When the idler assy is cooled, white cracks are often formed on the surface and thin sections.
The white mouth structure is hard and brittle, with poor processing performance and easy to peel off.
Therefore, annealing (or normalizing) must be used to eliminate white mouth tissue. The annealing process is: heating to 550-950 ℃ for 2-5 hours, then furnace cooling to 500-550 ℃ and then air cooling. During the high temperature holding period, the high-temperature cementite and eutectic cementite decomposed into graphite and A, and the secondary cementite and eutectoid cementite also decomposed during the subsequent cooling process, resulting in a graphitization process. Due to the decomposition of cementite, the hardness decreases, thereby improving machinability.
Normalizing of ductile iron
The purpose of ductile iron normalizing is to obtain pearlite matrix structure, refine grains and uniform structure, so as to improve the mechanical properties of Dandong steel castings. Sometimes normalizing is also the preparation of ductile iron surface quenching on the structure, normalizing is divided into high temperature normalizing and low temperature normalizing. The high temperature normalizing temperature generally does not exceed 950 ~ 980 ℃, and the low temperature normalizing temperature is generally heated to a total folding temperature range of 820 ~ 860 ℃. After normalizing, four people are generally required to deal with it to eliminate the internal stress generated during normalizing.
surface hardening
In order to improve the surface hardness, wear resistance and fatigue strength of some guide wheel assemblies, surface quenching can be used. Both grey cast iron and ductile iron castings can be case hardened. Generally, high (medium) frequency induction heating surface quenching and electrical contact surface quenching are used.
The box-type structure idler shell is shaped and casted by alkali phenolic resin sand or water glass sand process. After the matrix normalizing and rail surface medium frequency induction quenching heat treatment, the surface hardness reaches HRC48-58, and the hardening depth is above 4-6mm (HRC45). It has the sturdiness to withstand high impact and the wear resistance due to harsh working conditions.
Post time: Apr-23-2022
