Find the Air in Your Ways - Go Electric

by Christopher Nook

Getting some fresh air is always a good idea right? It wakes you up, refreshes you or even changes your mindset. But what happens when the air starts to get stale?

Getting some fresh air is always a good idea right? It wakes you up, refreshes you or even changes your mindset. But what happens when the air starts to get stale?

Pneumatic actuators have been the staple of industry for years, and have been sold as being compact, fast and low cost. Their compact size is due to the remote location of their power unit, the air compressor. Fast response is due to the sudden inrush of air for activation. Low cost because the air cylinder by itself is inexpensive. Electric actuators have made steady inroads to the air actuator market due to advances in control technologies, materials and automation disciplines.

But are air cylinders really low cost? Or is their low cost an illusion? Design engineers sometimes are looking at them individually, not the sum of the system’s costs and ignore the costs of providing air. For example, to control the cylinder you need an electrically operated solenoid valve, regulator, air lines, flow control valves and a reliable source of clean dry air. If the cylinder needed to be moved in both directions, which is the requirement in most cases, a dual stage cylinder and solenoid valve is required, increasing the costs and plumbing complexity.

Most automotive plants are switching to electric cylinders to eliminate an estimated 3% of their plant operating costs of providing air. Electric actuators only require a power source which is always readily available and only needed when the actuation is in process. Air compressors run full time wasting vast amounts of energy creating heat and noise. It is estimated that electric actuators have an 80% advantage over air cylinders in energy efficiency. The air source has to be chilled, dried, oiled and filtered which is 24% of the compressor energy costs. The maintenance cost of this equipment is staggering, in addition to the always present leaks in the system, further raising the cost curve. Air actuators are also very noisy in their operation and their oiled air is released into the environment.

Electric actuators require control to move them. If we are putting in a move profile, which is difficult to do with air actuation, the costs used to be prohibitive. With the advancements in control technology, stepper motor drivers that can be easily interfaced to the machine via can bus are around the same cost as a dual solenoid control valve mounted to a manifold. Helix offers a simple lead screw stepper driven actuator for under $80 and a control can be purchased for $90 to $230 depending on application.

Electric actuators, unlike their air counterparts can stop mid cycle, have a programmable move profile, handle higher loads, move more smoothly, provide variable speed and stroke, require no hard stops, provide high levels of precision motion and only use power during actuation. With the use of different leads of the screw and motor packages, the electric actuator can be customized to the application to optimize the move profile. Furthermore, in the event of a power failure, or in the case of an air cylinder, an air line rupture, the electric actuator stops and usually does not crash, unlike the air cylinder. Because air is compressible, it is not possible to achieve uniform and constant piston speeds and air cylinders may move after positioned because of the compressibility, causing other system issues. Manual set up of the air flow control valves for air cylinders is also a little tricky and odds are they will need adjusting regularly. Electric actuators are cleaner, as they do not have the oiled air mist that is discharged from the air cylinders.

If your process requires routine changeover, electrical actuation is the way to go because it becomes a programming issue that can be easily downloaded to the family of actuators, rather than manual adjustment of a multitude of air cylinders. Electrical actuators don’t require full retraction which may reduce cycle times. Electrical actuators also can be integrated into touch controls to maintain a certain pressure, which is very popular in welding applications.