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 Quality assurance of sandwich panels Quality criteria, inspections, approvals, certificates using the Hoesch Siegerlandwerke as an example With sandwich panels, a product has become established during the last few decades which is attractive not only thanks to its measurable characteristics, such as
but which also fulfils the requirements of our customers, architects and building owners in respect of
and which is attractive not least, thanks to its quick availability and reasonable price. In order to fulfil the increased expectations of customers, manufacturers need to constantly check and improve the quality level. We will use the example of the Hoesch Siegerlandwerke
to describe the quality criteria, measures and inspections required.
1. What is quality? This simple question can be answered with a vast number of definitions, yet the core statement of them all is the same: Quality is when the customer comes back - not the material. This statement also clearly and appositely describes
the quality of our Sandwich Panels market segment. The central focus of
the quality concept is the overall expectation of the customer.
Fig. 3.1.1 Quality-assured sandwich panels were used exclusively for the new airport in Istanbul - Source: Hoesch Siegerlandwerke GmbH
The customer's first priority is the problem-free and safe use of the sandwich panels as façade or roof components. The basis of their usability for this purpose is compliance with the technical criteria which are precisely defined in
However, the customer's expectations go considerably beyond these requirements, as
are further central requirements, which largely determine the quality concept.
Quality results from a combination of the following factors:
Effective quality assurance must therefore begin in these areas. Let's start with material
Machine/method During the last few years, great progress has
been made with machines and methods for the manufacture of sandwich panels.
Electronics, in conjunction with improved measuring and control technology,
enable deviations from set values to be detected and corrected while production
is in progress.
Fig. 3.1.2 Sandwich system control room
Fig. 3.1.3 Employee engaged in product development
People operate, monitor and maintain the machines and systems, check product quality and make decisions. This can, however, involve "human" errors. Therefore, people - staff - are the most important aspect of quality assurance. Staff are entitled and obliged to constantly monitor the quality of work, products and processes, because quality is the result of the co-operative work of all staff. However, this goal can only be achieved if the staff is well qualified and extensively informed. Working together in an atmosphere of mutual trust and effective collaboration is an important prerequisite. The basis of HSW quality assurance for sandwich panels
is the building inspection approval, RAL-GZ 617, the applicable DIN standards
and the quality management handbook, which will be explained below.
When building products are put into circulation, their usability must be proven by a usability reference; this is required by the regional building regulations. As sandwich panels are not regulated products in
the sense of the law, i.e. they are not based on any technical regulations
(DIN standards or similar), these products require a General building
inspection approval as proof of their usability.
Fig. 3.1.4 Cover sheet of a "General building inspection approval" This clearly defines, amongst other things, the material
characteristics and composition of the facings, the core layer and the
panel as basis for the stability, serviceability, thermal insulation and
fire behaviour. The manufacturer confirms this conformity with the
conformity mark (Ü symbol), visible on the building product or on
its packing. The Ü symbol gives the user the assurance that this
product has building inspection approval and that the quality has been
monitored.
Fig. 3.1.5 Ü symbol for sandwich panels
In addition to the approval requirements, quality and inspection regulations have been developed for steel sheet structural components by the Guetegemeinschaft Bauelemente aus Stahlblech e.V. [Quality Association for Steel Sheet Structural Components] and published in conjunction with RAL, deutsches Institut fuer Guetesicherung und Kennzeichnung e.V. [RAL, German Institute for Quality Assurance and Certification], as RAL - GZ 617. The focal points of this quality assurance are the product requirements relating to dimensions, geometry and dimensional accuracy.
The measured variables, measuring points and permissible limit dimensions are precisely defined as an appendix to the regulations.
Fig. 3.1.7 Example: Thickness measurement, definition of measuring points Regular internal monitoring of the products and production parameters occurs In accordance with these quality regulations with verifiable documentation of the results. In addition, a control monitoring is performed twice a year by a recognised inspection body - for HSW, this is the Versuchsanstalt Stahl, Holz, Steine der Universitaet Karlsruhe [Karlsruhe University Test Institute for Steel, Wood and Stone]; for these inspections, samples are taken from the current production. This consistent, objective monitoring by a neutral body guarantees products of special quality. When the initial inspection has been passed, the Quality Association grants the manufacturer the right to use the protected quality symbol for the respective product.
Fig. 3.1.8 Quality Association certificate
Internal production controls are performed on a daily basis to ensure the high quality of the sandwich panels. These ensure that the high quality requirements of the building inspection approval, RAL - GZ 617, as well as additional internal quality regulations, are complied with. 6.1 Insulating core The technological characteristics of the insulating core provide the basis for the outstanding static values of the sandwich panels and are indispensable for the visual appearance of the surfaces. The following are inspected, in detail:
In addition, shear strength, tensile modulus, compression
and rigidity modulus are checked, and the dimensional change in the foam
is measured after 3 hours' warm storage at 80°C. Incoming inspection
of the raw materials, thermal conductivity and closed-cell testing are
a matter of course.
The requirements, tests and test pieces for inspecting the facing quality are defined in detail in the General building inspection approval, in accordance with the relevant DIN standards. Testing of the apparent yielding point, tensile strength and breaking elongation is obligatory, as is measuring the thickness of the zinc layer. These tests are performed by the supplier of the
ingoing material, Thyssen Krupp Stahl AG, and the technological data of
each main coil is certified with a works test certificate in accordance
with DIN EN 10204.
Fig. 3.1.10 Tensile test
An example of the procedure for the required coil coating tests is shown below. Irrespective of the use (internal - external use) and the coating system, the quality assurance of our coater, Thyssen Krupp Stahl AG, begins with the coil coating plant.
Fig. 3.1.13 Coil coating control room Thanks to constant process conditions, consistently high coating qualities are achieved throughout the continuous process on high tech systems. The Pladurâ and Platalâ coatings, used as coatings for Hoesch trapezoidal profiles, cassettes, ceiling profiles, sandwich panels and much more, have proven themselves in tough building use over decades. In addition to quality controls on the coating, extensive
laboratory tests are carried out on samples using the latest techniques
and equipment. The following are inspected:
Fig. 3.1.14 Production controls on the coil coating system
In a weathering chamber, xenon arc radiation is used to simulate the effect of UV radiation from the sun, enabling weather exposure characteristics such as changes in colour, changes in gloss and chalk resistance to be measured and compared with permissible values.
Fig. 3.1.16 Weathering installation at Baltrum Salt spray test The corrosion resistance is tested in the salt spray
test. The material samples are sprayed with a 35°C 5% salt solution
for 360 hours, and then the corrosion behaviour assessed at defined scratch
tracks.
Fig. 3.1.15 Salt spray test All procedures and inspections are performed and recorded in accordance with the authoritative DIN standards and the test procedures of the ECCA (European Coil Coating Association, Brussels) and made available to Hoesch Siegerlandwerken.
In addition, Thyssen Krupp Stahl AG subjects the coil-coated sheets to natural weather exposure over several years and assesses the corrosion behaviour through measurement and visual assessment. Several weathering chambers in the various atmosphere types, including a marine atmosphere, are available here on Baltrum island.
The building inspection approval requires that the internal production inspections be performed by an external monitoring body at least twice a year. These inspections are performed by a recognised monitoring body. At HSW, this has been undertaken by the Versuchsanstalt fuer Stahl, Holz und Steine der Universitaet Karlsruhe. Various material tests are used to monitor the internal production, determine the thermal conductivity and fire behaviour, check the cell gas composition and the "closed cellness" of the foam, as well as deformation resistance under the influence of heat. Single-span girder bending tests are performed to check the permissible static values, and the buckling tension and rigidity modulus are determined. The results of the external monitoring must be kept
for 5 years and presented to the Deutschen Institut fuer Bautechnik [German
Institute for Building Technology] and the competent higher building inspection
authority on request.
Fig. 3.1.17 Single-span girder bending test
The HSW management system is based on the requirements of DIN EN ISO 9001. This standard describes the processes for quality assurance, starting with design (development) through to the finished product. The necessary processes and procedural instructions
are set out in the quality management handbook. This begins with a declaration
of principle by the Management, which clearly describes the company's
quality goals. The effectiveness of the system is measurably shaped and
continuously improved by analyses and regular audits. The certification body is KPMG Certification GmbH, which certifies (by certificate) that a quality management system for the
of building products has been introduced in accordance
with the guidelines of DIN EN ISO 9001, and that this system is also applied
in HSW.
The manufacture of quality products is the company
goal of Hoesch Siegerlandwerke. This requires constantly high efforts
and the greatest care, at all levels and from all staff. Thus the correctness
of the quality definition "Quality is the conformity of planning
and execution" is proven again and again.
Fig. 3.1.18 Certificate - Certification Autor: Karl-Heinz Wickel
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