Rolling mill industrial plant
The purpose of the technological processes, equipment and systems is to roll the plain carbon steel billets and blooms in order to obtain different wire and profile standard size, in coils and bars.
The total area of the premises is 261,448.40 sqm, out of which:
- Built area: 86,952.83 sqm;
- Transportation routes, alleys and concrete platforms: 67,070.78 sqm;
- Network areas: 14,652.50 sqm;
- Clear area: 92,882.29 sqm.
The technological system operates continuously, five days per week, in three shifts. The annual maintenance program includes current and capital repair works, technical overhaul and current maintenance works which require for the technological systems to be stopped for an approximate 30 days period. Technological downtimes of 2-3 days/month are also provided for the replacement of equipment in order to modify the standard sizes of the finished product (wire). All of these downtimes also include accidental outages, in this way resulting an approximate number of 190 days/year of operation for each source of emission.
In 2015, the company had approximately 170 employees working 24 hours/day, 5 days/week.
The wire mill is of continuous type, the half-finished products can be rolled alternatively on two wires, the raw material being steel billet with 130 mm x 130 mm and 12 m long square section.
The chemical composition ensures that hot-rolled concrete steel is obtained in 12 m long rolls within the size range of 8 mm – 12 mm diameter, PC52 or B500 quality, conductivity class C, in coils within the size range of 6 mm – 16 mm diameter, OB37, PC52, B500C quality.
The raw material is supplied in railway waggons on the internal network of yard tracks, and it is unloaded and stored by using two 12.5 tof x 34 m bridge cranes. By using the electromagnets of the bridge cranes, the billets are deposited on a de-stacker and inserted into the continuous discharge heating furnace for heating by using an elevator, roll tracks, pushing machine and weighting system, for the purpose of rolling.
The continuous discharge heating furnace has a production capacity of 50 tons/hour, with an installed capacity of 20.66 Mwh and it uses for heating a mixture of natural gas with air on 1 to 10 ratio. The technical parameters of the heating process are monitored and regulated with an automatic AMCR equipment.
The preheating-heating area where the billets are heated at 950-980oC is equipped with 11 burners of 250 Nmc/h and the heating-equalization area where the rolling temperature of 1,160-1,180oC is obtained is provided with 11 burners of 165 Nmc/h.
The combustion air is provided by a 52,000 Nmc/h fan and the system recovering the heat from the flue gas allows the heating of the combustion air up to approximately 400C, depending on the rolling process. After heating, the billets are inserted into the rolling train by using the evacuation machine and the engaging-tilting device.
The preparing gear consists in six double horizontal stands driven two at a time by an electrical motor of 1,100 Kw and a reducer. Using rotating scissors, the ends of the bars are
removed before inserting them into the intermediate gear. This intermediate gear consists in eight double horizontal stands driven by motors of the same type.
The rolling tools are cast iron rolling cylinders of various quality, with the diameter between 320 mm and 475 mm, lengths of the panels of 800 mm and 1,050 mm. After the last stand of the intermediate gear (k14), the half-finished product can be guided on one of the two flows – on the coil line or on the bar line.
The coil line consists in a finishing block with 8 stands (4 on the left + 4 on the right) arranged at 45o and driven by a motor of 1,100 Kw at 550 rpm through a double outlet sync reducer. After obtaining the final size upon the last passage, in order to obtain the physical and mechanical features, the rolled material with the temperature of approximately 930oC is passed through the automatized thermal treatment equipment where it is forcedly cooled at 650oC with pressurized water (12.5 bars).
After forming the threads and placing them on the chain conveyor, the coils are made and carried to the packaging press. After weighting, labelling and entering the data into the computerbased management system, the coils are taken over by using the bridge crane of 5 tof x 19.5 m and stored in the dedicated space depending on their standard size and quality.
On the bar line, for the small sizes with 8, 10 and 12 mm diameters, the half-finished product removed from the stand 14 is driven into the finishing block, which has identical features with the one from the coil line. For sizes within the range of 14-32 mm in diameter, stand 14 becomes a finishing stand. After the last passage, the 900 oC rolled material is passed through a thermal treatment equipment where it is forcedly cooled under pressurized water (11.5 bars) in order to obtain the physical and mechanical features of each product.
After hot cutting at 60 m length by using the driving and braking devices, the bars are laid on a cooling bed with walking beams. From here, the bars are transferred on the roll track and carried to the cold cutting scissors which cut at 12 m length.
By using a chain carrying device, the bars are transferred into the formation, packing, weighting and labelling equipment and entered into the computer-based management system, afterwards being carried with the bridge crane and stored in dedicated spaces depending on their standard size and quality. An automation equipment connected to a process computer allows a real time monitoring and adjustment of the functional paramet ers within the rolling process.
The electricity from the national energy system is supplied in the Deep Connection Station of 110/6.3 Kv through a TTUS-FS 25 MVA transformer of 110/6.3 Kv. The electricity is distributed from the interior 6.3 Kv station of SRA through 6 ELC routes in three 6.3 Kv substations;
The compressed air is provided by two worm screw compressors of 19 and 23 Nmc/min. at a pressure of 7 bars;
The water for the thermal treatment, cooling of the rolling tools and rolls from the furnace is
provided from the water tank through a closed circuit with cleaning, filtering, cooling and
pumping equipment. The water is 95% recirculated. The water is supplied through a connection to
the potable water town network;
A significant part of the spare parts and also the processing of the rolling tools are done with
universal equipment from the mechanical shop;
The physical and chemical qualities of the products are verified and certified in own authorized laboratories.
The designed productivity of the mill train is of 37.5 tons/hour;
The average productivity is 20 tons/hour;
The maximum design production capacity is 220,000 tons/year.
For more details, please contact us.