Making cereal bars is a piece of cake for McVities

Demanding powder processing environment requires a combination of real-time data, accurate weighing, safety, cleanability and quick changeovers.

The need for a fully automated, flexible manufacturing and plant control system with “real time” data able to handle different recipe types, and increase and decrease throughput to match packaging rates, demanded an innovative approach for McVities’ Tollcross site in Scotland. Successful implementation would require gentle handling of the ingredients while maintaining hygiene standards, a challenging job because of the many recipe changes required over a short period. In addition, McVities’ production of high quality, value-added confectionery products demanded accurate weighing, especially for minor ingredients.

Gericke, a supplier of powder processing systems, equipment and solutions, identified the production process steps and conducted pilot trials at its UK test laboratory to ensure the correct selection and optimization of equipment. Safety issues were addressed by a comprehensive risk analysis of the plant, taking into account the risk for a dust explosion and other potential hazards within the operation.

The system specified by Gericke initially assembled the raw materials of oats, crispies, sultanas, nuts and flakes in a batch preparation and tipped them into a reception hopper. Minor ingredients were tipped into a separate sack tip station, which included extraction and a reverse jet filter to maintain a dust-free environment around the tipping area.

The material was then screened and metal checked prior to entering a Gericke GMS 700-liter batch mixer. This unit uses the “Multi-Flux” cross flow method employing twin, counter-rotating paddles to create a “fluidized zone” in the mixing chamber combined with fast and efficient blending times, typically 90 seconds to 3 minutes. The mixer’s relatively low power consumption minimized the energy transfer into the product and the gentle mixing action resulting from the paddle design ensured minimized particle degradation and creation of a high quality, homogenous blend. In addition, the variable speed drive on the mixer was able to adjust paddle speed and optimize the mixing action to suit the characteristics of the various ingredients used in the recipes. The entire batch was then rapidly released into a surge hopper, allowing the mixer to be refilled while the previous recipe is processed downstream, maximizing the plant utilization.

At this point, the Gericke system converted to a continuous process where the gravimetric weigh belt feeder controlled the rate of the material into a vacuum pneumatic conveying system. As the material was conveyed along the belt, it passed over a load cell that instantaneously measured the mass throughput and adjusted belt speed to control flow within specified tolerances. This vacuum transfer system conveyed the material at low velocity to a continuous mixer for the addition of the liquid binding agent. The vacuum exhauster included a variable speed drive to reduce the airflow to required minimums to entrain the product, therefore reducing the risk of segregation and product breakdown.

In order to eliminate cross-contamination in other recipes, a separate system to transfer ingredients from sacks to the mixer was used when the recipes incorporated ginger. A fully extracted sack tip assembly was used to accept 25kg sacks and a separate vacuum transfer system conveyed the ginger to a volumetric screw feeder metering the ingredient directly into the mixer.

To meet hygiene and fast changeover requirements, all Gericke equipment was designed for easy access. The mixer included side and top cleaning ports and FCT (fast clean) rotary valves were used, allowing the rotor to be fully extracted without special tools. The weigh belt feeder also offered a fast belt changeover system where the belt mechanism is drawn outside of the machine to allow full access to the working components.

“The principle reason for the selection of Gericke as the main contractor for the project was their proven ability to supply single-source turnkey installations, the opportunity to undertake trials in a UK-based test facility and their flexible approach to engineering the best solution for the application,” said Phil Griffiths, project engineering manager at McVities.

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