(Last Updated On: June 15, 2023)

Now, much large mechanical equipment is fastened with super bolts (high-strength bolts). This kind of bolt has a large pre-tightening force, precise adjustment, wide application range, and convenient installation. Only a torque wrench can meet the pre-tightening force requirement, which greatly reduces the maintenance time of the equipment.

The installation process of super bolts (high-strength bolts):

High-strength bolts come in two forms:

One is that the nut has a ring of pre-tightening bolts, also known as super nuts.

The other is that the bolt itself has a circle of pre-tightening bolts, both of which generally have hard washers.

On this basis, the type of pre-tightening bolts can also be changed according to needs, but these are commonly referred to as super bolts, which require a final pre-tightening force of 600kN.

Take Super Nut for example. (with pre-tightened bolts on nuts)

When installing, tighten the nut first to eliminate the gap between the nut and the joint surface.

Then use a torque wrench to operate according to the conventional multi-bolt symmetrical fastening method with a specified pretightening force of 10%-50%, and then tighten them sequentially around the circumference with 75% and 100% of the pretightening force respectively.

If the pre-tightening bolts used are longer, it is necessary to repeat the process of the last step to eliminate the error caused by the elastic deformation of the long bolts to achieve the final pre-tightening force.

Disassembly process of super bolts (high-strength bolts):

Starting with the first pre-tightening bolt, loosen it completely counterclockwise.

Then turn clockwise again so that the bolt just rests against the mating surface. Then repeat the above steps for each bolt in turn.

When the last pre-tightening bolt is loosened, the first bolt will be tightened again, and it usually takes 2-3 repetitions to completely remove the nut.

Although this pretightening and loosening process is complicated, the stress on each bolt is consistent, which can avoid damage to individual bolts due to excessive load.

Routine maintenance of super bolts (high-strength bolts):

It is required to regularly use a torque wrench to check whether the preload is at the specified value.

When encountering maintenance or disassembly, strictly follow the disassembly steps.

After disassembly, lubricate the screwing parts, replace the nut washer, or turn it over for use when its deformation is less than 0.01mm.

If it is difficult to disassemble, you can use a lubricating spray such as WD-40, lubricating oil, etc., at least try to remove one pre-tightening bolt, lubricate it, and tighten it with 110% pre-tightening torque.

At this time, the two adjacent bolts will loosen.

Repeat the above steps, and finally remove all the nuts according to the removal steps.

In the end

The use of high-strength bolts (super bolts) greatly facilitates the installation and maintenance of large mechanical equipment. For the pre-tightening of super bolts/nuts, bolt tools such as high-torque special fastening tools such as hydraulic wrenches should also be considered. However, in the case of damaged or missing bolts, it is strictly forbidden to use ordinary-grade bolts instead of high-strength pre-tightening bolts. To ensure the safe use of high-strength bolts (super bolts) and prevent accidents.

TorcStark provides years of experience in solving bolting and dismounting problems, please contact us for custom bolting solutions.