The Key Technology Of Preparation Of Natural Gas Compressor Block Castings

Natural gas compression units play an important role in modern production and life. Two types of natural gas compressors——RDS series and CNG series were produced by a factory. RDS compressor units developed by Denise- Rand Company possess the advantages of high efficiency, energy saving, reliable operation and high degree of automation. After importing RDS units, the factory is responsible for implementing localization. CNG compressors are specifically targeted at domestic CNG automobile LPG stations and have been listed in new key product plans by ministry of national science and technology.Cylinder block castings for the RDS and the CNG are key components of natural gas compressor. Because of their complex structure, uniform wall thickness and high performance requirements, the castings is easy to leakage and become rejects that caused by casting defects such as loose material, cracks and so on. This not only directly affects the unit's installed process, but also increases the cost of the casting. In addition, the continuous expansion of the petrochemical capacity, equipment has become a clear trend in large-scale, the industry made a supercharger requirements on the units, so the original RDS compressor cylinder material has been difficult to meet customer requirements. Therefore, it is very necessary that research the key fabrication technology and improve the material of natural gas compressor cylinder castings.As the tensile strength of compacted graphite cast iron and stiffness are higher than ordinary gray iron, exceeding 75% and 45% separately. Comparing the ordinary gray iron, the fatigue strength of compacted graphite cast iron is almost two times of that. Therefore, it is a better choice that compacted graphite iron use as material of the cylinder block casting of natural gas compressor, not only meeting the requirements of service life, but also receiving the stable sizes.For this application trends and the actual situation of the cylinder block casting of two series of RDS and CNG, based on the analysis of casting defects, the thesis studied and improved the key technology of preparation of cylinder body castings. The main contents included that the trial-produce of RDS compressor cylinder body was implemented, in which compacted graphite cast iron was used to instead of the alloying gray cast iron, and the further revision for improved material were carried on. For CNG compressor cylinder body castings, statistical analysis of casting defects was done, and then the key technologies of preparation were improved accordingly. Meanwhile, the microstructure and phase of castings were analyzed by optical microscope, electron microprobe analysis and other testing equipment, and solidification simulation analysis of the typical castings with higher rejection rate in two types of cylinder body ware carried on by InteCAST software. Through the simulation of process of filling and solidification, the flow field and temperature field were analyzed in order to achieve the purpose of process optimization. Targeted materials, technology and other improvements, basically solved the problem of casting loose material, which reduced the rejection rate caused by leakage, cracking and so on, get a better economic efficiency. The results in this thesis possess important reference value for the application and production of the vermicular iron castings in the cylinder block castings.