Process industries are generally engaged in performing physical and chemical changes on materials. In order to build the desired properties, performance characteristics and economics into the finished products, processes must be controlled. Other aspects that seek attention include properties of raw materials, characteristics of the unit processes & operations, temperatures, pressures, concentrations and methods of measurement.
Three distinctive problems
In addition to conventional quality problems faced by process industries, they experience some unique ones that are quite different to those of batch mode manufacturing. First, the measurement methods by themselves could be miniature chemical, physical, or biological processes requiring control. Second, the testing time could take relatively long compared to batch reaction time. Hence, control decisions should be anticipated. Also, product specifications may not fully define performance under widely varying customer conditions.
As in the case of most industries, the process industries share problems of rapid product obsolescence and the need for prompt conversion of research effort into profitable production. The quality needs of the marketplace change rapidly and, often, unpredictably. For example, matters related to ecology and consumer safety may require development of different fuels & lubricants for automobile engines; flame-retardant paints & textiles; biodegradable detergents, fertilisers, and insecticides.
Since some of its end products - particularly drugs and food - are directly consumed, the process industries have become further involved in how products from one sector (eg, fertilisers, pesticides) influence the composition & properties of products in another sector (food, drugs). Further, the ability to measure minute quantities has raised questions about the effect of pesticide residues accumulating in fish and drinking water from surface water runoff of fertilized fields.
And third, human response to materials - either in process or as finished goods - varies widely both in its intended usage or in accidental exposure. This necessitates extensive toxicity studies and clinical trials, which are time consuming, expensive, and frequently complex. Hence, statistically designed experiments have become the order of the day.
Traditionally, responsibilities for achieving quality controls are concentrated in three broad areas:
· R&D laboratory
· Analytical or control laboratory
· Manufacturing plant
What is control?
Quality control can be defined as a managerial process during which one can:
· Evaluate actual performance
· Compare actual performance to goals
· Take action on the differences
The concept of control is holding the status quo - keeping a planned process in its planned state so that it is capable of meeting the operating goals. Unfortunately, a process that is designed to meet operating goals does not remain unaffected. In fact, all sorts of events intervene to damage the ability of the process to meet the predetermined goals. The main purpose of control is to minimise this damage either by prompt action to restore the status quo, or better yet, by preventing the damage from happening in the first place.
The control process takes place by use of the feedback loop and addresses sporadic problems.
· The sensor evaluates actual performance
· The sensor reports performance to an umpire
· This umpire also receives information on what the goal or standard is
· The umpire compares actual performance to the goal. If the difference warrants action, the umpire energizes an actuator
· The actuator makes the changes needed to bring performance in line with the goals
Scope for improvement
Improvement means the organised creation of beneficial change; the attainment of unprecedented levels of performance. This involves recognizing and eliminating chronic problems.
Quality improvement is considered necessary for two dimensions of quality: product features and freedom from deficiencies. To maintain and increase sales income, companies must continually evolve new product features and new processes to produce those features. Customer needs are a moving target. To maintain costs at a competitive level, companies must continually reduce the level of product and process deficiencies. Competitive costs are also a moving target.
The way ahead
Most of the conventional approaches to quality improvement are directly applicable to the process industries. However, the tools for analysis must be quite sensitive, since quite a few of the industrial products are high- volume, low- profit (commodity) materials. In such cases, a large amount of money rest on small differences in yield. Also, the tools of analysis that deal with such small differences must be flexible enough to accommodate numerous variables, many of which are non-linear, and may interact with other variables as well. Today, such tools exist, and the industry has progressed significantly by using these to improve yields and controls.