During the process bloom is being passed by several passes and stages, To get an appropriate desired profile of rail section as per requirement. So basically in “Universal Rolling Mill” and “Rail & Structural Mill” of BHILAI Steel Plant there we face some common Issues related to Quality of product during manufacturing process I.e. Rejection of Rail (Some Common Reasons are as follows): Due to uneven Symmetry, Due to Surface Roughness, Un-appropriate or out of tolerances, Defect caused by more Scaling on surface, Development of Fracture in Rail, Internal Defects, Shrinkage of hot rail profile. All the above are which directly affect production parameters and lead to increase in the production time, cost and the material wastage. Here this article is about the study and analyse of the defect parameters and the cause of defects occurs during Rail rolling technique and also to provide the correction measures in Roll profile to maintain and improve the Quality of product which is being manufactured in Inline rolling process.
SAIL Bhilai Steel Plant is the sole supplier of rails to Indian Railways. Since rails are classified as long-hot rolled products, their manufacture is associated with a generation of number of defects alongside the regular production regime. Complicating matters even further, is profile of rail that poses a difficulty in pass design for accurate dimensional tolerances during rolling. Therefore the production of these rails is difficult and the rejection ratio for per ton turnover is high. Moreover since railways are the sole buyers, their norms are as stringent as possible to ascertain production of best quality rails. These specifications encompass the three core factors of metallurgical quality, dimensional accuracy and surface uniformity; hence making acceptance of rails difficult through a narrow window of quality constraints. The target of the project is to understand the manufacturing technologies of theses rails, identification of defects, and observation of instances where the production deviates from regular performance and to analyse as to how these defects can probably arise.
Overall height of rail: + 0.8mm
– 0.4mmWidth of Head: ± 0.5 mm (This will be measured 14mm below the rails top)Width of the flange: ±.01 mm (for section less than 60kg) +1.2 mm (for sections 60kg/m)
-1.0 mmThickness of web: +1.0 mm
-0.5 mm (This will be measured at the point of minimum thickness)
Flange: The base of the rail shall be true and flat, but a slight concavity not. Exceeding 0.40mm shall be permissible.
a) LENGTH OF RAIL:The standard length of rails shall be 13 meters. However, in case rails are to be procured in longer lengths, the same shall be prescribed by the purchaser. The manufacturer shall be entitled to supply in pairs short lengths up to 10% by weight of the quantity contracted for or ordered. Such short lengths shall not be less than 8.0 m in lengths.The short lengths shall be in multiples of 1.0m.Tolerances in length of all rails shall be + 20.0 mm-10.0mm
b) END SQUARENESS:The deviation from square in both horizontal and vertical Direction shall not exceed 0.60 mm on a length of 200 mm.
c) STRAIGHTNESS:The straightness of the whole rail shall be judged by naked eye but in case of doubt or dispute, the affected portion shall be checked using 1.5 meters straight edge. The maximum permissible deviation shall be 0.7mm measured as the maximum ordinate on a chord of 1.5m. Wavy, kinky and twisted rails shall not be accepted Length of rails.
III. PROBLEM IDENTIFICATION & METHODOLOGY PRIMARILY THE TWO METHODS CONSIDERED FOR INVESTIGATIONWERE.
Defect based – This method involved a set of post inspection activities that would lead to defect origin pointers. The major flaw with this approach is the time in which the defect was noted. Since the defect was already present on rails and its reporting being done before the time of investigation.
Production Based – This method is completely pre inspection oriented. This was the most favourable option since it would lead, both to study and archiving of defect. When the production-based method was decided upon it was made sure that all the prerequisites of the method were checked to have existed in the records of either in-plant MES or on-the paper records of inspection staff.
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