Heat Treatment Processes
Heat Treatment Application Challenges:
Heat treatment processes such as brazing, carburizing, annealing, sintering, nitriding and hardening are sensitive to the presence of water vapour (humidity/moisture). The table below lists some examples and includes the effects when water vapour limits are exceeded.
In general, any process requiring a protective or reducing atmosphere (e.g. H₂, N₂, vacuum, Argon) is highly sensitive to water, since even small amounts of water will oxidize surfaces and interfere with the intended metallurgical changes.
Process | Water vapour sensitivity | Problems/Defects | Typical Water Vapour Limit |
Vacuum brazing | Extremely sensitive – joints will fail if even trace water vapour present | Oxidation, poor filler wetting, weak joints | < 1ppm -80°C dew point |
Vacuum heat treatment (hardening, annealing) | Very sensitive – vacuum quality depends on dryness | Staining, oxidation, poor surface finish | ~ 5ppm -60 °C dew point |
Bright annealing (stainless steels) | Requires ultra-dry H₂ or N₂/H₂ | Staining, oxidation, poor surface finish | ≤ 10 ppm H₂O ≤ –60 °C dew point |
Nitriding | Case formation disrupted by water vapour | Oxide formation, poor case quality | ~100 ppm H₂O ≤ –40 °C dew point |
Carbonitriding | Atmosphere balance upset by water vapour | Oxide formation, poor case quality | ~100 ppm H₂O ≤ –40 °C dew point |
Carburizing | Carbon potential reduced by water vapour | Decarburization, oxidation, hydrogen embrittlement | –20 to +20 °C dew point depending on carbon potential |
Sintering (powder metallurgy) | Powder surfaces very reactive | Oxidation of powders, reduced density/strength | ~100 ppm H₂O ≤ –40 °C dew point |
Metal process engineers use dew point sensors (DPS) to measure and control the water content of gases and the production environment, which is critical to maintaining quality standards in production. But metal production environments are harsh, with high temperature, variable/high humidity, chemical and particulate contamination. This is the worst environment for DPS, where maintenance is often challenging, complex and expensive.
Users are increasingly looking to test and maintain DPS in-house to validate performance and save the cost of external service or exchange. This is where the FPG, the world’s first self-contained transportable dew-frost point calibrator, is increasingly applied.
Quality enhancement for processes
The FPG allows users to check instrument performance and carry out calibration on-site, without removing equipment from site or sending it to the manufacturer or a calibration laboratory.
With an FPG on-site, metal heat treatment engineers have immediate control:
- Calibration process can include the control loop or monitoring system for full system validation
- Regular calibration enables unbroken traceability of calibration and measurement data to meet the requirements of ISO9001 and other quality systems
- Less change control documentation is needed when exchanging/replacing probes or sensors
Reducing cost with the FPG
The FPG can also reduce the overall cost of maintaining dew point sensors, cutting out the need to stock multiple sensors and eliminating the cost, administration and maintenance time associated with swapping out DPS for traditional calibration methods.
Simple set-up and easy to use
FPG is easy to set up and only requires an AC power supply, making it suitable for use wherever calibration is needed.
Fit the correct FPG PA adapter for the instrument under test (IUT), install the sensor, and make sure the system is sealed. Set the first (lowest) required dew/frost point and allow the system to stabilise. Record the result, then repeat the process for each calibration point until the test is complete.
The initial results provide the As Found calibration data. If the instrument is outside specification and requires adjustment, follow the manufacturer’s adjustment procedure. Repeat the calibration to produce the As Left results. These results can then be recorded in a calibration report or certificate if required.
Universal Compatibility:
The FPG has been developed to be easily configurable to suit all types of DPS. The FPG-PA probe adapters can be specified to suit the device under test and changed by the user if needed.
FPG features a back panel sample loop interface, so it can also be connected using sample tubes to dew point chilled mirrors and moisture analysers.
