What are the advantages of direct rolling of as-cast billets? Has the process been successfully implemented in steel mills yet? What kind of expertise does ANT Steel Engineers (Asia) Pvt. Ltd. offer in this regard?
When oil prices were soaring in the early years of this century Indian re-rollers were exploring various techniques to reduce fuel cost in order to maintain their competitive edge. Coal gasification and pulverised coal were used to replace costly furnace oil. As a result, fuel cost could be substantially curtailed. However, this led to increasing pollution and space constraints in a majority of units. In many mills, the presence of the rolling units in congested locations was posing to be a health hazard. To overcome these difficulties, the idea of direct rolling of continuous casting machine (CCM) billets was floated.
Direct rolling of as-cast billets from CCMs was initially successfully implemented by some companies in China. The method was adopted for production of rebars and small sections and later for medium sections too. Direct rolling of as-cast hot billets not only saved precious fuel cost but also bolstered yield by reducing scale loss to the tune of about 1%. Direct rolling also reduced the manpower cost of billet handling and operational activities of reheating the furnace.
ANT provides the required know-how to several steel mills in India and abroad and most of our clients today have the operational capacity to roll more than 95% of their overall production of as-cast billets with our assistance.
ANT Steel Engineers helps clients adjust the secondary cooling parameters of the casting machine, increase casting speed, in re-routing of billets for length optimisation and to maximise the speed of approach roller tables to achieve the desired temperature of the billet at the roughing mill stand. It has been observed that rolling at the 3Hi-roughing stand at high speed helps equalise the billet temperature. This ensures smooth rolling at the intermediate/finishing stands and the wire rod block.
For mills with continuous roughing stands and those that roll out 12-meter long billets, induction heating is necessary. Normally, 32 kWh/per tonne power is consumed by way of induction heating.
With respect to the electric arc furnace (EAF) steel-making route, what are the advanced engineering solutions that ANT Steel Engineers provides to remove impurities and ensure high quality of finished alloy steel products?
For production of alloy steels, usually, eccentric bottom tapping, ladle refining furnace (LRF), closed casting, mould-level control and electro-magnetic stirring have been more or less successfully implemented to improve the quality of the finished product. However, many other improvements required to manufacture clean steel call for special expertise with respect to critical applications that ANT provides.
We have the expertise to produce quality steel by providing know-how by way of tundish metallurgy and casting parameters.
In tundish metallurgy, selection of refractory materials, dams and wares, right covering materials and proper temperature control all play crucial roles in the production of clean steel. Heating of the tundish, proper metal stream shrouding by purging with argon and close casting, selection of proper casting powder to avoid contact of atmospheric air with the liquid steel are some of the key parameters closely monitored by ANT engineers. We also help manufacturers select the right quality of mould tube with desired tapers depending on the grade of steel and billet/bloom size being produced.
ANT also provides engineering solutions for developing special grades used in various applications. We offer engineering expertise related to manufacturing stainless steel and other high-grade alloy steels through the induction furnace route.
How is it possible to improve the quality of IF steel through de-phosphorisation and other processes to ensure the production of premium grade steel?
The IF route has become popular for manufacturing of construction steel mainly due to low operational and infrastructure costs. The garbage-in garbage-out process has been rejected for good. The IF route was always dogged by the absence of a suitable and cost-effective mechanism for phosphorus removal. However, this problem has been addressed successfully. Today, alloy steel production by necessary process modifications can lead to quality enhancement. ANT can help steel mills de-phosphorise liquid metal tapped from induction melting furnaces with high levels of phosphorus. While tapping of steel from the induction furnace, a required quantity of de-phosphorisation mixture is added and the slag is removed before further processing in the LRF.
LRFs, in combination with vacuum degassing and suitable casters, can ensure quality steel. We have provided know-how to a reputed steel unit in India that produces quality alloy steel and high alloy grades through IF/LRF/VD/CCM.
What mechanical expertise and process/equipment specifications are required to manufacture high-grade stainless steel through the IF route?
Selected scrap of stainless steel/mild steel along with the required quantity of ferro-chrome and nickel with ferro-manganese are melted in the IF and transferred to the AOD converter. The converter is designed for bottom/side blown tuyere. Top blowing can also be carried out for fast processing. To achieve the desired composition, the ferro alloys and nickel are added during blowing.
Oxygen and nitrogen in various ratios are used for reducing the carbon. Upon achieving the desired carbon level, the reducing mixture is added and argon stirring is carried out. For making low-nickel grades, use of nitrogen is essential.
What are the main advantages of the multi-slit rolling technology? How has ANT Steel Engineers helped manufacturers implement this technology over the years?
Multi-slit rolling technology is a low-cost solution for ramping up production in hot rolling mills. I developed slit rolling in the rolling mills of the Al Tuwairqi Group of Saudi Arabia which now produces about 2.5 million tonnes of rebars per annum. In 2001, production at one of the mills of the Al Tuwairqi Group spiked from 120,000 tonne/per year to 240,000 tonne/per year, thanks to the introduction of single slit two stands rolling. Later, the multi-slit rolling technology was introduced and production rose by about three-fold in the same mill. Mills that adopted the technology after 2001 have three slit-four stands rolling and the Al Tuwairqi Group reached a production capacity of 2.5 million tonnes by 2008.
Our Technical Director, V M Chandekar, developed slit rolling in various mills in the Middle East and South East Asia.
ANT Steel Engineers (Asia) Pvt. Ltd. was founded in November 2008. The company has developed multi-slit rolling technology for up to four slit-five stands rolling. We provide assistance in developing slit rolling technology by examining the equipment capabilities for implementation of slit rolling. For example, the kilowatt of motors, gear ratios, condition of finishing mill stands and parameters of the TMT system, pinch rolls, dividing shear and cooling bed all need to be factored in. Necessary recommendations are made for changes required in a particular mill. Specifications for additional equipment are worked out by ANT.
We also offer training and commissioning services. ANT has to its credit many units in India where three slit-four stands rolling has had a multiplier effect on productive volumes.
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