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Vacuum Heat Treatment Furnace

Vacuum Sintering Furnace

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Minimize deformation in high temperature vacuum

Vacuum heat treatment deformation will cause serious losses to the accuracy obtained in the early processing of the workpiece. These losses are sometimes difficult to recover even through complex and advanced modification techniques (gear grinding, alignment, etc.). This will directly affect the accuracy, strength, noise and vibration of the workpiece during operation, transmission power loss, and service life. In this way, even if we have the most advanced machine tools and grinders in the world, it will be difficult to process high-precision, high-value-added products.
Although vacuum heat treatment equipment is becoming more and more advanced, it is difficult for the temperature changes of various parts of the workpiece to be completely consistent when heating and cooling; the non-synchronous temperature changes of various parts of the workpiece during heating and cooling will cause thermal (expansion) stress in the workpiece and tissue (volume changes during transformation) stress changes. When thermal stress, organizational stress or the combination of the two is greater than the plastic resistance of a certain part of the workpiece at the instant temperature, irreversible deformation – vacuum heat treatment deformation – will occur in this part.
a) If the process temperature is reduced, the high-temperature strength loss of the workpiece is reduced and the plastic resistance is enhanced. In this way, the workpiece’s comprehensive ability to resist stress deformation and high temperature creep (the workpiece is deformed due to its own weight or pressure, especially large and thin-walled parts) will be enhanced and the deformation will be reduced.
b) If the process temperature is lowered, the temperature time for heating and cooling of the workpiece is reduced, and the temperature inconsistency of each part will also be reduced, resulting in thermal stress and tissue stress, which will also reduce deformation.
c) The vacuum heat treatment process time is shortened, the high-temperature creep time of the workpiece is reduced, and the deformation will also be reduced.
Methods to reduce vacuum heat treatment temperature
Lowering the process temperature and increasing the speed of vacuum carburizing or carbonitriding have always been the ideal goals pursued by people in the vacuum heat treatment community. However, due to the limitations of basic technical conditions and the constraints of traditional heat treatment theory, it has been difficult for everyone to break through for many years.
At present, a new vacuum carburizing technology has emerged. This technology can achieve rapid carburizing or ammonia co-carburizing when the process temperature is reduced by more than 40°C, and can reduce the vacuum carburizing temperature to a minimum of about 830°C. It also It also has the advantages of energy saving, environmental protection, high efficiency and high benefits.
The biggest factor affecting vacuum heat treatment deformation is the vacuum heat treatment process temperature:
1) After the process temperature is lowered, the high-temperature strength loss of the workpiece is relatively reduced, and the plastic resistance is enhanced. In this way, the workpiece’s comprehensive ability to resist stress deformation, quenching deformation, and high temperature creep is enhanced, and the deformation will be reduced.
2) After the process temperature is lowered, the temperature range for heating and cooling of the workpiece is reduced, and the resulting temperature inconsistency in various parts will also be reduced. The resulting thermal stress and tissue stress will also be relatively reduced, so that the deformation will be reduced.
3) If the process temperature is lowered and the vacuum heat treatment process time is shortened, the high-temperature creep time of the workpiece will be reduced and the deformation will also be reduced.
4) In order to ensure the final accuracy of the workpiece, a more ideal method is to find the vacuum heat treatment deformation law of the workpiece, and set aside a certain amount of deformation during processing, so that the size of the workpiece can migrate to the required size after vacuum carburizing and quenching. within the range. This requires the workpiece deformation to have good consistency, that is, the deformation rules and deformation ranges between workpieces in the same heat and between workpieces in different heats are close to the same.