Selecting the Right Vacuum Oil Quenching Furnace for the Job

Considerations for selecting a vacuum oil quenching furnace
The variety of vacuum oil quenching furnaces has increased significantly in recent years. There are now many options to choose from, and the user must carefully analyze the equipment that best suits their production needs. The following factors must be considered:
Volume and total charge: These are the first parameters to be determined, depending on the size, shape and output of the most troublesome parts. Depending on the type of furnace (single chamber or double chamber), the process cycle time will change, which also affects the furnace capacity.
Vacuum requirements: Although rough vacuum is usually sufficient for hardening low alloy steels, some more special applications may require higher vacuum. Double chamber furnaces can add a diffusion pump.
Flexibility in cooling: Oil quenching can be supplemented with forced convection of inert gas to accelerate cooling, which allows (for example) carburizing and annealing. The oil/gas quenching process can be equipped with a high-pressure cooling chamber, which expands the range of steel grades and improves the versatility of the equipment.
Necessity of charge thermocouples: Some applications (such as the processing of aerospace parts) may require these high-temperature measurements. However, the complexity of the system and the short life of oil-cooled thermocouples greatly restrict their use.
Charge transfer time: Low hardenability alloys require very short transfer times. While almost all modern furnaces are capable of 20-40 second transfer times, the requirement for transfer times shorter than 15-20 seconds limits the range of equipment available on the market.

Types of oil quenching vacuum furnaces
If you are planning to purchase an oil quenching vacuum furnace, there are a number of products to consider, each with different advantages and limitations.
For example, horizontal furnaces are available in single or dual chamber versions, in both oil and gas quenching designs. Some are designed for larger charge volumes, while others are best for smaller charge volumes. There are also multi-chamber vertical furnaces, which are very effective for controlling deformation of long parts, but usually require a pit and have a larger initial investment. Be sure to determine your specific needs before purchasing your vacuum furnace.
Vacuum oil quenching is a less popular process. However, it combines the safety of a vacuum with the high quality of the process to provide an efficient, clean and competitive industrial solution.
These advantages are subject to many misconceptions, including:
Parts immersed in oil will deform. In fact, with properly adjusted and precisely controlled hardening conditions, deformation is often better than with high pressure gas quenching.
Parts immersed in oil need to be cleaned. Cleaning and degreasing are indeed required after quenching, but the oil film on the surface protects the parts, making it impossible to see the difference between oil-quenched and gas-quenched parts by naked eye. In addition, cleaning is usually required before heat treatment, and adding a cleaning step generally does not require adding more equipment or paying too much extra cost.
Vacuum oil quenching furnaces are expensive. Like any equipment, the competitiveness of vacuum oil quenching furnaces must be measured in combination with investment costs and performance. Considering that low consumables costs are one of the advantages, this solution may be more competitive in the medium term. In addition, the cost of single-chamber oil quenching vacuum furnaces is also attractive even compared with traditional furnaces.

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