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Products
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High-strength blackened nuts
High-strength blackened nuts are nuts that form a black Fe₃O₄ oxide film on the surface of alloy steel through chemical oxidation (blackening treatment). The base material is usually 42CrMo or 65 manganese steel. After quenching + tempering treatment, the hardness can reach HRC35-45.
Description
marker
Product definition and core technology
High-strength blackened nuts are nuts that form a black Fe₃O₄ oxide film on the surface of alloy steel through chemical oxidation (blackening treatment). The base material is usually 42CrMo or 65 manganese steel. After quenching + tempering treatment, the hardness can reach HRC35-45.
Core materials and characteristics
Material:
42CrMo alloy steel (static high load): tensile strength ≥1000MPa;
65 manganese steel (elasticity requirement): hardness HRC40-45, suitable for spring nuts.
Features:
High temperature resistance: The oxide film is stable below 200℃, which is better than the galvanized layer;
No risk of hydrogen embrittlement: The chemical oxidation process avoids hydrogen embrittlement of electroplating, which is suitable for precision equipment;
Wear resistance: The oxide film hardness is HV300-400, which can resist slight friction.
Functions and applicable scenarios
Functions:
Withstand high-frequency vibration or impact loads to prevent bolts from loosening;
Maintain stable performance in high temperature environments (such as engine cylinder block connection).
Scenario:
Automobile engine (cylinder head bolts), mining machinery (crusher connection), wind power equipment (spindle flange).
Installation and maintenance
Installation:
When used with high-strength bolts, tighten strictly according to the torque coefficient (such as 0.11-0.15);
Clean the surface oil before installation to ensure that the oxide film is tightly bonded to the substrate.
Maintenance:
Check the integrity of the oxide film regularly, and the damaged parts need to be re-blackened;
Avoid long-term immersion in electrolyte to prevent the oxide film from being damaged.
Purchase suggestions
Select materials according to load: 42CrMo is suitable for static high load, 65 manganese steel is suitable for elastic requirements;
For high temperature scenarios (>300℃), ceramic coating or stainless steel nuts should be used instead.
Comparison and selection guide of the six major nuts
| Type | Electroplated galvanized flange nut | Electroplated galvanized nut | Colored zinc-plated nut | Anti-loosening nut | High-strength blackened nut | Welding nut |
| Core advantages | Dispersed pressure, anti-loosening | Low cost, strong versatility | High corrosion resistance, color identification | Anti-vibration, removable | High strength, high temperature resistance | Permanent connection, convenient |
| Salt spray test | 24-72 hours | 24-72 hours | 72-120 hours | 48 hours (nylon) | 48 hours without red rust | 48 hours (galvanized) |
| Applicable temperature | -20℃~80℃ | -20℃~80℃ | -20℃~100℃ | -56℃~170℃ (all metal) | -40℃~200℃ | -20℃~200℃ |
| Typical scenarios | Pipe flange, steel structure | General machinery, indoor environment | Outdoor equipment, humid environment | Engine, vibration equipment | High temperature machinery, vibration equipment | Automobile manufacturing, construction machinery |
| Installation method | Torque wrench tightening | Torque wrench tightening | Torque wrench tightening | Torque wrench tightening | Torque wrench tightening | Welding fixation |
| Environmental protection | Cyanide-free process complies with RoHS | Cyanide-free process complies with RoHS | Trivalent chromium is more environmentally friendly | Nylon complies with RoHS | No heavy metal pollution | No special requirements |
Selection suggestions:
High sealing requirements: electroplated zinc flange nut, with gasket to enhance sealing;
High corrosion environment: color-plated zinc nut, chromium-free passivation process is preferred;
Vibration environment: anti-loosening nut, all-metal type is suitable for high temperature scenes;
High temperature and high load: high-strength blackened nut, matched with 10.9 grade bolts;
Permanent connection: welding nut, projection welding or spot welding type is selected according to the process.
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Hexagon socket colored zinc-plated bolts
The hexagon socket bolt head has a hexagon socket hole and needs to be tightened with a hexagon socket wrench (standard GB/T 70.1). Common materials are 35CrMo or 42CrMo, and the surface treatment is divided into three types: electrogalvanized, color zinc-plated, and black zinc-plated.
Hexagon socket electrogalvanized bolts
The hexagon socket bolt head has a hexagon socket hole and needs to be tightened with a hexagon socket wrench (standard GB/T 70.1). Common materials are 35CrMo or 42CrMo, and the surface treatment is divided into three types: electrogalvanized, color zinc-plated, and black zinc-plated.
Hexagon socket hot-dip galvanized bolts
The hexagon socket bolt head has a hexagon socket hole and needs to be tightened with a hexagon socket wrench (standard GB/T 70.1). Common materials are 35CrMo or 42CrMo, and the surface treatment is divided into three types: electrogalvanized, color zinc-plated, and black zinc-plated.
Electrogalvanized hexagonal bolts
Hexagonal bolts are the most common standard bolts with hexagonal heads and are used with nuts (standard GB/T 5780). Common materials are Q235 or 35CrMo, with galvanized or blackened surfaces.
Colored zinc flange bolts
The head of the flange bolt has a round flange to increase the contact area and disperse the pressure (standard GB/T 5787, GB/T 5789). Common specifications M6-M30, material Q235 or 35CrMo, surface galvanized or blackened.
Electrogalvanized expansion bolts
It consists of countersunk bolts, expansion tubes, flat washers, spring washers and hexagonal nuts. The material is mostly carbon steel (such as Q235), and the thickness of the electrogalvanized layer is 5-12μm, which meets ISO 1461 or GB/T 13912-2002 standards.
Black zinc flange bolts
The head of the flange bolt has a round flange to increase the contact area and disperse the pressure (standard GB/T 5787, GB/T 5789). Common specifications M6-M30, material Q235 or 35CrMo, surface galvanized or blackened.
Welded plate anchor (welded plate anchor bolt)
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Colored zinc-plated expansion hook
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Stud bolts
Stud bolts have threads at both ends and a bare rod in the middle, which is used to connect thick plates or penetrate installation (standard GB/T 901). Common materials are 45# steel or 40Cr, with galvanized or blackened surface.
Anti-loosening nut (locking nut)
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The head is a cross-groove countersunk design, which can be hidden in the installation surface to keep the surface flat. The drill bit diameter matches the thread diameter (such as ST4.2 drill bit diameter 4.2mm), which complies with GB/T 15856.1-2002 standard.
U-bolts
U-bolts are U-shaped with threads at both ends, and are used to fix cylindrical objects such as pipes and plates (standard JB/ZQ 4321). Common specifications are M6-M64, made of carbon steel or stainless steel, with galvanized or blackened surface.
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