Silicon Bronze Hex Flanged Bolts

Silicon Bronze Hex Flanged Bolts

Electrical Accessories India manufactures silicon bronze hex flanged bolts where the hex head is integrated with a wider bearing flange, combining the bolt and washer function in a single corrosion-resistant component. These bolts are manufactured from C65500 (High Silicon Bronze A) and C65100 (Low Silicon Bronze B) alloys, offering outstanding resistance to seawater corrosion, stress corrosion cracking, and dezincification. Silicon bronze hex flanged bolts are widely specified by electrical OEMs, marine engineers, EPC contractors, and offshore platform fabricators who require a non-magnetic, non-sparking, long-service-life fastener that eliminates washer assembly handling and reduces corrosion risk in aggressive environments.

Product Overview

Flange Bolt Design and Engineering Benefits

Hex flanged bolts (DIN 6921 / ISO 1665 profile) feature a hexagonal driving head with an integrated circular flange at the underhead bearing face. The flange diameter is typically 1.4–1.6× the hex across-flat dimension, providing a bearing area 2–3× larger than the equivalent standard hex bolt head. This design distributes clamp load over a greater surface area, reducing surface pressure on soft or brittle substrates (aluminium alloy panels, GRP enclosures, composite cable tray sections), while simultaneously reducing the risk of under-head corrosion from trapped moisture between a separate washer and bolt head. The flange-to-bolt-head geometry eliminates the gap that allows moisture and chloride ingress in coastal and marine environments.

Silicon Bronze Grade Options and Properties

C65500 silicon bronze hex flanged bolts (3% Si, ~560 MPa UTS) are specified for: submerged marine applications, buried earthing hardware, offshore splash zone fasteners, and chemical plant fasteners in sulphide or chloride atmospheres. C65100 silicon bronze flanged bolts (1.5% Si, ~450 MPa UTS) are used for: above-waterline marine electrical panels, coastal substation outdoor hardware, industrial earthing bus fasteners, and general corrosive-atmosphere electrical installations. Both grades are dimensionally identical, allowing upgrade from C65100 to C65500 without tooling changes or drawing revision.

Dimensional Standards – DIN 6921 and ISO 1665

Hex flanged bolts are dimensioned per DIN 6921 (metric) and ISO 1665 for the standard hexagon-flange-head geometry. The bolt shank is full-thread (all-thread up to 125 mm length for M5–M16) or partial-thread (for M16–M24 and lengths above 125 mm) per the proportional thread length rules of ISO 4017/4014. Thread tolerance 6g. The flange underside may be specified smooth (standard) or serrated (self-locking, similar to DIN 6923 flange nut serrations on the bolt underhead) for vibration-resistance without a separate lock washer. Serrated underhead flanged bolts are increasingly specified in motor control centres and marine MCC panels subject to vibration.

Applications in Coastal Substations

In outdoor coastal and island substations (AIS, GIS, hybrid), silicon bronze hex flanged bolts are used for: earthing bus connection hardware, equipment structural support bolts in C4/C5 corrosivity zones, cable tray mounting brackets, earth electrode connection covers, outdoor enclosure cover bolts, surge arrester base mounting hardware, and conductor support fittings on overhead line structures. The flange design eliminates the risk of lost washers during outdoor installation in wind, and the silicon bronze material survives 25+ years without replacement in salt-fog environments where hot-dip galvanised steel bolts require replacement every 5–8 years.

Cable Tray and Containment System Fasteners

In offshore and marine cable tray systems (aluminium, GRP, and stainless-clad trays), silicon bronze hex flanged bolts are used for: tray splice plate connections, support hanger bolts, cable tray cover fixing, cable cleat attachment, conduit support bracket fasteners, and cable management channel connections. The flanged bolt eliminates the need for a backing washer on the bolt head side, reducing hardware inventory in offshore installation projects where component counts must be minimised. Alloy compatibility: silicon bronze flanges in contact with aluminium trays should use PTFE or nylon insulating washers under the flange to prevent galvanic corrosion in immersed or wet environments.

Offshore HVAC and Process Electrical Fasteners

Silicon bronze hex flanged bolts are specified for offshore topside electrical equipment including: HVAC drive panel mounting, MCC cubicle structural fasteners, hazardous area junction box hardware, FRP enclosure cover bolts (non-ferrous requirement), intrinsically safe barrier bracket fasteners, offshore telecom cabinet mounting, and classified area (Zone 1) lighting fixture bracket hardware. The non-sparking property is essential in Zone 1 and Zone 2 classified areas per IEC 60079-14 installation requirements.

Comparison with Standard Hex Bolt + Washer Assembly

Using a silicon bronze hex flanged bolt vs a standard hex bolt + washer assembly: flanged bolt eliminates one component (washer), eliminates the risk of washer loss in confined or elevated installation locations, provides consistent clamp face area every time (washer position invariable), eliminates the corrosion gap between separate washer and bolt head, and reduces installation time by approximately 15–20% in production panel assembly. For project bill-of-materials, flanged bolts simplify procurement and reduce part numbers.

Pricing

Silicon bronze hex flanged bolts are priced at USD 14.90 per kilogram (EXW Jamnagar, India). MOQ: 10 kg per size. Volume discount available from 100 kg. Matched silicon bronze flanged nut and washer sets available.

Key Features

• Integrated flange – eliminates separate washer, reduces parts count and assembly time
• C65500 and C65100 silicon bronze – 490–560 MPa UTS, maximum corrosion resistance
• Serrated or smooth flange underhead – optional self-locking for vibration environments
• DIN 6921 / ISO 1665 dimensional compliance
• Non-sparking, non-magnetic – ATEX Zone 1/2 suitable
• M5–M24 metric range; custom lengths to 300 mm
• ISO 9001:2015 manufactured; EN 10204 3.1 MTR available

Mechanical Strength for Electrical Hardware Loads

C65500 silicon bronze hex flanged bolts achieve tensile strength of 490–560 MPa, proof load 350–400 MPa, suitable for the full range of mechanical clamp loads encountered in electrical hardware: cable lug termination torques (M8 bolt: 12–15 Nm), panel-to-structure mounting (M10 bolt: 30–45 Nm), earthing bus connections (M12 bolt: 50–70 Nm), and equipment structural bolting (M16 bolt: 100–140 Nm). For each application, verify torque against silicon bronze yield strength to avoid over-stressing the lower-strength alloy compared to Grade 8.8 steel.

Corrosion Protection Without Surface Coatings

Unlike galvanised or epoxy-coated steel fasteners that require periodic inspection and recoating, silicon bronze hex flanged bolts provide corrosion protection inherently through the material alloy composition—no coating to chip, delaminate, or corrode-through at thread roots or cut edges. This is a critical advantage in subsea, buried, and permanently inaccessible fastener locations in substation earthing grids, offshore structural connections, and buried cable tray support systems.

Technical Specifications

International Grade Equivalents – Silicon Bronze

Product Variants

Applications in Industry

Manufacturing Process

Silicon bronze hex flanged bolts are manufactured from silicon bronze hexagonal bar or round rod by CNC turning and milling (for smaller sizes M5–M12) or hot press forging followed by CNC finishing (for M16–M24). The flange geometry is formed in the forging die or machined by CNC. Thread rolling (preferred) or thread cutting is applied to the shank. Serrated-flange versions undergo secondary knurling or milling of serration teeth on the flange underface. Dimensional inspection includes: thread GO/NO-GO gauging, flange diameter and thickness measurement, head height and AF measurement, and length verification. Hardness spot-checks and tensile testing on sample bolts per lot.

Quality Standards and Certifications

Why Choose Electrical Accessories India

• Complete silicon bronze fastener system – flanged bolts, flanged nuts, hex nuts, studs, washers from single source
• DIN 6921 compliant with serrated or smooth flange option
• USD 14.90/kg competitive pricing; volume and project discounts
• Non-sparking ATEX and IEC 62305 earthing documentation available
• ISO 9001:2015 with EN 10204 3.1 MTR and dimensional reports
• Custom lengths and special configurations to drawing

Frequently Asked Questions (FAQ)

1. What is the main advantage of hex flanged bolt vs hex bolt + washer?

One-piece design: eliminates washer handling, washer loss risk, and the corrosion gap between washer and bolt underhead. Also provides consistently correct washer positioning (no off-centre washer). In production assembly, reduces component count and speeds installation.

2. Can silicon bronze hex flanged bolts be used with aluminium cable trays?

In dry/indoor environments, direct contact is acceptable. In wet, splash, or immersed environments, use a PTFE or nylon insulating washer between the silicon bronze flange and the aluminium tray surface to prevent galvanic corrosion of the aluminium. This is standard practice in offshore topsides cable tray installation.

3. Are serrated flange bolts reusable?

Serrated flange bolts are reusable for 5–8 cycles in the same hole. After this, serrations flatten and locking action reduces. For permanent installations, one-time use is recommended and inspection at re-use is advised.

4. What is the maximum temperature for silicon bronze hex flanged bolts?

Silicon bronze retains good mechanical properties up to 200°C continuous service. Short-term excursions to 300°C are tolerable without permanent strength loss. For higher temperature applications, consult our engineering team for chromium-copper or aluminium bronze alternatives.

5. Do you supply silicon bronze hex flanged bolts in inch UNC sizes?

Yes. Inch flanged bolts in UNC 5/16″, 3/8″, 1/2″, 5/8″, 3/4″, and 1″ thread are available in C65100 or C65500. Used primarily for North American standard electrical equipment installations in offshore and chemical plant projects.

6. Price and lead time for silicon bronze hex flanged bolts?

USD 14.90/kg, EXW Jamnagar. M5–M16 sizes: 2–3 weeks; M20–M24: 3–5 weeks. Project quantities with advance notice can be expedited. Contact our sales team.

7. Can these bolts be hot-dip galvanised or further coated?

Hot-dip galvanising of silicon bronze is not standard practice and is technically unnecessary given the alloy’s inherent corrosion resistance. Electroless nickel plating can be applied for specific requirements (food industry, high-temperature). For most electrical and marine applications, mill finish silicon bronze is the optimal supply condition.

8. Are these bolts certified for use in Lloyd’s Register classified vessels?

Silicon bronze C65500 meets the material requirements for copper alloy fasteners in Lloyd’s Register (LR) Rules for Ships. We can supply material test certificates to LR Type Approval requirements. Specific project certification requests should be submitted with survey details.

Equivalent Terms and Multilingual Reference

Related Products and Linked Terms

• Silicon Bronze Bolts
• Silicon Bronze Flanged Nuts
• Silicon Bronze Hex Nuts
• Silicon Bronze Studs
• Copper Bolts, Copper Hex Set Screws
• DIN 6921 flanged bolts, ATEX non-sparking bolts, marine hex flange bolts, silicon bronze washers, offshore fasteners

Request a Quote

Electrical Accessories India supplies silicon bronze hex flanged bolts for marine, offshore, coastal substation and chemical plant applications. Pricing: USD 14.90 per kilogram (EXW Jamnagar, India). Contact our engineering sales team for project quotations and BOM pricing.

Email: info@elecaccs.com | Location: Jamnagar, Gujarat, India

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