I. Introduction
Precision hardware parts play a crucial role in numerous fields such as electronics, machinery, aerospace, etc. However, the problem of oxidation and rusting seriously threatens their performance, reliability, and service life. For example, in electronic devices, rusting of precision hardware connectors may lead to poor contact and cause equipment failures; in the aerospace field, rusting of components is even related to flight safety. A thorough analysis of this problem and exploration of effective solutions are of far-reaching significance for improving product quality, reducing maintenance costs, and ensuring the stable operation of systems.
II. Principles of Oxidation and Rusting
2.1 Electrochemical Corrosion
This is the main form of corrosion for precision hardware parts. When hardware parts are in a humid environment, a thin water film is adsorbed on their surface, which dissolves oxygen, carbon dioxide, etc. in the air to form an electrolyte solution. At this time, different metal components in the hardware parts or different parts of the same metal form numerous tiny galvanic cells due to differences in electrode potential. Taking iron-based metals as an example, iron acts as the anode and loses electrons in an oxidation reaction: Fe - 2e⁻= Fe²⁺; while the cathode undergoes a reduction reaction. For instance, in weakly acidic or neutral conditions, oxygen gains electrons and reacts with water to form hydroxide ions: O₂+ 2H₂O + 4e⁻ = 4OH⁻. Ferrous ions further combine with hydroxide ions to form ferrous hydroxide, which is gradually oxidized to ferric hydroxide in the air, i.e., the common rust.
2.2 Chemical Corrosion
In specific environments, hardware parts are directly corroded by chemical reactions with surrounding media. For example, in high-temperature environments, metals react with oxygen to form metal oxides. In sulfur-containing environments, metals may react with sulfides such as hydrogen sulfide to form metal sulfides. The rate of chemical corrosion is usually closely related to factors such as temperature and medium concentration. The higher the temperature and the greater the medium concentration, the faster the corrosion rate.
2.3 Stress Corrosion
When precision hardware parts are subjected to a certain tensile stress and are in a specific corrosive environment, stress corrosion cracking will occur. The existence of stress increases the activity of atoms on the metal surface, accelerates the corrosion reaction, and at the same time, the cracks generated by corrosion continue to expand under the action of stress, eventually leading to the fracture of the material. This kind of corrosion is highly concealed, and often, there are serious crack defects inside the material without obvious signs of surface corrosion.
III. Influencing Factors
3.1 Environmental Factors
3.1.1 Humidity
Humidity is one of the key factors affecting the rusting of hardware parts. When the relative humidity of the environment exceeds 60%, an imperceptible water film will form on the metal surface, providing the necessary electrolyte conditions for electrochemical corrosion. In high-humidity environments such as coastal areas and the plum rain season, the rusting rate of precision hardware parts accelerates significantly.
3.1.2 Temperature
Increasing temperature accelerates the rate of chemical reactions, including oxidation and rusting reactions. On the one hand, increasing temperature speeds up the migration of ions in the electrolyte solution, promoting charge transfer in the galvanic cell reaction; on the other hand, high temperature may cause the performance of the protective film (such as a passive film) on the metal surface to decline or even be damaged, making the metal more susceptible to corrosion.
3.1.3 Corrosive Gases
Corrosive gases such as sulfur dioxide, nitrogen oxides, and hydrogen chloride in industrial waste gas, as well as salt in the air in coastal areas, will aggravate the corrosion of precision hardware parts. When these gases dissolve in the water film, they will increase the acidity of the electrolyte solution and accelerate the dissolution of metals. For example, sulfur dioxide is oxidized to sulfur trioxide in the air, which then reacts with water to form sulfuric acid, which is highly corrosive to metals.
3.2 Material Factors
3.2.1 Metal Composition
Different metals have great differences in chemical activity, and their corrosion resistance is also completely different. Among common metals, iron, zinc, etc. are relatively active and prone to oxidation reactions and rusting; while precious metals such as gold and platinum have strong corrosion resistance. For alloys, their composition and proportion directly affect their corrosion resistance. For example, stainless steel contains alloying elements such as chromium and nickel. Chromium can form a dense passive film (Cr₂O₃) on the metal surface, effectively preventing the erosion of oxygen and water and improving the corrosion resistance of stainless steel. However, if the alloy composition is unqualified or the proportion is improper, the passive film may not form effectively, thereby reducing the corrosion resistance.
3.2.2 Microstructure
The microstructure of metals, such as grain size, grain boundary distribution, and dislocation density, also has an important impact on their corrosion behavior. Generally speaking, metals with fine grains have higher corrosion resistance because the increased grain boundary area makes the diffusion path of corrosive media at grain boundaries longer, hindering the progress of corrosion. In addition, defects inside the metal (such as pores, inclusions, etc.) will become the starting points of corrosion and accelerate the development of corrosion.
3.3 Processing and Usage Factors
3.3.1 Processing Technology
In the processing process of precision hardware parts, such as machining, heat treatment, surface treatment, etc., improper selection of process parameters may have an adverse impact on the performance and surface state of the metal, thereby affecting its corrosion resistance. For example, residual stress generated during machining may cause stress corrosion cracking; excessive heat treatment temperature or too long time may lead to coarse metal structure and reduce corrosion resistance; if the surface treatment is not thorough, an effective protective film cannot be formed, which will also make the hardware parts susceptible to corrosion.
3.3.2 Usage Conditions
The type, size, and frequency of loads borne by hardware parts during use, as well as whether they are subjected to friction, impact, etc., will affect their corrosion behavior. Hardware parts that bear alternating loads for a long time are prone to fatigue cracks in stress concentration areas. These cracks provide channels for the intrusion of corrosive media and accelerate the corrosion process. At the same time, friction will damage the protective film on the metal surface, exposing fresh metal to the corrosive environment and increasing the risk of corrosion.
IV. Analysis of Existing Problems
4.1 Problems in the Cleaning Process
4.1.1 Improper Selection of Cleaning Agents
Some enterprises choose inappropriate cleaning agents when cleaning precision hardware parts to reduce costs or due to lack of professional knowledge. Some cleaning agents may contain corrosive components such as chloride ions and sulfate ions. If they remain on the surface of hardware parts after cleaning, they will react chemically with the metal and cause corrosion. For example, using chlorine-containing cleaning agents to clean stainless steel parts, chloride ions will damage the passive film on the surface of stainless steel, leading to pitting corrosion.
4.1.2 Imperfect Cleaning Process
Insufficient cleaning time, inappropriate temperature, unreasonable cleaning methods, etc., may lead to incomplete cleaning. Oil, impurities, etc. remaining on the surface of hardware parts not only affect the effect of subsequent surface treatment but also form corrosion microcells in a humid environment, accelerating rusting. In addition, excessive cleaning or the use of inappropriate cleaning methods, such as high-pressure water gun flushing, may damage the surface of hardware parts, destroy their original protective film, and increase the risk of rusting.
4.2 Insufficient Protective Measures
4.2.1 Poor Quality of Anti-rust Coatings
When some enterprises apply anti-rust coatings on the surface of hardware parts, due to improper process control, such as uneven coating thickness, poor adhesion, and pinholes, they cannot effectively isolate corrosive media, resulting in a greatly reduced anti-rust effect. At the same time, if the selected anti-rust coating material is not suitable for the service environment of the hardware parts, it is also difficult to play its due protective role. For example, in high-temperature and high-humidity environments, ordinary oil-based anti-rust paint may blister and fall off, losing its anti-rust function.
4.2.2 Inadequate Packaging Protection
Packaging protection is crucial during the storage and transportation of hardware parts. If the packaging materials do not have moisture-proof and anti-rust properties, or the packaging method is unreasonable, causing hardware parts to collide and rub against each other during transportation, damaging the surface protective layer, it is easy to cause rusting. For example, using ordinary cartons to package precision hardware parts, in a humid environment, cartons are easy to absorb moisture, making the hardware parts in a high-humidity environment and accelerating rusting.
4.3 Lack of Quality Inspection and Maintenance
4.3.1 Lack of Effective Quality Inspection Means
Many enterprises lack effective testing methods for the corrosion resistance of precision hardware parts in the production process. Relying solely on visual inspection cannot find internal micro-defects and potential corrosion hazards. Some advanced testing technologies, such as metallographic analysis, salt spray test, electrochemical test, etc., have not been widely used, making it difficult to detect and solve quality problems in the early stage.
4.3.2 Neglect of Daily Maintenance
For precision hardware parts in use, some users neglect daily maintenance work. They do not clean and inspect the hardware parts regularly, and fail to find and deal with slight rusting problems in time, which makes the rusting gradually worsen, eventually affecting the performance and service life of the hardware parts. For example, in mechanical equipment, some key precision hardware connectors, if not maintained for a long time, may cause equipment failure and affect production once rusting occurs.
V. Solutions
5.1 Optimizing the Cleaning Process
5.1.1 Selecting Appropriate Cleaning Agents
According to the material of hardware parts, the type of surface pollutants, and cleaning requirements, select special cleaning agents with no corrosiveness and strong decontamination ability. Before selection, the cleaning agents should be strictly tested and trial-used in small batches to ensure that they will not cause corrosion or residue on the hardware parts. For example, for aluminum alloy precision parts, weakly alkaline special cleaning agents for aluminum alloys can be selected, which can effectively remove oil and impurities without corroding the surface of aluminum alloys.
5.1.2 Improving the Cleaning Process
Formulate a scientific and reasonable cleaning process, and strictly control parameters such as cleaning time, temperature, and pressure. For hardware parts with complex shapes, blind holes, or inner cavities, combined cleaning methods such as ultrasonic cleaning and multi-step cleaning should be adopted to ensure thorough cleaning. At the same time, strengthen the rinsing and drying links after cleaning, use deionized water for rinsing to remove residual cleaning agents and impurities, and adopt hot air drying, vacuum drying, etc. to ensure that the surface of hardware parts is completely dry and avoid water residue.
5.2 Strengthening Protective Measures
5.2.1 Improving the Quality of Anti-rust Coatings
Adopt advanced coating processes such as electrostatic spraying and electrophoretic coating to ensure that the anti-rust coating has uniform thickness, strong adhesion, and no defects. When selecting anti-rust coating materials, fully consider the service environment and performance requirements of hardware parts, and choose materials with good weather resistance and corrosion resistance. For example, for precision hardware parts used outdoors, fluorocarbon coatings can be selected, which have excellent UV resistance and acid-alkali resistance and can effectively extend the service life of hardware parts.
5.2.2 Improving Packaging Protection
Select packaging materials with good moisture-proof and anti-rust properties, such as vapor-phase anti-rust paper and anti-rust plastic bags, to package precision hardware parts individually. During the packaging process, add an appropriate amount of desiccant to reduce the humidity inside the package. At the same time, reasonably design the packaging structure to avoid collision and friction of hardware parts during transportation. For hardware parts transported over long distances or stored for a long time, vacuum packaging or nitrogen-filled packaging can also be used to further isolate oxygen and moisture.
5.3 Establishing a Quality Inspection and Maintenance System
5.3.1 Implementing Comprehensive Quality Inspection
Introduce advanced quality inspection equipment and technologies to conduct all-round inspections on the raw materials, processing processes, and finished products of precision hardware parts. In the raw material stage, ensure that the metal composition and microstructure meet the requirements through means such as spectral analysis and metallographic testing; in the processing process, conduct online inspections on key processes, such as film thickness testing and adhesion testing on hardware parts after surface treatment; in the finished product stage, conduct durability tests simulating the actual service environment, such as salt spray test and damp-heat test, to evaluate the corrosion resistance of hardware parts.
5.3.2 Strengthening Daily Maintenance
Formulate a detailed maintenance plan for hardware parts, and regularly clean, inspect, and maintain precision hardware parts in use. Timely remove dirt, dust, and rust on the surface, and adopt appropriate methods to repair minor rusting problems found, such as local treatment with anti-rust agents. At the same time, monitor the operating status of hardware parts, such as through vibration analysis and temperature monitoring, to timely find potential fault hazards and take preventive measures in advance.
VI. Conclusion
The oxidation and rusting of precision hardware parts are caused by the combined action of various factors, which seriously affect their performance and service life. By deeply understanding the principles of oxidation and rusting, analyzing the influencing factors in the environment, material, processing, and usage, and aiming at the existing problems in cleaning, protection, quality inspection, and maintenance, a series of solutions such as optimizing the cleaning process, strengthening protective measures, and establishing a quality inspection and maintenance system can effectively reduce the risk of oxidation and rusting of precision hardware parts, improve product quality and reliability, and provide a strong guarantee for the stable development of related industries. In practical applications, enterprises should comprehensively use these solutions according to their own product characteristics and service environment, and continuously carry out technological innovation and improvement to cope with the increasingly complex corrosion challenges.
