Abrasive blasting, painting, polishing with glass microspheres

ABRASIVE BLASTING

The processes are monitored by internal coating inspectors qualified by AMPP (NACE coating inspector).

Trater is also able to offer its valued customers this service by operating in closed, automatic or manual plants, with the recycling of the abrasive and the complete elimination of dusts.

In addition to the classic shot blasting with the use of metal abrasives, it can perform, in specific booths, the corundum blasting and polishing processes of the items with glass microspheres. If requested, after the surface cleaning treatment, the painting of the products is carried out according to the most suitable cycles, in relation to the operating conditions of the items.

ABRASIVE BLASTING PLANTS

As already mentioned, the abrasive action of granules accelerated at very high speed by means of compressed air, through a nozzle or turbines in automatic plants, determines the surface cleaning of the items. The recovery of the abrasive, its sieving for the elimination of particles that have shattered and reduced in size, as well as the abatement of the dust generated by the abrasive and by the material that detaches from the surface of the items, takes place automatically through special equipment installed in the plants guaranteeing the necessary level of cleanliness, uniformity of the surface roughness and optimal conditions, from a hygienic and health point of view, for the operators as well as not causing environmental pollution.

DEGREE OF ABRASIVE BLASTING

In the process, the “degree of abrasive blasting” refers to the percentage of mill scales, rust, old paint, etc. remained on the surface at the end of the operation. According to the classification given by the Swedish regulation SIS055900-1967 (still frequently in use) and recalled from the more recent ISO8501-1, the various degrees of abrasive blasting are defined through the following acronyms:

white metal blasting: Sa3

near-white metal blasting: Sa2 1/2 or Sa2.5

commercial blasting: Sa2

White metal blasting, at grade Sa3, consists in the complete removal of all corrosion products, all mill scales, all traces of old paint and in general all impurities from the metal surface. The process results in a gray-white metallic surface with a uniform appearance, with a roughness that allows perfect anchoring of the layers of protective paint that will subsequently be applied.

Near-white metal blasting, at the cleanliness level Sa2.5, consists in the almost total removal of all impurities from the metal surface (scale, rust, dirt, old paint, etc.) with the exception of very light shadings, very light veining or light discolouration caused by rust stains, calamine oxides or light adhering residues of paints or protective coatings.

Commercial sandblasting, at the cleanliness level Sa2, refers to good but not perfect sandblasting and usually requires the removal of virtually all rust, scale and other foreign matter on the surface of the metal. The surface obtained does not necessarily have to be uniform both in terms of degree of cleanliness and appearance and this is because any differences in the initial conditions of the surface affect the final result. The surfaces, however, must have a very suitable roughness to ensure a firm adhesion of the layers of paint that will subsequently be applied. The final appearance of the metal is greyish.

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ABRASIVE BLASTING PROFILE

The abrasive blasting profile indicates the surface roughness that is obtained regardless of the degree of abrasive blasting chosen and is mainly a function of the grain size and quality of the abrasive and the initial conditions of the metal surface to be abrasive-blasted.

Processing price

To guarantee our valued customers a valid criterion consistent with the actual work process carried out, the work processes are calculated per square meter measured. Abrasive blasting and painting a square meter of sheet metal with a thickness of 50mm involves the same effort required to abrasive blast the same surface, with a thickness of 10mm. A final calculation “per kilogram” would cost the customer 5 times more than the real value of the work process.

Roughness parameters

The most used parameters to control the roughness of an abrasive-blasted surface (expressed in microns) are (according to DIN 4768):

Ra: average roughness – arithmetic average of the absolute values of all crests and valleys measured along the sample section

Rmax or Rt: maximum or total roughness – distance between the highest crest and the deepest valley measured along the sample section;

Rz: average roughness – arithmetic average between the 5 largest crests and the 5 deepest valleys measured along the sample section.

Automatic abrasive blasting

Automatic abrasive blasting is carried out in closed systems, equipped with turbines for projecting the abrasive, with recovery, sieving and elimination of dust. The effect of the detachment of the oxides and contaminants from the surface is obtained through the impact of large quantities of abrasive accelerated at medium speed by the turbines. Delivery times for this process are rapid and it is particularly suitable for metal structures oxidized by water or heat treatments. It is not suitable, however, for items that have closed chambers or difficult to access and low thickness, easily deformable items, which must be treated with the manual technique. Furthermore, this abrasive blasting method cannot be adopted as a surface preparation process for the application of painting cycles which involve the use of inorganic zinc (ethyl silicate) or high thickness products (applied in a single coat or in multiple layers) for the poor adhesion offered by the profile of the surface which, despite having a high roughness, obtainable by using spherical abrasive with the addition of small cylinders, is made up of spherical imprints not suitable for determining a valid mechanical anchoring of the paint on the surface. The degree of cleanliness that can be achieved is related to the time of exposure to the abrasive jet of the turbines and to the geometry of the product and varies from grade Sa2 to degree Sa3.
In Trater, this process is carried out in closed booths, with the recirculation, recovery and sieving of the abrasive and elimination of dust. As previously mentioned, in many cases it is essential that abrasive blasting is performed manually because:
  • the item has hidden chambers or confined spaces that only the intervention of an operator can reach;
  • the product has dimensions and weights such that it cannot be managed by an automatic system;
  • it is necessary to abrasive blast only certain surfaces and avoid damaging parts that have already been worked or, in any case, not to be treated;
  • it is essential to minimize the mechanical effect caused by the impact of the abrasive on the surface of the items to avoid deformations in items with low thicknesses;
  • a jagged profile or a specific surface roughness is required which can only be achieved with angular abrasives, which cannot be used in automatic tunnels.
As with automatic sandblasting, the degree of cleanliness obtainable varies from white metal (Sa3), to almost white metal (Sa2 1/2), to commercial cleanliness (Sa2).
Corundum blasting is a manual abrasive blasting process carried out with an inert abrasive (aluminium oxide or garnet) used mainly on materials that must not be contaminated by iron, such as stainless steel, nickel alloys, aluminium, copper etc… The method is particularly controllable and produces a degree of cleanliness compliant with the standards indicated and with all the technical requirements connected with subsequent coatings. Abrasives of all grain sizes are used: from the coarsest, to produce a marked profile, ideal for adhering paints, to the finest for abrasive blasting of delicate or light surfaces, which would deform if worked differently. Corundum has a sharp shape and always produces an extremely jagged surface, suitable for the application of any type of coating.
Trater has large manual abrasive blasting and corundum blasting booths to abrasive blast items with a width and height of up to 7,500 mm and a length of up to 60 metres. Furthermore, in its Nova Milanese facility it operates with two automatic plants capable of abrasive blasting big items.
In Trater work more than 45 employees, 9 of whom are involved in the abrasive blasting, painting, flame spray and PTFE coating sectors. The core of the company is the technical office with 12 people including specialists, engineers and quality workers, specifically trained for the corrosion protection and job management sector.
It is important that our customers can count on a structured and reliable supplier like Trater, who has staff and resources available to carry out every job in the best possible way. For the sandblasting sector, the operating departments have the most advanced equipment to carry out the work entrusted to us by our customers and the quality control staff have the possibility of carrying out the most sophisticated tests required today in compliance with the regulations applicable for the sector using reliable and periodically subject to periodic calibration at external, accredited laboratories.
Trater recommends always asking couriers for covered transport of only abrasive-blasted items because otherwise, in case of rain, the surface would rust immediately.

PAINTING OF METAL STRUCTURES

The market offers various solutions for specific corrosion resistance needs. For the industrial market the primer must necessarily be a solvent-based product. Trater has all the environmental authorizations to be able to apply solvent-based products. A solvent-based primer is more tolerant on metal structures products than water-based products, which are instead formulated for "ideal surfaces", with perfectly smooth welds, perfectly rounded edges, total absence of spatter. Water-based primers on metal structures typically suffer from "rust blistering". Once the primer has been applied, it is possible to continue with the water-based painting cycles, even at our customers' workshops for touch-ups or finishes. Depending on customer needs, Trater offers the following coating cycles:

For low corrosive environments, without exposure to the sun, one coat:

pigmented epoxy finishing of the required colour

For low corrosive environments, finishing by the customer authorized to use solvents:

non-pigmented epoxy primer

For low corrosive environments, finishing by the customer with water-based products (typically acrylic):

epoxy polyamide primer

For mildly corrosive environments, finishing by the customer with water-based products (typically acrylic):

Epoxy polyamide primer reinforced with zinc phosphates

For mildly corrosive environments, finishing by the customer authorized to use solvent-based products:

Epoxy zich rich paint

For environment highly exposed to sun, atmospheric agents, corrosion:

epoxy zinc rich paint, epoxy intermediate, polyurethane finish pigmented with the required colour.

For work at temperatures (150-530°C):

inorganic zinc rich paint

Epoxy polyamide primer: Primer specially formulated to be covered with water-based paints. Also available in the zinc phosphate version for greater resistance to atmospheric agents and corrosion. Inorganic zinc: This primer gives galvanic protection, sacrificing itself towards the steel. It is therefore suitable as a paint applied in direct contact with the surface of items in which, during assembly or operation, damage to the covering layers may occur after scratches or impacts, with direct exposure of the metal. The sacrificial effect of the paint is determined by the rapid formation of zinc oxides, rather than Fe oxides, which are sufficiently adherent and stable to protect the steel substrate. It is one of the few coatings that can be applied with relative simplicity and is suitable for components that operate hot (up to 649°C, 538°C continuously). To avoid product detachments after short periods of operation, it is essential to abrasive blast to near white (Sa2.5) or white (Sa3, especially for hot operation of the products) metal and a high roughness is required, with jagged profile, achievable only by manual abrasive blasting, with angular abrasive, at high pressure, which Trater can perform in its closed cycle plants. Abrasive blasting of products in automatic plants in which cylindrical/spherical abrasive is used is therefore be avoided. It resists sun exposure better than an epoxy primer not protected by a polyurethane finish. It is advisable, after application and completion of the polymerization phenomena, to cover the surface with polyurethane paints (an epoxy intermediate is needed), acrylic or silicone paints for high temperatures, to preserve the thickness of the layer of product applied. Epoxy zinc rich paint: It creates a protective film (barrier) on the surface, which separates humid environments from the oxidizable metal, providing at the same time sufficient galvanic protection (the zinc particles present in the epoxy resin get sacrificed in place of the metal in the event of damage to the film). It also adheres well to complicated surfaces such as edges, welds, etc. It is an excellent product when high operating temperatures are not expected. Epoxy primer enriched with zinc phosphates: It creates a protective film on the surface, enriched by zinc phosphates which are corrosion inhibitor pigments. It adheres well to complicated surfaces such as edges, welds, etc. Our customers can overpaint it after mechanical processing and assembly of the components, even with water-based products. Epoxy primer: It creates a protective film on the surface, which separates humid environments from oxidizable metal. It adheres well to critical surfaces such as edges, welds, etc. Our customers can overpaint it after mechanical processing and assembly of the components, even with water-based products when there are no authorizations to work with solvent-based products. Anti-rust-Anti-oil: these paints create a protective film on the surface which is particularly suitable for resisting the corrosive action of oils. It is a process particularly applied to the internal surfaces of gearboxes’ casings, after careful abrasive blasting. Epoxy mastics: they are the best solution when it is not possible to adequately prepare the surfaces by abrasive blasting. They are particularly grippy and have a reasonable ability to bind oxides if present onto the surfaces (they are so-called “surface tolerant” paints). They can be overpainted directly with finishing products. Synthetic paints: they are used only on request. They are not particularly high-performance and have extremely long drying times; they are mainly used for civil uses (for example: on-site brush painting of gates, parapets, etc.).

Epoxy Intermediate:
It creates a film on the surface to protect and cover zinc rich primers, to which finishes usually do not adhere directly. Our customers can overpaint it after mechanical processing and assembly of the components, even with water-based products when there are no authorizations to work with solvent-based products.

Micaceous polyamine epoxy:
the epoxy intermediate is also available with the addition of micaceous oxides, further corrosion inhibitors which increase the mechanical resistance of the protective film.

Polyurethanes: they create a shiny surface, easily washable and with high hardness. Polyurethanes have excellent resistance to UV rays: they do not age in the sun as happens with epoxy paints. They exist in a wide range of standardized colors (RAL, MUNSELL, etc…). Epoxy finishing: It can be applied directly to the abrasive blasted surface avoiding primer and intermediate; it creates a shiny protective film that can already be considered a finish. However, it does not have the mechanical resistance of a polyurethane and ages if exposed to sunlight. It doesn’t even confer galvanic protection; it is an economical and quick painting cycle as it requires only one coat of paint. It is designed for environments that are not particularly humid and aggressive (machine tools, workshop equipment, etc.). Silicone paints: they are the best paints available designed to hot work (up to 649°C). However, they are generally delicate and easily damaged. Silicone can only be overpainted with other silicone. They exist in a wide range of colours. Work process price To guarantee our valued customers a valid criterion consistent with the actual work carried out, the work is calculated afterwards per square meter measured. Abrasive blasting and painting a square meter of sheet metal with a thickness of 50mm involves the same effort required to abrasive-blast the same surface, with a thickness of 10mm. A final calculation “per kilogram” would cost the customer 5 times more than the real value of the work process.

POLISHING WITH GLASS MICROSPHERES

To clean the marks of welding processes from stainless steel, especially in the food, chemical and architectural sectors, polishing of stainless steel with glass microspheres is often required. Trater has a specific big plant available to manage components of any kind.
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