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Chapter 19: B. Statistical Process Control 287
Continued
Table 19.7 Total number of nonconformities in samples of five rolls of paper.
Total number of Total number of Total number of
Day nonconformities Day nonconformities Day nonconformities
1 8 11 7 21 9
2 6 12 6 22 6
3 7 13 6 23 8
4 7 14 8 24 7
5 8 15 6 25 6
6 7 16 6 26 9
7 8 17 8 27 9
8 7 18 9 28 7
9 6 19 8 29 7
10 9 20 9 30 8
c Chart of Nonconformities
16
14
UCL = 15.56
12
Sample count
10
8
6
4
2
c – = 7.4
Part IV.B.4
0
3 6 9 12 15 18 21 24 27 30
Sample
LCL = 0
Figure 19.13 c control chart of nonconformities for the data in Table 19.7.
From Figure 19.13, it is quite clear that the process is stable. In other words, there
are no special causes present and the only causes that are affecting the process are
common causes. Thus, to eliminate the imperfections in the paper, the management
must take action on the system, such as examining the quality of wood chips and pulp,
changing old equipment, or providing more training for the workers. Also, to enhance
the process further and eliminate the nonconformities, the quality engineers should
use the techniques available in design of experiments.