• Heat treatment processes for quenching furnaces
• Hardening
• Annealing
• Brazing
• Sintering
• De-gassing
• Heat treatment processes for retort furnaces
• Tempering
• Nitriding
• Oxidizing
• Annealing
• De-gassing
• Advantages of single chamber vacuum furnaces
• The load is not moved during the whole process.
• Thermocouples can be fixed to the treated workpieces for visualization and documentation of
• Surface temperatures,
• Core temperatures,
• Temperature uniformity in the load and for controlling process like
• isostatic quenching (martempering)
• annealing with slow cooling.
• The process control is repeating a given program with high accuracy.
• The various processes can be programmed load by load.
• This is the background for the fact that single chamber vacuum furnaces are the most flexible
equipment in a heat treating shop.
• The flexibility enables even commercial heat treaters to reach 7500 production hours per year.
• The equipment is cheaper than double chamber furnaces
• Less and easier maintenance.
• Gas quenching
The traditional classification of quenching types of
• air quench
• warm bath (salt or fluidized bed)
• oil quench
• water quench
are obsolete since the latest vacuum furnaces cover all types except water quench. Click here to obtain more detailed
data about quenching of different diameter steel
parts at different media.
Practical and theoretical research during the last 30 years came to the result that the
following criteria have an influence to the quenching results:
• the kind of the quenching gas
• the pressure of the quenching gas
• the flow rate of the quenching gas
• the efficiency of the gas recooling
• the gas flow direction and turbulences
• shape and position of the workpieces.
Click here to compare heat transfer coefficients for different gas and cooling medium.
• Hydrogen and Safety
The heat transfer values on one side and the required fan motor capacities on the other indicate that hydrogen is the most interesting atmosphere for gas quenching.
The gas flow rate comes to limits, when the limits of the mechanical strength of the fan wheel are reached.
The quenching pressure comes to limits, when the needed motor power creates more heat by the gas circulation than the gas can transport to the heat exchanger.
This knowledge is not new, but the realization of vacuum furnaces with hydrogen quenching was blocked for many years due to safety reservations.
Fortunately hydrogen is harmless as long as it not mixed with oxygen. This has been used by Sistem Teknik to develop a safety package for vacuum furnaces by which oxygen cannot reach the area of hydrogen, and hydrogen cannot reach the area of oxygen, without being detected and eliminated before.
Special care has been given to the sealing and tightness-control of the loading door which therefore got the name “ Golden Door
®
”.
In addition to that, a HAZOP-study was made where the safety influence of all vacuum furnace components hardware, software, operating conditions, installation and documentation has been checked.
Safety experts from T Ü V-Rheinland Group contributes their knowledge of relevant regulations and industrial methods. A furnace prototype was constructed, tested and approved. The approval no. is TIE – 432 – ET 218 2005 T1.
• Low pressure carburizing
This technology developed during the last years very successfully and several ways are found to get good carburizing results even in blind holes.
The process cycles became shorter by operating in vacuum furnaces at higher temperatures.
By using acetylene or mixtures with other gases at low pressures also problems like soot and tar contamination of the furnace were solved so the key condition for this process remains to be the quenching rate.
As this condition is fulfilled in the furnaces with hydrogen quenching, these furnaces are predestinate for low pressure carburizing.
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