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Electrical Steel


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  • is it possible to make thickness .35 mm CRNGO sheet..????
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  • Definition of CRGO and CRNGO in slide# 5 is unclear. Rolling is done always along one direction for regular CRGO and CRNGO (along the length of the coil). When the grains develop during annealing, they get to decide their orientation. In the case of CRGO, the grain orientation is preferably Goss (110)[001] orientation.

    Explanation on slide# 9 is wrong for 'grain orientation'... etc.. etc..
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Electrical Steel

  1. 1. • CRGO • CRNGO• Electrical steel properties• Reason for the properties• Manufacturing Process• CRGO CRNGO and MS• ES grades• GOS industry in India and abroad• Challenges Pratyush Srivastava Pawandeep Singh Arora B-tech IIT BHU
  2. 2. Electrical steels Electrical steel, also called lamination steel or silicon electrical steel, silicon steel or transformer steel, is special steel tailored to produce certain specific magnetic properties. It has specific proportion of silicon that is responsible for its unique properties.
  3. 3. Properties of Electrical steel The hysteresis loss is low ie. The magnetic domains get easily aligned in one or the other directions and not much of electrical energy is required for this process.(hysteresis graph on following slides) The magnetic permeability is high ie the material easily allows formation and accumulation of magnetic field within. Electrical resistance is high to prevent eddy current losses.(current that flows on the surface as a result of electro magnetic induction over the core coil)
  4. 4. Raw material for manufacture : ferro silicon alloy (15-90% Si) is the base material. The alloy is processed to lower the silicon content { 3.5% } and remove constituents like Mn ,S etc. Finally the density becomes around (7600+-50) kg/m3
  5. 5. CRGO Vs CRNGO CRGO : Cold Rolled Grain Oriented steel. Rolling done in one direction such that the grains elongate along one direction. CRNGO: Cold Rolled Non Grain Oriented steel Rolled in random directions such that the grains are elongated along different direction. CRGO needs precise alignment due to its anisotropy( the properties that are different along different directions are anisotropic properties) but CRNGO can respond to flux changes in all directions (ie. Its properties are isotropic) hence CRNGO is used in motors.
  6. 6. CRGO CRNGO grainsIsotropy and anisotropy arise from grain orientations CRGO CRNGO
  7. 7. CRGO /CRNGO manufacturing• Hot rolling• Pickling• Cold rolling• High temp anealing• Inspection
  8. 8. Why CRGO/ CRNGO overMS In mild steel there is much loss in electrical energy due to hysteresis and eddy current hence use of mild steel is The uneconomical when it comes to usage in hysteresis loss is electrical devices. equivalent to the area of the enclosed loop. Electrical steel Mild Steel
  9. 9. How CRGO reduces losses Grain orientation: When cold rolling is done the grains get elongated in one direction and get narrowed in the perpendicular direction. Hence due to the shape it becomes easier for the domains to change polarity back and forth along the elongated direction. Grain enlargement: when heated at temperatures around critical temperature (temp at which the grain boundaries begin to diffuse ) followed by slow cooling grain enlargement occurs. This reduces electrical losses due to hysteresis.
  10. 10. Manufacturing Ferro silicon steel is heated in a decarburizing environment(N with H20 and H2 ) S N and O must be as low as possible More silicon content increases resistivity but at the same time makes it more brittle. Si reduces magnetostriction. (change shape/size when placed in a electromagnetic field)
  11. 11. ManufacturingIn the final processed material – C should be less than .06% Mn +Al = .5% (approx.) Si =3.2%Then it is cold rolled to increase grain size : 2-5 in case of CGOS 5-20 in case of HGOS as compared to MS ( .5 mm)
  12. 12. Manufacturing PAIR = Pre Annealing Intermediate Rolling This is done to improve uniformity of grains. This will ensure easy conformation of domains when a varying magnetic field is applied. MnS , carbides, oxides, or nitrides used as the grain growth inhibitors. Finally carlite coating is done. It helps reduce eddy losses.
  13. 13. Manufacturing Anisotropy correct to 7% in GO and 3% in Hi-B GO(better grade of CRGO) ie the direction of elongation should not vary beyond these angles. This elongation is obtained by careful cold rolling. This makes switching cost effective and improves operational efficiency.
  14. 14. Applications CRGO (or CGO) is used in transformers where we require the cost of operation to be less but efficiency more . Nickel Iron is an alternative but -> high installation cost. Relay steel used in direct current conditions (not good with AC current) CRNGO in motors and generators due to isotropy (Since in motors the coil is wound on axis and rotates with it so direction of flux keeps changing and we require similar properties in all directions), ballasts, small Transformers generators for steam turbine and water wheels. CRGO needs precise alignment and this often increases the length of appliance.
  15. 15. CRGO Production No CRGO production in India. SAIL made an abortive attempt to produce CRGO steel at its Bokaro plant in Jharkhand (1990s) but failed. The improvements in GOS have led to an ever increasing demand of this grade of steel due to operational cost reduction
  16. 16. CRGO Production Inspite of being classified as a "steel" is very rarely impacted by the international price movement or other factors influencing mild steels or other categories of steel products. No competition from substitutes Metglass Amorphous Boron Strip / Mu Metal /Nickel Iron -- various technical problems and have already been relegated for use in special purpose applications (mainly high frequency) only in developed countries. (suppliers are mainly developing countries)
  17. 17. CRGO Standards
  18. 18. CRNGO Standards
  19. 19. CRGO Types
  20. 20. CRGO Types
  21. 21. CRGO Types
  22. 22. CRGO Types
  23. 23. CRGO Types
  24. 24. End Users
  25. 25. Challenges : Indian testers are widely used but are in-consistent. SOKEN (Japanese) single sheet tester is best in category. Transformer noise must be low because all the transformer characteristics depends on core. Nomenclature needs to be reviewed in most places. Many organizations still use obsolete nomenclature. For CRGO no definite standards when it comes to manufacture of transformer cores because there is always ambiguity in testing and most transformer manufacturers use secondary/used cores.
  26. 26. Grades, Nomenclatures andMaterials Different mills have different brand names and nomenclatures whilst producing GOS and HGOS. Most mills have now switched over to the following method of grading Grain Oriented Steels: (Thickness) (Brand Name) (Core loss at 1.7T/50Hz) For eg. Nippon Steel grade 23ZH100 means thickness 0.23mm, ZH is the brand name for Hi-B for Nippon Steel and 100 means 1.00W/kg at 1.7T/50Hz. Similarly 23 RGH100 IS Kawasaki Steel nomenclature for the same material and 23ORSIH100, the Thyssen Krupp Electrical Steel (TKES) nomenclature for the same material.