2024 Author: Howard Calhoun | [email protected]. Last modified: 2023-12-17 10:16
Threaded connections depend on the outer and inner surface of the location. They are internal, external, conical and cylindrical. They differ in section and profile of the part: round, rectangular, persistent, trapezoidal. Appointment can be running or fastening.
The fastener has a triangular profile and is divided into two groups: inch and metric.
An inch threaded connection is measured in inches (hence the name), the pitch is 25.4 mm. It is characterized by the number of helix threads per inch of the cut part.
Inch threads are used to connect pipes (called "pipe threads"). Also used for cutting on spare parts of various equipment. In machines that are produced in our time, inch threads are not used. Standards are designed for metric, so the design is under this standard.
Threaded connections with thrust threads are used for heavy loads. Trapezoidal fasteners serve as a fastener when transmitting movement (lead screws) and forces, but do not produce rigid fastening of parts. Forfittings use round threads, in machines it is used extremely rarely.
With a triangular profile, threaded connections are the most reliable, even with
same diameter. Thrust is less durable. Trapezoidal threads will be even less reliable. The weakest is rectangular. Due to smooth rounding, the round one has a high dynamic strength.
Threaded connections are divided into groups: screw, combined, bolted and stud.
The simplest connections consist of a nut and a screw.
To avoid self-unscrewing in the connections, locking parts are used that soften vibration and shock load, reduce friction.
There are many ways to stop self-unscrewing in the reference books.
Car threads are made with carbon metal bolts. In fasteners that require increased reliability and strength, alloyed chromium steel is used. At the moment of tightening the threaded connections, a dynamic key is used (it normalizes the load torques). Such keys are used in mechanisms where the connection force is strictly defined in the technical documentation.
Threaded connections are first clamped, then slightly loosened and tightened again. This controls the correct clamping force.
The calculation of threaded connections is made in order to determine the stress that occurs in the connection. Also needcalculate the margin of safety for the bolts used.
The calculation is performed by elements:
- without nut and with nut;
- with eccentric and concentric loads;
- with pin fastening;
- the contact zone is determined by the geometry of the thread;
- if there are many cylindrical shaft sections;
- with many plates.
The calculations use the same statistical loads.
Threaded connections are good because they can always be disassembled without damaging the parts themselves.
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