Current Status Of Roulette Cast Iron Parts Casting Process
Roulette cast iron parts refer to a type of castings whose diameter is much larger than the height. Generally, the processing requirements of the intermediate shaft hole are relatively high, the hub and the rim are thicker, and the wall at the spoke is thin, which easily causes uneven temperature and large temperature difference. The hub and the rim are two hot spots. If the casting process is unreasonable, the casting is prone to shrinkage cavity, shrinkage porosity and crack defects. At present, most domestic manufacturers produce roulette castings using ordinary clay sand molding, single-piece casting, tangential gate injection, and riser feeding or casting methods used in conjunction with chilled iron at the hub. This method occupies a large space, the process yield, yield and production efficiency are low, and the surface quality of the casting is poor.
After we received the production task of roulette-type iron castings-cooling bed rollers (more than 5700 pieces), the first problem to be solved is the research of the casting process. The process is required to be simple, so that workers who are not familiar with casting can operate. It is required to reduce the molding and pouring area, and meet the production needs under the existing production conditions. When studying the casting process, we encountered material problems again. The roll plate made was very brittle and could not be used in production at all. Through the research on the casting process and material of the casting, a new type of casting process for roulette cast iron parts was researched, and qualified rollers were produced.
Main Research Contents And Key Technologies
1.Material research
Roller plate is one of the key components of cooling bed equipment. It requires good surface quality and high heat resistance. The heat resistance of cast iron depends mainly on its high temperature oxidation resistance (that is, whether the oxide film formed on the surface of the cast iron has Protective effect) and the growth of cast iron (that is, the irreversible expansion of the size of cast iron parts that work at high temperatures). These two properties are closely related to the chemical composition of cast iron. The strength and impact resistance of iron castings mainly depend on the number of alloying elements, so the study of the material of the castings becomes a very important issue. For this reason, we have conducted research on the material and made a reasonable choice of chemical composition, which not only improves the heat resistance of the casting, but also ensures the mechanical properties of the casting. The original design material of the roller is RQTSi5, and its chemical composition (%) is: wC = 2.30% ~ 2.89%, wSi = 4. 5% ~ 5.5%, wMn = 0.50% ~ 0.77%, wP = 0.06% ~ 0.09%, wS＝0.062%～0.089%, wCr＝0.38%～0.49%. Its mechanical properties are as follows: tensile strength 140-220MPa, hardness 160-270 HBW. The maximum operating temperature is 750～900℃. Due to the high silicon content of this material, the brittle transition temperature of cast iron is increased. Therefore, the casting is very brittle, and it is not suitable for the production of brittle-sensitive parts with uneven wall thickness. The roller plate belongs to the casting of this structure. As a result, the production has just started. At that time, a lot of waste products were caused by material problems. In addition, because the material of RQTSi5 is brittle and the yield is low, most domestic manufacturers no longer use this material to make rollers. In view of the above situation, in order to avoid batch scrapping of roll plates and ensure the smooth start of the medium and heavy plate project, trial production of an emerging material for the production of roll plates has become a top priority. Through many experiments and demonstrations, we have decided to use the new material we developed. Its chemical composition is: wC=3.05%～3.51%, wSi=2.9%～3.5%, wMn=0.24%～0.56%, wP＝0.05%～ 0.09%, wS=0.010%～0.030%, wMo=0.29%～0.6%. Its mechanical properties are as follows: tensile strength 580～695MPa, elongation 8%～18%, hardness 210～280 HBW. The maximum operating temperature is 750～900℃. Due to the good properties of the materials developed and the high yield rate, it has been recognized by users.
After the material was determined, the material ingredients, spheroidization process, inoculant and inoculation process, quality control in front of the furnace, etc. were tackled and succeeded. The mechanical properties of the roller reached the best in the history of the cast iron workshop. Level.
2.Tackling key problems in smelting process
To obtain high-quality molten iron after the chemical composition is determined, a reasonable smelting process is necessary. For heat-resistant ductile iron castings, the spheroidizing treatment is particularly important (that is, the choice of inoculant and spheroidizing process). The mechanical properties of the castings are also good when the spheroidization is processed. We have selected a suitable inoculant through research and developed a reasonable spheroidization process, so that the molten iron can be well spheroidized, which not only improves the strength of the casting, but also increases its elongation, and the effect is very good.
The spheroidization process uses a dam bag, which must be dried thoroughly. Various alloys must be preheated. The alloys added to the dam bag from bottom to top are: light rare earth alloy 1.8% → inoculant 0.8% → cover iron plate or iron powder (according to molten iron temperature) → alkali surface 0.5%. 2/3 of the iron is tapped, and after the reaction is completed, the iron is tapped again to the required amount, and 0.6% ferromolybdenum, 0.6% inoculant are added along with the flow, and the slag is removed.
3.Tackling key problems in casting process
In order to create a high-quality project, our company has put forward requirements higher than the national standard for the surface quality, dimensional tolerances, and processing volume of the rollers. However, the rollers have large batches and tight schedules. In order to grab the schedule, the workshop had to use some casting techniques. Unfamiliar temporary workers produce roll discs, which puts forward extremely high requirements on the process of roll discs. We have made research on the casting process.
Quality Inspection
In order to ensure the quality of the rollers produced, we have established a strict inspection system: each roller must be attached with a test block for casting testing, and the mechanical properties, metallographic structure and chemical composition of the test block are 100% tested. The unqualified ones will not leave the factory.
Production Effect
Since the roll plate produced by our company was put into production in the medium and heavy plate plant, it has been running well, working smoothly and normally, and there have been no cold bed scratches, bumps on the steel plate, or deviation of the steel plate due to the quality of the roll plate. Efficiency guarantees the normal operation of our factory\'s production and creates good economic benefits.
Conclusion
Through the research on the material and casting process of the roller plate, we completed the casting task of the roller plate on time and in quality and quantity, laying the foundation for the smooth start of the medium and heavy plate project of our company. Due to the high efficiency of this process and the good surface quality of the castings, on the basis of the completion of our cooling bed rolls, we have undertaken more than 20,000 rolls production tasks from Lingang, Xianggang and other manufacturers. The promotion and application prospects are broad and economical. The benefits are very significant.
