Hilde S. Tellesbø,a Helle Fossheimb and Kim H. Esbensenc
aWeber Leca Rælingen, Saint-Gobain Byggevarer AS, Rælingen, Norway. E-mail: [email protected]
bSaint-Gobain Byggevarer AS, Oslo, Norway. E-mail: [email protected]
cACABS research group, Institute of Chemistry and Biology, Aalborg University, campus Esbjerg. Denmark. E-mail: [email protected]
This work illustrates variographic analysis applied to industrial production processes to identify and reduce adverse production deviations (over-specification, loss) and evaluate profitability. A first example concerns production of light-weight expanded clay aggregates (Exclay), produced in cement-like rotary kilns. Clay raw material is heated to 1150 °C to be expanded. An adverse periodicity was observed in a specific plant cooler manifested as fluctuations in the material volume (height level) causing a periodic variance in the production output from the kiln. This problem must be resolved by instigating a more stable cooler, which could in fact be engineered by a very small investment of about 5,000 Euro. A variogram characterization was carried out to evaluate the amplitude of the periodicity, and the quantities involved (losses), which information was used to calculate the investment pay-back time. From the variogram it was observed that the reduced kiln output volume was at least 0.7%. During one year with improved cooler level control, this translates into savings of about 100,000 Euro, i.e. a pay-back time will be less than one month. A second example is from a LRM-project (Loss and Reduction Model) at a plant producing bagged pre-mixed mortars, in which the variance of the weight of the produced bags was found to be consistently too large. A pilot variographic analysis was applied with an aim to identify the root causes of this problem (three filling stations at the same line were investigated, all with identical filling systems and scales): Two stations were found to have a total material loss of 1.2%, while the third was running perfectly well (low V(0) and low sill), but with a too high set point. The technical resolution shows that it is possible to reduce material loss with existing equipment by improved monitoring/recording routines but no need to acquire new expensive belt scales a.o. For two of the stations V(0) (MPE) was in fact at a level almost identical to the sill making it structurally impossible to keep bag weight within specifications. Recurrent monitoring of V(0) and moving average smoothing should be evaluated at the very many similar production lines in the multinational corporation involved to gain improved process control to reduce overfilling. While relatively small on the basis of an individual filling line, the potential accumulated corporate savings take on a quite different economic significance. Variographic analysis is a powerful tool for industrial technicians and process engineers to improve processes —and in the present cases for industrial managers as well for evaluating ultimate investment profitability in industrial processes.
Publication date: 9 June 2015