Tempering Furnace

What isTempering Furnace

A tempering furnace is a type of industrial oven designed to heat treat a ferrous metal product and increase its toughness. In metallurgical terms, the toughness of an alloy describes its capacity for elastic deformation and energy absorption before the material fractures. It is part of a complex relationship between a metal's ductility and its strength, with high toughness values requiring a delicate intersection of the two.Typically, high strength materials are not ductile – and vice versa – but heat treating certain materials in a tempering furnace can unlock beneficial values on both axes of this mechanical dynamic.

Advantages of Tempering Furnace

Improved strength and durability

One of the primary benefits of tempering furnace is that it improves the strength and durability of metals. When metal is heated and then cooled slowly, the molecules within the metal align themselves in a more orderly fashion. This process makes the metal stronger and less likely to break or shatter.

Increased hardness

Another benefit of tempering furnace is that it increases the hardness of the metal. Harder metal is less likely to be dented or scratched and can therefore maintain a more polished appearance for longer periods of time.

Ductility

In addition to increased strength and hardness, tempering furnace also improves the ductility of the metal. Ductility is a measure of a material's ability to deform under stress without breaking. By improving ductility, tempering makes the metal less likely to crack or break under stress.

Corrosion resistance

Tempering furnace also helps to improve the corrosion resistance of a metal. When metal is heated and then cooled slowly, the outer layer of the metal becomes harder and less porous. This improved surface layer helps to protect the metal from corrosion and oxidation.

Trolley Type Furnace

Trolley tempering furnace is mainly used for tempering of high chromium cast steel roll,

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Trolley Type Industrial Tempering Furnace

The trolley tempering furnace is mainly used for heat treatment of general large and medium-sized

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Electric Furnace

The electric furnace is a standard energy-saving periodic working furnace, which is mainly suitable

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Trolley Tempering Furnace

Trolley tempering furnace is mainly used for tempering of high chromium cast steel roll,

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Well Type Tempering Furnace

The well type tempering furnace is a period operation type furnace, which is used for tempering the

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Box Type Tempering Furnace

Box type tempering furnace is cycle operation type furnace. The utility model is mainly used for

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Trolley Type tempering Furnace

Trolley Type tempering Furnace (short for electric furnace) is mainly used for heat treatment of

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Types of Tempering Furnace

Convection Furnaces

Convection furnaces use fans to circulate hot air evenly around the glass panels. This ensures uniform heating, which is essential for achieving consistent tempering results. Convection furnaces are often preferred for tempering low-E (low emissivity) glass and other specialized glass types.

Radiation Furnaces

Radiation furnaces use infrared heating elements to heat the glass panels. These heating elements emit infrared radiation, which is absorbed by the glass surface, causing it to heat up. Radiation furnaces are known for their energy efficiency and fast heating rates.

Top and Bottom Heating Furnaces

In these furnaces, the glass panels are heated from both the top and bottom sides simultaneously. This ensures uniform heating and helps prevent distortion during the tempering process.

Roller Hearth Furnaces

Roller hearth furnaces use a system of rollers to transport glass panels through the heating and cooling zones of the furnace. This continuous processing method is well-suited for high-volume production and can achieve consistent tempering results.

Bend Glass Furnaces

These furnaces are specifically designed for tempering bent or curved glass panels. They use specialized molds or bending mechanisms to shape the glass during the tempering process.

Chemical Strengthening Furnaces

While not strictly tempering furnaces in the traditional sense, chemical strengthening furnaces are used to strengthen glass through a chemical process involving ion exchange. These furnaces immerse glass panels in a bath of molten salt or other chemical solutions to create a compressive stress layer on the surface of the glass, increasing its strength.

Tempering Furnace Temperature Setting

1. Understand the Material Properties

Material Type: Different materials require different tempering temperatures. For instance, steel, aluminum, and glass each have specific temperature ranges.
Material Thickness: Thicker materials might require longer tempering times or slightly different temperatures.
Previous Treatments: Consider any prior heat treatments the material has undergone, as this can affect the tempering process.

2. Determine the Desired Tempering Outcome

Mechanical Properties: Define the desired hardness, toughness, and ductility. For example, higher temperatures typically reduce hardness but increase ductility.
Industry Standards: Refer to industry standards or manufacturer's guidelines for specific tempering ranges.

3. Consult Technical Documentation

Equipment Manual: Review the furnace's manual for specific instructions on setting temperatures.
Process Specifications: Look for any existing process specifications or standard operating procedures that outline tempering parameters.

4. Set the Temperature Controls

Control Panel: Access the furnace's control panel, which typically allows you to set and adjust the temperature.
Temperature Zones: If the furnace has multiple zones, set each zone according to the required profile. Some continuous furnaces have preheat, heating, and cooling zones.
Ramp Rate: Set the ramp rate if the furnace has this capability, which controls how quickly the temperature increases to the set point.

5. Programming the Temperature Profile

Initial Setup: Enter the desired temperature for the tempering phase. For instance, tempering steel might require a temperature range of 400-600°C (752-1112°F).
Soak Time: Program the duration the material should be held at the tempering temperature. This can vary from minutes to hours depending on the material and desired properties.
Cooling Rate: Set the cooling rate if the furnace allows. Controlled cooling might be necessary for certain materials to achieve the desired properties.

6. Monitoring and Adjustments

Thermocouples and Sensors: Ensure thermocouples and other temperature sensors are properly placed and functioning to monitor the furnace temperature accurately.
Initial Run: Perform an initial run and closely monitor the temperature profile. Adjust settings as needed based on the performance and output.

7. Quality Control

Sample Testing: Test samples of the tempered material for desired properties like hardness and tensile strength.
Adjust Parameters: If the results are not as expected, fine-tune the temperature settings and soak time.

Tempering FurnaceSystem Composition

Heating system
Furnace chamber: The main body where the glass is heated. It is insulated to retain heat and ensure uniform temperature distribution.
Heating elements: These can be electric (resistance heating elements) or gas-fired burners, providing the necessary heat to bring the glass to the tempering temperature, typically around 620-700℃ (1148-1292℉).
Temperature control: Thermocouples and sensors monitor the temperature inside the furnace. A control system adjusts the power to the heating elements to maintain the desired temperature profile.

Quenching system
Air blowers: High-power fans that force air onto the heated glass to cool it rapidly. This rapid cooling is critical to developing the tempered glass's strength properties.
Air distribution system: Includes nozzles and ducts that direct the air flow uniformly over the surface of the glass. The design ensures even cooling to prevent stress imbalances and potential breakage.
Cooling control: Adjusts the air pressure and flow rates to achieve the desired cooling rate and ensures uniform tempering across the glass surface.

Conveying system
Roller conveyor: A system of heat-resistant rollers that transport the glass through the furnace. These rollers are designed to handle high temperatures without deforming.
Drive mechanism: Motors and control systems that precisely regulate the speed of the rollers, ensuring consistent travel speed and timing for each glass piece.

Control system
Programmable logic controller (PLC): Manages the operation of the entire furnace, including heating, quenching, and conveying systems. The plc ensures precise timing and coordination of each step in the tempering process.
Human-machine interface (HMI): Provides operators with a user-friendly interface to monitor and control the furnace parameters, such as temperature, conveyor speed, and air flow rates.

Cooling system
Heat exchangers: Used to cool down the air used in the quenching process to ensure it is at the optimal temperature for rapid cooling of the glass.
Water circulation system: Often used to cool the air in the heat exchangers. It includes pumps, pipes, and cooling towers or chillers.

Exhaust system
Ventilation: Removes hot air and fumes from the furnace chamber to maintain safe operating conditions and improve energy efficiency.
Filters and scrubbers: Clean the exhaust air to remove particulates and pollutants before releasing it into the atmosphere.

Safety systems
Emergency shutoff: Allows operators to quickly shut down the furnace in case of an emergency.
Temperature alarms: Alert operators if temperatures exceed safe limits.
Pressure relief: Protects the furnace from overpressure situations in the quenching system.

Tempering Furnace Operation Process

Preparation

Load the furnace: The pre-hardened material is loaded into the tempering furnace. This could be done manually or using automated systems depending on the size and type of furnace.
Select the heating medium: The furnace uses a heating medium like air, salt bath, or oil, depending on the material and desired temperature.
Set the temperature and time: The operator sets the desired tempering temperature and time based on the material and desired properties.

Heating

Temperature ramp-up: The furnace heats up the material to the desired tempering temperature. This can be achieved through various methods like direct flame heating, resistance heating, or induction heating.
Soaking time: Once the material reaches the target temperature, it is held for a specific time, known as the soaking time. This allows the material to reach a uniform temperature and achieve the desired microstructure.
Temperature control: The furnace automatically regulates the temperature using sensors and control systems, ensuring consistent and accurate heating.

Cooling

Cooling method: After soaking, the material is cooled down to room temperature. Cooling methods can include air cooling, water quenching, or oil quenching. The cooling rate influences the final properties of the material.
Controlled cooling: For precise control of the final properties, some furnaces have controlled cooling capabilities, enabling slow and controlled cooling to achieve specific microstructural changes.

Unloading

Material removal: Once the material has cooled down, it is unloaded from the furnace.
Inspection and evaluation: The tempered material is then inspected to ensure it meets the specified quality requirements. This may include testing its hardness, toughness, and other relevant properties.

Additional Processes

Further treatment: Depending on the application, the tempered material may undergo further processing, such as surface finishing, machining, or coating.

The Purpose of Tempering Furnace

01.

Softening metal

Tempering furnaces can heat metals through tempering processes, reducing their hardness and strength. In this way, metals can be processed, cold bent, and cut more easily.

02.

Immersion and surface coating

A tempering furnace can heat treat metals before surface coating, making it easier for the surface to absorb the coating material. The tempering furnace uses stable heating and cooling methods to ensure that the coating can evenly cover the entire surface.

03.

Stress relief

After the processing or welding, the metal will generate stress. A tempering furnace can eliminate these stresses and prevent problems such as fracture or stretching during metal use.

04.

Metal quenching

A tempering furnace can help control and adjust the speed and temperature of metal quenching. By adjusting the heating time and temperature, the metal material can reach the ideal quenching state to obtain the required hardness and strength.

What Is the Difference Between Tempering and Quenching

Different technological processes
The quenching process is to quickly immerse the material in water or oil after reaching a certain heating temperature, and rapidly reduce the temperature of the material to room temperature. Tempering, on the other hand, involves heating the material to a specific temperature after quenching, followed by cooling treatment.

Different purposes
The main purpose of quenching is to improve the hardness and strength of the material, achieving the maximum hardness and strength of the material. The main purpose of tempering is to enable the material to maintain both a certain level of hardness and toughness.

Different temperature parameters
The quenching temperature is generally extremely high, preferably around 250℃; The tempering temperature is generally lower, with a suitable range of 150-250℃.

Different shapes and types of workpieces
Quenching is generally only applicable to certain specific shaped workpieces, such as cutting edges, gears, etc; Tempering is suitable for heat treatment of most metal materials.

Differences in repetitive processing
Quenching is a very sudden heating method that generates significant stress. Tempering, on the other hand, involves progressive heating, which can effectively ensure the repetitive processing quality of the steel.

Operation Precautions of Tempering Furnace

The tempering furnace is used for tempering general metal parts in air and for quenching, annealing and aging heat treatment of light alloy parts such as aluminum alloy die casting, piston and aluminum plate. The fan tempering furnace produced by our heat treatment company is suitable for pure vacuum, atmosphere protected tempering, annealing and quenching of mould, high speed steel and tool steel.

01/

The furnace temperature of tempering furnace shall not exceed 650℃. The products shall be placed in order without skewing, and the height shall be suitable for not hanging the power supply in the furnace and leaving a 100mm spacing after entering the furnace.

02/

Before the tempered workpieces are put into the furnace, power on the distribution box, drive out the return trolley, check whether the instruments and meters are normal (set temperature value), and whether the fan motor, heater, etc. are in good condition.

03/

When returning the trolley to the furnace, slow down. Observe whether the trolley is running smoothly and whether the power line is blocked. Close the door after entering the furnace, heat up and start the fan motor, adjust the temperature, and calibrate the temperature with a thermometer.

04/

At the end of loading and unloading the products in the furnace, it is necessary to check whether the thermocouple is inserted into the tempering furnace (the thermocouple is the data value of measuring temperature), and pay attention not to touch the thermocouple (the workpiece is not allowed to contact with the thermocouple).

05/

During the operation of fan tempering furnace, the staff on duty must observe whether the temperature of tempering furnace instrument is normal.

06/

At the end of tempering, first turn off the heating switch, then turn off the fan motor, then open the door and drive out the trolley.

07/

In case of circuit failure or fire due to failure, turn off the switch to extinguish the fire. In case of fire in the furnace, immediately open the door and drive out the trolley, and close the switch to put out the fire.

08/

When the electrical system breaks down, it shall be repaired by electricians. Non electrical personnel are strictly prohibited to repair by themselves.

Tempering Furnace Maintenance on Key Parts

Regular roller cleaning
When the optical effect of the glass is less than desirable or there is a spontaneous explosion inside the furnace cavity, the tempering furnace should be turned off promptly. Allow it to cool down before you start to clean the rollers. Follow the steps below: First, use scraper to scratch off the glass debris or other foreign objects off the ceramic roller. Brush them off the track with soft plastic brush; Sand the rollers with 400 – 600 grit wet sandpaper until you get a smooth hand feeling on the ceramic surface. Vacuum the rollers and wipe them from the center to the ends with lint-free towels damped in soft water to remove the dust on the surface. Ceramic rollers should not be over sanded to damage the enamel layer. Use distilled water or pure water only. Never use alkaline cleaning detergents or chemical agents. After the cleaning, close the furnace immediately to avoid more dust. After cleaning, heat up the furnace to 200 degree for 1~2 hours before raising the heating temperature. Do not raise the temperature too fast.

Changing ceramic rollers
Do not change ceramic rollers until the furnace cavity is completely cooled down to prevent the metal end cap from coming apart. It takes at least three people to replace the rollers with one on each end and 1-2 handling the middle. Remove the belt first. Loosen the screws on the bearing spacing block and remove the bearings from the holder. Insert a piece of thick cardboard in the holes of the pullout end. Hold the roller firmly. Lift and pull it out slowly to avoid bumping in or scratching.

Furnace top lifting and transmission gears
To ensure the smooth lifting of the furnace, the trapezoidal lead screw rods inside the pillars need be lubricated with N46 oil after every lift (or at least once a month). Apply lithium grease to the bevel transmission gears once every quarter. Furnace lifting chain: have it lubricated once a month with N46 lubricant. If the chain trips out of gear when pulling, the chain doesn’t have enough tension. Correct that by adjusting the chain tensioner. Furnace lifting motor reducing gear: keep the lubricant level on the center mark of the window gauge. Change the oil once a year. We recommend to use 30# or 40# premium lubricating oil.

Bearing lubrication
Regular inspection and lubrication are needed for the tempering furnace main drive shaft bearings, roller hearth bearings, insulating door joint bearings, bearings for the furnace top lifting transmission gear, and bearings for the trapezoidal lead screw rods in the furnace top lifter. Use lithium grease for lubrication. The lubricating cycle for ceramic rollers is twice a year. All others need to be lubricated once every year. The grease in ceramic roller bearings should maintain an ample but the least level needed to get the best working temperature for the rollers. Apply lithium grease to the bevel transmission gears in the furnace top lifter once every quarter.

FAQ

Q: What is the purpose of tempering?

A: Tempering helps to relieve stress making the metal easier to weld or machine. Increases strength while making the material more flexible and ductile. Increases hardness and introduces wear-resistant properties to the surface or through the entire metal.

Q: . What is the difference between quenching and tempering?

A: Quenching：increase strength and wear resistance. Tempering：adjust the hardness and increase toughness together with hardening. Annealing：soften the steel and improve workability. Normalizing：uniformly change the structure of the metal and impart strength and mechanical properties.

Q: What is the use of tempering furnace?

A: A tempering furnace is a type of industrial oven designed to heat treat a ferrous metal product and increase its toughness. In metallurgical terms, the toughness of an alloy describes its capacity for elastic deformation and energy absorption before the material fractures.

Q: Do you quench steel after tempering?

A: Tempering is usually performed after quenching, which is rapid cooling of the metal to put it in its hardest state.

Q: How long between quenching and tempering?

A: The part remains in the quench until it is at approximately the temperature of the quenchant. The part is then removed from the quenchant and immediately tempered. If the part is not tempered immediately (usually within 90 minutes of quenching), the part may be prone to quench cracking.

Q: What happens to steel during tempering?

A: Tempering is the process of heating steel to a high temperature, though below the melting point, then allowing it to cool in still air. This process improves the machinability of the hardened steel while reducing the risk of cracks due to internal stresses.

Q: What happens if you temper steel too long?

A: Brittle metal is dangerous as it can crack when you least expect it, causing injuries or damage to your tools or equipment. Brittleness is a problem that occurs when you apply too much heat to metal.

Q: What is the best temperature for tempering steel?

A: To reduce the brittleness, the material is tempered, usually by heating it to 175–350°C (347–662°F) for 2 hours, which results in a hardness of 53–63 HRC and a good balance between sharpness retention, grindability and toughness.

Q: What is the difference between heat treating and tempering?

A: Tempering is a heat treatment process which serves to further increase the beneficial properties of such alloys, specifically by increasing strength. It is typically used after other heat treatment processes which increase hardness, but cause the metal to become brittle.

Q: Can you temper steel too many times?

A: Steel can be tempered multiple times if necessary, but there are practical limits to the number of tempering cycles a piece of steel can undergo. The number of tempering cycles a steel component can endure depends on several factors: original hardness, alloy, tempering temperature(s), and section thickness.

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