Why convert hydraulics to electric high-force linear actuators
By Ryan Klemetson on April 30, 2019
Got a high-force linear motion application? If you do, chances are the first product solution to come to mind is hydraulic cylinders. After all, they’re relatively inexpensive (if you already have a hydraulic power unit – HPU – in place), compact (if the HPU’s somewhere else) and power-dense.
But what about the disadvantages of hydraulic cylinders? Leaks, operation and maintenance costs, and more? Now that there are electric high-force linear actuators, machine designers have a choice. It’s possible to convert an application from hydraulic to electric linear motion easily. Our guide, How to convert hydraulic cylinders to an electric actuator alternative, gives you a step-by-step explanation of the process.
Why use electric high-force linear actuators
Electric linear actuators use current to produce torque that drives the screw assembly and generates force. Many electric high-force linear actuators use roller screws which have excellent force transmission capabilities (40,000 lbf, 178 kN, and higher).
With an electrical actuator, force is instantaneous. Without extra equipment or additional considerations, a hydraulic actuator has to wait for pressure to build.
Control of variables
An electric linear actuator with a servo motor can control position, velocity, output force, acceleration/deceleration and more. Adjustments are quick, plus accuracy and repeatability are far better than a hydraulic system.
An electric servo actuator system (actuator, motor, cables and drive) takes up only a fraction of the space needed for a hydraulic cylinder with HPU.
Electric actuators offer improved performance at extreme temperature ranges because they are designed to run in these conditions. Hydraulic systems often suffer from sluggish and slow performance during start up in cold temperatures and degradation of hydraulic fluid in hot temperatures.
Life and maintenance
If the electric linear actuator is sized correctly for the application, there is minimal maintenance required so there is no unexpected downtime. Proper electric rod actuator selection starts with an accurate understanding of thrust force and calculations for actuator life. For correct sizing, rely on sizing software and the advice of a linear motion specialist.
Sensing capability is built into an electric actuator’s servo system. Motor current-monitoring tracks force and repeatability. The motor’s feedback device registers position and velocity. Reporting can be accomplished through the drive and PLC.
Electric linear actuator systems are very efficient, typically operating at 75 to 80 percent efficiency, so they use less power than hydraulic systems. Hydraulic systems are only 40 to 50 percent efficient. (See page 11 of our white paper, Electric rod actuators vs. hydraulic cylinders: A comparison of the pros and cons of each technology, for an explanation of how to make this cost calculation.)
Hydraulic systems leak which can create safety hazards, contaminate products and pollute the environment. Clean-up can be costly.
Electric actuation is one of the cleanest linear motion technologies. Grease on the screw is the only potential contaminant. Special greases (food grade, cleanroom, etc.) are available for different applications to further minimize potential contamination.
The bottom line
In the long run, an electric rod actuator’s higher purchase price is offset by its long-term operating efficiency. Utility costs are lower, and there’s superior process control and reporting which improves product quality. Electric roller screw actuators offer long service life with no messy, costly leaks. In many applications, electric actuators offer lower total cost of ownership than hydraulic systems.
For a step-by-step explanation of the process of converting a hydraulic linear motion application to electric, see the video: Sizing Electric Actuators for Hydraulic Replacement.