Metallurgical Foundry Cranes (YG/YZ series) are heavy-duty lifting equipment rated at Work Duty A7~A8 with a lifting capacity of 50–400 t. They operate continuously in high-radiation heat zones near ladles, melting furnaces, and continuous casting machines. Surface temperatures on the lower flange plate of the crane main girder can reach 300–500 °C, the trolley frame bottom 100–200 °C, and the interior of the electric control cabinet 60–80 °C. The high-temperature-resistant design integrates four key technologies: heat shields (blocking over 80% of radiant heat), forced air/water cooling, heat-resistant cables with Class F insulated motors, and high-temperature coatings—ensuring structural strength and electrical reliability of the overhead crane under extreme thermal conditions.

---

Heat Shield Solutions for High-Temperature Overhead Cranes

Heat shielding is the primary protective measure for metallurgical overhead cranes. During ladle handling (ladle temperature 1,400–1,600 °C), radiant heat transfers intensively to the crane main girder, producing a radiant heat flux density of 8–12 kW/m² at a distance of 2.5 m from the ladle. Installing multi-layer stainless steel heat shields on the lower flange plate of the main girder reduces radiant heat transfer by 80%–90%, while aluminum alloy reflective screens achieve an infrared reflectance of >90%. The heat shields are designed as a detachable structure to allow periodic inspection of the coating condition on the main girder. Fixing bolts are made of heat-resistant steel (0Cr18Ni9) and coated with anti-seize compound.

heat insulation location	heat source temperature(℃)	target surface temperature(℃)	thermal insulation scheme	insulation layer material	insulation layer thickness(mm)	thermal insulation efficiency
Main Girderbottom flange	800~1200(ladle radiation)	≤120	Stainless Steelmulti-layerheat shield(3~5multi-layer)	SUS304(0.8mm)+ceramic fiber felt	50~80	>85%
Trolley Framebottom	300~500(ladle radiation+convection)	≤100	aluminum alloy reflective screen+rock wool board	1060aluminum plate+rock wool(Density120kg/m³)	30~50	>70%
hook beam	200~400(contact heat)	≤200	heat-resistant steelProtective Cover+gap insulation	15CrMoheat-resistant steel(5mm)	10~20(gap10mm)	>60%
electric control cabinet	60~80(ambient heat)	≤45	heat shield+overhead forced air coolingUnit	double-layerSteel Plate+polyurethane foam	40~60	>75%
cable tray	150~250(radiant heat)	≤60	ceramic fiber wrapping+metal sheath	ceramic fiber blanket(1260grade)+GalvanizingSteel Plate	20~30	>80%

---

Heat Dissipation Design & Thermal Balance Calculation

The forced-air cooling system on the main girder routes airflow through ducts located behind the heat shield. Fan selection is based on the thermal balance equation: Q_vent = (Q_rad × η_insul) / (ρ × Cp × ΔT). Here, Q_rad is the radiant heat from the ladle (approximately 8–12 kW/m²), η_insul is the insulation efficiency (85%), ρ is air density at 1.2 kg/m³, Cp is the specific heat of air at 1005 J/(kg·K), and ΔT is the target temperature rise (30°C). This yields a required airflow of roughly 0.4 m³/s per square meter of girder surface. For a 50 t metallurgical overhead crane, the lower flange area is about 12 m², so the total fan capacity must be ≥ 4.8 m³/s. This is achieved with two axial fans (each rated at 3.0 m³/s) in a duty/standby configuration.

Motor selection requires careful attention to the insulation class. Hoisting motors for metallurgical cranes are recommended to use Class H insulation (temperature rating 180°C), which provides a higher thermal margin than Class F (155°C). The motor protection rating is IP54 (dustproof and splash-proof), with the junction box rated IP65. Built-in PTC thermistors monitor winding temperature: an alarm is triggered at 155°C (attention level), and a shutdown command is issued at 175°C (danger level). The crane's Safety Monitoring and Management System (see the SIL3 safety monitoring solution) integrates motor temperature into the safety interlock logic, automatically limiting speed when temperature limits are exceeded.

For large metallurgical cranes with a lifting capacity above 100 t, the main hoist uses a four-redundancy configuration: dual motors, dual gearboxes, and a double drum. If one side fails, the other side can still support 50% of the rated load for a safe lowering operation. A 10 mm air gap between the heat shield and the main girder provides secondary insulation. The shield's fixing brackets are designed to be detachable, allowing easy access for periodic inspection of the lower flange coating and weld seams. Periodic inspection of metallurgical cranes is required every six months. Inspection items include ultrasonic thickness measurement of the lower flange plate (a reduction of >10% requires evaluation), heat shield integrity, and insulation resistance testing of the hoisting motor (≥ 1 MΩ).

---

High Temperature Resistant Coating System

working temperature(℃)	coating system	Surface Treatment	Dry Film Thickness (DFT)(μm)	expected service life(years)	application area
≤120	EP-Znbottom+EP-MIOmiddle+PUtop coat	Sa2½	200~280	8~12	main girder web plate,End Carriage
120~200	silicone aluminum paint+silicone topcoat	Sa2½	120~150	5~8	heat shieldrear,Trolley Frame
200~400	inorganic zinc-rich primer+silicone intermediate coat+silicone topcoat	Sa3	100~120	3~6	Main Girderbottom flange,Hook
400~600	inorganic zinc silicate+aluminum silicone	Sa3	80~100	2~5	heat shieldhot face,ladleLifting spreader
600~800	plasma-sprayed ceramic coating	Sa3+roughening	60~80	2~4	molten steel contact area

---

Solution Advantages of Kelude Metallurgical Overhead Cranes

Kelude Heavy Industry's YG/YZ series Metallurgical Foundry Cranes feature a comprehensive high-temperature-resistant design. The main girder heat shield employs a multi-layer SUS304 stainless steel reflective structure (test data: at 2.5 m from the ladle, the lower flange temperature ≤ 85 °C, outperforming the national standard requirement of ≤ 120 °C). The hoisting mechanism comes standard with dual brakes (service brake + safety brake), Class H insulated motors, and IP54 protection. The electric control cabinet is equipped with a heat shield and a top-mounted air conditioner. Kelude Heavy Industry also offers retrofit design solutions for high-temperature-resistant metallurgical overhead cranes, along with on-site thermal field testing.

FAQ

Heat-Resistant Design for Steel Mill Overhead Cranes: Insulation, Cooling, and Material Selection

Thermal Challenges in Steel Mill Crane Operation

Steel mill overhead cranes (YG/YZ series) are routinely exposed to extreme radiant heat from ladles, furnaces, and molten metal. The bottom flange of the main girder can reach temperatures of 300–500°C during normal operation, while localized hot spots near the ladle may spike even higher. This sustained thermal load accelerates structural fatigue, degrades electrical insulation, and shortens the service life of critical components.

Insulation Screen Design for Radiant Heat Shielding

The most effective first line of defense is a well-designed insulation screen installed between the heat source and the crane structure. Typically fabricated from polished stainless steel or aluminum-coated panels, these screens reflect a significant portion of radiant heat before it reaches the girder. Key design considerations include: - **Panel spacing and air gap**: A 50–100 mm air gap between the screen and the girder flange promotes natural convection and prevents heat bridging. - **Surface finish**: Polished reflective surfaces reduce emissivity and maximize heat reflection. - **Modular construction**: Segmented panels allow for easy removal during maintenance and accommodate thermal expansion without buckling. For cranes handling ladles directly above the main girder, a double-layer screen with a ventilated intermediate space is recommended to further reduce radiant heat transfer.

Forced-Air Cooling: Heat Dissipation Calculations

When passive insulation alone is insufficient, forced-air cooling provides active heat removal from critical zones. The required airflow rate can be estimated using the basic heat balance equation: [ Q = dot{m} cdot c_p cdot Delta T ] where: - ( Q ) = heat load to be removed (kW) - ( dot{m} ) = mass flow rate of cooling air (kg/s) - ( c_p ) = specific heat capacity of air (≈ 1.005 kJ/kg·K) - ( Delta T ) = allowable temperature rise of cooling air (K) For a typical steel mill crane with a heat load of 15–25 kW on the main girder flange, an airflow of 5–8 m³/s is generally sufficient to maintain flange temperature below 100°C. High-temperature centrifugal fans with heat-resistant motors should be mounted at the crane's end carriage, with ducting directed along the girder's bottom flange.

Heat-Resistant Electrical Components: Cables, Motors, and Controls

Standard electrical components fail quickly in high-temperature environments. Selection of heat-rated components is therefore critical: - **Cables**: Use silicone-rubber or mica-insulated cables rated for continuous operation at 180°C or higher. Avoid PVC-insulated cables, which soften and deform above 90°C. - **Motors**: Choose motors with Class H insulation (180°C) or better. For hoist and travel motors located near heat sources, add forced ventilation or heat shields around the motor housing. - **Control panels and limit switches**: Locate these in a cool area of the crane, or enclose them in ventilated, heat-shielded cabinets. Thermally insulated junction boxes with high-temperature gaskets prevent moisture ingress and heat damage.

Heat-Resistant Coating Systems for Structural Protection

The paint system on a steel mill crane must withstand both high temperatures and thermal cycling without cracking, peeling, or losing corrosion protection. A three-coat system is recommended: 1. **Zinc-rich primer** (60–80 μm DFT) for cathodic protection of the steel substrate. 2. **Intermediate coat** — heat-resistant epoxy or silicone-based intermediate (80–120 μm DFT) for film build and barrier protection. 3. **Topcoat** — silicone-based or inorganic zinc topcoat rated for 400–600°C continuous service (40–60 μm DFT). For areas directly exposed to radiant heat above 400°C, a specialized high-temperature aluminum or ceramic-filled coating should be applied. Surface preparation must meet ISO 8501-1 Sa 2.5 (near-white metal blast cleaning) to ensure coating adhesion and longevity.

Structural Design Considerations for Thermal Expansion

Thermal expansion is a major concern in steel mill cranes. A 30 m main girder subjected to a 300°C temperature rise will expand approximately 100 mm. Design measures include: - **Expansion joints** in walkways, handrails, and piping systems. - **Slotted bolt holes** in bolted connections to accommodate relative movement. - **Flexible cable carriers** and hose loops to prevent stress on electrical and hydraulic lines. The crane runway and end stops must also be designed to accommodate the additional longitudinal movement caused by thermal expansion of the bridge structure.

Inspection and Maintenance for High-Temperature Cranes

Regular inspection is essential to detect heat-induced damage before it becomes critical. Recommended inspection intervals and focus areas: | Component | Inspection Interval | Key Checks | |-----------|-------------------|------------| | Main girder flanges | Monthly | Visual check for discoloration, distortion, or cracking | | Insulation screens | Monthly | Panel integrity, loose fasteners, reflective surface condition | | Electrical cables | Quarterly | Insulation resistance test, visible cracking or hardening | | Coating system | Semi-annually | Blistering, peeling, or rust spots; touch up as needed | | Cooling fans and ducts | Quarterly | Airflow rate, bearing condition, motor temperature | Any signs of excessive thermal deformation or coating failure should be addressed immediately to prevent accelerated corrosion and structural degradation.

FAQ: Heat-Resistant Steel Mill Crane Design

**Q: What is the maximum operating temperature for a standard steel mill crane?** A: Standard cranes are typically rated for ambient temperatures up to 40°C. For steel mill applications with radiant heat, the design must incorporate insulation, cooling, and heat-rated components to keep structural temperatures below 100°C and electrical components within their rated limits. **Q: Can existing cranes be retrofitted with heat-resistant features?** A: Yes. Retrofitting typically involves adding insulation screens, upgrading cables and motors to heat-rated versions, installing forced-air cooling, and reapplying a high-temperature coating system. A structural assessment is recommended to verify that the existing crane can handle any added weight from cooling equipment. **Q: How long do heat-resistant coatings last on steel mill cranes?** A: With proper surface preparation and application, a high-quality silicone-based system can last 5–8 years in steel mill environments. Regular touch-up of damaged areas extends the overall system life. **Q: What is the difference between YG and YZ series cranes in terms of heat resistance?** A: The YG series is designed for general steel mill duty, while the YZ series is specifically engineered for ladle handling with enhanced insulation, cooling, and heat-rated components. The YZ series typically features a more robust insulation screen system and higher-rated electrical components.