Static and dynamic load

C_a Dynamic load (daN)

This is the constant unidirectional concentric axial load under the effect of which 90% of a high number of screws having the same characteristics reach a working life of 10 6 rotations.

C_o Static load (daN)

This is the concentric axial load applied to the non rotating screw which produces a permanent deformation of both the balls and rolling track of 0.0001 times the diameter of the ball tself.

Life calculation

Taking into consideration the concept of "fatigue life", according to which in a series of screws having the same characteristics 90% of them will show no signs of wear after a certain number of cycles, their life can be calculated as follows L_h stands for life in terms of hours and L for life in terms of number of revolutions).

n  

RPM

K_a

load coefficient:

1-1.5 for moderate loads with no vibration

1.5-2 for loads with slight knocks and vibrations

2-3    for loads with strong knocks and vibrations

C_a

dynamic load (daN)

F_a

constant axial load or F_m  if the load is variable (daN)

F₁, F₂, ...F_n

axial load values (daN)

n₁, n₂, ...n_n

RPM

If load varies linearly the following can be assumed:

F_min

minimum axial load value

F_max

maximum axial load value

n_min

minimum RPM

n_max

maximum RPM

Example of life (in hours) in various recirculating ball screw application fields:

1.000÷5.000

Electro-medical instruments and equipment

5.000÷10.000

Machines operated intermittently or for brief periods

10.000÷20.000

Machines run 8 hours a day but not continuously

20.000÷30.000

Machines run 8-10 hours a day continuously

30.000÷50.000

Machines run 16 hours a day continuously

oltre 50.000

Machines run 24 hours a day continuously.