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Powder Coatings and Metal Powder

Powder Coatings and Metal Powder

Summary

Powder coatings are powdery, solvent-free coatings formed by the influence of heat during melting and hardening processes.
They are applied to work piece and/or components by means of electrostatic or triboelectric spraying. Small powder coating particles of only a few µm in size fly through an electrostatic field surrounding a coated work piece, forming a coating that is uniformly between 20 and 60 µm thick on all sides.

Once the powder coating has been applied, it is burnt in for a few minutes at temperatures of between 120 and 200°C. Depending on the individual requirements, the surface can be a high-gloss, satin finish, matt, structured, colored or transparent coating with an enamel-type finish.

Composition of powder coatings
Powder coatings consist of a mixture of resins (epoxy, polyester, polyurethane and acrylic), fillers, additives, hardeners and pigments. The composition depends on the required features such as reactivity, storage properties, gloss, mechanical properties and resistance to solvents, etc.

Applications
- Standard paints & lacquers:
clear lacquer, base coat and topcoat for the automobile industry, for all kinds of metallic parts, bicycles, plastic components and others.
- Thin-film powder coatings:
for shelves, office furniture, household appliances, the electronics sector, coil coating, etc. The ability of achieving a particularly thin layer with these thin-film powders helps to reduce the coating costs.

Requirements
- Top-size limitation with no oversize particles
- Minimum ultrafine portion because the extreme
adhesive properties might adversely affect the
application
- Low energy requirement

Fig.1 Tire wheel (Example of powder coating)

Fig.2 ACM40 CX PSR 11 system

Fig.3 Schematic figure of ACM Pulverizer

Grinding with ACM Pulverizer

To produce powder coatings, the chips must be ground to specifications and then classified. Great attention is paid to ensuring that the systems and components used are easy to operate, clean and maintain. With this objective in mind, we constantly refine our machines in order to meet the increasing demands in terms of powder coating quality.

The system concept shown here, comprising an air conditioning unit, ACM classifier mill, Micron Separator MS, cyclone, ultrafines filter as well as screening machine and packing unit, is designed for either cyclone or classifier operation. The cyclone is mounted to pivot, meaning that both operating modes can be realized quickly and easily by simply adjusting the position of the product ducting. The screening and packing unit is in mobile design and is positioned underneath the cyclone or classifier as the case may be.

Fig.4 Continuous milling system of powder coating

Besides the established ACM, Hosokawa has many other innovative system components geared to efficient powder coating production:

The Micron Separator MS with excellent precision of cut and compact design results in optimum product yield and quality.
Optimized cyclone geometries plus the use of flap valves reduces product losses.

Agglomeration

There is a modern technology of powder coating, Computer Color Matching (CCM). For CCM application, powder paint has to be milled finer than ordinary coating paint. Basic colors have to be milled down to d₅₀ = 10 – 15 μm. These basic colors are to be mixed according to color matching recipe. Simple mixture shows poor fluidizability and not applicable for coating purpose. Here, agglomeration technology plays an important role. Cyclomix with precise temperature control gives either CCM agglomerates or metal-bonding powder.