Quality Assurance Plan
Metal Roll is a tailor made products for crafting various types of steels in different shape sand sizes (Angle, Channel Beams, Girder, Flat, Strips, Round, Square, TMT & Wire Rod etc.) it has to perform under many critical conditions during Hot Rolling. So it requires below mentioned characteristics:
- High wear resistance due to friction.
- A firm structure against breaking high mechanical resistance even at high temperature .
- Resistance against sudden heavy Impact and Bending load due to reduction.
- Resistance against thermal and fire cracks on surface which gets in contact with constant hot materials.
- Machining ability so that can be machining according to pass design and assembling with bearing.
- Resistance against Tensile load due to high RPM.
To fulfill above entire characteristics, we need very careful operations at each and every step of production process. Therefore we have Quality Assurance Plan (Q.A.P.) to achieve better Quality Parameter which provides more Pass life with better finishing in Rolling Products controlling with Breakdown in Rolling Mills:
(i) Melting of Spheroidal (Nodular) Graphite Iron (S.G.I.) Rolls
Melting is carried out through Induction Furnace by charge-mix of selective alloy based melting fresh scrap after chemical composition analysis by Spectro lab of each lot. Addition of Ferro Alloys (Carbon, Silicon, Manganese, Chromium, Nickle, Molybdenum & Vanadium) are to be done at initial stage during melting depending upon requirement of grades as per charge-mix. After successfully achieving required elements (Ferro Alloys) we use to do Soda Ash-Treatment in Ladle applying with Orgon Gas Treatment (Purging) to De – Sulphurising on High Temperature (1500°C to 1550°C) to reduce Sulphur (Max. 0.020%) as well as proper homogeneity of liquid metal. After De – Sulphurising liquid metal again re-pour to the Induction Furnace then Post-Nodulising by Magnesium (NiMg) to get Spheroidal (Nodular) Structure to done in another second ladle. During melting, we used to get multiple bath samples for chemical composition to determine formation of microstructure Pearlitic Matrix with Nodular Graphite, Carbides and some Pearlite as well as Bainitic – Martensitic Matrix with Nodular Graphite and Carbides). As well as to achieve required chemical composition - range which is aimed by view point of application in rolling mills.
(ii) Melting of Alloy Cast Steel Or Adamite and Graphitized Or Graphitic Steel:
Melting is carried out through Induction Furnace by charge-mix of selective Alloyed Based Melting fresh Scrap after chemical analysis by Spectro lab analysis of each lot. Ferro Alloys are to be added during melting depending upon requirement of grades. During melting we take multiple bath samples for chemical analysis to achieve required chemical composition range which is aimed by view point of application in rolling mills. After melting, molten metal is being taken in Ladle Refining Furnace (L.R.F.) at 1500°C to 1550°C temperature for the purpose of spheroidization, Seeding, De-Oxidation and Grain Thinning and achieve casting temperature.
2. Moulding & Casting
Moulds of Metal Rolls are prepared by applying of Directional Solidification Static Vertical Casting with Tangential Gate through Bottom Pouring System. In preparation of mould we apply green sand process with proper contraction and machining allowances then take the moulds to baking oven before assembling. Casting of entire Rolls are carried out in closed Pit to avoid direct air contact of moulds. Moulds of single roll are assembled in five parts as per below:
- (i) Bottom Journal (Drive Side) - Moulding with Green sand along with Cast Iron Side Segment Chills with Bottom Chill Plate for the purpose of directional solidification.
- (ii) Barrel – Barrel of Rolls Casted in Cast Iron Chiller (Chill Die) for the purpose of directional solidification due to Higher Conductivity of Heat.
- (iv) Riser (Feeder) – Through Exothermic Sleeves to provide long time temperature in liquid metal for feeding against shrinkage.
- (v) Runner & Getting System – Moulding with Refectory Sleeves, Washer and Tangential Gating of high alumina refractory. In our Pouring technique, liquid metal poured throughout in mould through bottom Tangentially Gate with high pressure so that direction of liquid metal filling inside the mould in vertical upward in circular motion (clock-wise). Therefore casting becomes free from any type of inclusion and air-blow. We apply re pouring after few times again direct in riser with hot metal to extra feeding as well as apply exothermic powder time to time in riser to make liquids. Entire moulds of roll covered with vermiculate in close pit till certain period according to volume and shape of Roll-Castings to controlled cooling.
3. Heat – Treatment (FOR ALLOY CAST STEEL & GRAPHITIZED STEEL ROLLS)
We used to apply Double Annealing followed by Tempering Cycle in Heat Treatment furnaces with modern pulse firing system and high speed burners with automatic zone & individual burner control systems ensure high precision heat treatment. Entire Alloy Cast Steel & Graphitized Steel (Graphitic) Rolls undergo a sophisticated multistage with high temperature H. T. cycle with proper soaking period to achieve combination of Hardness, Toughness and Wear Resistance require d for particular application.
4. Machining
Machining of Metal Rolls carried out after Primary Inspection like Dimensional, Chemical Composition and Micro Structure. Machining is being done in two Phase – in 1 st Phase Rough Cast Rolls machined i.e Proof Machined Condition then secondary inspections is done like Dimensional and Physical Testing (Hardness, Tensile, Bending & Impact) and in 2 nd Phase Proof Machined Rolls again machined to Finish Machined Condition as per approved drawing. Machining process is carried out with controlled RPM and tolerance. During machining strict supervision about measurement and surface conditions is maintained throughout the machining process .
5. Quality Inspection
Our Quality Control Engineers and Experts go through final Inspection by latest calibrated Measuring, DT & NDT equipments of Finished Rolls for Dimensional, Chemical Composition as well as DT & NDT according to requirement from party or need to application of Metal Rolls in rolling mills.
