Flange screws are mainly composed of a hexagonal head and a flange plate (the gasket under the hexagon is fixed to the hexagon) and a screw (a cylinder with external threads). They need to be matched with the nut. , used to fasten two parts with through holes.
Flange bolts are widely used on highway and railway bridges, including industrial and civil construction, cranes, excavators and other heavy machinery, with a wide range of applications.
Several common flange screws:
There are two types of hexagonal flanges, one is flat and the other is concave. The surface is plated with white, military green, colorful yellow, and Dacromet which never rusts.
Depending on where the flange screws are used, the size requirements of the discs are different. There are also flat bottoms and toothed ones. The toothed ones have an anti-slip effect.
According to the force-bearing method of the connection, there are ordinary ones and those with reamed holes. The flange screws used for reamed holes should match the size of the holes and are used when subjected to lateral forces. In addition, in order to meet the need for locking after installation, there are holes in the rod. These holes can prevent the bolts from loosening when they are vibrated. Some flange bolts have thin unthreaded polished rods, which are called thin-rod flange bolts. This kind of flange bolt is conducive to connections subject to variable forces. There are special high-strength bolts on the steel structure. The heads will be larger and the sizes will also change.
Common materials for flange screws:
High carbon steel C%>0.45% Hexagonal flange screw product materials are basically not used in the market at present;
Medium Carbon Steel 0.25% Hexagon Head Screws Medium carbon steel materials are usually called No. 35 and No. 45 steel in China, and are basically called 1035, CH38F, 1039, 40ACR, etc. abroad. Mainly used for grade 8 nuts, grade 8.8 bolts and grade 8.8 hexagon socket products;
Low carbon steel C%≤0.25% is usually called A3 steel in China. Abroad, they are basically called 1008, 1015, 1018, 1022, etc. Mainly used for grade 4.8 bolts, grade 4 nuts, small screws and other products without hardness requirements. (Note: Drilling tail nails are mainly made of 1022 material.)
Flange screw fastening methods and requirements:
Torqueless torx wrench or hammer wrench is suitable for fastening general equipment and pipe flanges, and is selected according to the screw size and flange pressure level. Fastening requirements are as follows:
- The maintenance unit shall formulate a fastening plan, fasten the flanges symmetrically, and number 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 other stud screws and tighten to balance the load, ensuring that at least 2 threads are exposed at each end of the nut.
- According to the on-site equipment and flange, one tightening circle is calculated as one time, and the number of tightenings (at least 3 times) and the hammering load (strength) of each tightening should be reasonably determined. The tightening hammering load (strength) should be calculated according to Tighten in order from small to large (such as 50%, 80%, 100% increments). Do not load the load too fast or too large to prevent gasket seal failure.
5.The tightening sequence for each torqueless box wrench or hammer wrench:
Tighten two diametrically opposite screws to the set hammering load (strength) of the screws;
Tighten another pair of screws about 90 degrees apart from the previous two screws along the circumference;
Continue tightening until all remaining screws are tightened to the established hammer load.
Torque wrenches are suitable for high temperature, high pressure, flammable and explosive and other important equipment and pipe flanges. Fastening requirements are as follows:
Screw tensioner is suitable for high temperature, high pressure, flammable and explosive and other important equipment and pipe flanges. Fastening requirements are as follows:
The maintenance unit formulates a fastening plan and appropriate tensile force, and conducts design review based on screw strength, initial sealing specific pressure and working sealing specific pressure of the gasket, medium pressure and other parameters to prevent the screws from breaking and the gasket from being compressed. If the tightening force is too high and elasticity is lost, the seal will fail.
When the screw tensioner stretches the fastening screws individually (step by step), follow the principle of screw tightening uniformity and refer to the tightening sequence of the torque wrench.
During the stretching and tightening process of the screw tensioner, the number of stretching and tightening should be reasonably determined, and the pressure should be increased from small to large (such as 50%, 80%, 100%), and the pressure should be evenly applied. Each time the pressure is increased to a certain level, It is necessary to stabilize the voltage before increasing it to avoid excessive impact tension and affecting the pre-tightening effect of the screw.