A bonding question I can't find the answer to

[JoyfulNoise]

One has to be careful with painted metal surfaces. Paints are emulsions that contain all sorts of chemicals including the colorants, binders and inhibitors. Back in the old days, leads paints had excellent resistance to chloride and sulfate permeation because the lead compounds would immobilize the chlorides and sulfates as insoluble compounds. Paints nowadays don’t contain lead and so other additives must be used to ensure resistance against water and salt permeation. If the aluminum is coated in a cheap paint, then it would be easier for moisture and salts to permeate it. This will then lead to corrosion of the metal surface between the paint film and the metal casing. Chlorides and sulfates will catalyze aluminum reactions with water to form hydroxides. Once those reactions are initiated, there’s very little you ca do to stop them. So it may be that that corrosion gets started by some galvanic processes but it proceeds due to the moisture in the environment. Sort of like lighting a fuse … once lit, it just keeps going.

 

[JoyfulNoise]

I would also look at all the connection points too. It seemed from the earlier photos that steel screws were used to secure the bonding wire to the bonding lug. If the lug and wire are both copper, I would use only brass machine screws or bolts. You can also find ones made out of aluminum too but brass should be fine. If you’re seeing corroded steel screws at the bonding points, then just change them all out with brass in equivalent thread sizes.

 

[JamesW]

 

[JoyfulNoise]

So are you just driving around your neighborhood and pulling up every IntelliFlo you find to prove they're all rotted the same way ?? I hope you at least check that no one is home first, some people might get angry at a random person ripping up their pumps ...

 

[JamesW]

I just explain that it's for science and hope they understand, but in this case, they let their Doberman loose.

Dobermans don't really care about theories of corrosion.

 

[JoyfulNoise]

A lot of these images look like failed paint seal. With aluminum you’ve got a choice of coatings - paint, powder coating, or anodization. Paint is the cheapest but if you don’t get the surface prep right it won’t stick well. I suspect whoever is manufacturing these motors and casings is trying to cut costs with cheap painting. My guess it that they are not using a self-etching primer on the aluminum and so the paint has poor adhesion.

Powder coating is superior to paint especially if it’s a hard coating type that needs heat treatment afterwards. Powder coatings are very good at covering all surfaces evenly. Powder coating is also way more expensive than paint so that probably precludes it’s use.

Anodization is a surface treatment that grows a microscopic porous aluminum oxide surface on top of the metal and allows aluminum surfaces to be colored with dye treatments but it’s not mechanically strong. Anodization could be done prior to painting for better adhesion and corrosion resistance but it’s additional costs would probably preclude it’s use.

 

[JamesW]

Note: Dobermans can run really fast, and unless you have a good head start, they will catch you and they will bite you and it’s not nearly as much fun as you might think; in fact, it’s rather unpleasant.

In any case, while Spike was gnawing on my leg, I had a few minutes to think about what other metals they could use other than aluminum.

My top 4 are sodium, lithium, potassium and calcium.

Maybe I will contact Lafert to see what they think.

 

[JamesW]

Powder coating is also way more expensive than paint so that probably precludes it’s use.

It's not that expensive in a mass production setting per unit.

Maybe a dollar or two.

When you consider the cost of a failed pump at more than $1,500.00 plus labor at maybe $350.00, it's well worth the extra cost.

In any case, aluminum is probably not the best choice.

It acts as a sacrificial anode to all other more noble metals on the bonding grid, so it will probably still corrode even if the coating is really good.

A good stainless steel or maybe brass or carbon fiber might be better choices.

I know where a few other Intelliflo pumps are and I can go tomorrow to see how they are holding up.

 

[JoyfulNoise]

Cast aluminum is probably the cheapest and easiest to come by. It’s fine for applications where mechanical stresses are minimal (non-load bearing) and it’s a good enough thermal conductor. It’s low density as well so it makes the pump lighter weight (good for shipping).

If it is aluminum then I suspect they went with the cheaper 2000 or 3000 series alloys. Those are not very corrosion resistant. 4000 and 5000 series alloys are better and have very good corrosion resistance but are more expensive.

 

[JamesW]

I think that aluminum is a poor choice for this application.

Also, I think that there is something about this system that is going to cause metal corrosion on all of the metals and this can end up being a huge problem.

The gas line to the heater is corroding at an accelerated rate and it will fail prematurely.

In my opinion, all metal on the bonding grid is going to fail much faster than it should.

So, this is about more than just the pump.

 

[mas985]

I agree that aluminum is probably a poor choice. Both my Hayward pumps (Spa & VS) use steel motor housings. The older spa pump motor is a little scratched and you can see a little red rust where the scratches are but there is no bubbling like what happens with the aluminum, just a thin coat of red dust. Steel just seems to hold up better. I thought it was cheaper than aluminum as well.

 

[Bperry]

I agree that aluminum is probably a poor choice. Both my Hayward pumps (Spa & VS) use steel motor housings. The older spa pump motor is a little scratched and you can see a little red rust where the scratches are but there is no bubbling like what happens with the aluminum, just a thin coat of red dust. Steel just seems to hold up better. I thought it was cheaper than aluminum as well.

Put me in for electrical problem. I can’t believe three pumps died that fast from just bad paint. Aluminum is used for lots of stuff that’s in worse environments. It’s also more expensive than steel so it’s not like they are trying to save money by using it.