Webster Chemical Company produces mastics and caulking for the construction industry. The product is blended in large mixers and then pumped into tubes and capped. Webster is concerned whether the filling process for tubes of caulking is in statistical control. The process should be centered on 8 ounces per tube. Six samples of 8 tubes are
Webster Chemical Company produces mastics and caulking for the construction industry. The product is blended in large mixers and then pumped into tubes and capped. Webster is concerned whether the filling process for tubes of caulking is in statistical control. The process should be centered on 8 ounces per tube. Six samples of 8 tubes are taken and each tube is weighed in ounces.
| Tube number | ||||||||
| Sample | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 |
| 1 | 7.98 | 8.34 | 8.02 | 7.94 | 8.44 | 7.68 | 7.81 | 8.11 |
| 2 | 8.23 | 8.12 | 7.98 | 8.41 | 8.31 | 8.18 | 7.99 | 8.06 |
| 3 | 7.89 | 7.77 | 7.91 | 8.04 | 8 | 7.89 | 7.93 | 8.09 |
| 4 | 8.24 | 8.18 | 7.83 | 8.05 | 7.9 | 8.16 | 7.97 | 8.07 |
| 5 | 7.87 | 8.13 | 7.92 | 7.99 | 8.1 | 7.81 | 8.14 | 7.88 |
| 6 | 8.13 | 8.14 | 8.11 | 8.13 | 8.14 | 8.12 | 8.13 | 8.14 |
a. If taking only 6 samples is sufficient, use the data in the table to construct the appropriate three-sigma control chart(s). Is the process in statistical control?
b. The process variability for the first and sixth samples appears to be out of control. Webster looks for assignable causes and quickly notes that the weighing scale was gummed up with caulking. Apparently, a tube was not properly capped. The sticky scale did not correctly read the variation in weights for the sixth sample.
Delete that data and recalculate the control chart(s). Is the process in statistical control?
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