Slit Rolling Technology-A Solution for Productivity Improvement

V. M. Chandekar, Director (Technical)

ANT Steel Engineers (Asia) Pvt. Ltd.

r. Sudarshan Singh, during his Dtenure with Al-Tuwairqi Group of Companies , as Group

Technical Director, introduced multi-slit rolling technology in the year 2000 in their Rolling Mills. Slit rolling with other technological improvements resulted into many folds jump in the overall production level.

Later in the year 2009 Dr. Sudarshan Singh founded ANT Steel Engineers (Asia) Pvt. Limited, Pune, India with the view to serve the growing steel industry worldwide for setting up of new plants and turning around of sick units as well. There has been overwhelming response and many steel rolling mills were benefitted from slit rolling technology and other technological changes recommended by Dr. Singh.

Since the production of rebars is highly sensitive to cost of production, selection of technology must meet the client's requirement of capital cost, operational cost and simplicity of its adoption. These requirements are fulfilled in a conventional bar mills, already in operation, by making a few changes for introduction of slit rolling technology.

It is found the production of smaller sizes in many steel rolling mills is a bottleneck in the capacity utilization as compared to the bigger sizes. This results in uneconomical operation of the plant

and underutilization of reheating furnaces and melting units. ANT Steel Engineers assist such units for increasing the production of smaller sizes to a level at par with the bigger sizes by introducing slit rolling.

Sustained efforts in making slit rolling a user-friendly process have resulted in crossing the milestone of 1000 tons per day in hot rolling of smaller size (8mm Rebar) in several plants.

Slit rolling is a simpler process with a few changes in existing set-ups. The other options like high speed rolling through block mill in coil form or HSD systems in straight lengths require huge investment.

Brief History

Slit rolling technology was developed thin beginning of 20 century for slitting of

rail sections into head, web and flange and subsequent rolling to various sections. During sixties Swedish engineers adopted this technology for increasing the production of simple sections.

Striking features of Slit Rolling Technology

Higher production rates in smaller sizes

Slit rolling technology was initially developed for production of rebars in two strand rolling and later developed to multi-strand rolling upto five strands. Obviously for a given speed the production rate for two strands is almost

doubled compared to single strand. When the number of strands are more (like three, four or five strands) production rates are multiplied.

Safer, simpler, easier and reliable mill operations by operating at low or moderate speeds

Rolling at lower speeds means less wear & tear of moving parts, less vibrations, less breakdowns and higher mill utilization.

Full capacity utilization of billet reheating furnace for all sizes

When the production rates are same for each size the furnace can be utilizes in the most optimum manner. The most important cost parameter –fuel cost- is thus controlled to optimum level.

Mill capability to produce smaller rebar sizes like 8mm, 10mm and 12 mm with less expensive equipment and with less number of mill stands.

Due to multiple number of strands in the finishing stage, total numbers of passes required in the mill are less than those required for single strand rolling.

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Low investment

High investments usually required for high speed rolling are not necessary. All these factors make rebar rolling economical from the point of view of initial investment as well as operating cost. Finishing mill does not require vertical stands.

Less Space

Due to increased cross sectional area at finishing mill passes and less number of passes total space occupied by the rolling mill is reduced. Similarly less space is required after finishing stands due to comparatively lower finishing speeds.

The process of slit rolling

The p rocess e s sen t i a l ly makes longitudinal division of bar while rolling into two or more number of strands. Roll Pass Design for slit rolling is a specialized subject and the guiding system is devoted to the spec i f ic des ign . Recent development of software for roll pass designs makes it possible to produce tailor-made designs to suit the plant configurations. Similarly specific designs of guiding equipment are developed to make the process more reliable. Since the process is sensitive to dimensional accuracy good quality mill stands – usually housing less mill stands -are used for the finishing mill.

In order to accommodate handling of multiple strands downstream equipment like TMT, dividing shears and cooling bed need suitable modification.

Four Strand Slit Rolling at Mahalaxmi TMT.At Mahalaxmi TMT Wardha near Nagpur in Maharashtra State of India, ANT Steel Engineers (Asia) Pvt. Ltd. introduced four strand slit rolling and crossed all the records by producing 950 tons on the first day of commissioning and 1000 per day mark in the subsequent period.

Courtesy Mahalaxmi TMT

Combining Slit Rolling With Direct Charge

In the recent years several plants could gain confidence in practicing slit rolling. However there was a debate whether this technology could be used when direct rolling of hot billets from CCM is adopted. This concept could be successfully resolved when ANT made complete engineering of Madhav Alloys Pvt. Ltd in Punjab. By following a specific discipline in the CCM area the company started production of 8mm slit rolling with 100 percent direct charge.

A special roll pass design for this purpose was developed by the Chairman Dr. Sudarshan Singh and today the plant is producing 8 mm slit rolling at a speed of 20 m/sec eliminating use of reheating furnace. Specific design of handling the slit bars at high speeds from finishing stands to cooling bed proved that slit rolling can be also be adopted at higher speeds.

Limitations of Slit Rolling

Slit rolling is not recommended for plain rounds

Fin i sh ing mi l l stands need to be of g o o d q u a l i t y -preferably pre-stressed or housing-less.

B i l l e t w e i g h t o p t i m i z a t i o n i s n e c e s s a r y t o g e t improved yield. A view of Madhav Alloys, Punjab

Courtesy Madhav Alloys

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