We all know that the threads of bolts, screws and nuts of fasteners play a very important role in the fastening of fasteners. The thread refers to the continuous convex part of spiral shape with specific section made on the surface of cylinder or cone parent body. So today, Xiaorui will introduce the main parameters of fastener threads.
Fastener threads can be divided into the following three types according to the number of thread lines:
Single thread: Z=1, low efficiency, good self-locking, easy processing;
Double thread: Z=2, higher efficiency than Z=1;
Three-wire thread: Z=3, high efficiency, poor self-locking, difficult to process.
Main parameters of fastener thread:
The main parameters of the fastener thread are illustrated by taking the cylindrical common external (internal) thread as an example.
1. Major diameter d: the diameter of the cylinder tangent to the top of the external thread or the bottom of the internal thread, which is specified as the nominal diameter of the thread (excluding the pipe thread).
2. Minor diameter d1;: The diameter of the cylinder tangent to the bottom of the external thread or the top of the internal thread. It is often used as the calculated diameter of dangerous section in strength calculation.
3. Pitch diameter d2: the diameter of an imaginary cylinder between the major diameter and the minor diameter. The thickness of the thread tooth on the generatrix of the cylinder is equal to the width of the tooth groove.
4. Pitch P: the axial distance between two points corresponding to two adjacent teeth on the pitch line.
5. Lead Ph: the axial distance that any point on the thread moves around the helix.
6. Ascending angle λ : The included angle between the tangent of the helix and the plane perpendicular to the thread axis, usually the rise angle at the pitch diameter λ express. The calculation formula is:
7. Profile angle a: the included angle a between the two sides of the thread in the thread axis plane. The included angle between the side of the thread profile and the vertical line of the thread axis is called the profile bevel angle γ。 For symmetrical tooth profiles such as triangular and trapezoidal threads, γ = a/2。
