Compounding machinery for Powder Coating

Powder coatings today mainly comprise thermosetting powders applied electrostatically. Afterwards they are baked to initiate curing by crosslinking according to the specific surface requirements. These can be functional and/or decorative, with an enormous range of colours in matt, semi-gloss or high-gloss finish as well as metallic, structural and soft-touch effects. Functional powder coatings feature a range from antibacterial characteristics to corrosion protection. Main applications are metal coating in general, household appliances, facades, furniture and automobiles, as well as highway reinforcing bars and oil pipeline coatings.

Polymer powder coatings came into use in the mid twentieth century. They were first applied by the whirl sinter process to a preheated workpiece immersed in a whirlbath of powder coating particles. This was and still is used for high coating thicknesses up to 500 μm.

Thermoplastic powder coatings were the main material to start with, followed gradually in the 1960s by thermosets: epoxy, epoxy-polyester hybrid, polyester/PRIMID, polyester/TGIC, polyurethane, and acrylate based formulations.

Apart from their excellent surface coating qualities, powder paints have several other advantages as well. First of all they need absolutely no solvents, with or without VOCs. This makes the entire powder coating process clearly superior to other systems with regard to application and utilization efficiency (up to 95%) as well as environmental and energy relevant aspects. Another important advantage is the clearly defined thickness of each coating.

Typical applications

The latest powder coating development trends include new crosslinking technologies (such as UV), lower baking temperatures, thinner coatings and wider substrate possibilities (glass, wood, plastics). One of the biggest breakthroughs for powder in the heat sensitive substrate market is on medium density fiberboard, or MDF, a combination panel bonding particles of wood with a synthetic resin. MDF is very suitable for powder coating application because of its low porosity and homogeneous surface. MDF products include office furniture, kitchen and bath cabinets, doors, store fixtures and displays, barbecue trays and ready-to-assemble furniture for the office and home. Customizedformulations for correspondingly small lot sizes are also gaining ground.

Compounding requirements for Powder Coatings

Powder coatings are prepared in a compounding machinery in the solid phase by medium-intensity premixing the weighed-in components including base polymer, additives, pigments and fillers. This mixture is fed in the BUSS compounding machinery to the BUSS Kneader and compounded in the viscous melting phase. The melt is then fed to a cooling conveyor or similar, rolled out into a friable sheet, cooled and broken into chips via a mechanical knibler, and the chips are then ground down to precise grain size distributions or particle sizes.
Decisive for the compounding stage is highly efficient dispersive and distributive mixing at low product temperatures well below the base polymer crosslinking temperatures.

The BUSS Kneader’s specific capabilities really come to the fore in this application: Due to the operating principle of the compounding machinery, the enormous number of mixing cycles at moderate and uniform shear rates enables unsurpassed mixing efficiency and resultant product quality at maximum throughputs. The well-proven screw geometries cover a wide range of applications, and the modular process configuration system enables uncomplicated adaptation. The hinged barrel casing of the BUSS Kneader enables rapid access, easy cleaning prior to extreme colour changes, and high availability.

The emergence of powder coatings in the heat sensitive substrate market, on medium density fiberboard, or MDF, is a perfect example of application that are extremely well suited to the BUSS Kneader technology and the BUSS poweder coating compounding machinery. Together with the broadly-based BUSS process expertise, this makes the BUSS Kneader first choice for compounding powder coatings with the highest investment security for over fifty years.


Typical compounding plant layout for Powder Coatings

Typical plant layout for a powder coating compounding machinery

BUSS compounding systems offer the following specific benefits

  • Intensive mixing at low specific energy input
    BUSS multiple-flight Kneaders of the latest generation achieve better mixing at 15-40% lower overall specific energy input. This is because of an increased number of mixing cycles according to the needs of each individual process section. The energy for melting and mixing is provided almost entirely mechanically and optimally dissipated according to the imparted shear rates.

  • Excellent self-cleaning capability
    Self-cleaning assures that materials do not adhere to surfaces, overheat and degrade. It ensures that contamination that would affect product quality is not caused. The BUSS compounding machinery and the BUSS Kneader achieves this with its reciprocating (both oscillating and rotating) screw motion: All kneading blade surfaces are wiped off on the fixed pins in the barrel, resulting in continuous cleaning and product conveyance at the same time.

  • Wide range of formulations with one screw configuration
    While processing a wide formulation range with one screw profile is challenging, the BUSS reciprocating single screw technology is well known for this capability, thanks to a process length typically half that of most other systems and great flexibility in screw configuration design.

  • Low process temperatures
    The separation of mixing in the BUSS Kneader and pressure build-up in the discharge unit allows mixing at low pressure and temperature. The requirements of each individual process section are addressed with ingenious screw designs for optimized temperature profiles.

  • Easy access to process parts
    Screw elements, liner shells and pins are easily exchangable components of the BUSS gum base compounding technology and are easily accessible through opening the hinged process part of the BUSS Kneader. All these elements can be exchanged without removing the screw or barrel.

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  • BUSS Kneader Technology for Powder Coatings