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Posted by Daniel Schmit on Tuesday, October 16, 2018

Electric high-force linear actuator choices. Ball vs roller screw

sawmill high-force applicationMany applications require high-force linear actuators – like moving equipment in a foundry or powering a press in metal forming or guiding heavy logs in a sawmill.  Whatever the application, a machine designer is faced with a choice…whether to specify a ball or roller screw in the electric high-force linear actuator.

There are multiple factors to consider in this choice, like:

  • Duty cycle Ratio of the actuator’s working time to total cycle time.
  • Expected service life Number of cycles the actuator is expected to last.
  • Footprint of the actuator   Space your design allows for the actuator.
  • Budget Total cost of ownership budgeted for the actuator.

You can find a discussion of the pros and cons of roller and ball screws on our website.  And we offer a complete guide to all actuator power screws in our publication, Which Screw? Download your copy here.

 

Screw technologies

  • Roller screws have triangular-shaped, precision-ground threads that match multiple precision-ground threaded rollers in the nut. Screw roller screw illustrationcomponents are designed with a fine pitch, providing many points of contact and a large contact radius. The result is less stress per point of contact.

These screws have very high force transmission capabilities since the rollers have significant contact with the screw threads. They can deliver high force, operate at high speeds, are long-lasting and require little maintenance. 

  • Ball screws are named for the re-circulating ball bearings that fit between arch-shaped screw threads and corresponding threads in the nut. The ball bearings transmit force and relative motion efficiently as they roll through one or more circuits in the nut.

ball screw illustrationThese screws have fewer points of contact and are less effective in transmitting force. While ball screw actuators can be back-driven and are often noisy, their lower cost and reliability make them ideal for applications that require moderately high thrust and speeds.

 

A comparison of screw types

In terms of the factors listed above, here’s how these screw types compare:

  • Duty cycle   Roller screws operate well in high duty cycle applications. Ball screws are better suited to lower duty cycle uses.
  • Expected service life   A roller screw’s higher Dynamic Load Rating (DLR) means it will last much longer than a ball screw.

SPECIFICATION

ROLLER

BALL

Dynamic Load Rating

Very  High

Medium

Screw Life

Very Long

Moderate

Space Required

Minimal

Moderate

(DLR is an industry term that represents the highest load a power screw can handle and achieve 1 million revolutions of rated life at 90% reliability.   DLR is usually provided by the actuator manufacturer.)

  • Footprint of the actuator   Because roller screws pack more force into a smaller package, the actuators they power are more compact.
  • Budget   It takes some analysis to determine which screw type is more affordable for an application. Ball screw actuators are usually less costly initially, so in the right application they can have a lower total cost of ownership. However, if the application’s requirements will break down a ball screw actuator prematurely, a roller screw actuator that can stand up to the demands may be the lowest cost solution in the long run.

We have a staff of experts in electric linear motion ready to help you choose the screw type that fits your application exactly.  Contact us.

 

Our high-force products

We offer a range of electric high-force electric linear actuators, many with the option of either screw type.

ServoWeld

ServoWeld Resistance Spot Welding Actuators

  • High-force efficiency
  • Multiple designs
  • Best-in-class performance

RSA-HT

RSA-HT heavy duty electric rod actuators

  • 4 body sizes
  • Strokes from 18 to 60 inches (457 to 1,524 mm)
  • Maximum force/thrust up to 13,039 lbf (58,001 kN)

RSX

RSX extreme force electric rod actuator

  • RSX-096 is capable of 30,000 lbf (133.5 kN) 
  • RSX-080 is capable of 18,000 lbf (80 kN)
  • RSX096P (press version) is under development and will have 40,000 lbf capacity
  • Offering will expand to 50,000 lbf capacity

IMA

 IMA integrated servo motor actuator 

  • Ball and roller screw selections
  • Forces to 6,875 lbf (30.6 kN)
  • Integrated servo motor design

IMA food grade linear actuator

  • Ball and roller screw selections
  • Food grade white epoxy paint
  • Forces to 6,875 lbf (30.6 kN)

ERD hygienic

ERD hygienic electric actuator

  • USDA and 3A approved
  • Clean-in-place
  • Force/thrust capabilities up to 7,868 lbf (35 kN)

 

 

 

 

Watch our video on industrial linear actuators.

 

 

Resources

You can find a discussion of the pros and cons of high-force screw types on our website.  And we offer a complete guide to electric linear actuator power screws in our publication, Which Screw? Download your copy here.

Interested in linear motion? Join the discussion at our LinkedIn group.

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