How to prevent rusting

Rust is a type of corrosion, which is a process that occurs when metal deteriorates. This deterioration is the result of oxidation – when iron and oxygen react to water.

Protecting metal surfaces and parts from corrosion is essential to ensure they function properly and to extend their lifespan.

There are various ways to prevent rusting and one of these is to apply powder coating.

What Causes Metals to Rust?

As a form of corrosion, rust affects iron or iron alloys. Rust forms when iron reacts with oxygen and water. This reaction is oxidation. It produces rust in iron and steel. In other materials, corrosion causes different reactions.

Rust appears as a reddish-brown flaky coat on metal surfaces. If you leave iron exposed to water and oxygen long enough, it will start to rust. However long the process takes, it is inevitable.

The problem of rusting is, therefore, commonplace.

There are two reactions in the chemistry of corrosion:

• First, there is an anodic reaction, where the iron goes into a ferrous ion solution
• Then, there is a cathodic reaction, where the ions released during the first reaction meet a portion of the surface and react with it, removing them from the metal.

Once both these reactions have occurred, the process of corrosion begins.

Certain factors stimulating either anodic or cathodic reactions can release aggressive ions, such as chloride, which will cause further corrosion.

Corrosion produces harmful effects in metal, affecting the lifespan and performance of machinery, appliances, equipment, vehicles and buildings.

What is Rust?

Rust is hydrated iron, also known as iron oxide. Different types of rust result from the different ways in which corrosion affects metal:

• Pitting and cavity corrosion –occurring on unprotected steel used in building and infrastructure, where the pitting reduces the metal’s strength and thickness
• Crevice corrosion – occurring in gaps in metal parts and structures, such as in between nuts and bolts, in confined spaces
• Contact corrosion – occurring when non-rusting stainless steel is in contact with another piece of rusting metal, with iron oxides deposited at the point of contact then potentially spreading beyond it.

Various conditions can cause rust to increase, including temperature changes, increased humidity and geographical elements – for example, if the metal is exposed to windy or rainy conditions, or near the coast, where salt in the moisture will increase the speed of the corrosion reaction.

How to Stop Rusting?

There are various materials, processes and applications for preventing rusting:

• Using rust-resistant alloys
• Galvanising
• Bluing
• Organic coating
• Powder coating.

Rust-resistant alloys include stainless steel and weathering steel. Stainless steel includes a minimum of 11% quantity chromium. Chromium forms a protective chromium oxide film on the steel, which acts as a shield against rust. If the surface gets damaged, the protective film will re-form over it.

Weathering steel contains up to 21% of alloying elements, such as chromium, nickel, copper and phosphorous. These alloys will form a protective layer, reducing the metal’s corrosion rate.

Galvanising is a process that protects iron and steel by applying a zinc coating. This process prevents galvanic corrosion from occurring. This is an electrochemical reaction that occurs when one metal has prolonged contact with another.

For this to happen, one metal must be an anode, and the other a cathode. Because zinc is an anode metal, by using it to coat the cathode metal, you prevent the galvanic corrosion reaction from happening.

Bluing is a passivation process, a chemical treatment using nitric acid or citric acid. The resulting electrochemical conversion coating comes from the oxidation of iron on the surface. This coating is magnetite, a black oxide of iron. Bluing is normally applied in a furnace.

Its most common application is in the manufacturing of firearms. It is also used for seasoning cast iron cookware.

Organic coating refers to various types of paint, varnishes and enamel applied as primers, adhesive cements and topcoats to metal parts and surfaces. Organic coatings work by being chemically inert and impermeable. They have both technical and decorative properties.

They form a barrier against corrosive elements.

Powder coating is a dry powder finish that you apply using an electrostatically charged spray gun. After spraying, you then cure the coated part in an oven, to create a hard, even surface.

How Powder Coating Prevents Rust

Once you cure it, powder coating provides a durable, even finish that protects the substrates it adheres to.

This is a highly effective coating method because the charged powder particles will cover the surface evenly and comprehensively, and then form a protective layer once the curing process causes the particles to melt and merge.

Powder coatings are a combination of resins and pigments. They are resistant to cracking, peeling, chipping, abrasion, impact damage, and rust. Powder-coated surfaces are also protected from damage from UV rays, chemicals, water and severe weather conditions.

Unlike some other methods for preventing rust, powder coatings are highly versatile. You can use them to protect:

• Steel architectural parts
• Outdoor equipment, such as farm machinery
• Industrial fabrications
• Automotive parts
• Office furniture
• Outdoor signage, including traffic signs.

If you look after the powder-coated surface and keep it clean, it should provide long-term protection from rusting.

For more details about using powder coating to prevent rusting, please contact us.