Equipment
Better, faster and at lower costs
Inline process control of chewing gum production lines: reaching higher throughput, tighter tolerances and less waste of product. By Stephan Strelen, Strelen Control Systems and Patrick Gabler, Gabler Gmbh + Co. KG.
Above left: Patrick Gabler Above right: Stephan Strelen Left: Gabler Extruder-Combi Below: Thickness control sensors
etter, faster and at lower costs – this is, in three words, what producers are expecting from their equipment manufacturers. The speed of the production line shall increase and so shall the overall equipment effectiveness. Achieving this goal is everything but easy. Usually, only a well coordinated process control - combined with the matching equipment - is able to reach major steps towards the goal: a faster production that produces more products on each line with a higher quality. Why this is so important is obvious: labour costs, as well as energy costs stay almost stable if you compare an automatic line with high output with a production line of a lower capacity. The simple equation is ‘effectiveness equals higher margins’.
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Where the difficulties lie - and what role process control plays - shall become clear by observing the following example: Chewing gum tabs are produced with the following process:
34 Kennedy’s Confection September 2012
The ingredients are mixed in a batch or continuous process and then fed into a pre-extruder which has the job to create a uniform and homogeneous mass. A cooling tunnel follows the pre-extruder. From the cooling tunnel, the gum is then fed into the main extruder (in case of a modern multi layer product, this can also be a co- or multiple layer extruder). This extruder is equipped with a nozzle, or die, which already forms the gum ribbon into the desired shape. Rolling and scoring laminates the extruded ribbon to its final thickness. Sometimes a rolling and scoring line is equipped with an intermediate cooling tunnel in order to get a more precise cut, run a faster process and safe time with cooling at the end. At the end of the line are stations to do length and cross cut. After the product has been in the cooling and curing room for several hours, it is packed in several steps. The quality of the final product depends on several processing steps
of the whole line. Extruding, rolling, scoring, cutting and even the cooling: they all have an impact on the geometrical dimensions of the final product. If deviations shall stay as small as possible, a fast reaction of the control unit is required. The goal is to recognise deviations as early as possible and to react automatically on further process, mass or environmental disturbances such as deviations of mass, temperature or humidity in the air. To achieve this, a modern process control which is custom designed and supplied by Strelen Control Systems for the Gabler processing line has been implemented.
The process is difficult to control. Its slow reaction times and multiple parameters determine its behaviour. If an adjustment is made at the extruder speed, it takes up to 12m until the result can be observed at the entry of the packaging machine - and there are various parts of a production line that have an impact on the product dimensions. Because of this behaviour, a multi-loop state space controller was chosen to do this job. State space controllers rebuild a process with mathematical equations in an
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kennedysconfection.com
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