What is the nitriding process like in a nitriding furnace?
Depending on the workpiece material the requirements for the nitrided layer, the process duration ranges 3 to 90 hours. This process creates a nitrogen-enriched hardened layer on the workpiece surface, resulting in high hardness, superior wear resistance, a high fatigue limit, excellent tribological properties.
Operating Procedures:
1. Prior to nitriding, the molds workpieces must have already undergone normalizing quenching tempering treatments.
2. First, scrub the workpiece surface with gasoline alcohol; it must be completely free of rust spots, oil stains, dirt.
3. After loading the workpieces into the furnace, symmetrically tighten the bolts securing the furnace lid.
4. Introduce cooling water into the inlet ports of both the furnace retort the lid to establish a circulating water-cooling system. For the piping on the furnace lid, the lower ports serve as inlets the upper ports as outlets; the furnace retort utilizes separate inlet outlet ports. Alternatively, all water pipes on the furnace lid can be connected in series—following the principle of "low-in, high-out"—so that water enters through a single inlet exits through a single outlet.
5. Before raising the temperature, nitrogen gas must be introduced to purge the furnace atmosphere; during this purging phase, the gas flow rate should be more than double the rate used during the actual nitriding process.
In the context of ion nitriding, the operating temperature directly impacts the quality of the nitrided layer the duration of the nitriding cycle. Furthermore, factors such as high voltage, glow discharge, the specific gas atmosphere present challenges for accurate temperature measurement. Currently, the following methods are employed for temperature measurement in ion nitriding furnaces:
(1) Visual Inspection Method
The high-voltage power supply is temporarily switched off, the temperature is estimated by visually observing the color of the workpiece through a viewing window. (Within the darkened interior of the furnace chamber, metal appears faintly reddish at approximately 520°C dark red at approximately 550°C.) Evidently, this method is highly subjective varies person to person; consequently, the potential margin of error in temperature estimation is significant, leading to poor control over the quality of the nitriding process.
(2) Thermocouple Measurement Method
This method typically utilizes a sheathed thermocouple—configured as a specialized temperature-sensing probe—which is placed in close contact with the workpiece surface. The nitriding temperature is then measured controlled via a connected display instrument. To prevent the thermocouple acquiring a negative high voltage, insulating materials—such as mica sheets quartz tubes—are typically placed between the thermocouple tip the workpiece. However, this arrangement tends to result in temperature readings that are lower than the actual values. Furthermore, after prolonged operation, the insulating surfaces can become contaminated with metal particles due to the cathode sputtering effect, thereby rendering them electrically conductive. Consequently, the thermocouple may still acquire a negative high voltage, leading to nitridation of the thermocouple material itself an increase in measurement error. In some instances, poor contact between the insulating material the workpiece can destabilize the glow discharge, triggering electrical arcing disrupting the normal operation of the multi-purpose nitriding furnace.
(3) Temperature Measurement Using Photoelectric Pyrometers Photoelectric Color Pyrometers
Both of these types of pyrometers enable continuous, rapid, non-contact temperature measurement control outside the nitriding furnace, utilizing a glass observation window located on the sealed vessel. This represents a relatively advanced method of temperature monitoring. When employing a photoelectric pyrometer, one must account for the influence of various factors on measurement accuracy—including changes in the workpiece's surface condition (specifically its surface finish geometry), the workpiece's surface emissivity, contamination of the observation window, the presence of ionized gases within the furnace, glow discharge effects, cathode sputtering. When utilizing a photoelectric color pyrometer, the impact of these aforementioned factors is significantly reduced; consequently, it is currently considered the most ideal instrument for measuring the temperature of workpieces within an ion nitriding furnace.