Rigid thin sheet material and method of making it

Details Rigid thin sheet material and method of making it Rigid thin sheet material and method of making it

1998-09-03

2001-02-06

Jones, Deborah (Department: 1775)

Stock material or miscellaneous articles

All metal or with adjacent metals

Nonplanar uniform thickness or nonlinear uniform diameter

C428S687000, C042S030000, C029S592000, C029S421100, C072S199000, C072S212000, C072S226000, C072S234000

Reexamination Certificate

active

06183879

ABSTRACT:

CROSS-REFERENCES TO RELATED APPLICATIONS
Not applicable
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not applicable
BACKGROUND OF THE INVENTION
The invention relates to a method of making thin sheet metal material relatively rigid.
In our prior patent application WO 94112294 published on Jun. 9, 1994 (Agent's Ref: P01448PCT) we have disclosed a method of forming projections in a thin sheet to increase the stiffness of the sheet. We have now discovered an improved method of treating the sheet material.
BRIEF SUMMARY OF THE INVENTION
According to the invention in one aspect there is provided a method of producing lightweight flexure-resistant thin metal sheet, the method comprising passing flexible sheet material of relatively thin gauge between two rolls each having teeth, each tooth having four flanks, each flank facing in a direction between an axial direction and a circumferential direction, the teeth having radiused corners, the rolls being arranged so that the teeth of one roll extend into gaps between teeth on the other, the rolls being rotated at substantially the same speed about generally parallel axes to form rows of projections on both faces of the sheet passed therethrough without damage to the surface material of the sheet.
We have realised that when flexible sheet material of relatively thin gauge is passed in the nip between rollers having teeth, the sheet surface can be damaged so that fragments of the sheet come away and accumulate in the spaces between teeth. The fragments then cause further damage to the sheet material which is following behind. most preferably the teeth are radiused in two areas: at the corners of the peak and at the peak. In other words it has been found according to the invention that by radiusing the comers of the teeth, preferably both at the peak and the root thereof, it is possible to cause the sheet material to flow in the clearance between opposed teeth to become more rigid with little or no thinning and without spalling of the sheet material or of the teeth. As a result the rolls suffer less wear and need less cleaning and last longer; the sheet material is rigid and yet lightweight. So far as we are aware it has not previously been the practice to radius the corners of teeth on rolls, and the benefits of doing so were unrealised.
The corners of the teeth are preferably radiused in the range from about 0.05 to 15 mm, most preferably 0.1 5 to about 4 mm. The extent of radius is related to the size of the tooth which in turn relates to the gauge of the sheet being processed. Where the tooth is relatively small for use with thin gauge sheet, the corner radios is Roput 0.2 and the peak is preferably about 1 mil; where the tooth is relatively large for thicker gauge sheet the corner radius is about 1 mil and the peak about 2.5. The ratio of the corner radius to the peak radius thus decreases with increasing size of the tooth. It has been observed that outside these parameters the tooth tends to have corners which can cut into the surface of the sheet material being treated. By virtue of the radiusing of the comers and the peaks of the teeth there is no risk that a sheet will occur. Such cracking releases fragments of the sheet material which tend to foul the space between the teeth of the roll which risk breaking the integrity of the surface of the sheet following on behind. We have surprisingly discovered that in the method of the invention not only does the sheet surface maintain its integrity but the formed sheet undergoes an enhanced stiffening effect as a result of which the mechanical strength, e.g. rigidity of the sheet is enhanced. The method of the invention may even be applied to a thin flexible sheet carrying a coating, e.g. a paint or like film without risk that it will be harmed.
In another aspect the invention provides a set of rolls, rows of teeth being present on the outer surface of the rolls, each tooth having four flanks of involute form, and each flank facing in a direction between an axial direction and a circumferential direction, the corners of the teeth being radiused as defined.
In another aspect the invention provides sheet material having projections on both of its surfaces, a corresponding depression being on the surface opposite each projection, the relative positions of the projections and depressions being such that lines drawn on the surface are non-linear, the sides of the projections lying a line extending between a longitudinal direction and a lateral direction, the overall distance between adjacent projections and depressions being within the range of 2 umm to 5 mm and in the range of four to ten times the gauge, wherein the corners of the projections and depressions are radiused.


REFERENCES:
patent: 486281 (1970-02-01), None
patent: 0 139 066 (1985-05-01), None
patent: 0 167 874 (1986-01-01), None
patent: 2279596 (1995-01-01), None
patent: WO 94/12294 (1994-06-01), None

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