Control of pressure in ion nitriding based on L298N chip

Abstract: The ion nitriding process requires precise control of the pressure within the furnace. This paper presents a gas flow controller designed using the L298N chip to drive a DC motor, which is used to regulate the pumping gas flow rate in the reaction furnace, thereby improving the accuracy of pressure control and reducing production costs.

1. Ion Nitriding Theory Ion nitriding takes place in a low-temperature plasma environment. A low-pressure gas is ionized by an electric field, generating high-energy ions and neutral atoms. These particles enhance the microstructure of the surface layer and promote chemical reactions, accelerating the formation of the nitrided layer. The process occurs through a glow discharge. During ion nitriding, the pressure inside the furnace must be controlled with high precision, typically within a deviation of tens of Pascals. According to Paschen’s Law:

Where: - P is the gas pressure, - d is the distance between parallel plate electrodes, - V is the cathode secondary electron emission coefficient, - B is the Stolz constant, - A is a constant. From equation (1), we derive the breakdown voltage expression (2):

It can be observed from equation (2) that the breakdown voltage depends on both the gas pressure and the electrode distance. Since d is generally fixed in experiments, accurate pressure control becomes crucial for successful ion nitriding. 2. System Flow and Pressure Measurement and Control Block Diagram A flow meter is used to regulate the gas flow at the inlet. When the inflow and outflow rates are balanced, the furnace pressure remains stable. However, due to gas leakage and other disturbances, the pressure may fluctuate, causing the system to deviate from equilibrium and affecting plasma processing. To address this, a common DC motor is driven by the L298N chip, which controls the rotation of a cone via a gear mechanism. As the cone rotates, it adjusts the amount of gas being extracted, allowing the furnace pressure to be maintained at a desired level. The pressure changes are monitored by a pressure sensor, which sends feedback to the gas flow controller. Instead of using an expensive electric vacuum butterfly valve, the system employs a simpler and more cost-effective approach. Figure 1 illustrates the overall system block diagram.

Figure 1: System flow and pressure measurement and control block diagram

3. Introduction to the L298N Chip

Figure 2: Internal function modules of the L298N chip

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