Inch Thread Tightening Torque | Online Calculator

Bolt Connection Calculators







Inch Thread Tightening

In this calculation, a bolted connection consisting of a bolt with an inch thread of diameter d with a pitch h and two parts having a total thickness L in the junction is considered. The bolt is tightened applying torque T.

The connection is under a load with a tensile component FH and shear component FK. As a result of calculations, the tightening force Ft, tensile force F and equivalent stress σ acting in the bolt are determined. With a tight connection, the tensile force in the bolt is constant and F = Ft. If the loads FH and FK/μ exceed the tightening force, the connection becomes loose, and the safety factor K becomes less than one. In this case, bending stresses start to appear in the bolts due to the shear component of the load.

In this calculation the coefficient of friction μ is same for thread and for connecting surfaces.

Calculation of Inch Thread Tightening
Calculation of Inch Thread

INITIAL DATA

d - Tread outer diameter;


h - Thread pitch (see table below);


T - Tightening torque;


μ - Coefficient of friction (see table below). In this case it is installed uniform for bolt and for connection elements;


Fн - External tensile load on the connection elements;


Fк - External shear load on the connection elements;


L - Thickness of the connection elements.

RESULTS DATA

Ft - Tightening force;


F - Tensile force;


σ - Maximal equivalent stress (von-Mizes) in threaded part of the bolt;


K - Safety factor of tightness. K >= 1 to ensure that there are no gaps and displacements in the connection.

Thread diameter (d)

Pitch (h)

Torque (T)

Friction coefficient (μ)

Tensile load (FH)

Shear load (Fk)

Connection thickness (L)

Tightening force in bolt (Ft)

Tensile force in bolt (F)

Equivalent stress (σ)

Safety factor (К)

BASIC FORMULAS

Connection tightening force:

Ft = [2T*cosα / d]*[1 / (2cosα*μ + sinα)];

α - angle of thread inclination.

Tensile load in bolt:

F = Ft;

Equivalent stress:

σ = F / (π*(d0 / 2)2);

d0 - smaller thread diameter;

Safety factor:

K is less from the ratios: Ft / FH and [Ft - FH] / FK

These formulas are applicable for the tight connection. The algoritm of the program takes into account a loose connection in the case of insufficient tightening torque.

INITIAL DATA

d - Tread outer diameter;


h - Thread pitch (see table below);


T - Tightening torque;


μ - Coefficient of friction (see table below). In this case it is installed uniform for bolt and for connection elements;


Fн - External tensile load on the connection elements;


Fк - External shear load on the connection elements;


L - Thickness of the connection elements.

RESULTS DATA

Ft - Tightening force;


F - Tensile force;


σ - Maximal equivalent stress (von-Mizes) in threaded part of the bolt;


K - Safety factor of tightness. K >= 1 to ensure that there are no gaps and displacements in the connection.

INCH THREAD SIZES

Thread

3/16

1/4

5/16

3/8

7/16

1/2

9/16

5/8

3/4

Pitch

24

20

18

16

14

12

11

10

Thread

7/8

1

1 1/8

1 1/4

1 3/8

1 1/2

1 5/8

1 3/4

1 7/8

Pitch

9

8

7

6

5

4 1/2

Thread

2

2 1/4

2 1/2

2 3/4

3

3 1/4

3 1/2

3 3/4

4

Pitch

4 1/2

4

3 1/2

3 1/4

3

COEFFICIENTS OF FRICTION

Friction contact materials

Surface conditions

Friction coefficient

Steel-Steel

Dry

0.15

Greased

0.11

Steel – Cast iron

Dry

0.3

Steel - Copper

Dry

0.36

Greased

0.19

Steel - Bronze

Dry

0.12

Greased

0.09

Steel - Brass

Dry

0.35

Greased

0.19

Steel - Titanium alloy

Dry

0.3÷0.7

Steel - Aluminium alloy

Dry

0.61

Bronze - Bronze

Greased

0.1

Cast iron - Bronze

Dry

0.22

Greased

0.08

Cast iron – Cast iron

Dry

1.1

Greased

0.1

Aluminium alloy - Aluminium alloy

Dry

1.2

Greased

0.3

Titanium alloy – Titanium alloy

Dry

0.5

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