For each glass manufacturer, the use of cullet (recycled glass) is very
beneficial in many ways e.g. energy consumption reduction, CO2
waste gas reduction, reduced landfill. The most important disadvantage of
using cullet is the risk for glass quality decrease due to contaminated
cullet. The enormous quality gap between the input waste glass and output
of a glass recycling plant, the quality fluctuation of the input waste
glass and the possible failures (e.g. poor adjustment) of the high tech
equipment of the cullet treatment plant result in an eminent risk for the
glass manufacturer to contaminate its glass melt with cullet of (very)
Consequently, the cullet quality control procedures have a very high
impact on the quality level and performance of the cullet treatment plant
and on the final glass quality at the glass plant. As this quality control
is time consuming (and costly), the glass quality control procedures at
the cullet treatment plant and at the glass plant need to be optimised so
that the best guarantee on the quality of the cullet can be given at the
As cullet is for many glass manufacturers one of their most important
(secondary) raw material, quality control (QC) errors must be kept to a
minimum. For cullet treatment plants and glass plants familiar with 6
sigma quality objectives, a 95% reliable (≈2σ) cullet QC is a must.
However, our calculations prove that probabilities of making quality
control errors are usually much higher, resulting in unacceptable
producer's and consumer's risks.
Using our statistical calculation programs, taking into account cullet
quality specifications, sample size(s), grain size distribution and weight
of the contaminating pieces, we determine the operating characteristics
curve(s) and the corresponding acceptance and rejection conditions
according agreed maximum risk level(s). Combining cullet quality
specifications and agreed maximum producer and consumer risk level, a
fair, transparent, verifiable and statistical relevant cullet quality
control procedure will be developed.
Interested in a free copy of our publications 'Cullet quality control'
(Glass International March 2013) and/or 'Reducing risk in cullet quality
control' (Glass International April 2016)? Please check the "Free
utilities - Tools" button on our "Home" page.