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AIR3-CT94-2077
Potential for Quality Improvement of Wood Based Panels Through Enhanced Process Control Based on Comparative Non-Destructive Testing Data |
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Proposal No: | AIR3-CT94-2077 |
| Date Prepared: | September 1999 | |
| Source: | Final report November 1997 |
Summary
Introduction The European wood based panel industry aims at producing boards of high and constant quality, in many cases designed for special end uses. Product quality depends on a lot of multiple linked input variables and production parameter. Up to now the production management normally is based on historical recipes, that have been developed over long periods of time by experienced technologists. In many cases trial and error is the strategy for optimisation. The operator's reaction (adaptation of production parameter) to variations of product quality mainly depends on experience. Therefore large safety margins are needed resulting in poor use of resources and production capacity. This unsatisfactory situation could be improved by the implementation of expert systems based production control systems.
First attempts for modelling the complex interactions during MDF and particle board production have been based on classical analytical statistics. Regression technique is used to analyse functional interactions between raw material properties, production parameter and quality data. Large quantities of data sets originating from past production cycles are needed to identify significant relations. Up to now these systems do not produce results good enough to model real production processes. They are not flexible enough to be adapted to different production concepts. In literature the potential benefit of modem control strategies based on the "Fuzzy Set Theory" has been described for a number of processes, such as production of, fertilisers, concrete, chemicals etc.
The prospect of using this new technique for the development of process control strategies for the wood based panel production were rated rather good because it simulates the know-how of the operator. Being aware of the fact that most production plants for wood based panels as well as the individual quality requirements for the various types of boards differ considerably, it becomes obvious that expert systems trained on individual production plants will lead to more precise and flexible production control systems. It is essential for both systems, for the classical analytical as well as for the Fuzzy approach, to get detailed and fast information about the current production parameter and about the quality features of the boards being produced. To build up automated feed back systems real time data are needed. For most of the production parameter this should not be a problem. Normally data acquisition systems are already installed in modem production lines. In order to determine quality properties of the produced boards non-destructive-testing (NDT) methods are needed.
Up to now only a few NDT-systems have been installed in wood panel production lines (measurement of particle/fibre moisture content, continuous measurements of panel thickness and area weight, blow (blister) detection systems, etc.). Other NDT measuring systems currently are being developed (in-line measurement of the density profile, MOE, internal bond or bending strength). Additional methods for on-line prediction/measurement of parameter with high significance for the panel quality have to be developed in the future (particle size, measurement of glue distribution).
One reason for the wood based panel industries management's low acceptance of NDT measuring systems is that an NDT system is expected to deliver absolute quality values of the final panel product, for example on internal bond or bending strength. In reality NDT measuring systems more likely will be capable of delivering comparative data indicating changing panel quality. Modem control strategies can easily use this information instead of absolute values for optimising the process. There exists an information gap between the potential users of NDT methods in the wood based panel industry and the scientists who develop such systems. The industrial management does not want to install NDT systems, because apparently these systems do not fit to their targets. The scientist cannot prove the practicability and usefulness of the developed methods, because up to now feedback control systems capable of using information on relative property changes have not been realised.
Objectives In order to fill the information gap between potential users of NDT methods in the wood based panel industry and researchers working on the development of NDT measuring systems two major objectives have been formulated:
Activities
There are quite a number of research institutes in Europe that are or have been engaged with the development of NDT-systems for wood based panels. The limited amount of research funds provided for projects normally does not allow an efficient dissemination of the results in a form that is understood by industrial people. The SME sized wood based panel industry only has limited access to scientific publications and if it has, these publications are not fully understood. To remedy this and to achieve the goals described above the partners of the Concerted Action group decided to edit a Directory of Non-destructive Testing Methods for the European Wood-Based Panel Industry, as well as organise a workshop on Non-destructive Testing of Panel Products for the European Wood-Based Panel Industry.
A standard format for collection and presentation of specific information on NDT systems used in the wood-based panel industry was drafted. A list of suppliers of NDT systems was compiled. It was decided that each participant of the Concerted Action project should be responsible for collecting and compiling information in specific fields, so that the full range of fields of NDT application was covered.
A large number of suppliers of NDT systems were contacted and asked to provide technical information on the systems produced and additional literature searches were carried out. The information collected was then processed into a neutral and objective form, describing for each NDT method the physical principle involved, the boundary conditions, the achievable accuracy and other important information. The resulting directory consists of six major chapters:
From the flow charts the user will get an overview of the locations in the wood-based panel production line where NDT systems are already being used. The coding system used in the specific descriptions of the different NDT systems enables to locate the possible points of application of the systems in the production lines. All description of NDT methods have the same structure, Each description is identified by a commonly accepted title for the method on which the NDT system is based. This is followed by a description of what the method is capable of measuring in terms of the production process and a reference code is used for indexing. The actual physical parameters measured by the NDT technique are specified. The next section describes the physical principles on which the method is based. This section contains diagrams of the measurement set-up or apparatus involved, as well as elementary theoretical background information useful for a better understanding of the method. The next section gives a description of how the physical parameter measured relates to the property under investigation. This may include the presentation of equations and graphs.
The next boxes describe the "quality" of the measured values in terms of duration, resolution, measuring frequency and range. For the wood-based panel production in particular, the elapsed time between a measurement and the presentation of the result is very important. Resolution in terms of accuracy is a very sensitive piece of information, because it is often greatly dependent on correct calibration. It should be noted that absolute values are not necessary in all cases; comparative values, indicating a shift of properties, may also be valuable tools for controlling a process. The measuring frequency is either characterised as batchwise/off-line, discontinuously/in-line or continuously/in-line.
The range of measurement indicates in which range of the measured properties valid and reliable information can be achieved by using the NDT method. The information on boundary conditions and interference by other factors refers to possible limitations of the specific system. Furthermore the current state of the application of the NDT method is specified. The methods, described, may already be applied in industry or in research laboratories. Some of the methods are still under development, but have potential for being used in industrial applications in the near future.
For each NDT method a list of suppliers is given. A full listing of company names and addresses can be found in the supplier index. In some cases the systems provided by individual suppliers may differ to some extent. In this directory a generalised description of the principles involved has been given. It is recognised that a specific solution of a given supplier may be quite different to that of others. The list of suppliers has been compiled based on the information collected during the production of the directory. This does not imply that the list is exhaustive.
In addition to the Directory of Non-Destructive Testing Methods for the Wood-Based Panel Industry, the group also produced proceedings of the Workshop on Non-Destructive Testing of Panel Products.
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