What Is a Hydraulic Bolt Tensioner?
Hydraulic bolt tensioners are hydraulic tools used to tighten bolts using oil pressure (hydraulic pressure).
Hydraulic bolt tensioners generate a tensile load without applying torsional torque to the bolt, thus maximizing the bolt’s material strength as a fastening force. Another feature of the bolt tensioner is that it can directly adjust the axial force (axial force value control) to precisely tighten the bolt.
Uses of Hydraulic Bolt Tensioners
Hydraulic bolt tensioners are used in manufacturing and industrial applications where the durability of large bolts is more important than ever, due to their ability to precisely tighten bolts. For example, wind turbine generators (propellers) on the ocean, chemical plant factories, and other sites that require high-precision bolt tightening and durability.
Furthermore, the hydraulic bolt tensioner is indispensable in the tightening of bolts with high precision and durability for giant structures such as the Tokyo Sky Tree. In addition, hydraulic bolt tensioners take up less space when fastening than conventional torque wrenches, so they can be used in tight spaces, such as between complex structures.
Features of Hydraulic Bolt Tensioner
Fastening bolts with hydraulic bolt tensioners offers the following advantages:
1. Maximizes the Strength of the Bolt
As explained in the principle section, when torsional torque is applied to a bolt, the bolt elongates or breaks due to plastic deformation at a lower tension than when tension alone is applied. Only a lower fastening force can be obtained than the bolt’s material strength.
In contrast, the hydraulic bolt tensioner does not exert torsional torque on the bolt, so high fastening force can be obtained.
2. Accurate Determination of Axial Force
When a bolt is fastened by rotating an ordinary bolt or screw, the fastening force (axial force) generated by the bolt is not known. However, when determining the axial force from the tightening torque, the coefficient of friction of the bolt’s thread surface and seat surface must be known.
It is difficult to accurately determine the coefficient of friction, and it is common practice to use a surrogate value. If there is a large difference between the coefficient of friction used in the calculation and the actual coefficient of friction as a surrogate value, problems can occur, such as insufficient axial force or bolt breakage during fastening operations. With the hydraulic bolt tensioner, the axial force applied to the bolt can be accurately determined from the hydraulic pressure applied.
3.The Same Axial Force Can Be Applied to Multiple Bolts
Since hydraulic bolt tensioners use hydraulic pressure, the same axial force can be applied to multiple bolts simultaneously by supplying a single source of hydraulic pressure to multiple hydraulic bolt tensioners.
Other Information on Hydraulic Bolt Tensioners
How to fasten with hydraulic bolt tensioners
Hydraulic bolt tensioners start by tightening a nut on a bolt by hand or with a torque wrench in the usual way. Then set the hydraulic bolt tensioner in this state and seat the bolt on the seating surface.
Next, a high-pressure hose is attached to the side of the hydraulic bolt tensioner to apply hydraulic pressure, and the pressure can be set according to the conversion table. The pressure setting can also be converted from the initial required tensile force of the bolt and the effective cross-sectional area.
When pressure is gradually applied with the high-pressure hose connected, the hydraulic pressure pulls the bolt upward and the seated nut floats. By turning this floating nut, the bolt is tightened with several tons of force. After the nut has been turned, the hydraulic pressure is released and the bolt is tightened.