172 replies to this topic

[fezzasus]

 

Wouldn't compare 747 metal pairing to the VX. 747 has a much more proactive maintenance and no exposure to salt.

 

I also wouldn't rely on coating as the clamping force of very rough surfaces will likely penetrate any coating.

 

Ultimately, you're trying to design a problem away that doesn't exist. The corrosion resistance of the spacers is not the issue (and only exist to create a barrier between the subframe and chassis), they are only replaced as they are a cheap item to replace and often deform as the aluminium chassis builds up aluminium oxide at the chassis-spacer interface. Just spec a like-for-like part

 

True though the principal is the same, to get as many of the components as close to each other as possible in the Galvanic table either by base material or plating though both is a superior solution. If you are going to have to plate the steel option anyway then it is no different to plate a stainless version.

400 series active stainless is almost identical to steel with the advantage of not decaying itself.

Always worth looking at improving the OE if possible, most OE material decisions were heavily based on cost.

If the material cost is going to be £60p for steel and £1.20 for 400 SS then it would be a no brainer as in the total production costs this would be negligable.

Might be worth a little research on the latest compounds as there is probably something more suited with superior capabilities available today.

Some of the latest off shore use compound technology lasts for years.

 

If you can design the problem out altogether why wouldn't you try?

 

Anyone know why the plate is bent?

 

 

 

The principle isn't the same. Stainless steel is significantly more active than steel when coupled to aluminium. If the coating is damaged (visual inspection of the plates will confirm it will be penetrated) then steel has a much weaker galvanic couple than stainless steel with aluminium.

 

Suspect the plate is bent to aid seating before mounting the subframe.

[Spitfire Engineering]

I understand the principle, I didn't realise we cannot isolate the shim due to the expected physical damage of any coatings, thanks.

 

The local laser fabricators has S355 normally in various thicknesses, I'll take a look at that with a zinc/passivate/lacquer to see if the lacquer will cause any issues when trapped.

In the meantime I will research other protecting coatings/applications to see what is sensibly available.

 

Roughly how large is this shim including bent sections?

Any reason why there cannot be a tab rather than bends? I assume the bolts could keep it in place while mounting?

If the bends are negated then the shim can be made perfectly flat then rumbled to give a good base for any treatments.

 

 

[The Batman]

Rough guess at 23.13 on a sat night is 250mmx60mm

[The Batman]

Here's a picture of some corrosion just for reference

[Spitfire Engineering]

Wow, that is quite a nice garden you have growing there  

 

Plate thickness?

[The Batman]

Wafer thin, 1-2mm will do some measurements and drawing on an old beer mat next one I do

[Aerodynamic]

I till mine apart yesterday and it didnt look that bad at all. Anyyway should I take duralack on the washers used when bolting together everything? Br,Per

[fezzasus]

Durlac should go on any dissimilar metal interface.

 

 

[vocky]

I till mine apart yesterday and it didnt look that bad at all.  

 

prevention is far better than leaving them to corrode

[Aerodynamic]

What im afraid of is if the Duralac is building between the clamping surfaces when tighting the bolts and then later disapear (floats away) and maybe the clamp force disapears or becomes less. Om not worried about to Good surfaces protection. :-)

[fezzasus]

What im afraid of is if the Duralac is building between the clamping surfaces when tighting the bolts and then later disapear (floats away) and maybe the clamp force disapears or becomes less. Om not worried about to Good surfaces protection. :-)

 

It won't. It will set as the solvent evaporates.

[Mopeytitan]

Why not just use titanium? Maybe slightly more expensive but not much

[garyk220]

Gaz,

 

I still have the original plates I removed from my car last month. Corrosion/oxidation of the aluminium was minimal and car had done less than 28,000 miles so they would be a good base to measure for a pattern part.

 

If no one else has supplied a set yet, pm me with your address and I'll pop them in the post to you. Cheers,

Gary

 

 

Well it sets as it dries so would act more of an anti-slip agent.

 

 

Original anyone??

 

 

[Spitfire Engineering]

Thanks Gary

 

Please.

 

[fezzasus]

Why not just use titanium? Maybe slightly more expensive but not much

 

It will still cause corrosion.

 

Even if a material doesn't corrode itself. The electron density of materials is different (effectively the available negative charge), if you place a material of high electron density next to a material of low electron density, the electrons/charge will flow from the high area to the low density area. This will cause a flow of cations to balance the charge which is typically metal oxides/sulfides (depending on the environment) from the higher electron density material to balance the charge. This is the material loss/corrosion you see on the surface. For iron/steel it's iron oxide, for aluminium it's aluminium oxide.

 

You need to select a material which has the smallest difference in electron density at the interface. Titanium is massively cathodic so will effectively pull electrons/charge towards it, this means the titanium won't corrode but the materials attached to it will corrode much faster than other materials.

 

[Mopeytitan]

Why not just use titanium? Maybe slightly more expensive but not much

  It will still cause corrosion.   Even if a material doesn't corrode itself. The electron density of materials is different (effectively the available negative charge), if you place a material of high electron density next to a material of low electron density, the electrons/charge will flow from the high area to the low density area. This will cause a flow of cations to balance the charge which is typically metal oxides/sulfides (depending on the environment) from the higher electron density material to balance the charge. This is the material loss/corrosion you see on the surface. For iron/steel it's iron oxide, for aluminium it's aluminium oxide.   You need to select a material which has the smallest difference in electron density at the interface. Titanium is massively cathodic so will effectively pull electrons/charge towards it, this means the titanium won't corrode but the materials attached to it will corrode much faster than other materials.  

I see! So would it it be plausible to use an aluminium one instead? Almost like a sacrificial part?

[fezzasus]

 

 

Why not just use titanium? Maybe slightly more expensive but not much  

  It will still cause corrosion.   Even if a material doesn't corrode itself. The electron density of materials is different (effectively the available negative charge), if you place a material of high electron density next to a material of low electron density, the electrons/charge will flow from the high area to the low density area. This will cause a flow of cations to balance the charge which is typically metal oxides/sulfides (depending on the environment) from the higher electron density material to balance the charge. This is the material loss/corrosion you see on the surface. For iron/steel it's iron oxide, for aluminium it's aluminium oxide.   You need to select a material which has the smallest difference in electron density at the interface. Titanium is massively cathodic so will effectively pull electrons/charge towards it, this means the titanium won't corrode but the materials attached to it will corrode much faster than other materials.  

 

I see! So would it it be plausible to use an aluminium one instead? Almost like a sacrificial part?

 

 

The part isn't really sufficiently accessible to consider sacrificial. the only material that will realistically work is mild steel coated with a zinc doped epoxy. This will mean the zinc still remains on the interface when the faces are crushed together (unlike a simple zinc coating). These are commonly available and low cost.

[ditonics]

I still think a non metallic material world be the way forward. No electrolysis to worry about

[fezzasus]

I still think a non metallic material world be the way forward. No electrolysis to worry about

 

It'll take a lot of material testing to identify a material that can take the clamping force and vibrations of that application.

 

Personally I feel the OEM parts have a suitable lifespan, they last for around 10 years before significant corrosion, which is in line with the lifespan of the bushes, suspension and far longer than the engine side mounts. I think it's reasonable to expect a full rebuild of serviceable parts at 10-15 years.

[Mopeytitan]

 

 

Why not just use titanium? Maybe slightly more expensive but not much  

  It will still cause corrosion.   Even if a material doesn't corrode itself. The electron density of materials is different (effectively the available negative charge), if you place a material of high electron density next to a material of low electron density, the electrons/charge will flow from the high area to the low density area. This will cause a flow of cations to balance the charge which is typically metal oxides/sulfides (depending on the environment) from the higher electron density material to balance the charge. This is the material loss/corrosion you see on the surface. For iron/steel it's iron oxide, for aluminium it's aluminium oxide.   You need to select a material which has the smallest difference in electron density at the interface. Titanium is massively cathodic so will effectively pull electrons/charge towards it, this means the titanium won't corrode but the materials attached to it will corrode much faster than other materials.    

I see! So would it it be plausible to use an aluminium one instead? Almost like a sacrificial part?  

  The part isn't really sufficiently accessible to consider sacrificial. the only material that will realistically work is mild steel coated with a zinc doped epoxy. This will mean the zinc still remains on the interface when the faces are crushed together (unlike a simple zinc coating). These are commonly available and low cost.

I get what you mean with it's not as accessible but surely it would be better to have a spacer pieced corroding away than the chassis legs?...