Tighten
a joint is an action less trivial than you would expect. Standard bolt
tightening torque is a screw at the rated torque is not itself a promise of
a proper tightening stable over time. The preload within the joint is the force
that binds the two pieces together. The preload lengthens the screw and stops
the unloading of the joint:
A coupling must be
strengthened to:
·
Know
the characteristic torque / angle of the joint
·
Joint
mechanics analysis
·
Using
a tightening technique with a screwdriver or lock
· Implement
a method of quality management, review the tightening quality at the end of the
assembly process
Furthermore,
tightening must be "certified" during essential stresses along the
production lines. A calibrated tool must conduct the tightening process and
parameters of the tightening must be tracked, connected to the production
component and saved on a database.
You
want the warranty that the tightening torque for metric bolts reaches
the screw production point for such applications ( for example, vital
tighteners in car assembly). The torque / angle characteristic must have enough
area to prevent breakage past the yield point. Dedicated screws of a mechanical
design allow the screw itself to be stretched further.
What
is a goal torque?
The
goal torque is typically set below the yield point. Certain stresses (e.g.
critical strengthening of the cars) are done at the point of return precisely.
The spring-effect of the screw is maximised by having greater preload in the
junction and a decrease in the probability of decommissioning. In certain
situations the couplage must be planned.
· Do
not use flat washers; the application thereof can lead to a relative motion,
during tightening, to changing the nut from the washer to the joint surface.
This influences the torque-tension relation by changing the friction radius. If
a wider support face is appropriate due to the extreme bearing strain, the use
of flanged nuts and bolts should be considered.
· By
completion of the measurements, assess the best tightening torque. The pressure
gauges should be applied to the bolt shank and the real joint is tightened. A
loading cell should be used under the bolt head, although it is not as exact as
stress calculation because the joint properties have been altered.
The
key way of managing preload is to control the torque of which the connexion is
tightened. The nominal torque required to tighten the bolt to a preload can be
calculated either by means of tables or a measurement using the torque-to-bolt
ratio.
A
quick guide to tension in torque
The
torsional tension generated by the torque acting on the threads strengthens the
shank directly by the elongation tension and torsional stress. The torsional
stresses are neglected by the rest of the bolt tightener torques and a direct
tension in threads, usually 75 per cent, is assumed. The severity of the
torsional pressure for high frictional conditions will result in a failure if
it is coupled with the direct stress.
The
exact preload of the chosen bolt straightening process is one of the key issues
in the use of bolt joints.
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