During the disassembly and assembly of turbine bolts, a common problem is often encountered: with the same heating time, some bolts can elongate smoothly, while others remain unmoved, and temper colors even appear on the wall of the center hole. After investigation, it was found that in most cases, the issue is not insufficient power of the heating rod, but rather poor control of the heating position and fit clearance. The bolt electric heating rod heats the threaded section from inside the bolt center hole, and heat is transferred from the inside out, causing the bolt to elongate uniformly along the axial direction, thereby reducing the torque required for disassembly and assembly. Compared with induction-type bolt heaters, resistance-type heating rods do not require coils to be wound around the outside of the bolt and have smaller requirements for surrounding space, making them suitable for occasions where cylinder bolts are densely arranged; compared with flame heating or hot air gun heating, their heat is concentrated within the center hole, and the nut and threaded portion are less likely to be directly heated, resulting in a more uniform temperature distribution.
Induction-type heaters generate eddy currents on the bolt surface through an alternating magnetic field and heat up quickly, but the equipment is large, there are requirements for the bolt extension length, and different specifications of bolts require replacement of the induction coil. Bolt electric heating rods, however, are selected according to the diameter and depth of the bolt center hole, and after insertion directly contact the hole wall for heat transfer. The structure is simple, making them suitable for alternating operations on multiple specifications of bolts during on-site maintenance. It should be noted that an appropriate clearance should be maintained between the outer diameter of the heating rod and the center hole. If the clearance is too small, insertion will be difficult; if too large, heat transfer efficiency will decrease.
Taking the DJR-22 series suitable for a center hole diameter of 22.6±0.2 mm as an example: DJR-22-1 is suitable for M56×4 bolts, with a sleeve length of 255 mm, a heating length of 100 mm, and a power of 550 W; DJR-22-6 is suitable for M56×4, with a sleeve length of 405 mm, a heating length of 250 mm, and a power of 1400 W; DJR-22-7 is suitable for M76×4, with a sleeve length of 315 mm, a heating length of 125 mm, and a power of 900 W; DJR-22-13 is suitable for M76×4, with a sleeve length of 540 mm, a heating length of 350 mm, and a power of 2350 W. In actual procurement, specifications are usually customized according to bolt size. The heating section should avoid the threaded and nut areas, and the temperature of the center hole wall must not exceed the maximum service temperature of the bolt material.
When used in special working conditions such as power plants and petrochemical facilities, products with explosion-proof certification and compliance with electric power industry standards should be selected. In some high-requirement scenarios, an intelligent temperature control cabinet can be used to achieve precise temperature control, adjusting output power through thermocouple feedback to reduce human judgment errors.
