What is Hydraulic Nut?
Hydraulic nut is an advanced bolt assembly method, especially suitable for mechanical fastening with small space and large load vibration.
The working principle of the hydraulic nut is to use the hydraulic cylinder to directly apply external force to the bolt so that the applied bolt is stretched in its elastic deformation area. After the bolt is stretched, the locking ring on the hydraulic nut is tightened so that the bolt will be locked in the stretched position by the locking ring. The hydraulic cylinder is located at the central axis of the bolt and is used to axially stretch the bolt to achieve the required tension of the bolt. And it is the amount of tension in this bolt that determines the clamping force required for bolt tightening. When the hydraulic nut is pressed, the bolt is stretched, and the hydraulic nut and the joint surface are close to each other. Thereby the axial deformation of the locking bolt, i.e. the residual bolt load in the locking nut.
Many connection surfaces are fitted with gaskets. Gaskets only work when the joint faces are under pressure, so it is especially important that the joint faces remain clamped at all times. The load applied to the bolt is proportional to the oil pressure in the hydraulic cylinder. This design holds the payload very precisely. Because the load is applied directly to the bolt and all the force is used to lengthen the bolt, the space required to generate the load can be minimized.
Hydraulic nuts are used for bolts that need to be frequently disassembled; pre-tightening of oversized bolts; locking large workpieces, etc. It can also be used as a hydraulic interference connection and disassembly tool. Installing or removing bearings on tapered shafts or bushings is often a difficult and time-consuming process. Using hydraulic nuts can improve work efficiency and reduce such problems. The principle is that the hydraulic oil is input into the nut by the high-pressure oil pump to generate the force to push the piston so that the installation or removal of the bearing is effortless, accurate and safe.
The locking of ordinary threads is to use the friction between the threads to lock by turning the wrench to generate torque. For large-diameter threaded connections, due to the influence of manpower, tools and working space, the pre-tightening force cannot meet the design requirements at all, so it is easy to loosen in vibration situations.
Hydraulic nuts completely change the traditional way of tightening, the torque locking is axial tension locking. With the help of the power of the ultra-high pressure oil pump, the threaded screw is elongated axially, and the thread is locked by the elasticity of the material itself. Therefore, the hydraulic nut has a very high pre-tightening capacity and the unique feature that multiple groups of bolts can be tightened synchronously to achieve the same pre-tightening force, and has gradually been widely used in various industries.
Hydraulic nuts are mainly used for bolt connections that are often disassembled or axially tightened in various occasions, with pre-tightening and anti-loosening requirements, and can be used as a hydraulic interference fit connection and disassembly tool.
Features of hydraulic nut:
1. It is especially suitable for the tightening of narrow spaces and heavy-duty vibration machinery, and multiple bolts of the same specification can be assembled at the same time.
2. The torque-free design is adopted to avoid friction, bolt twisting and other factors that affect the bolt tightening force, and the tightened bolt is pure tensile force.
3. Preload can be set accurately with an accuracy of up to ±3%.
4. With a stroke indicator, allows for observing, measuring, and controlling the piston stroke during the operation.
5. Due to the ultra-high pressure hydraulic system, the size of the hydraulic bolt matches the original traditional nut, and there is no need to modify the original bolt pair design.
6. There is no need for a wrench and a socket space, and the size of the bolt pair is more compact.
7. Screw working and pure tension state, the same size screw can provide 20%-30% more output contribution, and the bolt pair is safer.
8. The predetermined load is more accurate and the tightening is more reliable through hydraulic tension bolts.
9. The overall sealing structure of polyurethane/metal composite seal is adopted, with few sealing parts, and the sealing form takes into account low pressure, high pressure and ultra-high pressure sealing, especially suitable for working under ultra-high pressure.
10. The oil cylinder has good running rigidity, stable and reliable work, and easy operation.
11. When the piston overtravel, the system automatically releases the pressure, and the operator’s mistakes can be effectively corrected by the system.
12. All bolts can be fastened at the same time, which greatly improves the assembly efficiency, and the pressing force of the flange is the most uniform.
Hydraulic nut specifications: M20—M300 (special specifications can be customized according to special requirements).
Working pressure: 500bar-2200bar, up to 3300bar when special requirements.
Tensile force: 190kN—25655kN (different tensile force is used according to different bolt specifications).
Hydraulic nuts are divided into lower and upper lock rings according to their structure. The lower lock ring type is used for general purposes, and the upper lock ring type is used for applications in countersunk holes.
A hydraulic nut is an advanced bolt tightening system with the same working principle as hydraulic tensioner. It is mainly used for fastener assembly in narrow spaces and the tightening of heavy-duty vibration machinery. It reforms the traditional fastening method, using the hydraulic system to make the fastened bolts through pure axial tension, accurately reach the predetermined load, and then mechanically lock the fasteners to complete the fastening work.
Since the screw is only subjected to pure tensile force, the pre-tightening force of the bolt pair can be increased by 20%-30%.
Typical application: accurate and reliable fastening of machinery with high load and strong vibration under various working conditions.
Oilfield: Oilfield BOP.
Mining: Shearers, roadheaders, bucket wheels, super heavy vehicles.
Power plants: high-pressure feed water pumps, compressors, rock mills, steam turbines, backrest wheels.
Petrochemical: Reactor, high-pressure feed water pump, compressor, rock mill, smoke turbine.
Ships: Diesel engine, main train, back wheel.
Steel: rolling mills, hydraulic presses, billet shears, backrest wheels.
Thread forms are:
Ordinary thread, trapezoidal thread, rectangular thread, etc., users can choose according to their needs.
The characteristics of hydraulic nuts guarantee a wide range of applications. It has the unmatched advantages of other nuts in terms of manpower saving, accuracy, and safety.