1　薄壁超长缸筒　　某起重机的伸缩缸筒如图1所示，材料为45号钢，内径精度为H9，圆度为0．025，缸筒内表面粗糙度为R　a　0．4μm，内径与壁厚比 ＝16．25，长度与内径比 ＝57，壁厚均匀程度为最大壁厚与最小壁厚差不大于2mm。　　本例属于薄壁超长缸筒。这类缸筒内径加工的 A thin-walled long cylinder A telescopic cylinder cranes as shown in Figure 1, the material is 45 steel, the inner diameter accuracy of H9, roundness of 0.025, the inner surface of the barrel roughness R a 0.4μm, inner diameter and Wall thickness ratio = 16.25, the length to diameter ratio = 57, the average thickness of the wall thickness of the largest and smallest wall thickness difference of not more than 2mm. This case belongs to the thin-walled cylinder. This type of cylinder diameter processing