How to prevent metal corrosion

Before the metal painting process a particular attention should be paid to preparatory work, especially to the metallic corrosion processes.

There are different types of corrosion development on metal:

Rust Stains – this type of corrosion usually extends in breadth, instead of in depth. It looks as small stains on metal.

Pinpoint corrosion – small points which get deeply into a material body. Development of a pinpoint corrosion on a steel surface affects the appearance of through holes.

Rust-through – harmful influence on the material from two sides (through).

Surface Film Corrosion: rust formed under the coating of paint. A layer of paint in places of rust formation is peeling. In some cases surface film corrosion remains imperceptible until the moment of steel destruction.

We would like to remind you that powder coating can not be laid on a surface with any type of corrosion. Otherwise you risk to receive a poor-quality and unstable coating.

Methods preventing metal corrosion process

There are 3 main methods of metal processing:

• mechanical
• chemical
• thermal

The mechanical method of metal processing

The mechanical method is considered to be one of the best and practical. It might be done both manual and with use of automated tools.

1. Surface cleaning with wire brushes. This type of cleaning is suitable for removing small amount of corrosion and stripping welds. It can also be used as a primary surface treatment covered with a thick layer of rust. This process has a poor quality because the brush’s scale is not removed at all. In addition, a lot of dust is generated during processing.

2. Abrasive processing of metal is carried out by using grinding discs. It is used for small amount of corrosion. But this method has 2 drawbacks: material consumption; high requirements to work performance skills.

3. Metal processing with usage of sandblasting plant. This method consists in feeding a jet of sand under pressure on the metal. Sandblasting is the best, fastest and highest quality option for processing metal products from corrosion.

River sand and artificial ones might be used. It is necessary to dry sand before sandblasting. Sand can be used again, preliminary having sifted, but efficiency of cleaning in this case decreases several times. And the quantity of a dust increases. And the amount of dust is increasing.

Sandblasting removes not only rust, but also scale, carbon deposits, layers of old paint. This treatment method is recommended for those places that are not accessible to the grinder and sandpaper (for example, the junction of two parts).

4. Hydro abrasive metal processing (water sandblasting): rust removing under a stream of mixed water and abrasive.. The intensity distinguish hydra abrasive treatment:

• under ultrahigh pressure;
• under high pressure;
• under low pressure.

The quality of metal processing depends on the pressure intensity.

Chemical method of metal processing

This method is characterized by the destruction of corrosion under the influence of chemicals. As cleaning agents, hydrochloric, phosphoric and sometimes sulfuric acid are used. Diluted acids are used, a substance that allows you to remove corrosion – the urotropin inhibitor. Most often, metal is processed with phosphoric acid.

It is important to note that in this article, we discuss the processing of metal from corrosion, but when you choose which solution for chemical treatment to take, it is worth paying attention to the peculiarities of metal contamination.

Different  chemical composition should be applied to different  type of contamination:

• Inorganic – corrosion outgrowths, rust patches, machining residues (chips, metal dust);

• Organic – oils, lubricants, resin, acids;

• Combined / mixed – organic contaminants mixed with abrasive particles.

Chemical compositions are applied to the affected surface with a brush or spray. These formulations are divided into 2 groups:

● washable – a more effective method (aggressive chemical compounds). The composition must be washed off under water. If you do not dry the metal product immediately to dryness, then rust may again appear on it.  Therefore, a drying oven is a prerequisite for rinse-off chemical compositions.

● indelible – in this case, there is no need to wash the composition from the surface. Usually use an acid solution with water.

Metal heat treatment

Heat treatment of metal occurs using an oxygen-acetylene burner. But this method is practically no longer applied in practice. The fact is that in such ways you remove all mill scale, but rust may remain in some places.

After qualitative processing of a surface it is possible to start its painting.Powder paint can protect metal products from future corrosion.

Important! During metal processing remember about  personal protective equipment: gloves, protective clothing, and a respirator.