Ball screw systems

Fast & precise linear motion with ball screws

Ball screw systems consisting of a ball screw and a ball nut achieve linear motion with high precision and/or high speeds.  Efficiency is high at about 90% and ambient temperatures up to 110 degrees are possible.  Compared to mechanical belt driven systems they are more precise.  Compared to electric linear actuators they are faster and more precise. Compared to pneumatic and hydraulic systems they offer advantages of precision, controllability and efficiency.  When combined with a motor drive they make up a complete linear motion system.

Techdrives offer the Servomech range of ball screws that are manufactured on modern machine tools to exacting standards of precision.  The whole manufacturing process is done in their 8 year old Bologna factory meaning that their complete control allows specials and short lead times.  Large stocks of screws and components are held.

See FAQs on Ball Screws
Ball Screw -323px

How they work

The ball screw is an accurately machined threaded shaft with specific levels of precision and usually with customised shaft ends.

Ball nuts consist of a steel body, a quantity of balls, ball recirculation elements and wiper seals.

Rotation of the shaft causes the balls to roll in the ball screw threads and the matching threads inside the nut.  The rolling action achieves high efficiency linear motion.  The balls make a single, or several, revolutions inside the nut and then a recirculation element diverts the balls back to the start of their path.  DIN69051 defines standard nut dimensions although specials are possible.
ball-screw-diagram

Materials

Ball screws are machined from 42/50Cr Mo4Steel hardened to 58-61 Hrc, on request with chrome plating for severe environments.  Accuracy grades are IT7 for transport and general duties, IT5 for positioning and IT3 high precision.

Ball nuts are machined from 18NiCr Mo 5 steel hardened to 58-61 Hrc.  Recirculation elements are plastic or steel for high temperature applications

Ambient Conditions
Ball screws can be used in ambient temperatures from -20 to +90°C.  Higher temperatures up to 110°C are possible by changing the material of the liners which divert the balls from their tracks.

Lubrication is required and an oil splash environment is optimum.  However many applications use grease lubrication where the grease is periodically recharged at the ball nut.  Although the ball nut can be provided with wipers, use in conditions with severe dust and dirt needs careful consideration.

Performance
Typical dynamic load ratings for industrial ball screws are from 1 to 150kN although operating factors will reduce these loads in real life.  Performance is usually a compromise between speed, load, duty cycle and life time.  Dynamic load ratings are based on 1 million revolutions at that load.  Linear speed depends on the rotation speed of the screw and the screw pitch which is typically in the range 5 to 40mm.  Up to 2m/s linear speed is possible for light loads.  All loads should be in-line with the screw as radial loads are detrimental to lifetime.
 

Scope

Servomech ball screw systems are available with single or multi-start screws from 16 to 100 mm diameter.
Screw lengths up to 5.7m
Linear speeds up to 2m/s
Standards ISO 3408 and DIN69051
Accuracy grades IT7 (general purpose)  to IT3 (machine tool precision)
Ambients -20 to +90 degrees (110 degrees on request)
Oil or grease lubrication.
Special dimensions possible

Making it easy

We aim to make the selection and ordering process as easy as possible.  From your application data we make a preliminary assessment before referring it to the factory.
A visit to your site is made if necessary.
Based on the factory recommendation we will make a proposal that is technically correct for

speeds
forces
accuracy
duty
lifetime
environment

This process allows us to optimise the selection from the number of starts and the nut types available.

2D and 3D CAD drawings can be provided. 

You have no need to make selection calculations although if you wish to do so guidance is given in our catalogue download

International standards

ISO3408 and DIN 69051 define the screw accuracy and nominal dimensions for screw and nut.  As a general guide, the performance of systems manufactured with the same accuracy grades to these standards will be very similar. However individual components will not be interchangeable.

 

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Article - basic facts on ball screws for machine designers