ROLLED PRODUCTS

P R O D U C T I O N OF H O T - R O L L E D N O R M A L I Z E D

P I C K L E D S H E E T S

g u . V. L i p u k h i n , V. T. R y a b i n k o v , a n d M. V. G u t n i k

An effect ive method of improvingthe mechan ica l properties and the duct i l i ty of hot-rol led me ta l is heat t rea tment in the form of normal iz ing or annealing. In the co ld- ro l l ing shop of our plant the hot- rol led meta l manu-

factured to GOST 914-56 , 4041-48 , and 5520-62 is normal ized in a continuous unit put into use in 1967.

During the first phase of operation of this unit, it was observed that the hardness of the hot-rol led strip in - creased, its duct i l i ty decreased, and the quali ty of the surface deteriorated. In this period numerous shortcomings in the unit i tself were noticed, e .g. , insufficient length of a i r -cool ing zone, adhesion of the scale (build-up) to the furnace rollers and a bu i ld-up on the bodies of the burners. Scale st icking to the rollers leads to the formation of cer tain impressions on the surface of the strip while it is passing through the high- temperature zone. Consequently,

the unit was rebuik (Fig. 1). In the new design the length of the cooling zone was increased by e l iminat ing the fifth and sixth zones of the heating furnace.

This provided an increase in the output of the deep-drawing quali ty sheets according to COST 4041-48 up to 97.5% and those according to GOST 914 -56 up to 96% After normalizing, the meta l had a homogeneous (with respect to the grains) microstrueture, lower hardness, and higher elongation.

Also, all the furnace rollers in the heating zone were dismantled except the one at the entry to the fifth zone. The surface of this rol ler was coated with zirconium dioxide (ZrOz). After modernizat ion, the strip was made to bend around the pinching rollers in front of the furnace in the shape of the le t ter S. It was pulled through the fur- nace by another set of pinching rollers which were provided beyond the air cool ing zone.

In order to prevent the scale from sticking to the furnace roller, a wate r -ba th tub was fabricated and instal led so that the surface of the roller was cooled by water (Fig. 2). After this, adhesion of the scale to the surface of the

roller was found to be prac t ica l ly absent during normal

z o n e s I Z 3 4 5

/ / I ff s N g ~ / / , /

# a

I 2 3 4 5

Fig. 1. Schematic diagram of the equipment of the middle portion of the normal iz ing unit. a) Before,

and b) after reconstruction. 1) Pinch rollers No. 3; 2) normal iz ing furnace; 3) furnace roller; 4) water - cooling chamber; 5) pinch rollers No. 4.

working of the unit. But when the strip was held over in the furnace for more than 1 5 - 2 0 rain, build up formed on the furnace roller. However, this was easily removed by

l 2 3 4 5- \ X "

Fig. 2. Arrangement for cooling the body sur- face of the furnace roller. 1) Shaft; 2) roll bo -

dy made of heat-resis tant steel; 3) fire c lay covering; 4) key; 5) bath for cooling the ro l l - surface.

Cherepovets Metal lurgical Plant. Ministry of Ferrous Metallurgy of the USSR. Translated from Metallurg, No. 11, pp. 30-32, November, 1970.

�9 1971 Consul tants Bureau, a d iv is ion o f Plenum Pub l i sh ing Corporation, 227 West ]7th Street, New

York, N. Y. 10011. A l l rights reserved. This art icle cannot be reproduced for any purpose whatsoever

without permiss ion o f the publ isher. A copy o f this art icle is avai lable from the publ isher for $15.00.

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TABLE 1. Grading of the Normalized Pickled Metal

Operating conditions of the normalizing

furnace

T

grade, % I

First for ] Rejects,

g r a d e , % I total i scale [ % L___I

pits

Period of master ing the unit, a l l six zones op-

erating 35. 4 61. 7 44. 1 2. 9 Four zones working un-

der creep conditions, the furnace roller coated with ZrO 2 22,3 74,3 57.8 3,4

Four zones working in the region of creep, furnace roller cooled

in water bath 47.5 51.4 48.2 1,1 The same, but using

the new pickling technique (1969) 75.2* 23;7 9.6 1.1

*Without taking into account the meta l accepted in the cutting unit line.

e e N |

7 , 5 8 / / . ~ 1 /

9 / 2

Fig. 3. Schematic arrangement showing a part of the pickling unit. a) Before and b) after reconstruction.

1) Pinch rollers; 2) looping pit; 3) double pinch rol- lers, diam. 500 ram; 4) two-high stand; 5) double pinch rollers diam. 400 mm; 6) second scale break-

er; 7) hydraulic scale breaker; 8) water inlet to pinch rollers.

means of a special device, in addition, rollers ;-~aving grooves along the edges of the body for 400-450 mm

were fabricated and instailed, and arrangements were also made to feed water on the pinching rollers beyond

the water -cool ing chamber and the bending toilers of the coiler. However. the output of f irst-grade sheets after

pickling was found to be about 50% because of the re- jects due to scale pits. since the thick layer of scale formed on the normalized strips is easi ly broken down

during the passage of the strips through the lead portion of the pickl ing tine and the scale sticks to the pinch rolls, causing the creat ion of scale pits on the strip.

In analyzing the operanon of the equipment of the lead portion of the continuous pickling line, it was es t a - blished that while passing through the first scale breaker, the normal ized strip is made to bend twice, the acale breaks down, and, sticking re the main pinching rolle~. leaves scale pits up to 0, 5 - 0, 7 mm deep on the surface

of the strip. The depth of these marks is governed by the force of int ia l compression of the springs of the main

pinch rollers and by the thickness of the Iayer of scale sticking to the surface. After welding in the but t -weld ing machine, the strip is passed on to the looping pit by means of pinch rollers, Here, also. the scale is partly brokeE down. From the looping pit the strip is transferred to the acid baths by means of double pinching rollers. The scale adheres to these rollers also and then gets pressed into the strip,

To e l imina te this defect during the passage of the strip through the lead portion of the pickling line, the lat ter was part ly reconstructed (Fig. 3). Arrangement was made to feed water onto the pinching rollers in front of the looping pit and also beyond the two-h igh stand so that the scale sticking to them was washed away. On the housing of the double pinch rollers beyond the looping pit, a second scale breaker was erected and, beyond it, the hydraulic scale breaker device (pressure 4 arm),

While passing through the second scale-breaker the strip is made ~o bend twice, and, as a result, the scale on both sides of the strip is comple te ly broken down and washed away by the hydraulic scalebreaker , From the looping

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pit into the acid baths the strip is transported by means of a two-high skin pass mill or by pinch rollers beyond it. The step-by-step operation of the equipment of the lead portion of the unit during pickling of the normalized me- tal is given below:

1) The first scale-breaker is out of action (rollers are separated).

2) Only one pair of the main pinch rollers operates with minimum compression of the springs sufficient to ensure unwinding of the roll strip.

3) The straightening machine ensures straightening of the leading and trailing ends of the strip, and on switching over to the normal unwinding speed, the upper cross bar is lifted by means of hydraulic cy - linders.

4) Pinching rollers in front of the looping pit operate.

5) Second scale breaker and hydraulic scale remover operate.

6) Transfer of the strip from the looping pit into the acid baths is carried out by means of a two-high stand or pinch rollers beyond it.

7) The strips are unwound at a lower speed in the lead portion of the unit.

8) In the first loop pit only one strip is accommodated.

When roiling strip of 0 8 - 1 0 KP types of steel, one of the common surface defects of the normalized metal is fissures, which occur mainly during unwinding and rewinding of the strips on the normalizing and pickling units. This defect i~ removed in the two-high skin pass mill. Normally, during unwinding of the roll of the strip without tension, fissures occur, their frequency depending upon the thickness and the properties of the me ta l Winding of the strips at a temperature higher than 90~C also facilitates the occurrence of fissures because the roll is formed by continuous bending of the strip in the bending rollers of the winder. Skin pass rolling of the normalized metal in the pickling line makes it possible to avoid fissures on the extreme boundaries and to obtain strip with a smoother and cleaner surface.

A considerable improvement in the surface finish of the normalized metal as a result of all the steps taken (Table 1) permitted the sorting of the metal in the cutting unit. At present about 65% of the normalized p icked sheets are accepted in the line.

For completely eliminating the scale pits on the strip surface, a system of feeding water under pressure to the pinch rollers of the lead portion of the unit is being worked out by the plant in collaboration with the design or- ganizations which would enable us to get rid of excessive dirt and also eliminate the possibility of broken scale getting pressed into the strip and the formation of scale pits on the pinch rollers.

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