Mill rolls production:
Melting: In order to be able to produce virtually all types and dimensions of rolls, we work with EAF, ESR, and Induction smelting equipment.
Forging: Automated forging presses can process the heaviest plate mill back up rolls.
Casting: Cast Rolls are produced in vertical and horizontal spin casters, and static casters.
Heat Treatment: 16 different furnaces, electric and gas heated are available. Quenching by means of electric or sprays. Deep Freezing tunnels are also used.
Finishing: Full range of CNC lathes, and grinders are used, totaling up to 50 units.
Quality: ISO 9001, ISO 14.001; OHSAS 18.001
Full inspection of rolls with all available testing equipment. Each roll is 100% traceable.
Classification of Roll Materials
Steel Base Rolls (Cast or Forged)
Cast steel rolls:
These cast steel mill rolls have qualities and grain structure like steel although the carbon content may be quite high (up to 2.5%). The cheapest rolls in this group are plain carbon steel rolls. To get better wearing properties, molybdenum and chromium are added and nickel is introduced for imparting strength and resistance to fire cracking. These rolls with small alloy contents are used in big sizing mills such as Blooming Mills.
The most common rolls in this group are called ‘Adamite’ rolls. Depending upon carbon content these Adamite rolls are classified as A, B, C, D or E. Adamite ‘A’ is the softest but toughest and Adamite ‘E’ the hardest but least tough.
All these rolls are cast, heat treated and machined and have nearly uniform hardness throughout the transverse cross section.
Forged steel rolls:
These mill rolls are made by forging. Forged rolls contain less carbon compared to cast rolls because high carbon content would cause cracks during the forging process. The structure of forged rolls is denser than cast steel rolls and therefore, are tougher and can absorb more load. However, because of the lower carbon content the hardness is low and more subject to wear than cast rolls. These rolls are primarily used where they have to withstand high loads as in Blooming Mills or in Heavy Section Mills. Forged and hardened rolls are also used as back-up rolls in 4 high mills although normally alloy cast steel rolls are used for back-up.
Special refined tool steels serve as the base for a range of long life high precision rolls for the Aluminium Rolling Mills. With unique grades unparalleled tonnages are achieved between regrinds. Chromium content is available up to 7 – 9%.
Iron Base Rolls (Cast)
This type of rolls is used most times in rolling mills, mainly because they result in good finish and possess good wearing properties.
Many years ago, cast iron or chill cast iron rolls were the only types used. In order to increase the strength, finish quality, wear – and heat resistance, a number of alloying elements are currently added to the iron rolls. Improved casting technology over the years also contributed to enhanced properties of Iron Base Cast Rolls. There is a wide range of cast iron rolls available in the market. Below just a few relevant types are specified.
Chill Cast Iron: The roll casting is performed vertically with barrel in chill moulds. The chill surface is very hard and provides good finish. These rolls are used for rolling flat products like sheets and plates and small sections. The addition of Molybdenum increases the strength and heat resistance properties. The composition is more or less similar to cast iron but its structure is different. The outer surface of the barrel is chilled (Fe3C) providing very high hardness. The thickness of the chill varies. It may be even up to 20 mm thick depending upon its application. Beneath the chill zone there is a transition zone known as Mottle Zone where carbon is gradually flaking from a few specks to the full flake. The core portion is called Grey. Hardness drops down if the chill is worn out.
Nichillite Golls: These are also chill rolls but Nickel is added in order to increase hardness and strength. The high hardness allows excellent surface finish of the product rolled. The hardness characteristics are same as that of chill rolls. These rolls are used for flat rolling, in the Finishing Stand of Strip Mill.
Alloy grain Rolls: As the name suggests alloy grain rolls are made from iron having carbon more than 3% with Nickel, Chromium and Molybdenum added as alloying elements. The free carbon is present in the form of flakes. These are sand cast rolls and have reasonably good strength and wearing properties. These rolls are useful in section rolling mostly in the intermediate passes where light drafting is possible. The hardness drop from surface to core is gradual.
Indefinite Chill Rolls: These are alloy iron rolls and are cast in chill moulds. After casting the hard top chill layer is cut off and the remaining part of the roll has a hardness which is more or less of the same level all the way down to a great depth. In fact, the hardness drop zone from the surface to the core of the roll is gradual up to 10 to 15mm depth compared to chill roll where the hardness drop is sharp. Therefore, indefinite chill rolls are used in the intermediate and finishing stands of Section Mills where deep grooves may have to be cut to make the required profiles for the sections to be rolled. These rolls have better resistance to fire cracking and spalling than the chill rolls and also have a higher strength. They are reasonably tough with good wearing properties and can be used in the intermediate stands of Strip Mill.
Spheroidal Graphite Rolls: This is another type of alloy iron rolls where the structure is completely different from that of cast iron rolls. The carbon is present in the form of spheroids or nodules which increases the ductility and provides a higher fracture resistance. Nodularisation is achieved by the addition of Calcium Silicide and Magnesium or cerium. The nodular structure of carbon provides an improved tensile strength higher than cast iron combined with better wear properties. However, such rolls are more receiptive to fire-cracking and need more external cooling. Due to greater strength such rolls are used to replace other types of iron base rolls. Their wear properties are also better than steel base rolls and at times they are also made to replace steel base rolls. The hardness drop in such rolls is minimal. They can be used in Medium & Light Structural Mills, Sheet, Bar & Billet Mills, Merchant Mill and also in Reversing Mills.
Double Poured Rolls: In order to obtain both high wear resistance and high strength, roll makers have developed a roll making technology where the outer shell is made hard and the inner core tough by double pouring of metal of different compositions. The shell composition is maintained to give very high wear resistance properties and the core composition to give more strength.
Centrifugally Cast Rolls: The composition of centrifugally cast rolls is more or less similar to that of double poured rolls. First, metal which gives high hardness and better wear properties is poured in the mould, which is then revolved at high speed. After sometime molten metal of different composition is poured in for the core of the roll to make it more tough. These rolls are superior to double poured rolls as the shell portion is denser giving better properties. Double poured and centrifugally cast rolls are also known as Duplex Rolls