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Screw Fastening Systems
5.1 Corrosion Resistance for Screws

The ability of any fastener to maintain a fastening is directly related to its ability to maintain its embedment in the base material and to avoid loss of engagement with that material. Any corrosion of the fastener may diminish this engagement and lessen the performance of the fastener. To help prevent this, a corrosion resistant finish may be applied to the fasteners.

A standard reference to corrosion resistance, the salt spray test is considered a bench mark. The salt spray results given in the following table are for comparison of the relative corrosion resistance of each coating. The actual performance of any coating is directly related to the quality of the coating, the actual environment for the application and the application method used to install the fastener.

Hilti Screw Fastening Systems Guide to Corrosion Resistance


CARBON STEEL COATED
Protective Coating Composition/
Appearance		 Salt Spray Test Results Anti-Corrosion Properties Comments
Phosphate and Oil Black oil finish 24-48 hours Fair to Poor Basic coating for drywall screws
Good adhesion to drywall mud
Galvanizing - hot dipped Dull gray - rough 48-144 hours Good Corrosion resistance is dependant upon the thickness of the coating
Not suitable for threaded or internally driven fasteners
Zinc plating with Chromate Silver to gray - bright 48-144 hours Good Standard for industrial applications
Superior to cadmium in most industrial atmospheres
Cadmium withChromate Silver/gray - dull to bright 48-144 hours Good Low cost, good appearance
Superior to zinc in salt environments
Zinc/Chromate/Organic
(Kwik-cote or Equal)		 Gray, Black or Green 560-800 hours Excellent High performance coating
Superior to most plated finishes
Nickel/Zinc/Chromate Silver to gray - bright 640-1000 hours Excellent High performance - bright smooth finish resistant to abrasion or damage
HIGHER GRADE STEELS
410 Stainless/ Cadmium Silver to gray - bright 144-300 hours Good Good appearance - high resistance to most corrosive atmospheres
Good choice for structural self-drilling fasteners
300 Series
Stainless Steel		 Silver - dull to bright N.A. Excellent Highest corrosion resistance available
Not suitable for self-drilling applications due to inability to harden beyond RC 32-36

WARNING: Because of the potential for delayed embrittlement failures, these hardened steel fasteners are not recommended for use with aluminum or chemically treated wood when moisture may be present; or in corrosive environments. For further information contact the Hilti Customer Service Department at 1-800-879-8000.

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