Surface Treatment Technology and Wear Resistance Enhancement Solutions for Elastic Springs
What are the main types and influencing factors of surface wear of elastic bars?
The main types of surface wear of elastic bars include adhesive wear, abrasive wear and fatigue wear. Adhesive wear occurs at the contact part between the elastic bar and the gauge block. Due to wheel-rail vibration, the metal on the contact surface adheres, and then the adhesion points are torn to form wear marks. Abrasive wear is caused by hard particles such as sand and rust from the outside entering the contact interface. These particles will produce scratches on the surface of the elastic bar and accelerate the wear process. Fatigue wear is that under the action of long-term alternating load, micro-cracks are generated on the surface of the elastic bar, and the expansion of cracks leads to material peeling, forming pitting wear. The factors affecting wear mainly include contact pressure, vibration frequency and environmental conditions. The greater the contact pressure, the faster the wear rate. Excessively high preload of the elastic bar will increase the contact pressure; the faster the train operation speed, the higher the vibration frequency, and the more the number of wear cycles; the humid and dusty environment will aggravate abrasive wear and adhesive wear, shortening the service life of the elastic bar.
What are the core technical types and process points of elastic bar surface treatment?
The core technical types of elastic bar surface treatment include phosphating treatment, shot peening strengthening and dacromet treatment. Phosphating treatment is to immerse the elastic bar in phosphating solution to form a phosphate protective film on its surface. The film thickness is controlled at 5-10μm, the temperature of phosphating solution is 50-60℃, and the treatment time is 15-20 minutes. The phosphating film can enhance the wear resistance and rust resistance of the elastic bar and improve the adhesion of subsequent coatings. Shot peening strengthening is to impact the surface of the elastic bar with high-speed steel shots to generate residual compressive stress on the surface. The diameter of steel shots is 0.2-0.4mm, the shot peening intensity is 0.2-0.3A, and the coverage rate is ≥100%. The residual compressive stress can inhibit the initiation of fatigue cracks and improve the anti-fatigue wear performance of the elastic bar. Dacromet treatment is to immerse the elastic bar in dacromet coating solution, and form a zinc-aluminum coating after baking and curing. The zinc-aluminum powder content of the coating solution is ≥80%, the baking temperature is 300-350℃, the time is 30 minutes, and the coating thickness is 6-8μm, which has excellent corrosion resistance and wear resistance. The three processes should be carried out in sequence, first phosphating treatment, then shot peening strengthening, and finally dacromet treatment to ensure the optimal surface treatment effect.
What is the enhancement mechanism of phosphating treatment on the wear resistance of elastic bars?
The enhancement mechanism of phosphating treatment on the wear resistance of elastic bars is mainly reflected in two aspects: reducing friction coefficient and forming a protective barrier. The phosphating film is a porous crystal structure that can store lubricating oil, form an oil film at the contact interface between the elastic bar and the gauge block, reduce the friction coefficient from 0.3 to below 0.1, and reduce the occurrence of adhesive wear. The hardness of the phosphating film is higher than that of the elastic bar matrix, the Vickers hardness can reach 300-400HV, which can resist the scratching of hard particles and prevent the damage of abrasive wear to the matrix. The phosphating film can also isolate the contact between air, moisture and the elastic bar matrix, prevent the matrix from rusting, and avoid abrasive wear caused by rust particles. In addition, the phosphating film can enhance the roughness of the elastic bar surface, improve the effect of subsequent shot peening strengthening, make the depth of the residual compressive stress layer deeper and the distribution more uniform, and further improve the anti-fatigue wear performance of the elastic bar. Through phosphating treatment, the wear resistance life of the elastic bar can be extended by 20%-30%, meeting the use requirements of high-speed railways and heavy-haul railways.
What are the selection differences of surface treatment technologies for different types of elastic bars?
The selection differences of surface treatment technologies for different types of elastic bars are mainly determined by the material and application scenario of the elastic bar. The W-type elastic bar used in high-speed railways is made of 55SiCrA with high elastic modulus and large preload, and needs to adopt phosphating + shot peening + dacromet composite treatment technology to ensure that the wear resistance and fatigue resistance meet the standards and adapt to the service environment of high-frequency vibration. The Ω-type elastic bar used in heavy-haul railways has strong bearing capacity and large contact pressure, and needs to add hard anodizing treatment on the basis of composite treatment technology. The thickness of the anodized film is ≥10μm, the hardness is ≥500HV, which further improves the anti-abrasive wear performance. The E-type elastic bar used in ordinary-speed railways has a relatively mild service environment, and can adopt phosphating + shot peening simplified treatment technology to reduce production costs and meet basic wear resistance requirements. Due to frequent starts and stops and large vibration impacts, the elastic bars used in urban rail transit need to adopt shot peening + electrophoretic coating treatment technology. The adhesion of the electrophoretic coating is ≥4MPa, and the impact resistance is ≥50kg·cm, adapting to the complex operating environment.
What are the detection methods and acceptance standards for the surface treatment quality of elastic bars?
The detection methods for the surface treatment quality of elastic bars include appearance inspection, film thickness inspection and performance inspection. The appearance inspection adopts the visual method, requiring the treatment layer on the surface of the elastic bar to be uniform and continuous, without missing coating, peeling, spalling and other defects. The phosphating film is gray or black, and the dacromet coating is silver-gray. The film thickness inspection adopts an eddy current thickness gauge. The phosphating film thickness is 5-10μm, the dacromet coating thickness is 6-8μm, the anodized film thickness is ≥10μm, and the thickness deviation is ≤±1μm. Performance testing includes friction coefficient test, salt spray test and fatigue wear test. The friction coefficient should be ≤0.1, the salt spray test corrosion resistance time is ≥1000 hours, and the fatigue wear test requires that the elastic bar has no obvious wear under 1×10⁷ cycles of alternating load. The acceptance standard is based on TB/T 3395-2015. The qualification rate of appearance inspection should be 100%, and the qualification rate of film thickness and performance inspection should be ≥98%. Unqualified elastic bars need to be re-surface treated until they meet the standards.