• Skip to primary navigation
  • Skip to main content
  • Skip to primary sidebar
  • Skip to footer

Linear Motion Tips

Covering Linear Motion Systems, Components and Linear Motion Resources

  • New
    • Editor’s blog
    • Industry news
    • Motion Casebook
    • Video
  • Applications
  • Slides + guides
    • Ball + roller guides
    • Track roller (cam + wheel) guides
    • Crossed-roller slides
    • Linear bearings
    • Plastic + composite guides
  • Drives
    • Ball + lead + roller screws
    • Belt + chain drives for linear
    • Rack + pinion sets
  • Actuators
    • Ball + leadscrew driven
    • Belt + chain driven
    • Linear motors
    • Mini + piezo + voice coil
    • Rack + pinion driven
    • Rigid-chain actuators
  • Encoders + sensors (linear) + I/O
  • Stages + gantries
  • Suppliers

How to make linear motion systems cleanroom compatible

January 22, 2021 By Danielle Collins Leave a Comment

While we often talk about the importance of keeping contamination out of linear motion components such as linear guides and screws, when these systems are used in a cleanroom, the goal is just the opposite — to keep these components from introducing contamination into the environment.

linear motion cleanroom
Cleanrooms are common in semiconductor manufacturing.
Image credit: Globalfoundries

What exactly is a cleanroom?

According to ISO 14644-1:2015, “Cleanrooms and associated controlled environments provide for the control of contamination of air and, if appropriate, surfaces, to levels appropriate for accomplishing contamination-sensitive activities.”

Cleanrooms are most commonly associated with applications in the semiconductor, electronics, and medical device industries, although other industries — such as aerospace, pharmaceuticals, and food and beverage — also use cleanroom environments in some applications.

The ISO 14644-1 standard rates the level of “cleanliness” of a cleanroom on a scale from 1 (best) to 9 (worst), based on the number of particles — broken down into six size ranges — that are present in a cubic meter of air.

linear motion cleanroom
Image credit: Blue Thunder Technologies

Notice that the cleanroom standard referenced above is from the International Standards Organization (ISO). You may also see the U.S. Federal Standard 209E referenced in some instances, despite the fact that it was revoked in 2001. The FS 209E ratings can be cross-referenced to ISO ratings, but note that the class numbers don’t align. For example, a cleanroom rated as class 1 under FS 209E is rated as class 3 under ISO 14644-1.  


Friction is the enemy of a cleanroom

The overarching goal when using a linear motion system in a cleanroom application is to keep its particle generation to a minimum. But linear motion components rely on sliding or rolling motions, which necessarily produce particles due to friction and wear between surfaces. So one of the main areas of focus should be to reduce friction as much as possible.

boxway
Plain bearings (left) rely on sliding contact, which typically exhibits higher friction and higher particle generation than the rolling contact found in recirculating bearings (right).
Image credit: Poyakar Co.

This means choosing rolling over sliding contact — making linear ball bearings and ball screws a better choice than plain bearings and lead screws for most cleanroom applications.

However, the standard, full-contact seals on linear ball bearings and ball screws experience sliding contact with the guide rail or screw shaft, so low-friction or non-contact seals are preferred over full-contact designs. And recently, some manufacturers have conducted particle-count tests that demonstrate how ball spacers, or ball chains — which separate the balls and prevent them from colliding with each other as they recirculate through the bearing — can reduce particle generation in profiled rail guides and ball screws.

SNR Ball Chain Graphic
Ball separators (also referred to as ball chains or caged balls) can be useful in cleanrooms because they prevent ball-to-ball contact, which can cause particle generation.
Image credit NTN-SNR

Lubrication is both friend and foe

Lubrication is useful not only for reducing friction and ensuring proper operation, but also for “trapping” some of the particles generated by a linear bearing or screw and preventing their release into the environment. But the lubrication itself can be a source of contamination if it’s released into the atmosphere. This is especially problematic with ball screws, which can “sling off” lubrication as they rotate.

Seals help keep lubrication inside the linear bearing or ball nut, but low-friction and non-contact types — while ideal because they don’t generate significant particulates on their own — can allow some lubrication to “slip by” and be released. This is why many cleanroom applications require a cleanroom-approved lubricant. These special formulations have no (or fewer) additives that contain solid particles, such as aluminum, silica, and PTFE.

Cleanroom-friendly materials are a must

The preferred materials for cleanroom environments are stainless steel and PVC, but aluminum and carbon steel are the primary materials used in linear motion components. However, there are ways to make aluminum and standard carbon steel cleanroom-compliant.

Anodizing aluminum, for example, gives it good corrosion resistance. And carbon steel components can be treated with a cleanroom-compatible protective coating, such as black chrome or nickel, to prevent oxidizing.

A wide range of miniature guides and miniature screws are available in stainless steel versions, making them good choices for cleanroom applications with shorter stroke lengths and lighter loads. And miniature versions are typically offered with low-friction seals and low preload as standard options, so their particle generation is inherently less than their full-size counterparts.

Also keep in mind that fasteners are often coated with a black-oxide finish, which has a high rate of particle shedding, even though these components are static. For cleanroom applications, stainless steel hardware should be used wherever possible.

Steinmeyer-miniature-ball-screws
Miniature linear guides and ball screws are often available in stainless steel versions, making them well-suited for cleanroom applications.
Image credit: August Steinmeyer GmbH & Co.

Systems with reduced contact and friction

One way to eliminate or reduce many of the concerns raised above is to use linear motion components and systems that are inherently “clean.” These include air bearings for guidance and linear motors for driving. Both systems eliminate sliding or rolling contact, so they have virtually no friction and no particle generation.

linear motion cleanroom
One solution to the problem of particle generation due to friction is to use non-contact components and systems, such as this linear motor stage with air bearing guides. Even the cable is a flat, self-supporting type that doesn’t require a cable carrier.
Image credit: Aerotech

For example, a linear motor stage with air bearing guides has —in theory — no friction and, therefore, no particle generation. However, in real-world situations, cable management is still a concern, because moving cables and cable carriers can generate particles. But this can be addressed by using cables and cable management systems specifically designed for cleanrooms.

Case in point: Some cable manufacturers offer products with special low-friction coatings to minimize particle generation, and some cable track manufacturers offer systems that reduce wear between chain sections through the use of abrasion-resistant joints. For shorter cable lengths, flat, self-supporting “trackless cables” can even eliminate the need for a cable track or carrier.

You may also like:


  • Linear bearing seals: Types, options, and applications

  • Ball screw seals: Types, options, and applications
  • linear guide for high temperature
    What makes a linear guide suitable for high temperature use?
  • vacuum applications
    How to specify linear motion components for vacuum applications
  • environmental challenges
    Environmental challenges for linear bearings, and how to address them

Filed Under: Applications, Ball + lead + roller screws, Ball + roller guides, FAQs + basics, Featured, Linear bearings

Reader Interactions

Leave a Reply Cancel reply

You must be logged in to post a comment.

Primary Sidebar

MOTION DESIGN GUIDES

“motion

“motion

“motion

“motion

“motion
Subscribe Today

RSS Featured White Papers

  • Identifying Best-Value Linear Motion Technologies
  • What are dual-motion hybrid actuators and where do they excel?
  • Considerations for adding Linear Guide Features to Industrial equipment

RSS Motion Control Tips

  • Digital servo drive with Combitronic system from Moog Animatics
  • New brushless motor features high speed, high power
  • How to calculate required input power for a gearmotor
  • What is AS-I Safety and what are its benefits for motion systems?
  • CVD stepper motor driver with RS-485 Communication

Follow us on Twitter

Tweets by Linear_Motion

Footer

Linear Motion Tips

Design World Network

Design World Online
The Robot Report
Coupling Tips
Motion Control Tips
Bearing Tips
Fastener Engineering

Linear Motion Tips

Subscribe to our newsletter
Advertise with us
Contact us
About us

Follow us on TwitterAdd us on FacebookAdd us on LinkedInAdd us on YouTubeAdd us on Instagram

Copyright © 2021 · WTWH Media LLC and its licensors. All rights reserved.
The material on this site may not be reproduced, distributed, transmitted, cached or otherwise used, except with the prior written permission of WTWH Media.

Privacy Policy