A survey of car service managers completed
in the United States, indicated that 23% of all service problems
were traceable to loose fasteners. Such problems are common
across many industries. A major cause of fastener loosening
is inadequate tightening. A single bolt, inaccurately or incorrectly
tightened, can lead to the failure of the complete product.
Torque Controlled Tightening
The most prevalent controlled method
of tightening threaded fasteners is by tightening so that
a specified torque is achieved. This method is generally known
as torque control. The major problem related to this method
is that the fastener clamp force (referred to as preload)
generated as the result of an applied torque is dependent
upon fastener design and the prevailing frictional conditions.
Despite these problems, it is still the most popular way of
ensuring that an assembled bolt complies with an engineering
The Importance of Tightening Torque
Most Engineers already know the importance
of a high preload in maintaining joint integrity. For torque
controlled tightening, achieving the right preload is dependent
upon the correct tightening torque being specified. Without
the proper analytical tools and information, specifying the
correct torque can be problematical. Whether you are a Service
or a Design Engineer, you frequently need to know what is
the correct tightening torque. For many types of threaded
fasteners, this information is either not available, or not
Analysis of Bolted Joints
A great deal of sophistication can
nowadays be applied to the analysis of structures. Frequently
however, the assumptions made in the analysis regarding the
scatter in a bolts preload, is either simplistic or is ignored.
That is, it is often assumed that a bolts preload will not
vary from a single calculated or test determined value. Frequently,
this can be a fatal flaw in the structural analysis. Fluctuation
in a bolts preload is mainly caused by variations in the frictional
conditions and the method of tightening being used. If this
fluctuation is outside the assumed value, product reliability
problems can result. Such reliability problems can manifest
themselves as fluid leakage past a gasket, fatigue failure
of the bolt itself or of the whole joint. Being able to predict
what will be the minimum fastener preload can be crucial to
the reliability of a product.
The TORQUE Program
TORQUE is a program which is designed
to assist the Engineer in the solution of problems related
to the torque tightening of threaded fasteners. The program
determines both tensile stress due to the elongation of the
fastener, and the torsional stress due to the applied torque.
It accounts for the frictional effects in the thread and between
the nut face and clamped surface. Account can also be made
for the effects of a reduced shank diameter (smaller than
the thread size) and a prevailing torque. The prevailing torque
is the torque required to run a nut down a thread before engagement
with the joint surface. This resistance can be provided by
a nylon insert or a distorted thread profile. A prevailing
torque can significantly affect the amount of preload provided
by the fastener for a given tightening torque.
Versatile Analysis Options>
program analysis options include the determination of :
Presented below is further information related to this program.
tightening torque and preload so that a given stress level is achieved
in the fastener.
tightening torque having specified the preload required.
c) The preload having specified the tightening torque.
An in-built database is provided containing
information appertaining to thread pitch, root, effective
and nut bearing diameters for standard fasteners. The default
metric coarse thread data used by the program can be changed
to metric fine, Unified Coarse or Unified Fine by selecting
the appropriate menu option. Similarly, the default metric
unit of measure can be changed to various imperial units by
selecting an appropriate menu option.
Help is available
which can furnish information relating to both the program and to threaded
fasteners in general. Help is available for each input value which is
required by the program by pressing the F1 function key at any time
The program has
menu options to allow :
a) Printout of
the results and the data to both the screen and printer.
b) The program
has the facility to store both data and the results to disk.
c) Previously stored
data can be retrieved and subsequently used by the program.
A user guide is
supplied as an Adobe pdf document and is installed with the program.
The manual, besides giving guidance on the use of the program, presents
valuable background information on the tightening of threaded fasteners.
under Windows operating system. TORQUE is provided
as a download from our web site.
calculations (METRIC) completed by TORQUE
calculations (Inch/Lb) completed by TORQUE
Datasheet in Adobe pdf format
The download for
our demo program is packaged in a self extracting exe file
that includes an uninstall facility if/when you want to cleanly
remove the program and associated files from your system.
To install the program when you have downloaded the file you
need just to run it by double clicking on the file from Explorer
or by using the Run option from the Start menu.
and ordering details for the program