Conventional Atmospheric Carburizing Versus Low Pressure Carburizing Furnace Systems
Authors:
Pierre Rousset – Technical Operations Director from ECM USA
Vincent Lelong – Metallurgist from ECM USA
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Advantages of LPC Furnaces over Conventional Furnaces:
The LPC furnace uses a cold wall technology so the exterior surface of the furnace stays at a low temperature, reducing the amount of heat emitted into the plant. Without any flames, or hot walls, the furnace can be located in the middle of the machining area within the plant. This allows for a better part flow in the plant, and eliminates the need for a fire proof wall enclosing the heat treat area. (See Fig 2 and Fig 4) With the cold wall technology, dangers specific to hot wall technology are also eliminated such as open flames and hot surfaces. In addition, the plant does not need ventilation hoods to get rid of the burnt gas. For these reasons, the LPC furnace occupies less floor space in the plant, especially as it allows a higher throughout.
Safety concerns regarding the use of acetylene are also easier to address. The acetylene suppliers now have supply solutions with reliable explosion proof systems and fire prevention systems. Since the endothermic gas is not needed, there are no concerns regarding carbon monoxide.
The biggest advantage of an LPC furnace is the reduction of the cycle time using higher carburizing temperatures. Some production parts are now carburized at 1030º C (1886F), reducing the carburizing time approximately 75%, and new trials are going to even higher temperatures.
The modularity of the equipment also provides advantages. All chambers are independent allowing a different cycle at different temperature to run in each. It is easy to add additional chambers on an LCP furnace to increase the overall production volume whereas a conventional furnace is limited to its original number of chambers. Moreover, in times of decreased production, it is easy to turn treatment chambers off, while the conventional furnace has to run at full capacity with empty trays.
Efficiency and energy savings are further advantages of the LPC furnace. The vacuum technology is the most efficient with only 35 KW to maintain 2200 LBS of steel at temperature. The gas usage is reduced tremendously as it is used in the most efficient way. LPC furnaces can be ready for production in as little as 90 minutes and each chamber can be turned on or off at any time to be ready for production in 30 minutes.
Finally, the LPC furnace is so similar to a machining center that both can be operated and maintained by the same team. The entire process control is done by the equipment, without the need for controlling the carbon potential or the dew point. The system control time, temperature and flows are the only process variables. Maintenance of an LPC furnace is easier with less danger and less permitted confined space requirements. With only electric heat, the system does not need a burner specialist, and standard maintenance tools can address equipment issues.
In conclusion, there are significant differences between a conventional furnace and an LPC furnace. Low pressure carburizing carried out in vacuum furnaces with cold walls offers many advantages compared to traditional conventional atmospheric carburizing: no oxidation, better carburizing homogeneity, excellent reproducibility of the load to load processing, tightening of the metallurgical tolerances such as the carburizing depth, and finally, core hardness. The LPC process respects environmental standards as it significantly reduces CO2 emissions and harmful chemical products. In an ever-changing industry, becoming familiar with the newest technology will push your production to perform at its very best and meet your demands for increased productivity and higher quality parts.
