Mnemonic for heat treatment audits
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--Conveyor Belt Continuous Furnace – Quenching and Tempering Section1. Zone Division: Separate areas for items to be heated and those already heated; products are stored in designated locations based on their type.
2. Empty Basket Inspection: Basket inspection is carried out daily when switching products; there should be no residues at the bottom of the empty basket.
3. Loading and Weighing: Items must be weighed before being loaded onto the conveyor; they should be spread out evenly with an appropriate thickness.
4. Tempering Delay: There should be a delay between quenching and tempering; if the process isn’t continuous, a proper interval must be set to avoid delays in tempering.
5. Inspection Items: Surface hardness is checked at two times; microstructural analysis is conducted daily; eddy current testing is recommended to detect hardness issues and cracks.
6. Tank Concentration: The concentration in the tanks poses risks; a refractometer should be used for daily checks, with special attention paid to phosphorus removal; it’s advisable to use separate tanks for this purpose.
7. Temperature Control: Thermocouples are used in each working zone; leaks in water and oil tanks must be prevented. Temperature fluctuations should remain within specified ranges: ±10°C in the heating zone and ±5°C in the tempering zone. After checking the temperature data, on-site verification using alarms is necessary. Cast iron types are commonly used; replacements are essential and should be done after one year of use in heating applications, and definitely after two years in tempering applications.
8. SAT (System Accuracy Test): SAT can be performed in both unloaded and loaded conditions; multiple comparisons using dual thermocouples in the same zone are recommended, with checks done monthly. If detection methods are used, checks should be conducted quarterly.
9. TUS (Furnace Temperature Uniformity Test): TUS uses a planar method; the number of thermocouples varies depending on the size of the furnace chamber. As for how often tests should be conducted, they should be done annually or after major repairs.
10. Carbon Potential Control: Carbon potential sensors and oxygen probes are used; data fluctuations must be kept within ±0.05. Alarm functions must be properly configured, and daily verification is necessary. Weight-based methods using carbon sheets, as well as direct measurement using three-gas analysis, can be used; these two methods generally yield similar results. Flow rates should be stabilized, and the furnace chamber should be regularly cleaned of carbon deposits, with nitrogen gas used to maintain a stable atmosphere.
11. Oil Tank Control: The level of oil in the tank and its mixing process need to be monitored continuously using alarm devices.
12. Oil Quality Inspection: The quality of the oil is crucial; inspections should be carried out every six months.
13. Instrument Calibration: Instruments for temperature and carbon control need to be calibrated regularly without any shortcuts