Rust prevention and countermeasures for iron parts of airsoft guns (blackening for beginners)

This time, we'll introduce how to deal with and prevent red rust on iron parts, which doesn't look very good.

Especially in humid environments like the rainy season, iron parts that haven't been properly rust-proofed will quickly develop red rust. Furthermore, when I installed a cooling fan (the type that uses water) in my house this summer, all the iron parts rusted.

Therefore, I'd like to proceed with treating the red rust and applying rust prevention treatment.

Before that, let me introduce some basic concepts about rust.

Iron rust (oxidation)

We will consider rust (corrosion, oxidation) of iron, a fundamental material in machinery (including airsoft).

Basically, iron on Earth is a metal that ionizes very easily unless it has been specially alloyed or surface-treated.

Looking at it using the familiar ionization tendency, it is as follows:

Li>K>Ca>Na>Mg>Al>Zn>Fe (iron)>Ni...

It is the eighth element to ionize among the more than 8 elements that exist, making it an extremely unstable element in nature.

Iron is easily ionized, so it will quickly ionize when it comes into contact with even a small amount of electrolyte (such as human sweat, salt water, or moisture).

When iron is ionized, it basically becomes a +3 valent cation, but under special conditions it can become a +2 valent cation.

$Fe^{+2} or Fe^{+3}$

When a substance is ionized, its charge becomes uneven and unstable. To stabilize itself, the substance tries to combine with other substances to stabilize its charge.

The quickest substance needed to stabilize these iron ions is oxygen from the air, and iron actively absorbs oxygen (this reaction generates heat, which is what hand warmers utilize).

Oxygen is basically a divalent negative ion, $O^{-2}$, so when it combines with a common iron ion (a trivalent cation), it looks like this:

$2Fe^{+3} + 3O^{-2} → Fe2O3 (iron oxide, red rust)$

This is what becomes red rust, and it represents the basic mechanism of rust formation.

This chemical reaction happens in an instant.

In my experience, when I touched a surface of iron that had been machined to a surface roughness of 6.3s (the lowest level of mirror finish), red rust immediately appeared in the shape of fingerprints.

In other words, if iron is left exposed to the atmosphere without any treatment, it will inevitably rust (if surface treatment is not possible, it should be soaked in oil).

This red rust has drawbacks such as being unsightly, but the real problem is that it's corrosive.

The corrosive nature of iron means that it's not just the surface that rusts, but it gradually corrodes, turning the entire component into red rust (Fe2O3) and causing it to decay.

Therefore, iron parts in conventional industrial products are always treated with a surface treatment to prevent rust from forming.

Typical surface treatments include painting, zinc plating, chrome plating, Dacromet treatment, and chromate, among others (the choice depends on the application).

The basic idea behind all these processes is to create a film on the iron surface to prevent ionization of the iron and avoid contact with oxygen in the air (zinc plating is slightly different).

This concludes the basic explanation of the rust formation mechanism.

Next, I will introduce blackening, a type of rust prevention method.

Blackening (a type of rust prevention)

Now that you understand that red rust is corrosive and problematic, let's look at the mechanism of blackening, a type of rust prevention.

I hope you now understand that when iron is ionized, it basically becomes a trivalent cation ($Fe^{+3}$).

However, under specific conditions, iron can become a divalent cation ($Fe^{+2}$).

In that environment, under an acidic electrolyte with a pH (a number representing the degree of acidity, where 7 is neutral) of less than 3, it becomes a divalent cation.

The oxidation reaction in this state is as follows:

$ Fe^{+2} + O^{-2} → FeO $

However, in reality, not all iron becomes a divalent cation, so the following occurs:

$ Fe^{+2} + 2Fe^{+3} + 4O^{-2} → Fe3O4 (iron tetraoxide, a mixture of FeO and Fe2O3) $

This process, using iron tetraoxide, results in a black color, hence the term "blackening."

One of the advantages of this type of rust is that it is not corrosive, so only the surface turns black, and the possibility of the rust penetrating deep into the material is greatly reduced.

Therefore, it is used as a type of rust preventative.

What's interesting is the idea of ​​"if it's going to rust anyway, let's actively generate rust that's convenient for humans." However, the thickness and strength of the iron tetraoxide film are not very high, so it's weaker compared to other rust-preventive treatments.

Because it's easy to apply, it's used when cost is a priority or for rust prevention in environments where rust is not a major issue.

Industrially, the process involves immersing the parts in an acidic liquid and leaving them to dry (electrical treatment is required for plating, for example).

This concludes the basic theory of rust.

If you're interested in chemistry or mechanical materials, please check this out as well.

Hair dyeing for beginners

From here on, I, a complete beginner, will try dyeing my hair black.

The part in question is Laylax's 17.5mm muzzle protector.

There is a considerable amount of rust.

We will blacken this to prevent rust.

Things I prepared

The solution I prepared is shown in the following picture.

・Foresight Gun Blue Solution pH 1.7~1.8

・WD-40 Rust Inhibitor and Lubricant

will be important.

Now, let's proceed with the pre-treatment before dyeing it black.

Pre-treatment for black dyeing

First, we will remove the red rust that has formed on the parts.

This can be removed with a file or sandpaper, but since that's tedious, I'll use a rotary tool with a buffing pad to remove it.

Dremel High-Speed ​​Rotary 4000
This is my go-to rotary tool that I always use. Having this expands the possibilities of your DIY projects. There are two popular models, the 3000 and the 4000, but I recommend the 4000 because it comes with a set of tools and has more power.

After removal.

If you want a clean, complete black finish, it's best to sand the surface down until the underlying silver is completely visible. However, since the purpose this time is rust prevention, we'll dye it to this level.

Next, I'll wipe off any shavings that have stuck to the surface. Ideally, I'd like to blow them away with an air compressor or something.

A word of caution: using parts cleaner or similar products to clean the surface will make it too clean (removing all oil and other substances), causing it to rust very quickly, so we recommend against using them.

Also, if you like the texture of this surface, applying a rust preventative (such as WD-40) in this state should prevent rust to some extent.

黒染め処理

Since the parts are small this time, I'll be applying the blackening solution with a brush.

First, divide the black dye solution into smaller portions.

Apply this to the parts. Be careful, as the solution has a pH below 2 and is not good for the skin.

I'll keep painting.

The interesting thing is that the areas I painted started to turn black very quickly.

Apply it to the entire surface as is.

Then, just leave it until it reaches your desired shade of black.

Post-processing

This is what the parts looked like after being left untouched for about 15 minutes.

It dyed fairly well.

I thought this was good enough, so I wiped off the blackening solution with a towel and then applied WD-40 rust preventative just to be safe.

While blackening alone provides some rust prevention, as explained, it's not a strong rust-preventive treatment, so we also apply a rust inhibitor.

Once the WD-40 has soaked in, it's done.

Complete

Product

I think it improved considerably with just a few simple steps.

Before work

After work

We will continue to monitor the situation.

It's been about a day, and no rust has appeared yet. I'll keep checking it regularly and post updates.

Even an amateur like me managed to do it.

Before and after processing of other parts

I'll also show you some other areas that I was curious about, including the parts that were blackened with red rust.

knurled screw

Before processing

After processing (the inside of the hole was not treated)

This is a sight, swivel, and port cover for an AEG (Airborne Enclosure) from an HK416 CAG.

Site

Before processing

After processing (it became a little patchy)

swivel

Before processing

After processing

Ejection port cover

Before processing

After processing

And that's how it went; each part took about 20 minutes.

Furthermore, the same procedure could be performed without disassembling the parts, using the parts as they were assembled.

Summary

While achieving a black finish that looks like an art piece might be difficult, even an amateur can easily achieve a rust-preventive black finish.

It's easy to do.

.

These two are the essential tools.

FORESIGHT Room Temperature Blackening Agent, Gun Blue Solution, 125g
When choosing other solutions, pay attention to the pH. A pH of less than 2 is recommended.
Apparently, the really skilled ones make their own solutions.

・WD-40 Rust Inhibitor
This is a standard rust preventative. I learned about it on Twitter.

In addition to this, you'll need sandpaper to remove rust. I personally find sanding troublesome, so I use a rotary tool's buffing wheel to polish it.

With this, I think anyone can take care of rust prevention and blacken their surfaces.

If you're feeling sad because your airsoft parts are rusty, give this a try. You'll probably be surprised at how clean they become, and you'll feel even more attached to them.

Even if you fail, you can easily try again by polishing it again and doing the same thing again.

Thank you for your time.