high tensile bolts
Difference Between High Tensile Bolts and Ordinary Bolts
The performance grade of bolts is an important indicator of their strength and yield performance, and common grades include 4.6, 4.8, 5.6, 8.8 and 10.9, etc. Bolts with a performance grade of 8.8 or above are called high tensile bolts according to the regulations. According to the provisions of the performance level of the bolt in the 8.8 grade or more, known as high-strength bolts. 8.8 and above bolts made of low-carbon alloy steel or medium-carbon steel and heat-treated (quenched, tempered), commonly known as high tensile bolts, and the rest of the collectively referred to as ordinary bolts. The routine is to roll the thread first and then do the heat treatment.
The main difference between ordinary bolts and high tensile bolts lies in the material, strength level, force characteristics and methods of use.
Difference in material
Ordinary bolts are generally made of ordinary steel (such as Q235).
High tensile bolts, on the other hand, are made of high-strength materials, and their screws, nuts and washers are made of high-strength steel, and commonly used materials include No. 45 steel, 40-boron steel, 20-manganese-titanium-boron steel, and 35CrMoA.
Difference in strength grade
High tensile bolts have higher strength grades, usually grade 8.8s and 10.9s, with grade 10.9 being the most widely used. In contrast, the strength grade of ordinary bolts is generally lower, usually grade 4.4, 4.8, 5.6 and some models up to grade 8.8.
Difference in force characteristics
The connection mechanism of ordinary bolts mainly relies on the shear resistance of the bolt rod and the pressure of the hole wall to transfer the shear force, and the pre-tension force generated when tightening the nut is small and negligible.
High tensile bolts, in addition to high material strength, will apply a large pre-tension force to the bolt, so that the connection between the members of the extrusion force, thus generating a large friction force in the direction perpendicular to the screw. This friction contributes to the integrity and stiffness of the connection. When subjected to shear, the high-strength bolt connection will first withstand the shear force through friction, and only when the load increases to a certain degree will relative slip occur.
Difference in the method of use
Ordinary bolts can be reused and are suitable for secondary structural parts or temporary connections.
High tensile bolts are generally used for permanent connections and are prestressed bolts. Friction-type high-strength bolts use a torque spanner to apply the specified prestressing force, while pressure-type high-strength bolts unscrew the plum head.
Bolts in the track system
Bolts in the crane rail system
High-strength bolts play a vital role in the crane rail system, mainly because the crane rail system needs to withstand large loads, vibration and impact during the working process, so the strength and performance of the bolts have high requirements.
In the crane rail system, common high strength bolts include:
Hexagon head bolts: suitable for most connection occasions, especially for connection parts requiring high preload.
High-strength pre-stressed bolts: used in critical connection parts that are subjected to extreme loads and can improve the robustness of the connection by means of pre-tensioning technology.
Bolts with locking devices: use of anti-loosening techniques such as nylon locknuts, thread locking adhesives, etc. to prevent bolts from loosening under vibration conditions.
Ordinary bolts in the crane rail system is more basic, mainly concentrated in the lighter load, not high strength requirements of the connection parts, or used in auxiliary connection, temporary connection, adjustment of parts and other non-load-bearing functions.
Bolts in railway systems
High tensile bolts are mainly used in railway track systems for the connection of rails, sleepers, turnouts and other components to ensure that the track system is able to withstand the high loads, shocks and vibrations generated during train operation. Its excellent tensile strength, fatigue resistance, corrosion resistance and vibration resistance make it an indispensable key component in the railway track system. Through the use of high strength bolts, the stability of railway tracks can be improved, maintenance frequency can be reduced, and service life can be extended, thus ensuring the safe and efficient operation of railway transport.
The application of common bolts in railway track system mainly focuses on the connection parts with lighter loads and less demanding strength requirements. They are commonly used in the connection of non-load bearing parts, fixing of auxiliary facilities, temporary connection and adjustment, connection of track joints and other occasions.
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