What Are Shear Wrenches?
Shear wrenches are power tools specially designed for fastening screws called shear bolts.
The term “shear” is derived from the fact that the part of the shear bolt called the tip threads off during fastening. A more technical term for a shear bolt is a Torsion-type high-strength bolt.
Shear bolts are typically used in buildings, bridges, and other steel structures, and shear wrenches are used for fastening them.
Similar to shear wrenches, electric screw fastening tools include impact wrenches. While impact wrenches can tighten and loosen screws quickly, shear wrenches operate quietly and tighten with slow rotation. The shear wrench is characterized by its low tightening reaction force, which reduces the burden on the operator.
Usage of Shear Wrenches
Shear wrenches are primarily used for fastening shear bolts, especially in the construction of steel frame structures.
Principles of Shear Wrenches
Shear wrenches are motorized screw fastening devices, but what sets them apart is the structure of the socket part. To understand the principle of shear wrenches, it is necessary to first grasp the principle of shear bolts. When the fastening torque reaches a certain level, the tip at the end of the bolt threads off.
The benefits of the tip threading off include:
- Confirmation that the fastening operation is completed
- Suppression of variations in tightening torque
- Prevention of intentional loosening after tightening
The torque at which the tip can be unthreaded is determined by the bolt material (breaking strength) and the thickness of the notch. Consequently, shear bolt fastening reduces the variation in tightening torque.
Additionally, the head of the shear bolt is round, not hexagonal. It is the tip that mates with the fastening tool, and once the fastening torque is reached, the tip breaks and disappears. Therefore, once a shear bolt is tightened, it cannot be intentionally loosened.
To fasten such shear bolts, shear wrenches have a shaft that mates with the tip inside a regular socket. The inner shaft grips the tip to secure the shear bolt, while the outer rotating shaft turns the nut that is connected to the shear bolt.
Types of Shear Wrenches
There are six major types of shear wrenches, each suitable for different tasks.
1. Standard Type
This is the most common type used when there is no space limitation during work.
2. Corner Type
Corner type shear wrenches are necessary when the working space is too small for the standard type.
3. Extremely Short Type
This type is used in narrower spaces where the corner type cannot be used.
4. Grip Rotation Type
The grip portion can be rotated in relation to the axis of rotation. The grip-rotating type makes it easier to use when fastening screws from the opposite direction of normal fastening, which is called cutting work.
5. External Type
This tool can be attached to a general electric screwdriver.
6. Cordless Type
Shear wrenches are used with a rechargeable battery. They are employed at sites where a power source is unavailable. The advantage of the rechargeable type is that it eliminates concerns about voltage drop in the power supply.