Expandable / Adjustable Winding Mandrel

BEST™ is a professional manufacturer of transformer coil winding machines. Relying on our rich experience in low-voltage coil winding, we have developed a comprehensive expandable winding mandrel solution. The BEST™ expandable winding mandrel adopts a heavy-duty steel structure and precision guide slot design, capable of withstanding the dead weight of 5 to 20-ton high-voltage coils and immense wire tension. The diameter deviation and cylindricity between any two points on the mandrel surface are strictly controlled within a tolerance of ±1.5mm. The drive system supports manual lead screw adjustment as well as pneumatic/hydraulic automatic expansion and contraction modes. The radial contraction design completely eliminates friction during coil unloading, reducing the demolding time from several hours to mere minutes.

BEST™ expandable winding mandrels are widely used in the coil manufacturing processes of various power transformers, distribution transformers, dry-type transformers, and reactors:

• High and Low Voltage Coil Winding Support: Suitable for low-voltage, high-current copper/aluminum foil winding on foil winding machines, as well as high-voltage continuously transposed cable (CTC) or flat copper wire winding on CNC/heavy-duty winding machines.
• Resin-Cast Dry-Type Transformer Coil Shaping: Ensures extremely precise inner diameter dimensions for dry-type transformer coils, facilitating subsequent epoxy resin casting and core assembly.
• Special-Shaped Coil Processing: In addition to standard round mandrels, we can customize rectangular and oblong (oval) expandable mandrels to perfectly match different core cross-section structures.

When purchasing or customizing an expandable mandrel, BEST™ offers several different drive methods and material choices. You can refer to the following customizable options based on your project requirements:

1. Drive Method: Manual Adjustment vs. Pneumatic/Hydraulic Automatic Expansion

• Manual Lead Screw Adjustment: Lower cost and simple structure. The diameter is adjusted and contracted manually by rotating the end lead screw with a wrench.
  • Best Recommendation: Suitable for small and medium distribution transformer production lines under 1000kVA, where the coil dead weight is within 1 ton.
• Pneumatic/Hydraulic Automatic Expansion and Contraction: Driven by pneumatic cylinders or a hydraulic station, achieving instant tensioning and contraction with a single button, offering extremely high demolding efficiency.
  • Best Recommendation: For large power transformer coils of 35kV and above, weighing over 3 tons, hydraulic or pneumatic mandrels are strongly recommended. It is very difficult for manual labor to overcome the immense friction caused by heavy-duty coils to manually contract the mold.

2. Outer Shield Plate Material: Metal Panels vs. Hardwood/Resin Boards

• Pure Metal Panels: Extremely high rigidity and long service life. However, if thick cardboard is not placed inside the inner layer of the coil, the metal edges may indent and damage the coil’s inner diameter under high tension.
• High-Hardness Wood / Laminated Composite Boards: Offers a relatively milder texture with a certain cushioning effect, and is resistant to moisture and termites.
  • Best Recommendation: In actual workshop applications, a hybrid structure of “Internal Metal Skeleton + External Hardwood/Composite Curved Staves” is usually adopted. This guarantees the heavy-load rigidity of the main body while ensuring the insulation safety of the contact surface with the coil. (Note: The specific load-bearing tonnage must be engineering-calculated and customized according to the maximum weight of the customer’s coil. Never overload to prevent structural jamming).