Bolt Electric Heating Rod
Bolt electric heating rod (referred to as bolt heating rod) is a special electric heater specifically used for bolt assembly and disassembly operations of large pressure-bearing containers in industries such as steam turbines, shipbuilding, petrochemical, and electric power. Its core function is to use resistance heating technology to cause the bolt to expand due to heat and reduce pre-tightening force, thereby safely and efficiently completing the tightening or disassembly of large bolts, avoiding damage to equipment and personnel caused by forced disassembly. Core Structure and Working Principle
The structural design of the bolt heating rod aims to achieve efficient heat conduction and electrical insulation. Its typical structure is as follows:
Heating element: Internally, high-resistance electric heating alloy wire (such as nickel-chromium alloy wire) like 0Cr27Al7Mo2 is used as the core heating element.
Insulation and thermal conduction layer: In the gap between the seamless metal tube (usually 1Cr18Ni9Ti heat-resistant stainless steel tube) and the heating wire, high-purity magnesium oxide powder is tightly filled. It ensures excellent thermal conductivity and reliable electrical insulation.
Forming process: The whole is formed by cold-drawing tube reduction process, making the structure more compact, with high mechanical strength, and the cold end is tightly sealed against moisture.
Working principle: When in use, insert the heating rod into the pre-drilled hole in the center of the bolt and energize it. The current passes through the high-resistance alloy wire to generate Joule heat, which is quickly conducted to the bolt body, causing it to expand and elongate due to heat. At this time, the nut can be easily tightened or loosened. After the bolt cools and contracts, the required tightening force can be achieved or disassembly completed.
Key Technical Parameters and Standards
The manufacturing and inspection of bolt heating rods must strictly follow relevant industry standards (such as ZBK54019-88). Its core technical indicators include:
Working temperature: Usually can reach 400°C.
Surface power density: Generally selected at 8-11 W/cm² to ensure uniform heating without damaging the bolt.
Power supply specifications: Supports multiple power supply methods such as 220V±20V AC, 100V DC, and 50V low voltage.
Insulation and withstand voltage: At room temperature, the insulation resistance is not less than 50MΩ, and it can withstand a 1500V withstand voltage test for 1 minute without breakdown.
Service life: Under standard intermittent heating (10-20 minutes each time) and reasonable clearance (0.8-1.3mm) conditions, the cumulative design life is not less than 50 hours.
Core Advantages
Protect equipment and bolts: By uniformly heating to expand the bolt, it avoids thread damage or cylinder deformation caused by forced disassembly with sledgehammers or hydraulic wrenches.
Improve maintenance efficiency: Greatly reduces the difficulty of assembling and disassembling large fasteners, shortening maintenance downtime.
Safe and environmentally friendly: Compared with traditional flame heating, electric heating rods have no open flame, no combustion exhaust gas, and precise temperature control can be achieved through the control cabinet, reducing operational risks.
Selection and Safety Operation Guide
Size matching: The heating rod must be selected according to the diameter and depth of the bolt center hole. The outer diameter of the heating rod should usually be about 1mm smaller than the bolt hole diameter (total clearance controlled at 0.8-1.3mm) to ensure heat conduction efficiency and extend the life of the heating rod.
Standard wiring and grounding: Must be used with a dedicated DC adjustable control cabinet. The control cabinet and the heating rod shell must be well grounded, and it is strictly forbidden to switch voltage gears under load.
Safe operation process:
Before use, the insulation resistance must be measured with a megohmmeter to ensure it meets the standard.
First insert into the bolt hole, then energize for heating; after heating, first cut off the power, then move the heating rod. It is strictly forbidden to move or touch the heating part while energized.
It is recommended to control each continuous heating time to 10-20 minutes to avoid local overheating.
Safety protection: Operators must wear heat-resistant gloves, goggles, and other protective equipment to prevent burns
