Flange bolt are mainly composed of hexagon head and flange plate (the gasket under the hexagon is fixed with the hexagon) and screw (cylinder with external thread), which need to be matched with nuts. , for the fast connection of two parts with through holes.
This connection form is called bolt connection. If the nut is unscrewed from the bolt, the two parts can be separated, so the bolt connection is a detachable connection.
Flange bolts are a common fastener. Flange bolts are widely used on road and railway bridges, including industrial and civil buildings, cranes, excavators and other heavy machinery. The scope of application is very wide.
Flange bolt classification:
1. Hexagonal flange type: There are two types of hexagonal heads, one is flat head and the other is concave head.
2. Surface color category: According to different needs, the surface has white plating, army green, colorful yellow, and Dacromet that never rusts.
3. Flange type: According to the different places where flange screws are used, the size requirements of the discs are different. There are also flat bottom and toothed ones, and the toothed ones play an anti-skid role.
4. According to the force bearing mode of the connection, there are ordinary and hinged holes. The flange screws used for hinged holes should match the size of the holes and are used when receiving lateral force. In addition, in order to meet the needs of locking after installation, some rods have holes, and these holes can prevent the bolts from loosening when they are vibrated. Some flange bolts without threads have to be thinner, called thin rod flange bolts. This kind of flange bolts is conducive to the connection of variable force. There are special high-strength bolts on the steel structure. The head will be bigger and the size will also change.
Common materials for flange bolt:
1. High carbon steel C%>0.45%. Hexagonal flange screw product materials are basically not used in the market at present;
2. Medium carbon steel 0.25% hexagonal head screws Medium carbon steel materials are usually called No. 35 and No. 45 steel in China, and 1035, CH38F, 1039, 40ACR and so on abroad. Mainly used for grade 8 nuts, grade 8.8 bolts and grade 8.8 inner hexagon products;
3. Low carbon steel C%≤0.25% is usually called A3 steel in China. Foreign countries are basically called 1008, 1015, 1018, 1022 and so on. Mainly used for grade 4.8 bolts and grade 4 nuts, small screws and other products without hardness requirements. (Note: Drilling screws are mainly made of 1022 material.)
4. Alloy steel: Add alloy elements to ordinary carbon steel to increase some special properties of steel: such as 35, 40 chromium molybdenum, SCM435, 10B38. The hexagonal flange bolts are mainly made of SCM435 chromium-molybdenum alloy steel, and the main components are C, Si, Mn, P, S, Cr, Mo.
Flange bolt fastening method and requirements:
1. Torx wrench or hammer wrench without torque:
It is suitable for general equipment and pipeline flange fastening, and is selected according to the screw size and flange pressure level. Fastening requirements are as follows:
1) The maintenance unit formulates a fastening plan, fastens the flange symmetrically, and numbers the fastening sequence, refer to Figure 1 and Figure 2 for numbering.
2) Use 4 screws to position the gasket at positions 1, 2, 3, and 4 to ensure that the center of the wound gasket is within the edge of the flange.
3) Tighten the set screw by hand, then insert the other stud screw and tighten to balance the load, making sure that at least 2 threads are exposed on each end of the nut.
4) According to the on-site equipment and flanges, one round of fastening is regarded as one calculation, and the times of fastening (at least 3 times) and the hammering load (strength) of each fastening are reasonably determined. Tighten in order from small to large (such as 50%, 80%, 100% increments), do not load too fast or too large, to prevent gasket seal failure.
5) The sequence of each tightening of torque-free ring wrench or hammer wrench:
a. Tighten the two radially opposite screws to the predetermined hammering load (strength) of the screws;
b. Tighten another pair of screws about 90 degrees apart from the previous two screws along the circumference;
c. Continue to tighten until all other screws are tightened to the specified hammer load.
6) Finally, according to 100% hammering load (strength), tighten all the screws clockwise or counterclockwise one by one.
figure 1
figure 2
2. Torque wrench:
Applicable to important equipment and pipeline flanges such as high temperature and high pressure, flammable and explosive. Fastening requirements are as follows:
1) The maintenance unit needs to formulate a fastening plan, formulate an appropriate torque, and conduct a design review based on the screw strength, the initial sealing specific pressure of the gasket, the working sealing specific pressure, and the medium pressure to prevent the screw from breaking and the gasket from being compressed. Excessive force and loss of elasticity lead to seal failure.
2) Fasten the flange symmetrically, and number the fastening sequence, refer to Figure 1 and Figure 2 for numbering.
3) Position the gasket with 4 screws at positions 1, 2, 3, and 4 to ensure that the center of the wound gasket is within the edge of the flange.
4) Tighten the set screws by hand, then insert the other stud screws and tighten to balance the load, making sure that at least 2 threads are exposed at each end of the nut.
5) According to the on-site equipment and flanges, one tightening circle is regarded as one calculation, and the number of tightening times (at least 3 times) and each tightening torque are reasonably determined, and the tightening torque is tightened in order from small to large (such as 50%, 80%, 100% increments), do not load too fast or too large, to prevent gasket seal failure.
6) The sequence of each tightening of the torque wrench:
a. Tighten the two radially opposite screws to the specified torque of the screws;
b. Tighten another pair of screws about 90 degrees apart from the previous two screws along the circumference;
c. Continue to tighten until all other screws are tightened to the specified torque.
7) Finally, tighten all the screws clockwise or counterclockwise according to the 100% torque value.
8) Record the torque value as a reference for future maintenance.
3. Screw tensioner: suitable for high temperature and high pressure, flammable and explosive and other important equipment and pipeline flanges. Fastening requirements are as follows:
1) The maintenance unit formulates the fastening plan, formulates the appropriate tensile force, and conducts a design review based on the screw strength, the initial sealing specific pressure of the gasket, the working sealing specific pressure, and the medium pressure to prevent the screw from breaking and the gasket due to pressure. Excessive tightening force and loss of elasticity lead to seal failure.
2) When the screw tensioner stretches the fastening screws individually (step by step), according to the principle of screw tightening uniformity, refer to the tightening sequence of the torque wrench to stretch and tighten.
3) During the stretching and fastening process of the screw tensioner, the number of stretching and fastening times should be reasonably determined, and the pressure should be increased in order from small to large (such as 50%, 80%, 100%), and the pressure should be uniform. It should be increased after the voltage is stabilized to avoid excessive impact tension and affect the pre-tightening effect of the screw.
