Overview of sand cast engine exhaust manifold castings
Sand casting engine exhaust manifold casting is a kind of casting parts used in automobile engine, its main function is to collect the exhaust gas from the engine and direct it to the exhaust system. Sand casting process is one of the main methods to produce exhaust manifold castings, its advantages are low cost, simple process, but the accuracy and surface quality is relatively poor. Materials for sand casting engine exhaust manifold castings Sand casting engine exhaust manifold castings usually use gray cast iron or ductile cast iron as materials. Gray cast iron has good casting performance and wear resistance, but the strength and heat resistance is relatively poor. Ductile iron has higher strength and heat resistance, but also higher cost. Production process of sand casting engine exhaust manifold castings The production process of sand casting engine exhaust manifold castings mainly includes the following steps: model making, core making, molding, pouring, cleaning and inspection. Model making is to make a model of the casting according to the requirements of the drawings, core making is to make a cavity inside the casting according to the model, modeling is to combine the model and core together to form the casting process, pouring is to pour the molten metal into the casting, cleaning is to take out the casting from the casting and carry out the surface cleanup, and inspection is to carry out a quality inspection of the casting. Exhaust manifold, is connected with the engine cylinder block, the exhaust of each cylinder will be centralized into the exhaust manifold, with the divergence of the pipeline. Its requirements are mainly to minimize exhaust resistance, and to avoid mutual interference between the cylinders. Exhaust is too centralized, between the cylinders will produce mutual interference, that is, a cylinder exhaust, just to encounter other cylinders to run into the exhaust gas is not discharged. In this way, it will increase the resistance of the exhaust, which in turn reduces the output of the engine. The solution is to make the exhaust of each cylinder as far as possible separate, each cylinder a branch, or two cylinders a branch, and make each branch as long as possible and molding - to reduce the gas in different tubes affect each other. To minimize exhaust resistance, some race cars use stainless steel tubing for the exhaust manifold.
Exhaust manifolds should take into account the engine power performance, engine fuel economy, emission standards, engine cost, matching the car's front cabin layout and temperature field.
Currently commonly used exhaust manifolds from the material and processing technology on the cast iron manifold and stainless steel manifold two types.
Exhaust manifold material characteristics and requirements
Early automobile engines, low power per unit weight, fuel combustion efficiency is not high, the exhaust gas temperature does not exceed 500 ℃. With the improvement of automobile engine efficiency, the exhaust gas temperature increased to 600~650 ℃. Developed countries in recent years continue to improve automotive emissions standards, catalytic technology and the application of worm-gear booster technology is a significant increase in the working temperature of the exhaust manifold, reaching more than 750 ℃. With the further improvement of engine performance, the working temperature of the exhaust manifold should be increased. At the same time, with the progress of engine technology, the structure of the exhaust manifold is also complicated, coupled with the cycle of alternating temperature state work, the requirements of the exhaust manifold material should not only have good high temperature performance, but also has good casting performance. Therefore, the exhaust manifold material must have the following characteristics.
Good high-temperature oxidation resistance
Exhaust manifold in the high temperature cycle for a long time under the state of work, materials at high temperatures under the oxidation performance directly affects the service life of the exhaust manifold. Ordinary cast iron obviously can not meet the requirements, the need to add alloying elements in the material to improve the material's high temperature oxidation resistance.