X-Ray Calibration Facility (XRCF)

XRCF Contamination Control / Clean Rooms

03/28/01

Material Selection Guidelines for Temporary Test Items Used in the X-Ray Calibration Facility (XRCF) Vacuum System at Ambient Temperature and Less

Objective- To provide the minimum requirements for materials that will be used to support testing in the XRCF vacuum system at ambient temperature and less. One of the outstanding features of the XRCF is the cleanliness of the vacuum system. These requirements are directed toward preventing unrecoverable contamination to this system. Stricter requirements apply to permanently installed facility items since these items can affect the ability to meet advertised performance criteria. Some programs may require stricter requirements to prevent contamination to the test article.

Project Material List- A complete list of materials must be submitted to XRCF at the beginning of the project. The list should include a description of the material, manufacturer, part number, lot number (if applicable), and the quantity used. Include TBD's since they need to be tracked and identified as early as possible. A product description sheet from the manufacturer may be helpful. Include information concerning cure conditions and mix ratios where applicable.

Metal Items - Metals with a high vapor pressure such as cadmium, zinc, and mercury shall not be used in the vacuum system. Stainless steels, bare aluminum, aluminum with a non-dyed sulfuric acid conversion coating, OFHC copper, and other suitable corrosion free metals with simple shapes may be used in the chamber following cleaning (see Precision Cleaning section). A structure that has holes, crevices, thread inserts, weldments or other features that could trap contaminants may need to be cleaned and baked (see Thermal Vacuum Bake section). Carbon and alloy steels can be plated with nickel or chromium to render them suitable for temporary use in the vacuum system.

Glass - Clean (see Precision Cleaning section).

Ceramic - Clean and bake porous ceramics(see Thermal Vacuum Bake). Clean nonporous ceramic (see Precision Cleaning section).

Non-metallic Items- Use MSFC-SPEC-1443, ASTM 595 or other approved material list to select materials. It is important to note the test temperature and preconditioning that was performed on the test sample when selecting a material. The use temperature must be less than the tested temperature. Items with large surface areas should be baked (see Thermal Vacuum Bake). Avoid materials such as Polyvinyl Chloride that contain plasticizers. Avoid materials that might produce particulate matter such as cable lacing.

Coated Surfaces, Tapes, and Epoxies - Same as Non-metallic Items above. Some paints and epoxies are suitable to use without a thermal vacuum bakeout if properly air baked and/or time cured.

Insulated Wire, MLI - Specify suitable insulation such as Teflon or Kapton insulated wire. Bare or nickel/silver plated wire is fine. Clean and bake (see Thermal Vacuum Bake) at ³80° C

Lubricants - Only baked and certified Braycote 600 series or Molub-Alloy 2115 lubricants may be used in the vacuum system. Silicone lubricants shall not be used in the vacuum system.

Motors, Assemblies - Motors and other assemblies should be selected so that the above requirements are met. Particular attention should be applied to the complete removal of improper lubricants, relubrication using acceptable lubrication (see Lubricant section), and the use of proper wire insulation. Motors should have thermal protection to prevent overheating. If the limitations of the material testing specification prevents adequate testing of all components of an assembly, then the item should be cleaned and baked (see Thermal Vacuum Bake). The bake temperature of an assembly must exceed the maximum expected temperature of the item.

Thermal Vacuum Bake - Generally, the hotter and longer the item can be baked, the better the chance that the item will not contaminate the chamber and or test article. Items are typically baked at ³50°C, £ 5X 10-6 torr for at least 48 hours unless otherwise noted Visible degradation of the material during bakeout will obviously result in the rejection of the material. Some materials must be qualified for use by monitoring the outgassing levels during the bake.

Precision Cleaning - Mil-Std-1246, Level 500A or equal.

Others and exceptions - Items not covered by these guidelines or exceptions must be noted and agreed to before start of test. XRCF reserves the right to reject the use of any material at any time due to concern of potential contamination to the XRCF vacuum system.

For more information regarding XRCF contamination control, please contact Jay Carpenter at (256) 544-1313.