Many 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.
- Roller screws have triangular-shaped, precision-ground threads that match multiple precision-ground threaded rollers in the nut. Screw components 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.
These 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 actuators
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.
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.
Our high-force products
We offer a range of electric high-force electric linear actuators, many with the option of either screw type.
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.
Original version of this article comes from Tolomatic blog and can be found here