断面图 Cross section

1、概念 Concept      

     假想用一个平面把物体切开，仅画出剖切到的切口图形，并且画上相应的材料图例，所得到的图形称为断面图。If an object is cut with an imaginary plane and only the cut graph is drawn and the corresponding material legend is drawn, the graph obtained is called section drawing.

2、与剖视图的区别 The difference with the sectional view

     剖视图 —— 要画出剖切平面后沿投影方向能看到的所有部分的投影

     Section view - to draw the projection of all the parts that can be seen in the projection direction after cutting the plane

     断面图 —— 仅画出剖切平面与物体接触部分的图形，即切口实形。

3、断面图分类 Sorts of cross section

      断面图主要根据不同的安排分为移出断面图和中断断面图。

      The sections can be divided into removed  and revolved cross section based on the different arrangement of the section.

（1）移出断面图Removed cross section

        绘在基本视图之外的断面图称为移出断面图，应用于断面变化比较多的构件。

      The section drawn outside the basic view is called the removal section and is applied to the component with more changes in section.

       绘制方法 Construction methods

       断面图的绘制方法与剖视图一样，但只需画出剖切平面与物体接触部分的图形，即切口实形。

       Same as section but don’t need to draw some visible outside just want to draw solid parts touching the cutting plane.

       符号 Label

       断面图的剖切符号只画出剖切位置线，不画投射方向线，而是用编号的注写位置来表示剖切后的投射方向。剖面图中的剖切平面可转折，断面图中的剖切平面则不能转折。

       In the section cut sign of section cut, only the cutting position line is drawn, and the projection direction line is not drawn. Instead, the numbered annotation position is used to represent the projection direction after cutting.The cutting plane in the section can be turned, but the cutting plane in the section can't be turned.

（2）中断断面图 Revolved cross section

       直接画在杆件中断处的断面图，称为中断断面图。多用于杆件细长，且只有单一断面的构件。无需注写断面符号。

      The section drawing drawn directly on the middle of the member is called the interrupt section drawing.It is used for long and thin member with single section.No cross section notation is required.

4、断面图的读图步骤 Reading of cross sections

       Reading steps are as follows.

Step1 understand the solid of given views.

Step2 know the representations of given views.

Step3 make sure the location of sectional views or cross section cutting location.

Step4 draw sectional views or cross section.

Step5 remember to draw sectioning line.

Tips: it is important to dimension the location and projection direction of sectional views.