| Equipment | Expandable Winding Mandrel (KTM Series) |
| Customer | A distribution transformer manufacturer in Santiago, Chile (serving South American mining distribution and grid modernization markets) |
| Application | Adjustable-diameter support winding and damage-free stripping for coils of 10–35 kV oil-immersed distribution transformers |
Customer information has been anonymized; only regional and industry attributes are retained. Performance figures represent typical reference values under standard operating conditions and may vary depending on actual production line conditions.
Customer Background
This distribution transformer manufacturer, based in Santiago, Chile, serves a diverse customer base across South American mining operations, urban grid upgrades, and renewable-energy interconnection projects. Their product portfolio covers oil-immersed distribution transformers from 10 kV to 35 kV, with annual output of approximately 1,200 units and per-unit ratings ranging from 100 kVA to 2,500 kVA. Because Chile’s mining regions are widely dispersed and each site has unique power requirements, the customer frequently receives orders for coils with different core diameters and outer dimensions. One week the line might be winding a 500 kVA coil with a 600 mm outer diameter; the next week it must switch to a 1,600 kVA coil at 900 mm.
Before introducing the expandable winding mandrel, the customer relied entirely on fixed-diameter wooden or steel mandrels. Every time the order specification changed, the workshop spent half a day swapping mandrels, re-centering, and calibrating tension. The mandrel warehouse held more than twenty sets of fixed mandrels in various sizes, consuming valuable floor space and requiring continuous maintenance against moisture, deformation, and wear.
Industry Pain Points
Transformer coil winding demands exceptionally high support precision and intact stripping. The customer’s fixed-mandrel workflow presented four critical problems:
Long changeover times and poor production flexibility. Swapping a fixed mandrel required crane lifting of the old unit, installation of the new one, manual centering, and trial winding. The entire process typically consumed three to five hours. Under a multi-spec, small-batch order pattern, frequent changeovers severely eroded available production time.
High mold inventory costs. Fixed mandrels are built for a single diameter. Coils of different core sizes and voltage classes each need a matching mandrel. The customer maintained more than twenty sets in stock, with per-unit costs ranging from several thousand to over ten thousand dollars. Regular maintenance to prevent moisture absorption, warping, and wear added further overhead.
High stripping damage rates. After repeated use, wooden mandrels developed surface wear and burrs. During stripping, these imperfections frequently scratched the coil’s insulation paper or inter-layer insulation pads, resulting in a rework rate of roughly 3–5%. Steel mandrels were more durable but heavy, difficult to crane-handle, and prone to thermal expansion that could make stripping even harder.
Progressive accuracy degradation. Fixed mandrels gradually lost diameter precision with use, and wooden units were especially sensitive to ambient humidity, which affected cylindricity. Once mandrel accuracy declined, the wound coil’s outer diameter and roundness deviated from design values, compromising subsequent core insertion and overall electrical performance.
Solution
After evaluating several options, the customer selected the TRANFOVIA KTM series expandable winding mandrel to replace their fixed-mandrel system. The mandrel’s design directly addresses each pain point:
Wide adjustable diameter range — one mandrel covers multiple specifications. The KTM series offers diameter adjustment from 180 mm up to 3,000 mm (models KTM-180 through KTM-2300) with load capacities from 1 ton to 20 tons. The KTM-600 unit selected by the customer covers a 600–900 mm diameter range and is adjusted via a precision reducer mechanism. What previously required three separate fixed mandrels now fits within a single expandable unit, cutting mold inventory by approximately 70%.
High-precision support with diameter deviation ≤1 mm. The mandrel uses a composite structure of cage, sliding-sleeve assembly, support-rod assembly, and strips, driven by a transmission system that achieves synchronous radial expansion. Design precision guarantees diameter deviation within 1 mm and cylindricity within 1 mm, ensuring uniform layer tension and consistent outer diameter throughout the winding process. This is essential for controlling the insertion gap during subsequent core assembly.
Damage-free stripping that protects coil insulation integrity. After winding is complete, the operator reverses the reducer to retract the strips inward, reducing the mandrel’s outer diameter and creating a clearance between coil and mandrel. The coil can then be lifted off smoothly without prying or hammering. This mechanism dropped the stripping damage rate from 3–5% to near zero, sharply reducing insulation rework and material waste.
Seamless integration with existing winding machines. The mandrel’s end-flange design interfaces directly with the chucks or spindles of both vertical and horizontal winding machines. Installation and removal use standard fittings, so no modifications to existing winding equipment are required. The customer’s current winding machines could be paired immediately, keeping total upgrade cost low.
Implementation
- Sizing and customization consultation. TRANFOVIA’s technical team reviewed the customer’s coil diameter distribution (concentrated between 500 mm and 1,000 mm), required strip lengths (1,400–2,200 mm), and winding-machine interface specifications, then recommended the KTM-600 model and supplied 3D installation drawings for advance compatibility verification.
- Production and factory acceptance. Before shipment, the mandrel underwent full-stroke expansion-contraction testing, diameter-deviation measurement (≤1 mm), and cylindricity inspection (≤1 mm), with a factory test report included. The customer confirmed key dimensions and surface quality through a remote video acceptance session.
- On-site commissioning and training. After the equipment arrived in Santiago, a TRANFOVIA service engineer completed installation, interfacing with the winding machine, and no-load running tests within one week. A two-day training program followed, covering reducer adjustment, diameter readout calibration, daily lubrication maintenance, and safety precautions.
Results
After six months of operation, the customer recorded the following improvements on the production line (Results may vary):
- Changeover time reduced from 3–5 hours to 15–20 minutes, significantly improving the line’s responsiveness to multi-spec orders and reducing unplanned downtime.
- Mold inventory cut from more than twenty fixed mandrels down to six expandable units, freeing warehouse space that was repurposed for coil semi-finished goods buffer storage.
- Stripping damage rate dropped from roughly 3–5% to below 0.5%, with fewer insulation rework batches and lower material waste.
- Improved coil outer-diameter consistency led to more stable core-insertion gaps and approximately a 4% increase in pass rate at the core-and-coil assembly pressing stage.
Figures above represent typical improvements under comparable conditions. Actual results will vary depending on the condition of previous fixed mandrels, operator proficiency, and production-line management practices.
Customer Feedback
“We used to keep a warehouse full of fixed mandrels in every size, and every changeover required the whole team to stop and coordinate. With the expandable mandrel, one operator can adjust the diameter in about fifteen minutes, and we no longer worry about scratching the insulation when stripping the coil. For a multi-spec, small-batch operation, the flexibility this system offers is something fixed mandrels simply cannot match.” — Winding workshop supervisor, Santiago plant
Learn More
If you are looking for a solution to changeover efficiency, mold inventory, or stripping damage in multi-spec coil production, contact us for detailed technical specifications and sizing guidance for the KTM series expandable winding mandrel. We can provide a customized proposal based on your coil diameter range, load requirements, and winding-machine interface.
- WhatsApp: +86-15958243831
- Email: sales@tranfovia.com
- Website: https://tranfovia.com/
