What are the key operating points of the tool tempering furnace?

The operation of the tool tempering furnace must strictly follow the process specifications to ensure that the tool performance meets the standards and safety is guaranteed. The following are the core points and precautions in operation:

1. Preparation before operation
Equipment inspection
Temperature calibration: Use standard thermocouples to verify the furnace temperature, ensuring a deviation of ≤± 3 ℃ (e.g. at a target temperature of 560 ℃, the actual temperature needs to be between 557-563 ℃).
Atmosphere system:
The nitrogen tempering furnace needs to be pre filled with nitrogen gas (flow rate ≥ 1.6m ³/h) to eliminate moisture, which can be reduced to 0.5m ³/h after 400 ℃.
The vacuum degree of the vacuum furnace needs to be checked (≤ 10 ⁻ ³ Pa) to prevent oxidation.
Circulating fan: Confirm that the fan is operating normally and the furnace temperature difference is ≤ ± 5 ℃ (if the temperature difference between any two points within a 2-meter furnace does not exceed 5 ℃).
Tool loading furnace
Placement method:
The cutting tools should be hung vertically or laid flat, with a spacing of ≥ 50mm (for example, when the milling cutter is tempered, the handle and blade should be placed in a staggered manner to avoid uneven heat conduction).
Large cutting tools (diameter>50mm) need to be fixed with specialized fixtures to prevent tilting.
Material classification:
High speed steel (such as M2) and stainless steel cutting tools need to be processed separately to avoid cross contamination.
The carburizing tool needs to be separately installed in the furnace to prevent carbon potential interference.

2. Operation process and parameter control
Heating stage
Rate control: ≤ 10 ℃/min (for example, it takes ≥ 56 minutes to rise from room temperature to 560 ℃) to prevent thermal stress cracking.
Segmented insulation:
Large cutting tools (diameter>50mm) need to be insulated at 300 ℃, 400 ℃, and 500 ℃ for 30 minutes each to balance the temperature difference between the inside and outside.
Thin walled cutting tools (such as razor blades) can be directly heated to the target temperature.
Insulation stage
Time accuracy: ± 5% error (e.g. 1-hour insulation needs to be completed within 57-63 minutes).
Temperature fluctuation: During the insulation process, the temperature fluctuation is ≤± 2 ℃ (for example, when tempering at 560 ℃, the actual temperature needs to be stable at 558-562 ℃).
Recording requirement: Record temperature data every 10 minutes, and immediately shut down for inspection in case of abnormalities.
cooling stage
Cooling method:
High speed steel cutting tools (such as W18Cr4V) need to be air-cooled to room temperature (to avoid cracking caused by oil cooling).
Aluminum alloy cutting tools (such as 7075-T6) require rapid water cooling (water temperature ≤ 30 ℃) to fix the structure.
Rate matching:
Thick walled cutting tools (thickness>20mm) have a cooling rate of ≤ 5 ℃/min to prevent thermal stress cracking.
Thin walled cutting tools (thickness<5mm) can be naturally cooled.

3. Safety and emergency response
safety protection
Protective equipment: Operators are required to wear insulated gloves, goggles, and heat-resistant shoes.
Warning signs: Set up “high temperature danger” signs around the furnace body and prohibit unauthorized personnel from approaching.
Nitrogen monitoring: An oxygen concentration alarm (automatically triggered when O ₂ ≤ 19%) needs to be installed during nitrogen tempering.
exception handling
Temperature out of control: If the temperature exceeds the target value by more than 5 ℃, immediately shut down the furnace and record abnormal data. Wait until the furnace temperature drops below 300 ℃ before conducting maintenance.
Circuit fire: Cut off the power and open the door to cool down. Do not use water to extinguish the fire (carbon dioxide fire extinguisher can be used).
Tool deformation: Check if the fixture is loose and adjust the furnace spacing to ≥ 80mm.

4. Post operation maintenance
Equipment cleaning
The residue inside the furnace needs to be cleaned with a vacuum cleaner, and it is forbidden to use metal tools to scrape (to avoid damaging the furnace lining).
The nitrogen pipeline needs to replace the filter element every month to prevent impurities from clogging.
Data archiving
Record the temperature curve, insulation time, and tool batch number for each furnace, with a retention period of ≥ 2 years.
Abnormal data needs to be analyzed separately and process parameters adjusted (such as reducing heating rate by 20%).
periodic calibration
Verify the furnace temperature monthly using standard thermocouples, and commission a third-party testing agency to calibrate the temperature control system quarterly.
The vacuum degree of the vacuum furnace should be checked every six months to ensure that it is ≤ 10 ⁻ ³ Pa.

5. Summary and Suggestions
Core principles:
Precise temperature control: Temperature deviation directly affects tool performance (such as a 10% decrease in wear resistance for every 1HRC decrease in hardness).
Atmosphere protection: Nitrogen or vacuum environment can prevent the formation of oxide scale and improve tool life.
Process optimization:
It is recommended to use graded tempering for large-sized cutting tools (such as pre tempering at 260 ℃ and final tempering at 520 ℃).
Carbonized cutting tools need to be directly quenched and low-temperature tempered after carburizing to avoid carbide precipitation.
Safety red line:
Do not open the door when the furnace temperature is above 300 ℃.
During nitrogen tempering, it is necessary to monitor the oxygen concentration throughout the process to prevent the risk of suffocation.
By strictly following the above operation points, it is possible to ensure stable tempering quality of the cutting tools and extend the service life of the equipment.