Preparing elements for powder coating

Shot blasting, sandblasting, galvanising, and other surface preparation methods.

Powder coating is an excellent way to protect metal elements against corrosion and wear, as well as to improve their appearance. However, the key to obtaining a durable and aesthetic powder coating is proper preparation of the metal surface — a step we treat with the utmost care in our ELMAL powder coating shop. In this article, we will discuss proven methods of preparing metal elements for powder coating: from removing the old coating, through shot blasting and sandblasting, to galvanising, chemical cleaning, and etching.

If your metal element has an old coating, such as paint, it is necessary to remove it before powder coating. The most effective methods for removing old coatings are shot blasting and sandblasting.

Shot blasting

Shot blasting involves using small particles of metal or ceramic, called shot, to remove the old coating and any other surface contaminants. The shot is propelled at high speed into the metal surface using specialized equipment. This method is particularly effective at removing thick, stubborn coatings or rust.

Sandblasting

Sandblasting involves introducing sand or other abrasive materials onto the metal surface into a compressed air stream and directing it at the surface to be cleaned. Abrasives are usually made of silica, glass beads, aluminium oxide, or other materials. Sandblasting is often used for lighter coatings or to prepare surfaces for further processing. This method can create a rougher surface than shot blasting, which can improve powder coating adhesion.

The surface profile created by abrasive blasting is measured in terms of its roughness or peak-to-valley height. The ideal surface profile for powder coating depends on many factors, including the type of metal being coated, the type of powder used, and the desired adhesion level.

Both shot blasting and sandblasting require specialized equipment and expertise for a safe and effective treatment process. This includes using protective equipment such as goggles and masks to protect against inhaling dust or contaminants generated during the process. Choosing the right abrasive media for the specific metal part and the coating being removed is also important.

After removing the old coating, the metal surface must be thoroughly cleaned and degreased so that no contaminants remain that could reduce the adhesion of the powder coating. This step is crucial to ensure a high-quality, durable finish.

Removing old coatings from metal elements is a necessary step in preparation for powder coating. By choosing the right abrasive media and following safety guidelines, you can ensure that your metal parts are properly prepared.

After removing old coatings and cleaning the metal surface, the next step is surface preparation. This step is crucial to ensure proper powder coating adhesion and durability over time. Surface treatment by shot blasting or sandblasting is a very good introduction to preparing surfaces for powder coating, however, depending on the metal part and the applied coating, other surface preparation methods or a combination of sandblasting and shot blasting with the solutions below may be more appropriate.

Chemical cleaning

Chemical cleaning uses chemicals to remove contaminants and prepare the metal surface for coating. This method is often used to remove oils, greases, and other organic compounds from metal surfaces. The chemical solution is applied to the surface, left for a specified time, and then rinsed with water.

Etching

Etching is another surface preparation method that involves creating a textured surface on the metal to increase the adhesion of the powder coating. This is done by applying an etching solution to the surface, which removes a thin layer of metal and creates a rough surface. This rough surface provides a larger adhesion area for the powder coating, resulting in a stronger bond.

Mechanical abrasion

Mechanical abrasion is another option for preparing metal surfaces for powder coating. This method involves using tools such as wire brushes or sandpaper to physically roughen the metal surface. This process can also be used to remove rust or other surface imperfections from the metal.

It is important to select the right surface preparation method depending on the type of metal and the applied coating. Each method has its pros and cons, and choosing the wrong method can result in poor adhesion and a substandard finish. By carefully considering the specific project requirements, you can choose the best surface preparation method to ensure a high-quality, long-lasting powder coating.

After surface preparation, it is crucial that the surface remains clean and free of contaminants until the powder coating is applied. Any residual oils, dust, or other impurities can interfere with the adhesion of the powder coating and lead to a suboptimal finish.

Galvanizing

If you are working with a metal part prone to rusting, such as steel, galvanising is an effective way to provide additional protection against corrosion. It involves coating the metal part with a layer of zinc, which acts as a sacrificial anode and provides cathodic protection to the underlying steel.

There are two main types of galvanising: hot-dip galvanising and electro-galvanising. Hot-dip galvanising is the most common method used for larger metal parts, while electro-galvanising is typically used for smaller parts or components.

Hot-dip galvanizing

Hot-dip galvanising involves immersing the metal part in a bath of molten zinc, which forms a metallurgical bond with the steel substrate. This process creates a thick, durable coating resistant to corrosion, abrasion, and impact. The thickness of the galvanized coating can be varied depending on the specific application, with thicker coatings providing better corrosion protection.

Electro-galvanizing

Electro-galvanising involves applying a layer of zinc to the metal surface in an electrolytic process. This process involves immersing the metal part in a plating bath and passing an electric current through the solution, causing zinc ions to deposit on the metal surface. The thickness of the electro-galvanized coating can be controlled by adjusting the voltage and current used during the process.

Both hot-dip galvanising and electro-galvanising provide excellent corrosion protection for metal parts, and the choice of method will depend on factors such as the size and shape of the part, the desired coating thickness, and specific application requirements.

It is important to remember that galvanized surfaces must be properly prepared before powder coating, as any residual oils, dirt, or other contaminants can interfere with the adhesion of the powder coating. Sweep blasting is typically used to prepare a galvanized surface, but care must be taken not to damage the zinc coating.

Galvanising is an effective way to provide additional corrosion protection to metal parts, especially those prone to rusting. The choice of method will depend on specific application requirements, and proper surface preparation is essential to ensure a successful powder coating finish.

Proper preparation of metal surfaces is essential for a perfect powder coating. At the ELMAL Sp. z o.o. coating shop, we help clients select the optimal surface preparation method for their specific element and application — from sandblasting individual parts to the duplex system (combining galvanising with powder coating) for elements exposed to harsh weather conditions. If you are not sure which of the described methods would be best in your case — contact us, we will advise you based on our years of experience.