Railroad tie plate for rail construction
The usage of railroad tie plate:
The railroad tie plate between rail and sleeper is one of the important parts in the track structure and plays an important role in the damping of the wheel-rail power system.With the development of heavy-haul railway transportation, axle load is increasing day by day. While the rail is gradually becoming heavier, higher requirements are put forward for the performance of the railroad tie plate, so as to obtain good vibration reduction performance, impact resistance and long service life of the backing plate.
Technological evolution of iron plate
With the increasing speed of the train, the stability requirements of the railway line are gradually improved, and the railway track pad has undergone four improvements.The initial use of steel plate welding pad, due to the presence of welding seam and the integrity of the plate is not high, and the presence of welding seam makes the mechanical properties of the plate weakened.Due to its good integrity and high mechanical properties, the section forging tie plate finally replaces the welded backing plate.However, due to the cost of plate is larger and the corrosion is serious.People gradually and now into the deformation of small, low - cost malleable iron plate.Since the production of malleable cast iron is obtained by the malleable annealing of cast iron, compared with the production process of casting obtained directly under the as-cast condition, this production method prolongs the production cycle and increases the production cost.Since its appearance, ductile iron has attracted much attention due to its excellent mechanical properties and good casting properties, and iron ductile iron tie plate that can be used in the casting state is the best choice to replace malleable iron backing plate.Ferrite nodular cast iron has been used in the manufacture of railway fittings for its strong anti-vibration and anti-impact ability, such as the subway line fittings, fast track fittings, type embedded iron seat, passenger dedicated railway and so on.In order to meet the needs of railway production, our factory has developed ductile iron.Based on the literature review and the study of the production process, we finally produced ferrite nodular cast iron that can be used in the as-cast state by the method of secondary inoculation and control of the amount of final silicon.
Production technology of iron backing plate and cases of problem elimination
Our factory adopts the method of vanishing mould to produce the castings of the underrail iron plate for the railway department. The castings of the railway cast iron plate are prone to fracture when subjected to impact after the casting state and annealing treatment, resulting in a large number of unqualified products and high rejection rate.We analyzed the causes of this defect and found that the main reason for the defect was the failure of the heat treatment equipment and the low heat treatment temperature.In view of this reason, the corresponding measures are put forward, and the defective castings are completely eliminated by heat treatment.
1. Production conditions of iron pad
The railway cast iron backing plate is produced by the vanishing mold method and smelted in 60kg intermediate frequency electric furnace. The vacuum degree during pouring is kept at 0.03mpa and the pouring temperature is 1580℃.Its chemical composition W was 0.46%C,0.23%Si,0.59%Mn,0.015%S and 0.024%P.After the casting is packed, it is cleaned by shot peening and then annealed.Heat treatment process: heating temperature 850℃;The holding time was 2h and cooled with the furnace to room temperature (12h in total).
2. Microstructure analysis of the fracture of iron backing plate
Bulk sampling was adopted, and the castings in the as-cast state and after heat treatment were cut open with a line cutting machine, respectively. Several 10mm×15mm metallographic samples were cut from the middle and prepared.Metallographic structure was observed by metallographic microscope.As - cast microstructure.It can be seen that the as-cast structure of iron plate casting is ferrite + pearlite + Wetenite.The wetensitic structure is in a continuous network, and a small amount of acicular Wetensitic extends into the grain.The results show that when the carbon content of cast carbon steel is more than 0.3% and the grain size is large, the weinberg structure will be formed.The main factors affecting the formation of Weissner microstructure include: austenite grain size, cooling rate and chemical composition.Therefore, normalizing or annealing heat treatment must be adopted to improve the impact resistance of plate castings.The original annealing heat treatment in this factory is the microstructure of the plate castings after annealing treatment.It can be concluded that annealing treatment did not eliminate a large number of strip Wetenite.Therefore, the existence of a large number of strip Wetensists leads to the fracture of the plate castings under impact after annealing treatment.After careful inspection of annealing equipment, it was found that the sealing performance of annealing furnace door was poor, the temperature-control instrument of annealing furnace had been damaged, and the temperature control was all judged by experience, resulting in that the furnace temperature could not meet the technological requirements;Not strictly follow the operation specifications, casting insulation temperature can not meet the process requirements.
3, iron plate production process improvement
According to the above analysis results, the improvement measures are put forward: repair the annealing equipment again, improve the sealing performance of annealing furnace door, and ensure that the temperature in furnace meets the technological requirements.After rectification, the original annealing process was still carried out, and the unqualified castings were reheat treated. After metallography inspection, it was found that there was no large amount of strip Wetensitic in the annealed iron plate castings.The results of impact test show that the quality problem of fracture is easy to occur when subjected to impact.Due to the simple structure of this part, in order to simplify the process, shorten the production cycle, improve the production efficiency and reduce the cost, according to the shape and structure characteristics of the casting, the normalizing process is adopted. The specifications are as follows: heating temperature 850℃;Heat for 1h and cool to room temperature.After adopting the normalizing process, the castings of iron plate do not break under the same impact.The production cycle is shortened, the production efficiency is improved and the cost is reduced.
Four, iron plate production quality assurance
Alex kunshan iron plate production attaches great importance to quality control and management.Our steel plate production is completely controlled by the material ISO9001-2008 quality system and we have obtained the railway product production license from the Ministry of Railways of China.We have a complete set of testing equipment to ensure the quality of all our iron plate products to meet customer requirements.
Kunshan Alex Railway Accessories Co., LTD. Is an ISO 9001/2008 certified company.All processes are in accordance with the REQUIREMENTS of ISO quality management system. From supplier quality control to finished products, we operate in accordance with standard procedures. We have a strict quality control system for suppliers:
1. For the inspection and testing of raw materials, we require the supplier to provide the production batch number, chemical composition, mechanical properties and other testing indicators.
2. Our quality control inspectors take sample sampling and batch testing and provide material material certificate for control during the testing process.
3. According to the different requirements of the products, we make corresponding physical and chemical tests and inspections.If the results do not meet our requirements, we will refuse to accept, only if the material meets our standards.
4. For semi-finished products and their outsourcing manufacturers, we often organize quality control coordination meetings, and provide technical support and guidance.Guarantee the delivery of qualified products to our customers before shipment.