Taking sections 3.7 and 3.8 of the third edition of CQI-9 as an example, the requirements include: continuous monitoring, automatic control and recording of the carbon potential (or dew point, CO₂) of the atmosphere in the atmosphere generator and heat treatment furnace. The carbon potential should be controlled within the set value ±0.05; there must be backup verification methods (dew point meter, hot wire resistance, three gas analyzer, carbon verification foil, carbon rod, etc.); use backup methods to verify the carbon potential of the main furnace every day. Industry sampling shows that the main gaps lie in verification frequency and control accuracy.
- Continuous monitoring + automatic control + recording, covering generator and furnace
- The carbon potential is controlled within the set value ±0.05
- There must be an independent backup method of verification
- Daily calibration of main furnace carbon potential
- Major gaps in the industry: insufficient calibration frequency and substandard control accuracy
Key points of the terms (taking the third edition as an example)
Sections 3.7 and 3.8 of the third edition of CQI-9 have clear requirements for the control, monitoring, recording and calibration of carbon potential in controlled atmospheres:
- Continuous monitoring and automatic control: The carbon potential/dew point (or CO₂) of the atmosphere in the atmosphere generator (RX furnace) and heat treatment furnace should be continuously monitored, automatically controlled, and recorded;
- Accuracy: The recorded carbon potential should be controlled within ±0.05 of the set value;
- Alternate verification method: There should be carbon potential/dew point verification methods independent of the main control system, such as dew point meter, hot wire resistor, three gas analyzer, carbon fixed sheet, carbon rod, etc.;
- Daily verification: Verify the carbon potential of the main furnace atmosphere daily through backup methods.
The clause numbers and details of different versions may be adjusted, and the actual implementation shall be subject to the version requested by the customer.
Current state of the industry: where are the gaps?
Gauss Control’s sampling statistics of 45 heat treatment companies in the automotive industry that use protective atmosphere heating show:
| Observations | Result |
|---|---|
| atmosphere type | Nitrogen-methanol plus propane carburizing atmosphere is the most common, accounting for about 80% |
| Verification method | About 90% use fixed carbon sheets, three gas analysis and hot wire resistance are less |
| Verification frequency | Most of them are once a week, and a few are once every six months. There is a clear gap with the daily requirements. |
| Control accuracy | About 55% of companies are unable to meet the set value of ±0.05 |
Conclusion: The main gaps are concentrated in Carbon potential calibration frequency and Carbon potential control level Both aspects.
Why can’t I check every day?
- Calibration tablets need to be placed, taken out, cleaned, weighed or sent for inspection, which is time-consuming;
- When there are many stoves, there is not enough manpower;
- The operator's skill requirements are high, and the results are easily affected by human factors.
therefore,Fast, accurate and easy The verification method becomes critical.
Improvement path
1. Improve verification efficiency
- Three-gas analyzer: Results are available in about 5 minutes, no consumables, applicable to many furnace types;
- Hot wire resistance method: measured directly after carburizing, the accuracy can reach about ±0.03 in the range of 0.7–1.2 carbon potential, and has low requirements on the operator;
- The fixed carbon sheets are reserved for regular comparison and dispute arbitration.
2. Improve control accuracy
- Temperature: TUS, SAT ensure furnace temperature measurement accuracy;
- Oxygen probe: establish probe files and trend management;
- Carrier gas: Use RX gas with stable composition or correct the calculation by measuring CO online.
3. Complete records
- Electronically record carbon potential curves, calibration results and process factor adjustments;
- The reaction plan is triggered when the calibration deviation exceeds the limit.
Frequently asked questions
Does the generator outlet also need to be calibrated every day?
Generator atmosphere also requires continuous monitoring and recording. The verification frequency and method should be implemented according to the CQI-9 version and process table required by the customer, and written into the control plan.
Can a dew point meter be used as an alternate verification method?
It can be used as one of the backup methods, but the dew point cannot directly derive the carbon potential. It needs to be converted based on temperature and atmosphere composition. Its applicability is not as direct as three-gas analysis or carbon verification foil.
What should I do if the calibration finds that the deviation exceeds ±0.05?
Process according to the reaction plan: confirm the validity of the measurement, evaluate the impact on the work in progress, find out the cause (probe, temperature, carrier gas), correct and record, and adjust process factors if necessary.