凹陷可分为长期发育型、早期发育型和晚期发育型三大类别。

There are three types of sag: long? term development type, early development type and late development type.

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前言： 凹陷可分为长期发育型、早期发育型和晚期发育型三大类别。

There are three types of sag: long?term development type, early development type and late development type.

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以135型三螺杆泵为例，对螺杆几何参数设计、螺旋型面的形成、螺杆啮合特性进行了探讨。

By taking 135 three-screw pump as an example, the geometric parameter design, the forming of spiral surface and the characteristic of screw gearing are investigated.

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