a special technology and produced an experimental batch of dinas r e f r a c t o r y blocks the durability of which in the soaking pits was 6-7 months. The result of the introduction of these blocks and the mechanization of their installation has been that labor costs decreased sharply and the time for renewing the lining has been reduced from 16 to 8 h per soaking pit.

TABLE I. Composition cretes, %

Material

of the Con-

[Composi- Composilion I tion II

Grain size of filler, mm

5--20 . . . . . . 0--5 . . . . . .

45-----3 35-+-3

Fine-ground quartzite Fine-ground dinas Sodiumsilicate solution of density 1.3 g/era a (on 100%) sodium fluosilicate (on lO0%)

20+--3

45-----3 35~3 20•

10 0,6

The r e f r a c t o r y blocks are produced f r o m dinas s c r a p , ground quartzite, sodium silicate solution, and sodium fluosilicate. The composition of the c o n c r e t e s is given in Table 1. The dinas s c r a p is crushed in S-182B type jaw c r u s h e r s and s h a k e r - s c r e e n e d to the required grain sizes. The batch was p r e pared in S-742A concrete m i x e r s . The starting m a t e r i a l s are charged into the m i x e r in the following o r d e r : c o a r s e filler, fine filler, fine-ground quartzite or dinas, sodium fluosilicate. Mixing is dry for the first 2 rain after which the sodium silicate solution is added and mixing continued for a further 5 rain. The composition is charged into steel molds in 50-60 mm deep layers and compacted with TR-1 type pneumatic rammers

Magnitogorsk Administration of Special Constructions and Installations of the "Uraldomnaremont" Trust. Translated from Ogneupory, No. 3, pp. 53-55, March, 1975.

9 76 Plenum Publishing Corporation, 22 7 West 17th Street, New York, N. Y. t 0011. No part o f this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any 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.

184

TABLE 2. C h a r a c t e r i s t i c s of the Blocks* Chemical composition,% SIO,

MgO

CaO

94,04 93,80 94,60

0,36 0,32 0,30

2,40 ] 0,65 2,50 0,65 2,50 0,70

~2

AI,O,

Cold-crushing[ C~en Icalcina_ strength, ~jt porosity vr Fe,O3 itionlo~s Ikg/cmZ i % " 1,15 1,15 1,30

0,90 I 131--165 I 22,6--23,4 0,82 130--171 20,6--24,0 0,60 150--175 21,0--21,4

*Refractoriness IqO0~ equipped with 80 m m square h a m m e r blocks. The molds are f i r s t g r e a s e d with used engine oil. After the f i r s t l a y e r has been laid the large filler grains a r e removed from the c o r n e r s of the mold by hand. Each l a y e r is tamped down c r o s s w i s e and lengthwise at an advancing pitch of 45 mm. Before the next l a y e r is laid the surface of the tamped l a y e r is loosened by hand. The top l a y e r is tamped with e x c e s s composition on top a f t e r which it is smoothed to a level surface. The blocks m e a s u r e 770 • 460 • 420 m m , weigh 300 kg and are dried in counterflow type tunnel kilns at 90-100~ The p r o p e r t i e s of the blocks are given in Table 2. Since 1970 dinas blocks have been in use at the Magnitogorsk, Nizhne-Tagi[, and Kuznetsk M e t a l l u r gical combines and other establishments. The installation of the blocks has been a l m o s t completely m e chanized. The blocks are conveyed to the soaking pits on r o l l e r c o n v e y e r s and laid with a beam c r a n e equipped with two t e t f e r s on guides which a r e used for removing the pit cover. A disadvantage of the method used at the Magnitogorsk Combine for installing the Mocks is that the conveying of the containers with the blocks along the kiln passage and the placing of the blocks on the r o l l e r c o n v e y e r are c a r r i e d out by a 10-ton bridge c r a n e which is engaged during the entire operation of the o v e r haul job and can be used for only one group of pit cells at a time. Changing the lining of a single pit is an 8-h job for 12 w o r k e r s . Experience has shown, m o r e o v e r , that the 300 kg blocks a r e not the best type for i n c r e a s i n g the durability of the lining of soaking pits which does not exceed 6-7 months. Like a brick lining, the e r o s i o n of a block lining s t a r t s on the s e a m s . It was decided to o v e r c o m e these disadvantages by constructing the lining in the form of two large blocks weighing 13 and 18 tons. The r e f r a c t o r y blocks of these weights are made in a steel mold, dried, and then installed with a bridge crane. Lining the soaking pits with two blocks r e q u i r e s a s m a l l e r labor force and the c r a n e time is short. The basic r e a s o n for using only two blocks was to minimize the number of components that can be fabricated in a m e t a l l u r g i c a l plant. In 1971 large blocks were tested and installed at the Magnitogorsk Combine for s l a b - r o l l i n g and blooming plant. A total of 20 blocks have been produced and installed. The durability of the lining has inc r e a s e d to a y e a r . The relining time has been reduced to 1 h and labor productivity has i n c r e a s e d s i g n i f i cantly. The bottom block weighs 18 tons and is provided with a r c h e s . The top block weighs 13 tons and is funnel-shaped. Each block is a parallelepiped with r e c t a n g u l a r t r a n s v e r s e holes in the middle. The lower p a r t of the block contains stiffeners to which the s h e e t - s t e e l installation brackets are secured. The block is handled and conveyed with a c r o s s b a r the latches of which engage the b r a c k e t s on the block and which is then picked up by the c r a n e hook. The large blocks are produced in a mold of 12 mm thick steel sheet r e s t i n g on a stand (Fig. 1). The mold is in sections and its inside c o r n e r s are rounded to facilitate relieving the drying and heating s t r e s s e s . The large blocks are produced by the same technology as the m e d i u m - s i z e d ones but the method of drying is different. The large blocks are dried on the stand with gas b u r n e r s . In the absence of gas, steel pipes 31 ram in d i a m e t e r for steam or hot air a r e installed inside and outside the block at a distance of 100 m m f r o m the surface. The drying t e m p e r a t u r e is 80-100~ In winter the block is c o v e r with a steel hood which helps to maintain a constant t e m p e r a t u r e .

185

7-+ +-7 TABLE a

4!

3. The P r o p e r t i e s o f t h e

Blocks ~o~ ~ ~ Cold-crashing Apparentporo-~ strength, kg/cm2 sity*, % b

Fig. 1. Mold for the large blocks: a) top block; b) bottom block with arch.

1670 190; 180; 200 1650 210; 215; 205 1050 25l; 250; 251

20,2; 20,1; 19,8 20,1;20,2; 20,0 22,1; 21,2; 21,8

*According to three measurements.

The blocks should not be made and dried in freezing weather. for 76 h. The p r o p e r t i e s of the large blocks a r e given in Table 3.

The installed block lining is w a r m e d - u p

According to the technical specifications of the Magnitogorsk Metallurgical Combine the c o l d - c r u s h ing strength of the c o n c r e t e blocks should be 125 k g / c m 2. The c o s t - e f f e c t i v e n e s s of using these blocks is illustrated by the following facts: a b r i c k lining is laid by 20 w o r k e r s in 16-18 h, a lining of m e d i u m - s i z e d blocks by 12 w o r k e r s in 8-10 h, and a lining of l a r g e blocks by three o r four w o r k e r s in 0.7 to 1.0 h.

186