Reasons to anodize:
To increase corrosion resistance. Sun uses 6061-T651 aluminum. It is one of the most corrosion resistant aluminum alloys there is. Whether or not anodizing improves the corrosion resistance of 6061 aluminum is debatable. We have yet to have a manifold returned because of corrosion.
Appearance (color). The 2 colors that would appeal to Sun would be blue or black. Unfortunately these are the colors that are hardest to do consistently.
To provide a hard wear surface. Sun does not make parts-in-body valves. The manifold is just plumbing. We don't need a wear surface.
Because everyone else does it. Bad reason.
Reasons to not anodize:
Cost. It's another process.
Logistics. When you make tens of thousands of manifolds a month and you anodize hundreds, it's a problem. Consistency. See above.
Stamping. After a body is anodized you cannot do any more stamping without making a mess.Inspection. Have you ever tried to look for burrs in a black anodized body? It's the old blackboard factory at night scenario.
Torque. You will experience an increase in breakaway torque when removing items from an anodized manifold.
Fatigue life. This is the best reason to not anodize. Fatigue failure is a very complex phenomenon. What it takes to initiate a crack is difficult to predict. What it takes to propagate a crack is readily defined. Anodizing produces a very thin, very hard, and very brittle surface on aluminum. The first time you pressurize an anodized aluminum manifold you have initiated fatigue cracks. Whether or not the stress is enough to propagate the cracks is a matter of pressure and manifold geometry. Anodizing an aluminum manifold grossly reduces the fatigue life by anywhere from 20% to 50%.
How big is a drop of hydraulic oil?
There are exactly 250 Sun drops in a cubic inch or 15 in a cc.
Why does Sun use 6061 aluminum?
6061-T651 is relatively strong, relatively inexpensive, difficult to machine, readily available in all shapes and sizes and very corrosion resistant. 2024 is stronger and machines beautifully, but is expensive and falls to pieces in a corrosive environment.
Important: Carefully consider the maximum system pressure. The pressure rating of the manifold is dependent on the manifold material, with the port type/size a secondary consideration. Manifolds constructed of aluminum are not rated for pressures higher than 3000 psi (210 bar), regardless of the port type/size specified.
