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TECHNOLOGIES AND AUTOMATIC CONTROL SYSTEMS FOR
THE PROCESSES OF ROLLING AND HARDWARE PRODUCTION
MULTISTRAND ROLLING-SLITTING (MRS) — UNTRADITIONAL
TECHNOLOGY OF REBARS AND MERCHANT BARS PRODUCTION
MRS technology was developed by the RPC "Donix" in cooperation with the specialists of Dotetsk State Technical University and a number of Ukrainian metallurgical works as an alternative for the prevalent "slitting process".
The "slitting-process", developed by "Co-Steel International Company" and improved by "Nippon Kokan Company", consists in forming the multistrand process workpiece from a square or rectangular billet. The multistrand stock is composed of "false round" sections coupled by the 0,75 - 1 mm thick bridge. The process workpiece slitting is carried out by means of breaking the crosspiece by the wedge-shaped rolls of a special device, installed at the exit from the working rolls, under the action of the expulsive force created by the rolls. After the process workpiece slitting, the "false round" sections are rolled concurrently into the finished sections, usually in two passes.
The process has a number of essential drawbacks, namely:
- The neck which appears after the bridge breaking at the point of slitting and deteriorates the quality of the finished rolled stock.
- Low durability of the forming pass.
- Slitting device of elaborate design.
- Low durability of the slitting wedge-shaped rolls.
- Low longitudinal stability of the process workpiece before the splitting device.
- Complexity of control over the enter roll gides.
The multistrand (double-strand) rolling-slitting technology is based on fundamentally new schemes of slitting: slitting by means of controlled break, shear, mutual shift in the sloping passes etc.
The main point of the DRS technology is: the process workpiece consisting of several billets with cross section of any shape, coupled along one of the axles by a relatively thick bridge, is formed in the multistrand passes of the rolling mill working rolls. The slitting of such a multistrand stock is carried out immediately in the slitting pass, while the ridges of the pass ensure the centering of the double-strand stock.
The realization of the MRS technology requires:
- Special roll pass design.
- Special equipment - enter roll gides and transmitting devices.
- Special double-strand devices for hardening the rebars by heat treatment.
When compared with the "slitting-process", the MRS technology has a number of indisputable advantages:
- Zero burrs at the point of stock slitting, ensuring a better quality of the finished rolled stock surface.
- A higher resistance of the forming groove.
- A higher specific resistance of the work rolls.
- No additional devices for roughing bar slitting and therefore no infrastructure for their maintenance are required.
The MRS technology allows:
- to use the billets with enlarged sections for existent rolled stock production.
- to increase the rolling mill yield by 20 ё 100%.
- to reduce the energy consumption for heating and rolling.
- to increase the existent range of shapes towards the production of light cross sections.
The MRS technology has successfully passed a number of the patent, laboratory and industrial tests on the breakdown billet and section mills of different types.
Double-strand rolling-slitting technology was introduced:
- in 1995 on the light-section mill 250-3 of KRIMMW "Krivorozhstal" - for reinforcing steel N°10 rolling.
- in 1996 on the small-section mill 250-4 of KRIMMW "Krivorozhstal" - for reinforcing steel N°12 rolling.
- in 1998 on the small-section mill 250-1 of KRIMMW "Krivorozhstal" - for reinforcing steel N°8 rolling.
- in 1999 on the linear mill 280 of the OJSC "Enakievo Metallurgical Works" - for reinforcing steel N°10 rolling.
As per condition in effect on 1 January 2002, more than 6,400,000 tons of reinforcing steel have been rolled on the rolling units of KRIMMW "Krivorozhstal" according to the MRS technology.
The author's rights of the technology's creators are confirmed by more than 40 patents and certificates of authorship of the USSR, Ukraine, Great Britain and Canada. In 1987 the licences were sold to the German Democratic Republic and the Republic of Cuba. More than 30 patents and certificates of authorship are introduced in industry on the rolling mills of Dnepr Metallurgical Works, KRIMMW "Krivorozhstal", the OJSC Enakievo Metallurgical Works.
At present the RPC "Donix" is developing the three-strand rolling-slitting (TRS) technology for continuous cast billet with the separation of the segregation zone into the middle strand.
The development stage - the first industrial tests of the large section slitting process have been carried out.
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