TUBE ROLLING USING A PIERCING MILL--PLUG MILL--SIZING

MILL SEQUENCE

V. Ya. Osadchii, I. G. Getiya, M. A. Levshunov, F. D. Mogilevkin, V, V. Frolochkin, L. I. Lapin, A. V. Saf'yanov, A. P. Shpyrev, and V. N. Emets

UDC 621.771.28.04

In collaboration with the Chelyabinsk Tube-Rolling Mill, the All-Union Machine- Building Correspondence Institute has developed a rolling technology and made investi- gations into the efficient redistribution of deformation between the mills when rolling thick-walled tubes in carbon steels on the 140 tube-rolling line. The line includes an annular heating furnace, a piercing mill with mushroom-shaped rollers and axial de- livery, an automatic mill, a three-roll plug mill with axial delivery, and a twelve- stand sizing and extension mill.

The reduction on the piercing, automatic, plug, and sizing mills was 3.1, 1.2, 0,98, and 1.06,respectively, which made it possible-to distribute the deformation be- tween the piercing and plug mills (Table i). The thick-walled tube-rolling technology using a piercing mill--plug mill--sizing mill sequence was worked out having regard to the following prerequisites. First, the possibility of piercing with substantial re- ductions on a mill with mushroom-shaped rolls; second, the possibility of increased wall reduction in a three-roll plug mill; third, the(pierced-billet external diameter adopted is equal to the tube diameter after the automatic mill, as in rolling in the generally accepted sequence; fourth, the tube external diameter remains unchanged after the plug mill; fifth, the maximum finished tube length is calculated according to the length of the piercing-mill output side.

TABLE i. Rolling Table for 140x(7-14)-mmTubes without an Automatic Mill (Pierced Billet diameter 140 mm, external diameter of tube 155 mm and roll-pass size 140 mm on plug mill, external diameter of hot tube 140.9 mm, number of working stands 7 and re- duction over diameter 14.1 mm in sizing mill)

JPiereing mill

o 2

pierced bi l le t size, mm

140• 1500 142 140• 1700 142 140x9 1800 142

re~:uc-. [ distance, diameter, tic n in, I inm, b e - go :ge [tween ram, of:

.0

0

7,5 7140 26 18,5 114 131 118 108 4,76 8,5 7190 26 18,5 114 131 116 t08 4,23 9,0 7220 26 18,5 114 131 115 108 4,01

Plug mill

tube size, diameter. mm mm, off

0

Sizing miI s i z e ~ f h ~ t

tube, mm

7,0 6950 137 121 0,97 7,0 7680 1,11 5,12 8,0 6940 135 121 0,97 8,0 7680 1,11 4,52 8,5 6940 134 121 0,96 9,0 7280 1,05 4,04

140KI0 2100 144 10,5 7190 24 17,0 I16 133 115 108 3,42 9,5 7290 132 114 1,01 I0,0 7700 1,06 3,67 140• 2300 144 11,5 7250 24 17,0 I16 139 I13 102 3,15 10,5 7280 131 114 1,0 i i , 0 7730 1,06 3,36 140• 2500 144 12,5 7300 24 17,0 1t6 133 111 102 2,92 11,5 7270 129 114 t ,0 12,0 7760 1,07 3,10 140• 2600 144 13,5 7090 24 17,0 116 133 109 95 2,72 12,5 6990 128 108 0,99 13,0 7510 1,07 2,89 140X14 2800 144 14,5 7160 24 17,0 I16 133 107 95 2,56 13,5 7040 126 108 0,98 14,0 7570 1,07 2,70

- All-Union Machine-Building Correspondencelnstitute. Chelyabinsk Tube-Rolling Mil~. Translated from Metallurg, No. 4, pp. 32-34, April, 1975.

�9 1976 Plenum Publishing Corporation, 227 West l 7th Street, New York, N.Y. 10011. No part of 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.

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TABLE 2. ing a 144• Billet (rolling temperature 1210-1230~

Roll revolution without load,

rpm

110 120 130

Load Distribution to Electric Motors and Unit Energy Consumption in Pierc-

I Load on motors, kW

left J right I total

890 688 1578 855 755 1630

1040 666 1706

Roll revolutions during piercing, rpm

left I right

99 99 108 108 114 112

I Unit energy consumption

kWh/ton [ kWhflinea~ m

17,2 0,538 16,0 0,500 14,9 0,466

TABLE 3. Load Distribution on Electric Motors and Unit Energy Consumption in Plu~ Rolling a 140 • lO-mm Tube

Rolling tern.. Roll revolu- Roll revolutions during plug perature tion without rolling, rpm

~ right left

Load on motors, kW

!load, rpm upper fight left upper total

Unit energy con- ramption

kNqa/to~ kWh/linear" rr

WRh automatic mill

990--1020 150 133,5 138 138 180 138 85,2 403,2 4,26 0,1340 160 147,5 150 145 195 150 52,5 397,5 3,82 0,1205 175 150 158,5 156 204 145 79,0 428 3,85 0,1210

Without automatic mill 1100--1130 150 129 131 133,5 224 217 164 605 6,47 0,1940

160 140 140 145 230 217 138 585 5,50 0,1650 175 150,5 156 150,5 269 263 79 611 5,38 0,1615

An increase in the reduction from 3.1 to 3.6 in the piercing mill and an increase in the wall-thickness reduction in the plug mill from 6 to 12% at a reduction of up to 1.06 are features of thick-walled tube rolling without an automatic mill. The increase of 10~12@~ (compared with the generally accepted sequence) in tube rolling temper-

ature favors this.

The increased reduction in the piercin~ mill was implemented with the existing roll-pass design, with an input taper angle of 2 ~ 30' and an output taper angle of 4 ~ , at a billet piercing temperature of 1210-1230~ A drop of 11-18 rpm in the roll rev- olutions was observed at the instant of bite, depending on the speed routine.

The loading distribution to the motors and the unit energy consumption in pierc- ing a 144 • 10.5-mm billet are shown in Table 2. It should be noted that the load on the electric motors is unevenly distributed and amounts to 52.5-61.0% of the total on the left-hand roll (from the entry side). As the roll peripheral velocity increases, the load on the electric motors rises, but the unit energy consumption falls becauses of the greater increase in rolling speed. Thus the load on the electric motors in- creases from 1578 to 1706 kW, or by 1.08 times, when the roll peripheral velocity rises from 0.467 to 0.532 m/sec, i.e., by 1.14 times. In these circumstances the unit en- ergy consumption falls from 17.2 to 14.9 kWh/ton, or from 0.538 to 0.466 kWh/linear m,

i.e., by 1.16 times.

Tubes were rolled with increased wall thickness reduction in the plug mill with two roll-pass design versions: with respective entry and exit taper angles of 2 ~ and 2 ~ 30' and 2 ~ and 1 ~ I0' at a billet-rolling temperature of II00-I130~ The distribu- tion of maximum loads on the electric motors of the plug mill and the unit energy con- sumption in rolling a 140 • 10-mm tube with and without an automatic mill using the sec- ond roll-pass design version are given in Table 3. The drop in roll revolutions is greater in the plug mill than in the piercing mill, amounting to 11.5-25 rpm in tube rolling in a sequence with an automatic mill and 15-24.5 rpm without the automatic mill.

The total load on the electric motors is distributed mainly between the right- and left-hand rolls (from the entry side). In tube rolling with an automatic mill, the load is distributed over the electric motors as follows: right-hand 45-49%, left-hand 34-38%,

280

a 1 0 0 , ~ i ' , , . ' ~ .~ "

80 ' " '

c

Time. sec Z 6 10 t,~ 18 3 6 9 12 f E

Transverse variation in wall thickness, %

Fig. i Fig. 2

Fig. i. Operations chart in rolling 140 x 10-mm tubes in a sequence with (a) and with- out (b) the automatic mill: A) piercing mill; B) automatic mill; C) plug mill.

Fig. 2. Effect of rolling sequence (a) and plug-mill tool design (b) on transverse variations in the wall thickness of 140 x 14-mm tubes: i) front end; 2) rear end.

and upper 13-21%; in rolling without the automatic mill the load distribution is right- hand 37-44%, left-hand 36-43%, and upper 13-27%. Consequently the load distribution is more even in tube rolling without the automatic mill.

As the peripheral velocity of the rolls increases from 0.47 to 0.53 m/sec in plug rolling of tubes with an automatic mill, the load on the motors increases by 1.06 times and amounts to 4.28 kW. The unit energy consumption in these circumstances falls by i.i times and amounts to 3.85 kWh/ton. When tubes are plug rolled without the automatic mill and the speed increases within the same limits, the load increases by a total of 1.01 times and amounts to 611 kW. The unit energy consumption decreases by 1.2 times and amounts to 5.38 kWh/ton. It should be noted that the load on the electric motors and the unit energy consumption in rolling 140 x i0 mm-tubes without the automatic mill increase by 1.4-1.5 times on the whole.

A time study of mill operation in rolling 140 x 10-mm tubes with and without the automatic mill was made and an operations chart plotted (Fig. i) to find the effect of the rolling sequence on tube-rolling installation output. With the normal sequence the rolling cycle takes 48.2 sec as against 36.1 sec in rolling without the automatic mill, i.e., capacity exists for increasing the output of the installation in rolling thick- walled carbon steel tubes.

An analysis of the quality of tubes rolled with various process sequences (Fig. 2) showed a considerable improvement in geometric dimensions and satisfactory inner and outer surface quality in rolling without the automatic mill. The data given are also reinforced by the fact that 2.7% of the experimental batch (604.6 tons) of 140x(10-14)- ram tubes were sent for repeated end cropping because of variations in wall thickness, whereas the amount of such tubes is 6-8% in rolling by the usual sequence.

Analysis of the effect of plug-mill tool design (Fig. 2) on the quality of 140- (10-14)-mm tubes rolled without the automatic mill confirmed the advantages of the new roll-pass design with an entry taper angle of 2 ~ an exit taper angle of i ~ I0', and a mandrel taper of i ~ 30' This tool design made it possible to obtain a wall tolerance of • in 90% of the tubes rolled.

Rolling of 140x(7-8)-mm tubes without the automatic mill was tested experimentally. All the tubes met the GOST quality requirements. These tubes can also be rolled with- out the automatic mill after redesigning the piercing-mill output side (to increase pierced-billet length).

Increased (by 100-120aC) temperatures can be used in rolling 140"(10-14)-mm tubes in carbon steels using the piercing mill-plug mill--sizing mill sequence. This increases output and improves tube quality. The new sequence has been put into production and gives considerable savings.

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