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 Program
Performance
Associates’ quality management programs are built with
the following elements:
- Management
commitment.
- Training
in simple statistical techniques, samples, and collecting
data.
- Organization
structure emphasizing work group authority and accountability
for results.
- Statistical
process control (SPC).
- Performance
reporting.
- Team
approach to problem solving.
- 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:
- Process
variable to be controlled.
- Accountability.
- Definitions.
- Process
standard.
- Reason
for control.
- Measurement.
- Reporting.
- Control
chart—the control chart is the tool that documents variation.
- Operating
procedure.
- Corrective
action.
The
control standards are included in the quality management manual
which, ideally, becomes a part of the process manuals covering
the plant.
Performance
Associates’ quality management programs provide the tools
to both minimize variation in the process and minimize production
costs. These programs might otherwise be called optimizing use
of resources to fine-tune the production process. To totally realize
the benefits, senior management must act when the quality management
system indicates that action is justified and necessary. Solving
problems and minimizing non-random variation is only half the
battle. Management must continue to emphasize the importance of
always taking the next step, eliminating the next bottleneck,
and in general, to continue to improve the process and reduce
random variation.
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