Firstly,

Will 304 Stainless Steel Actually Rust?

304 stainless steel is inherently highly corrosion-resistant, so why does it rust? In fact, under certain specific conditions and environments, "incidental corrosion" can still occur.

Based on internal sales data, with an average daily sales of 8,000 square meters of wire mesh, there have been less than 10 cases of rust reported in the after-sales feedback over the past year. Most of these cases have occurred in coastal areas. However, in the past two years, customers have reported more frequent instances of stainless steel wire mesh rusting than ever before.

Our纱网 raw materials are sourced from a domestic reputable large manufacturer - Baosteel Group, and are regularly sampled for inspection, including salt spray testing and material composition, all of which meet national standards. Under the principle of "producing high standards and high-quality raw materials," the frequent occurrence of rust in our products is unacceptable.

Therefore, we sent our technical staff to the project site. Upon seeing the "rusting" of the window screens, our doubts only deepened, as it exhibited a completely different pattern from what is typical of stainless steel rust.

After observing the mesh screen, the following phenomena were noted:

• Spot locations are primarily concentrated in the upper to lower sections of the mesh (forming a broken straight line), the middle to lower part of the mesh, and near the frame of the mesh fan.

• The纱网products uniformly exhibit a white substance around their periphery.

    •    

Initially, we stripped the coating from the suspected rust areas using tools, then observed under a high-power electron microscope. No rusting traces were found on the stainless steel wire.

After discussing with our clients, we have decided to disassemble and conduct further analysis of our shawl fan products.

Upon prying open the pleating of the bamboo fan, we discovered a surprising situation: a substantial amount of white material had accumulated beneath the pleating of the fan's frame. After removing the bamboo mesh, we found that the surface coating of the inner frame within the fan had blisters and damage. The white substance was seeping out from the damaged coating of the frame. Additionally, some screws securing the bamboo mesh and the corner pieces assembling the fan had varying degrees of oxidation.

Upon inspection, it was discovered that the white substances are actually aluminum oxides. Analyzing the content above, it turns out that this is actually oxidation corrosion of aluminum alloy profiles.

Under what circumstances,

Aluminum alloy prone to oxidation and corrosion?

After our industry visits and communications with material science experts, as well as a review of relevant literature, the following conclusions were drawn:

Case One:

Due to the pressing environmental situation in the domestic market, the original process of pickling and chromating aluminum profiles has been eliminated. As a result, the corrosion resistance of the profiles now demands a stricter coating requirement.

Scenario Two:

Aluminum alloy corrosion in the atmosphere is caused by surface contaminants such as dust, soot, iron powder, Sox, and Nox. These contaminants, influenced by moisture and rain in the air, transform into corrosive solutions, penetrating the surface of the aluminum panels. This degradation phenomenon manifests as pinpoint white pitting corrosion and perforation corrosion that occurs at specific points.

Scenario Three:

Long-term contact between aluminum and its alloys with dissimilar metals can easily lead to contact corrosion. Compared to high-potential copper (-0.20V) and iron (-0.58V), low-potential aluminum (-0.85V) in electrical contact with high-potential metal materials in an electrolyte solution will result in galvanic corrosion. As many components and auxiliary materials in the window and door industry, such as stainless steel, copper, and hot-dip galvanized materials, are more stable than aluminum alloys, this also accelerates the corrosion of aluminum alloy profiles.

So, combining our analysis of the above points,

The issue reported by the customer is not rust on the mesh, but rather oxidation corrosion of the aluminum profiles, with some screws securing the mesh also showing signs of corrosion. The oxidized liquid seeps out and runs down the mesh, hence the broken-line straight lines we observe. In some cases, both sides of the profiles have corroded, and the oxidized liquid runs across the mesh to the middle, leaving marks on the mesh.

We've discussed similar situations with many technical directors of window and door companies. Currently, it's quite challenging to eliminate such issues. So, what are the ways to avoid them?

Pay attention!!!

How to Prevent Aluminum Alloy Profiles from Oxidation?

Solution:

By technological processing and optimized design, the service life of aluminum profiles is extended.

We are utilizing pre-treated aluminum profiles to minimize oxidation and corrosion of the aluminum.

2. Optimized the design for sealing and drainage, aiming to keep the aluminum profile as dry as possible and minimize moisture conditions.

Due to the presence of aluminum and aluminum alloys in a wet environment, the missing parts (pores) of the surface oxide protective film absorb Cl ions, locally dissolving the protective film and forming minute pores on the aluminum matrix. These Cl ions, among others, penetrate, diffuse, and increase acidity within the pores, promoting the dissolution of aluminum. Additionally, if these corrosive byproducts accumulate and come into contact with hardware accessories for windows and doors, the acidity can accelerate the corrosion of these accessories.

3. Consider applying rust-proof paint at the contact points between aluminum profiles and hardware accessories. This can help isolate air and moisture, reducing the impact of contact corrosion.

According to the point corrosion prevention test, the coating of the Ducklang brand (a type of paint with zinc powder) and electro-phoresis spray paint effectively prevent the occurrence of electro-corrosion. Aluminum is a very corrosion-resistant metal material in nature, but when it comes into contact with other metal materials at high potentials and is exposed to a corrosive environment, it is often the first to be corroded.

That concludes the content.

If you have any insights, please feel free to contact Ji'an Screening Mesh.

Thank you for watching!