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Safety techniques for chemical heat treatment equipment. Chemical heat treatment of steel parts involves placing the parts in various chemically active media, heating them at specific process temperatures and maintaining that temperature, thereby allowing chemical elements to penetrate into the surface layer of the parts. This process alters the chemical composition and structure of the surface layer, enabling the attainment of the desired surface properties. There are many methods of chemical heat treatment; below is a brief introduction only to gas chemical heat treatment and liquid chemical heat treatment, which are widely used in current production, as well as the safety techniques employed in glow discharge ion nitriding. I. Safety technologies for gas chemical heat treatment equipment Gas chemical heat treatment equipment mainly includes shaft furnaces, periodic multi-purpose furnaces, and connected through-type muffle furnaces. It can be used for gas carburizing, nitriding, soft nitriding, and cyaniding. The penetrants used include: methanol, ethanol, kerosene, propane, triacetamide, urea, ammonia, endothermic atmospheres, natural gas, city gas, etc. In addition to being familiar with the performance of the equipment and the safety operating procedures, operators should also understand the properties of the chemical substances used, as well as their safe handling and storage. They need to be aware of the decomposition products resulting from these chemicals during chemical heat treatment processes, and of their impact on the surrounding environment. The waste gases generated in gas chemical heat treatment must be ignited, as they generally contain substances such as carbon monoxide, hydrocyanic acid, ammonia, and unsaturated hydrocarbons, which can be decomposed after ignition. For example, during gas soft nitridation, the HCN concentration in the furnace is 6–8 mg/m³; after the exhaust gases are ignited, the HCN level in the working environment drops to only 0–0.08 mg/m³, which is below the permitted limit of 0.3 mg/m³. The waste gas from gas nitridation contains some unreacted NH3, and passing this waste gas through water can reduce pollution. When chemical heat treatment is carried out using a liquid penetrant, the amount of penetrant added must be strictly controlled in accordance with the process requirements. During the heating phase, if an excessive amount of liquid is poured into the furnace, it will rapidly vaporize at higher temperatures, causing the furnace pressure to increase quickly. At this point, the titrator valve should be closed immediately, and the vent valve should be opened to allow the furnace pressure to drop naturally. Under no circumstances should one rush to open the furnace door when the pressure inside rises, as this would cause a large amount of flammable gas in the furnace to mix suddenly with air, leading to an explosion. In severe cases, it can cause the furnace lid and door to fly out continuously, damaging the equipment and endangering the lives of the operators. II. Safety Techniques for Liquid Chemical Heat Treatment Equipment Liquid chemical heat treatment refers to processes such as soft nitriding, cyaniding, sulfur-nitrogen diffusion, and metal infiltration carried out in chemically active liquid media. When operating, attention must be paid not only to the safe operation of the heat treatment furnace but also to the toxic substances used, as well as the issues related to the generation of toxic gases, waste liquids, and waste residues. The following focuses on the safety technologies for liquid cyanide bath furnaces. 1. Operators must strictly follow the operating procedures for cyanide bath furnaces and carry out the liquid cyanidation process with great care. 2. It is necessary to strengthen the storage of chemical substances and strictly implement a system for their classified storage. For highly toxic cyanides, the rule of two persons, two locks, and two approvals must be strictly enforced. Provided by Xueyi* Network 3. When operating a cyanide bath furnace, it is necessary to wear a mask and protective goggles (or face shield), appropriate protective clothing, and gloves. Take it off as soon as the work is done. These protective gear items must not be taken outside the workplace, and they should be cleaned twice regularly with a 10% sulfurous ferrous solution. It is not allowed to drink, eat, smoke, or store food in the workplace. Good ventilation and lighting are necessary in areas where cyanides are used; exhaust fans should be installed on all equipment to prevent cyanide dust and vapors from spreading and contaminating the working environment. 4. Parts made of liquid cyanide must be dried before being placed in the furnace; otherwise, the molten salt will explode and splash when it comes into contact with water, which can cause skin burns. In such cases, it should be immediately washed with 10% ferrous sulfate solution, followed by rinsing with clean water, and then taken to a medical facility for treatment. 5. The waste residues, wastewater, and dust generated during the cyanidation process must be handled carefully; they shall not be piled up or discharged arbitrarily. Waste residues and dust can be collected, neutralized with ferrous sulfate, and then disposed of properly. Wastewater can be treated by alkaline oxidation to convert cyanide into harmless carbon dioxide and nitrogen. Before discharge, samples must be taken to test for cyanide levels; discharge is allowed only if the levels are within acceptable limits. III. Safety Techniques for Glow Ion Nitriding Equipment Glow ion nitriding is a heat treatment technique that has seen rapid development in recent years. The furnace of the glow ion nitriding equipment is a vacuum vessel; under a certain level of vacuum (L33×10<sup>-2</sup> Pa) and a high-voltage direct current field (100–1000 V), a small amount of nitriding atmosphere is introduced. This causes the nitrogen atoms to become ionized, and under the influence of the electric field, these ionized atoms strike the surface of the workpiece at high speed, resulting in a glow discharge. This process raises the surface temperature of the workpiece to the necessary level for ion nitriding, allowing nitrogen atoms to penetrate into the workpiece’s surface. Compared with gas-phase nitridation, the ion nitridation process offers advantages such as higher production efficiency, less deformation, lower costs, and reduced pollution. When designing and manufacturing equipment, attention should be paid to the high-voltage insulation issue between the equipment’s anode and cathode. Since the equipment enclosure serves as the anode of the high-voltage direct current, it must be properly grounded. The cathode terminal to which the workpiece is attached in the equipment must have an insulation resistance to ground that is checked using a 1000V insulation tester; this insulation resistance must be no less than 20MΩ. In electrical circuits, protective devices must be present to ensure that high-voltage direct current is automatically disconnected when the vacuum chamber is opened. The facility housing the glow discharge ion nitriding equipment should be well-lit and well-ventilated; it must remain clean, tidy, dry, and free of debris. The following points must be observed during operation: 1. The ion nitriding equipment must have at least two operators before it can be started up, and a designated operator in charge must be appointed. The operator must be familiar with and comply with the safety operating procedures for ion nitriding equipment. 2. The workpiece must be thoroughly cleaned to remove burrs, iron shavings, and oil stains. 3. Operations must not be carried out under a vacuum chamber when reliable safety measures are in place. The vacuum chamber should be lowered smoothly, and the workpiece placed on the cathode base plate should be secured firmly. 4. The safety procedures for the use of gas nitriding and ammonia cylinders must be followed. When the vacuum pump is evacuating, the exhaust gas should be directed outside.