The determination of the effective heating zone of heat treatment furnaces shall comply with GB/T 9452‑2023. The core principle is to identify the chargeable zone within the furnace chamber that meets the temperature uniformity requirements through no-load temperature measurement. The main procedure includes test preparation, arrangement of temperature measuring points, heating and soaking, data acquisition and evaluation. The detailed operation method is as follows:
I. Scope of Application and Core Definitions
Applicable objects:Various types of heat treatment furnaces (batch furnaces, continuous furnaces, etc.).Not applicable to continuous heating zones without fixed process temperature or temperature uniformity requirements. Key terms
- Effective Heating Zone: The allowable chargeable zone within the furnace chamber that meets the process-specified temperature and uniformity requirements.
- Temperature Uniformity: The maximum deviation (±℃) of temperatures at all test points in the effective heating zone relative to the set temperature.
II. Pre-Test Preparation
Equipment status verification
- Furnace body, heating elements, temperature control / recording systems shall function properly, and instrument accuracy shall meet requirements (digital recording instruments).
- Thermocouples (platinum‑rhodium, nickel‑chromium–nickel‑silicon, etc.) shall be calibrated, with matching compensating cables and reliable connections.
Measurement cycle
- New furnace / after major overhaul: initial measurement;
- Normal service: periodic measurement (generally once a year, adjusted according to operating conditions).
Test conditions
- Test shall be performed under no-load condition, with heating rate at the normal setting;
- Vacuum furnaces shall reach the specified vacuum level.
- Confirm the process-specified temperature and allowable deviation (e.g., ±5℃, ±10℃).
III. Test Execution Procedure
1. Heating and Soaking
- Heat the furnace to the specified temperature per the process, and enter the soaking stage after stabilization.
- Stabilization criterion: temperature fluctuation of all sensors ≤ allowable deviation, with no continuous unidirectional drift.
2. Abnormal Handling
- In case of sensor failure (failure at corners / adjacent positions, number exceeding the standard), terminate the test and troubleshoot.
IV. Evaluation of Effective Heating Zone
Data processing
- Calculate the maximum deviation of temperatures at each test point relative to the set temperature, and verify whether it is within the allowable range.
- Eliminate abnormal data (e.g., abrupt jumps caused by sensor faults).
Acceptance criteria
- If temperature deviations at all test points ≤ process allowable value, with uniform distribution and no local out-of-tolerance, the measured zone is defined as the effective heating zone.
- If out-of-tolerance points exist, re-determination shall be performed after adjusting the zone range or repairing the equipment.
V. Records and Reporting
Record contents:Furnace type, process temperature, layout drawing of test points, raw temperature data, uniformity deviations, judgment results. Report requirements:Indicate dimensions of the effective heating zone, temperature uniformity index, test date and personnel. A formal inspection report shall be issued and filed.
VI. Management Requirements
- The effective heating zone shall be marked at an obvious position on the furnace body. Workpieces must be placed completely within the zone during charging.
- Re-determination of the effective heating zone is required after furnace maintenance, replacement of heating elements, or process adjustment.
- Establish measurement archives, keep test records and reports to ensure traceability.
VII. Special Points for Different Furnace Types
- Batch furnaces: Focus on temperature uniformity at the four corners of the furnace chamber and near the furnace door to avoid local overheating or underheating.
- Continuous furnaces: Measurement shall be conducted section by section (preheating zone, heating zone, soaking zone) to ensure all zones meet requirements.
- Vacuum furnaces: Maintain the specified vacuum level during testing to prevent temperature measurement from being affected by atmosphere.
