b.
Atomization Air Cleanliness. Compressed air used for atomizing
metallized coatings shall be tested using the method described in
paragraph Abrasive Blast Air Cleanliness.
c.
Metallized Coating Appearance. The Coating Inspector shall
visually inspect the appearance of the applied metallized coating
prior to sealing for compliance with the requirements of paragraph
Metallized Coating Appearance. Areas of defective coating shall
be reported to the Contracting Officer, documented, and marked for
repair by the Coating Inspector.
d.
Metallized Coating Thickness. The Coating Inspector shall
evaluate the thickness of the thermal spray coating for compliance
with paragraph Metallizing Thickness. Measurements shall be made
using an approved and calibrated magnetic film thickness gage.
Gages shall be calibrated on metal substantially the same in
composition and surface preparation to that being coated and be of
similar thickness or have a minimum thickness of 6 mm 1/4 inch.
Calibration thickness standards (shims) shall be of a metallic
composition similar to that of the material being sprayed. The
calibration shim's thickness shall closely approximate the
specified thickness. Calibration instructions and thickness
standards shall be obtained from the manufacturer or supplier of
the gage. Thickness readings shall be made either in a straight
line with individual readings taken at 25 mm 1 inch intervals or
spaced randomly within a 25 cm2 4 in2 area. Line measurements
shall be used for large flat areas and area measurements shall be
used on complex surface geometries and surface transitions such as
corners. The average of five readings comprises one spot
measurement. A minimum of 5 randomly spaced spot measurements per
9 m2 100 ft2 shall be made. For each 9 m2 100 ft2 area evaluated
the minimum average and minimum spot thickness requirements shall
be met. Areas of deficient coating thickness shall be marked and
corrected before sealing begins. The results of the thickness
measurements shall be documented by the Coating Inspector.
e.
Metallized Coating Adhesion. The Coating Inspector shall evaluate
the adhesion of the thermal spray coating for compliance with
paragraph Metallizing Adhesion in accordance with ASTM D 4541
using a self-aligning type IV tester described in Annex A4 of the
specification. A total of three randomly spaced adhesion tests
shall be performed for each 45 m2 500 ft2 of work area. Where
deficiencies are noted, additional testing may be performed to
help delineate the extent of area with poor adhesion. Areas of
deficient adhesion shall be repaired by removing and reapplying
the metallized coating. Areas damaged by adhesion testing must
also be repaired by abrasive blasting and reapplication of the
metallic coating. As an alternative to testing to the failure
point, the tests can be interrupted when the minimum specified
adhesion value is achieved. This method precludes the need to
repair coatings damaged by the test. The adherent pull stubs can
then be removed by heating to soften the glue or by firmly
striking the side of the stub. A strong (minimum 20.7 MPa 3000 psi
) adhesive with a rapid cure (maximum 1-hour at 21 degrees C 70
degrees F) shall be used to adhere the pull stubs to the
metallized coating. Methyl methacrylate adhesive Plastic Welder
manufactured by Devcon is known to achieve a 27.6 MPa 4000 psi
bond strength in 1-hour.
SECTION 09971A
Page 27
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