Mon 5th Feb 2018 - Select the Best Sealing and Shielding for Linear Mechanics in Harsh Environments
Why are the details of an application’s environment so important? Depending on the application, you may need to protect the actuator and its control from the environment. Electromechanical linear stages have critical, moving components that will only work properly within the correct environment. If you try to use the linear stage in the wrong environment, issues can range from the stage not working properly to causing damage to the unit that is beyond repair. If you have a "dirty” application (e.g., a cutting application that produces lots of scrap metal) the proper sealing and shielding are needed on the actuator to protect it from contaminants.
However, it is not always the actuator that must be protected from the environment, but the opposite. We know that linear stages will particulate over time due to normal wear and tear – no matter what application or environment. While we can minimize the amount of particulate from the actuator and increase its life cycle using proper seals and shielding, you must ensure the application’s environment is not compromised. Cleanroom or in-vacuum applications may require zero particulates, so it is critical that they use actuators with seals and shields to protect them. Remember, some linear mechanics are moving only microns at a time. Even the tiniest amount of contamination can compromise and ruin an application.
- Exposure to gases other than air
- Moisture presence
- Pressure level (does it need to be able to perform in-vacuum?)
- Cleanliness (does it need to be rated for cleanroom use?)
- Surrounding objects impacting performance (example – does another unit cause vibrations that will affect the linear stage’s specifications?)
- And more
Sealing and shielding for protection
Seals and shields are both in place to keep contaminants out of a bearing. External seals must be able to prevent contaminants from entering the actuator. Integral bearing seals need to keep contaminants out and lubricant in the bearing cavity. Seals in contact with sliding surfaces are called dynamic seals and are used to seal passages between machine components that move relative to each other either linearly or in the circumferential direction. These dynamic seals must retain lubricant, exclude contaminants, separate different media and withstand differential pressures. The materials from which the seal is made should also withstand a wide range of operating temperatures, and have appropriate chemical resistance.
Ingress protection rating
A complete reference standard for IP ratings may be found in IEC 60529. Following are some basic guidelines:
| First Number
|| Characterization of ingress limit
|0|| No protection
|1|| Objects larger than 50 mm
|2||Objects larger than 12.5 mm|
|3||Objects larger than 2.5 mm|
|4||Objects larger than 1 mm|
|5|| Protected from dust (limited ingress)
| Second Number
||Characterization of ingress limit|
|0|| No protection
|1|| Dripping water - vertical
|2||Dripping water -up to 15 degree angle|
|3|| Water spray
|4|| Water splash
|6|| Powerful waterjet
|7|| Temporary immersion
|8|| Continuous immersion
Parker offers a wide array of linear positioners suitable for applications in a variety of environments, even the harsh ones. Our IP rating differs from product to product and application to application, so we are confident the right fit can be found. Once determined, sealing and shielding guidelines are followed for all our linear mechanics to meet the required customer specifications. In addition to seals and shields, positive pressure ports can be included on linear stages as well. This allows customers to purge unwanted contaminants inside their unit, keeping the performance and life cycle at a maximum.
What if you are not certain which sealing and shielding technology is needed for their application? Parker will work directly with you to provide custom engineered solutions. We will discuss your requirements and can determine the best product to use based on the environment. Forming this partnership throughout the process ensures you receive the best solution for your application - which is Parker’s ultimate goal.
Article contributed by Patrick Lehr, product manager for precision mechanics, Electromechanical and Drives Division North America, Parker Hannifin Corporation.