Essential Bolting Tools
Introduction
Let us first understand some of the key bolting
concepts before identifying the essential bolting tools for bolt tightening.
1. What is Bolted Joint?
Bolted joint, is one of the oldest and
most common type of joint in many industries like construction, machinery
equipment and piping industry. The joint consists of fasteners that holds two
or more parts securely. Bolted joints come under
the category of temporary joints which means the joint is not permanent. Few
industries prefer bolted joints over permanent joints with a benefit of mainly
easy serviceability and weight requirements.
2. Why Joints fails?
For bolted joints, appropriate bolt
tightening techniques and right bolting tools are crucial for the safe
operation of many types of equipment. However, if not taken enough care for
selecting the method required for assembly and appropriate tool while assembly,
it may lead to failure of joint.
Failure of Bolts
and Bolted Joints
- The
bolt preload being insufficient to resist the forces acting
- Failure of
the bolts due to Fatigue
- The
bolt being directly overloaded by the force acting
- Excessive bearing stress
within the joint itself.
Joint efficiency is mainly depending on its bolt clamping or tightening force, which is generated by applying the torque on the bolt. It is a known fact that addition of a gasket in a joint is to prevent the leakage but it may work effectively as long as there is a sufficient clamp force generated by the bolts.
3. Necessity of Bolt tensioning
Bolt preload or Bolt tensioning refers to the stretching or elongation of a bolt that is needed to clamp two or more parts together. For a bolt to hold two components together securely, a certain amount of preload tension is required.
4. The Importance of Torque Control
It might appear that more torque may always be a
better choice when it comes to tensioning a bolt, but it is not the case, as too
little torque will not provide enough clamping force and too much torque causes
the bolt to break.
5. Determine the preload Torque
Several factors affect the required preload torque
calculations of a bolt. To calculate the amount of preload required, it is
important to know that the material of a bolt and its grade, the amount of load
it can withstand, the loss of torque due to friction and other aspects of the
load.
In General, Preload is specified as a
percentage of the bolt tensile yield strength. It can be calculated using
either a mathematical equation or an online bolt torque calculator. The joint
may fail, if it doesn’t meet the preloading conditions.
In simple words, to determine how much torque
is needed for achieving an efficient bolt joint, it mainly depends on the Material
and its properties of the bolt with which it is made up of and the application
of the joint.
6. Tools required for bolt joints
The Bolting tools required for bolt tightening can be classified by their bolting techniques. The
popular bolt tensioners and torqueing tools are as follows.
·
Tensioning tools:
Bolt
tensioners – Hydraulic bolt tensioners are suitable for all bolting applications. It can be operated with single
stage or multi stage.
Hydraulic nuts - the technology of Hydraulics replaces
the conventional hexagonal nuts to provide accurate and uniform bolt loading.
Using array of hydraulic nuts on a bolted joint gives a better uniform bolt
load across all bolts, which greatly improves the efficiency of the joint. This
type is suitable for tightening large diameter bolts without damage
that may occurs when conventional wrenches are used to loosen the
fastener.
- Torque
tools:
Torque Wrenches – These torques wrenches are operated either manual or
powered. Powered wrenches operate with the help of either Hydraulically,
pneumatically or electrically operated.
Nut Runners - Nut runners are the tools used for tightening of the nuts by pneumatically, electrically, or with the help of hydraulic power. Pneumatic nut runners are operated by compressed air. Whereas, Hydraulic nut runners are powered by hydraulic fluid and operates with either single stage or double stage cylinders.
7. Torque Tightening vs Bolt Tensioning
To identify, which method of tightening is suitable, it is important to
know its application. Below is Key difference of torqueing and tensioning methods.
·
While tightening large bolts use of Hydraulic or Mechanical tensioning
is preferable over torque tightening
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