4GA型汽油机缸体粘砂缺陷的防止措施

Measures to Prevent Burning-on Defect of Cylinder Block of 4GA Type Petrol Engine

介绍了4GA型缸体铸件的生产工艺和型砂、芯砂工艺参数,该缸体底面曾发生较严重的粘砂缺陷,浇注时还经常发生呛火现象。对比发现,粘砂铸件编号与呛火铸件编号不完全一致,说明粘砂缺陷并不是呛火引起。计算表明,型腔排气孔总面积为内浇道总面积的2.1倍,因而判定呛火并非排气面积不够引起。根据缸体出气孔呛火、缸体下表面粘砂这一情况,推断引起粘砂的原因是:型砂含水量高,浇注时水蒸气压力较高,使金属液钻入型砂空隙中而形成粘砂,属于机械粘砂。通过降低型砂含泥量,使型砂水分稳定在较低水平,粘砂缺陷已大幅度下降,并且由于水蒸气量减少,压力降低,呛火现象也得到控制。

The production process,process parameters of molding sand and core sand of 4GA cylinder block were introduced.Severe burning-on defect had been existing with this cylinder block,and the boiling phenomena were often occurring during pouring process. It was found by comparison that not all the numbers of castings having burning-on defect were consistent with the numbers of castings having boiling phenomenon. This situation showed that the burning-on defect was not caused by boiling. Calculation showed that the total venting area of the mold cavity was 2.1 times of the total area of ingates,therefore,it was judged that the boiling was not caused due to enough venting area. Based on the fact that the boiling occurring in the venting holes of the block,and burning-on occurring on the bottom surface of the block,the reason causing burning-on was explained as follows:the moisture content of the molding sand was too high,therefore,the vapor pressure was relatively high during pouring process that caused the metal liquid penetrating into the gaps of molding sand and forming buring-on,which exactly belongs to the metal penetration defect. Finally,by reducing the clay content of the molding sand to keep the moisture content of the molding sand at the some lower level,the burning-on defect rate had been largely decreased,and since the vapor volume reduced,its pressure decreased,the boiling phenomenon had been also controlled.