B27RK085 Silicon Steel Laminated Iron Core: Properties and Applications

What Is B27RK085 Steel?

B27RK085 is a cold-rolled grain-oriented (CRGO) silicon steel grade with a nominal thickness of 0.27 mm, produced by the high-permeability Hi-B route with laser domain refinement. In the designation, 27 indicates the thickness in hundredths of a millimetre, R indicates laser domain refinement, and 085 is the maximum guaranteed core loss of 0.85 W/kg measured at 1.7 T and 50 Hz. The material is a preferred input for laminated iron cores of distribution transformers and other magnetic components where no-load loss directly affects operating cost.

Key Magnetic Properties

The table below gives the typical magnetic values of B27RK085 and the related domain-refined grades supplied for transformer core production. Core loss is measured on Epstein strips or a single-sheet tester in accordance with IEC 60404-2, and induction values follow IEC 60404-4.

B800 expresses the flux density reached at a field strength of 800 A/m; the higher the value, the smaller the core cross-section needed for a given flux, which reduces copper and tank weight. The lamination factor of 97.5 percent reflects the share of solid steel in the stacked core after allowing for the insulating coating, and it is higher for 0.27 mm material than for thinner grades because the coating occupies a smaller proportion of each sheet.

Why Lamination Is Essential

The core of a transformer carries alternating flux, which induces eddy currents in the steel and produces heat. Laminating the core into thin insulated sheets breaks the eddy current path, and the interlaminar coating raises the transverse resistance. The combination of high silicon content, Hi-B grain alignment, laser domain refinement and thin lamination reduces total core loss to a fraction of what a solid iron core would dissipate. Interlaminar insulation also limits circulating currents between sheets, which would otherwise appear if burrs from cutting punched through the coating.

Manufacturing Steps for Laminated Cores

A B27RK085 laminated core is produced through a defined sequence: slitting the master coil to the required strip width, punching or cutting the lamination shape, deburring, applying interlaminar insulation where the base coating is not sufficient, stacking the sheets to the design stack height, and finally forming or clamping the core with a suitable banding system. Stress-relief annealing is applied where the magnetic properties have been degraded by cutting; the annealing cycle must be compatible with the coating system, otherwise the insulation layer is damaged and core loss rises.

Applications

B27RK085 laminations are used in three-phase distribution transformer cores up to medium ratings, dry-type transformer cores, instrument transformers, smoothing reactors and other 50 or 60 Hz magnetic components. The grade is also selected for energy-efficiency programs where regulators require distribution transformers to meet defined maximum loss levels, because replacing a 0.30 mm conventional grade with 0.27 mm domain-refined steel measurably reduces no-load loss at moderate cost.

Customisation Options

Laminated cores can be supplied in a wide range of shapes, including E, I, U, C, toroidal and rectangular geometries, with customised stack heights, window sizes and fixing holes. When requesting a quotation, specify the core shape and dimensions, the required grade and thickness, the lamination factor, the coating system, whether annealing is required, and the maximum acceptable burr height. Tolerances should follow the drawing standard agreed with the manufacturer, typically based on the finished core dimension and the stamping capability of the production line.

FAQ

What does the B27RK085 designation mean?

B indicates the high-permeability Hi-B production route, 27 the nominal thickness of 0.27 mm, R laser domain refinement, and 085 the maximum guaranteed core loss of 0.85 W/kg at 1.7 T and 50 Hz.

How does B27RK085 compare with B20R065?

B27RK085 is thicker, 0.27 mm against 0.20 mm, and has a slightly higher guaranteed core loss, 0.85 against 0.65 W/kg, but it is less expensive per tonne and offers a higher lamination factor, which suits designs where the loss target is not extremely demanding.

Can B27RK085 laminations be annealed after cutting?

Yes, provided the coating system is chosen for annealing compatibility. The annealing cycle must be confirmed with the material supplier because laser-scribed and coated grades have defined temperature limits.

What coating is used on B27RK085?

Grain-oriented grades are supplied with inorganic or semi-organic insulating coatings, often designated C-2, C-5 or T2/T4 types, which provide interlaminar insulation and in some cases act as a separator during annealing.

Which standard should be referenced for acceptance testing?

Reference GB/T 2521.2 for grain-oriented electrical steel requirements and IEC 60404-2 for the measurement of core loss. The mill test certificate should list the measured loss, induction and lamination factor per coil.