Quality Management for Metallurgical Process Plants

Whether you are producing copper cathodes, lead or zinc concentrate, or gold bullion, a total quality management program not only provides a more consistent product, it can allow you to produce it at a lower unit cost!To maximize quality, variation must be minimized. Variation is sometimes called the fundamental cause of poor quality. Variation can also be called the fundamental cause of high unit costs! For instance, variations in cyanide concentration will result in low recoveries when it is low (adding to unit costs) and high reagent costs when it is high (further adding to unit costs).Performance Associates’ quality management programs focus on reducing variation in the production process. To the degree that this is successful it improves quality and unit costs at the same time.

Variation

There are two types of variation: random and non-random. Random variation results from inherent characteristics of the production process. For example, a reagent metering pump will vary the quantity of reagent metered per unit time around some mean value. The amount of the random variation will be a function of the type of pump, clearances in its construction, stability of the control loop, type of variable speed drive, etc. Non-random variation results from influences from outside the process system which are generally under the operator’s control. Such non-random variation might result from equipment disrepair, changes in feed characteristics, etc.The first requirement for improving quality and costs is an understanding of the nature of variation and the means to determine the degree of random and non-random variation in the production process. The second requirement is to take appropriate action to reduce non-random variation. The third requirement is to take appropriate action to reduce the random variation. Actions effective in minimizing non-random variation are useless and counterproductive when used to reduce random variation.

The Quality Management ProgramPerformance Associates’ quality management programs are built with the following elements:

1. Management commitment.
2. Training in simple statistical techniques, samples, and collecting data.
3. Organization structure emphasizing work group authority and accountability for results.
4. Statistical process control (SPC).
5. Performance reporting.
6. Team approach to problem solving.
7. Continuing emphasis on reducing variation in the production process.

The production process is initially divided into major process areas. A process area usually performs a major function with measurable output, contains equipment dedicated to a single task, and has a regularly assigned work crew.Within each major process area, each unit operation is defined. A unit operation normally performs an operation that changes the physical or chemical characteristics of the feed material. Examples include a ball mill, cyclone, or filter.For each unit operation, the critical process variables are defined. Process variables represent parameters significantly affecting the performance of the unit operation and are controllable by someone that can be held accountable. Examples include temperature, density, size, or flowrate.A quality management manual is developed illustrating the process areas, unit operations, and variables. Accountabilities are also shown for control of each unit operation. A control standard is then developed for each process variable which establishes the method and accountability for control.

The format can be flexible, but usually includes:

1. Process variable to be controlled.
2. Accountability.
3. Definitions.
4. Process standard.
5. Reason for control.
6. Measurement.
7. Reporting.
8. Control chart—the control chart is the tool that documents variation.
9. Operating procedure.
10. Corrective action.