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CRGO Core Cutting Techniques: Mitered, Step-Lap, and Butt-Lap Explained

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Introduction


Cold Rolled Grain Oriented (CRGO) electrical steel is the backbone of India’s power transformer industry. The efficiency, magnetic performance, and noise level of a transformer largely depend on how the CRGO core is cut and assembled. Choosing the right cutting technique—Mitered, Step-Lap, or Butt-Lap—can make a significant difference in reducing core loss and improving transformer reliability.At S M Steels, we supply precision-cut CRGO laminations tailored for each of these cutting styles, ensuring optimal performance for every transformer design.


Understanding the Purpose of Core Cutting


CRGO laminations are thin sheets of silicon steel with grains oriented in a single direction to minimize energy loss. However, the cutting pattern and joint configuration between these laminations affect:


  • Magnetic flux distribution

  • Core loss (W/kg)

  • Noise and vibration

  • Assembly convenience


Each cutting method—Mitered, Step-Lap, and Butt-Lap—offers unique benefits depending on transformer size and design specifications.


1. Mitered Core Cutting

Mitered joints are created by cutting CRGO laminations at a 45° angle where the limbs and yokes meet.This allows magnetic flux to pass smoothly through the corner joints without interruption.


Advantages:

  • Reduces magnetic flux leakage at the corners.

  • Minimizes no-load losses.

  • Produces quieter transformers.

  • Ideal for medium and large power transformers.


Applications:Used in distribution transformers from 100 kVA to 2500 kVA and in power transformers where performance and efficiency are top priorities.

At S M Steels, we offer precision mitered CRGO lamination sheets using automated cutting lines to maintain perfect angular accuracy and edge smoothness.


2. Step-Lap Core Cutting


The step-lap joint is an advanced version of the mitered core, where laminations are overlapped in small steps (usually 3–5 layers) at the joint area.This ensures a gradual transfer of magnetic flux between the limbs and yokes, rather than a sudden shift.


Advantages:

  • Lowest no-load loss among all joint types.

  • Greatly reduces magnetostriction and audible humming noise.

  • Improves transformer efficiency and flux distribution.

  • Minimizes inrush current during energizing.


Applications:Preferred for high-efficiency distribution and power transformers (typically 500 kVA and above).

At S M Steels, we manufacture step-lap CRGO laminations with consistent overlap control for maximum performance, following precise tolerances and alignment to meet OEM transformer standards.


3. Butt-Lap Core Cutting


The butt-lap joint is the simplest and most cost-effective method where laminations from the limbs and yokes meet end-to-end (butt joint) without any overlap.


Advantages:

  • Easier and faster to assemble.

  • Ideal for smaller or low-voltage transformers.

  • Lower material wastage during production.


Disadvantages:


  • Higher magnetic flux leakage.

  • Increased core losses and noise.


Applications:Typically used in small distribution transformers (below 100 kVA) or for testing and prototyping purposes.


Precision Cutting and Customization at S M Steels


We specialize in custom CRGO lamination cutting and processing for transformer manufacturers across India.Our services include:


  • Mitered, Step-Lap, and Butt-Lap CRGO lamination cutting

  • V-notching, double V-notching, and gapping for core assembly

  • CRGO core kits (C-core, toroidal, and EI type)

  • Sorting and grading by watt loss (W/kg)

  • Prime, Secondary, and Oily CRGO sheets available


All materials are sourced from BIS-certified mills and cut using precision machines to ensure minimal burrs and uniform grain alignment.


Why Choose S M Steels for CRGO Core Laminations


  • Over a decade of experience in CRGO core material supply

  • Nationwide delivery across India (Chennai, Delhi, Pune, Kolkata, etc.)

  • Trusted supplier of CRGO coils, laminations, and scrap materials

  • Quality inspection and testing support for every batch


Whether you’re a transformer manufacturer, core assembler, or reseller, we can help you source the right CRGO core materials for your technical and budget needs.


Conclusion


The way CRGO steel is cut and assembled directly affects transformer efficiency, performance, and longevity. Mitered and Step-Lap designs may cost slightly more to produce, but their long-term benefits in reducing losses and noise make them worth the investment.


At S M Steels, we don’t just sell CRGO materials — we help you build more efficient, durable, and compliant transformers.


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