The SLB-36 type bolt electric heating rod is an insertion-type structure used for heating the center hole of large-diameter bolts of M36 and above. Compared with flame heating, heating rings, or heating blankets, its heat acts directly on the inner wall of the bolt hole, reducing loss to the surrounding flange, gasket, and exposed part of the bolt. The heating efficiency is more concentrated, and it also avoids the safety hazards caused by open-flame operations.
The outer shell of the heating rod uses 304 or 321 stainless steel seamless tubing. Common outer diameters are 12 mm, 14 mm, 16 mm, etc., and they need to match the diameter of the bolt center hole. It is generally recommended to control the single-side clearance within 0.5 mm to 1.5 mm. Inside the tube body is a nickel-chromium alloy resistance wire, filled and compacted with magnesium oxide powder. After the tube reduction process, the insulation resistance is not less than 100 MΩ, and the withstand voltage test is conducted at 1500 V/50 Hz for 1 min with no breakdown or flashover. The cold-state resistance deviation is controlled within ±5%. The lead end uses high-temperature-resistant ceramic or PTFE insulation and is equipped with a stainless steel flexible hose for protection to avoid damage from bending. The rated power of a single rod is usually 1 kW to 5 kW, the voltage can be designed as 220 V or 380 V, and the common length is 200 mm to 1200 mm. It can also be customized according to the depth of the bolt center hole. The heating rod itself does not contain a temperature control element and must be used with a temperature control box or PLC. It can be connected to a K-type or E-type thermocouple to collect bolt temperature.
Flame heating heats up quickly, but the temperature distribution is uneven. Local overheating of the bolt may change the material structure, and on-site open-flame operations are required, making safety approval cumbersome. Heating rings or heating blankets wrap around the nut or exposed end, resulting in relatively large heat loss. The middle of the bolt heats up later, and the judgment of disassembly and assembly torque is not accurate enough. The SLB-36 type bolt electric heating rod heats from the bolt center hole from the inside outward, so the heating is relatively uniform and the heat is concentrated. After being equipped with a temperature control box, it can realize heating curve setting and heat preservation control, making it suitable for the disassembly and assembly of flange bolts in steam turbines, compressors, pressure vessels, and other working conditions.
Procurement personnel can provide bolt specifications (such as M56×4, M85, etc.), center hole diameter, bolt length, and supporting control cabinet requirements to determine the diameter, power, length, and wiring method of the heating rod. Because there are individual differences in center hole size and depth, it is recommended to specify the fit clearance and cold-state resistance requirements in the contract. During use, note that the heating rod must not be heated in a no-load condition. Power can be supplied only after it is inserted in place. Keep it dry during storage to prevent a decrease in insulation performance.
