Bolt Electric Heating Rod
Bolt electric heating rod is an electric heating element specially used for heating and disassembling bolts (hot tightening/hot removal) of large equipment such as steam turbines and pressure vessels. By inserting the heating rod into the center hole of the bolt and energizing it, the bolt is heated and expands, thereby achieving tightening or loosening of the nut.
Working Principle
The core principle of the bolt electric heating rod is resistance heating:
Insert the heating rod: Insert the electric heating rod into the center hole of the bolt
Energize and generate heat: The current passes through the internal electric heating alloy wire to produce Joule heat, which is conducted through the magnesium oxide insulation layer to the stainless steel protective sleeve
Bolt expansion: The heat is conducted from the surface of the heating rod to the inner wall of the bolt, and the bolt expands axially when heated
Tightening/Removal:
Hot tightening: After the bolt expands, further tighten the nut. After power off and cooling, the bolt contracts, generating greater preload
Hot removal: After the bolt is heated and expands, the thread fit becomes loose, and the rusted or over-tightened nut can be easily unscrewed
Structural Composition
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Component Material Function
Electric heating alloy wire 0Cr27Al7Mo2 high-resistance electric heating alloy Core heat source, working temperature 400°C
Insulation layer High-purity magnesium oxide powder (MgO) Electrical insulation + thermal conduction
Protective sleeve 1Cr18Ni9Ti heat-resistant stainless steel tube Mechanical protection + corrosion resistance + heat transfer
Cold-end lead wire Heat-resistant wire Connects to power supply, cold-end length at bottom 25~30mm
Key Technical Parameters
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Parameter Typical Range
Execution standard ZBK54019-88
Rated voltage AC 220V±20V / DC 100V / Low voltage 50V
Surface power density 8~11W/cm²
Power deviation ±5%
Diameter specification 10mm~30mm
Length specification 100mm~4500mm
Insertion part diameter deviation -0.20mm / -0.50mm
Insertion part length deviation ±5mm
Working temperature 400°C
Insulation resistance ≥50MΩ
Withstand voltage 1500V/1min no breakdown
Hot-state leakage current No more than 0.5mA per kilowatt
Cumulative service life ≥50 hours (intermittent heating conditions)
Centerline straightness φ0.3mm within 1m length; φ0.4mm within 1~2m length
Main Classifications
Classification by structural form
Rigid tube type: Rigid stainless steel sleeve, suitable for straight bolt center holes
Flexible tube type: Bendable flexible heating rod, suitable for center holes with bends
Semi-flexible type: Between rigid and flexible tubes, with certain bending capability
Cable heater type: Spiral wound flexible heating cable, can be coiled into any outer diameter and length, suitable for occasions without top operating space
Classification by heating method
Resistance type (traditional): Inserted into the bolt center hole, heats the bolt indirectly through resistance wire heating, is the most classic and widely used method
Induction type (new): Utilizes electromagnetic induction principle, induction coil is placed outside the bolt or inserted into the center hole, the bolt itself generates eddy current heating, faster heating speed and more uniform heating, gradually promoted in the power industry in recent years
Typical Application Scenarios
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Industry Specific Application
Thermal power generation Hot tightening and removal of large bolts in high/medium/low pressure cylinders of steam turbines
Nuclear power Heating and disassembly of large bolts in high-pressure cylinders of steam turbines in nuclear power plants
Chemical/petrochemical Disassembly of large bolts on flanges of pressure vessels
Metallurgy Maintenance of flange connecting bolts on large equipment
Marine Disassembly of bolts on main engines and pipeline flanges
Supporting Equipment
Bolt electric heating rods usually need to be used with a DC adjustable control cabinet:
Output voltage: 0~220V continuously adjustable
Output channels: Up to 12 loads, supporting simultaneous operation of multiple heating rods
Functional features: Stable and adjustable voltage, balanced three-phase load, safe and reliable
Operating requirements: Power must be disconnected when installing or removing heating rods; strictly prohibited to change voltage with load
Parameters Required for Selection/Ordering
Bolt outer diameter
Bolt center hole diameter
Total bolt length
Nut length
Model of matching heating control cabinet
Usage Precautions
The heating position should be on the bolt shank section, avoid directly heating the thread and nut parts
The temperature of the center hole wall must not exceed the maximum service temperature of the bolt, and uniform heating is required to prevent local overheating
The total gap between the heating rod and the bolt center hole should be controlled at 0.8~1.3mm
Each heating time is generally 10~20 minutes
The outer shell must be well grounded
The cold-end seal must be tightly sealed to prevent moisture from entering and damaging insulation
Before first use after long-term storage, the insulation resistance should be checked; if lower than 50MΩ, drying treatment is required
Strictly prohibited to use open flames (such as torches) directly inserted into the hole for heating, to prevent local overheating and cracks on the hole wall
