Super Bolt (Nut) – One of the Best Bolt Fastening Technology
(Last Updated On: June 21, 2023)
The emergence of super bolts
On many large and super-large machines, bolt tightening requires a final preload of 600kN. Such as petrochemical, power station, mining, agricultural production, transportation, and other industries, the use of large bolts in the metallurgical industry is also very common. Because traditional fasteners and fastening methods can no longer meet the needs of these large-scale equipment connections. Therefore, there is a fastener with an ingenious design, safe and convenient use, and reliable performance – SUPER BOLT(NUT).
Its appearance can be called a revolution in bolt-fastening technology.
The application of super bolts is not only conducive to improving the integrity rate of the equipment, prolonging the service life, but also facilitating maintenance.
How do super nuts work?
1. By pre-tightening the jacking screw, a strong jacking force (axial) is generated. This jacking force acts directly on the hard washer, and the jackscrew has a small friction diameter, so a high preload can be achieved with a relatively small torque.
2. The load is transferred to the nut body which has been manually installed onto the main thread.
3. The hard gasket is used to transmit the thrust and protect the flange surface at the same time.
4. The (axial) jacking force of the jacking screw and the reaction force of the main bolt head together generate a strong clamping force on the flange.
5. The jacking force (axial) of the jacking screw produces a force (reaction force) of the same magnitude on the main bolt.
How to use super bolt
Super bolts consist of a central bolt and a nut with a ring of concentric multi-stage small bolts around it. To use, screw the nuts onto existing or new bolts by hand. After it is in place, it is only necessary to tighten a circle of multi-stage small bolts in sequence, and the fastening work is completed.
When the nut is screwed into the bolt, the multi-stage small bolt and the hardened gasket form a counterforce, which makes the nut leave the bolt surface under force. Small bolts have a strength of 300,000PSI, and hardened gaskets can transmit preload and protect the parts to be fastened. As the smaller bolts are tightened, the tension on the center bolt increases gradually. With the tightening of the small bolts, the pre-tightening force from the small bolts produces an equal reaction fastening force on the central bolt, thereby achieving a balanced high-strength fastening effect. Due to the unique fastening method of the super bolt, it can still maintain a tight state even under strong shock, high temperature, and high pressure.
Preload calculation of super bolts
Tightening a super bolt can produce a preload of 10,000 tons, and the stress water pump can withstand 250,000 psi.
So how does the Superbolt generate such a massive preload? The detailed calculation formula is as follows.
In order to ensure the reliability of threaded connection components and realize their design functions, the pre-tightening force should be determined by actual service conditions and strength calculations. During installation and use, it is necessary to ensure that the components reach the target preload. Therefore, it is very necessary to select an appropriate tightening method and precisely control the tightening torque.
In the elastic zone, the relationship between the preload F of the super nut and the tightening torque T
n——the number of jacking screws
D——thread nominal diameter
K is a comprehensive constant of various influencing factors. Including friction coefficient (thread friction coefficient, support surface friction coefficient), tooth half angle, pitch, and other factors. For screw parts with the same size, the same heat treatment state, and the same surface treatment method, the torque coefficient can be approximately regarded as a constant.
From the above relationship, it can be seen that for a given torque value, the more the number of jacking screws is, the smaller the diameter is, and the greater the pre-tightening force is applied. The smaller the screw pitch, the smaller the coefficient of friction, the greater the pre-tightening force generated by the same torque, and the higher the utilization rate of energy.
For the tightening of multiple jacking screws, it is very necessary to use a small and stable lubricating oil with a small friction coefficient to reduce the dispersion of the pre-tightening force. However, if the pitch is too small, it will cause tripping due to insufficient strength, and if the friction coefficient is too small, it will increase the risk of the screw loosening automatically. Using a relatively large number of jacking screws will significantly reduce the fastening speed and cost-effectiveness. Therefore, the best configuration should be selected as much as possible when selecting super bolts.
Advantages of multi-stage jacking super bolts
1. The super nut is easy to install, and with the pneumatic/electric torque wrench, it can greatly save operation time, and the disassembly and installation are equally convenient.
2. It can be used for large-scale bolted connections with narrow operating spaces and harsh working environments. Such as equipment and component connections with large vibrations.
3. The super nut is made of alloy material, which has super high strength and good wear resistance. Its advantages are more obvious when working at high temperatures, high pressure, and in the field. It does not require an additional power source, and there will be no problems such as high-temperature softening and aging of the sealing ring of hydraulic fastening tools.
4. Super nuts are more economical for large connections and larger vibrations, but not suitable for small connections and general fastening situations.
5. Super nuts have the advantages of suspension nuts, and their fatigue strength is greatly improved compared with ordinary nuts, and there is no loosening and tripping of ordinary bolts.
6. Super nut bolts are economical and safe, can be disassembled many times, reused, and have a long life.
Regular bolts VS Super bolts
There are many strength levels, which are not suitable for identification on-site, resulting in misuse. High-strength bolts require high torque, which is not easy to achieve with a general torque wrench. Due to the limitation of space and torque wrench, the tightening torque is uneven, causing the bolt to be broken due to uneven force. The life of the bolt is short. If it is not tightened in time after loosening, it is easy to aggravate the damage of the connecting parts, causing mechanical accidents or even personal casualties. The labor intensity of the maintenance personnel is high and the labor efficiency is low. And high-torque wrenches are expensive and costly.
Super bolts are easy to install, using hand tools can reduce the installation time by more than 60% compared with ordinary bolts, and it does not need gas cutting and electric splitting sometimes like ordinary bolts when disassembling. Due to the convenience of disassembly and installation, the use of super bolts greatly shortens downtime. At the same time, super bolts are also suitable for narrow spaces and harsh environments and can improve safety performance and work efficiency. It can be used repeatedly, ensuring safety and avoiding industrial accidents.
In the end
By using the technology of jacking pre-tightening bolts (super bolts), many problems in bolt installation, disassembly, and pre-tightening are solved. The installation of multi-stage jacking pre-tightening bolts can be completed only by an ordinary torque wrench and does not require traditional bolt fastening methods and tools such as a sledgehammer, heating, hydraulic tensioner, and hydraulic wrench. Really save time, effort, and money.