Special air cushion technology enables gentle treating, encrusting and pelleting through simultaneous treating and drying.

In the era of Heubach analyses, securing seed quality by means of treating technologies has become ever more important. Environmental aspects, legal guidelines and treatment recipes require technologies that minimize dust and grain abrasion. Customary continuous and batch treaters regularly lead to increased abrasion and Heubach values that exceed the legal limits. Furthermore, treating and mixing cause stress and grain abrasions reducing germabilities by up to 2 percent. To date, complex treating recipes with high dilution ratios for encrusting and pelleting have required separate process steps for treating and drying. With the CM100 MultiCoater, the German technology manufacturer PETKUS / ROEBER has developed a system where the treated seeds are already dried in the mixing chamber. This is facilitated by a special air cushion technology in combination with metal-free deflectors. The PETKUS / ROEBER MultiCoater “CM” simultaneously treats and dries, improves flow behaviour and guarantees a gentle treatment of seeds with a homogeneous and optimal surface coverage.

Dr. Raed, the rotor-stator principle is usually applied in the case of conventional treaters. Which advantages does this principle offer and which disadvantages does it have?

“In the case of treaters that function according to the rotor-stator principle, seed is loaded into the mixer – i.e. the stator – batchwise, moved by a rotating turntable and simultaneously sprayed with a chemical agent. This has the advantage that the mixing intensity and consequently the speed are high. The disadvantage is that the grains rub against the stator, are thus subject to stress and become partly damaged. This can lead to the fact that the germination capacity which was 97 % before treating is 94 – 95% afterwards. Furthermore, the grains do not only hit the stator: The movement of the rotary plate causes the seed to move evenly in a circle around the stator wall. In order to interrupt this regular flow and to prevent the spray of the chemical agents from reaching only one side of the grain, metal deflectors were installed in all previous treaters to ensure radial mixing. The rotation causes the seed to hit the so-called deflectors. This results in significant dust abrasions containing active substances. Using this common technology in practical everyday life often leads to statutory Heubach values being exceeded.”

How were you able to solve these problems with the MultiCoater “CM”?

“We have developed a new system which builds on the rotor-stator principle. However, we have supplemented it with a sophisticated airflow technology. Air is led via nozzles and an adjustable gap between stator and rotor. This creates an air cushion between the stator wall and seeds which dramatically reduces the friction stress. A key challenge was to harmonise the optimum air flow with the force of gravity, i.e. the specific weight and acceleration of the corresponding seeds. Grasses, for instance, already float with the slightest air movement. Corn in contrast would be the other extreme. The air must be dosed so that the grains neither fly away nor fall down. At the same time the air flow may not be too strong, thus blowing away the fine spray of the chemical agent. Therefore, we developed a special control motor where the parameters of the air flow can be set precisely and appropriately for each type of seed. The status is constantly controlled and adjusted by means of the PLC.”

Dr. Khaled Raed Innovation Manager at PETKUS Technologie GmbH and design engineer of the PETKUS / ROEBER MultiCoater

Do you still use metal deflectors with your new treaters?

“No! In order to support the friction-reducing properties of the air cushion technology, we have not installed any metal deflectors or other edges in the MultiCoater which could lead to seed damage. Instead, we use elastic deflectors made of plastic whose form is similar to that of an aircraft wing. Optimized aerodynamics direct the seeds to the middle and ensure an excellent mixture without stress.”

To what extent do these measures improve the abrasion values and the mechanical stress compared to traditional continuous and batch treaters?

“Normally the treating process takes 30 to 40 s. In an endurance test we increased the batch time of the MultiCoater to half an hour. This neither led to additional dust, nor were the grains damaged. Using the traditional procedure this test would not have been possible, since the seeds would have been grinded due to the long dwell time in the treater. The test result was confirmed by means of the Heubach test afterwards: all samples were clearly below the statutory limit value.”

Apart from the reduction of the abrasion, are there any other advantages of the air cushion technology?

“Definitely, because the airflow in the MultiCoater has a second function apart from friction reduction: it ensures that the seeds rise and fall in a spiral motion. Together with the plastic deflectors this leads to optimum mixing. The more the grain moves within one second, the higher the probability that all of the seeds will be evenly treated. Thus the high mixing intensity ensures a very homogeneous grain-to-grain distribution.”

During intensive treating with high application rates, during encrusting as well as during pelleting it is common that additional redrying is required after the coating process. Is this also necessary for the MultiCoater?

“No, because treating and drying take place in one step. After the coating process the air quantity in the mixing tank is simply increased so that the chemical agent dries on the seed surface. Thus all agricultural pesticides including dilution, dyes, polymers or other pelleting and coating masses can be applied in only one batch simultaneously, after each other and / or with different treatment times and intensities and they can be dried immediately. Additional stress-promoting transport and process steps are completely omitted. Furthermore, the agent better adheres to the grains due to the gradual and quick drying. Encrustings or pelletings become uniform in size and flawless, without cracks and fractures. Furthermore, dust containing the active substance is discharged from the airflow in this phase.”

Does the MultiCoater have any other special features?

“The system works very precisely. Chemical agents and additives are dosed via a proven loss-in-weight system which is equipped with special hose pumps with servomotors. The seeds are precisely allocated by means of an electro-pneumatic batch scale and gravimetric dosage. The application and seed amounts are constantly measured, the actual values are compared to the target values and they are adjusted fully automatically during operation. In order to further optimise the spraying result, the perforated spraying disc was redesigned: we have constructed it in such a way that the speed can be set individually. For instance, this is important in the case of viscous chemical agents where the speed must be increased in order to reach an optimum result. Furthermore, the spraying disc was modified in such a way that the chemical agent is finely spread with a broad spraying angle to ensure complete seed coverage. In addition, the new integrated PCA system (product, chemical, aspiration) facilitates a quick decoupling of the supply lines using a quick-release fastener. The special lid allows for good accessibility of the machine and thus for easy maintenance and cleaning. Other models often only allow for the lid to be opened half way or one third of the way. In our version it can be pivoted 180° so that each point in the mixing cylinder can be reached and cleaned without problems. This ensures absolute purity for variety changes and helps to avoid cross-contamination.”


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