Outer hexagon bolt is a kind of metal accessories, also known as outer hexagon screw, outer hexagon screw or outer hexagon bolt.
1. Ordinary bolts are divided into a, B and C. The first two are refined bolts, less used. Generally speaking, ordinary bolts refer to grade C ordinary bolts.
2. In some temporary connections and connections that need to be removed, grade C common bolts are commonly used. Common bolts commonly used in building structures are M16, M20 and M24. In some mechanical industries, the diameter of rough bolts may be relatively large, and the purpose is special.
High strength bolt
3. The material of high strength bolt is different from common bolt. High strength bolts are generally used for long-term connection. M16 ~ M30 are commonly used. High strength bolts with larger specifications have unstable properties and should be used cautiously.
4. The bolt connection of the main components of the building structure is generally high-strength bolt connection.
5. High strength bolts are not divided into bearing type or friction type.
6. In fact, there is a difference in the design and calculation method between the friction type high-strength hexagon bolt and the pressure type high-strength bolt
(1) The bearing capacity of friction type high strength bolts is the sliding between plates.
(2) The bearing capacity of high-strength bolts is determined by the failure of the connection and the slip between the plates.
7. Friction type high strength bolt can not give full play to the potential of bolt. In practical application, friction type high-strength bolts should be used for very important structures or structures bearing dynamic loads, especially when the load causes reverse stress. At this time, the potential of the bolts that have not been developed can be used as a reserve. In addition, the pressure bearing high-strength bolt connection should be used in other places to reduce the cost.
There are two parts in the performance grade mark of outer hexagon bolt, which respectively indicate the nominal tensile strength value and yield strength ratio of bolt material.
For example, the bolt with performance grade 4.6 means:
a. The nominal tensile strength of bolt material is 400MPa;
b. The yield ratio of bolt material is 0.6;
c. The nominal yield strength of bolt material is 400 × 0.6 = 240mpa
After heat treatment, the material of high-strength bolt with performance grade of 10.9 can reach:
a. The nominal tensile strength of bolt material reaches 1000MPa;
b. The nominal yield strength of bolt material is 1000 × 9 = 900 MPa.
Anti loosing method
Why should the hexagon bolt be prevented from loosening? It is for better, more permanent and more useful things. So, what are the anti loosening methods of hexagon bolt connection? Here to introduce five, one, friction anti loose method. 2、 Mechanical locking method. 3、 Anti loosing method. 4： Riveting and punching method; 5： Structural locking method.
This is a widely used anti loosing method. In this method, a positive pressure which does not change with the external force is generated between the thread pairs, so as to generate a friction force which can restrain the relative rotation of the thread pairs. This kind of positive pressure can be achieved by pressing the thread pair axially or in two directions at the same time. Such as elastic washer, double nut, self-locking nut and nylon insert lock nut. This method is more convenient for nut disassembly, but in the environment of impact, vibration and variable load, the bolt will cause the preload to drop due to relaxation at the beginning. With the increase of vibration times, the lost preload will increase bluntly, which will lead to nut loosening and thread connection failure.
Use split pin, stop gasket and string wire rope. The mechanical anti loosing method is relatively reliable, and the mechanical anti loosing method should be used to deal with important connections.
Permanent anti loosing
Spot welding, riveting, bonding, etc. This method mostly needs to crush the threaded fasteners during disassembly, which can not be reused.
Riveting and punching
After tightening, punching point, welding, bonding and other methods are adopted to make the thread pair lose the characteristics of the movable pair and become a non detachable connection. The disadvantage of this method is that the bolt rod can only be used once, and the disassembly is very difficult, so the bolt pair needs to be crushed before disassembly.
The structural locking does not rely on outside manpower, only on its own structure. The structural anti loosing method, that is, Down's thread anti loosing method, is also a good anti loosing method at the beginning and with good results, but it is not known to most people.
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