Cym Materiales SA offers special surface preparation lines for the treatment of road, agricultural, mining, railway, and truck rolling equipment. that, being subjected to extreme working conditions, require a correct surface preparation necessary to achieve a correct degree of cleaning and simultaneously an excellent level of adhesion to apply any type of coating or paint.

Why is it necessary to carry out a correct surface preparation prior to the application of a coating?

The success of a protective coating (paint) not only depends on its proper application, but also largely depends on a correct surface preparation, eliminating all contaminating agents, loose or poorly adhered particles, whether or not they are foreign to the treated surface. . Improper or careless surface cleaning can lead to premature paint failure.

The main contaminants found in hot rolled steel are rolling rust or slag (flake or calamine) and corrosion products such as oxides, sulfides, chlorides, etc. As for external agents, you can find grease, oil or even old paintings in poor condition. Of all these pollutants, the first one deserves special attention because it is one of the most damaging elements in rolling equipment.

Rolling slag is made up of various grades of iron oxide that are produced during the hot rolling process. The lamella is extremely hard and although it is well adhered to the base metal, it is brittle and brittle with a different coefficient of thermal expansion than steel. In practical terms, any break or crack that occurs in the lamella, as a result of a blow or thermal change, allows the passage of oxidizing agents, starting a corrosion process that will gradually detach the lamella as it detaches from the base material. The lamella is, in many cases, the cause of accelerated galvanic corrosion. For this reason, to ensure the protection of the steel, (especially in aggressive and humid environments) it is absolutely necessary to remove this slag before applying any type of coating.

Advantages of the Shot Blasting Treatment compared to the Phosphatizing process

When phosphating is used for surface preparation, both mixed and combined with degreasers, a clean surface is obtained, and by the attack of phosphoric acid, a small bite is achieved on the surface. Phosphating is used with good results when applied on cold rolled sheet without lamella and with paint schemes that do not require great roughness. On the other hand, when the phosphating process is used for a hot rolled sheet, which has calamine, the process degreases and creates a surface etch on the latter and not on the base metal. This makes the applied paint have a reasonable adhesion but on an unstable, fragile and brittle layer generating premature failure in the applied coatings, especially those where the coated parts are subjected to movements or torsional stresses, such as the case of rolling equipment.

The shot blasting process is an impact surface treatment technique with which an excellent degree of cleaning can be achieved and simultaneously a correct surface finish on a wide range of metallic and non-metallic parts. In general terms, we can say that blasting is the bombardment of abrasive particles at high speed (65-110 m / sec.), Which, when impacting with the treated piece, produces the removal of contaminants from the surface (lamella, oxides, etc.) generating a roughness in the base material according to the type of coating to be applied.

Shot blasting, unlike chemical treatment, is an easy-to-apply process that does not generate environmental pollution problems or the need for effluent treatments. Lastly, in rolling equipment that works under extreme corrosion conditions, mixed blasting and phosphating processes can be used, in order to achieve a contaminant-free surface, with good roughness for paint adhesion, adding a barrier with phosphating. Additional anti-corrosion chemistry in the event of a paint coating breakdown.

Basic applications of the shot blasting process in rolling equipment

In general, the shot blasting process of rolling equipment is used for the following basic functions

• In new units removing the calamine / lamella that brings the sheet or hot rolled steel profiles
• In used units, removing paints, putties and rust, leaving the areas to be repaired clean and suitable for a new paint application.
• Homogenizing surfaces such as welds, burrs, grinding, etc.
• Achieving a controlled roughness profile in such a way as to have a correct adherence of the coatings (paints) to be applied.

Selecting a shot blasting equipment

The size, the material, the shape of the parts and the quantity of parts to be processed have a direct influence on the correct selection of the blasting system to be used. Shot blasting equipment is differentiated by the shot blasting method that can be manual shot blasting (compressed air) or automatic shot blasting equipment (turbines).

Manual shot blasting by compressed air

This system is a manual and low-performance process compared to turbine blasting equipment, since each operator can process an average of up to 20m2 per hour of shot blasting.

This manual process has the advantage of blasting complex or large parts, to the detriment of the production level that a turbine team would have. The rooms are watertight enclosures subjected to depression by means of an extraction and filtering of air which allows, together with an adequate level of lighting, good visibility for the work to be carried out. Blast rooms can be built in different ways using different types of materials such as modular veneer panels, masonry, etc.

The number of operators to work within the room can be adapted to the needs of each particular client according to the required production. The operators work inside the room duly protected with equipment suitable for working with steel shot, positive pressure class CE system.

There are several options to recover the abrasive inside the room, manual sweeping, manual auger sweeping or 100% automatic sweeping Abrasive cleaning systems are designed to perform cleaning tasks, discarding all types of dust, scale and other contaminants from the process shot blasting. The room is completed by a dust collector with filter cartridges and automatic cleaning systems, which ensure correct extraction of the dust generated in the blasting process. Converting this process into a non-polluting process for the environment.

Automatic shot blasting by centrifugal turbines

Centrifugal turbine blasting is, among current surface cleaning techniques, the most economical method with an uncontaminated environment.

Due to its conception, it is ideal to be used in processes that require high productions or savings in labor times. Unlike manual blast rooms, turbine equipment does not require specialized labor, being much more productive than compressed air blasting. And achieving greater uniformity in surface preparation. According to the equipment model, they may have one or multiple blasting turbines positioned so that the abrasive reaches the entire surface of the pieces to be blasting.

The number of turbines mounted in a shot blasting machine is determined by the shape and size of the parts to be cleaned, allowing it to be processed from small auto parts to the chassis of trucks or train wagons.

Turbine equipment can be designed to carry out Bach work or passage equipment for continuous processes. The latter can be installed in line with the painting process in such a way as to considerably reduce the labor costs associated with handling parts.

For complete units, both blasting systems (turbine and compressed air) can be combined where the first process performs the coarse blasting of the part and in the manual blasting process, touch-ups in areas where the blasting of turbines is not effective and subsequent blow-off of shot (removal of abrasive accumulated on the chassis.