Screening machines for food and seed

In our long company history, we have gained experience especially in the screening of sugar, jelling sugar, sorbitol, dextrose, maltose and related substances. But our screening machines have also been used convincingly in screening  different types of seed, flour, cocoa, coffee, tea, baking powder, milk powder, protein granules, sorbic acid, flavors, tobacco and nicotinic acid.

In order to meet the high demands of the food industry, our screening machines are designed and built according to FDA conformity using food grade materials. This also makes them a perfect option for cleansing seed, for example by removing grit and other impurities.

Processing of flour

Flour is produced by grinding cereal grains. The resulting powder is obtained, for example, from the cereal varieties wheat, spelt, rye, oats, barley, millet, corn and rice. The state of the art is that the grain is most effectively ground between the grinding rollers of a roller mill in a mill. In modern roller mills, screening or sifting takes place in a plansifter (sifting machine) or a grain cleaner after each grinding operation to separate the different particle sizes. Check screening is used as a quality control step to ensure only flour within the desired particle size range proceeds further in the production process. This combination of roller mill (mill) and plansifter is called “passage”. In wheat milling, additional semolina cleaning machines can be used in such passages at the point between the grain cleaners and the roller mills. By reducing the distances between the rollers of the individual passages, the ground material is ground finer from stage to stage. Sieving is used to separate different particle sizes, and various components, such as bran and germ, are separated during the process. So-called endosperm particles smaller than 150 µm (0.15 mm) are immediately removed as flour using screens with specific mesh sizes, while larger particles are passed on to the next passage. In the plansifter or sifting machine, the screen surface is the area where the separation of materials occurs.

Screening of spices

The comminution and subsequent screening of spices is one of the most demanding tasks of processing technology in the food sector, because spices are very different in terms of both structure and grindability. Fine screening is essential for achieving the desired fine powder consistency in spices, ensuring high precision and efficiency in classification.

On the other hand, their properties can vary greatly depending on the type of cultivation or harvest time. Advanced processing technology often utilizes vibrating screens and vibratory sieves to remove impurities and oversize contamination from spices, ensuring product quality and consistency. In these industrial applications, industrial screeners play a crucial role in removing impurities and maintaining the purity of spice products. Removing impurities and oversize contamination is critical for maintaining the quality and safety of spice products.

The right screening machine for different requirements

A wide range of sharp separations in the medium and fine particle range from 20 μm can be achieved with the aid of the RHEstack^® flat screening machine. The material is transported according to the microthrow principle. This means that by driving two counter-rotating unbalanced motors, which ensure linear oscillation, the particles are subjected to a series of individual throws until they leave the machine. As a result, the screenings move in a straight line across the horizontal separation surface. Using a modular system, up to 15 screen decks can be assembled, allowing multiple repetition of the same screen deck sequences, thus providing the material with ample screening area to produce ultra-clean and ultra-fine particle sizes in a single machine without the need to change screen decks. 

When screening sticky food products, the RHEsono^® vibrating screen is recommended. Robust electromagnets operate outside the sieve housing, transmitting the vibrations to the sieve mesh via oscillating axes. This makes it possible to achieve accelerations of 15 g on the sieve cloth. Clogging of the screen cloth is also prevented by an installed program control unit, which achieves cleaning impulses of up to 50 g. The cleaning impulses are transmitted to the screen cloth by the beater bar. By means of the beater bar movement, the screen cloth is excited to high-frequency vibrations so that the adhesive forces of the particles are overcome. 

An alternative to the RHEsono^® is the high-performance screen RHEsonox^®. With the aid of two counter-rotating unbalanced motors, a linear motion is generated which serves to transport the material. An additional direct excitation of the screen fabric prevents clogging of the screen lining by plugged grain. Material that is difficult to screen can be classified precisely and at high throughput with this drive excitation principle, ensuring the best separation results in the ultra-fine and fine grain range.