Hot rolling at Alfa Acciai

Hot rolling

The hot rolling department is equipped with three independent systems which routinely receive technological upgrades and turnout high-quality products with excellent mechanical properties that are guaranteed homogeneous and uniform.

The maximum production capacity is 2 million tonnes a year and requires a workforce of 300. Intermediate products (steel billets) of the same size, measuring 130x130mm and 11 metres in length, come from continuous casting and feed three natural gas heating furnaces, which are accurately controlled by dedicated software to ensure less fuel consumption and full compliance with the latest regulations on  emissions.

REBAR MILL 1 – An extremely compact plant comprising 18 reduction passes, with an in-line heat treatment system, which – thanks to monitoring and control of the flow rate and pressure of a large amount of continuously treated and recycled water – produces weldable steels with mechanical properties complying with various standards. Downstream the hot-rolling process, the finished product is left to stay on a large still-air cooling bed, which automatically moves the rebar forwards and rotates it to guarantee a straight product with highly homogeneous mechanical characteristics. The rebars are then cut to size using a mechanised system and conveyed to the the automatic weighing, packaging and labelling station.

• Improved-adherence reinforcing steel in bars is made in diameters 12-32 mm and packaged in bundles that weigh approximately 2200 kg and range in length from 6 to 18 metres.

WIRE ROD MILL -  This is a very large installation as it comprises two parallel lines that run simultaneously. It is about 300 metres long, with twenty-eight continuous reduction passes, a series of complex articulated devices and a series of continual heat treatment systems, all sized to produce long smooth and ribbed rolled products, at a very high finishing speed rate. On both finishing lines, cooling is by means of a complex Stelmore system that ensures specific cooling cycles according to the grades of processed steels in order to:

• Optimize the mechanical features and make them repeatable;
• Meet metallurgical requirements with adequate microstructures;
• Control the quality and thickness of the surface oxide to facilitate chemical and mechanical pickling operations.

At the end of the line, the rolled looped product is dropped into coils on rotating trestles and sent on to the automated pressing, fastening and labelling stations. The product is packaged in coils that are fastened at four points. They can be uncoiled either vertically or horizontally, but always in an axial direction.
The wire rod mill produces:

• Wire rod, diameters 5.5-16 mm, in coils weighing 1,450 kg;
• Hot-rolled ribbed coil, diameters 6-16 mm, weighing 1,450 kg.

REBAR MILL 2 – A plant comprising fourteen reduction passes and two parallel blocks with a further four passes. It is the latest rolling mill installed (2004) and it has been designed to produce small diameters. Like the other systems, it uses the principle of “horizontal-vertical” continuous rolling and has an innovative semi-automatic system for charging the heating furnace. There is also a so-called ‘slitting’ system of rolling, whereby the rolled steel is split at a set point of the rolling process to allow high-rate output of low-diameter rolled products, using different finishing and packaging devices.

Downstream of the finishing mills, the two production lines use Tempcore heat treatment processes that are controlled according to specific settings to process products (reinforcing steel in bars and spools) with different characteristics, though with common analytical bases.

It is interesting to note that this plant is one of the few in the world equipped with such innovative and relatively complex devices as a butt welding machine for billets (EWR) and hot spoolers, as required to achieve a heavy-weight finished wound-up product. 

Rebar mill 2 makes:

• Improved-adherence reinforcing steel in bars, diameter range 8-16 mm, length 6-14 m;
• Reinforcing steel in hot-rolled spooled coils, diameter range 8-16 m, weighing up to 3000 kg.