Additional Case Study: Green River Chemical Company

Green River Chemical Company customers have complained regarding the sulfate
content of the company’s product. Every customer allows some sulfate content, but theoretically
there should be none. The usual customer specification is 90 parts per million (PPM) sulfate.
The quality control department at Green River feels that there is no problem with sulfate
content, which has been averaging just over 50 PPM. The production department estimates that
a substantial investment would be required to lower the amount of this contaminant. These two
departments, after consulting with the marketing department and customers, suggest that a
control chart be set up to monitor sulfate content. Five samples will be tested per day and
plotted as one point on the chart.
Use the data in Table 1 to set up the control limits. Then, after the limits are in place for
this process, use Table 2 to determine whether or not the process remains in control for the
week of April 6—10.

TABLE 1 Original Green River Chemical
Company data
Date 1 2 3 4 5 X R
March 2 57 54 62 45 36 50.8 26
3 56 54 47 42 62 52.2 20
4 40 70 58 45 44 51.4 30
5 52 58 40 52 46 49.6 18
6 57 42 52 58 59 53.6 17
9 62 49 42 33 55 48.2 29
10 40 39 49 59 48 47.0 20
11 64 50 42 57 50 52.6 22
12 58 53 52 48 50 52.2 10
13 60 50 41 41 50 48.4 19
16 52 47 48 58 40 49.0 18
17 55 40 56 49 45 49.0 16
18 47 48 50 50 48 48.6 3

Additional Case Study: Green River Chemical Company

19 50 50 49 51 51 50.2 2
20 51 50 51 51 62 53.0 12
23 51 50 49 50 50 50.0 2
24 45 47 70 46 36 48.8 34
25 50 35 48 39 47 43.8 15
26 55 70 50 30 51 51.2 40
27 49 38 64 36 47 46.8 28
30 59 62 40 54 64 55.8 24
31 36 33 49 48 56 44.4 23
April 1 50 67 53 43 40 50.6 27
2 44 52 46 47 44 46.6 8
3 70 45 50 47 41 50.6 29

 

TABLE 2 Data for week of April 6—
10
Date 1 2 3 4 5
April 6 63 49 50 45 53
7 57 70 45 52 61
8 45 38 46 54 52
9 48 52 39 57 61
10 45 53 48 46 66

Discussion Question
1.
Does the process remain in control? Does the data for March appear to be in control?

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