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Tech News
Weight of Zinc and Iron Phosphate Conversion Coatings Determined with
Proposed ASTM Standards
Two proposed standards that are currently being balloted will
offer coil coaters a definitive chemistry to evaluate the performance
of painting and finishing coatings on coil galvanized steel.
“These are meant to be precise and quantitative, to give a particular
number to tell what their adhesion or corrosion performance will
be,” said Duane Fudge, a chemical engineer with Betz Dearborn,
Horsham, Pa., who prepared the draft standards with co-members
of ASTM Subcommittee D01.53 on Coil Coated Metal who represent
the steel, chemical, and coatings industries.
Standard Practice for Determination of Phosphate Coating Weight
on Zinc Coated Steel will calculate the weight of phosphate conversion
coatings on hot dip galvanized and electrogalvanized steel. An
ammonium dichromate solution removes the phosphate, and weight
loss is used to calculate coating weight.
Standard Practice for Determination of Phosphate Coating Weight
on Cold Rolled Steel will determine the weight of iron phosphate
conversion coatings on cold rolled steel. A chromic acid solution
removes the phosphate compounds, and weight loss is used to calculate
coating weight.
Both standards address required reagents, preparation of stripping
solution, apparatus, test specimens, procedure, and evaluation.
“These will be used primarily by a coil coater or a coil painting
and finishing operation, that would clean and apply these conversion
coatings. These methods are used to monitor the quality of that
finishing operation,” Fudge said. Using the iron phosphate standard,
for example, a coil coater can apply this surface treatment chemistry
and via this method, periodically test the iron phosphate coating
weight that has been deposited and ensure that it stays within
the specification or range desired.
For further technical information, contact Duane Fudge, Engineering Manager, Betz Dearborn, 4636 Somerton Rd., Trevose,
PA 19053 (215/942-3276; fax: 215/ 942-3311). Committee D-1 meets
June 11-14 in Reno, Nev. For meeting or membership information,
contact D-1 Staff Manager Tim Brooke, ASTM (610/ 832-9729). //
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