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Two Component Paint & Coating Systems

More Details on Two Part Coating Systems

"2K" Paint Systems

Two-component paints (also referred to as 2K paints) are paints in which a chemical reaction results in paint hardening. Hardeners for two-component paints are usually polyisocyanates that combine with the base paint to form very durable coatings. Two-component paints are characterized by a very high level of corrosion resistance. Two-component paints consist of a base paint and a hardener. These two components must be mixed vigorously in the correct ratio and then applied quickly. The solid content in two-component paints can be very high (so-called high solid paints).

Two-component systems consist either of two piston pumps, one for the base paint and one for the hardener, or of sensors and valves with a tuned control circuit, which in turn feed the two paint components by means of feed pumps or pressure tanks. Regardless of which method is used, it is important that the components are conveyed to the static mixing tube in the correct mixing ratio. The static mixer ensures that the hardener is homogeneously mixed with the base paint. The mixed material is fed to the spray gun through a hose and atomized at the nozzle.

These systems are suitable for Airless, AirCoat and compressed air spray processes. One or two additional cleaning pumps per paint system are necessary to rinse the mixing tube, material hose, gun and nozzle during pauses in operation. Two-component paints do not harden if not mixed and can therefore remain inside the pumps and suction systems. However, it must be ensured that the hardener in particular does not crystallize since this usually leads to irreparable damage to system parts that convey material.

2K systems can be grouped into mechanical and electronic mixing systems. In mechanical systems, two pumps feed the components for mixing. Electronic systems, on the other hand, are subdivided into so-called continuous systems with gear pumps for the low pressure range and discontinuous systems. In discontinuous systems, the material flow is measured using gear or Coriolis meters and the hardener is metered into the base component using a timing valve.

Gear Flow Meters

Positive displacement flow meters with an inner mechanism, these are similar to that of a gear pump. The casing contains two gears that mesh with very little play. Enclosed chambers are created between the teeth and the casing wall in which the medium is displaced under force, causing the gears to turn. The gears turn freely in the current at a speed that is proportional to the flow rate and that is read through the housing wall by a non-contacting method. For evaluation purposes, the sensors delivery a digital pulse signal with a frequency proportional to the flow rate.

There are two kinds of gear flow meters: ball bearing flow meters and friction bearing flow meters. Gear flow meters are not suitable for abrasive or shear-sensitive materials.

Coriolis Mass Flow Meters

Two parallel tubes are excited by coils to oscillate at their resonant frequency. When a mass flow passes through the measurement tubes, Coriolis forces arise. Coriolis forces occur in oscillating systems when a mass moves toward or away from a rotation axis. Forces on the inlet and outlet sides act in opposing directions and minimally deform the measuring tubes. The deformation of the measuring tubes is detected by sensors at the inlet and outlet and is expressed as a phase shift in the oscillation frequencies of the two tubes. This phase shift is directly proportional to the mass flow rate.

The resonant frequency of the two tubes with material passing through them varies with the density of the measuring medium. This effect is taken advantage of to measure the density of the medium. Since the elastic properties of the measuring tubes are temperature-dependent, the temperature is also measured to compensate for this behavior. Thus, only one sensor is used to measure the primary quantities of mass flow rate, density and temperature. Additional quantities can be determined by calculation, such as the volume flow rate and the concentration.

Coriolis Mass Flow Meters

  • Exact and even metering of components.
  • Time and cost savings due to elimination of manual weighing and mixing.
  • No cleaning of mixing containers and mixers.
  • Material savings from avoiding the preparation of excess material.
  • No risk to pumps and suction systems from sudden hardening of 2K material.
  • Improved working conditions due to closed circuit of 2K systems.
  • Very small quantities of paint residue for disposal