1. Cause analysis
This type of cylinder head integrates the intake pipe and rocker shaft seat on the basis of the traditional cylinder head. It has a compact structure and forms many isolated hot joints. It is difficult to control the cooling and solidification speed of various parts during the cooling and solidification of the casting, and the casting measures that can be taken are limited. Therefore, there is no hot metal for feeding during the solidification of hot joints in valve guide holes, bolt holes and other parts, resulting in shrinkage holes Shrinkage defect (see Figure).
(1) Place 25mm at the valve guide hole × 60mm round steel cold iron, 8mm internal cold iron is preset in the duct hole on the upper part of the exhaust duct, the hole core of the fuel injector is made of chromite sand with high heat storage coefficient instead of ordinary coated sand, and the fuel injection hole is made of chromite coated cold iron instead of graphite, so as to speed up the cooling speed of the heat joint at this part and advance its graphite expansion.
(2) Chromite sand coated cold iron shall be set at the bolt hole of Φ 25mm, and the sand coated layer shall be controlled at 6mm ~ 8mm.
(3) An external cold iron is set at the edge of the inner gate of the intake pipe flange to speed up the heat transfer.