Screw Drive

1. What's a Screw Drive?

A thread drive is a mechanical system used to convert rotary motion into linear motion or vice versa. It typically consists of a threaded spindle and a nut, with the nut sitting on the spindle and moving along the thread. Depending on the type of thread drive, different types of threads can be used, including trapezoidal screws and ball screws.

2. Trapezoidal thread vs. Ball screw

3. What's the main difference between these two threads?

The main difference between trapezoidal screw spindles and ball screw spindles lies in their precision, efficiency, and ability to achieve high speeds. Trapezoidal screw spindles are more robust and cost-effective, while ball screw spindles offer better performance with high precision but are also more expensive. The choice depends on the specific requirements of your application.

4. When is a trapezoidal screw spindle the right choice for me?

Trapezoidal screws are suitable when a lifting speed of <=50mm/s is sufficient, when a duty cycle of <=50% is adequate, and when self-locking is a safety-relevant feature of the drive. For standard applications with low speeds and high loads, trapezoidal screws are appealing due to their low initial investment cost.

5. When is a ball screw spindle the right choice for me?

Ball screw spindles lose much less energy in the system due to rolling friction, making them suitable for speeds >=50mm/s and duty cycles up to 100%. Additionally, ball screws are used in applications that demand high precision.

6. What dangers do spindles in an electromechanical drive face?

The primary danger is side forces. Regardless of whether it's a trapezoidal screw spindle or a ball screw spindle, the longer the spindle, the greater and more dangerous the side forces become. Why do side forces occur? Here are three possible causes:

1. The installation of the screw jack is not free of stress.
2. The lifting elements aren't articulated.
3. The load isn't guided with sufficient accuracy.

All of this leads to high side forces, which should always be avoided. Why? Because side forces shorten the lifespan and, in the worst case, can even lead to failure.

7. Side forces in lifting screws: How to avoid them

Why are side forces and stress dangerous? Because they lead to increased wear and thus reduce the lifespan. Here are 3 tips on how to avoid side forces and stress in lifting screws:

7.1 First: Use bearing joints – allows for continuous compensation

There are various options for joint bearings, including joint heads, cardan plates, cardan adapters, and ball joints. The choice of additional element depends on the direction of compensation needed. A universal joint, for example, allows compensation in 2 axes.

7.2 Second: Follow the golden rule in mechanical engineering: never use 2 fixed bearings in one system

Over-determination in a system always leads to stress. Therefore, plan for at most one fixed bearing and one floating bearing in the system.

7.3 Third: As little play as possible, as much as necessary

In steel construction, it's often challenging to meet the tight tolerance requirements of mechanical engineering. Therefore, incorporate compensation options into your connection design. This allows assemblers to adjust for excessive tolerances.