In the tunnel construction, there is a kind of machine called shield machine, which is engaged in starting and driving, which has the functions of cutting and cutting soil, transporting dirt and assembling tunnel lining. However, when the shield machine is lining the tunnel, it is assembled with several pieces of pipe pieces. One kind of screw is connected with the fastening action, and the pipe is assembled into a cylindrical pipe. The tube is a cylindrical wall.Excavation can effectively control the ground settlement, to reduce the influence of the ground buildings and underwater excavation shall not affect the water traffic characteristics of each segment together, form the pipeline, the design into a straight line or a curved tighten fittings, bolt is lining segments.Pipe bolts are divided into ring and longitudinal. Some designs are consistent with the longitudinal specifications.There are two specifications, even two levels of strength, in the design of central and vertical. In general, the length of the ring bolt is longer than the longitudinal pipe bolt.
Type of pipe bolt:
1. Double head straight pipe bolt.
2. Double head curved pipe bolt.
3. Hexagonal head curved pipe bolts.
4. Hexagon head circular threaded pipe bolt.
5. Hexagonal flange face arc thread pipe bolt.
6. Non-standard pipe bolt.
High strength bolt is one of the most representative products in special bolt. It has very high strength and long service life compared with ordinary bolt. In general, high strength bolts are enhanced by hardening and tempering, and their tissue is tempered martensite. Once the tensile strength of this tempered martensitic steel is more than 1200MPa, due to the effect of trace hydrogen, the original grain boundary will be embrittled, and the phenomenon of delayed fracture in the process of use becomes obvious.
Difference between high strength bolt and common bolt:
High strength bolt pipe bolts are made of high strength materials. The bolts, nuts and gaskets of high strength bolts are made of high strength steel, and are commonly used in 45 steel, 40 boron steel and 20 mn titanium boron steel. General bolt is usually made of Q235 steel.
From the strength level:
High strength bolts are used more and more widely. There are two levels of strength: 8.8s and 10.9s. General bolt strength grade is low, generally 4.4, 4.8, 5.6 and 8.8.
From the stress characteristics:
High strength bolts apply pretension and resist force to transfer external forces. Generally by bolt rod bolt coupling shear and pressure on the hole wall to transfer shear, tighten the nut when the attack method is small, its influence can be neglected, and high strength bolts in addition to its high strength of materials, put great pretension bolt back, make the connection between components attack extrusion, which has a great resistance force perpendicular to the direction of the screw, and strong, resistance to sliding coefficient and steel varieties are directly affect the bearing capacity of high strength bolt.
According to the stress characteristics, the pressure type and the resistance type are divided. The calculation methods are different.High strength bolt minimum specification M12, common M16~M30, large specification of bolt function instability, planning should be used carefully.