Stock material or miscellaneous articles – All metal or with adjacent metals – Plural layers discontinuously bonded
Reexamination Certificate
2001-01-10
2002-08-06
Jones, Deborah (Department: 1775)
Stock material or miscellaneous articles
All metal or with adjacent metals
Plural layers discontinuously bonded
C428S600000, C428S626000, C228S173600, C228S185000
Reexamination Certificate
active
06428905
ABSTRACT:
BACKGROUND OF THE INVENTION
Double-layered sheet comprising two cover sheets with a space between them, with at least one of said cover sheets being a burled sheet welded to the other cover sheet at the extremities of its burls, and comprising a fill material made of at least two different materials, said fill material filling the space between said cover sheets.
Various types of double-layered sheets of this kind are known (DE 195 03 166 A1; DE 196 06 981 A1; U.S. Pat. No. 4,559,274; Stahl und Eisen [Steel and Iron] 117 (1997), no. 10, page 46).
Such double-layered sheets which are also known as burled sheets, are above all used in the construction of vehicles, because they are characterised by excellent rigidity at relatively low weight and within certain limits are still workable, in particular deep-drawable. The characteristic thickness of the cover sheets is less than 1 mm, in particular less than 0.5 mm; the characteristic thickness of the fill material is between 1 and 5 mm. In the known double-layered sheets various materials are inserted as fill material, for example perforated mats in particular made of plastic or cellulose, or perforated aluminium sheets. In the case of perforated mats or aluminium sheets, the burls of the burled sheet engage the holes of the mat.
In the case of a soft fill material such as cellulose, the fill material is compressed when the sheet is subjected to a bending load. Consequently, even at relatively light loads, the bending rigidity of the sheet decreases rapidly. If perforated aluminium sheeting is used as fill material, the aluminium sheet prevents close approximation of the cover sheets because the aluminium sheet supports the cover sheets. With increasing bending power there is however the danger of the double-layered sheet opposite the centre of pressure which acts as a tension chord, tightening and via the aluminium sheet buckling against the direction of force, the cover sheet facing the centre of pressure of the bending power which acts as a compression chord.
Apart from the requirement for creating a double-layered sheet with good rigidity at low weight per surface area, there is also a requirement for the most economical production possible. It goes without saying that the further apart the weld spots at the extremities of the burls, the lower the expenditure.
Furthermore, a double-layered sheet is known (U.S. Pat. No. 4,559,274) whose cover sheets are burled sheets, welded together at the burls. In the space between the cover sheets a fill material made of two different materials, namely a flexible middle layer of foam, jute, metal wool or similar, and exterior layers made of a synthetic foamable material, are arranged. When the double-layered sheet is heated up, the foamable material foams, thus completely filling the voids. The state of the art does not provide any information concerning the individual formability behaviour of the different types of materials.
SUMMARY OF THE INVENTION
It is the object of the invention to create a double-layered sheet of the type mentioned in the introduction, which provides a better ratio between geometrical moment of inertia and weight per surface area than is the case with conventional double-layered sheets, and which does not have a tendency to failure as a result of buckling.
According to the invention this object is met by a double-layered sheet of the type mentioned in the introduction, in that the behaviour of the fill material during pressing together of the double-layered sheet under operational loads is characterised by at least two stress-strain characteristic curves in perpendicular direction to the plane of the sheet.
In the double-layered sheet according to the invention, at light bending power, the fraction of the fill material with the soft stress-strain characteristic curve determines the elastic line of the double-layered sheet. If the bending force increases, the fraction of the fill material with the harder stress-strain characteristic curve becomes effective, which prevents further approximation of the cover sheets and thus further reduction of the moment of inertia of the double-layered sheet.
In order to better withstand the opposing shear load of the chords caused by bending in a minimum of weld points at the extremities of the burls, one embodiment of the invention provides for the fill material to be bonded to the cover sheets over the entire surface.
Preferably the softer stress-strain characteristic curve is selected such that the effective spring excursion determined by said curve is 2% to 8% of the thickness of the fill material. For the softer stress-strain characteristic curve, the E-module perpendicular to the plane of the sheet (Z direction) should be less than 50 MPa while for the harder curve it should be significantly more than 50 MPa and significantly less than 210,000 MPa. Preferably it should be at least 500, better still 1,500 MPa.
The behaviour of the fill material during pressing together of the double-layered sheet which is characterised by the two stress-strain characteristic curves without the supportive effect of the burls, can for example be realised in that the fill material comprises in particular a porous plastic as a matrix with embedded particles of a material determining the harder stress-strain characteristic curve. A fill material with an E-module in Z direction of less than 20 MPa is particularly suitable as the fraction of the fill material forming the matrix.
Preferably, the fraction of the fill material forming the matrix is formed by a plastic in which dispersed hollow spherules of plastic are distributed, which melt at an average temperature below the temperature for full curing (cross-linking). This is in particular a duroplastic material as this results in a duroplastic foam being created by the melting of the hollow spherules forming the pores. As an intermediate layer in the double-layered sheet, due to its dimensional stability, the said foam allows forming of the double-layered sheet, in particular deep-drawing, without significantly impeding rigidity of the double-layered sheet due to delamination and crack formation in the fill material. In addition it can withstand stove-enamelling temperatures of up to approx. 220° C.
In order to keep the weight per surface area of the double-layered sheet as low as possible, one embodiment of the invention provides for the fraction of the fill material constituting the matrix of plastic to comprise dispersed hollow spherules of plastic of up to 70% by volume, with the melting of said hollow spherules in the fill material of the finished component generating distributed pores sealed off from each other. The harder stress-strain characteristic curve of the fill material is preferably determined by hard bodies which can be contained in the fill material at up to 10% by volume or which can account for up to 5% of the weight of the double-layered sheet. In order to let the soft stress-strain characteristic curve display its full effect when hard bodies are used, the dimension of the hard bodies in the direction perpendicular to the sheet plane (Z direction) should be 2% to 8% smaller than the distance between the cover sheets. On average, the mutual distance between all hard bodies in the sheet plane should be 3 to 7 times the distance of the cover sheets. Glass spheres, ceramic spheres or metal spheres are suitable as hard bodies. However, hard bodies made of glass or ceramic can only be used if the double-layered sheet need not be weldable during assembly, i.e. if no current bridge need be required for resistance welding of the cover sheets. Otherwise the use of metal hard bodies is indicated. The hardness of the hard bodies should be less than that of the cover sheets, so that during forming of the double-layered sheet they do not damage the cover sheets. Hollow shapes such as for example bent chips, spattered grain, fragments of metal foam for example from unkilled steel melt, or aluminium hollow powder are suitable shapes for hard bodies. In the case of sharp-edged metal hard
Adam Frank
Behr Friedrich
Blümel Klaus
Hufenbach Werner
Mittelstädt Horst
Jones Deborah
Prokauser Rose LLP
Savage Jason
Thyssen Krupp Stahl AG
LandOfFree
Double sheet metal consisting of two covering metal sheets... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Double sheet metal consisting of two covering metal sheets..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Double sheet metal consisting of two covering metal sheets... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2884584