Modern carburizing processes include standard case hardening and low pressure carburizing methods. There are specific uses for each method but low pressure systems come with a number of benefits. Let’s take a look at conventional type applications and compare them to modern low pressure methods.
Conventional Carburizing
Although this method has been around for some time, it is still seeing use in some applications today. In fact, for many years, it was the standard for carburizing processes. The method takes place at atmospheric pressure, so there is a high chance of contamination from gases in the air. For example, because there is a significant amount of oxygen in the atmosphere, it creates a high potential for oxidation in iron. Carbon potential and gases must be continually monitored throughout the process.
Low Pressure Carburizing
In order to have the best results for carburizing, the absence of O2 is important. This virtually eliminates the possibility of oxidation and contamination from other materials. This is the basic principle for low pressure methods.
In order to remove oxygen, a vacuum system is used to pump the air from the furnace chamber. During the process, the metals are heated to temperatures higher than standard carburizing methods (as high as one thousand degrees Celsius). This provides a number of benefits from low pressure carburizing:
* Faster carburization times resulting in greater efficiency
* High degree of hardness (especially below surface level)
* Even and uniform hardness created
* Small holes in metal can be effectively carburized.
* Distortion is minimized.
* Cycle time can be reduced significantly and in some processes this can be as high as a fifty percent reduction.
* Greater resistance to stress and fatigue
* Cleaner products produced
* More precise control of the hardening process
* Eco friendly
Low Pressure Carburizing Applications
This method is often used to create parts which take a great deal of wear and tear. For example:
* Gears – transmission gears are created through low pressure carburizing followed by high pressure cooling or quenching methods. This creates exceptionally clean gears (which are needed for transmissions) and no additional cleaning steps are required.
* Axles
* Shafts
* Spindles
* Injectors
* Nozzles
Acetylene Low Pressure Carburizing
Some methods employ the use of acetylene gas for improved diffusion. Acetylene is not found naturally and is created synthetically with carbon monoxide and hydrogen, and makes it easier to control purity. This allows very large pieces of metal to be effectively carburized. It is also used to created sensitive components like diesel injectors.
