FEATURE LINEAR MOTION Facing the challenge
Electromechanical actuators used in challenging outdoor environments will often face extremes of temperature, liquids, dust, shock and vibration. Today’s devices, however, are built to withstand such threats, as Chad Carlberg, product line manager for linear actuators at Thomson Industries, explains
F
or outdoor applications that require lifting, lowering, pushing, pulling,
rotating or positioning a load, electromechanical linear actuators can prove to be a good choice. As a result, they are often used in agricultural, construction, recreational, marine, industrial and even residential automation. In such applications, however, the actuator may be faced with assault from solids, liquids, extreme temperatures, shock, vibration, corrosion and electromagnetic interference. A growing body of standard test methods has emerged around each type of threat and designers are now building in new protections that help meet those standards.
THREATS One of the greatest environmental threats to an electric actuator is penetration from both solid objects, such as dust and dirt, and liquids – ranging from rain, sleet and snow to high temperature, high-pressure washdown. The IP rating system was developed to specify the degree of environmental protection an enclosure provides against foreign materials that could impact performance. Industrial actuators use the same rating system to determine the degree of environmental protection required for specific applications. The IP rating is composed of two
numbers – the first represents resistance to solids, the second to liquids. An IP rating of 00, for example, means there is no protection from solids or liquids. An IP rating of 11 means protection from ingress by objects larger than 50mm and from rain or condensation. An IP rating of 66 means protection from penetration by particulates the size of dust and from high-pressure water jets from any direction. For dusty applications, IP54 is the
minimum rating, so for extremely dusty applications – such as those involving sawdust, paper or cardboard particles – IP65 may be more suitable. An IP65 rated device handles some moisture as well, but if operation in heavy rain is expected an IP66 rating is more suitable. If the
38 APRIL 2016 | DESIGN SOLUTIONS
actuator might ever be immersed in water, an IP67 rating would be even better. IP69K is most suitable if the actuator must withstand a high pressure, high temperature washdown process. Meeting the requirements associated with IP69K has, for example, become increasingly important in farming equipment and construction applications where use of pressure washing equipment is growing. To test a system for water resistance,
specialists would refer to the published test specifications for volume, pressure, temperature and distance of the water for each rating, and flood the actuator in all three planes. To test resistance to high- pressure washdown, they might expose it to 100 bar (1450 PSI) at a distance of 0.1 to 0.15m on all planes. After each test the specialist will disassemble the actuator looking for evidence of ingress of water.
The IP rating system was developed for enclosures.
Industrial actuators use the same rating system to determine the degree of environmental protection required for specific applications
First digit: Ingress of solid objects 0 1 2 3 No protection
Protected against solid objects over 50mm e.g. hands, large tools
Protected against solid objects over 12.5mm e.g. hands, large tools
Protected against solid objects over 2.5mm e.g. wire, small tools
4Protected against solid objects over 1.0mm e.g. wires
5 6
Limited protection against dust ingress (no harmful deposit)
Totally protected against dust ingress 7N/A 8N/A 9K N/A
Standard tests of this sort are typically done on static systems but greater reliability can be achieved by observing performance under IP test conditions when the actuator is in operation. Thus, it is important to know not only that a static actuator can withstand a pressure wash, but also that it remains well- protected when operating outside in the rain. An inadequately sealed actuator, for example, can act like a syringe, sucking rainwater into the actuator, compromising the electronics and rendering them worthless. This vulnerability would not show on a static test, but would show in dynamic testing. Achieving a higher IP rating is mostly a function of sealing strategy. Every component should be sealed, including motor mounts. Wipers, seals and gaskets are integral to successfully achieving IP ratings. The wipers brush off contaminants from the extension tube during operation and are the first line of defense to water intrusion. The seals back up the wipers to complete the protection. Gaskets provide sealing between housings, cover tubes, motors and rear mounting components.
STANDARDS
As there has become a trend to expand the operational temperature range for many outdoor applications, -40˚C to +85˚C is a new standard for agriculture and construction vehicle applications. The most widely applied test standard is
Second digit: Ingress of liquids No protection
Protected against vertically falling drops of water or condensation
Protected against falling drops of water, if the case is disposed up to 15˚ from vertical
Protected against sprays of water from any direction, even if the case is disposed up to 60° from vertical
Protected against splash water from any direction
Protected against low pressure water jets from any direction. Limited ingress permitted
Protected against high pressure water jets from any direction. Limited ingress permitted
Protected against short periods of immersion in water
Protected against long, durable periods of immersion in water
Protected against close-range high pressure, high temperature spray down
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