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A Guide to a Selection of Torque Values

In preparing this guide to torque values the following basic assumptions have been made:

Bolts and nuts are new, standard finish, uncoated and not lubricated*
The load will be 90% of the bolt yield strength
The coefficient of friction () is 0,14
The final tightening sequence is achieved smoothly and slowly until the torque indicates full torque has been obtained.

The information supplied here is an acceptable guide for normal conditions and includes information on:

  • Lubrication Factors
  • Conversion Factors
  • Formulae relating Torque and Tension
  • the Formula for calculating the effect of Torque Wrench extentions
  • Torque Conversion Scale

*  If lubrication has been applied to the bolt and/or the nut (other than the
normal protective oil film), multiply the recommended torque by the appropriate factor
shown in the Lubrication Factor table. n.b. Antiseize lubricants can reduce torque
required by approximately 20%.


Lubrication factor

 

Surface condition of bolt

Self

Electroplated

Zinc

Cadmium

Phosphate

Surface
condition
of nut

Self

1,00

1,00

0,80

0,90

Zinc

1,15

1,20

1,35

1,15

Cadmium

0,85

0,90

1,20

1,00

Phosphate and oil

0,70

0,65

0,70

0,75

Zinc and Wax

0,60

0,55

0,65

0,55


Conversion Factors

Torque
lbf.ft x 1.36   = Nm
Nm x 0.737 = lbf.ft

Force
lbf x 4.45   = N
N x 0.225  = lbf

Pressure
lbf/in x 0.069 = bar
bar x 14.504  = lbf/in

Flow
l/s x 2.119 = cu.ft/min
cu.ft/min x 0.472 = l/s

Power
hp x 0.746 = kW
kW  = Nm x rev/min

95555


Formulae Relating to Torque and Tension

 

Imperial

M = torque lbf.ft  
P = bolt tension lbf
D = bolt dia.ins
M =

PxD

60

Metric

M = torque Nm
P = bolt tension Newtons
D = bolt dia. mm
M =

PxD

5000


Formula for Calculating the Effect of Torque Wrench Extensions

M2 = M1x

L2
L1

where L1 in the normal length and L2 is the extended length, M1 is the set torque and M2 the actual torque applied to the nut.

eg. L1=500 L2=650 so
M2=100x 650 =130Nm
500


 
  Torque Wrench

Torque Conversion Scale



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