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Car Bottom /Trolley annealing quenching furnace
COOLDO LARGE-PART BATCH HEAT TREATMENT
Car Bottom Furnace for Annealing, Tempering, Normalizing and Stress Relieving
COOLDO car bottom furnaces use a rail-mounted, motor-driven bogie hearth to move large and heavy loads into the heating chamber. Electric, natural-gas, fuel-gas or oil-fired systems are engineered for castings, forgings, welded structures, steel billets, gear blanks, shafts and other parts that cannot be handled conveniently in a standard box furnace.
- Up to 1200°C
- Custom high-temperature configuration
- Electric or Fuel-Fired
- Resistance, gas or oil heating
- Rail-Mounted Bogie
- Motorized heavy-load transfer
- Custom Work Zone
- Designed around load and process
What Is a Car Bottom Furnace?
A car bottom furnace, also called a bogie hearth furnace or trolley furnace, is a batch heat treatment furnace in which the furnace floor travels outside the chamber on rails. Parts are loaded by crane or handling equipment while the car is outside, then the powered car moves the complete load into the insulated chamber for the programmed heating, soaking and cooling cycle.
The removable hearth simplifies loading of oversized or high-mass workpieces and protects the chamber from crane handling. It is commonly used for annealing, tempering, normalizing, stress relieving, solution treatment and preheating. When rapid quenching is required, the furnace is combined with a fast door, powered transfer car and an external water, oil, polymer or air-quench system.
- Main purpose
- Batch heat treatment of large, heavy or irregular metal parts.
- Loading method
- Rail-mounted powered car loaded outside the chamber.
- Heating options
- Electric resistance, natural gas, fuel gas or oil firing.
- Selection basis
- Part size, load weight, process, temperature, uniformity and cycle.
External Loading for Oversized Workpieces
The complete hearth moves outside the chamber, giving the crane operator open access to the load. Fixtures, supports and thermocouples can be positioned before the bogie enters the furnace.
This layout is especially practical for large castings, heavy forgings, welded fabrications, shafts, rolls and other workpieces that are difficult to load through a conventional fixed-hearth furnace door.
Car Bottom Furnace Configurations
The heat source and temperature class are selected from the process, energy supply and required operating cost.
Electric Car Bottom Furnace
Resistance elements are arranged along the chamber walls, door, rear wall and selected hearth zones to match the load profile.
- Precise multi-zone power control
- No combustion products in the chamber
- Suitable for tempering, annealing and controlled heating
- Electrical supply sized to connected load
Gas-Fired Car Bottom Furnace
High-velocity burners, recirculation and combustion controls provide fast heat input for large furnace volumes and heavy loads.
- Natural gas, LPG or qualified fuel gas
- Burners arranged for load-temperature uniformity
- Flame supervision and burner safety train
- Direct or indirect firing by process
Low, Medium and High Temperature
Insulation, heating elements, burners, seals and hearth refractories change with the required process temperature.
- Up to 750°C low-temperature reference
- Up to 950°C medium-temperature reference
- Up to 1200°C high-temperature custom design
- Final rating confirmed on specification
Annealing and Quench-Heating Configuration
This COOLDO furnace example shows how the chamber, powered car and large lift door can be arranged for heavy-load annealing or the heating stage before quenching.
The final system is engineered around the required transfer time, working-zone dimensions, maximum batch weight, alloy recipe and the selected water, oil, polymer or air-quench equipment.
Car Bottom Furnace Structure and Controls
The Zhejiang heat-treatment catalog and original COOLDO page support the following main design functions.
Insulated Heating Chamber
Steel frame and application-specific refractory-fiber lining are designed for strength, low stored heat and service access.
Powered Bogie Hearth
A motor, gearbox and chain or wheel drive move the car along rails; the hearth structure is rated for the distributed load.
Lift or Translating Door
The reinforced insulated door opens vertically or by the selected mechanism and seals against the chamber and car.
Multi-Part Sealing
Labyrinth, sand, fiber or pneumatic sealing limits heat leakage around the car, side rails, door and chamber joints.
Heating and Circulation
Resistance elements or burners are zoned around the chamber; recirculation fans may be added when required by temperature and process.
PLC and Safety Interlocks
Controls coordinate door, car travel, heating, fans, burners and alarms while preventing unsafe movement or heating sequences.
Interlock principle: car travel is enabled only when the door and heating system are in a safe state. Heating is enabled only after the car is in position and the chamber is correctly closed and sealed.
Typical Car Bottom Heat Treatment Cycle
The actual recipe is created from the material specification, section thickness, furnace load and required mechanical properties.
Load Planning
Confirm material, part weight, support points, spacing and thermocouple locations.
External Loading
Load parts on the car using crane, manipulator or custom fixtures.
Car Entry and Sealing
Drive the bogie into position, close the door and engage the sealing system.
Controlled Heating
Ramp at the specified rate while monitoring furnace and load temperatures.
Soaking
Hold after the required part-temperature uniformity and soak criteria are reached.
Cooling or Quenching
Cool in the furnace or transfer to an external quench system according to the process.
Unload and Record
Remove the load safely and retain cycle, alarm and temperature records.
Published Electric Car Bottom Furnace Reference Models
The original COOLDO page lists the following 380 V, three-phase electric models at a 900°C process reference. Final power, working zone, loading capacity and temperature uniformity are recalculated for each project.
| Model | Power | Phase | Voltage | Temperature reference | Working zone (L × W × H) |
|---|---|---|---|---|---|
| RT2-65-9 | 65 kW | 3 | 380 V | 900°C | 1200 × 600 × 450 mm |
| RT2-105-10 | 105 kW | 3 | 380 V | 900°C published reference | 1800 × 900 × 650 mm |
| RT2-120-9 | 120 kW | 3 | 380 V | 900°C | 2000 × 900 × 700 mm |
| RT2-180-9 | 180 kW | 3 | 380 V | 900°C | 2200 × 1050 × 750 mm |
| RT2-250-9 | 250 kW | 3 | 380 V | 900°C | 2800 × 1500 × 900 mm |
| RT2-320-9 | 320 kW | 3 | 380 V | 900°C | 3200 × 1530 × 950 mm |
| RT2-480-9 | 480 kW | 3 | 380 V | 900°C | 5500 × 1500 × 1200 mm |
| RT2-900-9 | 900 kW | 3 | 380 V | 900°C | 9000 × 2200 × 1600 mm |
Data correction: the legacy page shows the RT2-250-9 width as 150 mm, which is inconsistent with the model sequence and furnace geometry. This page uses 1500 mm as the corrected reference, but it must still be confirmed on the approved quotation and drawing. The RT2-105-10 model code and its published temperature should also be re-confirmed before order.
Heat Treatment Processes
- Annealing
- Tempering
- Normalizing
- Stress Relieving
- Solution Treatment
- Preheating
- Homogenizing
- Hardening Heat-Up
- Controlled Cooling
Large and Heavy Workpieces
Process note: an industrial car bottom furnace provides controlled heating and soaking for large-part annealing, tempering, normalizing and hardening heat-up. Rapid quenching requires an engineered transfer system matched to the alloy, batch weight and maximum transfer time.
- Large steel and iron castings
- Open-die and closed-die forgings
- Heavy welded fabrications
- Steel billets, ingots and bars
- Gear blanks and large gears
- Drive shafts, rolls and cylinders
- Mining and construction machinery parts
- Pressure-vessel and power-industry components
Information Required to Size a Bogie Hearth Furnace
Workpiece and Load
Material grade, part dimensions, individual weight, total batch weight, loading pattern and fixture weight.
Heat Treatment Recipe
Maximum temperature, ramp rate, soak time, cooling method, atmosphere and number of cycles per day.
Performance Requirement
Temperature uniformity class, recording points, load thermocouples, recovery time and acceptance standard.
Site Conditions
Available voltage, gas type and pressure, plant layout, crane capacity, rail arrangement, exhaust and destination compliance.
Car Bottom Furnace FAQs
Technical answers for large-part annealing, tempering, stress relieving and quench-heating projects.
What is a car bottom furnace?
It is a batch furnace with a rail-mounted movable hearth. Large parts are loaded on the car outside the chamber, then the powered car carries the complete load into the furnace for heating and soaking.
What is the difference between a car bottom furnace, bogie hearth furnace and trolley furnace?
These names normally describe the same basic arrangement: a heating chamber with a removable rail-mounted hearth or load car. Regional terminology and detailed drive construction may differ.
Which heat treatments can be performed?
Typical processes include annealing, tempering, normalizing, stress relieving, solution treatment, homogenizing and preheating. Hardening also requires a suitable external quench and transfer system.
Which parts are suitable for a car bottom furnace?
Large castings, forgings, welded structures, billets, ingots, gear blanks, shafts, rolls, cylinders and heavy machinery components are common applications.
Can the furnace be electric or gas fired?
Yes. COOLDO can configure electric resistance heating, natural gas, LPG, qualified fuel gas or oil firing. The choice depends on process cleanliness, connected power, local energy cost, heat-up rate and emission requirements.
What maximum temperature is available?
The product range uses low-, medium- and high-temperature configurations, with references up to 750°C, 950°C and custom designs up to approximately 1200°C. Final material and component ratings are process-specific.
How is temperature uniformity controlled?
Uniformity is engineered through zone layout, element or burner placement, circulation, pressure balance, load spacing, insulation and control tuning. It must be verified by the agreed empty-furnace or loaded survey standard.
How is the furnace car driven?
The bogie normally uses a motor, gearbox and chain or wheel-drive system. Limit switches, position sensors and PLC interlocks coordinate car movement with the door and heating system.
How is heat leakage around the car reduced?
Labyrinth, sand, fiber, soft-contact or pneumatic seals can be combined around the rails, side walls, door and car interface. The final arrangement depends on furnace temperature and maintenance access.
Can the furnace perform quenching?
The furnace heats and soaks the load. Quenching requires rapid door opening, powered transfer and an external water, oil, polymer or forced-air system engineered for the maximum load and transfer-time requirement.
Can a protective atmosphere be used?
A modified sealed design can support selected protective or controlled atmospheres. Gas tightness, purge sequence, pressure control, exhaust treatment and safety interlocks must be engineered as a dedicated system.
How is the correct furnace size selected?
Allow clearance around the complete load and fixtures for circulation and handling. The usable zone is selected from part dimensions, batch layout, weight distribution, crane access, temperature uniformity and production cycle.
Can COOLDO customize the car bottom furnace?
Yes. Work-zone size, loading capacity, heat source, door, bogie drive, rail layout, zones, fans, atmosphere, quench transfer, controls and data recording can be configured around the project.
What information is required for a quotation?
Send part drawings, material, maximum part and batch weight, working-zone requirement, heat-treatment curve, maximum temperature, uniformity standard, daily cycles, cooling or quench method, energy supply and installation layout.
Need a Car Bottom Furnace for Large or Heavy Parts?
Send the part size, load weight, process temperature, cycle and energy supply for an engineered bogie hearth furnace proposal.