High-strength fish-tail bolt
Fish-tail bolts (fish-tail screws) are mostly used in the connection of rail joint plates (fish-tail plates) and sometimes can be replaced by hexagon bolts.
I. Product Application
Fish tail bolts are mainly used in the metallurgical industry, coking industry, and steel industry for the laying of tracks, to firmly connect the joints of steel rails.
II. Product Models and Materials
The models include O14×60, O16×75, O18×90, D20×90, O22×135, 24×135, 24×145, 24×170, etc. They are generally formed by hot pressing in a friction press, with a length of 50mm. There are also cold-formed ones, which are mostly used for connecting rail joints.
Materials: Q235, 45#, 20MnTiB steel, 35CrMoA, etc.
III. Product Description
High-strength fish-tail bolts are classified into several grades, including 8.8, 9.8, 10.9, and 12.9. Bolts of grade 8.8 and above are made of low-carbon alloy steel or medium-carbon steel and undergo heat treatment (quenching and tempering), and are generally referred to as high-strength fish-tail bolts.
The rest are commonly called ordinary fish-tail bolts. The performance grade marking of the bolt consists of two parts of numbers, representing the nominal tensile strength value and the yield ratio of the bolt material respectively.
High-strength fish-tail bolts are those made of high-strength steel or those that require a large preload. They are often used in the connection of bridges and rails. The fracture of such bolts is mostly brittle. High-strength bolts used in ultra-high pressure equipment need to be pre-stressed to ensure the sealing of the container.
High-strength fish-tail bolts can bear a greater load than ordinary bolts of the same specification. Ordinary bolts are usually made of Q235 (i.e., A3) steel. High-strength bolts are made of 35# steel or other high-quality materials and undergo heat treatment after manufacturing to increase their strength.
In terms of material comparison:
High-strength fish-tail bolts are made of high-strength materials. The bolts, nuts, and washers of high-strength bolts are all made of high-strength steel, commonly using 45# steel, 40 boron steel, 20 manganese titanium boron steel, 35CrMoA, etc. Ordinary bolts are usually made of Q235 steel.
In terms of strength grades:
High-strength fish-tail bolts are increasingly widely used. The commonly used strength grades are 8.8s and 10.9s, with 10.9 grade being more prevalent. The strength grades of ordinary fish-tail bolts are much lower, typically 4.8 grade and 6.8 grade.
In terms of force characteristics:
High-strength fish-tail bolts apply pre-tension and transfer external forces through friction. Ordinary fish-tail bolts connect by the shear resistance of the bolt shank and the pressure-bearing capacity of the hole wall to transfer shear force. The pre-tension generated when tightening the nut is very small and can be ignored.
In terms of usage:
Ordinary fish-tail bolts can be reused, while high-strength fish-tail bolts cannot be reused. High-strength bolts are generally used for permanent connections. High-strength fish-tail bolts are prestressed bolts. For friction type, a torque wrench is used to apply the specified pre-tension, and for bearing type, the hexagonal head is removed.
Ordinary fish-tail bolts have poor shear resistance and can be used in secondary structural parts. Ordinary fish-tail bolts only need to be tightened.
Specifically:
High-strength fish-tail bolt connections have the advantages of simple construction, good force performance, replaceability, fatigue resistance, and no loosening under dynamic loads. They are a very promising connection method. High-strength fish-tail bolts are tightened with a special wrench to generate a large and controlled pre-tension in the bolt.
Through the nut and washer, the same magnitude of pre-compression is also applied to the connected parts. Under the action of pre-compression, a large friction force is generated along the surface of the connected parts.
Obviously, as long as the axial force is less than this friction force, the components will not slide and the connection will not be damaged. This is the principle of high-strength fish-tail bolt connections.
High-strength fish-tail bolt connections rely on the friction force between the contact surfaces of the connected parts to prevent their mutual sliding. To ensure sufficient friction force on the contact surface, it is necessary to increase the clamping force of the components and increase the friction coefficient of the contact surface of the components.
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