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Low Pressure Vacuum Carburizing FAQ

Simply put, carburizing is the process of carburizing iron or steel by heating in the presence of carbon, thereby hardening the surface of the component. Depending on the process regime, the hardness may vary with carbon content. The process can use either conventional (atmosphere) furnaces or low-pressure (vacuum) carburizing furnaces (LPC).

Low pressure vacuum carburizing furnace
There is no oxygen present in the low pressure carburizing (LPC) process, but carburizing gas (such as acetylene) is introduced. The low-pressure carburizing process was chosen because of precise process control, good reproducibility, excellent metallurgical results, and shorter process times than atmosphere carburizing at higher temperatures.
In order to develop new carburizing technologies for new applications, an in-depth understanding of standard processes is required. The low-pressure carburizing process alternately uses carburizing gas and inert gas for processing, which will not cause intergranular oxidation.
This process also ensures a uniform depth of the carburized layer due to its high control accuracy. The carburizing process regime was developed with the goal of using higher temperatures and more enriched gases without affecting material properties.

The main features of low-pressure vacuum carburizing are:
1) Thermal cracking of hydrocarbons at low pressure (7–13 mbar) in a vacuum-cooled fireplace
2) Alternately introduce hydrocarbon gas (carburization) and inert gas (diffusion)
3) The number and time of carburizing steps are determined according to the depth of carburizing layer that needs to be achieved.
Although the traditional technology is better known, the new advanced low-pressure carburizing technology has many advantages. This new vacuum carburizing technology utilizes the pyrolysis of a single carburizing gas (usually propane or acetylene) at low pressure to enrich carbon on the component surface. Therefore, vacuum conditions have the advantage of promoting carbon absorption. Carbon uptake is not only simulated while developing the process, but also tracked every time the process is executed.

Advantages of low-pressure vacuum carburizing furnace compared to traditional carburizing furnace
The low-pressure vacuum carburizing furnace adopts cold wall technology, so the outer surface of the furnace remains low temperature, reducing heat dissipation to the production site. It does not have any flames or hot furnace walls and can be installed in the middle of the machining area in the shop. This allows for better component flow and eliminates the need to rely on firewalls to separate heat treatment areas.
Using cold wall technology also eliminates the inherent risks of hot wall technology such as open flames and high surface temperatures. In addition, there is no need to install a ventilation hood in the workshop to exhaust combustion exhaust gases. For these reasons, low-pressure vacuum carburizing furnaces occupy a smaller production space but can achieve higher productivity.
As for the safety concerns of using acetylene, that’s also easier to address. Acetylene suppliers now offer reliable fire and explosion protection systems and solutions. Since no heat-trapping gas is required, there is no need to worry about carbon monoxide.
The biggest advantage of low-pressure vacuum carburizing furnace is that the process cycle is shortened by using higher carburizing temperature. Some parts are now carburized at 1,030°C, reducing carburizing time by approximately 75%. New trials to further increase temperatures are underway.
The modular design of the device also brings advantages. All furnace chambers are independent, meaning that different steps can be performed separately and at different temperatures. In order to expand the total production capacity, it is easy to add more furnace chambers to the low-pressure vacuum carburizing furnace, while traditional furnaces are limited by the original number of furnace chambers.
In addition, the processing furnace chamber can be easily closed when production needs to be reduced, whereas conventional furnaces must be operated at full capacity with empty trays.
Efficiency and energy saving are further advantages of low-pressure vacuum carburizing furnaces. The vacuum technology is extremely efficient, requiring only 35 kilowatts to keep a 2,200-pound steel component at process temperature.
Gas consumption is significantly reduced as it is used most efficiently. The low-pressure vacuum carburizing furnace can be ready for production in as little as 90 minutes, and each furnace chamber can be shut down at any time after startup and then ready and resume production within 30 minutes.
Finally, low-pressure carburizing furnaces are very similar to machining centers and can be run and maintained by the same team. All process control is assumed by the equipment; there is no need to control carbon potential or dew point. Time, temperature and flow rate are the only process parameters controlled by the system.
Low-pressure carburizing furnaces are easier to maintain, have lower risks, and are less constrained by limited space. The system uses only electric heating and does not require a burner expert; standard maintenance tools can solve equipment problems.

In conclusion
Compared with traditional atmosphere carburizing, the low-pressure carburizing process performed in a vacuum furnace using cold wall technology has many advantages: no oxidation, more uniform carburization, better reproducibility of different batches of charge, metallurgical indicators such as carburizing Carbon layer depth) tolerance is tighter, and the core hardness can better meet the requirements.
The low-pressure carburizing process meets environmental standards because it significantly reduces the emission of carbon dioxide and harmful chemical products. In an industry that is always changing, familiarity with the latest technology can allow you to achieve the best level of production and meet your requirements for higher productivity and higher product quality.