Pre-weld preheating equipment for power equipment welding
Welding induction preheating equipment is an efficient industrial device that achieves preheating of workpieces before welding based on the principle of electromagnetic induction. With features such as non-contact heating and strong temperature controllability, it is widely used in welding processes in fields like petrochemical, pressure vessels, and heavy machinery. It can accurately raise the temperature of workpieces, effectively reducing defects such as cracks and stress concentration caused by excessive temperature differences during welding, and is a key equipment to ensure welding quality. The following is a detailed introduction from aspects of core principles, equipment composition, technical parameters, technical advantages, and application scenarios:
I. Core Working Principle
The heating core of welding induction preheating equipment is electromagnetic induction and eddy current effect:
The medium-frequency or high-frequency power supply of the equipment outputs alternating current, generating an alternating magnetic field through a specially made induction coil (inductor).
When the metal workpiece (conductor) to be preheated is in the magnetic field, closed eddy currents are induced inside it.
When the eddy current flows inside the workpiece, Joule heat is generated due to the conductor's own resistance, causing the workpiece to heat up uniformly from the inside, realizing non-contact preheating.
This "internal heat generation" method is different from flame heating (surface heat conduction) and resistance heating (contact conduction). It can avoid local overheating on the workpiece surface and is especially suitable for uniform preheating of thick-walled and complex-shaped workpieces.
II. Basic Composition of Equipment
A complete set of welding induction preheating equipment usually consists of four parts, which work together to achieve precise preheating:
Power supply device: Converts industrial frequency electricity (220V/380V) into medium-frequency (1-10kHz) or high-frequency (above 10kHz) alternating current, determining heating power and efficiency, and is the "power core" of the equipment.
Induction coil: Customized according to the shape of the workpiece (such as circular, rectangular, special-shaped), it directly generates an alternating magnetic field, and its design directly affects the heating range and uniformity (for example, circular coils are commonly used for pipeline preheating, and flat coils for flat plate preheating).
Temperature control system: Real-time monitoring of the workpiece temperature through thermocouples and infrared thermometers, feeding back to the power supply device to adjust the output power, realizing constant temperature control (with an accuracy of up to ±5ºC) or stepwise heating, to meet the preheating process requirements of different materials.
Cooling system: For medium-high frequency and high-power equipment, water cooling or air cooling is used to cool the power supply and induction coil, preventing equipment damage due to overheating.
III. Technical Parameters and Corresponding Characteristics Table
Welding induction preheating equipment with different frequencies and powers have differences in heating depth, applicable workpieces, etc., as follows:
| Equipment Type |
Frequency Range |
Power Range |
Heating Depth |
Temperature Control Accuracy |
Applicable Workpiece Types |
Typical Heating Time (Example) |
| High-frequency induction preheating equipment |
10-500kHz |
5-50kW |
1-5mm |
±5ºC |
Thin-walled pipes, local preheating of small parts |
Φ114mm pipe preheated to 150ºC takes about 5-8 minutes |
| Medium-frequency induction preheating equipment |
1-10kHz |
30-200kW |
5-20mm |
±5ºC |
Medium and thick plates (10-50mm), pipe girth seams |
Φ325mm pipe preheated to 200ºC takes about 10-15 minutes |
| Power frequency induction preheating equipment |
50/60Hz |
100-1000kW |
>20mm |
±10ºC |
Large structural parts, thick-walled flanges (>50mm) |
50mm thick steel plate preheated to 250ºC takes about 30-40 minutes |
IV. Technical Advantages
Compared with traditional preheating methods, welding induction preheating equipment has significant advantages:
High heating efficiency: The thermal conversion rate reaches 70%-90%, which is much higher than that of flame heating (30%-50%), with lower energy consumption and fast heating speed.
Precise temperature control: The closed-loop temperature control system can stably maintain the preset temperature, avoiding welding defects caused by temperature fluctuations, and is especially suitable for workpieces sensitive to preheating temperature such as high-strength steel (e.g., X80 pipeline steel) and alloy materials.
Good heating uniformity: The workpiece generates heat synchronously inside, reducing the temperature difference between the surface and the core, and avoiding thermal stress cracks in thick-walled workpieces during welding.
Safety and environmental protection: No open flame or smoke, reducing the risk of fire and harmful gases, and complying with workshop safety and environmental protection regulations.
Strong flexibility: The induction coil can be customized according to the shape of the workpiece, adapting to local or overall preheating of various workpieces such as pipes, flanges, thick plates, and special-shaped parts.
V. Typical Application Scenarios
Welding induction preheating equipment is suitable for welding scenarios with high requirements on preheating temperature accuracy and efficiency:
Long-distance pipeline welding: Before girth welding of natural gas and oil pipelines, medium-frequency induction preheating is used to raise the pipeline temperature (usually 120-200ºC) to avoid cold cracks caused by high steel strength and poor weldability.
Pressure vessel manufacturing: Before welding the longitudinal and circumferential seams of thick-walled cylinders (thickness >50mm), overall uniform preheating is required to reduce welding stress. Induction heating can ensure that the temperature difference between various parts of the cylinder is controlled within ±10ºC.
Heavy machinery welding: When welding thick plates such as excavator structural parts and crane arms, local induction preheating is used to quickly raise the temperature of the welding area, ensuring the stability of the interlayer temperature in multi-layer and multi-pass welding.
Power equipment welding: For the preheating of boiler pipes and wind power tower flanges, the temperature must be strictly controlled to ensure the fatigue strength and tightness of the joints.
VI. Key Points for Equipment Selection
When selecting welding induction preheating equipment, it is necessary to consider the workpiece characteristics and process requirements:
Workpiece parameters: Determine the equipment specifications according to the workpiece material (carbon steel, alloy steel, etc.), thickness (thick plates require medium-frequency high-power, thin plates can choose high-frequency), and shape (customized matching coils).
Process requirements: Select equipment with appropriate power and temperature control accuracy according to the preheating temperature (e.g., 150-300ºC for low-alloy steel) and heating rate (to avoid workpiece deformation caused by excessive speed).
Usage scenarios: For on-site construction, portable medium-frequency equipment (weight <50kg) can be selected; for batch production in workshops, fixed high-power equipment is suitable, combined with automatic feeding mechanisms to improve efficiency.
In conclusion, welding induction preheating equipment provides a reliable guarantee for high-quality welding processes through precise and efficient heating methods, and is an indispensable key auxiliary equipment in modern industrial welding.
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