Thursday, November 21, 2013

Tips & Tricks - Vacuum Viewports

This had already been posted back in September 2007 on our old blog and as it had attracted tremendous interest I'm happy to give it a makeover with more detail !

For those who do not often change things on a UHV vacuum system, here's some tips if you need to mount a viewport. First, never use a viewport that appears to be, or is known to be damaged. A replacement viewport costs far less than repairing a system that has been subject of an implosion caused by a faulty viewport.

Pressure differentials: Kodial VPZ viewports are designed to withstand 1 Bar differential pressure. Other standard viewports are designed to withstand 2 Bar differential pressure. The pressure on the ‘vacuum side’ of the viewport must not exceed a positive pressure differential of 1 bar. The viewports are designed for vacuum applications.
  • WARNING: Pressures in excess of this or high reverse pressures may cause catastrophic failure and result in serious injury.

  • Viewport bolt-up procedure: Always use annealed copper gaskets and a washer with each bolt. Tighten opposing mounting bolts equally over several passes. Use a torque wrench to ensure equal sealing torque. Do not over tighten. Failure to follow this procedure will invalidate any warranty.

  • WARNING: The optic surface is very delicate and will scratch easily. Always wear lint-free or surgical rubber gloves when handling. Never touch the optic surface.
  • Storage: It is recommended best practice that all viewports are covered when not in use.
  • Use: If the viewport is to be used in a vacuum system where materials are deposited or plasma cleaned, an internal viewport shutter should be fitted.
  • Humidity: Anti-reflective coatings are durable and resistant to atmospheric moisture and other common contaminants
  • WARNING: All viewports are supplied UHV clean and ready for use. Optical coatings are typically 10-300nm thick and as such are extremely delicate. Any materials deposited or removed from the coating will affect optical performance. Cleaning should only be attempted when absolutely essential.
  • Dust: Dust should be removed using a particulate and water-free low pressure air-gun, aerosol or puffer.
  • Light smudges (e.g. finger prints): Smudges should be removed by wiping very gently using a lint free optical quality wipe moistened with isopropanol (IPA). Do not use tissue paper.
  • Other marks: Products with more serious marks and contamination should be returned to the supplier for cleaning and/or recoating.
Temperature Specs.
Baking: When baking, ensure the viewports are shielded from direct heat and strong temperature gradients, by, for example covering them with aluminium foil.
  • Heating/ Cooling rates: Heating and cooling rates must be kept below 3 °C/min.
    Max Temperatures: Exceeding the temperatures bellow can invalidate warranty:
Viewport Type|Max Temp °C
Brazed Sapphire |450
Standard VPZ Kodial| 350
Brazed Fused Silica |200
Brazed Quartz | 200
Bonded |120
Mechanically sealed |130
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