Vacuum chambers must remain clean and free of contaminants and volatile materials that would lead to contamination of the entire system. Assembly for critical applications requires a wide variety of fasteners and their effectiveness is the key to the machine’s overall ability to function as intended. The materials used in their creation and post-fabrication treatments are vital, particularly if the fasteners will be exposed to corrosive elements, extreme temperatures, extreme pressure, or high levels of physical strain. We recently posted an article that went over the issues and contamination problems O-rings can cause within a vacuum system that hurts or inhibits its proper function. Did you know that similar problems can occur when using improper fasteners?
What type of contamination issues are we talking about? Issues such as:
- Embedded and surface water
- Surface particulate
- Volatile organics
- Hydrocarbons
- And more
All of these cause virtual leaks, outgassing, and other catastrophic issues within a sealed vacuum system.
What are the sources of vacuum contamination from fasteners?
Fasteners can cause a variety of contamination issues due to:
- The materials they were made from
- Secondary treatments
- Not being properly cleaned
- Being touched by bare hands after proper cleaning
- Not being packaged correctly
- Utilizing the wrong type of fastener in a blind-tapped hole
- And more
As you can see, surface contamination in a vacuum system can come from a wide variety of sources; all beginning with the original metal the fasteners were created from. This includes any wire or lubricants added to the surface, machining, tooling for drawing, rolling, and heading. The material that the fasteners are manufactured from, or coated with, can also potentially release light-weight molecules that can interfere with the vacuum process; even materials that are not normally considered absorbent (such as metals and glass). Mild steel parts are often chrome-plated or black oxide-coated to prevent rusting. These types of rust or corrosion-preventing methods should be carefully vetted for their appropriateness for vacuum service. Particles are another, more direct form of surface contamination and should be a factor in the choosing of type and coating and the users particular process specifications. Plastics, elastomers, porous metals or ceramics, and lubricants are some of the worst sources of material outgassing. Vapor pressure and the rate of chemical reactions at higher temperatures can also cause outgassing.
Hydrocarbon-based lubricants can be a major source of contamination and are difficult to remove. Secondary hydrocarbon-based lubricants (such as oils and grease) can be major and destructive forms of contamination in vacuum systems since they have very low vapor pressure and will spread throughout a tool quickly, requiring both lengthy and costly cleaning to fully remove.
Packaging of all types can impart contamination on the parts within as well. Proper packaging, including low-outgassing, particulate-rated and/or static resistance is an additional consideration that must be taken into account.
Even handling a properly cleaned part with your bare hands can impart skin oils that will also outgas and drag your system down, emphasizing the need for gloved hands, and proper handling of a cleaned fastener.
How can these problems be solved?
A majority of these issues can be solved through the use of Vented Screws (also known as Vacuum Screws, Ventilation Screws, or Hollow Screws) and/or by vacuum baking. The rest of the issues come down to careful selection of fastener materials and platings, coupled with proper cleaning, packaging, and handling of the fastener after cleaning.
How does a vented screw help?
A vented screw features a hollow core and is specially designed to allow the release of gases, contaminants, and pressure through the fastener. Vented Screws are widely used within vacuum systems and enable faster, more efficient pump-down of HV, UHV, and EUV systems. These components allow the quick evacuation of trapped pockets of air and surface contaminants from blind-tapped holes.
How does vacuum baking help?
Vacuum Baking provides the ultimate level of contamination control for fasteners in very critical process environments. The vacuum baking cycle can be monitored and certified with a Residual Gas Analyzer (RGA) that can provide specific partial pressure peaks and ensure a contaminate-free product. Utilizing the proper fastener, and cleaning technique will ultimately provide the best product for your vacuum system.
How can we help you?
Pure Tech Components is the premier UK distributor for UC Components, Inc. RediVac® line of fasteners, washers, hex nuts, and O-rings. We provide only the best specialised fasteners to a wide range of industries, including medical, food processing, optical, vacuum, semiconductor, and R&D. Partnering with us gives you the confidence and reassurance you need to concentrate on your customer’s needs without worrying or compromising on cost, quality, or customer service. Contact us today for more information or to place an order.