What are the main geometric parameters of the threaded elements of the barrel mandrel?

Time:2021-12-11

By barrel mandrel thread element is meant a helically linear continuous raised portion of a specific cross-section made on the surface of a cylindrical or conical base body. Threads are divided into cylindrical threads and conical threads according to the female type; they can be divided into external threads and internal threads according to the position of the parent body, and can be divided into triangular threads, rectangular threads, trapezoidal threads, serrated threads and other special shapes according to their cross-sectional shape (tooth shape).

In machining, a tool or grinding wheel is used to cut threads on a cylindrical shaft (or inner hole surface). When the workpiece rotates, the tool moves a certain distance along the workpiece axis, and the trace cut by the tool on the workpiece is the thread. The thread formed on the cylindrical surface is called an external thread. The thread formed on the surface of the hole is called an internal thread. The base of the thread is a helix of the surface of the round shaft. Generally speaking, if the cross section of the thread is triangular, it is called triangular thread; if the cross section is trapezoidal thread; if the cross section is zigzag, it is called sawtooth thread; if the cross section is square, it is called square thread; If the cross section is circular, it is called round thread and so on.

What are the main geometric parameters of the threaded elements of the barrel mandrel?

1. Outer diameter (large diameter), that is, the diameter of an imaginary cylinder that coincides with the top of the external thread tooth or the bottom of the internal thread tooth. The nominal diameter of the thread is the major diameter.

2. The inner diameter (small diameter) is the imaginary cylinder diameter that coincides with the bottom of the external thread or the top of the internal thread.

3. Intermediate diameter, the diameter of the imaginary cylinder with a width equal to the diameter of the protrusions and grooves on the bushing passing through the tooth profile.

4. Pitch, the axial movement distance between adjacent teeth corresponding to one two points on the middle diameter line.

5. In the lead, the axial distance between two points corresponds to the center line of the same spiral on adjacent teeth.

6. Tooth profile angle, the angle between two adjacent tooth sides on the thread profile.

7. Pitch angle, that is, the angle between the tangent of the helix on the medium diameter cylinder and the plane perpendicular to the axis of the thread.

8. The working height, the distance between the overlapping parts of the two matching thread profiles perpendicular to the direction of the thread axis, etc. The nominal diameter of the thread is the nominal diameter of the pipe thread except the inner diameter of the pipe, and the rest is the nominal diameter of the outer diameter. Threads have been standardized, including metric and imperial. International standards use the metric system, and China also uses the metric system.

Except for the pipe thread with the pipe inner diameter as the nominal maximum diameter, the rest of the thread work is based on the theoretical outer diameter as the nominal size diameter. Thread angle is less than the friction angle of the thread pair, in the axial force does not loosen, called self-locking, the transmission technology efficiency level is low.

Among cylindrical threads, triangular threads have good self-locking properties. It is divided into two kinds of thick teeth and fine teeth, the general connection of the use of thick tooth thread. The fine tooth pitch is small, the rising angle is small, and the self-locking performance is good. It is often used for vibration or variable load connection of small parts of thin-walled tubes, and precision adjustment devices.

The tooth shape of the taper thread is triangular, which mainly depends on the deformation of the teeth to ensure the tightness of the product thread pair, and is mostly used for pipe fittings.


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