Technologie

Technology

Ballscrews convert rotary motion to linear motion. Balls are the anti-friction element between the ballscrew spindle and nut. Ballscrew dynamics and positioning accuracy primarily depend on the accuracy of production and the technical implementation of the stipulated tolerances.

Advantages of ballscrews over leadscrews

  • No axial play
  • High positioning accuracy
  • Low heat generation
  • High efficiency
  • Very high traverse speeds
  • Long lifetime
  • No stick-slip effect

Thread profile

Our ballscrews have “Gothic arch” track profiles, which, with optimal relationship of ball diameter to track radius, generate a contact angle between spindle and nut of around 45°. This gives our ballscrews excellent running characteristics at maximum axial loads. The ball track profiles for all miniature ballscrews are ground after heat treatment using the most advanced machines.

Nut systems

  • Low-play single nut
  • Anti-backlash pre-loaded single nut (4-point pre-loading)
  • Anti-backlash, pre-loaded double nut
  • Spring pre-loaded double nut

Pre-loading

The pre-loading force is the axial force within a nut system to increase positioning accuracy. As they are extremely precisely formed, our ballscrews can be pre-loaded as standard using the four-point system. Thus we attain optimum rating values. For applications which require very low variations in torque, miniature ballscrews are also available with a spring-loaded double nut.

As pre-loading results in absence of play and increased stiffness of the ballscrew, but also significantly affects the service life and rolling characteristics, it should be applied “as little as possible but as much as required”. If you have any questions, please contact us for consultation.

Quality

Karl Hipp GmbH has been DIN ISO 9001-certified since 1997. All ballscrews are checked using state-of-the-art measuring and testing processes and are coded accordingly.

On request, we can supply test reports regarding:
  • Lead accuracy
  • Torque
  • Dimensional tolerances
  • Shape and positional tolerances
Certificate

Tolerance classes

Tolerance classes IT 1 IT 3 IT 5 IT 7
Thread length Tolerances( µm )
         -   315 6 12 23 52
316   -   400 7 13 25 57
401   -   500 8 15 27 63
501   -   630 9 16 30 70
631   -   800 10 18 35 80
801   -  1000 11 21 40 90
Shape and positional tolerances, lead accuracy, and torques are specified in DIN 69051. Tolerance classes and tolerances for useful travel (lu) correspond to ISO/DIS 286/1.

Materials

Materials for standard versions
 
Ballscrew spindle:

Steel 1.1213  (Cf53) , ball track hardened to 60 +/-2 HRC

Ballscrew nut: Steel 1.3505 (100Cr6), hardened to 60 +/-2 HRC        
Balls: Steel 1.3505 (100Cr6), hardened to 60 +/-2 HRC
 
Materials for stainless versions
 
Ballscrew spindle:                                  Steel 1.4112, ball track hardened to 56 +/-2 HRC
Mutter: Steel 1.4034, hardened to 56 +/-2 HRC
Balls: Steel 1.4034, hardened to 56 +/-2 HRC

Efficiency

wirkungsgrad
wirkungsgrad

Rigidity

The rigidity of a ballscrew influences its geometric and positional accuracy. In our miniature ballscrews, we use 4-point pre-loading to obtain excellent rigidity values.

The rigidity can be increased and adjusted via pre-loading and the ball oversize. Please note that high pre-loading will have a negative effect on the lifetime.

Static rating

The static rating is an axial load acting concentrically, corresponding to a total permanent deformation of the ball or ball track of 0.0001 x the ball diameter at the most stressed contact area of the ball or ball track.

The static rating describes the maximum possible static load on the ballscrew. Reaching or exceeding this value will result in lasting deformation of the ball or thread profile, which will result in irreparable damage.

Dynamic rating

The dynamic rating is the concentric axial load under which a ballscrew can attain a nominal life of 10 million circuits.

This value should be used when designing a ballscrew. Karl Hipp GmbH recommends a maximum load of approx. 30% of the dynamic rating for continuous operation.

Radial loads

Radial loads may occur due to assembly tolerances, but they should be kept to below 5% of the smallest axial load.

Speeds

When designing a ballscrew, attention should be paid to the critical bending speed – at this point, resonances occur at the spindle – and the maximum speed, both of which are determined to a large extent by the nut design and by the type of ball return system used. 

Guidelines for maximum speeds


Lead:Ø 3 4 6 10  12  16  20  25  32  40 
0.5   4000                  
1 4500 4500 4500 3200   1800          
2     4500 4200 4000 3400 3000        
2.5       4200   3400 3000        
3       4200   3400          
4       4200   3600 4000        
5       4000   3600 4200 4000 3800 3500 2700
10           3600 4200 4000 3800 3500 3000

Lifetime

The lifetime (nominal life) is expressed by the number of circuits that 90% of a sufficiently large number of ballscrews achieve or exceed before the first signs of material fatigue occur. This figure is expressed in circuits or hours.

Karl Hipp GmbH recommends a maximum load of approx. 30% of the dynamic rating for continuous operation.
lebensdauer

Lubrication

Basically, the same lubricants can be used for lubricating ballscrews as are used for ball bearings. Make sure that the lubricants have the same saponification base.

Initial lubrication is done as standard with Staburags NBU12/300KP.

As a rule, a single lifelong lubrication is not sufficient for the ballscrew, as, despite the use of appropriate wipers, the ballscrew spindle continually removes grease.

Karl Hipp GmbH therefore explicitly recommends an appropriate maintenance interval, which should be adapted to the application. If manually relubricating the system, make sure that the ballscrew spindle is carefully cleaned. Further information can be found in our general lubricating instructions.

Several factors determine the selection of a lubricant. The most important ones are spindle speed, ball speed, operating temperature, and ballscrew load. Special lubricants for use in vacuums and clean rooms are also available. Please contact us if you have an questions.

Assembly specifications

Radial or eccentric forces should not act on the nut system during assembly.

When assembled, the nut should easily move at any position on the ballscrew. Possible misalignments and the resulting tension can be easily detected near the bearing or at the outermost end of the spindle. The ballscrew must be assembled with extreme care, as tension and misalignments will reduce the lifetime and may lead to premature breakdown.

Wipers

Various types of wipers, made of felt or plastic, for example, are available for protecting ballscrews from dirt and contamination:

Standard wipers:

Wipers made of POM plastic are used in normal applications. A special plastic made of PTFE may also be used if there are higher requirements for temperature stability.

Vulkollan wipers:

Vulkollan wipers are set apart by very good dynamic characteristics and high wear-resistance. The edges of the wipers are very close to the ballscrew spindle, thus reducing the loss of lubricant. The frictional torque of the ballscrew will be increased. These wipers are not available for all dimensions.

Felt wipers:

If the ballscrew requires special protection from fine dust, we recommend using a felt wiper. Please note that the frictional torque of the ballscrew will be increased. These wipers are not available for all dimensions.

No wipers:

If an application does not use wipers, implement a regular lubrication interval or relubrication in accordance with our lubrication instructions.

To prevent the nut system from being contaminated, additional protective measures, such as a pair of bellows, may be necessary.