The Principles of Process Control

Aims and administration

It is better to prevent making defective biscuits than to have someone remove defectives or to send a lot of production to waste.

A defective not made is a plus. The productivity is higher.

A plant that is not running, because of breakdown, failure to provide suitable dough or other aspects of poor control, will result in waste of time and maybe materials. Productivity requires that the plant runs at the correct speed and produces an expected weight of packed product in a given time. Process control keeps the plant running correctly and details reasons when this fails to happen.

The aim of process control is therefore to put in place procedures and techniques that detect when any critical processing parameters deviate from the acceptable. Having made these detections action is prompted to bring the process back under control.

Each piece of production machinery has a person responsible for its control and functioning. This person is a production operative. All production operatives must be trained to know what is required to control the machines to contribute to the making of a good product. They must also know who should be informed when adjustments or other action has to be taken.

In order to know when each of the stages of a process is working correctly standards must be established for each product. These standards will have acceptable limits of variation.

Where measurements are made at various points in the manufacturing process some sort of recording is needed and it is the responsibility of the production operatives to make these recordings. However the facilities for making these measurements and recordings should be provided by technologists who understand processes and control management. These technologists are usually members of the Technical Department.

Establishment of standards

During the final stages of product development the process is adjusted to deliver product that meets the quality required. At this point measurements are made to record the processing parameters. Control points will then be identified.

The most important control point is normally at the oven exit because this is the first time that a baked product can be assessed. The critical parameters of the products are normally,

• biscuit weight
• biscuit size (length, width, diameter, thickness)
• biscuit colouration (top and bottom surfaces)
• biscuit moisture content

Facilities for measuring and recording these parameters must be provided for the production operative.

The biscuit weight is paramount as changes in this will have an effect on all the other parameters.

There may be other critical control points for other aspects of processing. These must be defined and means of measuring and recording the critical parameters (such as temperature, viscosity or moisture content) provided.

It is normal for each of these parameters to vary slightly even when the process is running well. Before control instructions can be given to operatives it is necessary to quantify the natural variation. Knowledge of the natural variation allows the development of a control strategy when significant deviations in parameters occur.

The control strategy will usually result in the provision of control charts. Lines drawn on a control chart aid the operator in his decision-making for keeping the process in control after he has made a measurement and entered it onto the chart. When allowance is made for the natural variation a deviation from the target value may or may not be large enough to prompt action.

By following a control procedure operatives should contribute to avoiding production of biscuits that either cannot be wrapped, because of size, or will not meet the consumer's expectations.

Process standards document

All the standards for a production process should be brought together in one document. It is also useful to record all the plant settings at a time when a process is running to standard.

A collection of all this information is called a process audit and it is best presented as a diagram for ease of reference.

Records of times and speeds

For each production run operatives are also responsible for recording production timings.

Records should include:

The period of production,

• at what time production started and finished
• at what time the production stopped for a fault and at what time it recommenced
• the reason for each stoppage

The speed of production,

The production speeds are defined in the standards document but at the start of each production run the speed have to be set and records should confirm that these measurements have been made. Examples of the speeds that must be checked are,

• the speed of the cutting machine, rotary moulder, the cream sandwiching machine and other machines that determine the number of biscuits being produced.
• the speed of the baking oven
• the speed of the wrapping machine(s)

Records of changes made

From time to time changes will have to be made to keep the process in control. There may be small adjustments to the formulation to accommodate changes in ingredient qualities. Ambient temperatures may result in changes to some plant settings.

It is important that changes are recorded as they may affect product costing, or process efficiency. It is also useful to record why changes were made. Experience may suggest that the new settings should become permanent and if this happens the process standards document must reflect this.

Facilities must be provided for operators to clearly and accurately note the changes that were made.

Calibration of measuring instruments

At each control point, instruments are provided for making the necessary measurements. Some of these instruments must be calibrated to ensure that their readings are accurate.

Examples where the standard methods of measurement take a long time and the instruments provide a rapid means of making an approximate assessment. Electronic instruments for moisture and biscuit size are examples.

Packet checkweighers which reject underweights and machines that scan for foreign matter inclusion must be regularly tested for correct performance.

Calibration and correct functioning checks may be made by either production or technical department personnel. In each case record must be made that the checks have been done.

Communication

The key to successful production is team work.

Typically, biscuit manufacturing involves many machines spread geographically over a long distance. This means that if trouble or difficulties in maintaining control happens in one place other operators at distant parts of the plant may not know of something that could affect them.

The actions that operators have to make as a result of process control procedures should also include directives about communication with others running or maintaining the plant.

Running a biscuit plant is a team operation and the team is not limited to the production operatives. The machines have to be maintained and repaired by engineers, and to smoothly combine production and maintenance operations, management must be fully informed of requirements and problems encountered.