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Aluminum Bronze Eye Bolts (for Transformer Bushings)
Aluminum Bronze Eye Bolts (for Transformer Bushings)
Electrical Accessories India manufactures specialist aluminum bronze eye bolts for transformer bushings – a highly engineered application-specific fastener used in power transformer HV bushing assemblies, LV bushing terminals, neutral bushing connections, and instrument transformer (CT/CVT/PT) bushing hardware. Aluminum bronze (Cu-Al alloy, C95200/C95400) is selected for this application due to its critical combination of: non-magnetic property (preventing eddy current losses in the bushing flange circuit), high tensile strength (550–620 MPa), excellent resistance to transformer mineral oil, compatibility with copper and brass bushing hardware, and resistance to the electrical, thermal, and mechanical stresses at the transformer bushing connection point. These eye bolts are specified by transformer OEMs globally, including BHEL, ABB, Siemens, Hitachi, and TBEA supply chains.
Product Overview
Why Aluminum Bronze is Specified for Transformer Bushing Eye Bolts
The transformer bushing application imposes several demanding requirements on the clamping bolt material. Non-magnetic requirement: Ferromagnetic bolts (steel) in the high magnetic field region of a transformer bushing flange would experience induced eddy currents that generate heat and energy losses, reducing transformer efficiency. Aluminum bronze has magnetic permeability ≈ 1.0 (non-magnetic), eliminating eddy current losses entirely. High strength: Bushing clamping bolts must maintain precise clamping force on oil-tight gaskets under cyclic thermal load cycling from ambient to 100°C+ operating temperature. Aluminum bronze C95400 achieves 550–620 MPa UTS, providing higher preload retention than brass or silicon bronze. Oil compatibility: Transformer mineral oil (IEC 60296 naphthenic/paraffinic) has no adverse effect on aluminum bronze, which is fully compatible with petroleum oils, esters, and other transformer dielectric fluids.
Bushing Eye Bolt Design and Function
A transformer bushing eye bolt consists of: (1) an eye (circular loop) at the top for conductor connection via a cable terminal lug or busbar flat connection; (2) a shank body that passes through the bushing flange and tank cover; (3) a threaded end that accepts a locknut on the inside of the tank. The eye provides a mechanical and electrical connection point for the HV/LV conductor coming from the winding, and the bolted shank clamps the bushing flange against the tank/cover plate oil-tight seal. The eye geometry must be machined to accept standard cable terminals (round or tongue-type) and provide adequate current-carrying cross-section. Available in closed eye (fully-forged loop) and open eye (C-shaped, for bolt-in terminal installation) configurations.
HV, LV and Neutral Bushing Configurations
HV bushing eye bolts (33kV–765kV class transformers): M20–M48, high-clamping-force requirement, often with extended shank for deep tank penetration, precision oil-seal groove on shank body, PTFE O-ring sealed. LV bushing eye bolts (0.4kV–11kV class): M12–M30, higher current-carrying cross section required due to higher LV current, larger eye aperture for 2× ACSR or 4× LV cable terminal bolts. Neutral bushing eye bolts: M12–M24, commonly with dual eye for external and internal conductor connection, or with earth terminal provision. Generator transformer HV eye bolts (33kV–500kV, auto-transformers): special extended-shank, dual-seal configurations with bronze hex or square shoulder for torque application during bushing installation.
Thread Standards and Dimensional Configurations
Standard transformer bushing eye bolts are manufactured in metric ISO thread M8–M48 and inch UNC 3/8″–2″. Thread length on the nut side is designed for 1.5–2 × nominal diameter engagement with the locking nut inside the tank, providing adequate thread strip resistance for clamping force. Eye dimensions (eye ID, eye bore, shoulder diameter) are manufactured to match common bushing terminal fitting requirements per ABB, Siemens, GE, and BHEL bushing designs. Custom eye dimensions to OEM drawing are the standard supply mode; there is no single universal eye bolt standard for transformer bushings as each OEM has proprietary bushing designs requiring custom hardware.
Aluminum Bronze Material Grades – C95200 and C95400
C95200 (AB1 – Aluminum Bronze 9%): 88% Cu, 9% Al, 3% Fe – moderate strength (520–560 MPa UTS), good machinability, used for LV and neutral bushing eye bolts where machining complex eye geometry is required. C95400 (AB2 – Aluminum Bronze 11%): 85% Cu, 11% Al, 4% Fe – higher strength (560–620 MPa UTS), used for HV and generator transformer bushing eye bolts where maximum clamping force retention is required. Both grades are non-magnetic (µ ≈ 1.0), resistant to mineral oil, and have thermal conductivity 50 W/(m·K) – adequate for current-carrying bushing connections. CC331G (EN designation for cast AB2 equivalent) is also used for cast eye bolt heads on forged/machined shanks when complex eye geometry is more economically produced by casting.
Current Carrying Capacity of the Eye
The aluminum bronze eye provides a current path from the external conductor terminal to the bushing conductor. The eye cross-sectional area must be adequate for the rated bushing current at the operating temperature. EAI designs eye bolt cross-sections for the following current ratings: M16 eye bolt (standard eye section): up to 400A continuous; M20 eye bolt: up to 630A; M25 eye bolt: up to 1000A; M32 eye bolt: up to 1600A; M42 eye bolt: up to 2500A (double-eye design). For higher-current LV bushings above 2500A, parallel double-eye or fork-eye configurations are manufactured. Current rating based on maximum 80°C conductor temperature rise over 40°C ambient, per IEC 60137 bushing standard thermal requirements.
Sealing and Oil-Tight Designs
Transformer bushings require oil-tight sealing where the bushing bolt shank penetrates the transformer tank cover. EAI aluminum bronze eye bolts are available with: (1) O-ring groove machined on shank body for elastomeric seal (PTFE or Viton O-ring, rated for transformer oil compatibility per IEC 60296); (2) threaded shank with Teflon tape sealing for lower-pressure static seals; (3) flanged shank with gasket face for large-diameter bushing flanges. O-ring sealing option: groove dimensions per AS 568A (inch O-rings) or ISO 3601 (metric O-rings). Oil-tested to IEC 60137 pressure test requirements for the specific bushing voltage class.
Mechanical and Electrical Testing
EAI aluminum bronze eye bolts for transformer bushing applications are subjected to: dimensional inspection (eye ID, shank diameter, thread pitch, thread length, overall length, O-ring groove dimensions); tensile testing of shank (to verify minimum 550 MPa UTS per C95200 or 580 MPa per C95400); pull-out test of eye (minimum load = 2 × rated conductor termination load); electrical resistance test of eye cross-section (milliohm resistance per unit length, verifying current-carrying adequacy); and oil compatibility soak test (24h immersion in transformer mineral oil at 100°C, no corrosion, no swelling of O-ring material). Test certificates provided per EN 10204 3.1.
Pricing
Aluminum bronze eye bolts for transformer bushings are priced at USD 14.90 per kilogram (EXW Jamnagar, India). Note: these are custom-engineered items; the per-kilogram price applies to the finished machined weight. Typical weight: M20 × 150 mm eye bolt = 250–350 g; M32 × 200 mm = 800 g–1.2 kg. MOQ: 10 pieces per drawing. Please submit your OEM drawing or bushing specification for a formal quotation.
Key Features
- Non-magnetic aluminum bronze C95200/C95400 – zero eddy current loss at bushing flange
- High tensile strength 550–620 MPa – superior to brass and silicon bronze for clamping
- Compatible with transformer mineral oil (IEC 60296) and synthetic ester fluids
- Closed eye and open (C-type) eye configurations; double-eye for high current LV bushings
- O-ring sealing groove for oil-tight bushing penetration
- Custom-engineered to OEM bushing design drawings
- ISO 9001:2015; EN 10204 3.1 MTR; dimensional and tensile test certificates
- Supplied to BHEL, ABB India, Siemens, GE, Hitachi, TBEA transformer supply chains
Non-Magnetic Property – Critical for Transformer Applications
The non-magnetic requirement for transformer bushing hardware is specified in IEC 60076-1 (power transformer general requirements) and in most major OEM bushing specifications. Ferromagnetic hardware in the bushing flange magnetic field path causes: (1) flux concentration and increased stray losses in the tank cover/flange plate; (2) eddy current heating of the bolt itself, reducing oil-cooling effectiveness; (3) possible resonant vibration of ferromagnetic fasteners under 50/60 Hz electromagnetic excitation; and (4) risk of magnetic core saturation near the bushing in high-field regions. All of these effects are eliminated by specifying non-magnetic aluminum bronze eye bolts. This is not a premium option but a basic engineering requirement for correct transformer design.
Compatibility with Bushing Types
EAI aluminum bronze eye bolts are compatible with and have been supplied for: oil-impregnated paper (OIP) bushings, resin-impregnated paper (RIP) bushings, capacitor-graded bushings (condenser bushings), solid-type porcelain bushings, silicone rubber composite bushings, and SF6 gas insulated bushings for GIS transformer connections. The eye bolt contacts only the metallic terminal of the bushing conductor; compatibility with bushing insulating material is not a concern for the fastener itself.
Application for Instrument Transformer Bushings
Current transformers (CTs), capacitor voltage transformers (CVTs), and potential transformers (PTs) also require aluminum bronze bushing hardware for their primary terminal connections. In free-standing CTs (33kV–765kV), the primary terminal hardware (eye bolts, terminal connectors, clamping bolts) must be non-magnetic. EAI supplies matched aluminum bronze hardware sets for instrument transformer primary terminal assemblies, including eye bolts, clamping plates, terminal lug bolts, and cotter pins.
Technical Specifications
| Parameter | C95200 (AB1) | C95400 (AB2) |
|---|---|---|
| Composition | Cu 88%, Al 9%, Fe 3% | Cu 85%, Al 11%, Fe 4% |
| Tensile Strength | 520–560 MPa | 560–620 MPa |
| Yield Strength (0.2%) | 200–280 MPa | 250–350 MPa |
| Elongation | 15–25% | 10–18% |
| Hardness | 150–180 HB | 170–200 HB |
| Magnetic Permeability | ≈ 1.0 (non-magnetic) | ≈ 1.0 (non-magnetic) |
| Electrical Conductivity | ~12% IACS | ~10% IACS |
| Density | 7.64 g/cm³ | 7.45 g/cm³ |
| Max Service Temperature | 250°C continuous | 250°C continuous |
| Oil Compatibility | IEC 60296 mineral oil compatible | IEC 60296 mineral oil compatible |
| Metric Thread Range | M8–M48 | M8–M48 |
| Inch Thread Range | 3/8″–2″ UNC | 3/8″–2″ UNC |
Aluminum Bronze International Grade Equivalents
| UNS/ASTM | EN (Europe) | BS (UK) | DIN (Germany) | IS (India) | Description |
|---|---|---|---|---|---|
| C95200 | CC330G / CuAl9Fe3 | AB1 | CuAl10Fe3 | — | 9% Aluminum Bronze |
| C95400 | CC331G / CuAl11Fe4 | AB2 | CuAl11Fe4 | — | 11% Aluminum Bronze (high strength) |
| C95500 | CC332G / CuAl11Fe5Ni5 | AB3 | CuAl11Ni6Fe5 | — | Nickel Aluminum Bronze (max corrosion resist.) |
Product Variants
| Type | Eye Config | Sealing | Size Range | Application |
|---|---|---|---|---|
| Closed Eye Bolt – Standard | Fully closed loop | None / O-ring | M8–M48 | HV bushing terminal connections |
| Open / C-Eye Bolt | Open C-ring | None / O-ring | M12–M36 | Easy conductor installation, LV bushings |
| Double-Eye Bolt | Two closed loops | O-ring groove | M20–M48 | High-current LV bushing (>1600A) |
| Fork-Eye / Terminal Bolt | Forked tongue | O-ring groove | M20–M42 | Flat bus bar connection at bushing terminal |
| Bushing Stud w/ Eye | Eye one end, thread other | O-ring groove | M16–M36 | Generator transformer, EHV transformer |
| Instrument Transformer Terminal Bolt | Closed eye / flat | None | M8–M24 | CT/CVT/PT primary terminal hardware |
Applications in Industry
| Transformer Type | Voltage Class | Eye Bolt Application |
|---|---|---|
| Distribution Transformers | 11kV/0.4kV | HV and LV bushing terminal eye bolts |
| Power Transformers | 33kV–220kV | HV, LV, neutral bushing hardware |
| Generator Transformers (GT) | 220kV–765kV | EHV bushing eye bolts, dual-eye LV bushings |
| Auto-Transformers (ICT) | 220kV/132kV | Series and common winding bushing hardware |
| Instrument Transformers (CT/CVT) | 11kV–765kV | Primary terminal eye bolts, connection hardware |
| Reactor and Shunt Reactors | 33kV–765kV | Terminal bushing eye bolts |
| Phase Shifting Transformers | 132kV–400kV | Bushing terminal hardware, neutral connections |
Manufacturing Process
Aluminum bronze transformer bushing eye bolts are produced by closed-die forging (for the eye head and shank) followed by CNC machining of the shank, O-ring groove, and thread. The forging process ensures a fully dense, void-free eye structure with the grain flow aligned with the eye geometry – essential for maximum pull-out strength in service. The aluminum bronze billet is heated to 950–1050°C, pressed in closed forging dies to form the eye head and shank blank, then trimmed, heat-treated (quench + temper for maximum hardness in C95400), and CNC-machined to final dimensions. Thread rolling on the shank (preferred) produces work-hardened thread flanks. O-ring groove is CNC-turned to ISO 3601 or AS 568A tolerances. 100% dimensional inspection; periodic tensile, hardness, and pull-out testing. Material supplied with EN 10204 3.1 certificate including chemical analysis and mechanical test results for each heat lot.
Quality Standards and Certifications
| Standard | Scope |
|---|---|
| ISO 9001:2015 | Quality Management System |
| IEC 60076-1 | Power transformer requirements (non-magnetic hardware) |
| IEC 60137 | Bushing standard – compliance for bushing hardware |
| ASTM B148 | Aluminum bronze castings composition |
| ASTM F468 | Nonferrous bolts and studs |
| DIN 580 | Eye bolt geometry reference |
| EN 10204 Type 3.1 | Material Test Certificate |
| IEC 60296 | Transformer oil compatibility testing |
| REACH / RoHS | Hazardous substance compliance (no restricted substances) |
Why Choose Electrical Accessories India
- Transformer bushing specialist – custom eye bolt configurations to OEM drawing
- Both C95200 and C95400 grades; nickel-aluminum bronze C95500 on request
- Proven supply to major OEMs including BHEL, ABB India, Siemens, transformer exporters
- USD 14.90/kg – competitive against European and US sources for custom engineered parts
- O-ring sealed, oil-tested designs for fully oil-tight bushing assemblies
- Full electrical testing (resistance, pull-out) available on request
- ISO 9001:2015 with EN 10204 3.1 MTR, dimensional inspection certificate
- Fast turnaround on OEM drawings – DFQ (Design for Quote) within 5 working days
Frequently Asked Questions (FAQ)
1. Why is aluminum bronze specified instead of brass for transformer bushing eye bolts?
Three key reasons: (1) Aluminum bronze is non-magnetic (brass is also non-magnetic, but aluminum bronze provides higher strength); (2) Aluminum bronze offers tensile strength of 550–620 MPa vs 380–430 MPa for free-cutting brass – critical for maintaining bushing oil-seal clamping force over thermal cycles; (3) Aluminum bronze has better high-temperature strength retention above 100°C transformer operating conditions. For HV and generator transformer bushings specifically, the higher strength of AB2/AB3 aluminum bronze is essential.
2. Can you manufacture eye bolts to our (OEM) drawing?
Yes. This is our standard supply mode. Please submit your OEM drawing with: thread specification, eye ID and bore, shank diameter and length, O-ring groove dimensions (if applicable), material specification (C95200 or C95400), and required test certificates. We provide DFQ (design-for-quote) within 5 working days and first article inspection report with prototype.
3. What is the lead time for aluminum bronze eye bolts?
For new tooling (first production): 4–6 weeks including tooling, first article, and approval. For repeat orders on existing tooling: 2–3 weeks. For urgent OEM requirements (transformer factory shutdowns, breakdown replacement), expedited lead times can be discussed. We maintain tooling for key repeat customers.
4. Are aluminum bronze eye bolts suitable for SF6 GIS transformer bushings?
Yes. Aluminum bronze is compatible with SF6 gas environments and is used in GIS-transformer interface hardware. The material does not react with SF6 decomposition products under normal operating conditions. For SF6 applications, specify the surface finish requirement (typically bare machined with no lubricating oils or coatings that could contaminate SF6 gas purity).
5. What O-ring material do you recommend for transformer bushing eye bolt sealing?
PTFE or Viton (FKM) O-rings are recommended for transformer oil service. Viton (FKM) provides excellent resistance to mineral oil, synthetic ester, and silicone transformer fluids. NBR (nitrile) O-rings are suitable for mineral oil only. PTFE O-rings (PTFE cord) are used for highest-temperature and chemical-resistant sealing. O-rings are supplied separately or as part of a bushing hardware kit as required.
6. What is the price of aluminum bronze eye bolts?
USD 14.90 per kilogram (EXW Jamnagar). Typical M20 × 150 mm eye bolt weighs approximately 300–400 g; M32 × 200 mm weighs 800 g–1.2 kg. Tooling charges may apply for new designs; tooling is amortised over order quantity. Contact us with your drawing for formal quotation.
7. Can you supply a complete bushing hardware kit?
Yes. Complete bushing hardware kits (eye bolt + silicon bronze nuts + flat washers + spring washers + O-rings) in aluminum bronze and silicon bronze are supplied for transformer OEM production lines and replacement/repair. Kit part numbers aligned to transformer Bill of Material (BOM) can be established for repeat supply.
8. Is aluminum bronze compatible with the copper conductors and brass fittings in transformer bushings?
Yes. Aluminum bronze is galvanically compatible with copper (small potential difference, ~0.15V in mineral oil), brass, and silicon bronze. These metals are all copper-base alloys forming a compatible family for transformer terminal hardware with minimal galvanic corrosion risk in mineral oil or sealed environments. The combination is standard practice in transformer manufacturing globally.
9. Do you supply eye bolts for instrument transformers (CTs, CVTs)?
Yes. Aluminum bronze eye bolts for instrument transformer primary terminals are manufactured in M8–M24 for CT, CVT, and PT primary bushings. These are typically smaller and lighter than power transformer equivalents but require the same non-magnetic and high-strength material. Contact us with CT/CVT primary terminal drawings for quotation.
10. Do you hold stock of standard sizes or manufacture to order only?
Aluminum bronze eye bolts are manufactured to order due to the custom nature of each OEM design. However, we maintain standard blank forging stock in C95400 for common shank diameters (M20, M24, M30), enabling faster machining lead times for common size requests. For truly standard sizes (DIN 580 profile), some stock is maintained – enquire with us about stock availability for DIN 580 M12–M24.
Equivalent Terms and Multilingual Reference
| Language | Term 1 | Term 2 | Term 3 |
|---|---|---|---|
| Spanish | Tornillos de ojo bronce aluminio transformador | Cáncamos de bronce aluminio para transformadores | Pernos de ojo para boquilla de transformador |
| Russian | Рым-болты из алюминиевой бронзы для трансформаторов | Болты-кольца бронза для вводов трансформаторов | Немагнитные болты-кольца трансформатор |
| French | Boulons à œillet en bronze d’aluminium pour transformateurs | Pitons de transformateurs en bronze aluminium | Boulons d’œil pour traversées transformateur |
| Portuguese | Parafusos de olhal em bronze alumínio para transformadores | Ganchos de bronze alumínio para bucha de transformador | Parafusos de olho não magnéticos bronze |
| Italian | Bulloni ad occhio in bronzo alluminio per trasformatori | Viti ad anello in bronzo per passanti trasformatore | Bulloni non magnetici bronzo trasformatore |
Related Products and Linked Terms
- Silicon Bronze Bolts
- Silicon Bronze Studs
- Silicon Bronze Hex Nuts
- Copper Bolts, Copper Hex Set Screws
- Brass DIN 934 Hex Nuts
- Aluminum bronze castings, transformer terminal hardware, non-magnetic bushing bolts, CT primary terminal hardware, CVT terminal bolts, EHV bushing hardware, transformer bushing clamps, bushing kit
Request a Quote
Electrical Accessories India supplies aluminum bronze eye bolts and transformer bushing hardware to power transformer OEMs, EPC contractors, and transformer repair workshops worldwide. Pricing: USD 14.90 per kilogram (EXW Jamnagar, India). Custom engineering to your OEM drawing. Submit drawing for DFQ within 5 working days.
Email: info@elecaccs.com | Location: Jamnagar, Gujarat, India | Export Markets: USA, UK, UAE, Germany, Australia, South Africa, Brazil, Southeast Asia
