Desoutter CVIR II, Руководство оператора, Страница: 59 / 72

02/2014 59 / 72
6159933910
Issue no: 04
CVIR II
9.5 - yield point controlled tightening
The principle of the yield point controlled tightening is
based on the fact that the torque rate (ΔC / Δα) remains
constant as long as the tension stresses applied to the
screw are lower than the yield point and then decrease
beyond that point.
The torque rate is calculated throughout the torque
increase and it is compared to a reference torque rate
calculated at the beginning of the tightening cycle, in an
area where the constraints are much lower than those of
the yield point.
The calculation starts from the angle threshold.
The reference torque rate is known when the spindle has
run the first N degrees, N being the Δα value (number of
samples) allowing the calculation of the torque rate.
The system stops when the torque rate becomes lower
than the "reference torque rate" by X%, X being the
percentage of the target torque rate. It is the yield point.
The default values are: N = 16 and X% = 50
When tightening in the plastic zone, the system waits
until the spindle reaches a given angle (angle in plastic
zone) after the yield point, then it stops the motor.
The recorded values are the following: final torque, final
angle and final torque rate.
Torque (Nm) Angle (°)
Torque rate (mNm/°)
Time
Maxi torque rate
Angle and
torque
tolerances
Reference torque rate
Final torque
Final angle
Angle
threshold
1st sample
of 16 or 32°
0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
10
50
100
150
Mini torque rate
100
200
300
400
500
2.2 2.4
600
700
800
750
50
100
150
250
200
Target torque rate
=
Programmed % of
reference torque rate
e.g.:70%
Plastic zone
beyond yield
point
spindle stop
● IF (torque rate ≤ x% of the reference torque rate
OR angle in plastic zone exceeded
OR "reference torque rate" > max. torque rate
OR < min. torque rate)
● OR torque > max. torque
● OR angle > safety angle
● OR torque rate > max. torque rate
Accept report
● IF reference torque rate ≤ max. torque rate
● AND reference torque rate ≥ min. torque rate
● AND min. torque ≤ torque ≤ max. torque
● AND min. angle ≤ angle ≤ max. angle