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Improvements in rolling mills

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Page 1: Improvements in rolling mills

I M P R O V E M E N T S IN R O L L I N G MILLS

S. E. M e r k u r ' e v a n d 13. M. I l y u k o v i c h UDC 621.771.014

In our plant we have taken certain measures costing almost nothing, and such as could be adopted in any plant, in order to increase production in the rolling mills and to improve quality and working conditions.

Avoiding Overfilling of the Finishing Roll Pass of Mill No. 800. A common fault in all mills which roll prod- ucts through a box pass is the distortion of the profile in the final square section of the outlet rolls. It is difficult to

obtain an accurate square profile because of changing roiling conditions due to changing temperatures and wear in

the roils.

In order to avoid overfilling, the boundary lines of the preceding roll passes are usually made slightly concave.

However, concave outlines constructed of straight l ine segments do not assure constancy of dimensions and of shape. A concave outline constructed of circular arc segments helps to stabilize the shape of the section in the finishing pass

and prevents overfilling,

Knurling of the Roll Passes of Stand I in Mill No. 800. There are many types of knurling rollers for knurling

the roll passes. As a rule, any type of knurling, while it improves the grip of the rolls on the metal , contributes to

the formation of defects on the boundaries of the roll pass.

From practical experience it is known that it is best to use knurling rollers in the form of gear pinions with

parallel rows of straight teeth. Rhomboidally shaped teeth on the knurling rollers are a major cause of defects.

Use of the usual knurling tool re_suits in several rows of shallow depressions (Fig. la). This can also result in

defects.

In our plant we have introduced a method of knurling which produces long knurling marks across the full width

of the roll pass (Fig. lb). The width of the knurling tool is 25 mm. After setting up, and after the first row of knurl-

ing marks has been made, the saddle of the lathe is connected to the feed screw, and each subsequent row of knurling

marks partly overlaps the previous row, the tool advancing 1 mm along the length of the roll for every revolution. This method definitely cures all defects due to knurling, and the pressure on the support on the lathe is reduced at

the same time.

Changing Position of the Pass for the No. 10 Channel Section on the Rolis of Stand I. In order to util ize the

full length of the barrel of a roll it is better to use a set of four roils. This is often done in plants where section mills

use three-high working stands.

In our plant we could not make a four-roller set because there was not enough room for the bead, and because

of the way the feed tables are arranged, the slope of their intermediate partitions would not have been sufficient to

ensure normal feed of the metal into the pass. We have, therefore, developed a new design of feed table to make the

introduction of sets of four roils possible. This was done by providing a separate feed table for every three rolIs. This

made not only the introduction of four roll sets possible, but it improved the feed of the metal into the pass by mak-

ing room for steeper inclined partitions on the feed tables.

Changing Position of the Passes on Stand I in the Second Line of Mill No. 250. A set of four rolls was used on

stand I on the old scheme. This stand has two passes. When the passes were worn, the middle roll was changed, and the upper and lower roils were reversed. The disadvantage of this scheme was that the number of oval passes could not be increased. A better arrangement of passes was therefore devised. With this arrangement, when a pass was worn out, the middle roll was renewed and the upper and lower roll were interchanged. As a result of this change, t he t ime

interval between roli renewals was extended by 50%

Chusov Steel Works. Translated from Metallurg, No. 3, pp. 35-36, March, 1974.

�9 1975 Plenum Publishing Corporation, 22 7 West 17th Street, New York, N. Y. 10011. No part o f this publication may be repro- duced, stored in a retrieCat system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, mic~o- filming, 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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Page 2: Improvements in rolling mills

Fig. 1. Methods of knurling roll passes: a) using rollers shaped l ike gear pinions with several rows of teeth; b) transverse lines covering the whole width

of the roll pass.

Removal of In te rmedia te Beads on the Roils of the Polishing Stand of the Spring Steel Mill No. 370. A m a x i - real concavi ty of 0.2 mm on the flat sides of the spring steel stock is permit ted by the government standard. Usually a bulge occurs in the pass of only one roll, and the height of the bead which separates the passes is i ram. When the inlet pass is worn or the fastenings have weakened, the strip may be displaced to one side and may fouI the bead. This leads to spoiled mater ia l . In order to avoid this, the lower (shaped) roils of the polishing stand are now made without in te rmedia te beads. For purposes of a l ignment during instal lat ion and adjustment of fittings, the intervals be - tween the passes are painted with a band of color 5 to 6 mm wide. A small misal ignment of the painted bands may result in some distortion of the section, but there will be no spoiled m a t e r i a l

A New Method of Fastening the Roils in the Vert ical Stand Mil l No. 370. The two-high stand with v e r t i c a l c a n -

t i lever roils serves to control the width of the spring steel strip before the last pass. The permissible deviat ions are + 0.3 to 0 .7)mm depending on the width of t he strip and the accuracy required. It is diff icult to get good accuracy

because of the radial play in the ver t ica l rolls.

Careful f i t t ing of the components, use of both sides of the rol l and its supporting cone, and careful scraping of the tapers and bearing surfaces of the rolls before instal la t ion part ly improves the roll ing results but do not solve the

problem.

In order to improve the accuracy of the width of the product, roils were redesigned with a conical ring, and the

height of the roils was reduced by half in order m reduce the stiffness of the ring. The introduction of the new design of rol l is expected to improve the quali ty of the spring steel strip.

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