To make the right selection when specifying actuators, it’s important to consider the operating environment.
Bruce Ng
Valin Corporation
Actuators are required for a variety of operations throughout a multitude of different industries. With so many different potential applications, one would correctly assume that the options can often be overwhelming. Many of these actuators only require a base-level of sizing that is mostly driven by the load (for the bearings) and the desired motion profile (for the drivetrain). However, once the intended use is outside the realm of the basic 80 % or so of applications, it’s not uncommon to run across specialized requirements. Because these requirements may dictate higher costs, it doesn’t always make sense to implement them into standard “off-the-shelf” models for economic reasons. Furthermore, different industries may tend towards their own sets of specific needs.
Industry variety
Whether discussing aerospace and defense, semiconductor, food and beverage, oil and gas, entertainment, or biomedical/pharmaceutical, each industry has unique requirements for actuators. In terms of the different options and specifications available, material composition tends to be one of the main changes from industry to industry. For example, if one needs an actuator in an aircraft, overall weight may be a critical requirement, but if it’s also going to outer space, we also need to reconsider materials that outgas, how its affected by dramatic swings in temperature, and possibly radiation. In food and beverage, there are specific considerations for heat, corrosion resistance and the ease of cleaning. In the semiconductor industry, not only does heat resistance need to be considered, but many processes may need to be cleanroom rated to minimize contamination of valuable silicon wafers.
Specific environments are typically categorized according to a number of factors including extreme temperatures, high or low pressure (vacuum), cleanroom, corrosive, and explosion proof areas. Each of these types of environments require specific design considerations. Many of these design considerations revolve around material choice. This is where having a knowledge of what is available and what will work best in given conditions is critical.
Extreme temperatures
One of the first conditions to consider when determining the proper material for an actuator is the temperature of the environment where it will be operating. One of the materials that is first considered is the lubricant. The right lubricant minimizes wear and improves the overall life of the actuator. If the selected lubricant is not used at the correct operating temperature, it may be less effective and reduce the life of the actuator. As temperatures become more extreme, more and more components are affected. This can include seals, polymers, composites, and even metals. In high temperature-cycling applications, overall design choices may require unique seals or risk mitigation for ingress protection. On the other side of the spectrum with low temperatures, lubricants can become overly viscous, and a wide range of materials can become brittle. This reduces their effectiveness and can generally reduce the effective life of a normal actuator. In high-precision applications, temperature swings can also affect the overall precision of an actuator.
Cleanroom
As mentioned previously, cleanroom environments are often encountered in the semiconductor industry. Anytime that materials physically move over other surfaces, there will be some particulate from the wear. Certain processes require a high level of purity and this particulate can affect that purity. The most susceptible materials are polymers, but lubricants can also generate large amounts of particulate in certain processes at certain speeds. In cleanroom environments, manufacturers may swap out the normal oil or grease for one that is heavier to minimize any unwanted ‘shed’ once the equipment is in operation. Many manufacturers will remove polymers that are on wearing surfaces depending on what level cleanroom rating is needed. For example, a Class 1000 cleanroom allows for up to 1,000 particles greater than 0.5 microns in size per cubic foot. It’s much easier to meet this requirement compared to a cleanroom class 10 requirement. That requirement drops to 10 particles per cubic foot greater than 0.5 microns but also has thresholds for 0.3, 0.2, and 0.1 micron sized particulate.
High and low pressure
Extreme pressures will also affect the materials being used. This typically comes with temperature considerations as well. Certain materials will outgas in a vacuum, which could affect the life of the actuator, or even the process itself. In these cases, it’s important to select materials that are stable at these extremely low pressures to ensure performance. Less air in a vacuum environment also reduces normal cooling methods. Components that require passive air cooling may need to be redesigned to ensure they don’t overheat. Higher pressure applications generally come with additional environmental requirements like ingress protection or corrosion resistance as well. Each one will dictate materials, designs, and tolerances that are needed over the intended use conditions depending on the magnitude of the pressure.
Corrosive environments
Corrosion challenges are common across many industries and often come with additional special environments requiring things like ingress protection to protect sensitive components. Stainless steel is common in these applications as opposed to a harder carbon-steel alloy. Any material that is more prone to corrosion may need to be swapped out or otherwise protected. It’s a best practice to minimize or eliminate any material or design which contains exposed crevices where corrosive fluids/materials could potentially get trapped. In food and beverage applications, these hard to clean areas could lead to hazardous microbial growth. To mitigate this risk, the equipment typically needs to be easily cleaned with high pressure washdown with caustic solvents. If there is direct risk of contamination from leaks, food grade lubricants can also be used.
Explosion-proof environments
In highly combustible environments like oil and gas applications, the overall design may be more of a focus than the individual materials. In fact, many automated processes create the potential for a buildup in electrical charges. Not having a safe, insulated path to ground for this charge can eventually lead to tiny arcs which can be an ignition source when there are combustible gases, vapors, or fibers in the environment. All components for explosion proof ratings should have proper grounding and bonding between metal components to prevent static discharge. Electronics may have conformal coatings or some other encapsulation to contain or prevent potential ignition sources. IEC/ATEX classifications designate explosion proof components.
Price vs. performance
After the load and performance requirements are known, and after the intended operating environment is properly understood, then the discussion of price versus performance begins. In budget constrained projects, sometimes it’s best to get this out of the way first to avoid unnecessary work.
Everybody wants to get the highest performance possible at the lowest price, naturally. However, not every manufacturer necessarily uses the same standard for how they rate the life of their products, and certain environments may lead to de-rated performance specifications. Typically, an actuator has a rated life using a certain speed and thrust for a pre-determined amount of travel. Where one manufacturer may use 100 km as the rated life, another may use 2,540 km, so these ratings aren’t always apples to apples either. If your actuator needs to work once after it’s pulled off the shelf, its margin of safety may be dramatically smaller than if it needs to work 16 hours a day 365 days a year for at least 20 years. If an actuator failure just means you must start a small process over again, your margin of safety may be dramatically smaller than if it could hurt or kill someone. It is always best to get an understanding of what is behind the various performance ratings and understanding what the product’s expected lifespan will look like and how its environment may affect the overall lifespan or performance.
Like many instances where industrial equipment and supplies are specified and purchased, selecting the proper actuator for a given environment can be a high-stakes exercise. Operators don’t want to make a purchase only to find out (sometimes the hard way) that it isn’t compatible with what they are specifically trying to accomplish. It’s always best to at least consult with those in the field that have experience and expertise in the industry so they know all the factors that may affect the decision and can help select the best fitting solutions.
Valin Corporation
www.valin.com
Valin Corporation, a subsidiary of Graybar, is a leading distributor of automation, fluid management, precision measurement, and filtration products for the technology, energy, life sciences, natural resources, and transportation industries.
Filed Under: Actuators, Industrial automation, Motion Control Tips
