The maximum speed in the load collective refers to the maximum permissible speed that a threaded spindle may reach under the actual operating conditions of a defined work cycle. This takes into account all relevant load cases, including, in particular, axial load, acceleration, friction, and dynamic influences throughout the entire operating cycle.
This factor is crucial for:
- not to exceed the spindle’s critical speeds,
- to avoid resonance and vibration,
- to minimize vibration and wear problems,
- to properly size the drive and motor,
- to ensure the service life of the spindle, nut, and bearings.
Factors
- Spindle Length and Bearing Arrangement
Longer, freely cantilevered spindles generally have a lower critical speed. The type of bearing arrangement also has a significant influence on the permissible speed. - Load Profile
Higher axial loads, high accelerations, or shock loads can reduce the permissible speed, as they increase the dynamic stress on the system. - Lubrication
Proper lubrication reduces friction and heat generation. This can lower the thermal load, enabling higher operating speeds. - Spindle Material and Geometry
The stiffness, diameter, material, and design of the spindle significantly influence its behavior at high speeds. - Preload of the Nut
Although a higher preload often improves running performance and stiffness, it can also increase friction and heat generation. This can reduce the maximum permissible speed.
Distinction from Maximum Spindle Speed
The maximum spindle speed describes the upper limit of a spindle under idealized or theoretical conditions. In contrast, the highest speed in the load range is the value relevant in practice under real operating conditions.
It ensures that the spindle, nut, and bearings are operated within their permissible load limits and that no harmful vibrations, overloads, or signs of premature wear occur.
Practical Example
A ball screw in a CNC axis theoretically has a maximum speed of 5,000 rpm. However, taking into account the combined load, acceleration, and preload, the permissible speed in actual operation may be limited to 3,500 rpm to ensure the system’s safety, stability, and service life.