The present invention relates to an apparatus and method for determining the shearing strength of a thermal insulation, said thermal insulation being possibly manufactured e.g. from structural wool, or also from polyurethane foam or polystyrene foam. Structural wool, i.e. so-called hard wool, comprises a plurality of fiber layers of mineral wool, which make up a wool panel. Mineral wool panel can be used as such for a variety of thermal insulation applications, or it can be processed for a variety of sandwich structures, such as e.g. sandwich panels, comprising surface boards of e.g. plastic-coated sheet steel and a core layer of mineral wool therebetween. Said core layer can be made directly from a wool mat, the fibers lying in planes substantially parallel to the surface boards, or for example in such a way that a mat of mineral wool is cut for lengthwise lamellae, which are turned 90° about the longitudinal axis thereof in such a way that the fibers lie in a substantially perpendicular relationship to the surface boards of a sandwich panel. A number of lamellae are glued to each other laterally and successively for producing a wool core of a desired size, the width of a lamella cut from the wool mat defining the thickness of a core layer. Thus applied, a core section made from a wool panel functions as structural wool. In so-called lightweight sandwich elements, the core section can be made from e.g. polyurethane or polystyrene foams instead of structural wool. The inventive apparatus and method can also be used for testing a core section of such elements, as long as the core section is manufactured as a prefabricated unit which is then glued securely to the surface boards of a panel.
Structural wool is subject to several different strength requirements, one being its shearing strength. Thus far, shearing strength has been measured principally as defined in standard SFS-EN12090, which is nevertheless an inconvenient and slow process. The standardized method requires at least 30 minutes or more, as it involves waiting for the glue to dry. Hence, it is an object of the present invention to provide a novel method of determining the shearing strength of structural wool, an apparatus used therein being characterized in that the apparatus comprises a mobile clamping element and alongside the same at least one immobile clamping element, each provided with a cavity capable of receiving part of a strip-like test specimen to be cut off a thermal insulation, said apparatus being adapted to apply a force F to the mobile clamping element for moving the mobile clamping element relative to the immobile clamping element for achieving the shearing of the presently measured strip at a location between the mobile clamping element and the immobile clamping element, said apparatus being further provided with means for measuring the force F for its magnitude.
On the other hand, a method of the invention is characterized in that the method comprises cutting a thermal insulation for a strip-like test specimen, having certain dimensions in various directions, said strip being then placed in a measuring apparatus for shearing strength, said apparatus comprising a mobile clamping element and alongside the same at least one immobile clamping element, each provided with a cavity capable of receiving part of the strip-like test specimen, said apparatus being used for applying a force F to the mobile head for moving the mobile clamping element relative to the immobile clamping element for achieving the shearing of the presently measured strip at a location between the mobile clamping element and the immobile clamping element, said force F being measured for its magnitude, and the shearing strength being determined on the basis thereof.
An advantage offered by the inventive method of determining shearing strength is that a shearing strength test can be performed quickly, as it takes no more than 2-3 minutes and, thus, can be used for continuous production control.
A European product standard regarding sandwich structures is under development, the chosen test method being a so-called beam test. The beam test comprises cutting an element for a beam about 100-200 mm wide, having a length of about 1000-2000 mm. It is good for testing a finished product, but not for testing solely a core section and, moreover, it is tedious and hence inapplicable to direct production control.
The invention will now be described in more detail with reference to the accompanying drawings, in which:
An apparatus 1 as shown in
In operation, the strip-like test specimen 15 cut off a mat of mineral wool is placed, as shown in
A major advantage gained by a method of the invention is the simplicity and speed of the method, which makes it possible to apply the method also for continuous production control. The method and apparatus are described above principally in reference to mineral wool, and particularly in reference to mineral wool used for the core section of sandwich elements, but it is also applicable to other thermal insulations, in which shearing strength is an important factor. In addition to the core section of sandwich elements, structural wool can also be used e.g. for external heat insulation by gluing wool lamellae directly to a wall surface and by topping the same with a plaster coating.
Number | Date | Country | Kind |
---|---|---|---|
20012213 | Nov 2002 | FI | national |
Filing Document | Filing Date | Country | Kind |
---|---|---|---|
PCT/FI02/00863 | 11/6/2002 | WO |