Why choose vacuum gas quenching furnace

Why Choose a Vacuum Gas Quenching Furnace?

Vacuum quenching determines the ultimate microstructure and properties of the heat-treated workpiece. On the one hand, to achieve the ideal microstructure (generally martensite), the quenching cooling rate must be sufficiently high. On the other hand, to minimize deformation, the cooling rate should be as slow as possible and as uniform as possible across the entire workpiece cross-section. Typically, the cooling rate of a liquid medium cannot be adjusted during vacuum quenching; it has fixed characteristics. This is especially true when vacuum quenching deformation-sensitive workpieces, as quenching with oil or water-soluble media makes it difficult to control the quenching rate.

Principles of Vacuum Gas Quenching

Gas, as a vacuum quenching medium, generally has a lower thermal conductivity than oil- and water-based media. However, the vacuum quenching process can be tailored to the specific requirements of the workpiece shape and material, and its thermal conductivity can be brought close to that of oil- or water-based media by increasing the gas flow rate and pressure.

Gas quenching is generally considered to increase costs, thus limiting its widespread application. However, from an overall cost perspective, while the inherent cost of gas quenching is higher, it is offset by advantages such as reduced cleaning costs, improved quenching process reproducibility, reduced grinding during subsequent processing, and reduced hardened case depth.

How to Improve Vacuum Gas Quenching Capacity

There are various ways to improve cooling capacity during gas quenching: increasing the quenching pressure; increasing the gas flow rate; selecting different gas types (such as nitrogen, helium, and hydrogen); optimizing the flow pattern and increasing gas agitation. For high-pressure gas quenching, the gas type and pressure can be selected, while the gas flow rate is related to the furnace structure and load. High heat transfer is achieved when the workpiece is placed in a high-flow location within the furnace (such as the gas inlet). If the workpiece faces the gas flow, the flow rate is maximized, and thus heat transfer is likely to be maximized. When the furnace structure and influencing parameters are fixed, gas quenching results are reproducible. Proper design can improve cooling uniformity. Currently, issues such as gas flow reversal, both vertically and horizontally, through the load have been addressed, ensuring maximum cooling uniformity.

Another approach involves radially installing multiple nozzles around the furnace chamber to create a vortex field within the cooling chamber and furnace chamber, increasing gas agitation. Increasing quenching intensity by increasing flow rate and agitation, rather than pressure, is the basis of nozzle field gas quenching. In an adjustable nozzle field, complex workpieces are uniformly cooled through defined air inlets. This process allows for locally varying cooling rates, ultimately minimizing residual stresses. Rotating the workpiece or nozzle further improves cooling uniformity, particularly when quenching symmetrical workpieces. A dedicated cooling chamber can increase quenching intensity. The size of this chamber can be adjusted to the furnace load, minimizing gas losses, especially at higher quenching pressures. Currently, multi-chamber furnaces using cooling chamber technology have single-layer loads of up to 100 kg.

Vacuum Gas Quenching Furnace

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