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Requirements for deep carburizing on heat treatment equipment

1.Temperature control method

The following briefly introduces the difference between the main control method in the furnace and the temperature control method outside the furnace, and the effect of realizing the main control in the furnace on the carburizing quality during deep carburizing.

The main control in the furnace refers to a temperature control method that automatically adjusts the power of each heating zone by the difference between the temperature detected by the furnace cover thermocouple and the target temperature through a reasonable mathematical model, thereby controlling the furnace temperature. .

The advantage of this control method is that the furnace temperature can be controlled more precisely, the deviation of the furnace temperature can be reduced, and the reliability of the furnace temperature can be significantly improved.

The previous view holds that when thermal equilibrium is reached, there is a fixed temperature difference inside and outside the furnace, namely:

T inside = T outside – △T

Inside T——the temperature in the furnace;

Outside T—— the temperature outside the furnace;

△T——constant temperature difference.

According to this point of view, the method of temperature control outside the furnace is adopted. When the temperature outside the furnace is a constant value, the temperature inside the furnace should also be a constant value. For example, assuming that the deviation ΔT inside and outside the furnace is 20°C, when we want to carburize at 930°C (that is, T=930°C), we only need to control the temperature outside the furnace (outside T) to 950°C. We think this view is unrealistic.

Practice has proved that the temperature difference inside and outside the furnace is constantly changing with the extension of holding time, that is, △T in the formula is a function of holding time: △T=f (T guarantee)

According to this inference, we can predict that with the passage of holding time, the temperature difference inside and outside the furnace is constantly changing, and controlling the temperature outside the furnace can no longer ensure that the deviation of the temperature inside the furnace is within the range of process requirements. Therefore, the furnace temperature may be too high during carburizing, the austenite grains will grow, and the martensite structure of the workpiece will be coarse after quenching, thereby affecting the performance of the workpiece.

Another advantage of using the main control method of the furnace cover to control the furnace temperature is that it can significantly improve the reliability of the equipment during operation. This is mainly manifested in: when the thermocouple of a heating zone has a large deviation or damage, it can be directly judged by the temperature deviation between each heating zone displayed by the instrument and the main control thermocouple. For the temperature control outside the furnace, it is often necessary to judge the temperature in the temperature calibration or according to the speed of the heating speed, which not only requires rich practical experience, but also cannot find problems in time.

2.How to control carbon potential

Common carburizing equipment often relies on controlling the on-off of the solenoid valve to intervene in the dripping or stopping of the enrichment agent to realize the adjustment of the carburizing carburizing potential.

Because the formation of carbon potential requires a process, and this process often causes a delay in the adjustment of carbon potential. Therefore, using this adjustment method can easily cause the carbon potential to overshoot or be too low within a certain period of time, which affects the quality of carburizing.

The continuous control of carbon potential includes two aspects: one is to realize the continuous dripping of enrichment agent in different proportions through the continuous adjustment of the proportional valve; the other is to realize the continuous injection of air in different proportions through the continuous adjustment of the proportional valve.

This carbon potential control method can effectively avoid the phenomenon of carbon potential overshoot or too low caused by the on-off control of the carbon potential, thereby ensuring that the deviation of the carbon potential in the furnace is within a relatively small range.

Practice has proved that the carbon potential deviation can be controlled within ±0.02 % Cp by using large-scale carburizing equipment controlled by continuous carbon potential

3.Application of nitrogen-methanol atmosphere in deep carburizing

Compared with other endothermic atmospheres, nitrogen-methanol atmosphere is gradually accepted by more heat treatment manufacturers because of its high safety and good anti-grain boundary oxidation ability in addition to uniform carbon potential in the furnace. and attention.

The special application of nitrogen-methanol atmosphere in deep carburizing is introduced here, that is, the CO in the gas building is involved in the calculation of carbon potential.

The characteristic of this control method is to use the oxygen probe or L-probe to control the carbon potential, and CO participates in the calculation, so as to achieve the best effect of carbon potential control.

4.Summary

Based on the above points, we believe that the heat treatment carburizing equipment adopts the furnace cover thermocouple to control the temperature, nitrogen-methanol atmosphere carburizing, and adjusts the carbon potential in the furnace by continuously proportionally adjusting the quality of the deep carburizing of carburized steel. Clearly positive effect.

Selection of heat treatment equipment: GH-GCF series gas carburizing furnaces and RVC series vacuum carburizing furnaces produced by SIMUWU are high-quality products for vacuum heat treatment of tools and molds. Good temperature control accuracy and uniformity ensure the vacuum heat treatment process. of effective conduct.