Layered Stone Hob Structure to Prevent Thermal Hairline Cracks
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Induction cooking on stone slabs faces challenges such as high temperatures causing hairline cracks and potential tearing due to uneven thermal expansion, with existing stabilization methods like carbon fibers being inadequate in preventing hairline cracks and maintaining a flat surface.
Innovation Solution
A design that differentially thicknesses the stone slabs above and below a carbon fiber layer, with a thicker lower slab providing additional stiffness and using high-temperature-resistant adhesives and alternative fibers like glass or basalt to manage thermal expansion and prevent curvature, combined with forced air cooling to dissipate heat.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single stone slab is used for induction cooking, then the structure is simple and cost-effective, but the slab cracks or breaks due to localized heating and thermal expansion forces
Solution Approach 1:
The single stone slab is divided into two separate slabs (upper and lower), with the lower slab providing structural support and the upper slab serving as the cooking surface. This segmentation allows each slab to have optimized thickness and material properties, preventing the cracking issues that occur in single-slab designs while maintaining overall structural simplicity.
2Reliability
If carbon fiber reinforcement is applied to stabilize the stone slab, then cracking is prevented, but hairline cracks still form on the surface and the surface becomes non-flat
Solution Approach 1:
Carbon fiber reinforcement is applied selectively only in the cooking zones where thermal expansion forces occur, rather than across the entire slab surface. This localized application prevents hairline cracks in critical areas while maintaining surface flatness in non-cooking areas, resolving the contradiction between crack prevention and surface quality.
3Temperature
If the stone slab is made thinner to improve heat dissipation, then cooling efficiency increases, but the slab becomes more susceptible to cracking and deformation
Solution Approach 1:
The solution transitions from varying the thickness of a single slab to creating a multi-layer structure with different thicknesses in different dimensions. The lower slab can be thicker for structural strength while the upper cooking slab remains thinner for heat dissipation, achieving both goals simultaneously through dimensional differentiation.
4Temperature
If high-temperature-resistant materials and structures are used to withstand induction heating, then thermal stability improves, but the system complexity and manufacturing difficulty increase
Solution Approach 1:
The invention uses composite construction combining natural stone slabs with carbon fiber reinforcement layers and adhesive bonds. This composite approach provides high-temperature resistance and structural stability without requiring entirely new exotic materials, maintaining ease of manufacture by using proven materials in a cleverly configured multi-layer system.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Effectively prevents hairline cracks and maintains a flat surface by balancing thermal expansion forces, ensuring the stone slabs remain stable and resistant to high temperatures, while also optimizing heat dissipation through air circulation.
Implementation Method 1
induction coils are arranged below the surface of stone slabs, through which a relatively high-frequency alternating current flows. This current transfers electromagnetic energy into a magnetizable metal pot
Implementation Method 2
the remaining two-thirds of the energy is induced in the pot surface in the form of directed eddy currents
Implementation Method 3
the magnetizable dipoles of the ferromagnetic pot material, the so-called elementary magnets or Weiss domains, to be reversed in sync with the alternating field, following a hysteresis pattern
Implementation Method 4
Heat is generated when the electrical resistance (ohmic resistance) of the pot material is sufficiently high
Implementation Method 5
the milled-out area is left as open as possible so that heat can be dissipated by forced air circulation
Data Source
Figure 1
Figure 2
Figure 3
AI summary
The invention relates to the asymmetric structure, in terms of the layer structure, of two or more stone slabs - generally two - wherein the load-bearing bottom slab is designed to be thicker than the top slab which is to be stabilized and which forms the surface of an induction hob assembly. The thickness or stiffness of the bottom stone slab is designed in conjunction with an adequately dimensioned tension-resistant fibre layer such that the tensile stresses in the top slab resulting from the expansion of the top slab during cooking, especially on the surface, because of the bi-metal effect, that is to say from dishing up of the slab, are not exceeded to avoid any hairline crack formation. To this end, the cross-section and/or the stiffness of the bottom slab is to be designed to be so thick in the counter-stabilizing edge regions that the expansion forces of the top stone slab in the cooking zone are adequately compensated for by the compression zone beneath the tension-resistant fibre layer such that the maximum permissible tensile stress on the surface of the top stone slab, which makes up the hob, is not exceeded even if the maximum permissible cooking temperature is reached. In order to prevent deflection or dishing of the entire assembly as a result of the bi-metal effect, a sufficiently porous stone material is selected for the surface which is compressible in volume and/or preferably less resistant to compression than the bottom stabilizing slab, which provides the counter-pressure. To receive the induction coil, the slab assembly is milled out from below to close to the surface, so that the distance between the induction coil and the pan is as small as possible. The milled-out portion is designed to be domed to enhance mechanical stability against pressure and impact from above. Additional fibre reinforcement can be applied here to provide greater support. Circulating air layers are used beneath and, where necessary, on top of the stone surface to keep the surface temperatures on the hob and on the underside of the cooking zone as low as possible. These measures together serve the purpose of preventing the usual hairline cracking on the surface of the complete assembly.