There has been a wide debate in the industrial press in recent times regarding the comparisons of hydraulic and electric actuation. It would appear that the performance and cost analysis, the two factors which have driven decision making for decades, are not the only features on which to draw comparisons, and conclusions, in today’s environmentally conscious world.
Motion Control Products, a Bournemouth based distributor of motion control systems and solutions, has seen a steep leaning towards electric actuation in recent years. The performance and system cost may be comparable in certain situations. However, environmental compliance and other factors, has favoured the move away from hydraulics for an increasing number of their clients.
Many actuator customers of Motion Control Products are in scientific, food, packaging and other such “clean” environments. Companies in such sectors do not normally favour the presence of hydraulic systems, which can be prone to leakage, when there is an alternative system which offers comparable performance and cost, but with no risk of contamination.
There are other benefits to the user in choosing electric rod actuation too. The footprint and system components required for hydraulic systems means that much more floor space will be consumed in comparison to an electrical system. Electric rod actuators work from a servo drive which is only a fraction of the size of a typical hydraulic power unit, and they do not need hoses, fittings, filters, valves and other components. The electric actuator is built from a power screw and bearings and needs electrical leads, possibly a gearbox and a drive/amplifier, which is usually mounted in a control cabinet.
When comparing efficiencies of systems, electrical actuation typically operates in the 75 to 80% efficiency range for the work they complete; hydraulic actuators, on the other hand, operate in the 40 to 55% efficiency range. An additional factor in the cost of electricity is that electric actuators only demand current when it is required. When electric actuators are at rest, they require no current or only small amounts of current to hold position. Hydraulics systems on the other hand, need the power unit to keep the hydraulics pressurized whenever the system is turned on—an inefficient use of power.
In terms of performance, electrical actuators are normally chosen over hydraulic cylinders because they provide more accuracy, velocity, acceleration and control over positioning. It is also the repeatability of force, speed and positioning in which hydraulic systems compare unfavourably, as they are prone to leaks through seal failure, pressure drops and changes in viscosity and oil grade due to temperature variation.
Heat Management is a major problem for hydraulic systems due to their inefficiencies. High temperatures will create accelerated seal wear and oil degradation, whereas cold weather causes an inconsistency in operation until the oil is warm. Whilst electric actuation can also suffer from overheating, this is normally down to extreme changes in duty cycle or running the actuator harder than it was originally designed for. In most cases, applying the correct grease grade for the operating temperature of the roller screw, will vastly reduce the risk that ambient temperature variance will affect performance.
Electric actuators sized for the life of an application require virtually no maintenance. However, neglecting maintenance items on hydraulic systems leads to leaks or contamination and premature component failures.
Brian Prescott, Motion Control Products, Tolomatic Application Engineer, says “When correctly selected, electric rod actuators makes their total cost of ownership significantly lower over the life of the equipment and therefore provides an attractive alternative to hydraulics. Our range of electric actuators from Tolomatic are capable of providing bespoke solutions for many applications, including stainless steel IP69K construction and hygienic designs to resist wash-down problems. We work with our clients to help them to correctly size and specify the right actuator for the job”.
For more technical information, please contact our sales team at +44 (0)1202 599922.
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