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Directory of non-destructive testing methods for the wood-based panel industry

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EUROPEAN
COMMISSION
SCIENCE
RESEARCH
DEVELOPMENT
Practical information and Programmes
DIRECTORY
OF NON-DESTRUCTIVE TESTING METHODS
FOR THE WOOD-BASED PANEL INDUSTRY
EUR 18489 EN EUROPEAN COMMISSION
Edith CRESSON, Member of the Commission
responsible for research, innovation, education, training and youth
DG XII/E.2 — RTD actions: Life sciences and technologies — Agro-industrial
research
Contact: Mr Alexandros Arabatzis
Address: European Commission, rue de la Loi 200 (SDME 8/22),
B-1049 Brussels — Tel. (32-2) 29-69402; fax (32-2) 29-64322 DIRECTORY
OF NON-DESTRUCTIVE TESTING METHODS
FOR THE WOOD-BASED PANEL INDUSTRY
Concerted Action: AIR3-CT94-2077
Editor: Johannes Welling
Authors
Matthias Schulte Universität Hamburg;
Kai Kruse Ordinariat für Holztechnologie,
Hamburg, Germany
Bundesforschungsanstalt
Johannes Welling
für Forst- und Holzwirtschaft,
Hamburg, Germany
FORBAIRT, Jos Evertsen
Dublin, Ireland
forbairf
Jamie Hague The BioComposites Centre,
Bangor, United Kingdom
Danish Technological Institute,
Jens Ljørring
Taastrup, Denmark
Centre Technique du Bois
Didier Serrant
et de l'Ameublement,
Paris, France 1' LEGAL NOTICE
Neither the European Commission nor any person acting on behalf of the Commission nor the editor and authors are responsible for
the use which might be made of the following Information.
This directory was produced by a European team of experts under the aegis of a European Commission funded initiative — Concer­
ted Action, Contact AIR3-CT94-2077, managed by Directorate-General XII.
All due care was taken in compiling the information given In this directory. The descriptions produced were extracted from information
supplied by the relevant companies and from technical brochures or publications. Neither the European Commission nor the partners
of this Concerted Action are responsible for anyl inaccuracies or invalid claims.
Copies of this publication can be obtained from:
Address: Bundesforschungsanstalt für Forst- und Holzwirtschaft
Institut für Holzphysik
Dr. J. Welling
Leuschnerstr. 91
D-21031 Hamburg
This work has been carried out in the framework of the project "Potential for quality improvement of wood-based panels through
enhanced control based on comparative non-destructive testing data" funded within the AIR programme (contact n°: AIR3-CT94-2077)
A great deal of additional Information on the European Union is available on the Internet.
It can be accessed through the Europa server (http://europa.eu.int).
Cataloguing data can be found at the end of this publication.
Luxembourg: Office for Official Publications of the European Communities, 1998
ISBN 92-828-4381-5
© European Communities, 1998
Reproduction is authorised provided the source Is acknowledged.
Printed in Italy
PRINTED ON WHITE CHLORINE-FREE PAPER Foreword
During the last three decades, the European wood-based panel industries have
shown a continuous growth from 10 to 30% in the market place. Starting with the
production of particleboards in multi-opening presses, a rapid development led to
the introduction of new production techniques, such as single opening and
continuous presses. Furthermore a wide range of wood-based panel products was
developed, often tailored to meet the requirements of the furniture and building
industry.
Particleboard and Medium Density Fibreboard (MDF) are the principle board
types. There is currently a strong development in Europe directed towards
increased OSB production. For many years the wood-based panel industries have
experienced increasing pressure from their customers on aspects of quality and
just-in-time delivery. This has led to the introduction of ISO 9000 quality
management systems in the European wood-based panel industries.
Nowadays a close and accurate control of the production process is an
indispensable requirement in modern plants. Operator skill and experience are still
very important in order to manage the complex interactions between raw material
properties, production parameters and end product properties. However, the drive
towards ever increasing speeds of production and the necessity to produce a wide
range of different panel products in smaller batches requires in-line process
control. Non-destructive testing (NDT) and assessment of both raw material and
panel properties, contribute to reducing start-up time after change of batch recipe,
minimising the amount of product sub-quality and reducing production costs.
There are many different kinds of NDT systems available in the market. It is the
aim of this DIRECTORY to inform the potential user of such systems about the
physical principles of these systems. The descriptions detail the relationship
between the measured values and the targeted properties, the effect of
influencing factors and boundary conditions under which the NDT systems can be
used.
NDT systems which are capable of in-line monitoring of raw material and panel
properties are helpful tools for plant operators and quality controllers. The
information resulting from such systems really becomes valuable when they are
integrated into an overall production control concept. In such a case the
interaction between raw material and panel properties and production parameters
may be taken into account by complex process models, which - after a tuning
period - facilitate very close control of the production process leading to optimised
quality and cost reduction.
This directory has been produced by a group of experts within the Concerted
Action project (AIR3-CT94-2077), which was funded by the Commission of the
European Communities during the period 1994-97. The members of the Concerted Action working group were:
• Dr. Johannes Welling (project co-ordinator and editor)
Federal Research Centre for Forestry and Forest Products (BFH),
Hamburg, Germany.
• Diplom Holzwirt Kai Kruse, University of Hamburg / OHt, Germany.
• Diplom Holzwirt Matthias Schulte, University of Hamburg / OHt, Germany.
• Dr. Jos Evertsen, FORBAIRT, Dublin. Ireland.
• M.Sc. Jens Ljorring, Danish Technological Institute (DTI), Taastrup, Denmark.
• Dr. Jamie Hague, The BioComposites Centre, Bangor, United Kingdom.
• Didier Serrant, Centre Technique du Bois et de lAmeublement (CTBA)
Paris, France.
The group received assistance from many suppliers of NDT systems, who
provided background information about their products and the principles involved.
Their contribution is gratefully acknowledged.
This directory is by no means claimed to be complete or free of errors. The reader
should consider that there is a continuous development in the field of NDT
systems. Information collected yesterday on NDT systems may easily be
overtaken tomorrow by new developments and findings.
The inclusion of products in this directory does not imply that these products are
approved by the editorial group or that they have been especially selected or are
preferred over others. Similarly, those products which have not been included in
this directory have not been intentionally omitted; either the editorial team was not
aware of the specific products, or no information was available to them during the
preparation of the directory.
This directory has been edited for technologists in the panel products industries,
companies designing and supplying process control equipment, students and
teaching staff.
Hamburg, August 1997
Dr. Johannes Welling
(Editor) Table of Contents
Page
1. Introduction to the use of the directory 1
2. Flow charts
• Particleboard production 3
• MDF production 5
3. Process control concepts 7
by M. Schulte (Universität Hamburg)
4. Description of Non-Destructive Testing(NDT) methods 22
5. Statistical process modelling 102
(A tool fors control and optimisation
in the wood based panel production)
by J. Welling (Bundesforschungsanstalt für Forst- und Holzwirtschaft)
and K. Kruse (Universität Hamburg)
6. Index 109
7. List of EN Standards related to wood-based panel products 122
8. List of suppliers of NDT systems 126
9. Acknowledgements9 1. Introduction to the uso of the directory
The objective of this directory is to provide manufacturers of wood-based panels
with a reference guide to non-destructive testing (NDT) techniques for use in the
manufacture of wood-based panels. A technical description of some of the
equipment available to perform the required measurements is also included.
The directory consists of six major chapters:
• schematic flow charts for particleboard and MDF production
• process control concepts
• descriptions of NDT systems
• statistical process modelling
• index
• list of EN standards related to wood-based panel products
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 systems used in the specific descriptions of the different NDT systems
enable the point of application of the systems in the production lines to be
determined.
Each NDT description has the same structure. Each description is identified with 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 may contain 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 can either be 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 suppliers 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.
Most NDT descriptions end with some literature references, which might be useful
if the reader needs more specific information.
The index at the end of the directory can be used to identify NDT systems for a
specific purpose or where in the production process a specific NDT system may
be applied.