Barrel-Coating / Hot-barrel Coating

Coating and drying in one process

The small technical parts are coated at Rotover using the special hot-flow painting process. In this process, the components to be coated are fed as bulk material to modern coating drums. At speeds of between 8 and 14 revolutions per minute, the components are then gently agitated. At the same time, the special paint system is sprayed in fine atomized form onto the surface of the moving components by automatic spray guns.

During the painting process, filtered, preheated air is fed into the spray drum. It heats the small parts to a temperature that is matched to the material, the geometry and type of the components, and the paint system. Temperatures of 30 °C to 90 °C are usually set here. The object temperature of the components is permanently measured and controlled by an infrared sensor. In this way, the special coating system bonds intensively with the base material and dries even during processing. At the end of this batch process, the components are ready for packaging.

For new components, Rotover first performs test runs and determines process parameters such as drum size, speed and inclination, paint quantity and spray pattern, as well as the optimum part quantity per batch.

Rotover's painting process allows a large quantity of components to be painted in a single pass. This also makes the Rotover drum painting process the most economical application process for mass small parts.

Drum coatings from Wuppertal as a milestone in development
Different processes for coating small parts in bulk existed many years ago. At that time, so-called "Rommel" was one of the best-known processes, as was dip coating with zapon lacquers or glaze lacquers in centrifuges. Cold tumbling with baking enamels was also used for painting small parts.

However, the so-called hot-drum coating process was then developed primarily by the zipper industry. At that time, an efficient and clever alternative was sought to the cumbersome coating of sliders as rack goods or to the time-consuming interval process consisting of coating in drums and drying in separate drying ovens. The latter had to be carried out up to 10 times in succession, depending on the color shade. The difference between hot barrel coating and the above-mentioned types of coating lies in the continuous process of coating and simultaneous drying of the parts as a single process within the coating line. This painting technique was then significantly further developed by paint systems from the paint manufacturer HÜLSEMANN, which had specialized in paint products for the painting of mass-produced small parts many years ago.

Today, the painting process is known by numerous other terms. For example, coating in the Ellerwerk coating rotary kiln, IMEL or Rotover coating (ROTOVER is also the name of the machines from our Italian partner company IMEL spa), Rotamat coating (Rotamat coating system from our German partner Walther Trowal), or SC-Coater coating. Other common terms are drum coating, EPITAL coating, spray drum coating, hot-barrel coating or cold drum coating.

Technology that is in the details
The painting or coating of small parts (bulk small parts as bulk material) is often also carried out in the dip-spin process. In this process, the basket or the immersion drum is the most important tool.

The bulk material is fed into the basket. The quantity depends on the shape of the parts and the bulk density of the part determines the filling quantity in the basket. The basket is then dipped into the dip tank. The paint wets the entire surface of the parts. Mechanical agitation by slowly rotating the basket improves the wetting process by removing bubbles and changing the contact surfaces. After the dipping process, the basket is lifted out of the dipping bath and rapidly rotated or centrifuged so that the coated parts are thrown against the outer wall of the basket. The centrifugal force causes the excess coating to drip back into the dip tank through the holes in the basket. The process of dip spinning is influenced by several parameters. The most important are: Immersion time, basket size, spin speed, spin time and loading, and viscosity of the paint. In addition, there are other parameters that affect this process. These depend on the coating and equipment technology, which can lead to an improvement in quality.

ROTOVER uses this process primarily for smaller batch sizes and has also specialized in combining complementary coating processes. Examples of applications in the dip spinner are the application of different bonded coatings, zinc flake coatings and special top coats.

The perfect solution for small series
In a modern paint booth, ROTOVER can also spray-paint small parts individually as lay-up or rack goods using flow cup guns. This process is designed for individual or very small batches. Customers appreciate the added value in offering this complementary painting process.