Mild Steel Angle Iron and Brass Screws

[Simon Pettitt]

Hello, I have a project where I'd like to use mild steel angle iron and countersunk holes for brass countersunk slotted woodscrews.

I know that in brass and mild steel together would in theory galvanically corrode where the screw head sits against the face of the countersink. If I put a little clear lacquer on the countersunk hole, would this be enough to stop the corrosion? Or it's best to just not mix them at all?

 

[The_Yellow_Ardvark]

A bit of silicon grease will be better.

 

[Simon Pettitt]

Great! Thanks

 

[--Tom--]

Whilst hypothetically true I doubt you’d find it to be an issue in normal usage- unless you’re making something safety critical I image you’ll be completely fine

 

[sawtooth-9]

Why use brass screws ?
Stainless steel screws would be better

 

[SLM]

Why use brass screws ?
Stainless steel screws would be better

No they wouldn’t. The further apart the materials are in the galvanic series, the more readily they will form a corrosion cell. Brass is actually fairly close to mild steel, and so as long as there is no electrolyte (eg salt water), there’s unlikely to be a problem with those.

 

[--Tom--]

No they wouldn’t. The further apart the materials are in the galvanic series, the more readily they will form a corrosion cell. Brass is actually fairly close to mild steel, and so as long as there is no electrolyte (eg salt water), there’s unlikely to be a problem with those.

That was my thinking, and given its mild steel salt water will corrode it badly even without any galvanic reactions

 

[Lons]

You'll be fine. An example is a fair number of hand planes are made with brass sides and steel sole dovetailed together as well as brass screws through the sides and I've never seen one with a chemical reaction between the metals.

 

[SLM]

You'll be fine. An example is a fair number of hand planes are made with brass sides and steel sole dovetailed together as well as brass screws through the sides and I've never seen one with a chemical reaction between the metals.

It’s not a direct chemical reaction that is the concern with diss-similar metals; an electrolyte is required in order for galvanic corrosion to occur. So, as long as the tools you describe do not come into contact with an electrolyte, corrosion will not be a problem. Otherwise, a simple barrier such as a suitable lubricant, prevents issues

 

[SLM]

That was my thinking, and given its mild steel salt water will corrode it badly even without any galvanic reactions

So how would a stainless screw help?

 

[--Tom--]

So how would a stainless screw help?

I wasn’t clear I was trying to say I agree with your thinking that brass would be fine without an electrolyte.

I then added that if the whole thing was exposed to salt water then the mild on its own would rust so any concerns of galvanic reactions would be overtaken by just general corrosion.

 

[SLM]

I wasn’t clear I was trying to say I agree with your thinking that brass would be fine without an electrolyte.

I then added that if the whole thing was exposed to salt water then the mild on its own would rust so any concerns of galvanic reactions would be overtaken by just general corrosion.

Ah, I see. Well you’d still have galvanic corrosion, probably preferential, so the steel would rot more rapidly; those nice brass screws would fall out of the rotted steel, and whatever they were holding together would fall apart.

However, if one were exposing these materials to salt water by design, appropriate coatings would be used, together with protection system such as anodes.

 

[Phill05]

I have used washers made of Silicone rubber sheet 1mm to 1.5mm thick with a Shore hardness of 60, you can get it in different colours.
I just punched out the washers I need screw up and trim off any protruding edge.

I would think if you used grease or wax as the screw tightens it would scrub off back down to metal.

 

[ChaiLatte]

I have used washers made of Silicone rubber sheet 1mm to 1.5mm thick

Could you please show a sketch of a washer suitable for a countersunk screw in a countersunk hole.

 

[SLM]

Hello, I have a project where I'd like to use mild steel angle iron and countersunk holes for brass countersunk slotted woodscrews.

I know that in brass and mild steel together would in theory galvanically corrode where the screw head sits against the face of the countersink. If I put a little clear lacquer on the countersunk hole, would this be enough to stop the corrosion? Or it's best to just not mix them at all?

What’s the actual application of this? I take it, from your query about clear lacquer, that the steel is to be in-coated, or clear lacquered all over.

 

[Phill05]

Could you please show a sketch of a washer suitable for a countersunk screw in a countersunk hole.

Here you are just done 3 quickly so not centred properly it is quick to punch and you don't get any problems in the future.
This sheet is 0.53mm thick but it is firm and does not rip as well.
You can see in the 2nd image after punching it leaves it dished to accept the screw head.

 

[Simon Pettitt]

It's only decorative - fitting some mild steel angle to some rustic furniture pieces and then using some brass screws (that will be aged somehow) to contrast to the blackened mild steel. I would spray lacquer the steel to prevent it rusting but leave the natural rolled steel appearance.

 

[SLM]

So indoors? I really wouldn’t worry about galvanic corrosion. Assessing such corrosion is part of my job.

I tend to use a dab of glue or oil on screws into wood; that would give you a belt and braces peace of mind.

You can leave the screws in a sealed container with a boiled egg, to give them a patina.

 

[Simon Pettitt]

So indoors? I really wouldn’t worry about galvanic corrosion. Assessing such corrosion is part of my job.

I tend to use a dab of glue or oil on screws into wood; that would give you a belt and braces peace of mind.

You can leave the screws in a sealed container with a boiled egg, to give them a patina.

This is great, thank you

 

[Lons]

It’s not a direct chemical reaction that is the concern with diss-similar metals; an electrolyte is required in order for galvanic corrosion to occur. So, as long as the tools you describe do not come into contact with an electrolyte, corrosion will not be a problem. Otherwise, a simple barrier such as a suitable lubricant, prevents issues

I didn't say there would be, rather suggested the opposite.