Cathode rust protection

[carrerachimaera]

I'm thinking of purchasing one of these.Has anyone tried this method yet?

www.rustguardian.co.uk/testimonials.html

Colin

[Roobarb]

There was a topic on this a while back. I think it was decided it probably was a con. The principle its based on should be happeining anyway as the -ve side of the battery is connected to the chassis. As all budding 'O'level students know, electrons run from -ve t +ve so in theory is 'flooding the chassis with spare electrons already'

[carrerachimaera]

Thanks Roobarb - Good points

I'll save my money and buy a few tins of POR-15!

Colin

[swilly]

Cathodic protection is tried and tested technology widely used to protect the steel reinforcement in concrete structures and steel/iron pipework etc etc.

Using it on a cars chassis though??????? Not sure.

Simply attching your battery -ve to the chassis of your car does not mimic a CP system.

A CP system works by utilising the item to be protected as a cathode and introducing an anode, typically a conductive paint coating.

Corrosion occurs as -ve ions migrate away from the parent metal.

Introducing a current to the anode creates a potential difference(voltage) between cathode/chassis and anode.

By manipulating the current to the anode and thus the potential difference between anode and cathode you can reverse the -ve ion migration and prevent corrosion.

One BIG problem with CP systems is that all metal objects within the system need to be electrically continous with all others. Any isolated metal will in fact corrode at an accelerated rate as the CP system causes -ve ions to migrate away from the isolated metal.

[carrerachimaera]

Thanks Swilly

"Any isolated metal will in fact corrode at an accelerated rate as the CP system causes -ve ions to migrate away from the isolated metal".

As in the wishbones!isolated by rubber bushes

Back to the drawing board.

[jtong]

<stoopid question>
if the metal is isolated, how can ions be drawn away from it?

[swilly]

jtong said:

<stoopid question> if the metal is isolated, how can ions be drawn away from it?

The potential difference and a voltage across the anode-cathode will cause ion migration between cathode and anode.

It depends on what form the anode takes. My experience is with reinforced concrete structures with an anode coating painted over the complete external faces of the structure. Any electrically discontinuous reinforcement within the structure is then affected by the application of current to the anode coating.

How the anode would be applied in this application to a chassis, I do not know.

[deeen]

On a boat, you just bolt a lump of zinc on and make sure it's connected to any steel. Dunno if this would work on a chassis - only when it's wet, maybe? Then again, that's when it rusts?

[zumbruk]

Boats are immersed in a conductive medium (salt water). That means a circuit can form between the cathode (the protected structure) and a sacrifical anode. I don't see how this could work on a car.

[Roobarb]

I think thats the deal, no one is arguing that CRP doesn't work, it does ie boats & RS concrete as pointed out, but any metal on a car is simply part of a closed circuit driven by the battery, there isn't much else you can do to alter that fact. Even if you do give it a fancy name and a years guarantee. What you need unfortunately is rust eater, paint and elbow grease.