Analysis of factors affecting the surface hardness of gray cast iron cylinder head

The major assemblies of auto parts, such as drive axle assembly, engine assembly and gearbox assembly, are inseparable from the production of castings, of which the castings on the engine account for about 75% of the total weight. The proportion of casting blank parts invested in automobile processing industry has also increased from 20% to 30%. The diesel engine market consumes 90% of gray cast iron and ductile iron parts. The engine processing unit puts forward the requirement that the surface hardness of the cylinder head must be stably maintained at the high limit.

(1) The holding time of molten iron in the production process of gray cast iron cylinder head should not exceed 10 h.

(2) With the increase of water content in molding sand, it is easy to form a ferrite layer on the surface of casting and reduce the surface hardness; In actual production, the amount of pig iron should be controlled at about 5% and the water content of molding sand should be controlled at 3% ~ 3.4%.

(3) Aging heat treatment temperature shall not be higher than 550 ℃.

(4) Using silicon barium inoculant instead of 75sife inoculation can improve the section sensitivity and make the hardness value of the product more uniform.

(5) In normal production, the overheating temperature shall not exceed 1 550 ℃.

As one of the important parts of the engine, the combustion chamber of the cylinder head bears the explosion pressure of nearly 70 MPa and the wall temperature of nearly 300 ℃ when the engine works, and the working environment is very bad. In order to improve the hardness of castings, it may be necessary to sacrifice the tool life and production efficiency of machining units, reduce the hardness of castings and improve the cutting performance, but the wear resistance and reliability of subsequent castings will be greatly affected. Therefore, study how to stably control the body hardness of the cylinder head and better improve the cutting performance, and explore the root causes affecting the body hardness and cutting performance of the cylinder head, so as to meet the needs of machining units for cutting performance on the premise of obtaining better service performance.

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