Aluminum Mold Cavity Hard Anodized
Cylinder Rods Hard Anodized
Mold Inserts Teflon Hard Anodized
Hydraulic cylinders, wear surfaces,
actuating cams, pistons, cylinders,
and hydraulic gear. Other applications include the coating for the production
of flame and chemically resistant surfaces.
[MIL-A-8625F] Type III, Class 1 &
Hard anodizing is a term used
to describe anodic coatings with surface hardness and/or abrasion resistance
as their primary characteristic.
These anodic coatings are
usually thick, greater than .001" (50%-buildup & 50%-penetration),
by normal anodizing standards, and they are produced using special anodizing
conditions. Thick coatings (over .004") will
tend to break down sharp edges. Alloys
with a very high copper or silicon content are less suitable for this process.
The color of the natural
anodic coating depends on the alloy and the coating thickness. e.g. 6061
has a tan or gray color which darkens to almost black at .003"; 6063 has
an amber shade which darkens to bronze. Both are considered clear
After hard anodizing
surfaces may be sealed in boiling distilled water, sodium dichromate solution,
dewatering oil, wax or PTFE solutions.
Dichromate sealing improves
the fatigue properties, but decreases the abrasion resistance to some extent
(in common with other aqueous sealing solutions). For this reason, aqueous
sealing processes are not normally used where high wear resistance is required.
Hard anodized coatings may be impregnated with oils, silicones or dry lubricants
for improvement of anti-friction properties during this seal procedure.
Corrosion resistance could be improved by PTFE impregnation.
For the best resistance
to wear and abrasion it is preferable to use pure aluminum or alloys with
the lower values of alloying additions.
Hard anodized aluminum shows
a good heat resistance, and the coatings give also very good electrical
insulation. This property can be further improved by hot water sealing
Abrasion resistance for unsealed coatings
are tested by method 6192 of FED-STD-141 using CS-17 wheels with 1000 gm
"The anodic coating shall have a maximum
wear index of 3.5 mg/1000 cycles on aluminum alloys having a copper content
of 2 percent or higher. The wear index for all alloys shall not exceed
1.5 mg/1000 cycles".
Type III: Thickness as specified
on drawing. If not specified nominal thickness shall be 0.002" ±
Class 1: Not dyed or pigmented.
Class 2: Dyed. (Specify color
Hard anodic oxide coatings
find application in the engineering industry for components which require
a very wear resistant surface."Flash" hard anodize
may be used instead of conventional anodize for corrosion resistance