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Powerful cocoa screening machine: First rotating, then compulsory clearing

Whether it's chocolate, ice cream or baked goods - cocoa is a key element in virtually everything sweet and tasty. But the plant-based product is rather time-consuming to process and manufacture. Cocoa beans are often delivered to the processing plant dirty and particles have to be removed during the production process using sieves, magnets and air flows. Here, extraordinary requirements are placed on the machinery used, as illustrated by a current project undertaken by screening technology specialist J. Engelsmann AG.

A leading cocoa processing plant produces high-quality semi-finished cocoa products, such as natural and deodorised cocoa butter, as well as natural cocoa paste and cocoa powder / cocoa cake that has been alkalised with a variety of fat contents upon customer request.

Cocoa makes screening tricky

For the purposes of sieving out foreign material and dissolving caking that can occur during the production process, the cocoa manufacturer was looking for two new screening machines, which could boost the existing screening capacity to 4 t/h at a finer mesh width of 500 μm. The lubricating and sticky consistency of the different cocoa varieties - which have different properties - make sieving an extremely complex task. Due to the cocoa products, the sieve fabric ends up clogged time and again after a relatively short period of time, which means that the machine has to be completely cleaned after every shift and product change to prevent the build-up of bacteria.

Thanks to their extensive experience with complex sieving tasks, the Engelsmann engineers were familiar with the problem encountered when sieving fatty products. The machine solution they provided was the centrifugal screening machine of the VIRO type, which has particularly proven its worth when used as a checking or classifying sieve for poor-flow products that require sieving, such as baking powder, sulphur or phosphate.

High-frequency vibrations keep sieve fabric open

The VIRO screening machines for cocoa processing are made of an elastically supported perforated basket, in which a rotating shaft with rotating blades pushes the cocoa product through the fabric. The perforated basket is sealed on the outlet side by an adjustable baffle plate, which prevents the sieved product from simply being conveyed through the machine. If there is a narrow gap between the baffle plate and perforated basket, the product dwell time on the mesh fabric is increased, thus improving the degree of sieving.

Depending on the fat content and temperature of the cocoa product, this inevitably leads to the sieve fabric becoming clogged. To prevent this, two pneumatic vibrators with a rotary speed of more than 20,000 rpm displace the sieving cylinder at a high-frequency oscillation level and ensure that the mesh of the sieve fabric remains open.

Discharging device prevents bridging

To achieve the customer's desired capacity of 4t/h, the VIRO screening machines were also equipped with a discharging device as well as the vibration cleaning system. This is attached underneath the perforated basket and ensures that the sieved cocoa product does not bridge in the outlet, thus clogging the machine. Due to the slow shaft rotation with two holding arms made of stainless steel, the outlet funnel is "cleared by compulsion" and the greasy cocoa paste is fully discharged from the machine. To meet the high hygiene requirements in the foodstuffs industry, both centrifugal screening machines - apart from the drive and the bearings - are made of stainless steel, while all of the seals and adhesives used were designed to be food-safe.